Fitting an external skin tank

[blackrose]

I've been given a quote of around £500 to do the steelwork for an additional external skin tank for my widebeam. I'd be connecting it to my engine's cooling system myself. The guy said 3' long x 2' high but I think it would need to be longer than that. My existing skin tank is about 5' x 2' so wouldn't I want the same on the other side?

[colin stone]

I've been given a quote of around £500 to do the steelwork for an additional external skin tank for my widebeam. I'd be connecting it to my engine's cooling system myself. The guy said 3' long x 2' high but I think it would need to be longer than that. My existing skin tank is about 5' x 2' so wouldn't I want the same on the other side?

 

Depends on the BHP etc. Your curent tank is good for 35Hp, cooling area required is 1 sq ft per 3.5 Hp. But you could use an array of steel pipes running up and down the swim - if that it is where it goes. You could do most of the work yourself - cut 2 holes for supply and return. Get someone to weld sockets through holes. Then just assemble with pipe fittings and tube. Many dutch barges have just that.

[Mick_B]

Hi Mike, Would this not affect the flow of water to the prop? Do you already have 2 skin tank?

[blackrose]

Hi Mike, Would this not affect the flow of water to the prop? Do you already have 2 skin tank?

 

No, just one skin tank - LB stitched me up and because I was running in the engine at low revs and going down the Thames with the current I never realised it wasn't sufficiently cooled. It's only a problem when I push the engine over 1500rpm for more than about 15mins.

 

I don't think a 2" thick external skin tank along the swim would interfere with with water flow to the prop.

 

Depends on the BHP etc. Your curent tank is good for 35Hp, cooling area required is 1 sq ft per 3.5 Hp. But you could use an array of steel pipes running up and down the swim - if that it is where it goes. You could do most of the work yourself - cut 2 holes for supply and return. Get someone to weld sockets through holes. Then just assemble with pipe fittings and tube. Many dutch barges have just that.

 

You mean vertical pipes? Wouldn't that require a lot of holes in the swim? I would worry about one of them leaking or getting smashed against a rock or something, not to mention one of the pipes getting damaged and then the boat would have to be taken out the water to fix it and the engine couldn't be run. At least with a skin tank there's only 2 holes and more protection - I would imagine the steel used would be 4mm thick?

Edited May 28, 2010 by blackrose

[RobinJ]

I've been given a quote of around £500 to do the steelwork for an additional external skin tank for my widebeam. I'd be connecting it to my engine's cooling system myself. The guy said 3' long x 2' high but I think it would need to be longer than that. My existing skin tank is about 5' x 2' so wouldn't I want the same on the other side?

One of the problems with skin cooling is any skin tank will work, it is the length of time over which it will continue to work effectively.

The bigger the skin tank the more volume of water there is in the cooling system and if and when it does heat up the more expansion you have to cope with.

Even if baffles are fitted, and that is essential to make sure the water stays in contact with the outside long enough to cool down, an engine run for long enough at a high enough power will begin to take water back which is starting to increase in temperature. At some point the inlet temperature will be to high to cool the engine properly and overheating will start.

If you plan to do a lot of river work especially with strong currents, I would suggest a tank as big as you can accomodate and as thin as possible to reduce volume.

[Grace and Favour]

No, just one skin tank - LB stitched me up and because I was running in the engine at low revs and going down the Thames with the current I never realised it wasn't sufficiently cooled. It's only a problem when I push the engine over 1500rpm for more than about 15mins.

 

I don't think a 2" thick external skin tank along the swim would interfere with with water flow to the prop.

 

 

 

You mean vertical pipes? Wouldn't that require a lot of holes in the swim? I would worry about one of them leaking or getting smashed against a rock or something, not to mention one of the pipes getting damaged and then the boat would have to be taken out the water to fix it and the engine couldn't be run. At least with a skin tank there's only 2 holes and more protection - I would imagine the steel used would be 4mm thick?

