Recommissioning Fuel Tank in Keel

[Winf]

Hi all

Our yacht, a Southcoast 36 (Australian design and build) came originally with a fuel tank built into the keel under the engine bay. I only have a very basic plan with no detail on the tanks construction or fitting.

At some stage, a previous owner has decommissioned this tank and now we just have a 100 litre tank under the quarter berth. This is a bit limiting for us and our only solution at the moment is to carry another 100 litres in gerry cans.

So, what would I need to do to see if it was viable to recommission the old tank? I am not interested in cutting into the side of the keel or cutting into the top of the tank. If it was leaking and is stuffed then so be it, I will live with the limited storage.

Access is not good, all the lines are under the engine but I can probably get connections to them by some lurid contortions of my 6'5" bod.

Any suggestions for how I would go about it to see if it is a viable tank or not worth the effort?

Cheers

Winf

[Wotname]

Hmm... if the PO went to the trouble to fit a smallish tank in lieu of the original then I'm suspecting the original tank has some serious issues.

Even if it hasn't, there seems to be several bad aspects about it - mainly really poor access, no inspection or cleaning ports, no sump, no idea where the pickup is in relation to bottom, unknown baffles etc. Sounds like a problem in the making .

But if you want to find out more, perhaps try pressurising the tank with air (tyre pump or compressor) and seeing how long it will hold the pressure and where it might leak.

[GordMay]

ABYC has a standard for Diesel Fuel Systems in ABYC H-33.
➥ https://law.resource.org/pub/us/cfr/....H-33.1989.pdf

Static Pressure Testing:
“... After installation, the fuel system of every boat shall be pressure checked to at least 3 psi or at 1.5 times the maximum hydrostatic head to which it may be subjected in service, whichever is greater.
The fuel system shall evidence no leakage under such testing, checked at a minimum of 5 minutes* after application of the test pressure, for systems of 50 or less gallons capacity, with one additional minute for each increment of 10 gallons, or fraction thereof, from 50 to 500 gallons...”

* I’d highly recommend at least 4 Hours.

[Winf]

Thanks gents. Pressure test, why didn't I think of that!

Agree though that most likely a potential problem.

These are probably very dumb questions but let's say the tank is leaking, what is the issue with that? The tank appears to be fully encapsulated within the keel. If so, where is any leak going to go? Wouldn't it just contain the leaked diesel? Is there a problem of the diesel being in contact with the fibreglass in the containing well? Contamination issue?

What do they make these tanks out of anyway?

Let's just say it holds pressure, how on earth are these sort of tanks ever cleaned out properly with the lack of any inspection port? Why would you make it that way?

Cheers

Winf

[Wotname]

Second last question - it can't be cleaned


Can only speculate an answer for your last question.
Cheap and easy to make at the time of construction with no concern for the future problems.

[boden36]

Maybe there is an owners' association. Someone may know the history of your boat.
From memory, they were built near Albion Park, a southern suburb of Wollongong.
I had a passing acquaintance with Rudi, who was one of the two guys who owned the show.
The boats were well built and have a good reputation as cruisers.

Regards,
Richard.

[JPA Cate]

Win,

You can probably use your dinghy pump to pressurize the tank, if you decide you want to bother.

I think Wotname is right: there is a reason the PO decommissioned it, and it has to be something related to the tank. If it leaked, fuel could slosh over the floorboard, making them very slippery in a seaway. If it had crud in it, there's no way to clean it. It's inconvenient to remove the engine to gain access to the top of the tank, where you could gain access for cleaning. The PO decided it was easier to install a new tank, sacrificing all that space. There has to be a good reason someone would do that.

Maybe there's a way you could use the engine less? I agree carrying jerry jugs is a hassle and a bit unseamanlike, but it may be the better alternative. And you already have them. Do cover them with acrylic canvas or WeatherMax to protect them from the UV, they'll last ever so much longer.

Ann

[hpeer]

Who knows why PO's do anything?

You haven't told us much about the boat or the tank itself.

There may or may not be problems. There may or may not be solutions.

If it holds fuel, even if it is dirty, you can put in a transfer pump and pump the fuel to the tank you are now using, with a filter in the middle. Consider the small tank a day tank.

