Replacing rusted out fuel tanks

Still haven't gotten in to see why my 350 gallon 1981 Formosa port tank spilled lots of fuel into the bilge abd subsequently into the harbor, (50 to 100 gallons!) But I suspect I have at the very least, a rusted out area on the top of the tank and most likely a split or cracked or detached hose from the deck to the tank... Assuming I have to replace the tank, wouldn't it be easiest to cut a whole in the hull and take it out the side? Seems easier than wrestling with the engines and bulkhead... Any thoughts??

Once you put the new tanks in there is no good access behind them to put the side back together. Fiberglass needs a wide fairing to adhere properly. Steel boats are just welded from the outside.



Cut up the steel tank from inside the engine room using a saws-all. Replace with pre-made plastic tanks that fit the existing space and will fit around the engines. Connect them all together for less but more appropriate tank volume.

If you are concerned about costs, I would not recommend breaching the hull.

It may be easier to cut the hull initially but there will be H**L to pay when you go to close the hole. As already mentioned, in a fiberglass hull, repairs of that nature REQUIRE good access to BOTH sides of the hull which you will no longer have.

Unless the hull strength is rebuilt the boat may no longer be trustworthy/safe.

I know I am hammering but find out what you must deal with by removing/ cutting those panels blocking access. A couple or three hole saw holes should get you visual access with a flashlight.

No, it'll never look right again, and if done in a way that makes it look as good as possible AND maintains structural integrity will cost a LOT. People with those skill don't work 100 hours for free.

You've been posting about this and dancing around it for weeks now, and haven't made any progress.

Mister C lectric is one of the people that has been trying to tell you that you need to get in there, with the sawsandhammers and start tearing in to it until you get holes big enough so you can see what the problem is. Then there's a good chance you'll make the holes big enough to take the POS out and replace it with something else.

There is no ointment, spray or spell that is going to fix your problem.

Just put on your big girl panties and get to work already. Or get out the checkbook. However it doesn't have to be expensive, just gonna be a lot of grunt work.

That or walk away from it and list it with the known defects. Plenty of people that know how to take this on for the right price.

Welcome to boat ownership.

It would definitely be easier to cut a hole in the side to remove the tanks. Patching the hole though, might be a lot more expensive. I disagree that this can't be done, or would not look right, or not be structurally sound - it can be done, but this sort of work is labor intensive by skilled persons. Also, done this way should you need to get at them again, out comes the saws-all again....

Sorry that you are having these troubles, no fun at all. Were you able to confirm if the fuel fill hose is intact? If not I'd start there before going down the path of ripping out a tank. The tank could be fine however the hose could be rotten.

Leaving aside the structure of the hull, another reason not to cut a hole in the side of the boat is cross section of the tank is not square or rectangular. The outboard side will be shorter than the inboard side so the bottom roughly conforms to the slope of the hull. You may have to cut through the chine of the hull to get it out, and getting a new one in would be extremely difficult unless you made it a fraction of the size. There should also be a bed the tank sits on that will interfere.

The attached pics show a rough sketch of my tank, and the beds the tank rests on. I think you will see the problem of going through the side. In the end, you have to decide if it's easier to R&R the engine or cut/repair the hole. You will find a lot more expertise in R&R the engine than the fiberglass work which will be structural.

I found a better picture of one of my four 100-gal tanks being dry fit. I have a displacement hull, so the taper is more extreme than your boat probably is, but you can see the issue immediately of trying to go out the hull side - sort of like pulling a pencil through a sharpener point first. You need more information, but I'd guess going out the hull side is not workable, but maybe.

I'm 70 years old with two hernias from major liver surgery two years ago.. I'm not getting in there with a sawzall... Access is extremely limited from the inside. Another thought was to cut out the deck above the tank, cut off the top, cut out the baffles and slide in a slightly smaller poly tank...

Bigfish said:

I'm 70 years old with two hernias from major liver surgery two years ago.. I'm not getting in there with a sawzall... Access is extremely limited from the inside. Another thought was to cut out the deck above the tank, cut off the top, cut out the baffles and slide in a slightly smaller poly tank...

