Thursday, October 31, 2013

How I Built My Skin On Frame Canoe



I have been looking for a super light boat that I could load by my self.  Health issues have limited my options.  I just don't have the strength that  I use to have.  I want the boat to be light enough load on the lumber rack of my truck.  The boat also needed to be stout enough to carry my weight (210 lbs.).  It would be used for fishing on ponds and small lakes.



One of my hobbies has been boat building.  I have been at it for about 50 years, and have used several methods of boat construction.   Skin on Frame (sof) is technique that I have been interested in but have never tried. A light frame is made using stringers going the length of the boat and ribs running across the boat and glued or lashed where the rib crosses each stringer.  The framework is covered with a fabric (skin) like nylon or Dacron.  After the is applied to the frame it is sealed with varnish or paint.  The main advantage of this boat building method is a very light weight boat.

I decided to make a canoe which I have never built before.  This canoe is 12 feet long and about 30 inches wide.  It was designed to weigh about 22 lbs but it ended up weighing 31 lbs.   I use a double paddle and a very small electric trolling motor to move around.  And fishing from this boat is a joy.

The following photos will show how I built my canoe.
The framework is built over a strongback and molds.  A wire is stretched over the length of the strongback and is the reference to set the molds to.
Here the stringers are being attached to the molds with zip ties.  The stringers are 3/8 x 3/8 spruce.  All 4 edges of the stringer were rounded over.

video
This is a short video that show all the stringers in place.  Note that the stringer ends are lashed and epoxied to the stem.

 The ribs need to be bent into shape.  Here is the setup I used.  First boil water in the kettle, then fill the PVC pipe the the boiling water.  I stuffed a rag in the open end to minimize heat loss.  Let the two ribs soak for 15 minutes.  The ribs are 1/4 x 1/2 inch ash wood.  All edges were rounded over.
One at a time I clamp the rib to the keel. Then bend the rib and clamp it to each stringer working from the keel down to the gunwale.  I could only do a few ribs at a time because I ran out of clamps.
After the ribs have dried, each joint between the rib and stringer need to be lashed or glued.  I used epoxy.  Remove one clamp, separate the rib and stringer, work some thick epoxy between and then re-clamp the joint.  The epoxy that I used was like peanut butter so it would fill any gaps.

Its time to lift the canoe off the molds.  Cut and remove all the zip ties.  Then the sides needed to be sprung out and then lift.
The tab on the stem was used to clamp the stem in place on the strongback.  It will be sawed off later.
The inwales were installed next.  Just a small dab of epoxy at each joint.  After the inwales are set the ends of the ribs were sawed off.
This photo shows the floorboard being positioned before gluing.  Here I used 3M 5200 Marine Adhesive.  This stuff is amazing.   It adheres to almost everything and remains flexible. 
Heat-n-Bond tape is attached to the keel and the gunwales.  Kevlar roving is applied running diagonally from gunwale to gunwale.  The Kevlar is used to counteract the hull racking.  Heat-n-Bond is like hot melt glue with a paper backing.  I used the tip of an iron to attach the tape to the gunwales then removed the paper backing.  The Kevlar is laid against the gunwale with a short piece of HnB on top of the Kevlar.  then I use a hot iron to melt it all together.  The Dacron skin is also attached the same way.

 
Here the Kevlar is complete.
The cut water is laminated from two pieces of rib stock.  Its easier to make it now before the skin is applied.  The stem is being use as a form
Here I an applying the Dacron skin.  This skin is the same Dacron used on small airplanes.  Dacron will heat shrink using an hot iron. 
It took about 4 hours to complete.
Almost doneAttach the rub rails.  Fill screw hole with bungs, install the cut waters and apply 4 coat of water base exterior varnish.

Finished.   Had to let the varnish harden for a couple of days.
Off to the lake.
My son took the canoe out for its maiden voyage.  He was amazed at how far it will glide.  My wife tried it and said "this thing really scoots".  I had my turn, no leaks, vary stable, tracks like an arrow and the only noise was water dripping off the paddle. 
Last summer we had both my daughter and son and all 6 grandchildren for 3 weeks.  So we did a lot of fishing and boating.  The boat stood up to the kids just fine. 
That's all for now.  Your comments and questions are welcome.

-mike