Built in place tanks

The two fuel tanks on our MT 36 are original and will need replacing soon. They are very rusty on the tops, but so far I have not detected any leakage. I have been doing a little research on replacing them. My question is has any one built fiberglass tanks in place. I have the skills to do the glass work and I know some boats come from the factory with tanks glassed in to the structure of the boat, but I haven't heard of anyone doing it as a refit. The materials would be minimal compared to paying someone to build metal tanks and I only work about 4 months a year so time is not a problem. Any thoughts?

Greetings,
Haven't got a clue regarding your question BUT something to consider...If diesel is ever "cut" with ethanol, your FRP tanks may go belly up.

Are you talking about buying tanks and glassing them in place or are you considering closing up part of the boat with fiberglass and making the space into fuel tanks?

Peronally, I would sleep better at night with fuel tanls made to spec by a reputable company. Fuel that goes where it's not supposed to be can be a problem.

Tank replacement

Here is the skinny, I replaced both tanks on my 1977, M/T, 40' sedan. The tops of mine were rusted to the point water (hint) was getting in the fuel. I removed the walls in the engine room, used a drill and saw-z-all to cut the tanks out. Replaced them with alluminum ones. Now here is the scoop, I thought the tanks were shot "wrong" only the tops were rusty, ends, back, front, bottom & inside were fine. What I did find was where the water causing the rust was coming from. The decks were rotting because the rail cap seal had broken and allowed water inside the gunnel walls. The builder glassed the house, deck and gunnel wall but not the area behind the gunnel wall. Hind sight is 20/20, I could have and should have just glassed the tops of the tanks once I removed the decks and saved a bunch of time and money. Think about it, why are they rusting?
J.T.Duncan

What awttpdp said.
The tops of steel tanks can get bad quick but the remainder can often be fine. Check out this stuff (Por-15) it's the greatest stuff if you can get at the rusted areas. Goes right over tight rust, comes in liquid and paste form, and the rust WILL NOT RECUR, ever.

A small built-in tank may be fine, I've done it. A larger tank, requiring baffles like yours, would be near impossible to build in place I would think. If accomplished it would devalue your boat considerably.

If your tanks are indeed done and your don't want to remove your engine to get them out; consider cutting them open, cleaning, and installing a bladder inside???

Greetings,
I second the POR 15. POR sells a fabric which you can overlay holes, coat with POR and effect a good seal. Probably just VERY thin FG matte.

These are some pics I took of the top of the tanks recently. Like I said in the opening post I have not seen any leaks, but the rust on top is bad. I was considering cutting up the tanks for removal and then building fiberglass tanks in the engine room. They would be complete tanks, just built and installed in the engine room. If there is an easier way, I am all ears.

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What looks like a lot of rust actually consumes very little metal. To properly use the Por-15 you must only remove the loose rust and clean with their cleaners. I would the coat with the liquid 2-3 coats and sqeegee on some paste over any deep pits you see. You can do amazing things with a hooked scraper on an extended handle & a mini roller on a stick.

I repeat, IMHO you will never build a proper, baffled, FG tank in place.

If they don't leak POR may well be the best answer. If they do leak, I'd use Belzona.

I second the Belzona idea if they leak, but you've noted that you haven't detected any. If they were my tanks, I'd get myself a cheap hand-pump garden sprayer and squirt them down with Ospho, and inexpensive product with water-like consistency. This chemical actually converts iron-oxide into iron-phosphate. I've used it to spray on areas on the inside of boxed frames and door bottoms where I couldn't scrape any loose rust. I've also used it extensively on flaked truck frames without scraping, and the surface held together well enough to fill and paint. Iron-phosphate is a decent paintable surface. If there is a lot of rust, you may need to air-out the boat while the chemical works, but a day should do it.

My fear is that they are too rusty. I took a screwdriver and scraped on top of one to try and see how deep the rust went. The screw driver went so deep I thought it would go through the tank. Will this stuff work on metal that far gone?

READY2GO said:

My fear is that they are too rusty. I took a screwdriver and scraped on top of one to try and see how deep the rust went. The screw driver went so deep I thought it would go through the tank. Will this stuff work on metal that far gone?

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Look into Belzona. You have to buy it from a rep. They will help you with a scope of work for the job to be successful. I've used it for years. I recommended it to a guy on the T&T for this exact same application and he did it and seemed quite happy. I can look up the email and P-mail it to you if you are interested.

Greetings,
Mr. R2G. I think the first and foremost thing you should do is fully determine the extent of the deterioration BEFORE you get out the cutting implements. IF the rust is limited to just the top, a lasting repair could, most probably, be done using POR or Belzona (NO experience with that stuff). The worst that could happen is it wouldn't work BUT it will be a lot cheaper and easier than replacing your tanks.

Northen Spy, thanks I am intrested, please send me what you have.

