How can I figure out my board's volume?
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How can I figure out my board's volume?
so i had a pretty interesting & enlightening email conversation w/ Whitney Guild the other day after he emailed me about this thread.we conversed back & forth a bit & here's what he had to say:
"The Guild Factor was created to make surfboard selection a level playing field for surfers of different body weights.
The selection of one's surfboard should be directly related to one's body weight. Also in consideration should be your ability, fitness, age, and type of wave you ride.
Shortboarders that are fit and riding hollow waves, should be GF .34 to GF .37. Shortboarders less fit or riding softer waves, should be GF .37 to GF .42. Novices should be between GF .40 and GF .50.
This is across the board, for all surfers of all body weights. It is simply a ratio of your surfboard volume in Liters to your body weight in Kilos.
This will allow surfers to choose their surfboard volumes within 2 to 3 liters and will allow a larger surfer to compare his board's volume ratio with his smaller friend's board in direct proportion. If they surf the same surf spot and have similar abilities, it creates an even comparison.
Of course, length, width, and thickness are very important parts of choosing a surfboard, but volume should be just as important.
Whitney Guild Volumetrics"
Swaylocks had this formula up a while back:
1/2 length x width x thickness + 10 for every inch over 6'
Divided by 60.02 = L volume
It's not exact and doesn't account for certain variances in design but I've done the equation for dozens of boards I have, was looking at getting, or was just testing the math out on and it's a pretty damn good estimate.
i've used this formula in the past & when i compare my results w/ boards i know the #s for, it always seems to come out on the low side. for example, my rusty bali single is 6'2"x20"x2.5", 33.7L. that formula gets me 31.2L. the bali is pretty thinned out in the tail, but the rails are full & there's no way the computer program is that far off.
but back to the topic at hand, i'm surprised no one on here has commented on the words of wisdom from whitney guild himself clarifying the subject. has anyone played w/ it at all? it was interesting to see how little my GF varied (.37-.39, depending on board), compared to the volumes i ride & feel comfortable on.
Low tech way - building your own tank wouldnt be that difficult. for shortboards, just constructing a 7' x 2' x 6" plywood box with some numbered black line increments (say 1 liter increments) on the inside wouldnt be that difficult.
remove fins, stand box on end, fill box up so the water level is somewhere in the middle of the increments, slide board underwater so it is barely submerged, see how many liter increments the water goes up. it would be perfectly accurate, and was invented by Archemedes oh about 1500 years ago.
i've found the GF to come in handy.
i'm 6'4" 220lbs so not your average shortboarder.
I rode a ...Lost Round Nose Fish for years and loved it. it was
6’4 21.5 2.75
(42.1cl)
GF = .43
I wanted something with more performance on the bigger days so i talked with Matt Biolos at a shaper's night last fall and he suggested a V2 Stub
6’4 21.00 2.75
(42.5cl)
GF = .42
i love this board but not on < waist high and/or mushy waves.
so i played around with the GF to find a new shortboard for smaller days.
i went with a ...Lost bottomfeeder. i wanted to make sure that this board not only had more volume but would allow me to shortboard when i used to have to longboard. it is a wave catching machine.
6’4×1 23.50 2.88
(49.something cl)
GF = .49
conclusion:
i was able find a board to ride on smaller days that would make me stoked. (i rode it all weekend)
if you've never ridden mayhem shapes, the Guild Factor is a great starting point...but be sure to follow the skill level and other advice, too. Firewire puts too much emphasis on age (skews volume way high), CI's calculator seems a bit low and Rusty's seems slightly high.
strange thing is, the GF recommends me 35 cL vol at max, but, a while back, Matt recommended I get 39.5 cL...he was way off as that board was a friggin boat on me
for those that say volume is overated, I disagree. Any bit of info to get you closest to the best shred stick possible, the first time, is a good thing...or you can buy three or more wrong boards in the search
You wouldn't have to build a box that's as long as your board. You'd need it to be only 1/2 as long as your longest board. Tape off the board someplace in the middle, dip the board vertically up to the tape, measure the displacement, flip the board and then measure the other side and add together.
But you wouldn't need to build anything if you had a large plastic trash can. The large 64+ gallon recycling ones are perfect because they're at least 41" deep and 24" wide (the diagonal is even longer) so you could easily measure a 6'8" board. And it wouldn't matter if you didn't know the can's capacity. Poke a hole near the can's rim and insert a small piece of PVC pipe or something to act as a drain. Fill the can until water starts pouring out of the pipe. Dip 1/2 the board and catch the water that pours out in a 5 gallon bucket. Measure what came out and there's your volume.
A while back I tried another way that was fairly accurate with a lot less work. The only thing I had to measure was the average thickness of the board using calipers. I think I measured every 4" along the stringer and every 3-4" out to the rail. It was a lot of measurements but it took less than 10 minutes. You can take the measurements closer together (every 1") in the nose and tail but you'll need to average those areas separately from the areas where you did the measurements every 3" apart.