 

I assume (dangerous) that it would be one pipe, doubled back upon itself several times, horizontal and flat to the swim . . and would therefore need just one exit & entrance feed through the hull (?)

[blackrose]

I assume (dangerous) that it would be one pipe, doubled back upon itself several times, horizontal and flat to the swim . . and would therefore need just one exit & entrance feed through the hull (?)

 

I see. In that case why not just fit a domestic radiator down there?

 

Seriously though, I would worry about hitting the pipework against something and suddenly having no coolant in the engine. It only needs to be a big log on the Thames or something.

 

Is there such a thing as a flexible radiator that I could stick to the inside of the swim? I still have a kilo bag of thermally conductive epoxy resin that I bought for another job but never used.

 

Edit: What about a curved radiator for a bay window?

Edited May 28, 2010 by blackrose

[Guest]

I'll stick my neck out; I think skin tanks are fine for low power cut work, but indirect raw water is more suitable for river/sea, where more power is required for pushing tides. That doesn't help Blackrose much, but I agree that the extra skin tank will have to be very thin to avoid expansion problems; I get loads of water expansion off my modest skin tank.

 

I am sure there is scope for experimentation using raw water pumped through an existing skin tank (via an enclosed coil), using an extra pump. A kind of hybrid system. Road tankers carrying molasses that I once worked on where heated in a similar manner with half round pipes welded longitudinally to the shell, and steam blown through them. That is the reverse I know, but if similar pipes were welded to the inside of the skin tank within the boat, then raw water could be pumped through them, effectively making both sides of the skin tank surfaces cool instead of one. No extra expansion, and you would only switch the (electric?) pump on when needed. Water through weedhatch chamber to tank in order to avoid avoid hauling boat? Just a few thoughts, don't bite me head off

 

I see. In that case why not just fit a domestic radiator down there?

 

Seriously though, I would worry about hitting the pipework against something and suddenly having no coolant in the engine. It only needs to be a big log on the Thames or something.

 

Is there such a thing as a flexible radiator that I could stick to the inside of the swim? I still have a kilo bag of thermally conductive epoxy resin that I bought for another job but never used.

 

Edit: What about a curved radiator for a bay window?

The best thing I ever did on our boat was fit a Smiths heater in the cabin, which in turn is piped to the calorifier coils. Using the fan, it dumps LOADS of heat from the engine in a very short time. Lovely in winter, leave all doors/windows open if using in summer thoguh :-)

[ChrisPy]

my skin tank is fitted on the left side of the swim, I guess it is the same as yours, for a 55 Isuzu?

why do you propose an external skin tank?

why not just duplicate what you already have, on the right side?

[blackrose]

I'll stick my neck out; I think skin tanks are fine for low power cut work, but indirect raw water is more suitable for river/sea, where more power is required for pushing tides. That doesn't help Blackrose much, but I agree that the extra skin tank will have to be very thin to avoid expansion problems; I get loads of water expansion off my modest skin tank.

 

I am sure there is scope for experimentation using raw water pumped through an existing skin tank (via an enclosed coil), using an extra pump. A kind of hybrid system. Road tankers carrying molasses that I once worked on where heated in a similar manner with half round pipes welded longitudinally to the shell, and steam blown through them. That is the reverse I know, but if similar pipes were welded to the inside of the skin tank within the boat, then raw water could be pumped through them, effectively making both sides of the skin tank surfaces cool instead of one. No extra expansion, and you would only switch the (electric?) pump on when needed. Water through weedhatch chamber to tank in order to avoid avoid hauling boat? Just a few thoughts, don't bite me head off

 

 

The best thing I ever did on our boat was fit a Smiths heater in the cabin, which in turn is piped to the calorifier coils. Using the fan, it dumps LOADS of heat from the engine in a very short time. Lovely in winter, leave all doors/windows open if using in summer thoguh :-)

 

I don't see any need for raw water cooling and I can't envisage any major expansion problems - I don't have any coolant expansion problems at the moment. Ok, there's going to be more cooant in the new system so perhaps more scope for expansion, but if that's an issue I can always fit a small header tank.

