SUP design: stability and planshape curve, a question from Dave


SUP Design - Constructive Criticism please!

I've attached a PDF of my ( AKU shaper ) design so far, any feedback would be gratefully received.  I'd like the board to be a bit of an all rounder, so I don't mind a bit of compromise as far as flat water performance goes.

Out of interest, what are you thoughts on stability of a narrow tailed SUP if it's got a lot of fin surface area? Do you think the fins would counteract the narrow tail to any degree?

Very nice, almost identical in planshape and volume to my Baron 12 footer. The Baron is only 2.25 thick and is only 27" wide though.

The board will ride waves very well, but don't underfin it !

If you have enough stability for paddling you'll definitely enjoy the surfing characteristics. . . making the rails more parallel will tend to kill those good qualities.

Although I don't currently standup paddle I've been riding very wide longboards with narrow tails for a long time, since way before the SUP revival happened and as you are probably aware I believe in them.

This is how it works regarding stability: When paddling the wide point area of your board will be in the water. When surfing this area will rise out of the water as speed increases, allowing the board to use the narrower tail. This means that with a wide midpoint and a narrower tail you get the advantage of width when you need it ( paddling and taking off ) and the advantage of the narrower tail for control and ease of turning when going faster.

So it's a good idea to increase overall width and reduce the tail width as you have done. If you wanted to increase the stability of your design ( which is probably fine as is ) I'd do one or more of the following three things:

1) Increase the overall width, while maintaining your drawn in tail

2) make the board longer

3) Flatten the tail rocker

I'd also pull the rocker apex forward to the same position as the wide point, this is a foolproof way of matching the planshape and bottom curves, and m,akes sure that the long rail ine is used to best advantage. Having the apex behind the wide point makes the board lose drive, bringing it forward also flattens the tail curve which is good for speed . . the tail's what you are going to be using when going fast.

A big fin will help prevent fishtailing when paddling, and is a great secret weapon when waveriding on surfboards like this as that narrow tail gives precise control over the lift angle of the big powerful fin, a great combination !

I'd better stop before I suggest a big tunnel fin on the tail, even though it would be the icing on the cake :wink: