GB 36 classic twin diesel fuel leak

My husband and I have noticed a small pooling of diesel fuel accumulating in front of the fuel tanks, between the outboard hull stringer and the hull. We have investigated, and so has our local boat yard, but we have not been able to find the source of the leak. We are speculating, based on what we have read on this forum, that the fuel tanks might be the culprit. So, my question is: Has anyone replaced the fuel tanks on a twin engine GB 36? If so, what was your experience, and how did you accomplish the task?

Many thanks in advance.

AS a former GB36 owner I am following.

Did the investigation involve a borescope.
Those tanks are near impossible to see bottom or backside without one.

SteveK said:

AS a former GB36 owner I am following.

Did the investigation involve a borescope.
Those tanks are near impossible to see bottom or backside without one.

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I believe we used an endoscope, but it was used by my son, who is not an expert. We are considering having it checked again by an boat mechanic who will know what he is looking for. Thank you for the tip.

How old is the boat? My guess would be fuel tank leaking. Of course. You will probably have to pull the engine to get to it. You can cut up the old one to get it out but then you would have to go back with several smaller ones to get the new ones in. It isn’t too bad a job to pull an engine out as long as you aren’t taking it out of the boat. I was going to replace the fuel tanks in our last boat so I built a crane to lift one engine and then trolley it over above the other engine and store it on deck while I was replacing the tank. I got the engine out easily but then my back went out so I didn’t replace the tank but rather just cleaned, painted, did a lot of electrical work, rebuilt the shaft log, etc. The next winter I pulled the other engine and did the same work on that side because it looked so bad in comparison to the cleaned up side. It took a couple hours unhooking the wires and fuel lines , etc. Then 2 hours for 3 guys to lift the engine and stack it above the other engine. Reinstall took about the same time. If you search the forum there are posts about it and photos of the crane I built. Google search usually works better than the forum search. Look for my user name and something like fuel tank or engine removal.

Comodave, Sorry to hear about your back going out. The boat is a 1988. It is awfully nice of you to provide so much detail. I will look for it, as the pictures would be very helpful. Thank you for explaining how you did it.

I had a similar slow leak, Once located. I could keep it under control with a 4l jug as a catching tray under the low point of the tank.

I had more trouble getting a home for the fuel that I had to remove than with the repair, but in that process, siphoning the fuel out the fill, I was able to see the rate of dripping into the tray reduce gradually as its level dropped, so I knew, by the time I had all I could siphon out of the tank, that the leak was from the low point of the tank. Had the dripping stopped higher up I would have known what level to look for the leak.

When I learned the cost to replace, I looked into repair. I used a product from:
Belzona 1111 - BELZONA
I also cut an inspection hole first, then a larger hole to allow the repair, and closed the hole with a product from: https://www.seabuilt.com/about.php

I had a guy sent by the Belzona Co, as I had no experience with the product.
He was bulkier than me, so I ended up doing about 2/3 of the "in the tank" work, once I had seen what he was doing.

In total I spent $3500 Cdn and the repair worked.

River Song said:

Comodave, Sorry to hear about your back going out. The boat is a 1988. It is awfully nice of you to provide so much detail. I will look for it, as the pictures would be very helpful. Thank you for explaining how you did it.

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It goes out pretty regularly. I am scheduled for another procedure next month. Can’t wait.

Koliver, What did you end up using to hold the fuel?

koliver said:

I had a similar slow leak, Once located. I could keep it under control with a 4l jug as a catching tray under the low point of the tank.

I had more trouble getting a home for the fuel that I had to remove than with the repair, but in that process, siphoning the fuel out the fill, I was able to see the rate of dripping into the tray reduce gradually as its level dropped, so I knew, by the time I had all I could siphon out of the tank, that the leak was from the low point of the tank. Had the dripping stopped higher up I would have known what level to look for the leak.

