Hello Everyone,


My name is Guy and this is my first post in this forum.  I am here because I want to build a wooden drift boat and, undoubtedly, I will occasionally need advice of the pool of experts and experienced drift boat builders on this forum.


In preparation for this project I have read and studied three books: Drift Boats and River Dories by R. L. Fletcher, Boatbuilding with Plywood by G. L. Witt, and Covering Wooden Boats with Fiberglass by A. H. Vaitses.  I have also developed my own set of construction plans based off of the "Original McKenzie Double-Ender with Transom" in Fletcher's book.  I used and MS Excel spreadsheet to calculate all of the dimensions, cut angles, compound angles, and bevel angles of all frame components and I used Pilot3D software to calculate the as-cut dimensions of the plywood sides and bottom.  At this point I am pretty comfortable with the mechanics of construction and I think that I am just about ready to start purchasing lumber.


Presently, I plan to use Meranti Hydro-Tek plywood; 1/4-in. on the sides and 1/2-in. on the bottom.  I found plenty of places to purchase these materials, but they are all far away from Idaho Falls, Idaho, and as a result shipping costs more than the materials.  Are any of you aware of a business within a few hundred miles of Idaho Falls that sells this plywood?  I have a few requests in to the local lumber companies, but I have yet to talk with someone who has heard of this material before.


I also plan to use Port Orford Cedar (CVG) for the straight frame sections and White Oak (quater sawn) for the bent frame sections (chine logs and sheer rails).


Thank you, Guy

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My gut feeling is that a Catenary curve is the right choice.  One of the things it is known for is describing the arc formed by suspending a length of chain at both ends.  In one form the equation has a single constant.  Look here for more information...


And it has an equally simple form for the arc length.

As you "bend" the "vertical" panel, it conforms to the Catenary curve and the most forward point of the panel (the highest point of the sheer) is fixed to the X-Z plane (X is boat length, Y is boat width, and Z is boat height).  In other words, as the panel is "flexed" it all moves into the Y space except for the very tip of the stem.  The transom is offset into the Y space according to your specification for tansom width.

At this point the chine edge (now a curve) still rests on the horizontal X-Y plane and the sheer edge (also now a curve) is located in X-Y-Z space.  Then you rotate these two curves relative to the X-axis.  As this occurs, the chine edge moves into X-Y-Z space and forms the "continuous rocker bottom" that is typical of traditional drift boat design.

The rotation is continued until the face of the stem resides entirely on the X-Z plane.

The length of the side panel is related to the Catenary curve via the arc length of the Catenary curve along that section equivalent to the chine curve.

At this point the chine curve and sheer curve are described in some arbitrary X-Y-Z coordinate system imposed by the Catenary curve.  By simple arithmetic, each point can be moved into a new, more intuative, coordinate system.

If this all works, I'll send the spreadsheet to anyone who is interested.

Guy, thanks for the information. I would love to get a copy of your spreadsheet. amsrick@comcast.net


Rick Newman

Sure thing Rick.  I'll keep you posted on the progress.

Guy, I don't believe that stitch and glue will produce a lighter boat if you compare hull to hull.  A framed boat can hang the seats off of the frame.  I stitch and glue boat requires bulkheads and thwarts to stiffen the sides.  A S&G drift boat is made with 3/8 in plywood for the sides and a framed boat is made with 1/4 in plywood for the sides.  A S&G boat uses a lot of fiberglass and epoxy while a framed boat can use very little.  

It is best to make your decision on your choice of construction based on preference of building style and other characteristics besides weight. 

Some are building with Plascore bottoms that could be saving some additional weight.  I haven't tried that yet.  I am a fan of low center of gravity and a lighter bottom is counter productive to performance; however, there might not be much difference to COG after a boat is loaded. 

A few people on the Montana-Riverboats site are building the entire boat out of Plascore which would be lighter and could solve the COG issue. That could be a good boat, of course it's no longer a wooden boat boat but it is still built and used in much the same way.

Thanks Randy.  I see your point about weight: thinner plywood and ribbed frames are balanced against thicker plywood, bulkheads, and thwarts.

To me, the S&G drift boats have a more modern and refined look.  They are very nice, but for some reason I'm kind of hooked on the look of the framed boats and want to give that a try.

I've not seen a Plascore boat (or the material) other than through pictures.

The new design/calculation spreadsheet is working to the point of showing the plan and profile views of the chine-edge and sheer-edge.  Now I have to marry this with the original spreadsheet that calculates the frame dimensions.

This is where you specify the plywood and joint dimensions.

This is where you specify the side panel dimensions.

This page calculates the Catenary curvature.

This page shows the traditional plan and profile views of the sheer-edge and chine-edge.







I can use some advice.

I am at the point where I need to finalize the basic design dimensions of the boat.  I'd like it to be large enough to accommodate three people comfortably (forward passenger, center oarsman, and rear passenger).

The basic dimensions I am seeking advice on are the following:

1) centerline length

2) maximum bottom width

3) side height (at the oar locks)

The boat will be used in the Idaho Falls and Challis areas.