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Sounds like you're really jammed up and butcher options are on the table. If you're 70 and on a shoestring budget, I'm guessing resale is far down your priority list.

Old tank has to come out. Sawzall and die grinder (after fuel is gone) is your best option, even in small pieces because space is tight. From there, you can probably figure out 25-50 gallon tanks that will allow you to at least move the boat short distances. If longer distances are needed, drums on the aft deck.

Bigfish said:

I'm 70 years old with two hernias from major liver surgery two years ago.. I'm not getting in there with a sawzall... Access is extremely limited from the inside. Another thought was to cut out the deck above the tank, cut off the top, cut out the baffles and slide in a slightly smaller poly tank...

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Step by step.You may be to inspect the tank top and filler first with an endoscope type device, not expensive on ebay, without dismantling first. You may have to get aggressive accessing the right area, but at least you`ll know where the problem lies, or does not.

Me thinks cutting and repairing the fiberglass ( either the side or the deck ) to an acceptable level would be as expensive as moving the engine.

Still think your best option is to find another place to put a tank. Probably a smaller one than what you have now but that's no big deal.

Bigfish said:

I'm 70 years old with two hernias from major liver surgery two years ago.. I'm not getting in there with a sawzall... Access is extremely limited from the inside. Another thought was to cut out the deck above the tank, cut off the top, cut out the baffles and slide in a slightly smaller poly tank...

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Ok, understood.

Can you manage to at least use a hole saw and cut a few 2" diam access holes. Even one of those oscillating tools would do a good job although the hole would be square or rectangular. Doesn't matter as long as you can see in.
I would say two minimum so you can look and shine a flashlight in. If the tank top is rotten or there is a split or rotten hose hopefully you will be able to see which. The path will likely be far more apparent than all the guessing now.

I think , may be you should ask around the marinas for a decent shipwright who is not going to cost a bomb.. They are around without a big shop to support who basically work out of their home or a back alley shop. Guys like that will also know other trades people to help with the engine and the other work needed. He could even just advise you, properly, about how and what needs to be done. You may be able to keep the cost down by you doing some and he doing the heavy work needing heavy tools.

Sorry but that is about all I can suggest.

oscar said:

Just put on your big girl panties and get to work already.

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Wow, that's uncalled for. Especially since he's not insulting anybody in this post.

Maybe you need to take off your small girl thong.

There are no cheap and easy ways to do this. You can do it cheap by DIY. Or you can do it easy by paying someone else to do the work. But you can’t have both cheap and easy.

I was going to replace one of my fuel tanks this winter. I pulled the port engine and stacked it on top of the starboard engine. Then my back went out and I decided that I could not risk pulling out the old tank since I didn’t think I would be able to put the new one back in by myself. As the winter has progressed I have learned that it was the correct decision. I would not have been able to do all the work, I am struggling to just get everything cleaned up and replacing hoses, wiring and all the other stuff I can do with the engine out. But it was pretty easy getting the engine and transmission out. I built a crane over the engine and used a trolley to roll it over to the starboard side. Total cost maybe $1200. I paid a mechanic 2 hours to help me get the engine out and over. We are replacing the transmission damper next Wednesday while the engine is out and it is easy to get to. I think I will have about 4 hours of the mechanics time to get the engine back in. So it is certainly doable if you are physically able to do the work, which the OP probably isn’t.

Another approach is the cut out the side. I thought about going that way. Other than we just painted the whole boat 2 years ago and I couldn’t determine the exact shape of the current tanks since they are completely enclosed so I couldn’t be sure how big to cut out. And if I did cut the hull would the tank be just rectangular (easy to get out the hole) or angled down on the bottom (which might not fit out the hole). But cutting the hull and fixing the cut afterwards isn’t the impossible task that is being represented here. You do not have to access the back side of the cut out to reglass the hull. You put in a filler strip of glass that spans the cut and glue it in halfway inside the hull and halfway in the opening. With the adhesive mastics that are available now this can be strong enough to make the hull structurally sound. Then glass the cut out piece onto the filler strip and grind the cut so that it has about a 12 to 1 slope on both sides of the cut. Then reglass the cut and fair it then paint the hull. It is still a lot of work.

