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Monday, September 8, 2014

Kingfisher Drift Boat Build - Updated Rounded Transom

The plans that I have for the "Kingfisher" show the boat with the "how to" for a traditional squared off transom. I'd like to use a "Rounded Transom".  Problem is that I haven't the foggiest how to do it. I've searched for construction photos in various boat building forums and have gotten a few clues. In essence I'm having to wing it.

Here's the "Semi Finished" Rounded Transom. To find out the process and what was involved how I did  just continue reading this post.

So here's my thought process. I've stitched the hull together and have installed a temporary squared off transom to establish the shape of the hull. I've used epoxy peanut butter to install fillets between my stitches on the inside, so my hull is basically glued together. I'm leaving the stitches in during the "rounded transom" building process.

I purchased a piece of 1/8" x 5' x 5' "Finn-ply" to use as a template/form. I took the sheet and bent it around the transom to achieve a pleasant shape for the rounded transom. I then put a couple of screws from the Finn-Ply into the sides about 3/4" from the top of the sides to hold it into place. I then uses 16 gauge wire to stitch the "Finn-ply" to the correct shape making sure it was in full contact with the sides and maintaining the shape of the radius cut into the Plascore Bottom. The radius cut in the Plascore is really more of partial ellipse.

Once I liked the shape of the "Rounded Transom. I made a top and a bottom and scribed it to the shape. I scribed it 1/2" smaller than the Finn Ply attached to the outside. This is because I'm going to actually place the 1/8" Finn-Ply on the inside to make the actual form and then bend the 3 sheets of 3mm Okoume Plywood around it.

Here's the "Rounded Transom" form placed inside the hull. It is built to conform to the interior profile of the hull. I'm going to laminate the rounded transom taller and will cut it down once it is laminated. It fits perfectly to the inside contour. When I laminate 3 pieces of 3mm Okoume Plywood to the form it will flush out with the outside.

This photo shows the form fitting tightly to the interior sides and bottom. You can also see the top that was scribed and the bottom. The rectangular piece of plywood keeps the form square and stabilized.

Next I need to take the form out of the boat and prepare the form for laminating the Rounded Transom and cut the 3 pieces of 3mm Okoume Plywood. This will entail drilling holes in the top and bottom so I can use clamps when laminating. I also need to uses the form to construct a pattern to cut the 3 - 3mm Okoume Plywood to be used to laminate the "rounded transom".  I also need to cover the form with 3 mil plastic prior to doing the laminations.

I used Construction Paper to make a pattern to cut the 3 - 3mm plywood panels for the transom.

I used the pattern to cut 3 pieces for the trasom.

I drilled 1 1/4" holes in the top and bottom of the form to allow using clamps during the laminating process.

Here's the first lamination being clamped to the form, I've used 1 1/4" flat head screws to attached it on the ends. The screw holes will be cut off when the rounded transom is scribed and scarfed to the hull.

I've epoxied and applied the second and third laminations to the mold. You can see I made each layer a little shorter in length so I could screw each layer to the mold. 

The epoxy cured overnight and I detached it from the mold. I then had to layout and cut the transom piece to length. I had to do this to each end, The top and bottom are about 4" taller than the final cut with will be done once it is installed.

Once I cut the ends I had to layout for the scarf joint. The scarf joint will be 3" long and the material is being removed on the "inside" surface. I drew lines across the sheet every 1/2" for reference as I was sanding and planing the scarf. These reference lines make it much easier to take the material off in an organized way. I do the bulk of it with a 3x21 belt sander with a 100 grit belt. Then fine tune it with a sharp block plane.

I cut the sides with a skill saw. I attached a straight edge and cut a clean straight line. I then laid out the scarf joint which like the rounded transom piece is 3" wide. You can see the 1/2" gradations marked.

Next I had to layout the cut on the hull of the boat. This was a one shot deal so it's the old addage "measure twice and cut once".  This photo is where I've roughed in the scarf before fine tuning it with the block plane. The diagonal line running downwards from left to right is the original scarf joint made on the side panels. It's stronger than the plywood.

I mixed up some epoxy peanut butter and used an 1/8" notched spreader to even the epoxy ou on the scarf joints. I applied it to both pieces.  I used a 1x2 piece of white oak inside and outside to add pressure to the joint. I had to bolt the bottom with an 1/8" diameter bolt. I used screws and more bolts to tighten up the joint. This joint will be painted on the outside so you have a little leeway. I still tried to get the joint perfect.

You can also see how the transom piece is quite a bit taller than the final shape. This will allow me to create a nice sweep up to the rear of the transom. 

Here's a photo of the rounded transom from the rear.

And a shot from the inside

Here's the almost final shape. It will be fine tuned at the raised section to look something like the photo below.

This is what it will eventually look like. or something close to it.

Here's view from the side. It's looking pretty cool.

And finally a shot from the bow looking towards the stern. This was the hardest part of the build and I'm very happy it's turn out the way I'd hoped.

Next Up - Flipping Over the Boat and Glassing the Chines


  1. Where did you find 3mm Okume in Northern CA? I can't find it anywhere except far away...shipping starts at $125.

  2. I purchased the 3mm Okoume Plywood. from Forest Plywood in So Cal. The shipping is the problem. Being I ordered all my Okoume Plywood from them is wasn't bad. Their prices were good, it's the shipping that kills.


Have any Questions or Comments? Let me know, Clay.