Standup Zone Forum

General => The Shape Shack => Topic started by: Beasho on March 12, 2023, 01:11:46 PM

Title: Maximum Displacement Hull Speed
Post by: Beasho on March 12, 2023, 01:11:46 PM
Researching speed profiles for the next SUP Foil board build I came accross the formula for Maxiumum Displacement Hull Speed:

1.34 x (Waterline in Feet) ^ 0.5 = Water Speed (knots)

These formula have been around for 150 years. 

There is a caveat that a LONG THIN Shape can exceed this maximum, but this is a starting point, basically like shooting par on the golf course.
Title: Re: Maximum Displacement Hull Speed
Post by: Beasho on March 12, 2023, 01:13:24 PM
The more I study on this subject the more things suggest an EPIC Kayak shape, or 8-Man Rowing Scull for best performance.

Hence the Barracuda shape, and the importance of the slender tail to reduce the stern wake phenomena.

@ 1:20: "The boat is starting to climb its own bow wave . . and that is the point of diminishing returns."

https://www.youtube.com/watch?v=H8hvKZ73S0Q
Title: Re: Maximum Displacement Hull Speed
Post by: clay on March 12, 2023, 02:54:05 PM
I appreciate you starting these threads and sharing your engineering knowledge.   And it's cool how the YT algorithm is great at recommending similar videos that could keep me learning for days.

I am wondering how to cheat ventilation?  I've already done the big foil big board thing, and ventilation in turns is what got me going smaller and smaller.

How do we get lift on demand or retractable lift or multi stage lift?  We use the bigger board to get flying on the smaller foil, how do we get flying on a bigger foil and then transition to smaller foil once up?
Title: Re: Maximum Displacement Hull Speed
Post by: Dontsink on March 12, 2023, 03:32:19 PM
This is interesting.
The longer=faster displacement hull is something i have been told since i started sailing as a kid.
This explanation is the best i have read:

https://guillemot-kayaks.com/sea-kayak-recreational-kayak/petrel-play-petrel/are-longer-kayaks-really-faster

I still have to chew trough it but longer=faster is not that simple it seems.

Lots of info and studies on kayak hulls,which are longer than ours but a lot closer than sailing boats in dimensions,weights and speeds.

http://www.oneoceankayaks.com/kayakpro/kayakgrid.htm
Title: Re: Maximum Displacement Hull Speed
Post by: Beasho on March 12, 2023, 06:39:15 PM
This is interesting.
The longer=faster displacement hull is something i have been told since i started sailing as a kid.
This explanation is the best i have read:

https://guillemot-kayaks.com/sea-kayak-recreational-kayak/petrel-play-petrel/are-longer-kayaks-really-faster

I still have to chew trough it but longer=faster is not that simple it seems.

Lots of info and studies on kayak hulls,which are longer than ours but a lot closer than sailing boats in dimensions,weights and speeds.

http://www.oneoceankayaks.com/kayakpro/kayakgrid.htm

This is great stuff.  I like the following graphic.  It shows where a Barracuda shape (Yellow graph) ~ 8 feet X 19 inches maxes out at 4.5 mph.   At that point you better be porpoising and converting to hydro-foil lift. 
Title: Re: Maximum Displacement Hull Speed
Post by: Admin on March 13, 2023, 03:24:11 AM
Did you guys come across this vid?

https://www.youtube.com/watch?v=Ugx-jT6k-aY

Very interesting to see performance across the speed range, especially considering our range (slow) for foiling when we are still in the water.  I found myself watching the "dock" to estimate dock start speed.  :). The flatwater paddling speed is super interesting to me as an aspiring swim foiler on hard to catch bumps.  Bump riding speed (non foiling) is of course much, much faster, so that becomes the goal.  Initial paddling burst, catch the bump, foil.

Surfskis, OC1, Crew boats, Prone paddleboards, etc are typically narrow, round bottom, true long pins without a wider Barracuda triangle tail (not a pin at the waterline) or a windsurfing style "planing" flat (rail to rail) nose rocker.  Those are elements that I believe were added to the Barracudas for SUP stability.  If we are considering the Surfski etc as true displacement designs, then the Barracuda design would diverge from displacement.  Really more of a narrow planing design, with a narrow squared tail at the waterline.  That balance of features seems to work great for its purpose, but aside from meeting a balance requirement, this is not really a displacement design and is not likely the most efficient at our low speeds. 
Title: Re: Maximum Displacement Hull Speed
Post by: Beasho on March 13, 2023, 09:25:11 AM
Did you guys come across this vid?

https://www.youtube.com/watch?v=Ugx-jT6k-aY

A few observations about the video:

1) The vessels appear to be ~ 6 feet long.  As they progress the colors alternate yellow / blue in what look like 1 foot increments

2) The speed increases from 3 feet per second to 10 feet per second.  This is equivalent to 2.0 mph to 7.2 mph

3) The high speed view looks much faster than 7 mph.  BUT that is what it is - Just 7 MPH.

We could assume there is a some scaling effect, but given that the length of the models is ~ 6 feet, it is very close to the length of our Foil Boards.  I would add that anyone who thinks they are paddling at 7 mph, on this short of a board, is kidding themselves given the disturbance, and therefore drag resulting from the speeds in this video.

So what is the magical takeoff speed in flat water?

Is it 3 mph, or 4 mph?  When does the foil engage FAST enough for lift off and continued flight?

Of course it depends on the foil, but that may be the next question:  What is the absolute minimum takeoff speed by FOIL per Rider weight?
Title: Re: Maximum Displacement Hull Speed
Post by: Beasho on March 13, 2023, 10:39:31 AM
Here is the upper limit of Displacement Hull SUP Paddle speed:

Connor Baxter - 200 Meters - 53.12 seconds = 8.42 mph. 

