Author Topic: Maximum Displacement Hull Speed  (Read 9952 times)

PonoBill

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Re: Maximum Displacement Hull Speed
« Reply #15 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).
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

PonoBill

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Re: Maximum Displacement Hull Speed
« Reply #16 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.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Dontsink

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Re: Maximum Displacement Hull Speed
« Reply #17 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...).

PonoBill

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Re: Maximum Displacement Hull Speed
« Reply #18 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.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

tarquin

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Re: Maximum Displacement Hull Speed
« Reply #19 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.
 

Beasho

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Re: Maximum Displacement Hull Speed
« Reply #20 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. 


« Last Edit: March 15, 2023, 06:22:05 PM by Beasho »

Beasho

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Re: Maximum Displacement Hull Speed
« Reply #21 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 its a start.

Subber

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Re: Maximum Displacement Hull Speed
« Reply #22 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?
Jimmy Lewis Black & Blue Noserider 10'1"x31"x4.25," 164 liters, 24 lbs, 1 box
Pearson Laird Surftech Longboard 10'6"x23"x29.75"x18"x4.375," 154 liters, 24 lbs, 3 boxes
Takayama Ali'i II Surftech 11'x21.375x28.5x17.25x 4.25, 162 liters, 26 lbs, 3 boxes

DavidJohn

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Re: Maximum Displacement Hull Speed
« Reply #23 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?

PonoBill

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Re: Maximum Displacement Hull Speed
« Reply #24 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."
« Last Edit: March 18, 2023, 08:52:11 AM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

tarquin

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Re: Maximum Displacement Hull Speed
« Reply #25 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.

Admin

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Re: Maximum Displacement Hull Speed
« Reply #26 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.

PonoBill

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Re: Maximum Displacement Hull Speed
« Reply #27 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
« Last Edit: March 19, 2023, 12:29:50 PM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

deepmud

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Re: Maximum Displacement Hull Speed
« Reply #28 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?

sflinux

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Re: Maximum Displacement Hull Speed
« Reply #29 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
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)
Quiver Shaped by: Joe Blair, Blane Chambers, Jimmy Lewis, Kirk McGinty, and Bob Pearson.
Me: 200#, 6'2"

 


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