When I learned the cost to replace, I looked into repair. I used a product from:
Belzona 1111 - BELZONA
I also cut an inspection hole first, then a larger hole to allow the repair, and closed the hole with a product from: https://www.seabuilt.com/about.php

I had a guy sent by the Belzona Co, as I had no experience with the product.
He was bulkier than me, so I ended up doing about 2/3 of the "in the tank" work, once I had seen what he was doing.

In total I spent $3500 Cdn and the repair worked.

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What did you end up using to hold the fuel while the work was being completed?

I had some 55 gallon drums that I was going to put my fuel in and then pump it back in when the new tanks were installed.

Hi River Song,

Sorry to hear you've located a diesel fuel leak in your GB36. If you've perused this forum, you'll find dozens of related threads regarding diesel tank leakage, and many threads regarding this issue on your specific boat model. I suggest you spend some time poking through the forum. Lots of good information here, and some not-so-hot!

Some issues to consider here.

a. I don't know where you're located, nor your moorage situation. Here in the Pacific Northwest, at least in Everett, WA where I am moored in a Port-owned marina, you may take on fuel ONLY at the fuel pier. And, you can offload fuel ONLY on the hard, in the Port-owned boatyard. Thus, no lugging 55-gallon drums down the dock to empty a fuel tank for internal investigation or repair. Even routine fuel polishing must be done ashore. Again, your mileage may vary (YMMV), but please check with your local moorage authorities before you proceed. VERY expensive to mitigate a fuel spill these days!

b. Yes, borescope inspection is a valuable tool to locate potential leak site(s) in diesel tanks. Getting professional assessment of leaks (including borescope, if appropriate) is HIGHLY recommended, as it's a messy, cramped, awkward situation in poor lighting conditions. Experienced professionals are your friends here, if only to provide a definitive explanation of your options.

c. Living with a fuel leak, even on a diesel boat, is simply out of the question for me. No amount of catch trays, diapers, mayonnaise bottles, etc. to collect drips for me. Moisture of ANY KIND in my bilges is simply not acceptable. Again, YMMV, but diesel fuel is messy at best, and only belongs in proper tankage.

d. Access to your tankage, after the fuel is properly drained, will require installation of multiple access ports into every baffled portion of your tank(s). I'm not familiar with the specifics of GB36 tankage, but expect they are typically installed without regard to inspection and maintenance. To properly assess your tankage, you'll need to provide such access.

e. If and when you've located the source of your tank(s) leaks, you'll next be confronted with the "fix or replace" dilemma. Here's where the opinions and anecdotes expressed on this topic diverge. The old adage of opinions is absolutely right on, and most opinions are stinky. EVERYONE'S boating situation (and resultant experiences) are different. Having said that, here's mine! I'm in the "remove and replace" camp for any tankage leakage issues. Fixing a leaking diesel tank is a tricky proposition, and one I've chosen NOT to pursue on now multiple power and sailboats with tankage issues. Painful and expensive as it is, I have chosen to pay my money, and NOT take my chances that a diesel fuel leak fix will work in the long run.

f. And lastly, if one tank is leaking, the 2nd is not far behind. Sigh. Sad commentary on the marine industry's absolute lack of integrity and ethics when it comes to recreational vessels' fuel system design. Few volume boatbuilders provide even tank access, much less allow R&R of fuel tankage without massive, expensive internal modifications (carpentry, moving/removing engines, removal of cabin windows, etc.) to facilitate mitigation of fuel-related issues. Sorry for this rant, but builders that install tankage before decking their boats during the building process should be SHOT.

Regards,

Pete

Good morning Pete,

A borescope examination by a professional is now being scheduled, and I believe he also plans to view the back and side of the tank after removing the back exhaust. Thank you for taking the time to explain this to me. Frankly, I have been learning more from the Trawler Forum threads than I ever did from any boat yard.

Regards,

River

There was once a California based company specializing in replacing fuel tanks in Grand Banks. They would fly to your location and cut the tanks up to get them out supposedly without removing the engines. Then they squeezed in a set of several "pancake" tanks with a vertical hose connecting them in the footprint of the original tanks.

