Optimal DW hull shapes: concave or not

[yugi]

This 2008 thread on Foote 14’ Downwinder and DW shapes came up and was an interesting re-read.
   http://www.standupzone.com/forum/index.php/topic,2141.0.html

A few comments on concaves were mentioned like this one

…
These pics are a little off in that that they don’t really reflect that the board is actually pretty streamlined looking.  It is relatively slim at 27 inches, and the tail (which looks huge due to the wide angle lens) is actually only 5 inches wide.  The concave Bill was talking about is pretty deep up front, and just looks like it will send and accelerate a lot of water towards the tail.

I’ve been wondering about concaves for a while and really noticed something recently on a mild, ~20kn, but nice sharp clean bumps where planing was made easy. Very good planing conditions for little wind. I’ve been switching back and forth a lot between my 14’ Rogue Rage and buddy’s  14’ V1 Bullets, and did so back and forth on this recent DW. The Rage has a slight belly under the nose, similar to a 17’ V1 Bullet, then a pure fact mid section and a pronounced kick in the tail. 14’ V1 Bullet, which I’m sure most are familiar with, is concave up front going into double concave and little to no kick in the narrow tail.

We ride together regularly and have very similar speed. Making for a very noticeable distinction between the 2 boards. The Rage consistently managed to pull away from the Bullet in these conditions. In lighter conditions the Bullet typically picks up easier on a plane. In bigger conditions we tend to be closer together.

I’m thinking it’s the concave bottom up front. Conditions were so clean I could really pay attention to a few things and, on the Bullet, began to avoid the front touching the water at all and lost less speed. I felt if the front touched the water there is a “sticking” effect from the concave and it brushes a bit of speed off the plane or even drops the plane. Careful trimming could take care of most of it but even in clean conditions waves aren’t that regular and sometimes a bump mange to touch the hull and - boom, speed lost. The flat bottomed Rage with bellied nose  (and soft rails up front) just rocks on happily like a fast ball in a pinball machine.

Pretty much mid-80’s, ’85 I believe, I had a Cobra Radical 290 and 260 windsurf boards. Concave all over the place. Twin concave channels down the center and concave chimes with a lot of rocker. Cool board with great construction (as we now know).

Jibe machine, v comfy in chop, but not fast. As we now know in windsurfing flat bottomed hulls just blew them away. AHD boards then came back in vogue with a slightly concave bottom that was weirdly comfortable and pretty damn fast but those also gave way back to flat bottomed and no rocker in tail. Lesson learned, and clearly felt it the other day.

Meanwhile I need to spend more time on these 2014 14’ Javelin x26’s which have joined our gang quiver. Just need some more windy days (more of a spring, fall thing around here). Such a clean simple shape. I want to learn how to get the most of it.

New 2016 shapes going to be announced soon I expect, with some DW specific race shapes from Naish and Starboard.

So… what you board shape experts think? How to find the right tradeoff between helping the board jump up on a plane and the right shape to keep it on the plane?

[DavidJohn]

The new Starboard Allstar 'downwind spacific' board has the biggest concaves that Starboard has ever done in the past.

The new Naish Maliko Javelin 'downwind spacific' board has the biggest concaves that Naish have ever done in the past..

And about time IMO.. 

[yugi]

interesting!

[yugi]

Oh wow
2016 Allstar
   

Monster chines. Not sure how they work. Someone got an idea on their spacific purpose.

My old Cobra board chines had a rocker to them where the center channels zero rocker. Which meant when rolled over on edge it turned like crazy and flat the board tracked well. Worked like a dream.

Love the new term, "spacific", BTW DJ. Do we pronounce the a as in "spa" or "space"? Your call as inventor.

The new Starboard Allstar 'downwind spacific' board has the biggest concaves that Starboard has ever done in the past.

The new Naish Maliko Javelin 'downwind spacific' board has the biggest concaves that Naish have ever done in the past..

And about time IMO.. 

Love how internet forums spawn new words. A recent favorite being "spancered" by this kid on TGR posting a thread  "how to get spancered". Got adopted rapidly in the skier commnity. Hope this one does likewise. Has a similar fantastic ring to it.

[Eagle]

I think that any design works for DW once you dial a board in and find its sweet spot for your riding style and power level.  It seems that once the pros and cons are figured out - you basically avoid the cons and proceed to rock the board best you can.

More importantly it seems rider skill and strength matters most.  On a DW with a sponsored rider about the speed level of JR based on M2O results -> that paddler just pulled away from us with ease.  He was using his old beat up Bark Expedition from days gone by.  Now he was fast -> but comparatively he and JR were slow compared to the overall winners who were about an hour faster than them.  That puts into perspective how slow we Joe average paddlers in our little neck of the pond really are.

Back to the design question -> the SIC designs have not changed a lot over the years and seem to work really well.  I think the single and double concaves of the Bullet 14V2 and 14V1 allow the front end to generate good lift to get up on plane and keep the underbody loose.  You can clearly hear the underbody release when it does.  The best aspect in our experience though is the panel vee tail that allows the board to plant and turn on plane to catch the adjacent wave with ease.  We really have become addicted to planing and prefer that much more to gliding.  That slamming sensation at speed is what makes DW special and fun for us - it is a little adrenalin pop each time that happens.

Other boards with rounded bottoms and flat bottoms have a completely different feel.  They all work but we prefer the SIC design as it is so stable and forgiving at speed.  However, my wife who has been riding for less than a year still prefers and has more fun using our more stable flat bottomed M-14 when winds are 15-20 kts.

So it seems it comes down to whatever board you dial in and what works best for you in the conditions you ride in.  That 26.5" 14V2 / M-14 creation would be money though.   

[DavidJohn]

Oh wow
2016 Allstar
 

Monster chines. Not sure how they work. Someone got an idea on their spacific purpose.

My old Cobra board chines had a rocker to them where the center channels zero rocker. Which meant when rolled over on edge it turned like crazy and flat the board tracked well. Worked like a dream.

Love the new term, "spacific", BTW DJ. Do we pronounce the a as in "spa" or "space"? Your call as inventor.

The new Starboard Allstar 'downwind spacific' board has the biggest concaves that Starboard has ever done in the past.

The new Naish Maliko Javelin 'downwind spacific' board has the biggest concaves that Naish have ever done in the past..

And about time IMO.. 

Love how internet forums spawn new words. A recent favorite being "spancered" by this kid on TGR posting a thread  "how to get spancered". Got adopted rapidly in the skier commnity. Hope this one does likewise. Has a similar fantastic ring to it.

Ha.. just spelled specific wrong.. thought it looked wrong at the time .. 

I paddled that board soon after taking that vid.. You can feel the concaves working.. even on flat water..

[headmount]

New SIC 17 V3 has a double concave towards the back.