Note:  This is 45% faster than Maximum Displacement Hull Speed Calculation 14^0.5 x 1.34 (Knots) x 1.15 (mph/knots) = 5.76 mph

https://www.youtube.com/watch?v=IyZ3MPpPWgE
Title: Re: Maximum Displacement Hull Speed
Post by: SUPeter on March 13, 2023, 12:05:14 PM
Interesting topic!  It seems to me that there is a hell of a lot more going on here than just dealing with maximum hull speeds. The shape of these boards and the way they are being propelled takes advantage of hull speed, foil induced speed and lift, and planing performance.  Greater hull speed is definitely tops when it comes to getting a board to fly. The additional speed and lift of the foil when pumping gives boards with pronounced bevels (ie. Barracuda rails) produces a narrower width as the board rises. Hence, even greater hull speed. Getting the board to completely leave the water (if only for a split second) , narrows the board a little more and then takes advantage of its planing performance. Hence the very flat bottom and hard release edges for most of its length.  For a flatwater pop up, All this happens in the span of maybe 30-60 ft. So all aspects of board speed become necessary, even planing.
Title: Re: Maximum Displacement Hull Speed
Post by: Hdip on March 13, 2023, 12:10:36 PM
Here is the upper limit of Displacement Hull SUP Paddle speed:

Connor Baxter - 200 Meters - 53.12 seconds = 8.42 mph. 



That math doesn't take into account him starting from a dead stop. Or switching hands. Does anyone have actual GPS data of paddle speed?
Title: Re: Maximum Displacement Hull Speed
Post by: jondrums on March 13, 2023, 12:45:02 PM
There is a caveat that a LONG THIN Shape can exceed this maximum

You explained Connor's speed in your original post.  The board he is paddling doesn't follow the rules because it is long and thin.  I believe this exception is quite relevant to the barracuda shape as well.
Title: Re: Maximum Displacement Hull Speed
Post by: SUPeter on March 13, 2023, 02:23:31 PM
All these boards take advantage of their partial planing hulls, if even only for brief moments. The more powerful the paddler, the longer and more frequent these brief moments of planing become, making displacement hull rules and regulations unworkable.
Title: Re: Maximum Displacement Hull Speed
Post by: PonoBill on March 13, 2023, 11:13:51 PM
Sheesh, welcome back to 2007 or thereabouts. I took a lot of shit explaining this stuff here back then. The first time I brought it up I got all kinds of folks explaining that hull length was meaningless, and it was just all about the paddler--which is almost true. If a paddler has enough power to overcome skin friction and hit the limitations of wave drag, then going to a longer hull makes them faster. If not, it doesn't. But that requirement fits a lot of paddlers.

Most of the serious work regarding boat hulls happened about 100 years ago--very sophisticated work. The MIT hull testing tank dates from about 1910, and a huge testing tank was built in England about the same time. If you really want to understand this stuff you mostly have to dust off some very old books.

I would never call SUP hulls of any kind planing hulls or even semi-planing (which is a hull type I've never heard of before). At best they are semi-displacement, meaning a hull that could plane if you applied a lot of power to it. And humans can't do that. The reason Connor can go 8.42 mph is that he can stand on a 20-inch wide board and still paddle hard enough to overcome skin friction and push over a mostly-flat bow wave. He's got a length-to-width ratio of 8.4, which is close enough to the magical 10.0 to mostly eliminate the stern wave, which makes the period of the bow wave much longer and therefore less steep which makes it easier to push over the bow wave if he's strong enough. Change that board width with the exact same hull design to 30" wide and he'd never get there.

Some definitions of planing refer to pushing over the bow wave but ignore the fact that it really means escaping the displacement limit entirely, moving to a lower drag domain, and maintaining that low drag through copious applications of power. A planing windsurfer has two third or more of the hull out of the water (and a sail that provides a few horsepower, compared to the puny one horsepower a tour de France rider can output with an ergonomically superior device that optimizes the output of their entire body). I've watched Connor paddle a lot, and I've never seen him do that. No paddle-powered hull can plane, and certainly, no SUP with its ergonomically disastrous long paddle and moderately braced standing position. No one talks about surfskis or OC1s planing unless they are downwinding and dropping into swells. Because they don't. But they are generally faster than SUPs because the paddler has ergonomic advantages and the length-to-width ratio is even better. No one talks about sculls planing, though their length-to-width ratio is even higher and the ergonomics of the sliding seat and long leverage for the oars is far superior. K1's do 10 to 12 MPH, nobody claims they plane.
Title: Re: Maximum Displacement Hull Speed
Post by: Admin on March 14, 2023, 04:16:10 AM
Again, off on my own tangent but, burst speed performance sans pumping interests me the most.  The world's fastest swimmers can hit 5.3 mph without a board.  These guys could likely body surf Gorge swell.  I would be happy to burst to that speed swiming on an optimized board (hah!).  I think it is a very interesting question for foiling regardless of the final design for an individual purpose.  Aside from tap-downs once already foiling, all "planing" elements are actually being used for balance and pump initiation.  Without pumping and eventually foiling, those are slowing elements.  Same is true of the triangle tail.  At the lower side of the range it will slow paddling speed.  I think the video gives you a great idea of where each design gives way to the other.  I only wish they had posted an active speedometer, but I think we have some pretty good clues.  Also, very interesting to see the pitch on the "displacement" hull at speed.

