# upsizing/downsizing

i have a question to ask? i shape my self a new board every year for last 20 years. i have become very happy with what i have developed, it works real good. i have a son who is now 11,he is surfing well on my old boards. i want to make him a board, but i want to make an exact scale replica of mine. what formula should i use? i read here about profile and shaping machines. i look at 3d software and i can scale simply in it. its only demo so i cant save results. i live in brisbane so i ask if KR can downscale acuratly with his machine? i dont want to just make small board i want to scale proportionaly.

Rockers and thickness are scaled straight scale. Take any measurment from the original, divide by the length (in inches), then multiply by the new length for the new measurments. Center width is scaled 1/8 inch, plus or minus, in width for every inch of length. This keeps rail to rail transition similar up and down the scale. Rail to rail is the constant that must be maintained in any design. Nose and tail measurments actually don’t change much because the 1’ measurment actually moves in relation to different lengths.

For some reason this is a tough one. Go to a shop and find a 6’10" for instance and ask if they can make it the same proportionately, only longer. A response I’ve received is (and I quote), “No way dude… you go longer, you have to go NARROWER” Huh?! Can’t you cross multiply and divide like the teacher said back in school?

WOW Greg! At first i looked at that formula and went huh? does that really work? then i tried it and wow whaddaya know it works!

I was involved with a project through Ron Jon’s years ago that were scaled versions of surfboards built for statues. After finishing the project I became interested in scaling for different size guys. Since I could make blanks, the profile was easy and accurate to do. I used straight scale and it worked. But the outline was different. I eventually used standard longboard width for the top of the scale and shortboard width for the bottom. A 9’ longboard at 22.5 was the top and a 6’ X 18" the bottom. There’s 36 inches in length between 9’ and 6’ and 4.5 inches difference in the width. 4.5 divided by 36 comes out to .125 which is 1/8th inch per inch of length.

How is Barbie? l saw her in a smashing golf outfit the other day. As for scaling, you could use Gregs formula and knock up some new templates to use on the profiler but a profiler is basically the fancy name for a “JIG” it cannot work out mathamatical equations, the person controling the outcome is you, so l would suggest using Gregs advice and then go to someone to profile it if your not upto it. Good luck with it, l always try to scale my smaller groms boards down but you never really know how they go because each time l try to ride one it tends to not go so well due to my legs dragging through the water. KR http://groups.msn.com/MyKRSurf/krcomweb.msnw

Ken ,I use a marine architecks cad software proggrame for my profiling business .It can accurantly scale down ,provided propotioned measurements fit, a big board into a little board. Give me a yell in march when things are slower.

Here is my attempt at deriving a scaling formula for surfboards. Ideally, the surfboard needs to be scaled in geometrical proportion. Also, the water pressure distribution under the surfboard should be the same as the board is scaled. A perfect scaling law for surfboards is not possible but it can be made close enough for practical purposes. For similarity, the scaling of a surfboard should be based on the ratio of rider weight to surfboard plan area. (Or equivalently, based on the rider mass to surfboard plan area.) The linear scaling factor needs to be equal to the square root of the mass ratio of the two riders being compared. For example, if the reference rider weighs 100 kg and the comparison rider weighs 50 kg, then the board dimensions needs to be scaled down by 1.42 , which is 71% . The fins should be scaled down in the same way. There could be some geometric mis-scaling between the height of the riders and the surfboard size as calculated from this scaling formula, because the scaling formula is based solely on the riders mass. However, if the reference and comparison riders have a similar Body Mass Index (BMI), then the scaling formula works out very well, on a geometric basis. The BMI is defined as the body mass divided by the square of the height. It can be shown, that for riders with the same BMI, and having different heights and weights, they can be provided with equivalently scaled surfboards. Perhaps an averaged BMI can be used for scaling between riders with different BMI’s. The thickness of the board can be maintained above the outline, in order to provide the necessary reserve buoyancy for the board. Thanks.