[stillbuilding]

Anything can be done of course - just the degree of pain involved.
Can remove the engine, cut an access hatch, clean and polish, fix whatever needed and then away you go. Maybe a job for when you overhaul the engine. Good way to spend a week of your holiday! Have had to do that - wonderful!!


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[Winf]

Originally Posted by Ann T. Cate

Win,

You can probably use your dinghy pump to pressurize the tank, if you decide you want to bother.

I think Wotname is right: there is a reason the PO decommissioned it, and it has to be something related to the tank. If it leaked, fuel could slosh over the floorboard, making them very slippery in a seaway. If it had crud in it, there's no way to clean it. It's inconvenient to remove the engine to gain access to the top of the tank, where you could gain access for cleaning. The PO decided it was easier to install a new tank, sacrificing all that space. There has to be a good reason someone would do that.

Maybe there's a way you could use the engine less? I agree carrying jerry jugs is a hassle and a bit unseamanlike, but it may be the better alternative. And you already have them. Do cover them with acrylic canvas or WeatherMax to protect them from the UV, they'll last ever so much longer.

Ann

Pretty much sums up my thinking but you know, just hoping!

Not sure it could slosh out though. Looks to be fully encapsulated unless I am missing something.

The only reason we are considering this is because of up upcoming Kimberley - Cairns cruise. Other cruisers we have spoken to comment that they used more fuel than they thought they would need in the Kimberley.

Winf

PS am looking at some canvas I got hold of in front of me now and wondering how Much fun it is going to be to hand sew up the jerry can covers!

[RaymondR]

I have a 430 litre fuel tank in the keel of my steel boat. It does not have any access whatsoever other than the filler and an off-take, it has been in use for 27 years now and I have not yet needed to access it for cleaning.

One of the advantages is that because the tank is submerged it keeps a fairly constant temperature and consequently does not "breath" and pull in moist air from which the moisture condenses, there is never any water in the fuel even though I spend much of my time in the tropics.

The single biggest disadvantage is that the fuel has to be lifted, that is sucked up, by the engines lift pump and if there are any air leaks in the system air will get sucked in and cause fuel supply problems.

I solved the air-in-fuel problem by putting a permanent bleed orifice and return line back to the tank, the air still gets in but is "bled" off before it causes any problems.

What I would do in your situation is check whether there is any liquids in the tank and if so pump them out. If there is not salt water in the tank it is probably liquid tight.

I would then use a 12V electric fuel pump to lift fuel out of the keel tank into the in-hull tank and put an overflow from the in-hull tank back into the keel tank.

I would connect the 12V pump into the accessory terminal on the ignition switch so that any time the engine was running the electric pump would transfer fuel from the keel tank into the in-hull tank.

It was probably the sucking air problem which resulted in the previous owner installing the in-hull tank.

[UNCIVILIZED]

In some boats, the tanks are literally an integral part of the keel. Meaning that the keel's structure forms the tank. And when done properly they're quite handy. Both in terms of space usage, & for getting weight down low in the boat.
The one's I've seen were in fin keels, fabricated out of steel, & the tanks where the space in the fin, above the ballast.

In those sorts of tanks, it's easy enough to retrofit, or initially build in a drain plug/port in the lower end of the keel. Thus when you're hauled out, you simply open the drain, & flush the tanks (repeatedly). And also to build in a more typical, albeit small, inspection/cleanout port up high/on top of the tank.
Some even have glassed, & faired over external, bolt on plates, down low in the tank. Accessible only when the boat's on the hard.

As to inspecting your tank, after it's passing the pressure test, you could drill a small hole or two in the top of it. Or drill a hole, & tap the hole for a plug (like the one on a car's oil pan). And use said hole(s) to insert a fiber optic camera, in order to get a semi-decent look at the inside of the tank.
Said camera's aren't expensive, & also sometimes are also found under the name of borescopes. I've even seen them advertised at Harbor Freight. Inspection Camera - Save on this Digital Inspection Camera

On cleaning such a tank, while it's not ideal, it could be repeatedly flushed & pumped out. And or possibly even cleaned via a port (see above), with a semi-low pressure, pressure washer. Or via any other method which would work via inserting a cleaning nozzle or tube through a small inspection port/plug.
And then you could check your work with the camera, give it plenty of time to dry, & re-inspect.
Plus there are any number of pumps available which work via a vacuum hose type suction.