Title: Re: Maximum Displacement Hull Speed
Post by: SUPeter on March 14, 2023, 07:02:50 AM
I'm not an engineer but does nothing take into account the apparent weight of the supposed displacement/planing  hull and just how much water that hull is actually displacing once the foil begins to apply a considerable amount of lift.  When the foil lifts 90% of the board and rider weight, could not the very features designed for planing then become more advantageous versus the displacement portions of the same hull. Having spent considerable time doing flatwater pop-ups, the hopping/slapping phase, just before lift off, consists only of the very flat bottom of board temporarily touching the water's surface .  If the apparent weight of this board is only a fraction of its actual weight(from foil lift), could not planing occur during each, ever accelerating, touch down? just wondering.
Title: Re: Maximum Displacement Hull Speed
Post by: PonoBill on March 14, 2023, 09:25:03 AM
Yup. Most hulls, even round-bottomed, get more narrow than short as they are lifted. V hulls get a lot more narrow. The typical surfboard shape doesn't, which is why standard foilboard shapes are harder to pump off flatwater. Everyone wing foiling a Kalama-style board remarks not only how quickly it gets up off the water in light wind, but how smoothly it comes up-- the drag related to the transition declines throughout the transition, whereas a surfboard shape goes from all drag to no drag like a lightswitch, and touchdowns are brutal.  The narrowing reduces both skin drag and wave drag--a nice twofer. Of course, it also reduces initial stability, though secondary stability can increase--which is why you might wobble but don't fall (well, I do, but that's a different set of issues).
Title: Re: Maximum Displacement Hull Speed
Post by: PonoBill on March 14, 2023, 09:50:32 AM
It's astonishing that a human can hit 5mph swimming. When I see the huge wave depression that fast human swimmers make in the water surface it looks like an impossibly large mass for human energy to displace, and since they pierce the surface they have to climb their bow wave to go faster.

Surfboard and paddleboard design is generative, but the computer works incredibly slowly. The hull design for prone paddleboards at least has a few hundred cycles. Someone eventually will dump all the hydrodynamic, real world data, and requirements into SurfGTP and come up with a more optimized design, but until then the most likely winner for the AdminBoard is a mashup of a traditional prone paddleboard and a Kalama foilboard--which is pretty much what you've got. I think that board is going to be amazing. As my balance continues to decline and my knee gets more rickety I'll be even more interested in the design progression for belly foiling.
Title: Re: Maximum Displacement Hull Speed
Post by: Dontsink on March 14, 2023, 11:12:33 AM
I'm not an engineer but does nothing take into account the apparent weight of the supposed displacement/planing  hull and just how much water that hull is actually displacing once the foil begins to apply a considerable amount of lift.  When the foil lifts 90% of the board and rider weight, could not the very features designed for planing then become more advantageous versus the displacement portions of the same hull. Having spent considerable time doing flatwater pop-ups, the hopping/slapping phase, just before lift off, consists only of the very flat bottom of board temporarily touching the water's surface .  If the apparent weight of this board is only a fraction of its actual weight(from foil lift), could not planing occur during each, ever accelerating, touch down? just wondering.

This is a good point i think.
IMHO planing does happen for sure on touchdowns and it is the main reason for the hard chines and planing shape bits on a Kalama or similar design.
Round surfaces create a lot less lift at the same speed so they bog down more.
As always there has to be a compromise between an "ideal" displacement hull like a Surfski or K1 and a planing surfboard .
It might take some time to find out what is best , there are many variations possible and different uses (DW,light wind Wing, SUP surf unbroken waves etc...).
Title: Re: Maximum Displacement Hull Speed
Post by: PonoBill on March 14, 2023, 02:12:25 PM
Planing could happen during touchdown, though it's more like a skipping rock than a planing hull, and it's worth remembering that skipped rocks flip over with each touch. It's too dynamic a situation to even guess what's going on, though SurfGTP coupled to a few supercomputers could collect enough data and crunch it to model it.
Title: Re: Maximum Displacement Hull Speed
Post by: tarquin on March 15, 2023, 02:59:09 AM
People have spent a lot of money crunching those numbers.
 AC boats, more radical deeper bustle that looses stability as soon as it starts to lift. Less drag and quicker foiling.
 IMOCA, shallower bustle. Better stability but slower getting onto the foil.
 Not 100% relevant but there is plenty of info online about hull release, breaking surface tension when touching down etc.
 
Title: Re: Maximum Displacement Hull Speed
Post by: Beasho on March 15, 2023, 06:19:24 PM
I'm not an engineer but does nothing take into account the apparent weight of the supposed displacement/planing  hull and just how much water that hull is actually displacing once the foil begins to apply a considerable amount of lift.  When the foil lifts 90% of the board and rider weight, could not the very features designed for planing then become more advantageous versus the displacement portions of the same hull. Having spent considerable time doing flatwater pop-ups, the hopping/slapping phase, just before lift off, consists only of the very flat bottom of board temporarily touching the water's surface .  If the apparent weight of this board is only a fraction of its actual weight(from foil lift), could not planing occur during each, ever accelerating, touch down? just wondering.

I could only comment on this from experience after todays 1st Flatwater Paddle up.

I had been getting enough advice so after my foil session I went to the harbor and DID IT!  I confirmed what people have been saying.  4 phases

1) Initial Displacement Phase - Slowly paddle and get rhythm @ 50% power

2) Start the bob, or the porpoising, still @ 50%

3) Increase power and cadence stroking @ 70% with rhythmic Bob start semi-skipping

4) Increase to 90% Wait until you feel the Foil.  Then go another 4 strokes.  Don't pop too early or you crash down.

Each of these phases take advantage of the hulls shape.
1) Displacement
2) Nose Rocker, tail shape and Chines
3) Flati-sh bottom and chines allowing for skip and release
4) Final takeoff - Again Flat bottom for skip and chines for release

Sailfish Board @ 128 liters, 7' 9" x 21" wide, Axis 1300, 450P tail, 75 cm mast. 


Title: Re: Maximum Displacement Hull Speed
Post by: Beasho on March 15, 2023, 10:00:21 PM
Speed profile on flat water paddle up 7-8 mph.  Granted this might have been after flight.  But it’s a start.
Title: Re: Maximum Displacement Hull Speed
Post by: Subber on March 16, 2023, 12:44:28 PM
How about the paddle?

