Skin tank size?

[ronie]

Hi,

 

We have a 4 cylinder lister canalstar, which we need to figure out a cooling method for. The boat previously had a 1.5 BMC (before it was stretched to be a 70ft boat!) The skin tank for that is about 2ft by 1.5ft by 6" thick.

 

Now in searching google for info on how to determine skin tank size, there is not a lot of clear information, but some calculations suggets it would need to be about 11 square feet!!!! There is no way any boat I can think of could possibly have a skin tank that big is there????

 

It also seems to be that they need to be thin as well, further limiting the size they can be. Does anyone know how to calculate the size of a skin tank? Or does anyone have a similar engine with a skin tank they could say what size it is?

 

Any other advice would be welcome, as we are not having much luck in finding plausible answers!

 

Thanks a lot

 

Ronie

[alan_fincher]

Hi,

 

We have a 4 cylinder lister canalstar, which we need to figure out a cooling method for. The boat previously had a 1.5 BMC (before it was stretched to be a 70ft boat!) The skin tank for that is about 2ft by 1.5ft by 6" thick.

 

Now in searching google for info on how to determine skin tank size, there is not a lot of clear information, but some calculations suggets it would need to be about 11 square feet!!!! There is no way any boat I can think of could possibly have a skin tank that big is there????

 

It also seems to be that they need to be thin as well, further limiting the size they can be. Does anyone know how to calculate the size of a skin tank? Or does anyone have a similar engine with a skin tank they could say what size it is?

 

Any other advice would be welcome, as we are not having much luck in finding plausible answers!

 

Thanks a lot

 

Ronie

Well given they usually go on one side of the swim, and that is about 2 feet deep minimum, usually, then to get 11 square feet they would need to be 5 foot 6 inches long.

 

Perfectly possible if starting from scratch, but probably only realistic to add as a single tank on an existing boat if it's put on the outside of the current swim, (which is not a problem if it's kept slim, say 1" thick, max).

 

Alternatively you could have two joined tanks, one on each swim, when the length requirement falls to under 3 feet each.

 

There are as many sizing formulas as you could possibly imagine, and a lot depends on whether you ever expect to operate the engine anything like flat out, (under normal canal conditions, despite their 20 to 50 HP ratings, most endines are doing maybe no more than 5HP).

 

Tony Brooks says in his course notes that a 33 HP BMC is likely to need around 11 square feet, and from my experience that sounds good, although we are getting away with slightly less.

 

I suspect your Canalstar may well be more than the 33HP for the BMC, so in fact that 11 square feet size might be on the optimistic side. You need to increase proportionally, so if it were (say) 45 HP, then Tony's formula might indicate nearly 15 square feet.

 

In practice many boats get away with seriously undersized tanks, mainly because engines are seldom worked at full capacity for very long.

 

However the tank you describe that was 2 ft x 1 ft 6 ins x 6" is so dramatically undersized, I'm amazed if it was ever able to cool a BMC with no prpblems. It must only have been used very sedately!

[NB Alnwick]

In practice many boats get away with seriously undersized tanks, mainly because engines are seldom worked at full capacity for very long.

 

That's all well and good on shallow canals with a four miles an hour speed limit (which, in practice, is not often achievable without making a breaking wash) but on rivers and tideways it is essential to have something in reserve. Alnwick overheated yesterday pushing against an ebbing tide and fresh water currents on the tidal Trent. We were only making between six and seven miles an hour but clearly we were using a lot more power than we usually do. The obvious answer is to enhance the cooling tank capacity but this would then result in overcooling on canals. A possible compromise would be two tanks where one can be isolated when the extra cooling capacity is not required.

[alan_fincher]

The obvious answer is to enhance the cooling tank capacity but this would then result in overcooling on canals. A possible compromise would be two tanks where one can be isolated when the extra cooling capacity is not required.

A popular misconception, but not true if the engine has a thermostat.

 

If it has, then water will only pump to the skin tank when it is open, and if the engine starts to overcool, the stat will quickly do what it's designed to do, and shut to keep the engine at the design temperature of the thermostat.

