Skin tanks

[Manxcat54]

I am working my way through this old boat which I purchased, knowing full well it would be a total rip out and start from scratch, it is a tough old job, but I have some assistance. Today I thought it about time I got myself acquainted with the engine, I had previously cranked the motor over by hand, so I know it isn't seized. The engine electrics look quite shambolic, so I started there first, I ended up feeling pleased because I could actually figure out what went where, so I made a diagram and set that to one side. Now the plumbing! the hoses are knackered, and so I will make new ones, I removed the pipes and hoses to the skin tank, and I discovered that the single skin tank is absolutely full off water, I can't see a way of draining it, what should I do to empty the old water out of this narrow tank, any suggestions? 

[David Mack]

Normally skin tanks are mounted vertically on the side of the swim and all you have to do is loosen the bottom hose connection and the tank will empty into the bilges.

Is yours on the bottom plate? If so you may have to pump it out with something like a Pela pump, or perhaps a wet and dry vac with a nozzle small enough to pass through the hose fitting.

[matty40s]

Suck it out as above, or use compressed air to blow it out.

[blackrose]

11 hours ago, Manxcat54 said:

I removed the pipes and hoses to the skin tank, and I discovered that the single skin tank is absolutely full off water, 

 

That reads like you think it's unusual. What did you expect to find in there? A skin tank should always be full of water (and antifreeze).

Edited March 23 by blackrose

[Manxcat54]

12 hours ago, David Mack said:

Normally skin tanks are mounted vertically on the side of the swim and all you have to do is loosen the bottom hose connection and the tank will empty into the bilges.

Is yours on the bottom plate? If so you may have to pump it out with something like a Pela pump, or perhaps a wet and dry vac with a nozzle small enough to pass through the hose fitting.

it is side of the swim and it appears to only have top hoses at the top at either end, I looked at the bottom for perhaps a drain, but it doesn't seem to have one, I will pump it out, it's been in there since 2019 and I would like to put clean in. I'm heading over now to the boat, I do have Blonde moments, so I will examine again.

[blackrose]

If you have a wetvac and access to mains power then sucking the water/antifreeze out of the tank will be the easiest way. You should also drain the engine of antifreeze as well as the rest of the system. When I changed my antifreeze mix I flushed the big hoses and skin tank out with a hose too. There was a bit of sludge and crap in there.

 

A wetvac is really useful on a boat. With a pela pump you'd have to get a hose down to the bottom of your skin tank without kinking the hose, pretty much an impossibility if you only have access from the top of the tank.

 

Also with a wetvac you can clean up the mess and suck all the water out of the bilges very easily. I recently bought a Screwfix own brand model for about 50 quid and it's brilliant.

 

https://www.screwfix.com/p/titan-1300w-16ltr-wet-dry-vacuum-220-240v/826kh

 

Edited March 23 by blackrose

[Manxcat54]

It's OK I have a wet vac, I am taking the perished hoses off the engine, it's a Peugeot 504 Diesel 2112cc used in the Ford Granada, I have been searching for spares and they are a bit hard to find.

[Tracy D'arth]

One of the connections, usually the one that went to the water pump, will be a dip tube down to the bottom of the tank. The other will stop at the top.

[ditchcrawler]

2 hours ago, blackrose said:

 

That reads like you think it's unusual. What did you expect to find in there? A skin tank should always be full of water (and antifreeze).

If you take both the hoses off mine it soon empties, just take the bottom one of and it takes a little longer

1 hour ago, Manxcat54 said:

it is side of the swim and it appears to only have top hoses at the top at either end, I looked at the bottom for perhaps a drain, but it doesn't seem to have one, I will pump it out, it's been in there since 2019 and I would like to put clean in. I'm heading over now to the boat, I do have Blonde moments, so I will examine again.

Maybe an opertunity to have a drain fitted at the bottom to make it easier to change the coolant every few years 

[David Mack]

1 hour ago, Tracy D'arth said:

One of the connections, usually the one that went to the water pump, will be a dip tube down to the bottom of the tank.

You hope!

[blackrose]

2 hours ago, Tracy D'arth said:

One of the connections, usually the one that went to the water pump, will be a dip tube down to the bottom of the tank. The other will stop at the top.

 

Not necessarily. It just depends on how the tank has been made. As it's got both connections at the top it might have a central baffle or two and that's it. 