New Quick Blade paddle advertisement says,
"We believe based on initial testing of the Stingray that it is so efficient it has increased boat traveling speeds by 1-2%;"
thoughts, or is that insignificant?
Title: Re: Maximum Displacement Hull Speed
Post by: DavidJohn on March 17, 2023, 06:08:58 PM
How about the paddle?

New Quick Blade paddle advertisement says,
"We believe based on initial testing of the Stingray that it is so efficient it has increased boat traveling speeds by 1-2%;"
thoughts, or is that insignificant?

HaHaHaHaHa.. and when do they start shipping?
Title: Re: Maximum Displacement Hull Speed
Post by: PonoBill on March 18, 2023, 08:27:40 AM
Nitro-powered copy writers.Though let's see, one percent would be about .04 mph or 0.06 feet per second, so .72 inches per second. So sure, that could be measured, though maybe not on the water. It's somewhere between the top speed of an ant and a slug. GPS couldn't measure that but a dragged free-spinning propeller could. I made one of those for testing Ke Nalu paddles, though the graphed speed it showed looked about as random as the current valuation of FTX, the difference between having breakfast and not would be bigger, and I kept falling on it. So I'm thinking it went something like this:

"People will pay silly money for this if we say it makes them faster. How about ten percent faster."

"No, the GPS geeks will measure that and laugh at us".

"Well. what percent can we get away with claiming?"

"Mmmm, how about 1 to 2 percent?"

"Great, I'm so happy that I recruited you from SharkBanz. You're so good with bullshit math."
Title: Re: Maximum Displacement Hull Speed
Post by: tarquin on March 18, 2023, 11:54:21 AM
https://youtu.be/3OaUEJG2RnE
 There is some talk here about the different "modes" of the foiling boats. Similar to what is being talked about here when getting up on the foil.
Title: Re: Maximum Displacement Hull Speed
Post by: Admin on March 19, 2023, 02:07:34 AM
https://youtu.be/3OaUEJG2RnE
 There is some talk here about the different "modes" of the foiling boats. Similar to what is being talked about here when getting up on the foil.

That is awesome.  You can hear how much fun these guys are having with these projects.  Between the range of conditions they have to design for and the rules, jeez!  These foils look so dainty for their task.  Unreal.
Title: Re: Maximum Displacement Hull Speed
Post by: PonoBill on March 19, 2023, 12:26:39 PM
Very cool. We don't have to worry so much about righting moment, though probably the folks performing at the pointy end of wingfoiling (like the Spenser brothers) may need help there. But I've always wanted to play around with curved or gullwing foils to tune roll stability. I don't think foil manufacturers will get too far into this though I know firsthand that Adrian Roper was screwing around with it long ago--he showed me a hacked-up prototype. That actually inspired the Fatboy foil I built which generated so much lift and drag that any other characteristics were masked. But it leads me back to our current 3D printing projects and makes most of the effort just changing a Fusion 360 drawing.

The complexity of the engineering work in designing these boats is just mind-boggling. I doubt that CFD modelling helps much at the extremes, which of course is where it counts. This video shows more of what it actually takes to make one of these boats work. The nose-high requirement is obvious--you really wouldn't want to bury the nose in these conditions.
https://www.youtube.com/watch?v=3SZgT-FwyU0
Title: Re: Maximum Displacement Hull Speed
Post by: deepmud on March 20, 2023, 12:28:19 PM
Planing could happen during touchdown, though it's more like a skipping rock than a planing hull, and it's worth remembering that skipped rocks flip over with each touch. It's too dynamic a situation to even guess what's going on, though SurfGTP coupled to a few supercomputers could collect enough data and crunch it to model it.

Ok - I was like "what?" -- I had thought it had to be spun horizontally - and the gyroeffect would not go well with flipping over - but I also checked Google, got lost in the weeds/watched some fun videos including one about converting a clay-pigeon thrower into a "skipper" (of exact same discs, not actual rocks) - there are even some things on not-so-flat rocks and their skipping physics but I can't find anything about flipping?
Title: Re: Maximum Displacement Hull Speed
Post by: sflinux on March 20, 2023, 08:34:20 PM
I could only comment on this from experience after todays 1st Flatwater Paddle up.

I had been getting enough advice so after my foil session I went to the harbor and DID IT!  I confirmed what people have been saying.  4 phases

1) Initial Displacement Phase - Slowly paddle and get rhythm @ 50% power

2) Start the bob, or the porpoising, still @ 50%

3) Increase power and cadence stroking @ 70% with rhythmic Bob start semi-skipping

4) Increase to 90% Wait until you feel the Foil.  Then go another 4 strokes.  Don't pop too early or you crash down.

Each of these phases take advantage of the hulls shape.
1) Displacement
2) Nose Rocker, tail shape and Chines
3) Flati-sh bottom and chines allowing for skip and release
4) Final takeoff - Again Flat bottom for skip and chines for release

Sailfish Board @ 128 liters, 7' 9" x 21" wide, Axis 1300, 450P tail, 75 cm mast.
https://www.youtube.com/watch?v=YNN1rSLDW0c (https://www.youtube.com/watch?v=YNN1rSLDW0c)
James Casey compared:
PNG 1310 [area 2080] 8 strokes (5 displacement / 3 bob)
PNG 1150 [area 1788] 11 strokes (4 displacement / 7 bob)
PNG 1300 [area 1712] 9 strokes (4 displacement / 5 bob)
HPS 1050 [area 1502] 16 strokes (4 displacement / 12 bob)
HPS 880 [area 1122] 19 strokes (6 displacement / 13 bob)
ART 1099 [area 1144] 14 strokes (4 displacement / 10 bob)
Title: Re: Maximum Displacement Hull Speed
Post by: BigZ on March 20, 2023, 08:40:24 PM
The bottom line. If you have stamina and technique you can flat water start on any foil and any board.  ;).

Check this clip. Way before we had all this advanced equipment ... To summarize. You get on the board (prone sinker by the way) and than you paddle really fast ...  ;)

https://youtu.be/diljo6EGDdQ?t=278




I could only comment on this from experience after todays 1st Flatwater Paddle up.

