A Waterproof Hatch

Small boats such as Footys and RG65s are typically wet boats, so a good watertight hatch is essential. The photos show one I’ve come up with. No particular innovation is claimed, since most everything having to do with boats has been invented before.

The first picture shows the basic parts and their arrangement. The hatch is 1/4" thick with sides beveled to a 30 deg. angle and gasketed with “Funky Foam.” This is a closed-cell foam sold in craft and toy stores as a hypoallergenic substitute for felt. The hatch frame is similarly angled, so when the hatch is pressed down the gasket is compressed. Any other thin, waterproof and compressible gasket material could be used.

The dog wheel is cut from the sheet lexan sold in hardware stores as a substitute for window glass. Its center hole is drilled #42 and tapped 4-40 for a countersunk center screw which is closed off with a locknut as shown. The locknut is positioned so that when the dog wheel is snug against it, and the center screw is pressed down, the arms of the dog wheel just clear the hatch frame.

The two stop pins, A and B, are located as shown. Using a countersunk or counterbored screw means the hatch is flush with the deck and there is nothing to snag or foul any loose running sheets that may drop down onto the deck.

In the first picture the dog wheel is shown in the open position, with the center screw run out so that the wheel is snug against the lock nut and touching stop pin A.

To close, as shown in the second picture, tightening the center screw first rotates the dog wheel 1/4 turn until it comes up against stop pin B, which puts the dogs over the hatch frame. With the dog wheel held there, continuing to turn engages the threads in the wheel and causes its center to be pulled up against the hatch, with the springiness of the lexan applying the pressure to compress the gasket.

To open, loosening the center screw first relieves the pressure on the gasket, and then the dog wheel rotates 1/4 turn to the open position, being held by stop pin A.
Eventually the center screw is out far enough so that the dog wheel is snug against the lock nut, which enables it to be turned to the locked position again.

The prototype hatch was made from 1/4 ply to take the compressive pressure and is therefore heavier than it needs to be. I think it would be helpful to builders if a composite expert (coughnigelcough :-)) could make hatches and seating frames from carbon; the dog wheel could be laser cut from 3mm ABS. A carbon-over-structural foam hatch would be very light and strong.