Friday, November 4, 2011

The skinny boat

I volunteered at a wooden boat show a few weeks ago. A feature of the boat show was a boat building competition - Boatbuilding . Part of my gig was recycling the scrap wood that was produced by each of the 14 teams of competitors. This was after moving tents, unpacking food, setting up booths, and taking abuse from all sorts of (I assume) well meaning volunteers who were operating all sorts of fund raising booths, but couldn't be bothered with actual physical labor. The last pieces of scrap wood were two complete sides for the 12' skiff.  The sides were scarfed to 12' long and the gunwales were added for stiffness. I don't need a skiff, but on the ride home I pondered how to reassemble the two sides into something useful.

After a few days of noodling I came up with a scheme for a one man paddling boat.Sort of a canoe, but with transoms on the ends, so I guess it is a punt. If I flare the topsides I can get some rocker in it, so the transoms won't drag in the water. (Translation - If  I tilt the sides so the top is wider than the bottom, the bottom will be raised in the front and the back.)  A smaller front transom would make it look like a Chinese sampan, which would probably be unusual in South Carolina. Let's do some Googling to see if anyone else has built something like that. Several hours later I have no plan, but a lot of ideas. Some spreadsheet work says that a 12 foot sampan submerged three inches would give about 325 pounds of buoyancy. The sides are 14 inches wide, so lots of freeboard. Hmm, sounds promising.

Here is the starting point:

This one has the stem attached at the bow, so I will have to remove it.  You are looking at the outside, and the inside has a gunwale at the top and a chine log at the bottom. These are two pieces of  1x2 that run the length of the boat to make it stiffer and make the construction easier.  I move the sides into the carport to make sure they are exactly the same.

Then reality sets in. They are  EXACTLY the same. The reason these two sides are in the dumpster is that they are duplicates, not mirror images. They built two right sides. The stiffeners are on the same side, so if they finished it one set of stiffeners would be outside the boat. More thinking.

I lay the sides on top of each other to see how much they will have to be trimmed. Looks like I'll lose about 3 inches of height and five inches in length. Drill a couple of holes, bolt the sides together and start performing some sculpture with the circular saw.

Sawdust and smoke everywhere. Sides are close. Reattach some new gunwales. Thanks to the recycling project I have some nice 12' pieces of clear fir to use. Stainless steel screws, lots of clamps - it is looking like a project. Here are the inside surfaces part way through this process:





I left the new gunwales long when I attached them, which looks weird but makes things much easier now. Bolts go through the extensions, not the plywood. Now lots of planing and sanding to make things parallel, fair, and smooth. Pieces are smaller, so buoyancy is down to 300 pounds at 3 inch draft. I may have to widen it a tad.

It is time to try to get some shape to the boat. Normally you build a boat by selecting (or making) a plan, and cutting wood to fit the plan. Here we are starting with the wood, and trying to bend/cut/twist/force it into a shape that is pleasing to the eye, and hopefully, efficient to paddle and sail. Usually good looking designs function well, and vice versa.

I have an old aluminum step ladder that came with my resent house. My wife has been after me to throw it away for years, but I knew it would come in handy some day.  Today is that day. The ladder makes a great base for the boat.  If you plan on following my ideas, read the entire blog before doing any actual building. Some of the ideas will be false starts.

I need to be able to bend and twist the top and bottom of the boat to achieve the desired shape. Ideally I need to manipulate them separately. I started by laying the aluminum ladder on some saw horses to give me a convenient work height. Next I made a bunch of "stretchers" from some "scrap" wood. Originally I wanted to drill holes through the lower gunwale, which I think is called a stringer.  The problem is that as the sides are bent the position of these holes will change. So I compromised on doing four fixed holes in the sringers about where the seat will be. I want this to be 24 inches wide, and this occurs at the 4' and 5' marks from the stern.

