Mainship 400 Starboard Fuel Tank Leaking

I recently discovered that my starboard tank has a slow leak. I have not read much in this forum of folks having problems with the aluminum tanks in the 400. Has anyone had a leaking tank? What was the cause? Looks like this is very difficult to remove and replace. Has anyone had to replace a tank and how did you resolve it? I can see possibility to cut tank up and remove in pieces and put in smaller tanks all connected or cut out the hull and replace the whole tank. I am in touch with my insurance company and they are sending a surveyor to assess. Appreciate hearing from any who have faced this problem - and specifically for the 400 aluminum tanks - what was the cause - and how you resolved it.

It would be a first for me to hear an insurance company covered such a "casualty." Hope for your sake they do. One of our 30 Pilot II owners had an AL tank leaking, and after engine and tank removal he discovered a pinhole in the bottom where it looked as if a foreign object had rubbed its way in from the outside. He found the tank manufacturer's plate on it and got them to make him two new tanks a couple of inches shorter than the originals because the tanks were obviously installed before the deck mold which left NO clearance to slide an original sized tank in there.

Unfortunately, I too had this problem with my '04 twins. What started as a gradual manageable leak a few years ago, eventually turned into an all of a sudden gusher one day which required an emergency Friday evening call to a marine fuel spill specialist to come and drain the tank and drain and clean the bilge. Only way to get the tanks without tearing apart any fixed structures was to have them cut.

When the starboard tank was out, I could easily see the culprit. A small almost perfectly round hole about the width of a pencil. Only way to know this was to have the engine removed and the tank cut in halve to get it out. I ended up replacing with slightly smaller tanks thus sacrificing capacity. The smaller tanks fit perfectly into the openings available. I decided to forgo the other options presented to me such as cutting the floor to fit larger tanks or to have two tanks on each side plumbed together.

Skipjack - Thanks for this information! How bad was it to remove the engine on the starboard side? What else did you have to do or remove to get access to the tank to cut it in half and get it out? And get your two smaller tanks back in place? Did you remove both engines and replace both tanks? What size tank did you end up with on each side?

Since I did not actually do it myself, I can't comment on how difficult it was. I will say that the team I worked with did not mentioned that things were not routine. A leak started to develop on the port side, which now I suspect was the high pressure hose because I could not find any issues with the now cut-up tank. I decided to do both engines/tanks so that they would match.

Everything that was blocking access that could be disassembled pretty much was taken apart, except for the floor supports. See attached picture. I ended up losing about 25 gallons for each tank. Not having the added expense of cutting up the floors, or the increased complexity of multiple plumbed tanks was worth it to me. Grand Banks owners often have multiple plumbed tanks so to some it may not be a big deal. For me I didn't want the added costs of now having to have (4) custom tanks instead of (2) built and properly installed, and all of the additional fittings that I would have to now monitor. My fear was that a fitting or hose connecting two tanks would come loose in an impossible location to service without removing the engine.

As far as putting the new tanks back in, all I can say is measure once then twice and a third time for good measure. I would recommend creating a 2x4 mock-up of a tank to see what would fit through the openings. One of the best features of the 400 for major engine work is the double salon doors, it will save current and future owners a lot of grief and money.

Skipjack - what would cause a hole like that?

I have no clue!. I ran my hand over the section of the floor where the tank was placed and found nothing there that I could tell could have caused it. I couldn't find any evidence of significant corrosion anywhere near the hole. It's a mystery to me.

Wow - a picture says a thousand words. They really cleaned out the entire space and got those new tanks in. Not sure if you could get one of your new tanks in if you only had one engine removed. Since I am on the Cheseapeak Bay on the West River - I would like to know who did your work so I could contact them.
Thanks Butch

A great advertisement for single engine

i think the engine would still have to come out on a single.

Has anyone completed this repair by removing the side of the hull and replacing the tank in that manner without removing the engine? Is that more or less cost effective?

Oh no fuel tank leaking

Butch Hammel said:

Has anyone completed this repair by removing the side of the hull and replacing the tank in that manner without removing the engine? Is that more or less cost effective?

