One more project completed. This one took only about six months from inception to completion. This included visualizing, designing, testing prototype, then finally production and installation.
After having removed the propane chambers and sealing off the openings, I made my own hatches to make that area easily accessible from the cockpit. I also had two existing plastic 10" hatches in the aft corners of the cockpit. The existing plastic hatches were cracked and I wanted to have a total of four hatches in the cockpit seats to access the area that are hard to reach from inside the lockers.
I had a hard time finding hatches that were durable, easy to install, wouldn't break after a few years, easy to close and latch, water tight, about 10" ID, and not too expensive. These criteria eliminated all the hatches I could find on the market, so I designed and made my own. The only criterion not met was "easy to install", although the installation was not to bad.
The hatch is made from two parts:
1. The ring: Permanently glassed to the boat
2. The lid: snug fit to the ring and easily removable/lockable, even in the dark.
For each piece, I made a mold, then the part. The ring is solid fiberglass layup. The lid is cored with 1/4" Coosa board, except where the latch is installed; that area is solid. I used polyester resin for building the parts and epoxy resin for installation.
I achieved close tolerance between lid and ring by making the ring first, then using that as the mold for the lid. That gave me an almost perfect fit between the two.
Each lid has a single latch and opposite the latch is a stainless steel bar that pinches up against the underside of the ring. When I press the lid down, first the stainless steel bar, in at an angle, sort like a hinge, then close the latch side and engage the latch. I rotate the cam latch until it engages a fiberglassed protrusion, sloped so tightening the cam latch sucks the lid down into the seal. The hatch sits flush with the top of the cockpit seat with just the latch handle sticking up about 1/4".
Water-tight seal is achieved with a 3/16" EPDM foam cord that sits in a 1/4" groove routed out of the ring along an inner perimeter. The groove has a depth of about 1/2 the diameter of the foam cord. This allows compression of the lid into the cord without compressing the cord completely.
Although I used a mold to make these, the fit between the lid and ring is not perfect slightly non-round. My fiberglass/mold-making skills are just not good enough for a perfect fit; therefore, for the best fit, the lid has to be placed in the ring in one orientation; otherwise, the lid will rock a bit. To ensure the lid is correctly oriented, the metal tab on the lid fits into a groove of the ring. On the outside, I will add colored dots of gelcoat to the lid and ring as alignment dots.
Cutting the holes for installing the rings was a challenge because I wanted a near perfect circle with about 1/8" to 3/16" perimeter gap that I could back fill with epoxy paste. For two of the hatch holes, I had to cut through about 1" of solid fiberglass (I removed propane lockers and sealed up the holes). The other two were existing Bomar-like 10" plastic hatches.
After some experimenting, I found that the only thing capable of cutting the substrate without dulling quickly was a carbide burr. So, I made circle jib for the die grinder and used a 1/4" carbide cylindrical burr. The jig is screwed into a pilot hole in the center of the material to be cut out and I just swung it in a circle to cut the hole. I took three passes because the density was too much for the die grinder in one pass. For the two existing holes, I just free-handed, following a circle line to cut enlarge the holes about 1/2" all round.
The rings are installed by clamping them to wood cleats screwed to the outside of the cockpit surfaces so the top surface of the ring is flush with the top of the cockpit seats, then fiber glassing them to the underside of the cockpit (epoxy resin). Once underside was glassed, I back filled the perimeter hole with thick epoxy. after cured, I ground out about 1/4" deep groove around the ring. This grove was painted with vinylester resin as a tie coat between the epoxy and the gelcoat filler I used for the final back fill, color matched to the white-ish gelcoat color of the rings and hatch. Each lid/ring pair will have it's own color so I know where they fit. Although the lids are interchangeable with the rings, the fiberglass on the ring that engages with the latch and metal tab are slightly different. Making it necessary for each lid to be specific to its own ring.
The finishing will come later when I re-gelcoat the smooth parts of the cockpit and paint nonskid where traction is needed. The hatch lids will be mostly non-skid with a 1/2" smooth perimeter. There will also be a 1/2" smooth margin around the latch and the perimeter adjacent to the ring on the fixed part of the cockpit seats).
The seal groove was routed out with a 1/4" carbide ball burr chucked into the sane die grinder with the circle jig as a stabilizing base to keep it plumb as much as possible. I used the neck of the burr as the guide (like a bearing in a router) to run around the ring and make the groove for the seal.
The EPDM o-rings are made from EPDM foam cord that I spliced together. The o-ring fits snugly into the routed groove and is slightly larger that the OD off the groove so the ring puts outward pressure, helping it stay in place. The groove partly undercuts the vertical part of the ring, forming a lip, which holds the ring captive. I will test to see if this is all that is needed or if I need adhesive to prevent the o-ring form escaping when I lift the lid.
More pictures of this project: http://bodylens.com/Gallery/thumbnails.php?album=54
Parts used:
Stainless Steel Cam Latch:
https://www.ebay.com/itm/Boat-Cam-Latch-Marine-316-Stainless-Steel-Flush-Hatch-Lift/124137090978?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Note: Overall OD: 2 7/8", Hole cutout: 2 3/8"
EPDM cord:
McMaster part #8605K117
https://www.mcmaster.com/8605k117
Adhesive for making O-rings:
08008 3M Black Super Weatherstrip Adhesive
Did you save the old propane lockers? I'm looking for some for MiSamba
yes, I still have them. I'll send you some pictures this weekend.