RT, I agree, I have heard of several people cutting our their tanks only to realize that they weren't that bad. That is why I have not been in a hurry to do this. But the other day when I took those pics I took a screwdriver and scraped the top of the tank hoping the rust did not go very deep, but the screw driver kept digging deeper and deeper to the point I thought it would go right through the top of the tank. One reason I am looking at replacing is that we plan on keeping this boat for the next 20 years. We don't see any reason to change boats. She will do everything we plan on doing. I am not to worried about resale value or not getting my money back for improvements as it will probably be in my estate sale. That being said I am not made of money so I can not throw $10k at tank replacement. I can cruise a long time on $10K.

The rust is only on the tops of the tanks, right? And it's on the outside of the tanks, right? That means the rust is from outside sources (water) so find ot why and correct the problem.

As far as your tanks, if the rust is only on the top, even if they rusted through, they would only leak if completely filled. There's no pressure and any leakage would be minor (I'm assuming diesel, I wouldn't say this about gasoline).

My thought is, you could repair the tops using one of the products mentioned above and wait to see if you develop a leak at some time in the future. If you do, deal with it then. If not, you've saved yourself a lot of money and effort.

Greetings,
Mr. R2G. Hahaha...I'm not made of money either and if I ever loose my extraordinarily good looks and/or my rapier wit, I'm screwed. I would start off by vacuuming the tops of the tanks well without doing too much scraping. I think a little gentle scraping will suffice just to give you a better idea of what you're dealing with.
A thorough visual inspection can be done both by eye AND with a camera held at arm's length into those inaccessible areas you CAN'T readily see.
Is there any way you can easily remove, what appears to be, that plug between the pet-cocks and get a boroscope in there to get a look-see? It may mean transferring fuel to your other tank for a good look at the bottom.

SeeSnake® micro

I purchased one of these many years ago and it is helpful in ways I never dreamed when purchased. I have noticed the price come down to the level that it would be affordable for the DIY crowd. Can be had for just under $100.

READY2GO said:

Northen Spy, thanks I am intrested, please send me what you have.

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Done. Glad to hear it worked for Roger. Keep us posted with your decision and repair.

Our interaction this morning made me realize that I owe Delfin some information too. Sorry Delfin.

Boatgm, Got any pics? Sounds interesting.

I agree before you do anything drastic make sure you know the condition of the whole tank. When we bought the Eagle the middle tank leaked, so one rainy winter day I cut a 18” X 18” hole in the tank with my hand dandy saw saw. The hole was big enough for me to craw in the tank. A side seam split. However the tank as a whole was in great shape. Hired a welder, who climbed into the tank and welded it up. We used a wet vac as a smog hog, It was a little never racking as the tank as about 2 inches from a bulk head so we welded only a ½” at a time. Cost 150 bucks!

If the tanks need to be replace, I plan on opening the existing tanks, use them as a frame work for multiple smaller tanks fitted in side. However, I might be lucky enough that they can be repaired/welded.

Let me start off by saying that Angelina has replacement tanks. They are two custom built exact aluminum replicas of the original leaking sheet metal tanks. At the time, the engine and transmission came out, the entire engine room was "bilge coated", new shaft, log and packing were installed. My engine room is a work of art. About 8 large in 1994.

Would I do this again?

No. Never.

I would remove the leaking tanks and replace with several large plastic storage tanks and a day tank.

If the existing tanks were not leaking (and didn't appear likely) I would coat them inside and out with some of these magic coatings recommended here. And if in a few years they started leaking? See the previous paragraph.

You do need to immediately address all deck leaks and keep the engine room and tanks dry.

When we bought Island Queen she leaked badly. I think I counted 14 leaks the first serious rain after purchase. After much time and effort we are leak free (for now). I think what I am going to do is take one tank loose and move it out into the engine room where I can better get to everything and see how bad the top really is. If it does not look like the magic coating will effect a long lasting repair (5-10 years) then I will see if I can cut the top of the tank out leaving a two inch perimiter, throughly clean and coat the inside, and install a new top. If that doesn't look fisible them I will back up and punt.

alormaria said:

Let me start off by saying that Angelina has replacement tanks. They are two custom built exact aluminum replicas of the original leaking sheet metal tanks. At the time, the engine and transmission came out, the entire engine room was "bilge coated", new shaft, log and packing were installed. My engine room is a work of art. About 8 large in 1994.

Would I do this again?

No. Never.

I would remove the leaking tanks and replace with several large plastic storage tanks and a day tank.

If the existing tanks were not leaking (and didn't appear likely) I would coat them inside and out with some of these magic coatings recommended here. And if in a few years they started leaking? See the previous paragraph.

You do need to immediately address all deck leaks and keep the engine room and tanks dry.

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Bingo...that's what my plans are as well as dozens of others I have seen post.