Stiffening the frame

[Sailormon]

I suppose my solution is not going to be popular, but will not add much weight nor change the boat design. I am thinking of the short shot when I return to Michigan. I have noticed in photos and also others mentioning a flex in the frame of especially the longer craft and this more than anything concerns me. I also know many like to stick to tradition much like I did in building a lashed together 37’ catamaran in the 70’s.

 

I considered, being a building, making the side stringers into a rafter which solves the issue. The easiest way is to get some 1” styrene, blue board and filling in between the side stringers. Simple gorilla glue or foam will glue this in. Yea, I know it will look like crap unless camouflaged someway, perhaps with stain?  Glued only, 1” foam I feel would work considering the length of the joint. Better yet and I know many do not like working with epoxy and glass, but some six inch 6 oz glass wrapped every foot or so would triple the strength. 

 

As to outside finish, this would not show, it would just be a more solid side. I used this method on two airplane wings and they flew fine and the wings did not break. The concept is pretty much identical, two wing sections, one on each side to the kayak. I love the looks of the design and this does not change a thing other  than add stiffness to the kayak.  Also the lashing would still be used, just punch holes in the web and go for it.

 

I plan this and if I do build will post here this spring.

[andy00]

Cousin Sailormon:

That's an interesting design concept. The core question is whether the flex experienced with the standard design is, in fact, a problem.  There will always be some flex in a boat, even with your stiffening modification, so how much is acceptable? Some structures need to be quite rigid to fulfill their design requirements. Others require more flexibility. What degree of flexibility is optimum for a kayak? It is likely that flexibility improves hydrodynamics up to some point. 

 

To me, it feels a bit like a solution looking for a problem. I built and paddle a Ravenswood, which is 15.5 feet, not one of Jeff's longer boats. I can feel it flex, especially when there is chop of a certain size, but it doesn't constitute any sort of problem. If I were building a longer boat, I would pay attention to the type of the wood I used (both species and individual sticks), scantlings, and the grain (straight with minimum runouts). 

 

Fair winds!

[Sailormon]

2 hours ago, andy00 said:

Cousin Sailormon:

That's an interesting design concept. The core question is whether the flex experienced with the standard design is, in fact, a problem.  There will always be some flex in a boat, even with your stiffening modification, so how much is acceptable? Some structures need to be quite rigid to fulfill their design requirements. Others require more flexibility. What degree of flexibility is optimum for a kayak? It is likely that flexibility improves hydrodynamics up to some point. 

 

To me, it feels a bit like a solution looking for a problem. I built and paddle a Ravenswood, which is 15.5 feet, not one of Jeff's longer boats. I can feel it flex, especially when there is chop of a certain size, but it doesn't constitute any sort of problem. If I were building a longer boat, I would pay attention to the type of the wood I used (both species and individual sticks), scantlings, and the grain (straight with minimum runouts). 

 

Fair winds!

Can’t but agree. Due to the oblique angle and experience, this would allow flex, not prevent it entirely. Airplane wings do flex. I built one set of wings with pre stressed uni to stiffen them. I would not go that far of course. I had read on here that someone was looking for a way to reduce flex, thus my thoughts.

[Kudzu]

Your trying to fix a problem that doesn't exist. The designs are proven to work.  Never had a frame failure that I know of.  A little flex is part of the design.

 

You really should try one before you start trying to fix the problems.

 

 

[Sailormon]

Yep, agree to try one, will be ordering soon on I think the short shot, I may take the route  someone here mentioned and cross lace with Kevlar seeing this subject did not originate with myself. I just cannot help solving problems that do not exist. It should be known, epoxy slow cure is made in a flexible form that is not brittle as that also was mentioned. I manufactured landing gear of this and in tests I was impressed.  Nasty stuff however to use.

[Yankee Dog]

Interesting.  I have built a couple of fuselage boats, greenland style using anthropomorphic dimensions. Almost entirely lashed and I found very little flex when it was all said and done.