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Ideas and planning

Posted by mischievous 
Ideas and planning
April 10, 2019 04:40PM
First off, thanks to admin for their work.

I plan to build a 16'ish ft drifter. It's purpose is fly fishing and day floats. No significant white water. I am enamored with the Kingfisher and Cajune's Recurve. I fully admit it is their profiles that lure me. But, I need to go my own way, too. I have a roll of 3mm neoprene floor under-layment. My plan is to trace a Clacka Eddy, onto the neoprene, and use it for a template. Stitch and glue construction. The floor will be Plascore, hull walls 9mm Oakume.

I have built a frame and skin Broadbill duck skiff. But, I suspect this to be more detailed. I'm just getting started and have a huge learning curve. Please, if anyone sees a problem I am creating or headed toward... speak up. I have thick skin and welcome criticisms.

First question: why lay Aramid (kevlar) on both interior and exterior? It is expensive, hard to work with and sucks up a lot of resin. I see no benefit to interior use.
Re: Ideas and planning
April 11, 2019 02:53AM
I used Kevlar once and found it too hard to work with.

On the outside of a hull big rock hits won't in any way damage the fabric itself but they will shatter the surrounding resin. Normally, with glass or any other fabric you grind that soft spot out, tapering the edges, and then patch in some few fabric and resin. Patch a bigger piece over top of that, sand it smooth and finish coat it with resin. And hope not to hit that rock again.

With Kevlar it isn't easy to grind out the patch spot. Regular sand paper just turns it into a nightmare fuzz ball.

Okoume is among the lightest of mahogany family plywoods. It was popular among racing hull builders before the advent of vacuum bagging and carbon honeycomb core. It's not the strongest plywood. Sapele is known for its beauty but it is also stronger. And denser. After the loss of AA Marine fir Meranti Hydrotech is now thought by many to be the best compromise between cost weight and strength.

End grain balsa wood is an interesting core material. I used it for several boats back in the late 1980s. It makes a primitive stressed skin panel that holds up well, if you use enough glass. For drift boats it is no good below the water line. I learned that the hard way. Plascore is a lot like balsa wood that does work below the water line.
Re: Ideas and planning
April 12, 2019 12:39AM
Couple thoughts.

Sounds like you are going to somehow trace a claka eddy onto the neoprene underlayment. That maybe a bigger chore than it would seem. Also, the tracing may not be accurate enough to use as a pattern. Most boat builders loft from a set of offsets rather than using full size patterns, because non-trivial error exists in such large patterns...from copying etc.

The claka eddy has a raised area for the oar locks. Claka website says the side hight is 19 inches and the oar lock hight is 23. Supporting the sheer and supporting the raised section and oar locks might present an engineering challenge. In my experience the gunnel on a stitch and glue open boat is essential to provide appropriate rigidity to the hull.

I've copied two boats - a Willy 16 x 54 drift boat, and a Koffler RMT 14 x 54 skiff. The Willy I only built a model, the Kloffler is in my garage about 85% finishes and should be in the water for July.

For both of these boats I made lots of measurements from a boat, but didn't try to make a traced pattern. I measured the chine, the sheer, side hight, beam at the oar locks, beam at the chine, measured the transom, etc. For the Koffler I had access to a 14 x 49, and used dimensions from the Koffler website to scale to a wider bottom and oar lock beam.

Using the measurements from the boat I developed 1:12 or 1:8 scale patterns of the respective side, bottom, and transom panels. If the side panels have a straight sheer and chine you can layout a drawing just using a straight edge. For the bottom and if the side panels have an arch - convex or concave - then I used grid paper over a cork board, used pins to bend a 1/8 x 1/8 piece of ash to make the arc, and then drew the curved lines.

Then I measured offsets at various locations along the panel. Then using these measures I constructed models using illustration board for the sides and bottom, and foam board for station strong backs and the transom. Then I could decide whether my measures and panels would give me the boat I wanted.

For the Koffler I then used the model offset measures to loft at half scale to reassess the station offsets to cut full size panels. In your case, you certainly could use your underlayment to reassess using full scale lofting. I did it at half scale because I had a 8 ft length of plywood.

I built a drift boat about a decade ago and used kevlar on a 3/8 plywood bottom panel - inside and out. On my current skiff I used 2 layers of 6oz glass. Also was a plywood bottom. I have access to Hydrotec locally so I use it rather than paying for shipping on plascore.

Good luck with your boat building.
Re: Ideas and planning
April 15, 2019 02:33PM
Jason Cajune's recurve Kingfisher is designed for the flyfishing use you want and has an eye appeal design with great reviews. Why not just purchase the plans and build it and alter/customize it to your particular needs?
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