Input on SUP design

I am planning to build a hollow wood SUP, using the Grain Surfboards building method. I live and surf in Santa Cruz, CA and would use the board primarily for surfing small point break waves, and for shorter fitness runs or break to break surf tours. Most common wave size would be 1-4 feet, generally with good shape and quality. I’m an SUP novice, but longtime surfer, 5’7" 173, decent but not great fitness. I most frequently surf a 9’-0" performance oriented longboard, but also ride a 10’-0" nose rider and ocaisionally break out the 7’-8" hybrid for bigger days.

Thanks to all the folks here who have published a lot of great information on board design. I’ve been lurking here for a while now, and have spent hours reading and learning. I would very much appreciate any comments or suggestions, particularly related to rocker, rail shape and fin placement. Here are the critical dimensions, and a spec sheet for my current design:

Nose rocker= 5-13/16"; 1 foot back 3-5/16"

Tail Rocker=3-3/4"; 1 foot forward 2-5/16"

Length=11’-6"; width 28-11/16"; thickness 4-9/16"; volume=173.8 liters

I’m curious how you calculated the litres.


The AKU shaper program that I used to design the board performs the calculation automatically. It’s a free design program available at

you gonna be in the neighborhood…

stop by I’ll take you paddling

and the variety of shapes

I can pack on the car

will answer lots of parameter questions…

udder wise,

4;25 tick 10’6- 28.5 ‘’ wide 17’’ nose 18’’ tail…contep-speedy for monterey bay

4 7/8-5 3/4 - 12’ - 30’‘wide 20’‘nose 2’’ wide tail cowels to riermouth dream machine

6’’ tick 13’9’-14’+ 26 1/2 wide 14’’ nose 13’’ tail tippy down winder

four mile to rivermouth or pinkys to scott creek waimea kong killa…

the hypnotic resonance of fine crafted wood echos in my immagination

a spruce cormerant

flying close to the

surface dynamic

realizing potentials

heretofore beyond

the foggy distinctions

of reality…

yeah stained black

with high gloss

surface of rr poxy

and a taped off center

line of stark nat wood spruce

rr maybe stain the pieces before gluing

stained with epoxy and pigment…

an enviable project…


work on it every day and one day it will be finished

skip a day and it may never see completion…

173 liters sounds really corky to me. My metric conversions are a little sketchy but let’s see. 3.785 liters to a gallon so heck say 4 liters per gallon, you’ve got about 40-odd gallons (volume) of buoyancy, and if a gallon is about 8 pounds that’s 320 pounds of buoyancy. If the board itself is 30 pounds that leaves 290 pounds of float… somehow I don’t think you want that much. Agreeable that the math is rough, but still, that’s an awful lot of float.

move a decimal

change to hand height measurment

as with horses

divide by six

all of which can be over ridden by taking a half step back

displacing a quart of plasma

and accessing the




the unknown

to mathematics.


can you top turn it 1/2 mile offshore?

right brainers

your wave…

book em Dano

build it lets ride it.

how many gallons am I mom?


I would love to take you up on the offer to try some different boards, but there is a big ocean between where you are and where I am so I don’t think I’ll be able to any time soon. Some years ago when my wife and I were on Kauai, a nice guy named Ambrose loaned us some nice single fin boards . I think this may have been you. Thanks for the offer, then and now. As far as intended use, I’m thinking Cowells-38th-Privates kind of thing, a peak here and there, and move on to the next spot. I definitely have the glide in mind for this first board.


I’ve been pondering the volume a bit, keeping in mind that there needs to be reserve buoyancy to keep the deck above water. Dimensions and shape come from boards I’ve seen and ridden, and from folks that know a lot more than I do about board design, especially stand up boards. If I were to squeeze a bit of volume out, where should it come from? Make the board a 1/4" thinner over all? I gained some volume by making the deck pretty flat (suggested by many for paddling comfort) but perhaps it should only be flat in the sweet spot, and be more domed fore and aft. Thanks for the input all, keep it coming. Final coats of varnish go on the paddle this week, so the board building will start in earnest soon. All this complicated by a nice swell arriving yesterday…

Here are my latest tweaks: Made the rails less boxy, made the board overall just a tad thinner and pulled the nose in just a bit. Looks better to my eye, what say the experts?

Here’s the jpeg:

173 liters sounds really corky to me. My metric conversions are a little sketchy but let's see. 3.785 liters to a gallon so heck say 4 liters per gallon, you've got about 40-odd gallons (volume) of buoyancy, and if a gallon is about 8 pounds that's 320 pounds of buoyancy. If the board itself is 30 pounds that leaves 290 pounds of float... somehow I don't think you want that much. Agreeable that the math is rough, but still, that's an awful lot of float.

I would agree, looks like way more reserve volume than you would need.

Simple calculation can be done with… 1 Liter = 1KG of displacement.

~170# + 30# for board = ~200# → (google conversion: 200 lbs to kg) 90.7 KG == 91 liters.

Figure in maybe 30-40% reserve and your looking at between 118-127 Liters.

If it is mainly for surfing I’d cut it down to 10’6". No need for all that length. If you still have excess volume thin it out a little.

There is some good design info in the “SUP design basics” thread.

hum… though looking back some of the answers are PMs not the thread, but none the less still some good info there.

looks good…

qecision is surf inside with the rabble on regular days

or paddle way out and surf the tiny days

bigger is bigger

there is no durn thing wrong

with float for excercise and

distance paddling.

surfing yes

smaller volume is more surfy

and of course yyou dont have to walk…

Now I wiil look at the plan.

cliked on the little blue words and it said document not found

is it me?


Funny, the link was working a few hours ago. I’ll repost it on a more reliable host.

I fixed the link, and repeated it below.

Ambrose, I am on the same wavelength with you on float, glide and SUP as surfcraft, fitness machine and peak to peak transportation. This board will not be the ultimate high performance surfboard, but more of a small wave assault vehicle. I gotta learn to walk before I can run, and if this build goes well, then there’s plenty of lumber on the woodpile for the next one.

Construction will be with 6mm Okoume ply fishbone, planked with 1/4" redwood. Rails will be hollow bead and cove, per the Grain method. The wood for the planks was salvaged from some old redwood water tanks, and is tight grained, clear heartwood. I like the idea that this wood is getting a second lease on life, for something more dignified than landscape timbers or firewood. Sheathing will be a single layer of 4 oz S glass set in epoxy. Currently I’m planning a single fin in a 10" box. My thought is that this will allow some experimentation on fin design while keeping things fairly simple to build and change.

Thanks again everyone for the input, it’s all good.

It’s been a while, but I’ve made some progress. Here’s a peek:

I’ve decided to add sidebites. Looking at all that tail rocker makes me worry that there might not be much fin in the water at times. Opinions on this? I’ll probably use FCS plugs for sheer ease of installation in the HWS construction.