I doubt they could pull this off without removing the engines of a GB36 twin. I have seen how compact that ER is, and I have spent some time crawling around the much easier to access GB36 twin.

Insure to 100.00% certainty that it is a tank leak and not a pipe, valve or leaky fitting. Hopefully you’ve already done this assessment. Good luck.

River Song:

First the tank on the other side took only 150l or so, then I bought some more 25l containers, borrowed a few, topped up my furnace oil tank at home, topped up my brother's OA 50 and my son's diesel BMW, borrowed 3 55 gal plastic barrels. All in I had to find home for almost 1000l.

I waited a couple of weeks after the epoxy cured before putting fuel back in the tank. It took most of that time to get the Seabuilt cover and install it.
Then when I returned the boat to Vancouver I filled up at the fuel barge, so it sat, full over the winter and I used it all last season without any issues.
I returned the borrowed 25l containers and the 55 g barrels

The solution is very simple, really. (I didn't say cheap)

Remove the engines. Replace the tanks.

It is really your only option.

pete

rgano said:

There was once a California based company specializing in replacing fuel tanks in Grand Banks. They would fly to your location and cut the tanks up to get them out supposedly without removing the engines. Then they squeezed in a set of several "pancake" tanks with a vertical hose connecting them in the footprint of the original tanks.

I doubt they could pull this off without removing the engines of a GB36 twin. I have seen how compact that ER is, and I have spent some time crawling around the much easier to access GB36 twin.

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Hi, GB36 Classic owner who had this done about 5 years ago by American Tanks out of Southern California. They did not have to remove engines or ANY other gear. They neatly cut up and removed the old tanks, thoroughly cleaned the area, and dropped two new manifold-connected tanks in place of each old tank. Nice work, but be prepared to open that wallet wide!

sunchaser said:

Insure to 100.00% certainty that it is a tank leak and not a pipe, valve or leaky fitting. Hopefully you’ve already done this assessment. Good luck.

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Good evening Sunchaser,

I appreciate the tip. That will be our next step, to bring in a professional with his borescope to have him search everywhere that could cause a leak. We are just waiting to get on his busy work schedule.

Thank you,

River

Pete Meisinger said:

The solution is very simple, really. (I didn't say cheap)

Remove the engines. Replace the tanks.

It is really your only option.

pete

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Good evening Pete,

I understand that may well our final step, but we want to do our due diligence first so we do not install new tanks and as soon as we take her out, find to our frustration that we still have a small leak we failed to locate.

Have a good evening, River

Unfortunately with the age of your tanks it is most likely a tank leaking. But check to make sure it isn’t something easy, but be prepared for a tank replacement.

I have a 1992 GB36 twin engine which had fuel tanks removed (cut up) approximately 14 years ago due to leak. Replaced with 4 (2 either side) plastic type material tanks. No need to move the engines. Only downside is fuel capacity reduced from 1500lt to 1200lt. I can give you more information if you require.

Inspection ports

We replaced on 150 aluminum tank that had corrosion we found along the bottom after removal.
The other side we cut inspection ports and used por54 to coat the complete bottom and 4 inches up all sides.
We had easy access to the side (kinda) and made those out of pieces we cut from the old tank from the other side.

Leaking diesel tanks

Tigress said:

Hi, GB36 Classic owner who had this done about 5 years ago by American Tanks out of Southern California. They did not have to remove engines or ANY other gear. They neatly cut up and removed the old tanks, thoroughly cleaned the area, and dropped two new manifold-connected tanks in place of each old tank. Nice work, but be prepared to open that wallet wide!

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Talk to Vince or Carlos of American Diesel Tanks in San Diego. https://americandieselcorp.com/ They replaced the 2 X 300 gallon tanks in my Grand Banks 42 Classic last year & did a terrific job. Tore old tanks out w/o removing engines & replaced with stacks of aluminum tanks with little loss of capacity. And did so in my own berth. I highly recommend them.