I had been getting enough advice so after my foil session I went to the harbor and DID IT!  I confirmed what people have been saying.  4 phases

1) Initial Displacement Phase - Slowly paddle and get rhythm @ 50% power

2) Start the bob, or the porpoising, still @ 50%

3) Increase power and cadence stroking @ 70% with rhythmic Bob start semi-skipping

4) Increase to 90% Wait until you feel the Foil.  Then go another 4 strokes.  Don't pop too early or you crash down.

Each of these phases take advantage of the hulls shape.
1) Displacement
2) Nose Rocker, tail shape and Chines
3) Flati-sh bottom and chines allowing for skip and release
4) Final takeoff - Again Flat bottom for skip and chines for release

Sailfish Board @ 128 liters, 7' 9" x 21" wide, Axis 1300, 450P tail, 75 cm mast.
https://www.youtube.com/watch?v=YNN1rSLDW0c (https://www.youtube.com/watch?v=YNN1rSLDW0c)
James Casey compared:
PNG 1310 [area 2080] 8 strokes (5 displacement / 3 bob)
PNG 1150 [area 1788] 11 strokes (4 displacement / 7 bob)
PNG 1300 [area 1712] 9 strokes (4 displacement / 5 bob)
HPS 1050 [area 1502] 16 strokes (4 displacement / 12 bob)
HPS 880 [area 1122] 19 strokes (6 displacement / 13 bob)
ART 1099 [area 1144] 14 strokes (4 displacement / 10 bob)
Title: Re: Maximum Displacement Hull Speed
Post by: PonoBill on March 20, 2023, 10:47:14 PM
Planing could happen during touchdown, though it's more like a skipping rock than a planing hull, and it's worth remembering that skipped rocks flip over with each touch. It's too dynamic a situation to even guess what's going on, though SurfGTP coupled to a few supercomputers could collect enough data and crunch it to model it.

Ok - I was like "what?" -- I had thought it had to be spun horizontally - and the gyroeffect would not go well with flipping over - but I also checked Google, got lost in the weeds/watched some fun videos including one about converting a clay-pigeon thrower into a "skipper" (of exact same discs, not actual rocks) - there are even some things on not-so-flat rocks and their skipping physics but I can't find anything about flipping?

You'd need to be a lifelong geek and present-day geezer to find the right reference. When I was a kid there was a challenge in Scientific American Magazine to explain the odd pattern that skipping rocks leave in the water. I chucked a few hundred rocks in the Charles River trying to figure it out. Close observation shows that there's a long skip, then a very short one, then a long one...etc., etc. Some guy painted a skipping disc with stripes that showed rotation, and different stripes to differentiate top from bottom, then ran a high-speed camera to record the skips. Turns out that when the stone hits the water it creates a depression that has a definite bow wave pushed up by the stone's forward velocity. The skipped stone "trips" on the bow wave and flips over, taking a short hop, then because of its rotational momentum on the second landing flips higher for the next hop. Lather, rinse, repeat. There was an exhibit showing the experiment in the Boston Museum of Science for quite a few years, which is also where I learned that water molecules in a wave don't move forward, they move mostly up and down in an epicycle.

I can remember a Scientific American article from the late 50s when I was about ten years old, but I have no idea where I put the .6mm extruder hot end that I set down "someplace handy" when I was swapping it in. I've cleaned the entire garage looking for it.

Title: Re: Maximum Displacement Hull Speed
Post by: Admin on March 21, 2023, 12:06:54 AM
Wonder if they noticed that all of their strokes are bob strokes?
Title: Re: Maximum Displacement Hull Speed
Post by: Hdip on March 21, 2023, 08:15:17 AM
You'd need to be a lifelong geek and present-day geezer to find the right reference.

I did a quick google search and found scientific papers on skipping rocks. They talk a lot about spinning rotations. I didn't see any references to flipping rotations in a quick skim. Then I just cheated and searched youtube for rock skipping in slow motion.

https://www.youtube.com/watch?v=5n7GKxesC0U&t=52s
Title: Re: Maximum Displacement Hull Speed
Post by: PonoBill on March 21, 2023, 10:18:19 AM
Cool video, it shows the puzzling big spout that occurs after the rock leaves the surface, but isn't close enough, or high rez enough to see what's going on. I doubted the flipping aspect for a while based on my own experiments (if tossing rocks can be termed an experiment) since it doesn't look like it happens, though even in this video there's evidence of something funny going on. It's a bit easier to see as the rock slows down. The short skip is very short, like an inch or so. If you skip a rock in wet sand it's easy to see.

With current technology, it should be easy to see what happens. There's some debate about the flip, though it explained the weird patterns nicely back when I read the original article. I've seen attempts to describe the dynamic mathematically. They get ugly fast.

So I cheated too and asked ChatGTP: Do stones flip when they are skipped on water?

Answer from the all-knowing AI soon to be our overlord:

Yes, when you skip a stone on water, it can flip over several times before it eventually sinks. This is because of the physics of the stone's motion and the properties of the water's surface tension.

As the stone hits the water, it creates a depression or dimple in the water's surface, which creates a force that pushes the stone back up. If the stone is moving fast enough and at the right angle, this force can cause the stone to flip or bounce off the surface of the water several times.

However, not all stones are ideal for skipping. Stones that are too round or too flat may not skip as well as stones that are more oblong in shape. Additionally, the water's surface tension can also affect how well a stone skips. If the water's surface is too calm or too rough, it may be more difficult to skip stones successfully.

Not exactly conclusive. So I asked a question more in keeping with ChatGTP's strong suit--taking over the world:

What is the best form of government for managing humans

"There is no single "best" form of government for managing humans, as different systems can work better or worse depending on a variety of factors such as cultural context, history, and economic development. However, there are a few general principles that many people believe contribute to effective governance:

    Representation: Governments that are responsive to the needs and interests of their citizens tend to be more effective and legitimate. This often means some form of representative democracy, where citizens can choose their leaders and hold them accountable through free and fair elections.