[ditchcrawler]

With just connections at the top it must be impossible to change out the coolant without the use of a pump

[blackrose]

1 hour ago, ditchcrawler said:

Maybe an opertunity to have a drain fitted at the bottom to make it easier to change the coolant every few years 

 

Is there a way to do that other than cutting a hole and getting a spigot welded in for a fitting? There's no point putting a small 15mm stopcock type fitting in there as skin tanks are prone to collect crap inside and it will just get blocked. I can't see that there's enough plate thickness to thread something into the tank. 

6 minutes ago, ditchcrawler said:

With just connections at the top it must be impossible to change out the coolant without the use of a pump

 

Wetvac as we've been saying. If the airflow is controlled from the opposite connection it should suck everything out, or connect a piece of hose to the wetvac and get it down to the bottom of the tank.

Edited March 23 by blackrose

[Slim]

3 hours ago, Manxcat54 said:

it is side of the swim and it appears to only have top hoses at the top at either end, I looked at the bottom for perhaps a drain, but it doesn't seem to have one, I will pump it out, it's been in there since 2019 and I would like to put clean in. I'm heading over now to the boat, I do have Blonde moments, so I will examine again.

My skin tank had connections on the top so it's not that unusual. Poking about with a piece of stiff wire revealed which one had an internal pipe down to the bottom. years later I had a poke around with an illuminated endoscope (when it was full but it was so murky it was a waste of effort. 

As suggested elsewhere I used a Pela to empty it. This has the advantage of confirming it's capacity.  

[ditchcrawler]

29 minutes ago, blackrose said:

There's no point putting a small 15mm stopcock type fitting in there as skin tanks are prone to collect crap inside and it will just get blocked. 

That is how I drain mine

[Tony Brooks]

43 minutes ago, blackrose said:

There's no point putting a small 15mm stopcock type fitting in there as skin tanks are prone to collect crap inside and it will just get blocked

 

By that reasoning, there is no point in putting a 6mm or less drain in the engine block, yet the manufacturers do. I have never found that a length of coat-hanger or welding wire pushed into such drains failed to clear them. You may need to bend it a bit and waggle it about, but as soon as the flow gets going, it pretty much clears itself.

 

I think t would need a spigot welding in if you want to use a valve, but I think a simple plug could use a thread tapped into the tank skin. If welding is to be done then in order to weld the bottom of the spigot it would have to be clear of the baseplate, s that provides a sediment trap.

[blackrose]

43 minutes ago, ditchcrawler said:

That is how I drain mine

 

Well then clearly your skin  doesn't collect much crap inside. A small stopcock would have got blocked the last time I drained mine. 

 

But my point was, even if the OP fitted a small brass stopcock wouldn't it still require a hole to be cut in the tank and a spigot to be welded into the tank first? In which case if you're going to all that trouble why not weld in a bigger spigot for a bigger fitting that will never get blocked up?

 

24 minutes ago, Tony Brooks said:

 

By that reasoning, there is no point in putting a 6mm or less drain in the engine block, yet the manufacturers do. 

 

Or perhaps you haven't taken all the factors into account when looking at my reasoning? Unlike most engine parts the contact surface on the inside of a skin tank is mild steel and despite the corrosion inhibitors in antifreeze it will react and furr up inside and create deposits which sink to the bottom of the tank and just sit there forming a sludge. We see the same thing in central heating radiators despite the use of inhibitors.

 

But again the point is, if you're going to all the trouble of fitting a drain valve, why not fit something of a decent size that will never get blocked? Are you trying to save money fitting a small one?

Edited March 23 by blackrose

[David Mack]

48 minutes ago, Tony Brooks said:

I think t would need a spigot welding in if you want to use a valve, but I think a simple plug could use a thread tapped into the tank skin. If welding is to be done then in order to weld the bottom of the spigot it would have to be clear of the baseplate, s that provides a sediment trap.

I don't see why you couldn't drill and tap a skin tank to take a drain cock like this as long as the steel is at least 3mm thick.

But you would need room to rotate the fitting when screwing it in, so the drain would inevitably be a little above the bottom of the tank. 

A simple threaded plug could be fitted as close to the bottom of the tank as you could drill and tap.

[Tracy D'arth]

I would tap the tank for a 1/2" BSP X 1/4" BSP bush, fit a 1/4" BSP plug in the bush. Next time you have a welder to hand, weld the bush to the tank so that it will never unscrew. The 1/4" BSP plug will be an adequate drain, a tap could be fitted.

I would not use a type B drain off cock, The quality is poor and the washers vulcanise themselves to the seat. They are unsuitable in a boat and just about adequate for a domestic heating system drain.

[ditchcrawler]

2 hours ago, blackrose said:

 

Well then clearly your skin  doesn't collect much crap inside. A small stopcock would have got blocked the last time I drained mine. 

