When is an unlimited slower than a 14'?

[Eagle]

A Bullet 17.4 is slower than a Bullet 14V2 on flat and upwind.  Not sure about the UL SB Sprint.

[PonoBill]

For a typical flatwater semi-displacement hull with rocker flat enough to give a waterline length equal to the overall length, a 14 foot board starts to really feel a lot of wave drag at about 5.8 mph. If you can consistently reach and hold something in the range of 5.5-5.8 mph with a board of this type, then you can probably go faster with an unlimited board. If you can't, you won't. 

The unlimited board (say 18 feet) will have more skin friction because of the greater surface area exposed to the water, but wave drag doesn't start exceeding skin drag until about 6.5 mph. Understand that total drag for an unlimited will generally be GREATER than a 14' up until 5.5mph. After that, the total drag of the unlimited is less. At 6.5mph the 14' has a huge amount of drag that only the very best paddlers can overcome. Going 7mph unaided by current, swell, or wind is a real accomplishment.

The same factors are in play for shorter boards. It takes less power to go about 4.5 mph on a 10' race board than it does to go that same speed on a 14'. There is a perfect length for every paddler, and it's not 14'.

The fastest anyone has paddled a 14' boards in a 200 meter sprint is about 9.5 mph. That is well past the Froude "limit" (which is never a limit, but rather a steadily steeper resistance curve). If Danny Ching or Conner were on an 18 foot board the speed would have been something more like 11-12 mph for a similar power output. But you need that pro level of human power to make that happen.

I have to push hard to get 5.7mph on my 14 X 25" Blackfish and I can't hold that speed for more than a few seconds. With a similar level of effort I reach 6.8 mph on my 18' Speedboard and I can hold 6.5 for a minute or two. Or at least I used to. We'll see how that works out at this year's CCBC.

[Eagle]

When I did my sprint tests the first couple of weeks with my AS23 -> was able to hit 6.9 mph peak consistently.  But balance was quite a problem back then.  Even on my Bullet 14V2 though I got 6.7 - so was 100% convinced I could go faster on the AS23 if more cylinders were firing.  Was quite frustrating until I was able to put down a run 7.2 peak all out on the AS23.  Balance was on that day -> and that made all the difference.  Plus was using my SIC 7.0 fin - my smallest and fastest with lowest drag.  I could actually feel the difference btwn 6.9 and 7.2 -> the board kinda freed up drag for a moment and seemed to just go.

No way though I could power that 17.4 for any distance upwind.  I tried.  Even going 90 was super slow.  The board wanted to turn DW even with a ton of rudder correction.  The amount of skin friction surface area is huge comparatively.  Plus so much extra windage above water.  But turn a bit DW -> and that board goes like a freight train on rails.  So majestic feeling.  And fast as blazes in decent breeze.

[yugi]

When I did my sprint tests the first couple of weeks with my AS23 -> was able to hit 6.9 mph peak consistently.
…
Plus was using my SIC 7.0 fin - my smallest and fastest with lowest drag.  I could actually feel the difference btwn 6.9 and 7.2 -> the board kinda freed up drag for a moment and seemed to just go.
…

I have a hard time believing that a few sq in surface area less drag on a smaller fin makes that much difference. Sure, it’s makes a minute difference but that’s just infinitesimally small when compared to a paddler getting his stroke just 1% more efficiently.

3 reasons:
1. There just is no way you are ever going to get consistency out of a paddler to get such a minute measure as the drag difference between fins. There are so many things that go into going fast on a board. I know. I pound a lot of beer and I’m an old fart chained to a desk most of the week yet I can go a decent speed on a SUP. Mainly because I’m able to learn a decent technique. There are guys way more powerful than me I can keep up with. Which means that the slightest bit of better technique trumps raw muscle power. Too many things going on to get things perfect at all times.

2. I’ve done fin testing in a water tunnel. It was not just a fun little experiment but a test to be used to redo the International Offshore Yacht racing handicap ratings to account for keel shapes. Mainly surface area vs depth. So rigour was used and we worked with recognised experts. There was a team who each picked a shape, given a metal sheet and we cut out the shape, round the leading edge and tapered the trailing edge. We were specifically instructed to not waste time tuning a perfect leading or trailing edge. We were told that the difference in a perfect edge tune as compared to the basic shape was negligible. Leading and trailing edge shape makes much more difference than surface area drag, so there you go, negligible as compared to shape. I’m not buying this “deeper is more drag” myth being tossed around here either. The basic parameters are shape, surface area, depth.   