I have done a tank replacement on a GB 36 myself. It was a single engine boat but I don’t see a lot of difference of doing the job on a twin. The engines are more or less forward of the tanks so getting the old tanks out piece by piece is no big deal. It’s a little bit of a big deal to empty then cut the tanks up but it is totally manageable. Took me, working by myself about 3 hrs each to cut out the tanks … and 20 sawzall blades! My tanks were nearly full of course, so I bought a 175gal tote off Craigslist and was able to pump the fuel out of the tanks and install the new tanks one side at a time. The tanks pumped nearly dry due to the shape. A gross of bilge mats was handy to have. I had 4 tanks built to replace the original two so installed 2 tanks each side in a pancake design. It worked out great and didn’t lose any tankage. I have lots of pics of the job and am happy to share. I might even still have the drawings & specs of the new tanks. Send a PM if you want/need more details.

Chartwell said:

I have a 1992 GB36 twin engine which had fuel tanks removed (cut up) approximately 14 years ago due to leak. Replaced with 4 (2 either side) plastic type material tanks. No need to move the engines. Only downside is fuel capacity reduced from 1500lt to 1200lt. I can give you more information if you require.

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Yes, I would be very interested in learning more.

Last year I replaced the fuel tanks in my 1984 Island Gypsy (twin Lehman 135s & outboard fuel & water tanks). The engine room layout is similar to the GBs. Moreover, I suspect the major project tasks are not really specific to the trawler brand & model.

When researching the project, I found that most seem to opt for cutting up and removing the old tanks, then replacing them with multiple smaller tanks, which are plumbed together. I found both pros and cons to that approach.

I opted to go with a less common approach: We cut approx 6'x3' access panels out of the hull sides, removed the old tanks in one piece, custom built new one piece tanks and slid them in from the outside. Then we re-laminated the hull and painted the top sides.

The advantages I perceived were: No need to remove engines and mess with many engine room systems along the way (which can be many man-hours and hence $ costs), no loss of fuel capacity, avoids multiple tank inter-connections (which would be potential points of failure), and finally, aesthetically the repainted topsides made her look new again.

Interestingly, the (fixed) price quotes for both approaches were within $2k-$3k of each other. On that size job, that's a minor amount. Neither approach is inexpensive.

I think the choice of approach would be heavily influenced by what yard skills are available near you. I have a yard nearby that had done this specific task before, who also builds custom (mid 40ft range) carbon fiber racing sail boats - so I was confident in their lamination skills. Some other yards in my area would not consider the surgical approach.

I just wanted to mention this approach as I didn't find it a common method for smaller trawler tanks. It's more often used on larger vessels (I understand it's often used to replace large engines).

If you'd like more info, I'd be happy to provide it.

Lots of people here don’t recommend that approach because for replacing the fuel tanks. But it could certainly work if you have a really good fiberglass guy.

Comodave said:

Lots of people here don’t recommend that approach because for replacing the fuel tanks. But it could certainly work if you have a really good fiberglass guy.

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It's not my intention to recommend this for everyone. Just wanted to offer info from someone that's been through it in case someone wants to consider it.
I do think it's worth considering - no matter what the eventual decision is.

It took me lots of study and consideration before I decided this was the best approach for my particular situation. Yes, confidence in the engineering and the trade skills of the FRP crew are crucial.

It was scary to see the first access panel cut. OTOH, the new tanks, their mounts, and the hull are now all better than when she was delivered from the factory.

Could you share some photographs?

I was looking at a GB 36 that had tanks that needed to be replaced. I was thinking about buying and doing a major refit. In my research I came across John at Oxfords Yachts in Maryland. He’s a Grand Banks specialist and is a wealth of knowledge, and a very nice guy. He has also made a bunch of YouTube videos


https://oya.com/boat-repairs-and-maintenance/engine-maintenance/replacing-grand-banks-fuel-tanks/


Good luck with the project
S