Hi What are your view on weight versus foot size. I have always thought this might be a big factor. As the more weight and bigger footsize more leverage can be placed on the rail in the turn. Just wondering what you guys think. Cheers

I was asked for foot size on a custom order with a concave deck. Not sure how it relates to scaling down but leverage was the main consideration. Perhaps a scaled-up board whould include a concave deck to either: keep the thickness managable OR give better leverage. Rob Olliges

The wider the tail the more that you have to move your back foot when doing some turns, there is nothing worse than going to bottom turn and your foot is on the wrong side of balance and the board goes straight and you headbutt the water, my opinion is with alot of learners a wide tail is good for stability but as you get better you find that your tails get narrower because you have more control over them, Mick and Parko’s tails are around 13 1/4" on their short boards. girls can use narrower tails to help them rail the board over because they have such small feet, and that is why alot of them surf so flat (tails to wide) KR http://groups.msn.com/MyKRSurf/krcomweb.msnw

yes, KR, I´m into that tails. but what happend with some wider fish tails?

Hey reverb, todays fishes are not so much designed for full rail carving like you can do on narrower tails, they are designed to surf flat and skatey so that you can slide the tail around easily, if that is the way you want to surf in small waves go for it, they are better for that than a narrow tail.,old style fishes are a completely different ride and board, and that is why alot of younger guys have a hard time geting them to work. KR http://groups.msn.com/MyKRSurf/krcomweb.msnw

“yes, KR, I´m into that tails. but what happend with some wider fish tails?” When you ride a fish it is genrally in smaller surf. A wider tail does provide more lift enabling you to ride smaller waves and not plow through the water like on you standard board. In smaller surf you travel a slower speeds and therefore the opposing pressure on your foot is less therfore requiring less pressure from your foot to dig a rail. In larger surf the speeds are greater therefore the opposing pressure on your foot is greater. Requireing more pressure to dig as rail. If you have a big foot and more weight you are able to apply more pressure to the rail. Compare the width in the tails from your fish to your std shortboard to your semmi gun or gun. All these boards are designed for different speeds. I have a size 6 foot and weight 76kg till recently I was riding a fish once the surf got up to 5ft I found it more difficult to dig the rail in the turn. I have now moved to a round tail fishy type shape in the hope that this will provide me with the samilar lift and enable me to dig a rail a bit more in bigger surf. (It still need testing)

there is a degree off individuality( is that a word)I ride 7’0" round pin short boards. my mate rides 6’8" swallow tail off the same dimensions .20 x 2.3/4. big boys 92kgs.We do the same manuevers ride the same waves but that is the stick that works for him and myself.We could ride shorter boards (fish) and have a ball but at the moment what we are riding is doing the job and riding the waves how we like., what I am saying is It is up to the indevidual how he/she would like to ride the wave.I feel that asking for foot size on a custom stick is like saying “oh no your 8’6” is going to look totally f**cked on top of your suzuki.It is up to the indevidual size shape thickness and width. that is why we are custom shapers . we can only guide the prospective buyer at the end of the day it is up to them.Please don’t take this as rubishing fish as I find them totally enjoyable, and fun to shape.

So when a 6’ tall gromm comes into your shop and you give him your advice, and he say’s but l want a 5’10" narrow rounded pin, do you go alright, you see l would look down at his feet and quite often groms like that have whoping feet, so l give him my advice on the decision he has made because isn’t that what they come to you for, l only go to the extreme’s of foot size when it is called for because it can make a difference. l have shaped a lot girls boards who are at an above average level and when they first come to me l look at what they are riding and most of the time the shaper has made the tail wider than what they would do for a guy, l explain my opinion about foot size and tail width and they give it a try, all l have ever had is the response of WOW l can get it up on rail and my turns are way better, it might seem stupid to some but it works for me. KR http://groups.msn.com/MyKRSurf/krcomweb.msnw

So I have a 13" foot.would you “as a shaper go with a little wider tail?” I currently like a 14" TAIL ON MY 6’6" SHORTBOARD.

Depending on your center width Mike, l would definately go wider as an all round board for average waves, l recently did a board for a guy who has a foot at about your size and he was telling me that he was having trouble off the top with his current board, it was sinking to much off the top and therfore hard to bring back in, l talked him into taking his tail width out to 15 1/2" at 12" up with a slight hip to keep a bit of pivot, he rang the other day and was absolutley stoked and recons that he had been having the best surfs he’s had since he can remember, recons he is even making club finals which he’s never done before, amazing what a little thing like the right tail width can do, he freaked at first about going that wide because he thought that it was a step backwards going wider and thicker, thinking that it won’t turn as good, but some times you have to go backwards to go forwards and it is great to have that kind of feedback. KR http://groups.msn.com/MyKRSurf/krcomweb.msnw