3. I happen to have done some work in Clinical Trials. The double blinding of real and placebo pills is paramount. The placebo effect of a pill is so great so just imagine the placebo effect of gear on a paddler. The video with Connor Baxter comparing 2015 and 2016 Allstars springs to mind. Any paddling comparisons where the rider actually knows which board or fin he/she is on is always just going to be a joke.

What GPS app are you using? The “segments” part seems interesting.

[ukgm]

When I did my sprint tests the first couple of weeks with my AS23 -> was able to hit 6.9 mph peak consistently.
…
Plus was using my SIC 7.0 fin - my smallest and fastest with lowest drag.  I could actually feel the difference btwn 6.9 and 7.2 -> the board kinda freed up drag for a moment and seemed to just go.
…

I have a hard time believing that a few sq in surface area less drag on a smaller fin makes that much difference. Sure, it’s makes a minute difference but that’s just infinitesimally small when compared to a paddler getting his stroke just 1% more efficiently.

3 reasons:
1. There just is no way you are ever going to get consistency out of a paddler to get such a minute measure as the drag difference between fins. There are so many things that go into going fast on a board. I know. I pound a lot of beer and I’m an old fart chained to a desk most of the week yet I can go a decent speed on a SUP. Mainly because I’m able to learn a decent technique. There are guys way more powerful than me I can keep up with. Which means that the slightest bit of better technique trumps raw muscle power. Too many things going on to get things perfect at all times.

2. I’ve done fin testing in a water tunnel. It was not just a fun little experiment but a test to be used to redo the International Offshore Yacht racing handicap ratings to account for keel shapes. Mainly surface area vs depth. So rigour was used and we worked with recognised experts. There was a team who each picked a shape, given a metal sheet and we cut out the shape, round the leading edge and tapered the trailing edge. We were specifically instructed to not waste time tuning a perfect leading or trailing edge. We were told that the difference in a perfect edge tune as compared to the basic shape was negligible. Leading and trailing edge shape makes much more difference than surface area drag, so there you go, negligible as compared to shape. I’m not buying this “deeper is more drag” myth being tossed around here either. The basic parameters are shape, surface area, depth.   

3. I happen to have done some work in Clinical Trials. The double blinding of real and placebo pills is paramount. The placebo effect of a pill is so great so just imagine the placebo effect of gear on a paddler. The video with Connor Baxter comparing 2015 and 2016 Allstars springs to mind. Any paddling comparisons where the rider actually knows which board or fin he/she is on is always just going to be a joke.

What GPS app are you using? The “segments” part seems interesting.

1. My own stuff highlights that there is a gap from a cheap fin to one of the specialist brand fins. You can obtain reliable results of that but its neglible returns once you've got a decent brand fin.

2. Fin tests in flume or tunnel don't take into account paddler efficiency when using the fin. Using the wrong fin may well harm your speed if you can't handle it or don't have it set right. Matching the fin to the paddler is a must in my view.

3. I agree completely. 'New board syndrome' is a well know effect round these my local waters.

[yugi]

^ I agree with you, ukgm, that a paddler finds a fin that suits him/her. Largely, I find, that one an get used to a fin. I’ve tried fins that great paddlers loved and I was, like, “meh”, but in giving them enough time I could adjust and enjoy their qualities. Which brings us back to point1, if you have a paddler used to a certain kind of fin they may well underperform in testing when on one they aren’t jiving with.

I know fins make a lot of difference. It’s just always going be hard to measure. I just can’t see anyone but the elite best paddlers able to be consistent. Besides which, no-one but the best is going to even be paddling correctly, let alone silky smooth. You need a “stig” for your testing. He needs to be anonymous because top paddlers are spancered by fins. BTW with fins you CAN do blind testing. You just need two identical boards and someone to swap fins without you looking.

Sorry for the thread drift, lets stay on ULs.

Thanks for running those numbers, pono. Makes a lot of sense. I understand that.

Somehow, in my mind, I thought of UL’s as awesome for long distance outings. But given what you’ve pointed out, unless you’re keeping up an pretty good clip you may not be getting much advantage. Have you thought about that for that long CCBC, pono? Maybe a 14’ is a better tool for the long distances. What is Bart on for his epic trips?

