Monk 36 Fuel Tank Replacement

I'm considering a Monk 36 that recently went on contract and during the survey rust was discovered on top of the fuel tank. According to the owner the surveyor was not concerned about the rust. The buyer backed out of the deal. We all know rust does not go away and only gets worse.
Has anyone replaced the fuel tanks and at what cost?

Thanks in advance.

Hi,
For whatever it's worth, here is a thread about how I replaced the tanks in my Island Gypsy during 2022:
Whether you choose the "cut the old ones out then replace with multiple tank 'slices' " or the "take them out thru the hull and replace with new one piece tanks", there is a lot of labor involved and that makes it a significant project cost.

Frankly if a surveyor doesn't think that (anything more than trivial surface) rust on a tank is a NOT serious problem, well, go find a competent surveyor!

If it is a steel, black iron, tank then as the song said”rust never sleeps”. Same thing here. The top rust is probably from a leaking fuel filler. But if it has rust on top it will likely have rust on the bottom. I replaced a steel tank in a previous boat. They custom made a mold and then fiberglassed the tank. We had to cut the back of the cabin out to get the new tank in. It was a big tank, about 560 gallons. It wasn’t cheap.

As we are on the other side of the 'big pond' cost factors may be considerably different from what you could expect to pay. However, this may give you some idea.

Sarawana has twin 120 Lehman's with a 7 KVA generator. She had mild steel tanks that when we bought her some 17 years ago had mild rust issues on the top of the tank. We sorted that out by taking up the teak deck and re glassing. However the damage was done and the rust got worse.

This year we bit the bullet and replaced the tanks. The generator was taken out and the tanks cut up in situ. New poly tanks were made up and installed. Cost for that was AU $40K.

However, that was not the end of it. With the tanks out we inspected the engine room pretty carefully, this being the only time you can access some areas of the ER. We ended up replacing a lot of other items which pushed the costs up by another AU$10K. Plus we did a few other things that had nothing to do with the tanks.

I have no idea of US labour costs etc however over the years on TF it seems we pay more for like on like work, so you may find quotes cheaper than we did. Also, the yard we used was very highly rated, very experienced on working on Island Gypsy boats, and quite old fashioned in their approach to the work. However, I felt quite confident to follow their advice.

Our engine room now looks terrific.

That's our story.

Good luck with yours.

PS. This is not anything to do with the question posted by the OP but with the amount of sludge that came out of the old tanks it was amazing the engines could operate as they did. The old Lehman's may be dinosaurs but they are pretty robust and seem to be able to operate in less than ideal situations.

Don`t dismiss the boat without investigation. Assess the rust. The top of the tank may be decayed to the point of leaking, or it could be surface rust which may be treated by POR or similar. Check the condition of the filler tube and its attachments to deck and tank for rust damage.
Chances are if a buyer rejected the boat on account of it there is a problem, but buyers vary in tolerance and commonsense so check it for yourself with an inquiring but open approach.
Check the decks too. The salt water got in there somehow. A combination of multiple issues may be a potent deterrent.

The tanks on the Monk 36 I recently had surveyed were steel, 160 gallons each, which I believe was common, at least for that period. ( 2001 build ) Given the way the tanks were installed and positioned, replacing them would be a really major undertaking. If you have an experienced yard near where the boat is now, try and get an estimate for that work, so you can get an idea of what you might be in for before you close.
I would not simply trust what the owner or prior surveyor said; it is easy for them to not be concerned, since it won't be their problem once you own the boat!
Peter

I had a similar problem on an ex hire boat we bought so I designed and built my own tank, I made it with s/s bright annealed (polished) interior with a slightly sloping floor to a sump with drain valve. I set the tank on a bed of insulation, plus ends/sides and top when I installed it to eliminate condensation and noise from a partially empty tank. The fuel pickup is just slightly above the drain valve.
I fitted a bolted rectangular chequer plate with the level gauge on the top for inspection.
Once a month I take a glass jar and run off some diesel from the sump drain valve to inspect for water or impurities. I've never had any problems at all as the polished surface and natural motion of the boat means any minute sludge particles naturally graduate to the sump and drained off once a month. so no sludge buildup and no water interface to cause diesel bug. There's also no need for fancy filters or polishing systems as its self cleaning and the standard engine filters do the job they are intended to do.
Do it once, do it right, sleep content in your bed at night.