After pulling the engine in my boat, if I were to replace the fuel tanks in my boat (if I am ever able physically) I think that I would go the pull the engine method since it was pretty easy to pull the engine. I will have the crane to pull the engine in the future. Currently I am planning on pulling the starboard engine next winter and even if I can’t change that fuel tank, I will be able to clean up the wiring, hoses, etc on that side of the engine room. At least then the engine room will be pretty.

However you go, good luck. It is a huge job which ever way you do it.

Is the tank still holding fuel. From the previous thread and now it seems it is. I recall the suggestions of checking the filer hose and connections, top of tank, locating where the leak originates before a plan is put into play.
Have you done this yet? Maybe the problem is just the filler hose.

Bigfish said:

Thanks... I will check the deck fittings and the fill hoses next... They sure look secure but it is getting in somewhere...

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[QUOTE=Bigfish;847289] I suspect I have at the very least, a rusted out area on the top of the tank and most likely a split or cracked or detached hose from the deck to the tank...

A couple of points.

A rusted out roof tank is not going to spill that amount of fuel. Sounds like you have emptied a large portion of the tank. It must be coming from a failure in the lower part of the tank/hoses/sight gauge.

First things first, you have to find the source of the problem.

You have said yourself you are not up to this, so, as others have said engage a reliable shipwright to investigate. It won't take him long to find the problem and it won't cost more than about two hours or so of labour charge.

You will then know what your options are.

By the way the number one culprit of rusted mild steel fuel tank roofs is teak decks that have been screwed down.

Andy G said:

[QUOTE=Bigfish;847289] I suspect I have at the very least, a rusted out area on the top of the tank and most likely a split or cracked or detached hose from the deck to the tank...

A couple of points.

A rusted out roof tank is not going to spill that amount of fuel. Sounds like you have emptied a large portion of the tank. It must be coming from a failure in the lower part of the tank/hoses/sight gauge.

First things first, you have to find the source of the problem.

You have said yourself you are not up to this, so, as others have said engage a reliable shipwright to investigate. It won't take him long to find the problem and it won't cost more than about two hours or so of labour charge.

You will then know what your options are.

By the way the number one culprit of rusted mild steel fuel tank roofs is teak decks that have been screwed down.

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I dunno. My tanks were fairly accessible. I had a weep. I never did find the weep but just decided to replace the tanks. My sense is that by the time you figure out the problem, you're so far in its major surgery. Sure, large tanks have man-covers so you can get inside and repair. But the boats of most in this forum have tanks that are not that easy.

The OP has made several posts on this topic, each with a bit more info. He's broke, apparently not a DIY guy due to age, and this is his home. He's looking for a cheap fix to an expensive problem.

Drain and abandon the tank if you don't want to Sawzall it out. Put a barrel on your aft deck. Run the return line into a bucket and empty it into the barrel every few hours of running. It's by far your cheapest option. Not elegant, but will get you down the waterway when needed.

Previously we heard it leaked after filling past 270 gal in a 300 gal tank suggests the top. He was going to empty tanks into barrels. There is about 4 threads on this now.
would really like to know where it leaked.

I guess I wasn't moving fast enough for the know it all...

Soo-Valley said:

Previously we heard it leaked after filling past 270 gal in a 300 gal tank suggests the top. He was going to empty tanks into barrels. There is about 4 threads on this now.
would really like to know where it leaked.

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I'm sure the OP would like to know too. My stbd tank had a very small weep for 10-years. I just had them replaced with fiberglass. Never did figure out where the weep was. I'm guessing that under 20% of a saddle tank on a trawler is visible, and it's the least like portion of the tank to leak.

