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.


Mast Beam Project

Mast beam at time of purchase.

Mast beam at time of purchase.

When I purchased the boat in 2007, I knew that one day I’d need to deal with the mast beam. I could see the fiberglass tabbing around the V-birth door trim was cracked, and the trim above the door had sunk down 1/8th inch or more.

In the spring of 2012 when stepping the mast, and gingerly tightening the shrouds the mast beam collapsed slightly, bringing  the trim around it down another 1/8th inch. It was time to deal with this.


Mast beam at time of purchase.


The first step was to remove the old beam.  I removed the mast step and the long bolts that go through the mast step, cabin top and beam. After removing the many bolts that go through the beam and bulkhead, I used an oscillating multi-tool to carefully cut any fiberglass tabbing and wood support braces to free  the beam. This worked great.  The multi-tool is like a surgical instrument and makes clean accurate cuts with little mess or fuss. I had the beam out in less than an hour.



I decided that I’d laminate a new beam using epoxy and white oak. I went with white oak for  strength and rot resistance. Price is reasonable too.  I also decided that I’d build the new beam oversize in height to give it a bit more strength. The old beam measured 4 inches in height, my new beam would be 5 inches.  I knew there would be some fiddling with trim, and the v-berth door would overlap the beam, and I’d need to duck a bit more when passing under, but all these details seemed like a small price to pay for the added strength.  After the old beam was out, it was obvious that a number of plies has de-laminated.

I went wood shopping and bought a couple of 5/4 white oak slabs.   An afternoon at the table saw and planer turned the slabs into a stack of 3/8 thick, 4 inch wide by 5 feet long boards.  I calculated I’d need 13 plies (boards) to give me my 5 inches in height.

Next came the mold.  Using the old beam I traced the curve on my workbench as a start.  When laminating, you need to calculate springback, which is based on the number of plies v. distance of the curve.  “The Gougeon Brothers on Boat Construction” as a section on this.  With 13 plies and a 4 inch curve I’d have very little spring back so I added only about a millimeter to the ends of the curve.

I used some scraps of maple to screw stops to my bench that I could pull the plies to using clamps.


Testing to see how well I could pull the plies to the mold. Kind of a dry run w/o the epoxy.

Epoxy time.  White oak has a reputation of being difficult to glue so I took no chances.  Each ply was well sanded to 60 grit. I also stacked the plies in my car in the sun to warm them up before applying any epoxy.  Epoxy flows out nice on warm wood, and when the wood cools (moving it into the barn) it draws the epoxy into the pores of the wood.

Working quickly, I pulled a few pieces from the car and brushes some neat (no filler) epoxy to both sides then stacked them in the cool shade.  I use neat epoxy first and let it cure to the point that it feels like the sticky side of scotch tape; by doing this, you lessen the chances for squeeze out. Unlike many wood glues, epoxy does not like high clamping pressure, but unfortunately there’s no way to avoid it here.


Oak boards with straight epoxy, waiting to cure to a tacky state.

Once the boards were tacky to the touch, I mixed up a batch of epoxy mixed with colloidal silica, brushed it on each board and then carefully pulled the boards into shape starting from the center and working my way to the ends.  To keep the boards flat against the bench I clamped two short sections of 2×4 over the top.   I was pleased that the whole mess pulled into position easily.


Note the poly sheeting to keep the whole mess from sticking to the bench and the mold.

After 48 hours, I removed the clamps and knocked off the larger pools of epoxy with a chisel and sent the beam through the planner clean up the faces, and sanded the top and bottom with a random orbital sander.





The original beam was 4 inches in height, my new beam is 4 7/8 inches so I needed to cut the vertical posts on the bulkhead to allow fit.  After trimming the ends of the new beam to match the shape/width of the old beam, and giving all hidden sides a couple coats of epoxy to protect it from water,  I held the new beam to position and scribed marks on the support posts.  Using a sharp Japanese style pull saw made quick work of removing the top 7/8″ of the posts.

With the shortened posts, I was able to slide the beam into position.  We used a small jack and a 4×4 post to push up on the bottom of the mast beam, which restored the cabin top to the original curve.

With the beam in the proper position,  there were now small gaps between the support posts and the beam, so I cut back the posts again for exactly 1 centimeter of gap.   I could then cut 4 1cm thick pads out of some scrap oak to fill the gap.

I was also concerned that the fit between the beam and the cabin top would not be an exact fit.  What I did was apply a coating of wax to the cabin top and the bulkhead, mixed up some thickened epoxy, brushed it on to the top of the beam, and set it in place. With a bit of pressure from the jack,  a bit of the epoxy squirted out and was easily cleaned up.

With the beam in place, and the jack holding it tight, I drilled the 1/4″ holes for the 6 bolts,  bolting the beam to the bulkhead.  I left the jack in place overnight.



Next, I cut spacers to add to the top of each post that would serve to fill the gap. I shaped the pads a little so they wouldn’t look like I was fixing a problem. For the vertical posts, I cut 4′ long “braces” that are tapered to reinforce the posts.  I cut a shelf near the top of the post which would receive the stepped cut brace. This way, the wood would take the load and not just the glue/bolts. For now, the braces are epoxy glued only. I’ll add some mechanical fasteners in the spring.

For tabbing, I added tabbing back to the beam ends where the beam meets the cabin sides. The old beam had tabbing all across the top of the beam from the cabin roof to the face of the beam. The new beam fits flush to the top of the cabin, and I think it looks cleaner without the tabbing so I’m leaving it as-is for now. Structurally, I don’t see the need for the tabbing. I’ve primed the new fiberglass, leaving finish paint until the warmer weather of the spring.


It’s getting colder here in NH, and the remainder of this will wait until spring. I still need to add the fasteners to the braces, finish paint my tabbing, and varnish the new wood.