 

My understanding is that, (in cooling terms at least) you cannot make a narrowboat skin tank too big, (although if it's huge you need to cater for very large amounts of expansion, and be prepared to pay for a lot of anti-freeze - unless you believe the latter unnecessary ....).

 

People who design a second skin tank that can be switched of in canal use build in unwanted complications, and make the whole process of getting it to flow naturally that bit harder, in my view.

 

I know nothing of "vintage" engines, so if these are operated "sans thermostat", what you say might then apply. However OP was asking about a Lister Canalstar, which certainly should have a thermostat present, and for that a very big skin tank will not result in overcooling, I'm sure.

 

EDIT:

 

Whether you can do 4mph on a "typical" canal, (no such beast I know), without a breaking wash is, as you know, very much a factor of boat type. We can regularly get up to the full speed limit, and not only is there no breaking wash, there is generally very little wash at all. Even on the Oxford, (not the deepest), it was very seldom that the GPS has to dip below 3 mph on the boat free stretches, with 3.5 mph much of the time. Ours is not even what Carl would call a "CloneCraft", but Mike Heywood must have been doing something right, (even if skin tank design was not his forte!).

Edited June 6, 2009 by alan_fincher

[NB Alnwick]

A popular misconception, but not true if the engine has a thermostat.

 

Since most proper marine engines were originally designed for raw water cooling - something else that is impractical on modern canals due to the large quantity of plastic bags and similar detritus that now floats around - I cannot see how or why any would have been fitted with a thermostat. In my experience thermostats are usually fitted to modern road vehicle engines that make a nasty buzzing noise and run far too fast to drive anything along the canals except, perhaps, an egg whisk.

[alan_fincher]

Since most proper marine engines were originally designed for raw water cooling - something else that is impractical on modern canals due to the large quantity of plastic bags and similar detritus that now floats around - I cannot see how or why any would have been fitted with a thermostat. In my experience thermostats are usually fitted to modern road vehicle engines that make a nasty buzzing noise and run far too fast to drive anything along the canals except, perhaps, an egg whisk.

I think you are probably being a bit perverse, Graham!

 

The OP made it abundantly clear in their original post that they had a Lister Canalstar, and I gave my advice on that basis, and believe it is entirely valid.

 

Had they said they had a ton and a half, or two tons of something older, (though not necessarily any more a marine engine!), I wouldn't have been so confident.

 

Define "modern" anyway ...... Our BMC is undoubtedly well over 40 years old, but is still basically a road engine. It allows us to see far more of the canal system in our limited time than a deep draughted boat with a "vintage" lump, ever could, As I've said many times on this topic, horses for courses.

 

The OP should in my view fit the biggest skin tank they can accommodate - it will not over-cool. The bigger they make it, the less likely they are to suffer the kind of problems that Alnwick just has.

 

If engines such as you have genuinely have no thermostat, then that seems like another complication if you try putting them in a situation for which they were not designed - namely a closed cooling circuit in a boat that sometimes will not be worked hard, and that at others most definitely will.

[Tony Brooks]

Hi,

 

We have a 4 cylinder lister canalstar, which we need to figure out a cooling method for. The boat previously had a 1.5 BMC (before it was stretched to be a 70ft boat!) The skin tank for that is about 2ft by 1.5ft by 6" thick.

 

Now in searching google for info on how to determine skin tank size, there is not a lot of clear information, but some calculations suggets it would need to be about 11 square feet!!!! There is no way any boat I can think of could possibly have a skin tank that big is there????

 

It also seems to be that they need to be thin as well, further limiting the size they can be. Does anyone know how to calculate the size of a skin tank? Or does anyone have a similar engine with a skin tank they could say what size it is?

 

Any other advice would be welcome, as we are not having much luck in finding plausible answers!

 

Thanks a lot

 

Ronie

 

 

Beta say 0.25 sq ft per hp and a TVU physicist did some calculations for me that came up with about 0.33 sq. ft per hp, I may have overstated the temperature of the canal water which might explain the difference. Ignore the Beta name because the physics are the same for all engines.