The OP states a major leak. Tanks are inaccessible - not as if a manhole can be removed and a welder goes inside go repair. Ain't happening. Where the leak is is interesting, but if it's leaking 50-100 gallons, maybe he gets lucky and a hose fitting has come undone. But probably not. Age of boat and type of boat? New tanks are high on list.

syjos said:

Wow, that's uncalled for. Especially since he's not insulting anybody in this post.

Maybe you need to take off your small girl thong.

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I wasn't aware of his physical condition and in no way intended to make light of that. Still, as we all agree this problem requires tools and using them. Either do it, or pay someone. Talking about it on this forum is not going to fix it.

I just had two fuel tanks taken out and new ones put in. Neither job was easy, not me but accomplished by my refit guy and his employees, and it needed young guys to get the two in. It was definitely difficult for them, impossible for me. I think the only thing that is going to work for you is a cheque book, worked for me.

It didn't leak until it was full and being filled with high volume pump... My guess is bad fill hose and or hose clamps... Will be cutting hole saw hole in deck as soon as I'm off work, Wednesday..

oscar said:

No, it'll never look right again, and if done in a way that makes it look as good as possible AND maintains structural integrity will cost a LOT. People with those skill don't work 100 hours for free.

You've been posting about this and dancing around it for weeks now, and haven't made any progress.

Mister C lectric is one of the people that has been trying to tell you that you need to get in there, with the sawsandhammers and start tearing in to it until you get holes big enough so you can see what the problem is. Then there's a good chance you'll make the holes big enough to take the POS out and replace it with something else.

There is no ointment, spray or spell that is going to fix your problem.

Just put on your big girl panties and get to work already. Or get out the checkbook. However it doesn't have to be expensive, just gonna be a lot of grunt work.

That or walk away from it and list it with the known defects. Plenty of people that know how to take this on for the right price.

Welcome to boat ownership.

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I've been waiting on weather and pump parts, plus I'm still cleaning out the bilge and spent hours getting the port engine running again... Waiting on mechanics... Waiting on a boroscope... What's the rush?? Just because you can't think of a creative alternative to caveman tactics doesn't mean I can't... I got the engine running after it sat for three weeks with water in it while more than a few here were sure it was toast... You know it all's sound like liberal Democrats...

Pardon me if you already know this trick but here is one I use time to look in a difficult spot.

If you have a smart phone or any small camera you can set them to video mode and try to hold them where ever you can't see. I find video works better than pictures because you can move the camera back and forth to get many perspectives in one shot. You may need to get a flashlight in there so the phone or camera has enough light but you should get some type of image that may be helpful. You may need to try it a few times to get the right light and angles. What I am thinking if you can hold phone up to the gap between the deck and top of the tank that may tell the story. You may need to remove an insulation panel on the front or aft end of the tank to gain access. I am hoping you have decent access to one end or the other. I would try the video approach before using the hole saw in the deck. There are scopes you can attach to a smart phone which may make it easier but you may have luck just using what you already have.

Thanks... I have to pay someone to do that as I can't get down there anymore... There is obviously a major problem on the top of the tank and the deck plate will have to come off anyway... Seems it was glassed in or over at some point. Probably when the teak deck was removed... I have a boroscope that just arrived but I'm working from before sunup to after sundown until Wednesday... I still have to get 150 gallons of fuel out of the tank before I start ripping it out... I may just do a lot of trolling for mahi on my days off for a while... I live on a mooring ball... It gets pretty sloppy out here when the wind blows like it has for the last 3 weeks...

Well I'm glad you have a plan. Hope it works out for you. Sorry if I came on a little strong. However, you started this, your 4th or so, thread on the subject, with the question whether it was a good idea to cut a 12 square foot hole in the side of your boat.......

Never said 12' square hole... You did... Just exploring all possibilities.. I witnessed a local boatyard cut out the tanks through the hull on a 53' Hatteras and seal it back up where you couldn't even tell.. You obviously don't know what you're talking about... They did it in a few days too.