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I suppose it depends on how the boat was built. but most likely you have to get a both sides to repair the fiberglass and the tank would be in the way.With a single engine you usually can move the tank enough to possibly repair it or cut it up and replace with smaller tanks , steel tanks actually are better tanks in my opinion ,they usually develop holes in the top of them .quite often they can be repaired .aluminum quite often get small holes in the bottom usually we’re they sit on the stringers , same with the stainless tanks ,stainless will corrode due to lack of oxygen . aluminum doesn’t like sitting in water with stray electrical current, choose your poison . I would replace with steel if it were my boat you keep them dry they’ll last for decades . I’m sure there are many reasons why things go bad I’m not an expert by any means , the tanks that I have seen go bad have been steel . corroded from water sitting on the top of them , usually a leak where the deck fill is in the deck ,first thing you want to fix when you buy an older boat ,Make sure water isn’t leaking and sitting on the top of your tanks but quite often it’s too late

My port side tank had a small leak in it three years ago, it was in the bottom of the tank near the aft end.



I found a really good tank repair guy here in Stuart who repaired it. He drained the tank then cut an inspection port in the side of it. He then used a device that he has similar to a pressure washer with a long wand that sprays diesel fuel to clean the inside of the tank. Followed by multiple wipe downs with solvent and then I think some sanding. Next he coated the inside of the tank with a hard epoxy made for aluminum fuel tanks and let it cure. Lastly he put a flexible tank repair coating inside of the hard epoxy. He likes the flex coating as a second barrier in case the hard epoxy cracks from the tank walls flexing.



It cost me about $1,500 but I also had him add shut off valves to the fuel lines next to my racors which was included in that price.


I saved some money by pulling the house battery bank out of the way and removing the stb exhaust hose (which needed to be replaced anyway) giving him better access.


Three years in for me and no leaks. He says he has repaired a few boats that are on 10 years now with no more leaks using this method. I'm keeping my fingers crossed, but so far it was the right call for my boat. It may not work as well if the leaks are in the center of the tank rather than on the end, making access to them more problematic.


It's worth looking into it before you start pulling motors. Good luck and please keep us posted.

Scooby5959 said:

A great advertisement for single engine

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Oh, please. Give me a break.

I think you’ll change your mind

Dougcole said:

Oh, please. Give me a break.

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You’ll change your mind one day when you have to replace your engines . $25,000 each plus installation ,exhaust hoses ,propeller shaft ,collars ,propellers. or you just get tired of it trying to do maintenance on two engines .Don’t forget fuel cost. I gave up on twin engines at least 15 years ago .I can give you many reasons why twins are a bad choice you can give me maybe two why are you like them .the reasons are obvious but if you would like a list let me know .this is when I say give me a break

Scooby5959 said:

You’ll change your mind one day when you have to replace your engines . $25,000 each plus installation ,exhaust hoses ,propeller shaft ,collars ,propellers. or you just get tired of it trying to do maintenance on two engines .Don’t forget fuel cost. I gave up on twin engines at least 15 years ago .I can give you many reasons why twins are a bad choice you can give me maybe two why are you like them .the reasons are obvious but if you would like a list let me know .this is when I say give me a break

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I'm happy to have a friendly argument with you on the relative merits of twin vs. single in a mainship 400 and how they may or may not fit the needs of different types of boaters in another thread, but I am not going to do it here. This is not the thread for that.



My frustration is that some, not all, of the proponents of single engine boats in this forum are like evangelists, never missing a chance to make some sort of point that supports their narrow view. That is exactly what you did in this thread.


The OP is facing what must be a stressful situation regarding a major repair to his boat. I know how he feels because I faced the exact same thing in the exact same boat a few years back, it sucks. But your first inclination was to shame him because he has two motors instead of one, rather than helping him out.



News flash: Single engine boats have fuel tank leaks at exactly the same rate as twins. Second news flash: You can't get the fuel tanks out of a Mainship 400 without pulling the engine in a single either. It's not even close.


