12 steps to a new hatch & bulkhead

It worked! I now have 2 watertight bulkheads, and a new front hatch. So far the 3M 5200 is sticking perfectly.

Think of this as a fool-proof 12-step program to install a bulkhead/hatch.

(1) Remove everything reasonable from the inside of the hull - pegs, seat, backband

(2) Decide where you want the bulkhead. I moved my pegs back 3-4 inches - there’s no point in having 6" of empty space behind your feet. MAKE SURE this is where you want the bulkhead.

(3) Cut a template for the foam (you already bought the 12x20x3 inch minicell foam, right?). BY FAR the best way to do this is to take a large piece of cardboard, cut a notch out slightly larger than the size of your hull, and tape the cardboard where you want the bulkhead, but on the OUTSIDE of the hull. Now, take strips of cardboard and tape them so that one end of the strip is on the large cardboard piece, and the other end of the strip lightly brushes against the hull. Repeat this as far around the hull as you can. you’ll end up w/ a large piece of cardboard w/ a notch cut out of it w/ little “fingers” of cardboard extending inward tracing the outline of your hull. Now take the cardboard piece w/ the strips attached and lay it over a second large piece of cardboard. Trace the outline of your hull. [note: if you make your template starting on one SIDE of the hull, extending around the top and bottom of the hull, and go 2/3 of the way around the hull, you can trace the hull as I described above, then flip your “fingered” piece of cardboard over to trace the rest of the template on the second piece of cardboard.]

(4) Cut the cardboard template out, stick it on the inside of the hull & see if it fits well. Figure that you’ll want to SLIGHTLY oversize the foam so it squeezes into the hull, and then trace an appropriate outline on the 12x20 foam block. Cut the foam out w/ a serrated bread knife, or a carving knife. Saws suck for cutting foam. [Note: 12x20 wasn’t large enough for my bulkhead, so I cut what I could, then glued scraps to the top of the foam, traced the rest of the outline, and finished the bulkhead. It worked fine].

(5) Time to cut the hole for your hatch. Placement of the hatch is probably best done as far toward the middle of the boat as possible, but in front of the foam. Measure back 3”-4” from where you want the foam, and lightly mark this point. Chances are that your hull is domed on the top, so you won’t be able to install an infinitely large hatch. I used the round style “screw-in” hatch that others discussed on this thread. 6” was the largest I could fit, and that required that I let the port and starboard sides of the hatch stick up above the hull. These hatches also have a ½” lip sticking down so it is still a simple matter to seal the hatch. It’ll look like a homemade job, but who wants a 4” or smaller hatch? While you’re at the marine store, pick up some stainless steel hardware to screw the hatch to your hull. MAKE SURE the size hatch you selected is reasonable, and MAKE SURE you allowed at least 3” for the thickness of the foam. RECHECK this. Then trace the outline on your hull, RECHECK everything, and cut the hole w/ a drywall saw. The round hatches also have a ½” lip on the outside extending laterally so you don’t have to get it perfect, just remember it’s always easier to make a hole bigger than smaller. Stick the hatch into the hole, and then drill the holes in the hull for the stainless steel machine screws to go through. Assemble the hatch the way it’ll rest when you finish the job. Remember, the more you compress the hull on the sides of the hatch, the more you’ll warp the hatch and the less waterproof your hatch will be. I suppose you could even break the hatch if you tried.

(6) Now that you have a big freaking hole in your hull, it’ll be easier to fit the foam into position. Go ahead and do this and make sure you’re happy w/ the placement & fit. Mark the position of the foam. Pop the foam out.

(7) Prep the hull. Sand the area you’re going to be gluing, then hit it w/ some alcohol. DON’T NEGLECT THIS STEP.

(8) Cram the foam back into the hull, position it where you want it. Apply 3M 5200 adhesive. The owner of my local marine store swears the quick dry 5200 is sticks less than the regular 5200. Also, the marine store wanted ~$17 a calk tube for the stuff, while Home Depot sells it for ~$8. There may be other adhesives that work better, check around. NOTE: I didn’t apply any adhesive to the foam before I crammed it into the hull because you’ll get it all over the place and have a HUGE mess if you do. Use your finger to smooth a bead all the way around the bulkhead on both sides. I laid down ~1.5” on the foam, and the same on the hull.

(9) Apply another bead around the hatch hole, install the hatch, then run another bead around the hatch where it sticks up away from the hull. Smooth it out w/ your finger. BTW, the 5200 took about a week to come off my hands, even after washing w/ Gojo soap at the end of the project.

(10) If you moved the foot pegs back, fill in the old holes now.

(11) Wait a week for the 5200 to harden. You’ll find that a lot of the 5200-mess on your hull peels off when you rub it, but for some reason (hull prep?) it seemed to stick where I installed the bulkhead. Go figure.

(12) Fill the boat w/ water & see if it leaks, mine didn’t. It’s a good opportunity to also fill your hatches w/ water to see how much storage space you created. Count 5-gallon buckets to fill the hatches, and then go to an online volume conversion page to find the answer. Put the seat/backband back in, re-drill & reinstall the pegs if necessary.


Final Statistics
Final statistics for my 12.5 ft Dagger Crossover

Front compartment (new)

4,620 in3

Rear compartment (preexisting, newly sealed)

4,389 in3


8,649 in3 (original = 4,389 in3)

Total Displacement of water

312 pounds of water, not counting foam

52 pounds of water from the foam

364 pounds of water displacement total

Project cost = $65

sounds like it took more than the
original six pack of beer you started with. adding in cost of beer what was your total?

One comment
When installing foam bulkheads, I prefer to coat the area where the bulkhead will sit with sealer (I prefer Lexel or Goop) before pressing it in place. Most of the sealer will be pushed out by the foam and forms a bead on one side, but enough will remain to help edge bond it to the hull. All that remains is to add a sealer bead on the other side and smooth both beads.

Can you post some pictures?
I’d be particularly interested in the front hatch. I’ve been thinking about it for my Perception Antigua, but the foredeck doesn’t seem to be flat enough for a deck plate.

  • Steve

6-pack attack!
Holy wah, lees you ain’t kidding the initial 6-pack wasn’t enough. In a related story, this weekend a friend of mine noticed the words “glue toward cockpit” written on the compartment side of the foam. Coincidence?

I like bnystrom’s glue idea, except that I STILL have 3M 5200 stuck to the base of my fingernails. There’s no telling where I would have gotten the adhesive had I smeared it on the hull before inserting the foam. Hopefully the full 1+ inch bead of glue on each side of the bulkhead will keep it in place. It seemed to handle filling the cockpit with water, and that’s more pressure than it’ll ever see in the real world.

Pics are forthcoming, pending my digital camera situation.

5200 woes
"I STILL have 3M 5200 stuck to the base of my fingernails."

That’s what they make latex gloves for.

Be careful when choosing a caulk for plastic hatches… Beckson, for one, states that only silicone be used on their hatches. Polysulfide and Polylidamide compounds will attack some plastics, and some finishes, so be careful!

By the way, anybody know where I can get a really big round hatch? My Heritage Merlin has a flat circular molded area on the after deck, 14.5" in diameter. So far, all it’s good for is holding a pizza!