Despite having a total of 0 hatches on my boat I read this entire post. Great post and thanks for sharing the info.Recently while digging around in one of the rear hatches of my Skiff, my knee bumped the spring that holds the hatch open, and the whole enchilada came down swiftly on my hand.
I decided a solution was in order to prevent any future occurrences of my boat trying to eat me. I purchased two gas shocks from West Marine (come to find out afterwards they are much cheaper on Amazon) and the necessary hardware to install it all.
My boat is a 2017 Ankona Cayenne, so the dimensions for locating the drill points would only work for that specific boat, but the general premise applies to other boats.
Note, the 20# strength was perfect for my application, your hatch may need mo' powah depending on size.
(2) 20" x 20 lb gas shocks with ball connector ends. I bought mine at West Marine, but heres some cheaper ones: https://www.amazon.com/inch-Prop-Sp...=1516665713&sr=8-1&keywords=gas+shock+20+inch
(2) 10mm angled ball stud mounts. I bought SS ones at W.M., and the only ones I can find on Amazon are zinc plated, but here you go: https://www.amazon.com/10MM-Ball-Br...&keywords=10mm+ball+stud+-+gas+shock+mounting
(2) 10mm flat ball stud mounts. Same disclaimer, here you go: https://www.amazon.com/Small-Flat-L...&keywords=10mm+ball+stud+-+gas+shock+mounting
(1) tube of 3M silicone or equivalent shmoo for sealing purposes: https://www.amazon.com/3M-08019-Mar...e=UTF8&qid=1516666316&sr=8-3&keywords=3m+4200
Hardware, for my installation, I used primarily #8 x 1/2" LG SS pan head wood screws, with a few #8 bolts and nuts where applicable. Your mileage may vary.
Crack beer and proceed:
I'll include the dimensions I used for my boat here, but I'll also go through my thought process on how I mounted them (right or wrong as it may be). The mounts for the new shocks have to be placed such that the shock extends opening the hatch fully, and then when closed, the shock both retracts and rotates to a more or less parallel orientation to the hatch, eliminating its effective strength so that the hatch stays closed.
To do this, I propped the hatch open, and held the extended shock where I thought it should go, and marked both ends on the fiberglass. I then measured the fully retracted length of the shock itself (while bearhugging the crap out of it to keep it retracted). With the hatch fully closed, the distance between the two marks must be longer than the retracted length of the shock. The shock must also have reached a more or less parallel orientation to the hatch as mentioned above.
It may take a few tweaks of the position to get this right, but its not too hard. If you have an Ankona Cayenne, dims are in the 3D models. (note the model is a quicky and only serves as a basic explanation of geometries, not totally dimensionally accurate.)
Dimensions for lower (flat) bracket:
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Dimensions for upper (angled) bracket: (shock is shown on wrong side of the bracket, Im too lazy to go back and fix it)
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Fully closed position below: (the point to take away from this is that the shock is so far from being perpendicular to the hatch, it has only a small fraction of its 20# force, thus your hatch wont be opening all willy nilly by itself.
Also note that when fully closed, the shock is just shy of being fully retracted, this is the result of making sure the marks placed on the boat early on are far enough apart.
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Grab your crap in peace, the hatch no longer wants your blood.
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Feel free to ask questions.