The Flat End of the Boat

Building of the Transom

My first deckhand job was on the boat RB in Petersburg, Alaska. Glen, the skipper, yelled, "Go to the bow and fetch that buoy." I looked towards the front of the boat, towards the back of the boat, towards the front of the boat, towards the back of the boat...Then Glen yelled "The pointy end! The pointy end! The bow is the pointy end!"

The transom will be cut from 1½-inch meranti plywood. The 1½-inch plywood will be made by laminating two layers of  3/4-inch plywood.

Laminating

I was wondering how I would pre-saturate the two surfaces with un-thickened epoxy, apply thickened epoxy to one surface and flop the wet pre-saturated 4x8 sheet onto the gooey thickened epoxy surface without getting epoxy in my eyes, ears, nose and mouth. Then I thought, "Use your brain, not your back."

So I decided to pre-saturate the two surfaces with un-thickened epoxy and let them cure before proceeding. That eliminates flopping of a wet surface. The flopped sheet will be dry by then.

Pre-saturating with un-thickened epoxy.

Both surfaces pre-saturated and left to cure.

Install guides so the top layer will be positioned precisely
on the bottom layer. Use the overhead pulley system to elevate
the top layer.

Apply thickened epoxy on the bottom layer and lower
the top layer into place. Put two screws through both
layers so they do not wander like they did when I built the Sea Scull

Laminated layers wandering when building the Sea Scull

Weight it, clamp it, whatever it takes to see a  little excess
epoxy ooze out. Top it all off with a couple of peanut cans.

Transom Design

With a transom angle of 12° on the Lady C, I am unable to use the outboard motor tilt to trim the boat and lower the bow. I had to be travelling fast on step to keep the boat from porpoising and keep the bow down. As one can imagine, this creates quite an uncomfortable condition for a flat-bottom boat in chop.

Following Tracy O'Brien's advice, I mounted a set of permanently installed trim wedges at the base of the transom to lower the bow and put the Lady C on plane at lower speeds. In particularly nasty chop, I put 35 gallons of sea water in the anchor well in the bow so that the Lady C does not porpoise at 10 knots and I can safely navigate the chop at slow speeds without the bow blocking visibility. You should see the looks on the faces of other boaters at the launch ramp when the see me dump bucket after bucket of water into the Lady C.

The BW will have a 15° transom angle. Hopefully, this will allow me to use the outboard motor tilt to trim the boat and lower the bow. The BW's semi-V hull and lifting strakes should also minimize the need for as much trim as the flat-bottom Lady C required.

Since my twin Honda four-stroke 50hp engines on the Lady C will be mounted on the BW, the engine cutout of the BW transom will be the same as the engine cutout on the Lady C. After measuring the Lady C engine cutout, I laid it out on the design of the BW hull.

Hull Cross-Section with Transom in Background

I ran into a design challenge. I laid out the transom on an orthogonal cross-section of the hull but the transom will not be installed orthogonal. It will be installed at a 15° angle. I need the transom dimensions in a 15° cross-section so I can lay it out on the 1½-inch plywood. With a little searching of the catacombs of my memory, I recalled my high school class, Drafting 101, Lesson 23, Projecting Onto a Different Plane and overcame the challenge using graphical drafting techniques.

Transom Dimensions Projected onto 15° Plane

Then I determined where to lay out my cutting fences/guides for cutting the transom out of the 1½-inch plywood.

Cutting Guide/Fence Layout

I laid out the lines on the transom in the nice warm shop then moved it outside for cutting

Layout of the transom

Cutting the transom

Move the transom back inside and coat both sides with 4 ounce fiberglass set in epoxy.

Hand sanding

Laying up fiberglass/epoxy

Leave glass to cure

Fill the weave with un-thickened epoxy. Rough spread
the epoxy with a cheap window washing squeegee
then fine spread and tip out with a foam brush.

Almost looks like a piece of furniture.
It won't look as nice after a few trips across the bay

After the final coat of epoxy cures, cut away the dross
and sand the corner so it is not so sharp.

The transom hung from the ceiling for over 2 months while the bottom and continuous deck were constructed. Now the deck is ready for the transom. I installed some guides to brace the transom at 15°.

Guides to set transom at 15°

Then I dry-fit the transom in place...

Dry fitting of transom on deck

Then I installed a fillet of thickened epoxy (epoxy resin with hardener, silica powder, glass micro fibers and wood flour) and a layer of 4-inch biaxial fiberglass tape set in epoxy.

Transom bottom edge glued

Since I will be hanging two 200-pound outboards on the transom, I want a good sturdy connection between the transom, the deck and the bottom. I will install knees between the transom and the deck. The knees will go on top of the location of the substringers that were installed between the bottom and deck. The knees and substringers were all positioned to fall on the centerline of the outboard motors.

2x substringers beneath the deck at the transom. 

First I roughly designed the slopwell...

Rough design of slopwell

Then I designed the transom knees...

Transom knee design

I cut the transom knees from the 1½-inch meranti cut out of the transom for the motors. The knees were pre-coated with un-thickened epoxy then coated with 10oz. fiberglass.

Transom cut out

Pre-coating of transom knees

Knees coated with 10oz. fiberglass. The un-coated aft portion will
be covered by fillet and tape when these are installed

Now comes an interesting twist....

The compartments between the bottom and the deck are sealed air-tight. What happens when the temperature swings from 70°F in the shop to 45°F in the water? The air trapped in the compartments will contract creating a vacuum. Will that suck water into the compartments? It could be worse. What if the compartments very slowly breathe as if permeable to air but not water. Then the compartments could experience a temperature range of 70°F on a warm summer day to -30°F on a cold winter day. Too many issues for me to resolve so I will simply vent the compartments so they can breathe. I don't want to just drill a vent hole in the deck otherwise rainwater and snowmelt water will get into the compartments. Instead, there will be vent tubes from the deck to somewhere above water line.

The first vent tubes were installed on the transom knees. These will vent the aft 2 compartments below the deck. The vent tubes are select pine corners. I will drill a vent hole in the deck and the vent tubes will be filleted and taped over the vent hole.

Vent tubes on transom knees. Filleted and fiberglassed to the knees

Knees, with vent tubes, installed at transom

Without fiberglass tape, the end grain of the plywood that is exposed on the top edge of the transom will split. Finally, the transom is installed and I can access both sides. I sanded the top edge, routed the top edge corners quarter round and applied fiberglass tape to the top edge.

Taping top edge of transom

Tape installed and curing