Another Leaking Diesel Tank

[Wideocean7]

Thanks all for the feedback and suggestions. Much appreciate your views. Once I know all the options I'll be able to work out what's best for me in terms of effort and cost. But I'm not there yet by any stretch. I'm going up to take some measurements this week and will get back with anything useful. In the meantime:
1. She's a Roberts 370 Variant E but the internal layout is not per the standard Roberts' plans. Built by Astrolabe Industries (no longer around) in Canada and with some design work by Robert Harris (deceased). I have some construction drawings but no as-built plan showing tank locations. I could ask Roberts and pay them, but first, I will measure-up myself.
2. The hull is 5083 H32 aluminium (don't know what grade the tanks are made of). The tanks are bolted to the frame, not welded to the hull. Poultice corrosion is highly unlikely. Access to un-bolt is ok. But the tanks will not come out of existing apertures, so I'll get costs to remove the engine. Any views on what that might be ball park?
3. I'm not keen on a bladder that's why I wondered about replacement with 2-3 custom poly tanks inserted from the side using the remaining sides/top/bottom as a shell (I'll know if what can fit thru the apertures next week). Squanderbuck - why would it be a headache to manage a change from 2 to 4 tanks? I am obviously missing something. At this "imagination" stage, why couldn't I connect 2 tanks externally so that they act as one?

I take on board the number of suggestions to remove the engine. For overall effort and cost, that might be the best solution. But I'm not there yet.

Cheers

[mvweebles]

A skilled mechanic and helper can usually pull an engine in a day. Reinstall and alignment is a bit longer. Scope creep I'd likely as there are many things that make sense when engine is out. Engine mounts, engine room insulation, replace thru hulls, paint engine room, rewiring, etc.

Large tanks are often cut out and replaced with a pair of smaller tanks so you would end up with four 35 gallon tanks. A fairly common procedure, albeit expensive. I just replaced two 225 gallon tanks with four 110 gallon fiberglass tanks which ran around $9k including engine removal. This was in Mexico so labor was less expensive.

Good luck.

Peter

[Wideocean7]

Fore and Aft. Battery and box have already been removed. Still not enough wriggle room/aperture to remove tank as a whole. Big tank. Length-875mm; Height-580mm; Depth-830mm at top and 500mm at bottom.

[Wideocean7]

Thanks mvweebles/Peter. If I pull the engine, I think that I will be able to remove the tanks as a whole, to be replaced by single tanks not multiple. But if multiple tanks are necessary, I would be very interested to know how that set up works such as filling and ports to the engine.

Thanks Hpeer-the internal sealant you flagged might be an option but at this early stage I’d prefer new hard tanks. But without knowing effort and costs I don’t know enough to make decisions yet. So your suggestion might well ultimately be the most suitable. I will check out those links though.

[Fore and Aft]

Andy I don't think you need to remove the engine. A more practical solution is to lift the engine up slide it sideways until the tank comes out then put the engine back on its beds. You could easily set up a gantry system inside your pilot house. Worse comes to worse you could remove the two aft pilot house windows and put a beam through the wheelhouse for the chain block to rest on while lifting the motor.
A quick look on Gumtree found this engine hoist which you could sell after using it.
Cheers
https://www.gumtree.com.au/s-ad/hami...ock/1273431382

[mvweebles]

You may want to venture over to TrawlerForum. The heyday of Taiwan trawlers started in the early 1970s and tank replacement is now common for the same types of saddle tanks as you have. There is a lot good information on tank design, adding a small.sump to drain bottom water and gunk, valving of feed and return lines, crossover lines between tanks, etc.

The chain-fall hoist Fore and Aft showed is nice, especially with casters to wheel engine out of way a bit. Twin engine boats often remove one engine and stack atop the other one while the tank is replaced.

Peter

[Wideocean7]

Hi All. Thanks again for the feedback and the PM’s. It feels like these fuel tanks issues are bigger than Ben-Hur, when I have a bunch of other stuff to fix. I’ve only owned the boat 7 months and she is bringing on some quite unexpected challenges.
It’s taken a while but I have measured pretty much everything and I’m pretty sure that the tanks will not come out intact without a huge amount of messing around (and cost). I’ve attached some drawings which I hope are legible.
To remove the tanks intact, I’d have to dismantle major cabinetry and flooring above (which I don’t want to do) or take them out of the engine bay doors (there’s a big cavity beneath the raised deck saloon with the two tanks and engine). To get them out of the engine bay, I’d have to slide the engine to the other side, cut off two load-bearing floor joists and posts, remove two battery banks, re-rout a bunch of cables, cut off an aluminium raw-water inlet manifold and remove the water-maker. And then there’s the stuff I haven’t yet thought about! And even after that, the companionway would have to be widened to get them off the boat. Not a very appealing option. I could cut up the tanks in situ to remove them but this still leaves the question of how to install replacements of a similar size. Also, in cutting them up, apart from being a shitty job, I would be throwing away two useable enclosures for some other tank solution.
So I’m trying to think of other options.
Option 1 is to remove the side of the aluminium tank and baffles and then insert new polyethylene tanks, sized to fit into the engine bay. I’ve attached a sketch showing what I mean. The restrictions imposed by the size of the engine bay opening would mean that I’d need 2 tanks. If I went with this Option I’d only have about 470L with the 660L right now. I’m not ecstatic about losing 190L.
Option 2 is a variation of Option 1 but inserting a bladder instead. The plus about this is I might get more capacity if it’s made to the dimensions of the existing tank.
Any thoughts on my options or others I may well have missed?
Thanks Wideocean7/Andy

[hpeer]

Any thoughts on my options or others I may well have missed?
Thanks W

Did you miss the option if using a 2 part sealant?

Post 15 above.

[boatpoker]

This fella had another idea.

[hpeer]

Seen that in a ~100’ steel ketch. Took the motors out that way.

Probably not great on a glass boat.

[Wideocean7]

Originally Posted by hpeer

Did you miss the option if using a 2 part sealant?

Post 15 above.

No I hadn't forgotten - just trying to first work out if I could get the tanks out to repair/replace them. I'll investigate your idea next. Do you know of anyone who has done this on a yacht tank? Just wondering about its' permanency?

My son also suggested cutting out the hull last night when we were chatting through options. Sounds drastic but I get it if that's the only way of taking a tank out whole. Not the highest on the option list at the moment.

[hpeer]

Give this article a read.

Integral Tanks for Boats

[Wideocean7]

Good article. Thanks. Noted that he views bladders to be no more than a temporary solution. I’m not sure how I’d sand blast the inside (which he recommends) or how I’d avoid all the sharp internal corners when epoxying? I’m planning on cutting a decent sized access port in the top next week which fingers crossed will enable me to see the inside in all its glory.

[boatpoker]

Originally Posted by hpeer

Seen that in a ~100’ steel ketch. Took the motors out that way.

Probably not great on a glass boat.

OP says his boat is aluminum

[Wideocean7]

I cut out one side of the aluminium tank today. Up to 1/2" of sludge. After a brief clean, the tank seems ok inside, apart from the base which is extensively pitted.

Do you think it would work if I weld a new base over the old? The only problem I can see is there may end up being poultice corrosion between the two layers.