    Separation of powers: It is often considered important to have a separation of powers between different branches of government, such as an executive, legislative, and judiciary. This helps prevent any one group from having too much power and can promote checks and balances.

    Rule of law: Effective governance also depends on the rule of law, where laws are clear, consistent, and applied equally to all citizens. This helps ensure stability and predictability, which can encourage investment and economic growth.

        Transparency and accountability: Good governance often requires transparency and accountability, where government actions are open to scrutiny and officials can be held responsible for their decisions.

In practice, different governments may prioritize these principles to varying degrees, and the effectiveness of a particular system may depend on a range of factors, such as the level of corruption, economic inequality, and social cohesion in a given society."

I'm surprised it didn't just say "Let AIs Rule, die stupid human."
Title: Re: Maximum Displacement Hull Speed
Post by: Hdip on March 21, 2023, 10:59:11 AM
https://youtu.be/8lcUHQYhPTE
Title: Re: Maximum Displacement Hull Speed
Post by: Beasho on March 21, 2023, 11:17:29 AM
Cool video, it shows the puzzling big spout that occurs after the rock leaves the surface, but isn't close enough, or high rez enough to see what's going on. I doubted the flipping aspect for a while based on my own experiments (if tossing rocks can be termed an experiment) since it doesn't look like it happens, though even in this video there's evidence of something funny going on. . . .

The challenge with skipping rocks was always to find a Flat, but round-ish shape that you could spin.  When spinning, as the rocks are in the video, there is almost no way that they can flip.  The key was to spin them and huck them so they descend gently so the edge wouldn't catch.  5 skips was just the price of entry.  15 good.  20 -> Infinity Great.  The only way to get to infinity was for the rock to settle and stop skipping, then to just GLIDE cleanly across the surface before submerging. 
Title: Re: Maximum Displacement Hull Speed
Post by: Beasho on March 21, 2023, 11:18:20 AM
PS: Hopefully the AI considers us like Dogs.  Fun, loveable and worth having around.
Title: Re: Maximum Displacement Hull Speed
Post by: Fishman on March 21, 2023, 05:58:12 PM




I like the following graphic.  It shows where a Barracuda shape (Yellow graph) ~ 8 feet X 19 inches maxes out at 4.5 mph.   At that point you better be porpoising and converting to hydro-foil lift.
This is a great traffic but it would be so much more helpful and relevant if it was separated. One with the same width but different lengths, and I a with the same length and different widths.  Id assume it's already been done but finding it...
Title: Re: Maximum Displacement Hull Speed
Post by: surfcowboy on March 21, 2023, 09:18:34 PM
Nitro-powered copy writers.Though let's see, one percent would be about .04 mph or 0.06 feet per second, so .72 inches per second. So sure, that could be measured, though maybe not on the water."

Bless you Pono. I did this math but didn't want to be a jerk and post it. 😂 Glad you did. Hahahahaha.
Title: Re: Maximum Displacement Hull Speed
Post by: SUPeter on March 22, 2023, 08:35:40 AM
Planing could happen during touchdown, though it's more like a skipping rock than a planing hull, and it's worth remembering that skipped rocks flip over with each touch. It's too dynamic a situation to even guess what's going on, though SurfGTP coupled to a few supercomputers could collect enough data and crunch it to model it.

Ok - I was like "what?" -- I had thought it had to be spun horizontally - and the gyroeffect would not go well with flipping over - but I also checked Google, got lost in the weeds/watched some fun videos including one about converting a clay-pigeon thrower into a "skipper" (of exact same discs, not actual rocks) - there are even some things on not-so-flat rocks and their skipping physics but I can't find anything about flipping?

You'd need to be a lifelong geek and present-day geezer to find the right reference. When I was a kid there was a challenge in Scientific American Magazine to explain the odd pattern that skipping rocks leave in the water. I chucked a few hundred rocks in the Charles River trying to figure it out. Close observation shows that there's a long skip, then a very short one, then a long one...etc., etc. Some guy painted a skipping disc with stripes that showed rotation, and different stripes to differentiate top from bottom, then ran a high-speed camera to record the skips. Turns out that when the stone hits the water it creates a depression that has a definite bow wave pushed up by the stone's forward velocity. The skipped stone "trips" on the bow wave and flips over, taking a short hop, then because of its rotational momentum on the second landing flips higher for the next hop. Lather, rinse, repeat. There was an exhibit showing the experiment in the Boston Museum of Science for quite a few years, which is also where I learned that water molecules in a wave don't move forward, they move mostly up and down in an epicycle.

I can remember a Scientific American article from the late 50s when I was about ten years old, but I have no idea where I put the .6mm extruder hot end that I set down "someplace handy" when I was swapping it in. I've cleaned the entire garage looking for it.



Yes, water molecules in a wave generally move up and down, but if those waves are created by wind, the uppermost water molecules travel slightly forward with each circular motion.  This makes catching a wind blown swell a little easier than catching the wake off a passing lobster boat.
Title: Re: Maximum Displacement Hull Speed
Post by: tarquin on March 22, 2023, 01:07:50 PM
Unless you are foiling.
Title: Re: Maximum Displacement Hull Speed
Post by: StellaBlu on March 30, 2023, 05:58:23 AM
There is a ton of interesting content in this thread for a design newb like me (thank you to the contributors). 

One thing that I'm trying to better understand is how to compare hard chines vs a more rounded hull on a pintail downwind board.  I generally understand the pintail, but more designs have very hard chines in the rear portion of the hull leading into the pintail (Baracuda, FFB Dagger, Sultan, Axis, Etc...).  There are some exceptions with more rounded features (Dale Chapman and Sunova), but they are not the norm.

