Fuel tank inspection port

[AJA]

I’ve got an Irwin 37’ CCKetch, the diesel tank is glassed in under the salon floor. I need to inspect the tank so I am thinking of taking a jig saw and cutting in an inspection port. Is this sane? Will it help my to clean the tank or is the tank divided up by baffles to subdue rolling?
I bought the boat 10 years ago - it had sat unused beside a barn in Maine for 17 years with its 100 diesel tank nearly full. Oddly, the fuel turned out fine but with such a large tank it takes me a few years to use it ( it stops feeding the fuel line when I get down to about 15 gallons left. )
Anyway, I changed my filters recently and found so much gunk in the racor secondary filter that I was compelled to remove it, disassemble it, and clean it. I’m sure there must be gunk like that in the bottom of my tank. Oddly as well, the filters need to be changed only about every 90 hours ( for me that’s about 3 years). I have not had clogging problems.
The one exception is that last week there developed a blockage in the line coming from the diesel tank to the racor filter. I just blew about 90lbs if compressed air through it and things were fine again. That was the first and only time I’ve had that problem in 12 years of running the engine. (A Volvo Penta MD2040
Any ideas on inspecting and cleaning the tank?
Thanks
John Bianchi USCG 100T master.

[GILow]

Is the top of the tank made from fibreglass?

If so, I put a Perspex hatch in my day tank three years ago. At the time I spoke to the manufacturer’s chemical engineer who stated that Perspex would work well with diesel. After three years I have no discolouration and no leaks. And I live that I can quickly inspect the tank with a torch without undoing anything.

[AJA]

Thank you for your reply, GILow.
Yes the tank is fiberglass - at least it is fiberglassed over.
I can only see most of the top of it when I remove the salon floor cover.
Do you know if these tanks have baffles in them to limit sloshing while underway ? Or are they just a large box?
(This one holds 100 gallons)

[AJA]

Thank you for your reply, GILow.
Yes the tank is fiberglass - at least it is fiberglassed over.
I can only see most of the top of it when I remove the salon floor cover.
Do you know if these tanks have baffles in them to limit sloshing while underway ? Or are they just a large box?
(This one holds 100 gallons)

[GILow]

Sorry, but I don’t know anything about your tank.

However, at that size I would expect it have at least three or four baffles, maybe more.

[tkeithlu]

Drill a really small hole, confirming that you do not hit a baffle. Use a wire to probe for a baffle near your hole. Then drill a hole just big enough to get an inspection mirror in. Your cut out for you inspection port will include this hole, and you are safe.

[AJA]

Yeah - that would make sense. I’ll try to find a Irwin’s owners group to see if anyone has details of the tank configuration.
Thanks again for your reply.

[AJA]

Thanks, Tkiethlu, that’s a great idea. I wonder if I could use one of those tiny inspection cameras without ruining it!

[tkeithlu]

I have a 1920's proctologist's scope that I use.....

[kev_rm]

Originally Posted by tkeithlu

Drill a really small hole, confirming that you do not hit a baffle. Use a wire to probe for a baffle near your hole. Then drill a hole just big enough to get an inspection mirror in. Your cut out for you inspection port will include this hole, and you are safe.

USB Endoscope > mirror