how to scale yostwerk kayak plans

I am planning to build a Roldarka from yostwerks.com this is my first build so please forgive me.

I have encountered a problem:
I am trying to make the templates for the cross sections from the offsets here:
http://yostwerks.com/RoldarkaOffsets.html

However when i got them onto paper, i realised that there is no way i can fit my legs and body in there. I am 6' with a 32" waist and 34" legs. I am fairly slim but have cyclist thighs. my feet are size 11, and there is no way they will fit inside the current dimensions of the kayak.




Obviously, the plans can be scaled up or down depending on the size of the person the kayak is designed for. How do i do this, and how do i know how big to make it?

Thanks for your time

 

A very real problem.

'scaling' could be done on a simplistic level to end up with say .. a 1:1.03 version of the boat.

You could multiply the dimension by a fixed amount eg 1.03 x 5 metres, Gunwale Height .509 x 1.03 = 0.52427
frame spacing x 1.03 = x
etc etc

Where you would come unstuck though, is the Hydrodynamics. Making a hull wider, with an increased chine height could make the hull shape much less efficient or even less stable.

You will find it easier to find a design ( albeit for a small cost ) that suits your physical needs better, and cheaper than getting a professional to 'remix' an existing design.

 

Well, you have already established the current lines are not suitable for you. So how did you do this? Use the same method to establish how much bigger you need to make you fit.

Once you have that, it is a simple case of working out what scale ratio to make it.

But, as already noted, depending upon how much bigger the hull becomes how difficult the simple scaling will be for other aspects of the hull. Since it shall affect the scantlings too, the draft you float at etc etc.

So firstly, work out how much room you need...and from that how much bigger to scale the boat. Until you have worked that out...it is all guessing

 

Native kayak builders never had fixed sizes, that is a white-man idea. They would build each water craft to match the owners size along these general ideas (which should work for you too, no matter your size).

Length: two and three quarters (2.75) your arm span, you can add some length to this if you want a longer kayak to track better. Or two arm spans plus three lengths from finger tips to elbow. Usually works out about the same. For me this works out to about 16' 8"

beam: Hips plus two fists (one on each hip). I find this makes a comfortably wide craft and prefer mine a bit smaller, I use 1.5 fists plus hips (I end up with 21" beam-hips plus 2 fists gives me 23.5-too wide for me). You might want to add a bit to it if you do not have a lot of experience with narrow kayaks. There is no need to ever be wider than 24" IMO.

Depth at back of coaming: fist width including thumb out-streched, plus depth of keelson (about also the height of gunwale stringers at the back of the cockpit). A low back makes for easy entry/exit and ability to lean back to facilitate rolls. Larger cargo type kayaks are much deeper. Depth at mastic and foot may be adjusted for your size, but this is simply the amount of arch in the deck above the gunwale height. BTW, if your foot is 12" long, you do not need a hull 12" deep at your feet, they can relax and fit easy in a 10" deep hull if you avoid foot pedals or foot rests (another white-man invention).

There are no fixed size for traditional skin-on-frame kayak, they are always tailored to the owners size. The overall length and width can also be adjusted to suit your desires. But you can use these overall dimensions to scale the length and width of the yost kayak and you should have something that will paddle fine.

You can take some stringers and mock up the gunwales and block it up on books or scrap wood and do a "test fit". From there you will get a good idea on how high to make the mastic (first deck beam in front of the cockpit, where your thighs will brace, and also its size will determine how much room you have to slide your legs into the hull).

There is no magic formula, it is all a matter of what you desire in a hull as far as behavior on the water. If you do not have a lot of experience with narrow hulls, make the bottom a bit flatter and the max beam on the wide side of these general guild lines (do not be tempted to go too wide, you will regret it later for it makes a slow draggy kayak). If you expect to carry a lot of cargo you might want to add up to a foot of length to get more displacement.

Good luck and have fun with it.

 

You are right Petros, the advantage of small craft is that they are quite forgiving to thought out customisation - especially skin Kayaks.

There are some great discussions on this forum about the finer points of kayak hull design, but generally if you stick to sensible "standard" proportions, it is hard to make a mess of the design.