Also, the above mentioned, in the tank, fuel pump, is Very viable, as witnessed by the millions of them in cars.

Hope that that helps, & also that you can put that tank of yours back into service.

[Rustic Charm]

My yacht was made with a keel tank. The owner before me had the boat in a marina literally 2 minutes from the open sea. So he felt he had no need for the 175ltr keel tank. So he just shut it off and added a 20 ltr bladder. No where near adequate for me as I was 6 hours from the sea.

So I set about reinstating mine. I was lucky in the sense that mine isn't under the engine but under part of the gally. It also has two very narrow inspection lids about 100mm wide.

But, despite the inspection covers I couldn't get to the entire tank. I sucked out the five year old sludge, then threw rags into it, pushed them around with a stick and cleaned it that way.

But, my main help was in a product called 'fuel right'. It seems to have really cleaned my tank. And a good Raco 500 cleaning system and filter.

[GILow]

Hi Winf,

First, let me congratulate you on your choice of boat. The SouthCoast 36 was very high on our list of choices when we were looking for a good comfortable cruiser a few years ago, and I have many photos of Southcoast 36 interiors as a source of motivation for our own interior rejuvenation whenever that happens.

I am posting here because I just went through a process that I suspect is very similar to what you face. Our Swanson 42 had a failed keel tank (freshwater) which was located under the engine and gearbox. In December I finally got around to dealing with the tank, and I learned a bit in the process, which may apply to your situation.

First, I am going to assume that given the very similar pedigree of our boats that the construction methods will have been the same, and certainly my very careful analysis of the SC36 years ago suggests they have a lot in common with our Swanson 42.

Second, I am going to assume that the previous owner did not decommission the tank just for the heck of it, in the case of our boat they most certainly did not give up on 420 litres of fresh water storage just for a simple problem.

So, I won't bore you with the details, but I pulled out our engine (all 450kg) in December and opened up the failed keel tank from the top, using an electric jigsaw. Then I extracted the utter evil gunk, removed the hideous failed bladder tanks that had been inserted to get around the original problem, washed it all out, sat back and worked out what had gone wrong.

Well, it appears that the keel tanks were lined with some kind of epoxy or hard setting liner which had cracked and failed, exposing the inside of the keel to the tank and thus probably causing foul "osmosis" tasting water (Acetic acid?) When this happened (around 15 years ago) the owner at the time just pushed in some flexible bladder tanks and used these. But of course they failed (they did not fit properly, they never could have, so they chaffed to bits in under five years) and the result was two big black pvc bags floating in scummy solution of water and diesel and goodness knows what.

So, my point is, the pressure test is a great idea, and if it fails I would seriously recommend you do NOT put any diesel, or ANY liquid in those tanks as cleaning them out will become a nightmare, particularly if they are full of now-contaminated diesel. I suspect you will find they too have a failed liner coat (maybe someone here can tell us what the layer of brittle, semi transparent lining material is likely to have been) and that they need some kind of sensible insert to be used again.

Next, I know you don't like the idea, but I would suggest that pulling the engine is worth the hassle. The SC36 came with around 50+ HP from memory, so the weight should not be a major concern, and you'll have a chance to clean up the engine if it needs it, clean all those fiddly bits of the bilge, get to know a really critical and time consuming part of your boat (the engine) but most importantly, you'll be able to open up the tanks properly and make a smart decision on the best way forward.

I don't know what the best way forward will be. I don't even know what I will do with ours right now. We are ok for diesel and water storage, at least for coastal cruising, so there's no great pressure to do anything, but if I had to I would seriously consider custom made poly tanks based on the suggestions of a few CF regulars who's opinions I highly respect.

Certainly, after my experience, I will never fit a bladder tank, but I admit to a bias that may be blinding me to their virtues. So be it.

Happy sailing, very envious of your lovely boat...

Matt

[Snowpetrel]

I cut a 6 inch hole in the top of my steel keel tank and installed a stainless steel screw hatch in it with an o ring seal. Worked great for inspection, sounding and filling.

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