You can either take your own picture of the board (straight on, centered on the deck) or download one from the Internet. I did it with a CI board and grabbed the image from their website. Just make sure you're grabbing an image of a board the same length as yours.
Load the photo into Photoshop, Gimp, or one of the many free programs that can count pixels. Scale the image to the actual length of the board, select the board's outline and let the program count the number of selected pixels. Then, draw a 1" x 1" square and get the number of pixels in that area, divide the total number by this number to get total surface sq inches, then multiply by the average thickness and convert in cu to liters.
I think the only accurate way would be displacement because even the volume numbers listed on the websites are from the CAD software and I'm guessing they don't take into consideration the glass, hot coat or gloss coat.
You know, this whole thing has been bugging me cause it really doesn't say what "Guild Factor" really is besides a ratio between volume and bodyweight and I hate it when a value remains undefined. I figured I’d just ignore it and it and it would go away; but back it came to the front page so like a scab that itched, I had to scratch it and see what was underneath. A ratio should mean something right? A 1/4 oz is a ratio to a whole oz and represents “Danger, Will Robinson, Danger!” ; ) So I went on the ...Lost website and got the javascript for the Guild Factor widget and tried to figure out how they were calculating GF. And, this is what I found:
var m = axes.H/(axes.b-axes.a);//slope of gf line
okay so GF is just a slope of a line, simple algebra, just gotta figure out what values are being passed in:
axes.H = -(axes.top - axes.bottom)
okay so what are the .top and .bottom values:
//frame coordinates
axes.top = 0.110 * gridheight;//these are in canvas coordinates
axes.bottom = 0.928* gridheight;
And what are the b and a values:
W0 = axes.axisKg.min;
W1 = axes.axisKg.max;
V0 = axes.axisVol.min;
V1 = axes.axisVol.max;//max Liter value
var SFa = V0/W1;
axes.a = axes.W / (1 + ((SFa*(W1-W0))/(V1-V0)));
var SFb = V1/W0;
axes.b = axes.W / (1 + ((SFb*(W1-W0))/(V1-V0)));
Hmmm, all that’s left undefined is the axes.W value:
axes.W = axes.right-axes.left;
Grr, never mind better get the left and right values too:
axes.right = gridwidth - ctx.measureText("LitersWW").width;
axes.left = ctx.measureText("WWLBs KGWW").width; //hack-o-matic
Okay we got it all except whatever the grid width was originally set to:
{
//set the container size
$("#gf").height(500);
$("#gf").width( $("#gf").height()/1.275);
guild_chart_init( "sb", "guildfactor");
});
Well crap, when you put it altogether, it doesn't mean anything. Great there's a line on a chart and your guild factor is whatever value between .1 and .9 the line between how fat you are and how fat your board is happens to intersect on that Guild Factor line.
What's interesting to me is that they actually even fudge the line depending upon the input variable:
//
if( chartType === "sb" )
{
axes = { title: "Shortboard",
axisKg: new objAxis('KG',50,105,5),
axisLb: new objAxis('LBs',110,230,10),
axisVol: new objAxis('Liters',10, 60, 2),
axisSf: new objAxis('GF',.2,.9,.1), };
//we can test for size and load size-specific images
//imgfilename = "chart_sb.jpg";
}
else if( chartType === "lb" )
{
axes = { title: "Longboard",
axisKg: new objAxis('KG',50,150,5),
axisLb: new objAxis('LBs',110,330,20),
axisVol: new objAxis('Liters',50, 200, 5),
axisSf: new objAxis('GF',.4,3,.2), };
//imgfilename = "chart_lb.jpg";
}
else if( chartType === "sup" )
{
axes = { title: "Standup"
};
}
That's it, that's what guild factor is, just a line of arbitrary values between .1 and .9 for shortboards and .2 and 3 for Longboards that you draw another line through. You could figure all that out on a piece of graph paper. Apparently if you ride a SUP you have no GF, hmm maybe they are onto something here.
So the issue that I take with this is that the values that make up the Guild Factor are, except for your weight and the volume of the board, just a couple of numbers that really don’t mean anything. They could just as easily have left it whole numbers, but then it wouldn’t look as cool. If it were me, I would have measured guild factor as units that represented the weight of a single D cup breast. I weigh 197lbs, the board I rode this morning was 34 liters, my guild factor is 37 tatas.
That’s my gripe, because the numbers were just pulled out of thin air (.1 through .9) and have no correlation to any real world value, it’s fundamentally a meaningless ratio. “The selection of one's surfboard should be directly related to one's body weight.” It is, it’s called volume, back in the day we called it float and in crappy waves, I need more cushion for the pushin.
I dunno, maybe I’s too dumb to get this : (