T&T: Inspection ports

[Milt Baker]

Although I would not install one on a plastic tank, if you want a well-designed, well-engineered, 
well-built and leakproof inspection port for your tanks, check this one out: 
http://www.seabuilt.com/

I've had one on my aluminum day tank for two years and over 1500 engine hours and it's never 
leaked a drop.  No connection with the company, just a satisfied user.

Other than the emotional trauma of cutting a hole in a perfectly good tank, installation was 
quick and easy.  A lot easier than what Rudy describes, and I don't remember the price
as being too high.

--Milt Baker, Nordhavn 47 Bluewater, Southwest Harbor, ME 

> I strongly recommend against the inspection port. They WILL
> leak if you over fill the tank. The ports they use can be
> bought at any marine store, so wait till you need to get
> into the tank someday far in the future (probably never) and
> install one then if needed. The last Ronco tank I installed
> with a leaking inspection port, I called Ronco and talked to
> their production supervisor and he even said he wouldn't
> recommend these ports, and agreed they are likely to leak.

I tend to agree. For those who may be interested in knowing how, I've repaired several leaky inspection ports in plastic tanks. (This idea works for other tanks, with only the material being different.)

The covering plate and the inside backing ring are made out of fiberglass. Using fiberglass cloth, set in either polyester resin, or epoxy, layer up the fiberglass on a flat surface (covered with plastic, wax paper or being well waxed to allow the fiberglass to release from the surface) until the thickness desired is obtained (better too thick, than too thin).

The plate and backing ring are cut out with a masonry, or steel composite blade (available at hardware stores or home improvement centers) on an angle grinder, table saw or in my circular saw. The hole in the inside backing ring is cut first with a hole saw. (A jig saw could be used to cut out the hole, but fiberglass dulls the blades quickly.)

If the hole in the inside backing ring is smaller that the hole in the tank, it does not matter much, as long as the ring is big enough to get whatever implements are necessary into the tank. I tend to try for a hole that is at least 3 inches in diameter. What is important is that the inside doubling ring extends outside of the bolt pattern of the covering plate.

After being cut out, the inside  backing ring and the covering plate are clamped together and the bolt holes are drilled through both. I use no magic formula for the bolt pattern, as so much depends on the size of the cut out. I usually lay out the 0, 90, 180 and 270 degree holes, then I place intermediate holes as seems appropriate. Better too many, than too few. If the access hole is round, the inner ring is cut in half.

Drill the holes of a size that will allow them to be tapped. Use the covering plate to lay out the holes to be drilled in the tank and drill these also. 

After being drilled, tap the holes in the inside backing ring and the tank to fit the fasteners used. Drill out the holes in the covering plate to accommodate an easy fit for the fasteners. (The threaded holes in the inner backing ring and tank will allow the ring to be installed without the fasteners falling out.)  

The inner backing ring is placed inside, the fasteners run up through the backing ring and the tank, a gasket put on and the covering plate installed. (Gaskets are easily made, using the covering plate as a pattern.) Washers and nuts installed. I suggest using fasteners that are at least 1/4 inch longer than is needed, so if the fastener turns when trying to tighten the nut, a pair of vise grips can grab the top of the fastener while the nut is being tightened. (Damaging the threads do not matter, as the fasteners can be ground off, drilled out, or cut off if they need to be removed in the future, suggesting brass or bronze fasteners to make this job, if necessary, easier.)

Instead of a gasket, sealant can be used; put the sealant on, tighten the cover until squeeze out is obtained all around and wait for the sealant to cure. Once cured, finish tightening the fasteners. This will product a thicker seal, much like a gasket, greatly enhancing the ability to seal, compared to a thin, anemic layer of sealant that would occur if the cover was tightened immediately.

Rudy and Jill
Briney Bug, Panama City, Fl.