Hull to Deck Joint - “Coffee Can” Type - 1973 Havsfidra 20 Heavy Double-Ender

[Martin_T]

Hello friends,

This is my first post here and I’m looking forward to posting more often about my new ‘old boat’ project, so any advice and opinions are welcomed. I am not a newbie at refitting, as working alone on my old Rawson 30, she got a new diesel install, built-from-scratch mast, new rigging, bowsprit, and rudder, did complete a seven-year circumnavigation without any serious mishaps along the way. But, at the age of 75, I must admit, everything takes a bit longer these days, and a smaller boat is more to my liking now. However, described below is an area that I feel I AM new at; rebuilding the "Coffee Can" style hull-to-deck joint, which I have never encountered. From what I’ve read they never caught on due to their complexity in the molding-making process, and other methods came into play that were better. Still…I’m stuck with what I got...

Last year I acquired a 1973 Swedish-built Fisksatra Havsfidra 20’. She’s a heavy displacement double-ender, which I found here on the West Coast of the U.S. I had planned to be further along in the project by now but as they say; “life is what happens while you are making other plans”. So I am finally beginning the refit/restoration, and I am beginning with the hull-to-deck joint.

Removing the old damaged rub rail revealed this coffee can type deck joint fastened about every foot with 10-24 flathead bronze machine screws threaded into the hull, which do not go all the way through the hull, but are dead-ended in a built-up thick fiberglass bulge running inside the length of the hull. This inside joint is heavily glassed so the screws must have been there to hold the deck in place until it was glassed over on the inside of the hull. On the outside hull/deck joint some clear resin was applied in the gap but it had no structural strength. It was applied over the blue hull’s gel coat, more as a sealant, and being so old, it was cracked every few inches and easily fell out with my application of mallet and chisel. It was amber-clear resin with no fibers or fillers in it whatsoever — strange, and maybe a previous owner's afterthought. A lot can happen to a boat over 50 years.

I have removed the rub rail which covered this joint and all its old screws. So far the plan is to fill the old screw holes by counter sinking slightly and inject them with resin filler. (Epoxy, cabosil thickener, milled fibers).
Then I plan to fill the gap between the deck lip and hull flange by injecting (using syringes) structural polyester resin adhesive under the entire 1-1/4” lip of the deck cap around the boat, and this leaves a 1/4” gap from deck to hull, which I plan to glass by laying in some narrow over-lapping CSM strips, (perhaps some 1708 over, as well, then CSM over?), and fair it all into the curve of the deck to hull. Perhaps I could do away with glassing, and just fill in with structural adhesive? This may look ugly as the hull and deck are flush with each other at this time, so maybe the structural stuff would be easiest if strong enough.

I’m thinking too that perhaps a better idea would be to build up a very thick wide layer over this joint on which I could install a new wide rub rail. The hull is already 8mm thick at this joint, so building it up would give lots of “meat” to thread in rub rail threaded machine screws. Ugh… That would be a lot of work! But could be done.

That’s about it for now. Thanks ahead of time for any thoughts or suggestions.
Fair winds,

Martin

[atomvoyager]

Welcome Martin
Glassing over the outside seam seems like the best way to ensure it is sealed. Just filling the gap with any resin could allow cracks to appear as the hull flexes over time. That may not matter if the intruding water is blocked from reaching the inside and the joint is recovered by the rubrail. Filling the joint seam under the rubrail might also be done with a non-sagging structural sealant but if the gap is too wide, adhesives like 3m 5200 will sage before curing.
It also depends on if you are trying to add strength, watertightness, or both and how far you are willing to go in labor, weight and cost. Adding a raised block of some type to install the rubrail on doesn't sound warranted unless you are worried about strength. How well is the inside of the seam glassed and is it sufficient for strength and watertightness? If you were going to fiberglass the outside then that means repainting the hull or at least a wide stripe over the repair area.