The stretchers are pieces of 2x2 with a center hole and a series of adjusting holes. The holes are 1" apart and are drilled  about where I think the sides should land. The center hold is lined up with a center line drawn the middle of the ladder. The steps on the ladder are exactly one foot apart, so I have the beginning of a grid. I drilled a hold through the center of the stretcher and through the edge of the step. A 1/4 bolt attaches the stretcher to the ladder. This where I realized that I couldn't fix the stretcher to the stringer because it limits movement. Now I am using "dogs" to force the sides into shape. The dogs are 3" pieces of scrap with a hole drilled at the 1" point. This lets me make 1" changes on each side by flipping the dogs end-for-end. In retrospect, a 1/2" change would have been better since I can always move the do to thte next hold to get a full inch.

Hopefully some pictures will make more sense. Stretchers:


 Stretchers attached to the ladder and the four bolts inserted into the 4' and 5' bottom stretchers:


 As I moved forward i used dogs to hold the bottom in place:

The top of the sides needs to be pushed out, so the pressure is reversed. Another set of stretchers to hang over the sides with dogs underneath. First the components:


Then the installed stretcher:



 I have been wrestling with stretchers and dogs all afternoon. Pull it in a little here, push it out a little there. Get a little sliver here, add a blood blister there. So far the weight gained by adding slivers is directly offset by the weight of the blood lost due to cuts and blisters. More pictures as the shape comes together.

I now have a better understanding of the word "iterative". I have moved the dogs around and changed braces several times. Searching for just the right shape. The gunwales  and chine logs added to the original plywood make it much stiffer, meaning a lot more force to bend it. I think I have the final shape, but that is with all of the dogs and braces in place. I am trying to run some temporary internal braces in the boat to  hold it together when I take it off the frame. Here are some pictures:







The ladder is still a prominent part of the design. The boat will look funny without it. I spend a lot of time looking at the boat from the front while sitting on a drywall bucket. This is my thinking chair. It is strange for a woodworker who is used to right angles and keeping things square and plumb to suddenly have to deal with this many curves. Even though it is plywood, all of the braces and trim that is part of the final boat will be compound angles. Nothing is square. I am playing with some of the scraps from the skiffs, and the angles are often complimentary. I am putting a few braces on the topsides that will be permanent. Here are a couple under construction:






I want to add a couple of braces to the bow before I flip the boat.  Both need compound angles, so I am laminating the pieces. The angles came out correct, so now it is just working on the spacing. More photos soon.

I want to add sealed compartments  at the bow and stern for flotation. That means I need a rather substantial frame. Accurately measuring the pieces is difficult so I decided to laminate a bulkhead in place. Three plies of the 3/8 plywood should be more than sufficient. The lamination requires a bunch of mall clamps, so another project begins. I made some using more of the 3/8 plywood and a couple of short bolts. The parallel jaws will sit on the plies to be clamped. Spacers on the outer side will match the width of the pieces being clamped. The picture below has one clamp and the exploded view of the pieces being laminated:





And here are the pieces glued in place. There is more wood in the clamps than in the bulkhead:




The stern also has some more bracing:

I started putting the bottom together. I thought I had enough of the 3/8 Meranti to do it, but I didn't realize what a pain scarfing is. basically you are cutting a long diagonal across two adjoining pieces to increase teh amount of gluing area. I has a couple of pieces of fir from the skegs that had a nice 6:1 slope. I made a little jig and went at it with a router. It is amazing how much sawdust you create with a router. The shop is covered in a light dusting of mahogany powder.


The bottom has been attached. The edges were rounded over and covered with epoxy and fiberglass cloth. The outside of the hull was coated with epoxy also as a sealer. The RAKA resin is a bit harder to work with than System 3, since the hardener and resin are the same color it is more difficult to tell when they are totally mixed. I had a little trouble with unraveling on the edges of my tape. I think I applied the squeegee too hard. I used some rough sandpaper to bring down the high spots, which now show up as bright white in the photos. Varnish or bottom paint will cover this. The exterior will be bright, and the interior pained  a light color . Paint is easier to touch up and I expect the interior to get well used. I am going to seal up the ends and install half gallon juice containers and foam as flotation. Here are back yard photos on 1/2/2012.