 

Edit: I may end up scrapping the whole skin tank idea and try a circulation pump connected to the second coil of my calorifier (originally connected to my now skipped eberspacher). The engine would heat the calorifier and then when I switch the circulation pump on the second coil would take the hot water away from the calorifier to the radiators in the boat. I'm sure it would get the rads hot but whether it would cool the engine sufficuently I've no idea, but I guess any heat coming off the rads must come from the engine.

 

my skin tank is fitted on the left side of the swim, I guess it is the same as yours, for a 55 Isuzu?

why do you propose an external skin tank?

why not just duplicate what you already have, on the right side?

 

Because that would mean removing the engine in order to get in there to weld an internal tank.

Edited May 28, 2010 by blackrose

[Guest]

I don't see any need for raw water cooling and I can't envisage any expansion problems - I don't have any coolant expansion problems at the moment. Ok, there's going to be more cooant in the system so perhaps more scope for expansion, but if that's an issue I can always fit a small header tank.

 

 

 

Because that would mean removing the engine in order to get in there to weld an internal tank.

Some people have had success by simply adding a large vehicle radiator in the system.

[blackrose]

Some people have had success by simply adding a large vehicle radiator in the system.

 

Yes, but vehicle rads are designed to be exposed to a decent airflow, so you'd need a fan and some way for the heat to escape from the engine hole.

[GUMPY]

Some useful info here

http://www.betamarine.co.uk/newsite/downlo...inland/Keel.pdf

 

Now there comes a point where the skin tank is just to big to be fitted for example my barge 120hp would need 30sqft of tank

So if your engine is 55hp you will need 13.75sqft of tank so I guess his figures are slightly low.

Having said that I would go for the same both sides and do it internally..........

 

Just had another thought My new genny is keel cooled and I am just going to add a heat exchanger and water pump where the skin tank should be. Could be a very neat way of adding cooling to your system, but will cost about the same.

Edited May 28, 2010 by idleness

[blackrose]

Some useful info here

http://www.betamarine.co.uk/newsite/downlo...inland/Keel.pdf

 

Now there comes a point where the skin tank is just to big to be fitted for example my barge 120hp would need 30sqft of tank

So if your engine is 55hp you will need 13.75sqft of tank so I guess his figures are slightly low.

Having said that I would go for the same both sides and do it internally..........

 

Just had another thought My new genny is keel cooled and I am just going to add a heat exchanger and water pump where the skin tank should be. Could be a very neat way of adding cooling to your system, but will cost about the same.

 

Thanks for that Julian.

 

That PDF gives me another idea - my boat has a massive uxter plate so how about a horizontal skin tank? I could get it made and then stick it on with my thermally condutive epoxy. I know they're not as efficient as vertical tanks but it might be efficient enough?

[Guest]

Thanks for that Julian.

 

That PDF gives me another idea - my boat has a massive uxter plate so how about a horizontal skin tank? I could get it made and then stick it on with my thermally condutive epoxy. I know they're not as efficient as vertical tanks but it might be efficient enough?

My mate's boat had two horizontal skin tanks, which doubled as engine bearers (possibly a John White hull.) Now I have heard all the woes about horizontal skin tanks, and have never experienced them personally, but his boat was cooling trouble-free (Beta engine.)

 

I am told that the secret with horizontal tanks is to be sure that the pickup pipe extends down close to the base plate, and the return pipe passes back in at the top of the tank. Given your lack of space for a tank at the other side, this might be worth a try? I think I would try this if in a similar predicament; no holes through hull etc.

[WotEver]

I get loads of water expansion off my modest skin tank.

You've got an M3.10 too, haven't you Catweasel? It's just that I've noted a large amount of expansion with mine; I'm guessing it's a characteristic.

 

Tony

[GUMPY]

Thanks for that Julian.

