The original sole looking aft at left
Wednesday, January 4, 2012
Heap Big Job Mate! A new cockpit floor with Beckson Hatches
The original sole looking aft at left
A big job replacing the cockpit sole with Beckson hatches for access. Mark Corke explains how...
When I built Mallard my gaff rigged cutter I was never quite sure how to finish off the sole of the cockpit. On the one hand the cockpit needed to be water tight but on the other hand I also needed to have access for essential maintenance to the stuffing box and primary fuel filter. The other problem was that the cockpit sole was very close to the water line so rigging up the drains so that they would be self draining also became something of a headache, on a larger boat with more free-board the sole is higher and the water can run through drains and exit the boat above the waterline. This was not possible on Mallard so in the end I connected both drains to an inch and quarter sea cock in the bottom of the boat. This worked well enough but it meant that the sea cock had to remain open even when I was not on the boat and this made me nervous not least because if the clamps let go or the sea cock failed water would flood in and the boat would sink. I thought about the problem for several years not quite sure what to do. Finally I came up with the solution that you see in the following pictures, the old sole was completely removed and a now marine plywood sole installed. Two Beckson watertight hatches were fitted to allow continued access to the area under the cockpit and the drains were routed to a self contained sump pump which keeps the cockpit dry and means that the large sea cock can be dispensed with allow me to sleep easier at night.
Of course every boat will be different and if the hatches are installed in a cored fiberglass deck then I would recommend scooping out some of the core after the cut out has been made and filling with a thicken epoxy to prevent water from migrating into the core material.
One final point and that is to carefully think through the install before you go cutting into anything; will the hatch interfere with anything above and below decks, will it weaken the boat and do I have the necessary skill set and tools to enable me to complete the installation in professional manner.
Here's how I went about it in words and pictures.
Step one was to remove the old drains, which were big, mostly because they incorporate a non return ball valve to prevent water from sloshing back up into the cockpit.
The next step was probably the most time consuming of the whole project for me, it was certainly the messiest. Using a Fein multimaster I cut out the existing sole but left the bearers in place as I would need these later to support the new sole.
Once the old sole was out of the way I was able to accurately measure for the new half inch marine plywood that would make up the new section. I then cut this out with a circular saw with a fine tooth blade but I could have used a jigsaw. To allow a little room for the epoxy and also to make sure that the ply would not get jammed in I allowed an eighth of an inch clearance all the way around.
After cutting out the ply to the correct overall dimensions the cut outs for the hatches were marked and then cut out with a jig saw. Like the overall size of the play I made the cut outs and eighth oversize to allow for a little movement.
I then bored for the new drains which was much easier to do off the boat. I used a drill press which gave a perfect hole but a hand held drill would have been almost as good had the machine not been available.
I used a brass plumbing fitting from my local home store which has a screw on one end and a barb on the other which is perfect for three quarter inch inside diameter hose. With the holes drilled I had a dry run before permanently gluing them in position.
Mixing up some epoxy thickened with colloidal silica and wood flour to a mayonnaise consistency I used mahogany dust which gives it the brown color.
I then spread a goodly amount onto the screw threads and the inside of the hole and screw the fitting down into position, notice the squeeze out which is ideal. I then left the epoxy to set overnight.
With the epoxy set I used an 80 grit disc on the random orbit sander to sand the brass fitting which was slightly proud of the plywood flush. It is important to keep the sander moving for if the brass gets too hot it will soften the epoxy and could weaken the bond.
There are two things to do before the the sole can finally be permanently glued in place; drill and countersink holes for the fixing screws and coat both sides of the sole with unthickend epoxy to seal out any moisture.
The sole is then ready to be installed and I glued it in place with epoxy thickened to the consistency of peanut butter with colloidal silica which makes a very strong bond once set.
With the epoxy still wet the sole is screwed in place. In truth the epoxy is plenty up to the task without using any screws but the screws hold the sole in place whilst the epoxy sets up and don't do any harm if left in position. I used brass screws but if they were in an area that were to be subjected to a lot of sea water than I would have used bronze.
With the sole screwed in place I used some more thickened epoxy to fill over the top of the screws and form a fillet (pronounced fill-it) in the corner to provide a smooth transition from the cockpit side to the sole. A maxed out credit card with the corner trimmed to a large radius makes the perfect tool.
When the epoxy has set after a day or two the whole sole and fillets were lightly sanded and the paint applied to match the existing surrounding paint. I have found that the best paint over epoxy seems to be the Interlux Epoxy Prime Kote which is then followed up with the colored top coats.
With the paint dry the next and final stage of the job can start. The hatches are dropped back into position and the holes for the mounting bolts made. I used an automatic center drill to create a pilot hole. When all these have been completed I removed the hatch once more and set it aside.
On the underside of the hatch in hard to read writing is stamped 'use a 12 mm diameter drill'. This is to allow the hatch to move during temperature extremes. It may be tempting to simply fix the hatch in place with some suitable wood screws but it you do there is a good chance that the plastic around the mounting holes will crack as the hatch expands and contracts at different rates to the ply substrate.
Using the pilot holes as a guide I drilled the holes to the specified 12 mm with an auger drill.
The hatch is ready to be installed but before squirting on the silicone I taped some blue painters tape all around the opening where I knew it would project under the hatch flange. With the hatch dropped back in place a razor blade is run around the perimeter tracing the outline and cutting through the tape.
The hatch is once more removed and the tape on the inside of the cut is peeled off.
Some silicone sealant is applied around the entire perimeter.
The hatch is then bolted into position with 10-24 stainless steel flat head machine screws, backed up on the underside with fender washers and nuts which are also stainless.
Then the perimeter tape is peeled up pulling any squeeze out with it leaving a nice clean and tidy job with no need of any rags or chemical solvents.
The finished job all ready for another season. A teak floor grating will be installed in due course.