Boat Works: Small Hatch, Big Difference

When talking shop among sailors or reading about safety at sea, ventilation is not a topic that comes up much. Evidently it’s secondary to things like angle of vanishing stability, survival equipment, and overboard rescue skills. But that doesn’t mean it doesn’t have a big effect on safety and comfort on board.

Yacht designers have come up with various ways to keep a cabin ventilated even when all the hatches are closed since stale air and diesel fumes can contribute to seasickness, and carbon monoxide (CO) from things like cabin heaters can cause headaches at best and death at worst. Cowl vents through the deck are common in spaces where a little bit of rain or spray won’t be a big deal—places like the anchor locker or the lazarette. For the cabin, many boats have employed dorade vents since they were invented for the famous Sparkman & Stephens yacht Dorade. These are cowl vents built into a box through which air can flow into the cabin, but spray and rain are whisked away through a small scupper in the box. Hatches with small fans mounted into them, powered by mini solar panels, are a more modern ventilation system.

On board our cold-molded wooden sloop, Celeste, my husband, Seth, and I had all three of these types of vents. We had (and still have) solar-powered vent fans on our center hatch and our head hatch, and we have simple cowl vents in our anchor locker and lazarette. For the tiny aft cabin where we sleep at anchor, a dorade box provided ventilation, but it posed some problems that we needed to address.

We’ve done quite a bit of sailing in Alaska and the Arctic, which means that we often have had occasion to use our gravity-fed diesel heater. It draws well, so we didn’t worry about carbon monoxide poisoning due to a poorly drawing chimney. Instead, the trouble was that the chimney was positioned immediately forward of the dorade box.

This meant that at anchor, pointed into the wind, smoke from the heater could blow down the dorade vent into our cabin, raising CO levels while we slept. Since carbon monoxide is odorless and colorless, this could become a problem without anyone realizing it, and everyone knows that enough CO poisoning can kill a person.

Fortunately, this never became a critical issue in our time in the far north, but the potential existed, so we decided to replace the dorade with a small opening hatch. This would mean that when the stove was on, we’d have to rely entirely on the solar fan vents to keep the cabin ventilated at night. But better that than allowing the possibility of smoke and CO wafting into our sleeping quarters. In the daytime, we were in and out of the cabin often enough that the companionway effectively ventilated the cabin. And frankly, in the freezing (and below freezing) temperatures of the Arctic, keeping the cabin warm enough was always more of a struggle than keeping it ventilated.

The second impetus for the project was the opposite of the cold-weather issue: sailing in the tropics. We’ve sailed many miles in the South Pacific, Indian Ocean, and the tropical Atlantic, and we live in Hawai‘i. Both of us dislike trying to sleep in a hot, sticky cabin. In the tropics, even with the main cabin fully ventilated with a cloth wind scoop in the forward hatch and the companionway open, the dorade vent simply did not let enough air into the aft cabin to keep it cool. Replacing it with a hatch that would invite a breeze directly into our sleeping quarters would vastly improve our quality of life on board.

Removing the dorade vent was a fairly simple matter of removing screws and prying it off the cabintop. Fortunately it wasn’t bedded with anything extremely permanent (like 5200 sealant) that would have torn up the cabintop or the wood of the box when we pried it off. We then scraped the cabintop clean of sealant.

At the same time, we were also repainting the entire cabin coachroof, so we had all the various fittings and fasteners removed for scraping, sanding, cleaning, and painting. About 10 days later, once the coachroof was a newly gleaming white with multiple coats of paint to keep the elements away from the wood and fiberglass, we were ready to focus on the new hatch.

The first step was to trace the curve of the cabintop to build a frame for the new hatch. Seth used a piece of cardboard, carefully cutting it to follow the cabin’s curve. Then he traced the curve onto the wood he would use to build the hatch frame.

We had some suitable pieces of mango wood left from a land-based project we’d done here in Hawai‘i. Mango is a solid hardwood, and it is also a gorgeous wood used for fine cabinetry. So it felt a little strange to be using it for this project, but the pieces were basically leftovers, and we couldn’t justify buying any hardwood when we had some good pieces already. Also, they were thick enough to accommodate the curvature of the cabintop. Because mango is so beautiful, we hoped that we might be able to leave the hatch frame finished bright–varnished for the wood to show–but in the end we decided against that. Lovely as the wood was, it would be better sealed up with fiberglass and epoxy to maintain the cabintop’s watertight integrity.

To form the wood into the shape of the frame, Seth used a jigsaw to roughly cut the pieces that would run athwart to follow the curvature of the cabintop and then cleaned them up with a belt sander to get a smooth curve. The bottom of the pieces running fore and aft had to be angled to meet the curve of the cabin as well (a sharper angle on the lower piece, a flatter angle on the upper piece). For this, he angled the blade of the table saw and ran each bit of mango through, after testing the cut on a few pieces of scrap wood to get it right. Once each piece had the right shape, he could use epoxy to form the four sides of the frame, fitting the pieces around the hatch itself to make sure everything went together square.

Happily, the frame fit the curve of the coachroof exactly as it should. Because the corners of the hatch are rounded, we traced the shape using the wooden frame and drilled a hole in each corner, then used a jigsaw to cut the cabintop to shape—after making sure there wasn’t anything inside we would hit. (We did have to remove a light fixture first.) We also used painters’ tape to loosely secure a trash bag under the hole to collect the sawdust and debris from making the cut, so it wouldn’t make a mess of our aft cabin.

Then we removed all the beautiful new cabintop paint around the hole (with the trash bag still in place), so that when we epoxied the frame it could bond to bare fiberglass.

Of course, before we applied epoxy to anything we dry fit everything; there’s nothing worse than realizing a new piece of equipment won’t fit after the fasteners are in! Having verified the fit, we used epoxy and low-density filler to affix the wooden frame to the cabintop and clamped it into place. We didn’t use screws anywhere in this process, so that if we ever need to take the frame off, we can bang away with a chisel without worrying about running into anything too hard.

Seth then laid up fiberglass cloth over it to make it completely watertight. Once the wetted-out fiberglass was tacky but before it was completely cured, he applied a coat of epoxy and low-density filler to fair everything smooth. (If you apply epoxy to a layup too soon it might lose its shape or sag, but applying a fairing coat before everything is completely cured avoids having to clean and sand the surface again.) He then prepped and painted it with primer, followed by the same topside paint we’d used for the rest of the coachroof.

Finally, we were ready to install the hatch itself. We were onto the final steps of drilling the screw holes into the wood-and-glass frame, bedding the whole metal frame and the screws with silicon (again, this facilitates removal versus something like 5200, and in our experience everything on a boat will eventually need to be re-bedded, no matter what goop you use), and screwing it into place. Once the sealant had set, we cut away the excess, and we had a beautiful new hatch. Seth had mounted it to face forward when open to maximize airflow into the cabin when pointed into the wind at anchor.

We’ve had the hatch open most nights on board. And it’s made the difference we had hoped it would; we now sleep with a pleasant cool breeze wafting down the open hatch, and a lovely view of the night sky and its brilliant tropical stars.

Ellen Massey Leonard has sailed 60,000 miles on rudimentary classic boats, including a circumnavigation and a voyage to the polar pack ice.

August/September 2023