Flat bottom wakesurf board and speed

Last week was such a crazy week, with so much going on! Sponsorship deals for James Walker and then first test rides, we couldn’t quite get everything in! One of the things we left out was testing that old wakesurf board that we had made something like 4 years ago that was principally flat, without contours and with a fairly shallow rocker.

You may remember that we discussed the two schools of thought regarding bottom shapes; one being that bottom shapes don’t mean squat, that flat is the fastest and all of the shaping increases stiffness and reduces rocker and THAT is what impacts speed. The other school of thought is; of course they channel water and impact flow and therefore improve speed.

So we took an old wakesurf board that was principally flat on the bottom and refreshed our memories!

What did we find in those competing theories? It was pretty interesting, refer back to that picture above for a moment and look at the water coming off the outside rail. You can see two sort of segmented flows. The first towards the back of the board that is flowing UP like a rooster tail and then just in front of that sort of under the ridres front foot you can see water escaping out and away from the wakesurf board.  That second segement has a rather flat trajectory.

Much of the talk about the benefits of channels and concaves rely upon concepts that require a closed system. A closed system would be something like your garden hose, there is no way for the water to escape out the sides, it has to run down the length of the hose and out the end. So placing your finger over the end of the hose will impact the flow out of that closed system.  That’s the concept, that water is forced into channels or concaves because it can’t escape.

Do we have a closed system on the bottom of a wake surf board? No way in hell! So what happens with all of those theories about squeezing water through slots and the like? Total garbage, sort of. The underlying theories of water channeling and being squeezed just don’t hold water (sorry we had to). Water is lazy and will simply find the easiest way out and that isn’t in a channel or down a concave, except in the instance where that is actually the easiest way out!  So, that water that is shooting out the side of the wakesurf board in the picture…that was the easiest way for it to escape.

So if existing the backside of a channel is the easiest way out, that’s where the flow will go, but not because it’s trapped or being forced through, by some form of induction or venturi principle. Would water flow in that same direction if the wakesurf board didn’t have a channel or concave? Yeah, most likely and the deviation between the two is probably not that significant.

So does a channel or concave help in channelling water? Umm, sure sort of. Would the flow be the same without the channel and concave, yeah pretty much.

So flat is fast. Is it remarkably faster than anything with a bottom shape? No, but it’s fast, without a doubt.

Are flatter rockers fastest? Yeah, this is definately accurate, there is no doubt that a flatter rocker develops the greatest down-the-line speed. At least in terms of concaves, the flattening out of the effective rocker is probably the single most effective part of that design. But there is also something to be said for the stiffening effect that the concave offers.

Each of the bottom shapes offers other attributes though. On thicker wakesurf boards, concaves and channels can reduce volume and make it easier to sink that area of the wakesurf board. There are all manner of changes in handling that bottom shaping impacts, plus the increase in stiffening.

So that was definately a worthwhile exercise and it gave us a fresh perspective on just exactly what our bottom shapes are doing behind the boat!

Thanks so much for following along, we have a new concave deck wakesurf board that we’ll be introducing this week, we’re not quite sure which day but be sure to check back for the first glimpses.  Plus we want to springboard off this research into a new skimmer build that James Walker will be wakesurfing.

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