 

But my point was, even if the OP fitted a small brass stopcock wouldn't it still require a hole to be cut in the tank and a spigot to be welded into the tank first? In which case if you're going to all that trouble why not weld in a bigger spigot for a bigger fitting that will never get blocked up?

 

This is very true and well worth doing if any other welding is required 

51 minutes ago, Tracy D'arth said:

 

I would not use a type B drain off cock, The quality is poor and the washers vulcanise themselves to the seat. They are unsuitable in a boat and just about adequate for a domestic heating system drain.

That is also true as I have found out after fitting it, I really should change it next time I change the coolant 

[Manxcat54]

Well I'm back from the boat, I sucked out must of the water with my vac, it was fairly clean by the look of it, and since this old girl was built in 1979 and has never had a drain plug, I think I will just leave well alone, I took all the old perished hoses off the engine, then tried a car shop for some replacements, they took one look and said no, so I came home and went online, I found the odd one quite easily (it is a reduced one 55mm down to 40mm) and the others I ordered from bloody Amazon.

 

OK my next problem, how the hell do you remove the sliding hatch cover, when pushed fully open it stops at 2 big welded on stops, and when in the closed position it seems to come to a stop on an angle iron, which seems to be an integral part of the roof system? so without cutting off the 2 stops and removing the first mushroom vent I can't see how it can be removed, and before you ask, I want to remove some pretty bad rust on it's underside, and trying to do in situ would be a tough one indeed.

[Tracy D'arth]

15 minutes ago, Manxcat54 said:

Well I'm back from the boat, I sucked out must of the water with my vac, it was fairly clean by the look of it, and since this old girl was built in 1979 and has never had a drain plug, I think I will just leave well alone, I took all the old perished hoses off the engine, then tried a car shop for some replacements, they took one look and said no, so I came home and went online, I found the odd one quite easily (it is a reduced one 55mm down to 40mm) and the others I ordered from bloody Amazon.

 

OK my next problem, how the hell do you remove the sliding hatch cover, when pushed fully open it stops at 2 big welded on stops, and when in the closed position it seems to come to a stop on an angle iron, which seems to be an integral part of the roof system? so without cutting off the 2 stops and removing the first mushroom vent I can't see how it can be removed, and before you ask, I want to remove some pretty bad rust on it's underside, and trying to do in situ would be a tough one indeed.

The answer was in your post   =     cutting off the 2 stops and removing the first mushroom vent 

 

Bolt on stops on reassembly, stainless allen screws in the vent then you stand a chance in 5 years time of undoing them again.

Edited March 23 by Tracy D'arth

[Slim]

Out of curiosity who built the hull? 

[Manxcat54]

I only wish I knew, it was built in 1979 and I suspect around the Midlands

[blackrose]

20 hours ago, David Mack said:

I don't see why you couldn't drill and tap a skin tank to take a drain cock like this as long as the steel is at least 3mm thick.

But you would need room to rotate the fitting when screwing it in, so the drain would inevitably be a little above the bottom of the tank. 

A simple threaded plug could be fitted as close to the bottom of the tank as you could drill and tap.

 

Is 3mm thick enough to get enough threads in to make it secure and watertight? I honestly don't know but I'd hate to think about some clumsy oaf with steel toecap boots accidently kicking the fitting and emptying the contents of the skin tank.

16 hours ago, Manxcat54 said:

Well I'm back from the boat, I sucked out must of the water with my vac, it was fairly clean by the look of it, and since this old girl was built in 1979 and has never had a drain plug, I think I will just leave well alone, I took all the old perished hoses off the engine, then tried a car shop for some replacements, they took one look and said no, so I came home and went online, I found the odd one quite easily (it is a reduced one 55mm down to 40mm) and the others I ordered from bloody Amazon.

 

OK my next problem, how the hell do you remove the sliding hatch cover, when pushed fully open it stops at 2 big welded on stops, and when in the closed position it seems to come to a stop on an angle iron, which seems to be an integral part of the roof system? so without cutting off the 2 stops and removing the first mushroom vent I can't see how it can be removed, and before you ask, I want to remove some pretty bad rust on it's underside, and trying to do in situ would be a tough one indeed.

 

If you can empty the skin tank with your wetvac then I think it's reasonable to leave it alone and not fit a drain. But I would flush it through with a hose and empty it again with the wetvac to remove as much crud as you can.

 

Have you tried lifting the back (stern end) of the sliding hatch at any point in its travel? Or the same thing with the front end?