For example, how does 16 ft, 56 in., 25 in. sound?  Is that a little too large?  Does that sound about right?  I know this may sound knit picky, but I want to get it as close to right as I can.



Guy, here is my opinion. The size you mention is very close to the most popular size in the west for three people. 

Center line LOA  should be just under 16ft.  There are two reasons, one that is plenty of boat to float three people, two is that some states require a 16ft boat to be licensed while a boat less than 16ft does not. 

Max bottom width at 56 if you want to float higher in the water but don't back row against a current all day.  52 in max bottom width if you back row against a current to hold water in more than a 3mph current.  The extra four inches will give you more primary stability but less rowing efficiency so you get pretty tired if you are holding water all day.  If you are primarily floating along with slow water that shallows out, then the 56 is your best bet. Some split the difference at 54. 

24" height of the side so you can scarf your side panels to length and then cut both sides out of a 48 inch wide piece.  You can raise the stem and lower the transom to get more wave protection in the front if that is important to you. 

You can also go higher, two more inches (26) is common for a high side but that will give you a low side panel on the opposite side that is cut off.  It's common for builders that build a high side boat to save the 22' panels for a another low side boat.  High side to keep you dry in bigger water, low side to keep you out of the wind if you are not running Class IV water and standard 24" for maximum use of materials.

A boat with a 16ft LOA and continous rocker could have a little too much rocker if not tamed.  It would be a fine boat for big water but a boat that is mostly working fishing water doesn't need more than 12 inches of rocker.  I recommend that you leave your side panels developed as you have in your drawings and then lengthen the two frames either side of the center frame. That will pull down the two ends just a little giving you a longer Length of Waterline and a short flat spot along with the corresponding flat side.  If you want to play with this on a computer you can download a program called ProChine by New Wave Systems. It will let you enter in a bunch of math and then move nodes around to see what happens.  It's pretty fun; however there is nothing better than the cardboard or balsa model like Dave Z is talking about.  You can cut out a developed panel and put sticks in as frames to see the infinite variation of rocker and flair combo that you can build from the same panels.

The other way to tame rocker is to dish out the side panel a little bit.  See Roger's book that shows the developed sides of the Pritchett Rouge River Special.  You don't need to dish out that much but a little will also tame the rocker just a little.  

Man, I wish I had talked to all of you before I did my boat. A note on the rocker: For me, an important issue was draft because we spend a fair amount time on the Trinity and it gets pretty boney at 350 CFS - typical steelhead run flows. Draft being a function of weight over surface area, if you have a shallow curve or a bit of flat area amidships, the boat will draft shallower and with a 56" wide body bottom, you can get 3 people in a boat drafting no more than 5 - 6". Plus when you attach floor panel to the bottom battens at the rowers feet, you have a nice flatter area. 



Randy, again, thank you very much.  This is very useful information.

Holy cow. MATH!

Interesting approach. The Catenary curve is interesting.  However, does it only remain true in a single radius, right?  If you look at the half breadth of alot of boats, there are varying curves, and even straight sections.  Look at a standard 16x48.   Will this method still apply? 

Do you plan to build a model?  I can't say it enough on new designs.  before I built the Flyfisher skiff design in full scale, I built three poster-board models and one scale wood model to test the design.  I made tweaks along the way for the optimization of the use of wood panels and dimensions no tighter than 1/8". 

When I designed my boat, I started with a desired sheer length, bottom width and rocker.  everything else I pulled out of the air while making models.  re-measured it all, refined the dimensions so it was easy to scale, built another, and tweaked it a little more.  The end result took me little over two or three nights, and I had a functional design. 

I'm an engineer by trade, use all sorts of modelling tools (Pro-e, autocad, solidworks) and still found that using the modelling hands-on approach gave me something that looked good on paper and to scale. Its was easier too.

I owe my model building advice to Roger Fletcher.  he guided me through it and it as a valuable lesson.

give it a try.

I can see the relationship of the side panels to the curves and appreciate who they will work. Have you developed the shape of the bottom of your boat? I don't remember if you are including a transom. Past discussions by Randy Dersham have illuminated the need for difference in shape based on where you will be carrying weight. For example drift boats designed to carry two passengers in the front where they would pull plugs would be asymetrical with more width in the front third of the boat. Conversly when the weight will be distributed more fore and aft as you want to do the bottom shape will change as more surface is required to support the additional weight in the rear. The shape of your transom and the width will also change the bottom shape. With the catenary curve along the bottom edge of your panels the result is commonly a highly maneuverable fully rockered boat. Should you want a boat that tracks better a portion of the catenary curve can be removed. See the Briggs boat designs for an example.

My point and I believe Dave Z's is there are many interelationships between the parts of a driftboat. While the shapes of the side panels define two of the major parts of the hull the angles of the bow and stern and width and shape of the transom are also important. I second Dave's recommendation to build some models. Roger's book has great information.

There are also some great discussions on the Montana River Boats site.

I hope that my opinions help, there are also many discussions within these pages and past posts by many others. Designing your own boat is a wonderful challenge. You have made some great steps down the path, a few more hurdles and bumps before you finish.

Good luck, keep us informed!

Rick Newman


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