The boat has a thin bottom, so we need to disperse my weight across to the chines. Started cutting teak for the floor. I traded a woodworker in Little River for some old teak decking that he inherited when he bought a house in Wisconsin. It is from the Chris Craft factory back in the 30's or 40's. It is old enough that one piece said "Product of Siam" stenciled on the back. Siam changed its name to Thailand in 1939. Very nice wood. I hope to get it in the water tomorrow to test for leaks and see where the water line sits. Pix:



The weird pieces at the bow are some cutoffs from a mill work shop. I was trying them out to see what the front deck should look like. Still haven't decided.

On January 7, 2012 we took the boat down to the river and floated her for the first time. She sits a little lower in teh water than I would like. The front transom drags in the water just a little.  I did find the appropriate sitting position, so I can continue with the interior. I have been thinking about a pair of small outriggers and a sailing rig for it. It started out simple, so now it needs to get more complicated.





Okay, my bottom is too flat. I need some more buoyancy, and a bit of rocker would help. So I am going to add some foam to the bottom and glass over it. I started by running a couple of long strips from stem to stern to get a shape. Hopefully I can find some foam without foil bonded to it tomorrow. I like the shape. My calcs say it should bring the bottom up 2", which will allow the pram bow to be just out of the water. One of the shots of me paddling shows a bit of a bow wave.


The battens were used to define a pleasing shape that will give some rocker and extra flotation. Luan ply was screwed/glued to it and the void filled with polystyrene. A few voids were blasted with Great Stuff.  The edges were rounded with rough sandpaper and the first layer of fiberglass cloth was  epoxied over it. More sanding and some some shaping.  A few more voids need to be foamed.

I added a bunch of plastic containers in the end sections for flotations. A perforated panel separates it from an enclosed section. This will provide air circulation in teh event of dampness. I have about 30 pounds of flotation in it, not including the bottom.



The bow has had a rough shape since inception. I found a couple of arcs that looked good and mounted them. More of the three dimensional, non-right-angle carpentry. Here is the doorskin panel being finessed into shape:


I epoxied and screwed the front and rear decks.  Then epoxied and taped the edges to make a stronger unit. The birch door skins of the deck were stained rosewood to try to match the mahogany hull color. The next project is to roll it over and check for voids in teh foam/fiberglass interface.




March 1, 2012

The end decks consist of two compartments. The extreme section is filled with empty plastic bottles for flotation. They are contained by a perforated hardboard end plate. Originally I used the perforated hardboard because " 1. I had some on hand, and 2. It provides air circulation to dry out any water teat will get in thee. Today I discovered a couple of voids around the edges of the bottom where it was previously fiber-glassed. I drilled some small holes, large enough to insert the tip of a can of Great Stuff expandable foam. This also fits through the perforations, so I used the rest of the can to increase bouyancy and hold my plastic jugs together. 

June 2012

Time to think about sailing. On the Yahoo CANOE SAILING forum  someone posted about how a gust of wind ripped out the mast step and  tore a hole in the bottom of the boat. So it is time to strengthen the mast area. I fabricated a box beam truss out of 3/8 marine plywood and pine. A pair of braces triangulate the forces. I want to leave some flexibility in the design, so the mast step is changeable. Currently I am working on a Polynesian crab claw design with a stub mast. The stub mast is a piece of fiberglass radio tower with open ends.


The  fore bulkhead has been truned into a truss:



Braces added to triangulate the forces.


A little bit of sculptural licence on the aft brace base:

The braces were fiberglassed to join them to the hull on the inside and outside:


The sail design is a continuing project. Hopefully she will be in teh water soon under her own power.



1 comment:

  1. nice work. gotta be flexible right? thinking about making this style of boat for a bayou trip. good tips, thank you!

    ReplyDelete