Physics - why a wider surfboard paddles faster

General Discussion
1

It is probably not 100% ARCHIMEDES approved, but it floats! Can anyone explain more thoroughly?

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Why do wider surfboard paddle faster? I tried to come up with a GENERAL explanation.

Suppose you have two surfboards, a quiver! The boards are equally long, the slim one is a bit thicker, the wider one is less thick, both have the same volume.

Imagine yourself on both boards. In both cases you sort of float, you are in balance. you float because there is a buoyant force pushing you and the surfboard up. This force is created by the Volume of water displaced by you and the surfboard. In both cases the buoyant force is equal, the force floats you.

To obtain the buoyant force, the same volume needs to be displaced in each case. In the first case, the slim surfboard, the volume equals Widthlengththickness.

Since the the width of the slim surfboard is smaller than the wider wide, and you are seeking to match the same volulme, you need to put more surfboard length wise in the water. The boards sits low in the water. The wider surfboard needs less length submerged to have the same float, so this boards sits higher in the water.

Since a board that sits lower in the water has to displace more water + the fact that it induces more viscous drag because more rocker is in the water is paddles A LOT slower.

The wider board paddles faster, because due to its higher position in the water, less water needs to be displaced, and less viscous drag is incurred by the rocker underwater.

you can imagine that even if you add thickness to the slim board, you still need to put the same amount of volume under water to have the same float, thus still have the same drag, thus paddle still as slowly.

What about that?

2

Is that Princess Diana?

3

It IS Princess Diana! Seriously, no joke, I wish to God she were still on Earth. Drunk driving kills moms, tossers!

Good thread so far!

4

The wider board does not displace less water. All other things being equal, the narrow thick board and wide thin board will displace exactly the same amount of water.

My experience with boards over 10 feet is narrow boards paddle faster. No question. The same holds true for paddleboards and rowing shells, which are as narrow as practicable.

5

I think this is a very broad assumption. You would have to look at all things constant first. Assuming a long thin board would be like a 2 x 4 and a wide short board would be a 1 x 8 (of equal length to start). The paddler being constant, Im not so sure which one would be faster.

There is one thing I do know…

If you put me on a 19’ unlimited paddleboard and put Jamie Mitchell on a 10’6 rescue, he would still murder me. (but Im just going to blame his genitically ape like, knuckle dragging arms)

Personally, I like a lower riding board. I find shortboard(thrusters) paddle better under water, about equal to my 5’10 fish.

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Quote:

The wider board does not displace less water. All other things being equal, the narrow thick board and wide thin board will displace exactly the same amount of water.

My experience with boards over 10 feet is narrow boards paddle faster. No question. The same holds true for paddleboards and rowing shells, which are as narrow as practicable.

Hi Paul,

It is true that both the surfboards displace the same amount of water. Then why would, at small sizes, the wider board be faster?

Would it be that at 10feet the drag created by the surfboard surface would add so much drag that you have to make them narrow to keep going?

Still trying to figure it out…

Wouter

7

I think the difference in paddling speed with width would be minimal when your talking about shortboards, volume distribution, ie how much foam is under the heavier parts of your body, would be more noticeable. Width difference in longboards however is another kettle of fish. I, like ACheateaux, prefer shortboards that don,t have a lot of volume anyway, because they surf better.

As for Diana, don,t be fooled by her media front she was just an overblown tart.

8
Quote:

As for Diana, don,t be fooled by her media front she was just an overblown tart.

you shut your mouth when youre talking to me!!!

sorry, I cant resist a chance to throw some “wedding crashers” dialogue in the mix…

as far as a shortboard with less volume surfing better, thats a matter of opinion. I happen to enjoy the smooth clean lines of fuller boards, but find a shortboard with less volume is easier to pull through the water, similar to swimming. 20 years ago, you crawled across the top of the water and all technique focused on this. Now days, you pull just UNDERNEATH it. less drag.

a wider board is definatly more prone to “plowing water”.

one of the things I still cant figure out, is why a paddleboard will be just as stable as you go longer and thinner as it would be fatter and shorter??

and once again, I would just like to say, the only reason that the aussies have asserted such dominance over anyone else in the sport of paddleboarding, is that Jamie Mitchell is a knuckle dragging half ape man. If ol’ Chipper would discontinue all further experiments in the field of cloning, Im sure the US could catch up…

that is all for now…

9

I don’t know why, at small sizes, a wider board paddles faster. It probably has something to do with the drag of the paddler moving through the water. When I paddle my 11’-10" I’m completely out of the water.

For really long boards there are two components of resistance to consider. One is wavemaking resistance, the other being frictional resistance. For a given volume, long slender shapes tend to have less wavemaking resistance, and shapes with rounded bottoms tend to have less frictional resistance. That explains why longboards and paddleboards paddle as well as they do.

10

My take is this: The arguments for wider boards usually relate to planing ability, but you can’t plane while you’re paddling. Narrower boards, all things otherwise equal, have less profile, so less resistance in the water and greater glide speed. Look at boards built for speed, like a Frye Eagle or a G&S Speed Shape: very narrow for their length. Wider boards will plane earlier on a given wave but sacrifice speed. I like narrow boards that have some weight to give them more inertia when paddling, like the triple stringer Eagle, which I think compensates well for the delayed slower planing point on mushy waves. On bigger waves, the narrow boards seem to have no liabilities, and are better suited for the conditions. Other things that cut through the water that are designed to maximize speed are always narrower, as has been alluded to. Another example of that is the hull on racing catamerans, e.g. the Supercat, very narrow hulls.

11

A “tart.” Well, that makes you cool.

12

Sorry if that upset you but I could’nt resist the urge to redress the balance.

13

In relation to shortboards my experience when comparing a 6’3" Thruster with a 5’8" wide fish of the same thickness - is the Thruster is easier to paddle.

The fish floats better and if there isn’t a lot of waves in the way is pretty quick to paddle out, especially with a runout or glassy conditions.

however the thinned out Thruster is a lot quicker to get through turbulance, pushes through oncoming waves and doesn’t bob around - kind of slices through.

I’ve heard fishes paddle better or are faster to paddle - I think it’s more accurate to say they float better, which can be advantageous to paddling but can be a bitch in getting through unrelenting sets and turbulent mush.

14

In my experience, my 9’0" Simms Slimmer (9-0 x 16 3/4 x 21 1/4 x 13 1/2 x 2 3/4), even with its heavyish rocker, paddles faster than many wider, thicker boards I’ve borrowed from friends.

One reason is that I can get nearly my whole arm in the water when paddling this narrower board, and so paddling is more like a freestyle swimming stroke, but on really wide boards, I can’t get as good of a stroke.