Cockpit Core Replacement

The cockpit of Seagrass was soft when I bought her, and was likely soft from a water damaged core since the 70’s.  I’ve been stalling on this project mostly due to the mess, and hem-hawing about what we want for a new floor.

This past weekend, I dove into it before I had a chance to change my mind.  After removing the access hatch to the diesel tank fill, I used an oscillating tool to cut the top layer of skin all the way around the the edges, leaving enough edge for a good taper for the final fiberglass.  The oscillating tool is fantastic for this, making the cut easily in just a few minutes with hardly any dust.  So far this is painless.


Since the core was so completely rotten, it was easy to pry back the top skin in one piece, revealing the Masonite core below.



Next step: remove the core. This was easier than expected. Much of the core could be scooped out by hand since it was more like we cardboard than plywood.  For the sections that were a little (very little) more solid, I used the oscillating tool to separate the core from the fiberglass.

Note that my boat is #116 from 1965 and the lamination in my cockpit floor consisted of a bottom layer of fiberglass, a layer of Masonite, a thin layer of fiberglass, another layer of Masonite, and the top skin of fiberglass.  The middle layer of fiberglass is so thin that it adds no extra difficulty in removal.  4

This is the setup of my rudder post.  If you wanted to ensure that water from the rudder tube would find a way into the cockpit core,  I can’t think of a better way. Would it have been so hard to extend the tube a little higher?


I bet this core was getting wet from day one.   I’m still undecided about what to do with this.  My first thought was to laminate a fiberglass tube to the bottom fiberglass skin that would extend above the top skin, and top it off with a stuffing box.  The trouble with this, is that I don’t think I have enough rudder post above the new lamination.  Stuffing boxes for shafts this size are likely too tall.  The best I can do, is surround the post with a fiberglass tube, epoxied to the bottom fiberglass, and the top fiberglass. If I size the tube correctly I can add the bronze ring from the original setup.  This won’t keep water from bubbling up into the cockpit, but it should keep water from getting to the new core.

The next step was ugly. Out came the grinding wheel with a 40 grit sandpaper disk. In 15 minutes I was able to bevel the edges to a nice taper all the way around, ready for the new fiberglass top skin.  What a mess though.  The next 45 minutes were spent cleaning up.  We even tried holding a shop-vac near the grinder, and it may have helped some, but you wouldn’t know it by looking at the end mess. I also used the 40 grit disk on the fiberglass bottom skin to clean up the surface.



At this point, I need to remove the two drains so they are not in the way, and figure out a way to support the bottom fiberglass skin so the new core sits flat. Access is difficult.  I was thinking of stuffing a deflated motorcycle tire between the diesel tank and the fiberglass, and inflating until the floor sits flat. Or perhaps some strips of wood running across between the tank and skin.

DSCF2924The core (3/8) end grain balsa is in. Painted some neat epoxy on the fiberglass skin, and while that was getting tacky, we mixed up some epoxy and cabosil and used that to fill the gaps around the fuel hatch and the rudder post. I don’t want any water getting to this core!

Once we were sure the core was down and flat, everything was covered with Peel Ply,  an weighted with sections of plywood and various heavy items.

The next day, we peeled back the Peel Ply, cleaned up a few rough spots and began laying the cloth. Three layers of 1708 biax were added, over the course of the day, finishing up with a layer of neat epoxy.

*The big hole was also filled using many layers of 1708, and eventually faired smooth.

Unfortunately,  with the date fast approaching to launch the boat, images are scarce, but I faired the floor smooth, and gave the whole cockpit a couple coats of new paint after we nicked it up a little with this last job.


I’d already made a pattern of the cockpit floor, and after buying some epe decking boards, milled them into 1/4 thick strips for the cockpit floor. Each board was prefit to the pattern, so at the boat, I gave the floor a good sanding, wiped it all down and set each board down in a heavy bed of GFlex epoxy, using tile spacers to keep the gaps consistent.  Once each board was set, we weighted everything while we waited for the epoxy to cure.


The next day, we taped the bottom of each gap with a slippery vinyl tape so the caulk sticks to the sides only.


We taped each seam, and caulked with Teak Decking Systems Caulk,  This stuff is buttery smooth to work with, and a heck of a mess if you aren’t careful.



This is the result after we peeled the tape back.


The next step was to give the whole surface a quick sanding to clean it up. I’ve still got some details to address, but they can wait until the boat is back in my yard.