Access port cover plate

[malyea]

I’ll soon be cutting a 6”x6” access port thru the top of my 32 year old molded in fiberglass diesel fuel tank on my ‘87 Irwin 43 sailboat.

I’ll have the local machine shop fashion a 1/8” + thick aluminum cover plate (unless there’s a better material...?).

Question - how do I attach the cover plate to the tank top in a leakproof, seaworthy and shipshape manner?

What’s best ... 12 self tapping screws, glass in a “aluminum rim” tapped for machine screws, imbedded metal threaded inserts into the fiberglass to receive machine screws, drill and tap the surrounding fiberglass for course thread machine screws...or...?

Here’s a photo of the 12”x12” cabin sole opening under which I’ll be cutting the access port into the tank top.

The question is - how best to attach a cover plate to a fiberglass fuel tank?

Thanks

[Kokanee]

Aluminum would be best for a fibreglass tank.

One of these would be easier than trying to get one fabricated.

Seabuilt - Access Plate Systems

[malyea]

Originally Posted by Kokanee

Aluminum would be best for a fibreglass tank.

One of these would be easier than trying to get one fabricated.

Seabuilt - Access Plate Systems

True, but I’ll also need to fit 3 threaded 1/2” openings in the cover plate for the fuel pickup, return and dipstick opening (See the photo).

[s/v Jedi]

I recommend to make the cover out of 1/4” G10 fiberglass. Drill the cover for machine screws, transfer positions to tank and drill & tap straight into the fiberglass.
Last is the gasket. I would cut one from rubber. I source that as 1/16” or 1/32” neoprene sheet from Amazon.

[model 10]

You should use the thicker material and make an inner ring with tapped holes.

[mabowers]

Originally Posted by Kokanee

Aluminum would be best for a fibreglass tank.

One of these would be easier than trying to get one fabricated.

Seabuilt - Access Plate Systems

Yikes, those are nice, but 4X or 5X the cost of making one from G10.

[Reefmagnet]

I wouldn't trust screwing in to fibreglass on a diesel tank. make a backing out of 1/8" stainless steel that will aligns with the mounting holes in the cover plate. Fasten this backing to the inside of the opening using pop rivets or countersunk screws after drilling matching holes in the tank. Screw the cover plate into the backing using a thick cork gasket as the seal.



Depending on your skill set and access to facilities, the backing can be individual plates made from flat bar or CNC profile cut sections. Each section needs at least two rivets or screws to keep it in position.

[DeepFrz]

malyea, it would be a good idea to ask the mods to merge your 2 threads.

[s/v Jedi]

Thread tapping in fiberglass is done all the time and a proven concept. Even if the tank material is too thin, it’s easy to cut a G10 ring same size as the rubber gasket and use thickened epoxy to glue that on top of the opening, then tap into that plus the underlying tank material.

You can beat this with anything metal that will corrode, have galvanic issues etc.

[capt.rob]

Another thing I have done with fiberglass and other metal tanks that may not be thick enough to securley hold screws in is to cut the hole, make and drill the access plate then mark and drill snug fitting holes for bolts in tank, put bolts and washers in through the hole from inside tank using epoxy or 5200 to seal and hold them in place. Be sure and clean any excess glue that may have pushed through or be in threads off outside with acetone, laquer, or other solvient, put a little grease on threads and then a nut to hold them snugly in place wile glue cures. after epoxy or 5200 cures enough to establish a good bond remove outsude nut ( I generally do this at a hard tack but not full cure just in case I missed some in threads) install gasket and access plate with nuts and lock washers after curing is complete. It's a bit more than simply running screws in but makes a very secure mounting system for access plates even when cut in the side or near bottom of tank you can even use wing nuts if you want a quick easy way to remove plate in the future.

[gonesail]

the seabuilt access ports are very nice .. but they require a smooth surface to seal properly.

[David M]

Originally Posted by s/v Jedi

I recommend to make the cover out of 1/4” G10 fiberglass. Drill the cover for machine screws, transfer positions to tank and drill & tap straight into the fiberglass.
Last is the gasket. I would cut one from rubber. I source that as 1/16” or 1/32” neoprene sheet from Amazon.

For a fuel tank, nitrile rubber only.

[s/v Jedi]

Originally Posted by David M

For a fuel tank, nitrile rubber only.

Indeed, and readily available. This would be suited for the OP I think: https://www.amazon.com/Resistant-Har...s%2C191&sr=8-3

[Djarraluda]

Personally I would look at a circular hole. Use a large circular cutter, it is easier than a jigsaw or similar rectangular, perhaps inspection with dipstick at 150dia plus a connection one at 100dia. then you get the inspection port separate to the hose connections and it makes cleaning easier.
Roger

[malyea]

Thanks to all for the good info!

No intent to pit “idea A” against “idea B” per se, but I’m left with deciding the merits/pros/cons of “how to attach the cover plate” to the fiberglass tank...

A - tap threads directly into fiberglass, or
B - glue screws with 5200 pointing up from inside to outside, or
C - drill and insert threaded metal inserts into the fiberglass tank top

Final/additional thoughts?

Thanks