Wouldn't the harder chines create eddys and drag?  wouldn't softer chines allow for better water release and perhaps less wetted area?

Please help a newb understand the hull design philosophy!  Thanks again.
Title: Re: Maximum Displacement Hull Speed
Post by: SUPeter on March 30, 2023, 09:50:55 AM
There is a ton of interesting content in this thread for a design newb like me (thank you to the contributors). 

One thing that I'm trying to better understand is how to compare hard chines vs a more rounded hull on a pintail downwind board.  I generally understand the pintail, but more designs have very hard chines in the rear portion of the hull leading into the pintail (Baracuda, FFB Dagger, Sultan, Axis, Etc...).  There are some exceptions with more rounded features (Dale Chapman and Sunova), but they are not the norm.

Wouldn't the harder chines create eddys and drag?  wouldn't softer chines allow for better water release and perhaps less wetted area?

Please help a newb understand the hull design philosophy!  Thanks again.

Just the reverse-  water likes to stay attached to curved surfaces as it flows. Not only is water moving longitudinally along the length of the board but, it is also moving laterally as the board slaps down onto the waters surface as we pump and hop. These hard chines allow this lateral moving water to relaease .  When hulls are curved, the water will ride up along that curved hull trying very hard to stay attached to the hull.  All this added water weight is detrimental to an easy and clean separation of hull from water. I hope this helps.
Title: Re: Maximum Displacement Hull Speed
Post by: StellaBlu on March 30, 2023, 10:34:29 AM
There is a ton of interesting content in this thread for a design newb like me (thank you to the contributors). 

One thing that I'm trying to better understand is how to compare hard chines vs a more rounded hull on a pintail downwind board.  I generally understand the pintail, but more designs have very hard chines in the rear portion of the hull leading into the pintail (Baracuda, FFB Dagger, Sultan, Axis, Etc...).  There are some exceptions with more rounded features (Dale Chapman and Sunova), but they are not the norm.

Wouldn't the harder chines create eddys and drag?  wouldn't softer chines allow for better water release and perhaps less wetted area?

Please help a newb understand the hull design philosophy!  Thanks again.

Just the reverse-  water likes to stay attached to curved surfaces as it flows. Not only is water moving longitudinally along the length of the board but, it is also moving laterally as the board slaps down onto the waters surface as we pump and hop. These hard chines allow this lateral moving water to relaease .  When hulls are curved, the water will ride up along that curved hull trying very hard to stay attached to the hull.  All this added water weight is detrimental to an easy and clean separation of hull from water. I hope this helps.

Thanks for the reply - this is helpful.  If I understand correctly, my assumption that the hard chines were disturbing the flow, wasn't wrong, but it is an oversimplification (assuming linear flow).  My oversimplification didn't take into account the priority of releasing the hull from the water surface. 

So basically if the board weren't on a foil, the rounded chines would be faster, but because the board is on a foil and needs to release from the surface, the hard chines are a beneficial compromise.  But in that case, why do foiling monohull sailboats generally have rounded hull features (AC36)?

Taking this one step further, why do these boards then have soft chines towards the nose?  On a touchdown, isn't release a priority again (in which case harder chines would be beneficial)?

Am I understanding this correctly?
Title: Re: Maximum Displacement Hull Speed
Post by: Admin on March 31, 2023, 03:05:50 AM
Yes.  For surface paddling at low speeds, less paddling force will be required on an otherwise similar round bottomed, displacement board than on these narrow, flat bottomed, planing boards with hard angled chines.  The smooth flow of water around the displacment hull is exactly what makes the round bottomed design efficient in this limited lower speed, surface bound setting.  They do however, sacrifce stability, and I imagine they would be awful to pump off of the surface as a SUP Foilboard. The flat bottomed boards (which force water downards and outwards) have been narrowed and lengthened now to the point where they are much faster paddling than their short, wide, predecessors but as a paddling only solution this would not be the most efficient choice.  Fotunately, that is not what they were designed to do.

 
Title: Re: Maximum Displacement Hull Speed
Post by: SUPeter on March 31, 2023, 04:10:01 AM
There is a ton of interesting content in this thread for a design newb like me (thank you to the contributors). 

One thing that I'm trying to better understand is how to compare hard chines vs a more rounded hull on a pintail downwind board.  I generally understand the pintail, but more designs have very hard chines in the rear portion of the hull leading into the pintail (Baracuda, FFB Dagger, Sultan, Axis, Etc...).  There are some exceptions with more rounded features (Dale Chapman and Sunova), but they are not the norm.

Wouldn't the harder chines create eddys and drag?  wouldn't softer chines allow for better water release and perhaps less wetted area?



Please help a newb understand the hull design philosophy!  Thanks again.

Just the reverse-  water likes to stay attached to curved surfaces as it flows. Not only is water moving longitudinally along the length of the board but, it is also moving laterally as the board slaps down onto the waters surface as we pump and hop. These hard chines allow this lateral moving water to relaease .  When hulls are curved, the water will ride up along that curved hull trying very hard to stay attached to the hull.  All this added water weight is detrimental to an easy and clean separation of hull from water. I hope this helps.

Thanks for the reply - this is helpful.  If I understand correctly, my assumption that the hard chines were disturbing the flow, wasn't wrong, but it is an oversimplification (assuming linear flow).  My oversimplification didn't take into account the priority of releasing the hull from the water surface. 

So basically if the board weren't on a foil, the rounded chines would be faster, but because the board is on a foil and needs to release from the surface, the hard chines are a beneficial compromise.  But in that case, why do foiling monohull sailboats generally have rounded hull features (AC36)?

Taking this one step further, why do these boards then have soft chines towards the nose?  On a touchdown, isn't release a priority again (in which case harder chines would be beneficial)?

Am I understanding this correctly?

