Is longer always faster for Unlimited boards?

[Newcastle]

Is longer always faster for Unlimited boards?

Say your goal was to go 6.2 mphs average during a 7 mile race. Could a 16' board be as fast with less drag than a 19 foot board?

Obviously it has been shown that the strongest unlimited guys, (ching, rojas, maximus) are are fastest on the big boards. They have the strength to push them to their hull speeds. But if you were a smaller, less powerful paddler would less board make more sense. Is the extra three feet a just drag at 6.2 mphs (assumed hull speed for a 16 board)? I'm talking about more or less flat water racing here, not downwind.

[paddlestandingup]

I don't really know what I'm talking about but I'm going to say that "longer is faster" 

[corlot]

Glad you brought this topic up. It will be interesting to see if anyone can provide hard data on ultimate length to rider weight ratio. I have read that may mid sized paddlers prefer a 16 foot length board. I tried a 16 foot downwind board and if seemed to fly even on light chop for my weight (185lbs). It would be nice to know at what point waterline will work against you.

[PonoBill]

No. If it were always faster a 50 foot board would be faster than a 16, and you know it won't be. Given the same hull width, drag increases with length because surface area increases. You can make a longer board narrower, but there's a limit. So drag increases. It doesn't increase as rapidly as the drag from approaching hull speed does, but it's a steady increase. There are lots of people who will be faster on a 14 than a 16.  They require more motor.

So your main question, which is can the 16 ft board be faster than the 19, is yes, absolutely, if the paddler isn't capable of pushing the 19 to hull speed. As long as the paddlers stay clear of hull speed the drag is proportional to the surface area. Actually it's more complicated than that, or barges would slide through the water as well as sailboats. The drag is proportional to the prismatic coefficient, which is the ratio of displacement volume to the product of waterline length and maximum cross-sectional area. Pointy things have less drag.

There's an odd relationship of wave drag to shape that actually favors tubby shapes. At or above hull speed the wave drag is less on a fatter cross-section board. I think that's what Jimmy Lewis was aiming at when he did the Slice, though knowing Jimmy I doubt he did any hydrodynamic calculations.

[greatdane]

2 years ago I sold my 18' Bark to a guy who is about 150 pounds.  This was a board I could maintain 6.0 mph on is most races.  About two weeks later, we went for a training paddle and he was super bummed out that he couldn't stay with us since we were on 14's. So he eventually sold it to someone else. Several people in town (smaller stature, not necessarily weaker) tried the Bark and could not get it to maintain much over 5.5 mph. I assume these same folks would do better on 16's or even 14's.

[1paddle2paddle]

As others have said, the basic answer is "no," a longer board is not always faster.

For example, we have a SIC F-16 a Starboard ACE 14, and the ACE will smoke the SIC every time in a flatwater sprint, even though it is 2' shorter.

Obviously a flatwater race between those boards is not really a fair comparison since one is designed for flatwater speed while the other is designed for downwinding and riding bumps, so it is like comparing apples & oranges.




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[Area 10]

I think the opinions expressed here also pretty much also apply to smaller lengths than UL.

The overwhelming experience for most people when getting a longer board is disappointment at how little difference it makes to their speed.

Of course, the manufacturers aren't going to tell you that...

IMO you've got to be an advanced or elite paddler to really make extra length translate into a *much* faster pace, especially at the length extremes.

And in cross-winds etc. the longer board will often be slower.

But it's no use telling people that. I guess it's just one of those hard SUP lessons you have to learn for yourself.

But maybe you are an elite paddler. In which case it seems likely that you are just going to have to experiment because at that level there are too many variables and currently too little data (i.e. from similar paddlers) to make a confident prescription.

[pdxmike]

There are no races around here where there are more than a token number of unlimited boards, but in races where lots of people are on them, I'm sure your question would be answered by seeing that people show up on a variety of lengths. 

Obviously, not everyone is always on the ideal board for themselves, but on the other hand there probably aren't a lot of people who'd rather have a 17' board but only want to bother storing and transporting a 16' one. 

