Let's see if I can dig up some photos of the last couple of years.
Fuel Tank Clean-up (Circa 2019-2020)
I knew that Sam had issues with the diesel because he had recently had the injectors rebuilt after at least one of them got trashed. So I took a look at the tank. It had a serious case of diesel bug. Some of the stuff that came out of the tank was almost like gravel. It was bad. There was a significant layer of sludge also. I drained the diesel out of tank 5 gallons at a time and took it to a local oil recycle place that said they could use it. Then I pulled the tank and took it home. Once home, I opened it up and got to cleaning.
Not a great picture but you can kind of see some of the gravelly crud that was in the tank in the bottom of the bucket. I cleaned the inside of the tank. Then steamed it to kill anything inside the tank. The next issue I noticed while cleaning the tank was the inspection ports. They were tiny. I could barely get my forearm into the hole and my arms are skinny. This made it difficult to access many areas of the tank. Since I plan on owning the boat for a long time and the tank was otherwise in good shape I decided to install new ones.
I considered the sea-built aftermarket product but they are pricey. Probably well worth the money but I have tools.
IIRC they were $400+ (COVID prices) and I needed to two of them, one for each side of the baffle. They are nothing fancy just a cover and a split backing ring with gaskets. So I made my own. Honestly the longest part of the process was waiting for the guy at the shop to fix the waterjet and then finally getting fed up and doing it with one of the mills. Aluminum is pretty easy to work with with wood tools, so this is definitely a project that could be done without the fancy cnc mill. You just have to mind your feeds/speeds or it can gunk up your tools.
First order of business was to decide on the size I wanted. Since I was fabricating these myself I could have my them any size/shape I wanted but I chose to go with circles. IIRC, I went with 6" access holes and 8" covers. I sketched the design up in CADD and cut a plastic template so I could look at possible placements. I played with the placement/orientation of the template until all but one of the old screw holes was covered by the new bolt holes / access holes.
There was no helping the outlier hole as it wasn't part of the screw pattern for my old covers and it was only on one of the covers. I'm assuming it was an oops when the covers were originally installed. I opted to just plug the outlier screw hole as it is well within my gaskets. Our rogue screw hole was over drilled slightly and then tapped for the nearest size bolt. I ran a bolt into the hole with a diesel resistant sealant then cut it flush on top. I probably could've just left the hole and it would've been fine with the gasket and the backing plate,but I felt better plugging it.
To make the new holes in the tank and get everything lined up the way I wanted, I started with another template. I took my laser cut template from earlier and transferred the access hole to a piece of scrap plywood and marked the locations of the new bolts. I used the new bolt locations for a couple self taping screws to attach the new template directly to the tank. Because the screw holes line up with the bolt locations they will just get drilled out later. Then we used an endmill in my router, with a template bushing to mill out the new access hole. Then I drilled the bolt holes out to the appropriate sizes.
These are just the pictures I could find easily. I know I have more somewhere.
The new covers have a split backing ring that folds in half, much like the sea-built version. There are 8 bolts in each cover, 4 in each half. Three of the four bolts are tapped into the backing ring and a through hole in the tank. The fourth has through hole in the backing plate and a tapped hole in the tank. The result of this is that you can remove all the nuts/washers without the whole mess falling into the tank.
The last picture is a test fit of the the cleaned up tank. The PVC caps are just there to keep crud out.
With the new inspection ports installed, I can now reach every corner of the tank!
With the new covers installed the tank was pressure tested on my bench at 3 PSI for 24 hours. No leaks.