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Old 05-13-2023, 08:56 AM   #1
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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.
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Old 05-13-2023, 12:16 PM   #2
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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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Old 05-13-2023, 01:00 PM   #3
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Originally Posted by SteveK View Post
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.

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.
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Old 05-13-2023, 04:06 PM   #4
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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 isnít too bad a job to pull an engine out as long as you arenít 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 didnít 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.
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Old 05-13-2023, 04:19 PM   #5
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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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Old 05-13-2023, 05:40 PM   #6
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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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Old 05-13-2023, 06:05 PM   #7
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Quote:
Originally Posted by River Song View Post
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.
It goes out pretty regularly. I am scheduled for another procedure next month. Canít wait.
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Old 05-13-2023, 06:19 PM   #8
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Koliver, What did you end up using to hold the fuel?
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Old 05-13-2023, 06:20 PM   #9
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Quote:
Originally Posted by koliver View Post
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.
What did you end up using to hold the fuel while the work was being completed?
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Old 05-13-2023, 06:24 PM   #10
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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.
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Old 05-14-2023, 10:49 AM   #11
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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
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Old 05-14-2023, 12:40 PM   #12
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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
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Old 05-14-2023, 01:47 PM   #13
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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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Old 05-14-2023, 06:41 PM   #14
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Insure to 100.00% certainty that it is a tank leak and not a pipe, valve or leaky fitting. Hopefully youíve already done this assessment. Good luck.
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Old 05-14-2023, 07:30 PM   #15
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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
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Old 05-14-2023, 08:41 PM   #16
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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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Old 05-14-2023, 09:07 PM   #17
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Quote:
Originally Posted by rgano View Post
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.
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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Old 05-16-2023, 06:11 PM   #18
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Insure to 100.00% certainty that it is a tank leak and not a pipe, valve or leaky fitting. Hopefully youíve already done this assessment. Good luck.

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
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Old 05-16-2023, 06:18 PM   #19
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The solution is very simple, really. (I didn't say cheap)

Remove the engines. Replace the tanks.

It is really your only option.

pete
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
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Old 05-16-2023, 07:09 PM   #20
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Unfortunately with the age of your tanks it is most likely a tank leaking. But check to make sure it isnít something easy, but be prepared for a tank replacement.
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