Racing sailboats have almost unlimited power so all that is needed is/are hulls with a high hull speed. No hopping, pumping required. Paddlers have relatively very little power which requires the use of hopping and pumping to engage the foil for additional speed as well as to break free of the water's surface.  The reason the very hard edges generally do not go all the way to the nose is just a compromise to make a hull a bit more forgiving on high-speed touchdowns, as far as I can tell. Some makers bring the hard edges all the way forward and some totally round off the front end. They all work to greater or lesser degrees. Again, compromise is the order of the day.


Title: Re: Maximum Displacement Hull Speed
Post by: JohnnyTsunami on April 03, 2023, 09:04:33 PM
Just wanted to comment on the "bob" that is done with SUP foils and is likely not factored into anyone's historic equations. The video of the 1st page with the SUP racer you can actually see the tail sucking water up the back just like the scientific a/b test of the canoe and the planing hull. The SUP sucks the water for only a portion of the stroke because the board sort of gets out of the water in conjunction with the riders momentum and seems to almost plane for a moment.

These race SUPS have hard a vertical stern section to allow for this - I believe - as do the barracudas.

I have watched a world class SUP foiler get his sup up in flat water. Bobbing was a major factor. In fact, he mounted the same foil on a friends board +20L with a wider tail. The tail produced so much lift that he couldn't get it to sink for a pump and couldn't "bob" the board and pump the foil. Something to consider.

As with all things foiling I think there is a golden area. Bigger is safer and "easier" to not fall on, but actually harder in every other way.

I have a 4'8" wing board with no bottom contours and a vertical tail rail. The thing indeed won't go above 3mph slogging (I have been passed easily by beginners slogging on their 6' 130L boards!) But, I can pump the s*it out of the thing and unstick it and get it going 8-10mph required to take off on <600cm foils easier than a bigger board with rounded tails.

I'm building a SUP DW board, 7'6" x 19" 100L. I have it shaped with zero hard chines. I'm hoping it will get me up to speeds where I can bob the foil and catch big swell. Inspiration from KT's board for Kane. Maybe something there in ditching the chines. Obviously they would be good for clearing water at planing speeds, but just cause drag below those speeds?

instagram.com/p/Cosy8HiuTaL/

https://www.instagram.com/p/Cosy8HiuTaL/ (https://www.instagram.com/p/Cosy8HiuTaL/)

Title: Re: Maximum Displacement Hull Speed
Post by: StellaBlu on April 04, 2023, 05:23:36 AM
There is a similar chat going on at one of the other forums and there are a few firsthand comparisons between harder chine boards (barracuda) vs softer chine displacement hulls (Appletree, Chapman, Gong) and several people say the speed of the softer chine board makes it easier to takeoff than the hard chine.  Perhaps designs like the barracuda  overstating the impact of “release” and compromising speed too much?  Early days here…
Title: Re: Maximum Displacement Hull Speed
Post by: Solent Foiler on April 04, 2023, 05:52:03 AM
I'm currently waiting for the build of my DW board to be finished, and the tail design was a real headache. I opted for a Gong/Casey inspired, more displacement style tail with the hard chines ending just behind the box. The original drawing from my shaper had the hard chines finishing in front of the box, but I worried it might be too sticky on touchdowns.

The main reason for going for a more displacement style tail was I felt that as this was my first DW board I'll need all the help I can get in getting up, so a planing release edge wasn't going to be the answer there. Also, all the 3 boards I borrowed were pin style tails, and I wanted to pull in the max width as far as possible but keep that width out wide along the rail for as long as possible for stability which is the opposite to a pin tail. Volume is relatively aggressive for a first DW board with no SUP background being +20 my wet weight.

Board dims are 6'10 x 20 x 90L. Have another 10 days or so to wait to see how many design mistakes I made. Haha!
Title: Re: Maximum Displacement Hull Speed
Post by: StellaBlu on April 04, 2023, 06:26:48 AM
I'm currently waiting for the build of my DW board to be finished, and the tail design was a real headache. I opted for a Gong/Casey inspired, more displacement style tail with the hard chines ending just behind the box. The original drawing from my shaper had the hard chines finishing in front of the box, but I worried it might be too sticky on touchdowns.

The main reason for going for a more displacement style tail was I felt that as this was my first DW board I'll need all the help I can get in getting up, so a planing release edge wasn't going to be the answer there. Also, all the 3 boards I borrowed were pin style tails, and I wanted to pull in the max width as far as possible but keep that width out wide along the rail for as long as possible for stability which is the opposite to a pin tail. Volume is relatively aggressive for a first DW board with no SUP background being +20 my wet weight.

Board dims are 6'10 x 20 x 90L. Have another 10 days or so to wait to see how many design mistakes I made. Haha!

Care to share any pics of the design?  Sounds interesting.

Im getting a downwind inspired wingboard made, and am struggling with a few of the features.  I was thinking hard chines and V Tail, but now I'm second guessing it.  The purpose will be for (a) lightwind winging, and (b) downwind winging allowing me to use smaller wing sizes.  I don't intend to paddle up on it, and will probably have more power than a paddle (with the wing), but the design theories are largely overlapping.  Im probably going 6' x 19.5 / 80 Liters or so (Im 80L and daily driver wing board is 60L which I can get up in 8-10 knots). 
Title: Re: Maximum Displacement Hull Speed
Post by: JohnnyTsunami on April 04, 2023, 08:01:15 PM
There http://is a similar chat going on at one of the other forums and there are a few firsthand comparisons between harder chine boards (barracuda) vs softer chine displacement hulls (Appletree, Chapman, Gong) and several people say the speed of the softer chine board makes it easier to takeoff than the hard chine.  Perhaps designs like the barracuda  overstating the impact of “release” and compromising speed too much?  Early days here…

That was my hope! Thanks for the info. The more I thought about it the more like an Olympic sprint single canoe I was thinking of.

https://www.plastexboats.com/pliki/Hydromechanics-of-Sprint-canoes-ver-final+.pdf
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