1975 18' sf

[dave s]

Got the subframe built; used a 4x4, 2x4s, and a 5x4 sheet of Melamine board- it's set at 12 degrees.

[dave s]

Filled in some old thru hull holes, a strake, and cuts in the hull.
Beveled the glass back, laid some cloth on the outside and then thickened epoxy with cabosil and glass fibers and a bunch of 1708 layers on the inside. I'll go back over the outside spots when I do the exterior hull.
It's thick enough that I may put the seacock valve back at the same spot, esp. after the glass for the extension goes on.

[dave s]

After doing some testing, I'm concerned with the condition of the original woven roving; most of it seems dry and chalky white.
So to make some more work, I chiseled off much of the roving for about 24", to get some clean glass to bond to.
It came off fairly easily, compared to the leftover epoxy on the transom area.

What's a few more hours?
I hate grinding!

[dave s]

Glass cleaned up; I'm ready to finish the mold.
If only this rain would stop.

[dave s]

Mold almost done. Lots of carpentry work- almost fun!
All done with a cordless circle saw, straight edge, and angle finder.

Need to add keel section, cut off screws, and then do clay and wax.

Want to double check height of sides of tub. It's about 19" now, so should be right height, may need a bit more for the glass work.

With swim platform I'll be about 20" and I have 5-7" more for the motor mount lip.

[Blue_Heron]

I have a project 20 that I'm thinking of extending similar to what you're doing. My thinking at this point (at least one boat project away from starting on the 20) is this:

• Cut a piece of melamine board to match the outline of the transom.
• Turn the hull upside down and spray the aft 3' with PVA mold release.
• Spray the inner face of the melamine with PVA and screw it to the transom.
• Spray the aft 30" or so of the hull with tooling gelcoat and then lay up some mat and roving with some plywood stiffeners laid up in strategic locations. The layup will need to bond to the outer surface of the melamine board so it becomes the aft part of the mold.
• After cure, break it loose, flip the hull right side up, cut out the transom and prep like you've done.
• Then attach the mold so it extends behind the transom the desired amount.
• There's more detail, but you get the point.

For this to work, the steps in the hull have to be parallel all the way back. I haven't measured to confirm this, but they look to be. Not sure if this will be less work, or have better results than your approach, but it's what I was thinking of doing. More than one way to skin a cat...

Dave

[dave s]

Sounds like a plan!
I would have also pulled a mold off the hull, but flipping it over would be difficult on the side of my house.

Yeah a few ways to do this.
You could also cutoff the original transom and add in the molded section to lengthen the hull.

The simplest way would be to start with a longer boat and then make an integrated bracket out of the last few feet, but I started with an 18' instead of a 20'.
Maybe the next boat I'll cut a 23' down to 21'!

Btw. It's hard to tell from the pics, but the sides of the tub are slightly tapered in, about 3 degrees; my design is more of an integrated bracket than a hull extension.
It looks like the hull has some rocker built in so my tub tapers slightly up too.