Making a Hatch out of HDU Board and Coosa Composites

None of Phoenix's original hatches were intact when we bought her. The hatches that did come with Phoenix did not fit properly, as the previous owner resized each hatch opening when he began re-decking the boat. We had already built new hatches on the foredeck and aft cabin as well as the butterfly hatch on the main cabin, and had made a "temporary hatch" on the aft lazarette out of ipe and old Lexan.That hatch was never intended to be a permanent solution, and the time had come to design and build a new hatch.

Our other hatches are made of camaru or teak with Lexan, and were built to let light into the cabins. The lazarette, on the the other hand, is a storage area on the aft deck that doesn't need Lexan. With Phoenix's canoe stern, the aft deck is narrow, so we wanted to make the most of the real estate and have a strong hatch that could be walked on, so a nonskid surface was a must.

We had some 1/2" high density urethane (HDU) board left over from our windshield coaming rebuild, and some scrap 1/2" Coosa Bluewater board as well. As we mentioned in the windshield coaming post, HDU is a strong, naturally waterproof material that is much lighter than wood, thermally stable, paintable, and can be machined much like wood. It comes in a variety of thicknesses, and it works well with fiberglass and epoxy.

Coosa is HDU material reinforced with layers of fiberglass. It has all of the properties that we love about working with HDU, along with the strength and structural properties of fiberglass. It comes in two varieties: Nautical (reinforced with continuous strand fiberglass) and Bluewater (reinforced with layers of both continuous strand and woven roving fiberglass). 

Given the structural properties of both materials, and how much of each we had left over from previous projects, we decided to laminate two pieces of HDU together to serve as the top of the hatch and use the Coosa Bluewater material for the sides of the hatch.

Our lazarette hatch is a trapezoid with the largest edge forward near the aft cabin. When building the Coosa frame, we opted to make the front edge taller than the trailing aft edge so that water would drain down the hatch rather than pool anywhere on top. We glued the edges together with Precision Board's HDU Adhesives, and used screws to hold the pieces together while the urethane adhesive set up. [Note: HDU and Coosa tend to move when the adhesive is applied, so clamps, screws, weights, etc. are needed to help keep the pieces in place.]

While the framing was setting up, we cut out two trapezoid pieces out of the HDU board --a larger piece to sit on top of the framing and one slightly smaller (1/2" on each side) to fit just inside the frame. The two trapezoids were laminated together, then glued and screwed to the Coosa frame.

Next it was time to test fit the new frame in spot. We installed Whitecap stainless hinges on all of our other hatches (excluding the butterfly hatch), so we checked those for placement with the hatch as well.

Whitecap Cast Stainless Hinges

Test fitting our new lazarette hatch made of Coosa Bluewater board and Sign Foam HDU board

We were then ready to remove all of the screws and prepare to fiberglass the hatch. We filled all of the screw holes with thickened epoxy, routered all of the edges, and laid down 20 ounces of woven fiberglass on the top and a 10 ounce layer on the inside as well.

Another design consideration for our hatch that we had to consider is that our rudder post is in the aft lazarette; in the event we need to use our emergency tiller, which attaches to the rudder post, we wanted to be able to install the emergency tiller without having the hatch completely open. Chances are you will only need the emergency tiller when the proverbial sh*t hits the fan, in which case, the decks are probably awash. Why add insult to injury and deal with water dumping down the hatch if you can avoid it?

To combat this issue, we decided to install a 4" access port to the hatch that we could open and insert the emergency tiller through if needed. We could also install a cowl vent in the port to allow airflow into the lazarette when running the generator. We measured for placement to align the emergency tiller with the rudder post and used a hole saw to cut the appropriately sized hole.

Lazarette hatch glassed and first coat of microballoons applied

Next, we used epoxy mixed with microballoons to fair the hatch smooth inside and out, sanding with an orbital sander between coats.

Fairing the lazarette hatch

When we were satisfied with the fairing, it was time for primer and gloss coats of paint. The entire hatch was primed inside and out, and we concentrated the finish gloss paint on the edges, around the access port, and inside of the hatch.

After allowing the gloss paint to cure for several days, we taped off the main top portion of the hatch, lightly scuffed the paint and applied the white Kiwigrip nonskid paint. We've been very happy with our Kiwigrip nonskid on Phoenix, and have used it both on the decks as well as in our nesting dinghy.

Gloss coat done and taping off for Kiwigrip non-skid application

Kiwigrip non-skid on Phoenix's lazarette hatch

Kiwigrip has a thick, yogurt-like consistency that is applied with a notched trowel, about 1/4" thick. You then use their "loopy-goopy" texture rollers to roll in the desired texture. Kiwi-grip dries pretty quickly -- usually touch dry in an hour, and can be walked in after 24 hours. Once the paint was dry, we installed the access hatch with stainless screws and butyl tape to make a watertight seal.

Access port installed and ready for install

I will be sewing a sleeve or boot to go around the emergency tiller to keep water from entering the hatch in the event we need to use it (probably out of neoprene). We don't really need to run the generator at this point, but we can pop in the cowl vent when necessary.

We now have a strong, walkable, low profile hatch on the aft deck that looks great! HDU and Coosa have really become our new favorite boat construction media. They are slightly more expensive than wood, but if you want to do the job once and never worry about rot or water penetration again, I would highly recommend working with them.