Faced with this choice we did not cut the hull. Replaced each 300 gallon tank with two 110 gallon tanks. Love the ability to control the fuel storage with four tanks.
As to the second tank in your case, our story is a good lesson. Starboard tank leaked. Decided to replace both tanks without seeing a leak on port side. After replacing starboard tank went to remove the plywood covering the port tank and the port tank split along a rust seam releasing the three inches of water we had used in flushing the tank of diesel. Glad that didn't happen underway with a couple of hundred gallons of diesel.
IN a steel vessel , chopping a hole makes sense ,in GRP to me its insanity.Criminal.
I would have the tanks chopped out piece by piece , and install as many plastic tanks as required., with one real metal fuel tank per side.
The big advantage (besides cost and structural problems) is the tanks can be only filled as required.
Sitting with huge tanks watching bugs grow or ashphalting is not fun.
By installing a marine furl tank on either side ,(if there is room) and having boxes of fuel to refill the tank underway you have an ideal cruising setup.
As good as a day tank, but easier to service.
The only fuel aboard would be in the marine tank , where water can easily be removed , and the fuel boxes would be filled before any long trip.
There are many differences between a marine fuel tank and a box of fuel , that have been covered many times, in the archives.
I agree, last resort imo, exhaust every other financially and physically reasonable possibility before you do that.I really, really don't want to cut the sides of my boat.......
The PO of our KK42 cut out the black iron tanks with a saws all and replaced with one 200 and one 180 gal on each side. Replacement material was aluminum. The engine room is as dry as a bone and I doubt that there would be a corrosion issue anytime soon on the tanks. The PO also put in a fuel polishing system. Once the fuel levels are low enough, I move fuel from tank to tank to "polish" all remaining fuel at least once a year. I also keep track of the age of fuel, ensuring the older fuel is in the forward tanks from which the engine draws fuel.
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Racor 900's and a fuel polishing system.
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Jim
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Our boat has 4 new aluminum tanks . 2 @ 125gal and 2 @ 55 gal . I'm not sure what the original tanks were, but it played a big part in our decision to purchase this boat . The install is good but I wish they would have done a neater job getting the old ones out , but slicking the area up is on my long list of things to do .
If you can get any access to the side of the tank, I would look into cutting a hole in the side large enough to work with and then possibly drop a flexible rubber type bladder in there....have you looked at that option?
Much cheaper than the other methods and may work well.
I suggest you find a good marine surveyor to look at the boat, look at both tanks, look at moving the engine(s). At the boat yard where I work the yard management really likes a qualified outside surveyor to advise the owner and then there is never a question of the yard suggesting too much work at a higher cost. Plus the documentation from the surveyor will help when selling the boat sometime in the future, and might help in an increase in value, although the increase will be less than your expense.
Here is a picture of an aluminum yacht getting new engines but aluminum is easier to cut and weld back at full strength.
Not sure why so few mentioned plastic/synthetic tanks as an option. These are not attacked by corrosion, or dissolved by alcohol as long as the correct type.
If it were my boat I'd just let them cut the old tanks out and put in new ones.
I understand not wanting boat surgery but fiberglass is pretty easy to work with in the right hands.
Heck, I've seen several boats over the years that were literally cut in half and a hull extension glassed in. If they can do that kind of work safely they can fix the holes for your tanks.
"How would you get the tank baffles out?"
A cut off wheel and perhaps drilling any rivets .
After 2 days going over every possible scenario with boat yard, the cramped engine room left little choice in my decision towards those fuel tanks. The option of removing those 3208s, pulling the trans, turbos and risers then building an A frame hoist system to raise engines would have required taking out front windows then the side salon windows also. This would have torn up my newly finished salon and galley. I was shown 3 boats where the sides were removed to get to fuel tanks then reglassed both inside and out. I would say the repair was better/stronger than the original sides. No way to tell where cuts were made along with a new paint job to boot.
There was no access to the tanks with engines in place to cut out even the sides of those tanks to repair or place bladders inside. Repair cost would have been almost the same to pull engines if nothing needed to be replaced or repaired on them which we all know something will break doing that kind of work.
I went with side removal of tanks. I feel better knowing first hand the quality of fiberglass work that these guys do. I'll get a boat that her fuel system will be all new. No more worrying about a bilge dumping fuel all over Lake Pontchartrain. I have had nightmares over this...not any more.
To all potential boat/trawler buyers, please look closely at any boat with fiberglassed in iron fuel tanks! Be sure you have access to them without having to go through the tear down some of us have gone through.
There was no access to the tanks with engines in place to cut out even the sides of those tanks to repair or place bladders inside. Repair cost would have been almost the same to pull engines if nothing needed to be replaced or repaired on them which we all know something will break doing that kind of work.
I went with side removal of tanks. I feel better knowing first hand the quality of fiberglass work that these guys do. I'll get a boat that her fuel system will be all new. No more worrying about a bilge dumping fuel all over Lake Pontchartrain. I have had nightmares over this...not any more.