 

That PDF gives me another idea - my boat has a massive uxter plate so how about a horizontal skin tank? I could get it made and then stick it on with my thermally condutive epoxy. I know they're not as efficient as vertical tanks but it might be efficient enough?

 

Before I decided on a heat exchanger for the generator I was going to get a tank made that would be the base for the generator to sit on. may still do that if I can get it cheap enough......

[alan_fincher]

I don't think a 2" thick external skin tank along the swim would interfere with with water flow to the prop.

Try to go for thinner than that.

 

There is no reason why the internal width needs to be more than a couple of centimetres - you should aim for an inch maximum.

 

If you make it thicker than it needs be....

 

1) You will have to pay for a lot more anti-freeze than you need.

2) You'll have more to dispose of, if you ever want to change it.

3) You will have more expansion to deal with than you need to.

4) It's moor likely to have an adverse effect on water flow to the prop.

 

it must be baffled internally, not just a big empty tank.

 

We had one added to the outside of our swim, (full height, maybe 6 feet long) - replacement rather than additional.

 

It made no discernible change to handling or fuel consumption. can't see why a wide beam should be any worse.

[Guest]

You've got an M3.10 too, haven't you Catweasel? It's just that I've noted a large amount of expansion with mine; I'm guessing it's a characteristic.

 

Tony

Slightly bigger M 415. I did a mod. which improved things. Moved the small pipe feeding plastic expansion from the top of the thermostat housing and blanked hole. Drill and tap (M8) metal heat exchanger at highest point behind water filler cap. Connect pipe to plastic bottle at this point. Was lots better after.

 

click

Edited May 28, 2010 by Guest

[blackrose]

According to the Beta guide to keel cooling that Julian (idleness) posted, skin tanks should be sized according to the maximum attainable bhp, not to the maximum bhp of the engine.

 

Since my boat is over-propped I only get 2000 revs/min, which according to the Isuzu specs means I'm only getting a max output of 40 bhp from the engine rather than 55 bhp. So according to Beta I need a skin tank of 10ft2.

 

I've just measured my tank and it's 6'4" x 1'4" which is 8.4ft2. So from that it hardly seems like it's worth paying a lot of money for an additional tank and I should go for a cheaper supplementary cooling system.

 

By the way, why are so many canal boats over-propped? What's the advantage?

Edited May 28, 2010 by blackrose

[Grace and Favour]

Snippity>>

 

By the way, why are so many canal boats over-propped? What's the advantage?

It's so that we can tell Phylis we need them to go water skiing

[nb Innisfree]

We have 6.5 sq ft for 40bhp Lister Petter Alpha which is plumbed in to CH but haven't needed to use CH as heat sink despite hammering (2000+ RPM) up the Thames in Summer.

[colin stone]

Edit: I may end up scrapping the whole skin tank idea and try a circulation pump connected to the second coil of my calorifier (originally connected to my now skipped eberspacher). The engine would heat the calorifier and then when I switch the circulation pump on the second coil would take the hot water away from the calorifier to the radiators in the boat. I'm sure it would get the rads hot but whether it would cool the engine sufficuently I've no idea, but I guess any heat coming off the rads must come from the engine.

 

Even better get a Bowman tubular heat exchanger and plumb into the CH circuit. Heat it from the engine calorifier connections. Then use calorifier and rads as cooling when required - and free CH when cruising on cooler days or winter. I had an airlock in my keel cooling system in summer '08 and used the central heating system to cool the engine - 160 Hp/14 radiators - for several days until I could sort out the system.

[Albion]

snipped

By the way, why are so many canal boats over-propped? What's the advantage?

 

In my opinion they shouldn't be. It's probably more due to incorrect choice of prop size. One disadvantage of over-propping, ignoring the fact that the engine can't reach its designed max revs, is that it can cause too high a speed when, on idle, approaching moorings, the towpath etc.

Roger

[WotEver]

Slightly bigger M 415. I did a mod...

Thanks for the info

 

Tony

 

Edit to say (And PDF)

Edited May 29, 2010 by WotEver