So please just give the whole single engine insecurity thing (or whatever it is) a rest and help the guy out. The info you gave him about cutting through the hull was great and probably really helpful.

That comment wasn’t directed at the guy having the problem, simply said good advertisement for single engines ,it wasn’t directed at anybody in particular just somebody that might be interested in knowing the difficulties of twins ,as far as I’m concerned it’s not talked about enough how many people have lost their boat because they cannot afford an expensive repair like . And had to sell the boat for pennies on the dollar’s because of a problem like that .Makes me wonder why some people are so touchy on issues like this ,they take it personal ,I don’t know maybe because they made a mistake and are frustrated I don’t know ,I had to learn the hard way

The last boat I owned ,the one I sold a year ago had a bad starboard fuel tank, single engine. Transferred the fuel to the other tank ,wiggled the tank loose far enough away from the hull to cut it up and remove it . replaced it with a 50 gallon day tank and a generator worked out good for me .I had room for my generator ,didn’t need the fuel capacity 250 gallons for a single is plenty,The guy i sold the boat to loved it.”win win”

Thanks to all so far for great information. Interesting that so far no one has posted experience of removing tank through the hull. Maybe that is not as cost effective?

It’s not an option for most fiberglass boats

Dougcole said:

Oh, please. Give me a break.

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Butch Hammel said:

Thanks to all so far for great information. Interesting that so far no one has posted experience of removing tank through the hull. Maybe that is not as cost effective?

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I have bought quite a few boats let me say in distress . bad fuel tanks electrical fires etc. etc. that’s how I am able to afford boating .I’ve done a lot of extensive repairs ,Including fuel tanks if you had a specific issue with pictures I could probably help finding the most economical way to resolve the issue .sometimes you just have to bite the bullet and do what you Gotta do

Skipjack99 said:

I have no clue!. I ran my hand over the section of the floor where the tank was placed and found nothing there that I could tell could have caused it. I couldn't find any evidence of significant corrosion anywhere near the hole. It's a mystery to me.

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That hole almost looks drilled! Perhaps it had been there all along, and the cushion material sealed the hole... for a while. Poultice corrosion does not look like that, and would be more general, pitting the area rather than one single round hole.

stubones99 said:

That hole almost looks drilled! Perhaps it had been there all along, and the cushion material sealed the hole... for a while. Poultice corrosion does not look like that, and would be more general, pitting the area rather than one single round hole.

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Yeah, that does seem odd. The leak in my tank was very irregular. It was the only spot actually leaking but there were a few other spots within 6 or so inches of it that were getting close. The rest of the tank was fine though.


I had a battery charger go haywire and cook my batteries about a year before that leak sprang up. The batteries were not in a box and the acid from soaked that little neoprene pad that the tank sits on. The leak area was right over/around that pad. I think that contributed to my issue, but I'm not 100% sure.

I also initially thought it look like a drilled hole as well, but then realized that it would had to have been there for almost 15 years before leaks occured. Not to mention all of the flexing and stress that occurs on boats. Can't imagine someone pulled the engines to pull the tanks to drill a hole on the bottom of the tank at the far end, and then replaced everything.

45’jefferson with twins had tank leak. First one welded leak on accessible seam . Second one under tank so could not repair. Removed tanks by lifting engine with A frame across in saloon with support under lift. was able to cut up tanks and remove thru sidedoor. New tanks were smaller as to fit thru a side window that was shape of tank. Lifted engine move over other , pull tank thru window , lower into space with man power, then set engine back in place. X2 , tanks about $5,000, labor, gave diesel to friends , with lunch , yard bill two weeks with normal bottom job and lift cost. Total around $10,000.00 doing it myself with engine and disconnection , new items as needed

I am the owner of the pilot 30 2004 that rgano spoke of.
I would be happy to let you know how I went about tank replacement. Tiresome but not impossible
Art

Duetto said:

i think the engine would still have to come out on a single.

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The starboard tank will come out but not the port Tank for that the engine would have to be removed