Tribal Knowledge: Is anyone looking for SUP board design and or shaping tips?

[dpca10]

Wow, great post, I hope KingD is still around for some answers.  I posted on a different thread but wondered if you could talk about what extremes you've tried.  I specifically am interested in what happens when you overboard with a certain feature.  So my questions.

1. What happens when you add too much single concave?  Double concave? With blanks approaching 6" you could have a huge concave theoretically.  Have you ever heard of a tripple concave... big single in the middle and two small concaves at the rail.  Sort of like a catamaran. 

2. What if you over exaggerate a V in the hull?

3. If you keep volume constant what benefits and drawbacks have you wittnesed of going very very short?

4.  Channels? Big channels? 

5.  Extremes of the deck.  Extra domed, extra concave? 

6.  Can the rails ever be too thin, in respect to rail to rail carving? 

Thx. 
DP 

[kingdavid]

Hi DP, I've been out of the loop for a time. We've been relocating or manufacturing facility. We are now doing everthing under one roof; design, shaping, glass, sales... It has been a major project.

I'll try to hit some of your questions:

1. Concave is a great thing when done in moderation. It increases the speed the water flows under the board. In doing so it creates lift as well. This allows you to create a fast board while maintaining thin foils, narrow outlines, and thin rails. The modern shortboard is a prime example.

2. Over exaggerated V slows the board down. V helps the board cut through the water. V also allows you to maintain a straight rocker line down the center of the board while increasing the rocker on the rail line. Thus, when you bottom turn the board it will roll over on edge easily.

3. I use volume to control buoyancy and to control the thickness distribution down the rail line.

4. Channels are another great feature. Channels redirect the direction the water is flowing across the bottom of the boards. In doing so, channels can, and generally do, increase the speed of the board. Like everything, they need to be part of the whole design and should be used in moderation.

5. Deck really is not important. A domed deck can drag more when water crosses it. Concave decks allow for a lower center of gravity so the board will be more stable. Thus, you can get by with a narrower outline.

6. Rails can be too thin. Thin is better than thick in my opinion. Rails are used injunction with foil and outline to control your turns. The thickest part of the rail must be ahead of center for a board to turn correctly.

You may want to check our another thread I started called Anatomy of a Board. In this thread there is lots of great info.

Best

Dave

[PonoBill]

Dave,
Do you think deck height has any effect other than stability? I've heard folks say a low deck gives a paddling mechanical advantage as well. Seems like it would be really slight, but I can see how a really thick deck would make it harder to paddle efficiently.

[kingdavid]

Aloha Bill,

Your comments and observations are absolutely correct. The lower the deck height the lower the center of gravity will be. on We sink the decks about 1" to 2" on our race boards. Doing this gives a significant stability advantage. On the race boards it allows us to go narrower. I've not done the math, but, there is a large mechanical advantage. If we think about our body height divided by the width of the board we come up with a width to height ratio. For example: Let's take a 6' person with a 28" board. 72" divided by 28" = 2.57 height to width ratio. If we drop the deck 2" the ratio is now 2.50 (70"  divided by 28"). This represents about a 10% gain in stability. All of this is to say we can narrow the board by 10%. In other words, we can achieve the same stability with a 25.2" wide board. You check my logic.

Dave

[PonoBill]

I wonder if it's true that you're also getting a better application of force with a sunk deck. All the paddle force is transmitted through the feet so the center of effort is the board surface under the feet. If the feet are at the waterline more force would be transmitted forward.

Assuming the center of resistance is at the waterline (actually somewhere below it, but close enough) if the center of force is above it there is some component of the force directed downward and wasted. I'm just thinking while I'm "talking". Sooner or later I'll do the math and see how much. My gut tells me it isn't much, but while my gut may be large it isn't reliable.

Great thread by the way. Thanks so much for the information.

[kingdavid]

The only flaw in the theory is the spherical union we call our ankles. Maybe our SUP boards need bindings like snow boards, snow skis, water skis, and wake-boards??? Maybe I should even use my carbon fiber CTI knee braces??? You may laugh now, but I'll bet you that someone has or will try this. Just remember I predicted it first.

Any way we look at it; nothing is going to beat a blown 500+ cubic inch hemi under the hood. I know my race guys have volunteered to tape a sky rocket to their butts (or place it elsewhere) if it would help. Are we on to something or just a couple of freaks???