The races I know about with lots of unlimiteds are ocean races.  It'd be interesting to see what range of board lengths would show up at a flatwater race with lots of unlimiteds--not that that's necessarily ever going to happen.

[SEA]

I'll take my 17 foot bullet over a 14' out in our open ocean pretty much every time !! 

[jb]

No. If it were always faster a 50 foot board would be faster than a 16, and you know it won't be. Given the same hull width, drag increases with length because surface area increases. You can make a longer board narrower, but there's a limit. So drag increases. It doesn't increase as rapidly as the drag from approaching hull speed does, but it's a steady increase. There are lots of people who will be faster on a 14 than a 16.  They require more motor.

So your main question, which is can the 16 ft board be faster than the 19, is yes, absolutely, if the paddler isn't capable of pushing the 19 to hull speed. As long as the paddlers stay clear of hull speed the drag is proportional to the surface area. Actually it's more complicated than that, or barges would slide through the water as well as sailboats. The drag is proportional to the prismatic coefficient, which is the ratio of displacement volume to the product of waterline length and maximum cross-sectional area. Pointy things have less drag.

There's an odd relationship of wave drag to shape that actually favors tubby shapes. At or above hull speed the wave drag is less on a fatter cross-section board. I think that's what Jimmy Lewis was aiming at when he did the Slice, though knowing Jimmy I doubt he did any hydrodynamic calculations.

PONO- I'm sure you have answered this question a million times on the Zone. But one more time...how do I calculate my necessary speed to reach/maintain max hull speed? And I only use fingers and toes to count with. Meaning there comes a speed when my board (and I)  use less energy to go a certain speed. Like a boat that get up on plane. Is this making sense? I have heard Danny Ching and others quote hull speeds. I want to quote hull speeds too. Help Bill!

[TallDude]

One main reason all the top racers use unlimiteds in distance races is the track straighter. Less zig-zag, less wasted energy, shortest distance from a to b. It adds up. In the 38 mile Catalina to Dana Point race, all the top guys and girls use unlimiteds. There where a few people on shorter boards, but the unlimiteds dominated. Weight is a big issue with unlimiteds too. They got to be under 25# to be competitive in a non-downwind race. Most of the non-downwinding unlimiteds are in the 23" to 25" wide range as well.

[Celeste]

PONO- I'm sure you have answered this question a million times on the Zone. But one more time...how do I calculate my necessary speed to reach/maintain max hull speed? And I only use fingers and toes to count with. Meaning there comes a speed when my board (and I)  use less energy to go a certain speed. Like a boat that get up on plane. Is this making sense? I have heard Danny Ching and others quote hull speeds. I want to quote hull speeds too. Help Bill!

Vhull ~ 1.34x(waterline length)^.5  in knots.  Some texts go as high as 1.51x(WlL)^.5  Since it is the square root of waterline length, the difference between 14' and 16' is tiny.

I have a friend with a degree in naval architecture and she uses Froude number rather then hull speed.

[headmount]

Tall... Great point about tracking.

Wow less than #25?  Man I wish I had one that light.  Can you still strap them on a rack when they're that light?

My Bullet is #33 with a few patches on it... but it doesn't leak anymore.

[TallDude]

Head_, You lay them up thin as possible. Flex is usually an issue. If they flex to much, just add a little more carbon where it's needed. The lay-ups are not the same all over the board. These are race boards, and they can leak because of how thin they are laided up. You test and spot patch the leaks as you find them. Most people don't realize that most of the unlimiteds are custom one off's. I raced a 19' x 24" Richmond a few months back. It was a board I borrowed from a friend. I was talking to another friend of mine who races unlimiteds and he said "I saw you at that race with the orange and black Richmond that So-and-so used to own." It's like everyone knows that specific unlimited, they are that custom, and unique. Some have rudders, some don't. There is definitely a camaraderie among the unlimited racers, that you don't see in other classes. We are the few.

[surf monkey]

Tall Dude

Did you like the Richmond i have a older 18 bark and the last race i went too I saw some fast looking Richmound's they were narrow just wondering how stable they are they had a double concave on the bottom with double fixed fins?