I’m jonesing for a fast [on flats too] DW 16’ mainly because with nose rocker effectively it’d be like a 14’ at waterline. That’s my thinking in wanting a 16’, along with going yet again narrower without losing stability.

Next question is how effective difference skin friction reducing  methods are, and are they noticeably worth it for UL’s?

[PT Woody]

I think the greater weight of the unlimited board vs a 14' also has and effect on speed in flat conditions. I've paddled the Bullet 17-4 and the Bullet 14 on consecutive days in flat ocean conditions and just the shear weight difference of the 17-4 tires you out much quicker than the 14.

The Starboard 17'6" Sprint weighs around 11kg so you won't find too many 14s that weigh less.

[Pierre]

about 12 to 14 percent more wetted surface on a 17'6" than on a 14'... if the UL dissimilar outline asa sprint x23" and the 14 as a sprit x 24"... th wavedrag isles but friction more, stance and technique must be different, longer strokes on a long hull . Mathieu Rauzier,when he designed the Sprint 17'6", said that incresing the llength above would increase wetted surface too much. he said also the concept is totally different that on a 14' which is designed to "semi" plane using a "connor" stroke technique, for that reason a veryfit paddler on a semi-planing 14' goes over Froude limit and is may be less affected by shallow water effect.... may be because i have no clue of any tests.
One friend built a transom extension on his flatwater 14'; bringing length to about 15'6'', I have no news about speed benefits.

[Eagle]

yugi - my speed tests were not designed fin or board tests.  Just full on 100% sprint speed tests using my AS23 and Bullet 14V2.  My gut tells me though that my balance to power ratio probs impacted my GPS speed the most on my AS23.  The fin probs impacted a lesser amount.  The app uploaded to is Strava.  And there was no segment as it was one continuous file as graphed.

Would be interesting to see GPS peak speeds from Connor and Kai to confirm 9.5 mph.  That is impressively high.

[FloridaWindSUP]

a 14 foot board starts to really feel a lot of wave drag at about 5.8 mph. If you can consistently reach and hold something in the range of 5.5-5.8 mph with a board of this type, then you can probably go faster with an unlimited board. If you can't, you won't. 

The unlimited board (say 18 feet) will have more skin friction because of the greater surface area exposed to the water, but wave drag doesn't start exceeding skin drag until about 6.5 mph. Understand that total drag for an unlimited will generally be GREATER than a 14' up until 5.5mph. After that, the total drag of the unlimited is less.

It's interesting that, at below hull-speed, total drag on a shorter board could be less than on a longer board. It would be interesting to see the "drag vs. speed" plots for different board lengths, and where the cross-over point is. Even more interesting to see the same plots for different water depths.

[Eagle]

Here is an interesting speed test from BW that I had posted before.

[Area 10]

How is that review relevant to the topic, Eagle?

[Eagle]

Helps confirm that speeds around 7.0 mph can be achieved on a 14 -> and provides some basis for comparison to UL GPS speed tests.

[PonoBill]

Yes, I'm aware that the Speedboard will actually require more work to do the CCBC than my Blackfish does, but the Speedboard is what I have on the east coast for open ocean boards. The difference isn't huge, and the CCBC isn't a race. Average speed is about 4 mph. I'd probably be better off on a wide 12' board, but it really doesn't matter that much.

Yes, Florida, the graphs are interesting. The crossover point for wave drag vs. skin drag occurs before hull speed, since the hull starts climbing the bow wave well before the "limit".  You can create a graph for any hull using the formulae on the page I referenced.

No one has done much with actually measuring SUP hulls, but there's a huge body of work on other human or wind powered forms. This page on Kayaks is very useful: http://www.oneoceankayaks.com/kayakpro/kayakgrid.htm

As you can see, the skin drag (viscous drag) is sort of linear, while wave drag is sharply nonlinear. The point where they cross is where you start seeing an advantage from a longer hull. Before that point the longer hull has higher drag.

One thing to remember is that the speed of a paddled hull varies constantly. At the start of the stroke it's going substantially slower than at the end of the stroke. If the hull is close to the crossover point that acceleration is much harder to achieve, and you feel greater resistance than lower speeds. We translate that as glide. Longer hulls don't hit that barrier at the lower speeds we normally paddle at, so the sense of greater glide is easy to feel, even when the hull is actually experiencing higher total friction.

[Eagle]

^  That kayak link has a lot of good interesting information.