 

I get fed up to the back teeth with people warning that overlarge skin tanks will over-cool the engine. I have yet to see any engine in serious production since about 1960 that does not have a thermostat. This is the common "excuse" given by hull & boat builders who do not want to rectify undersized tanks or do anything other than they always do.

 

My DV36 is a proper marine engine and it uses a thermostat. It is also direct cooled but is perfectly happy running the direct cooling system through a skin tank OF THE PROPER SIZE.

[Gibbo]

Beta say 0.25 sq ft per hp and a TVU physicist did some calculations for me that came up with about 0.33 sq. ft per hp, I may have overstated the temperature of the canal water which might explain the difference. Ignore the Beta name because the physics are the same for all engines.

 

I get fed up to the back teeth with people warning that overlarge skin tanks will over-cool the engine. I have yet to see any engine in serious production since about 1960 that does not have a thermostat. This is the common "excuse" given by hull & boat builders who do not want to rectify undersized tanks or do anything other than they always do.

 

My DV36 is a proper marine engine and it uses a thermostat. It is also direct cooled but is perfectly happy running the direct cooling system through a skin tank OF THE PROPER SIZE.

 

My 4LW (which doesn't make much heat anyway) runs on a huge skin tank. It is thermostatically controlled. I have no problem whatsoever with overcooling. Yet it is also very happy with the engine running at very high power for hours and hours on end. I also fail to see how anyone could think a large skin tank could overcool a thermostatically controlled engine?

 

Come to think of it, how could it overcool one that was designed for raw water cooling?

 

Gibbo

[Albion]

Beta say 0.25 sq ft per hp and a TVU physicist did some calculations for me that came up with about 0.33 sq. ft per hp, I may have overstated the temperature of the canal water which might explain the difference. Ignore the Beta name because the physics are the same for all engines.

 

I get fed up to the back teeth with people warning that overlarge skin tanks will over-cool the engine. I have yet to see any engine in serious production since about 1960 that does not have a thermostat. This is the common "excuse" given by hull & boat builders who do not want to rectify undersized tanks or do anything other than they always do.

 

My DV36 is a proper marine engine and it uses a thermostat. It is also direct cooled but is perfectly happy running the direct cooling system through a skin tank OF THE PROPER SIZE.

 

That pretty well stacks up with what I had always heard to use a size of about 1 sq ft for every 4 to 5 hp. The critical thing though is that the tank should be suitably baffled inside to create a labyrinth path for the coolant to flow around. It is pointless having an inlet in one corner and an outlet in the other with no baffling as the coolant will run straight from one to the other and most of the skin tank area is wasted. The tank doesn't need to be very thick either. The 6 in thick tank of the OP is a waste of space and only needs to be about 1 to 1.5 inches thick.

I also agree with Tony that an over-specced tank size is perfectly OK on an engine with a thermostat. In fact it could well be useful if you find yourself pushing a tide for hours or in emergency situations; that's when you'll find out whether the tank is big enough and that is when you definitely don't want to find out that it is too small.

Roger

[LEO]

I think you are probably being a bit perverse, Graham!

 

The OP made it abundantly clear in their original post that they had a Lister Canalstar, and I gave my advice on that basis, and believe it is entirely valid.

 

Had they said they had a ton and a half, or two tons of something older, (though not necessarily any more a marine engine!), I wouldn't have been so confident.

 

Define "modern" anyway ...... Our BMC is undoubtedly well over 40 years old, but is still basically a road engine. It allows us to see far more of the canal system in our limited time than a deep draughted boat with a "vintage" lump, ever could, As I've said many times on this topic, horses for courses.

 

The OP should in my view fit the biggest skin tank they can accommodate - it will not over-cool. The bigger they make it, the less likely they are to suffer the kind of problems that Alnwick just has.

 

If engines such as you have genuinely have no thermostat, then that seems like another complication if you try putting them in a situation for which they were not designed - namely a closed cooling circuit in a boat that sometimes will not be worked hard, and that at others most definitely will.

 

Hi,

 

Interesting post. It is preferable to avoid using raw water to cool engines, especially vintage ones as this can lead to severe deterioration of the cast iron block causing it to become porous. I have some amazing pictures of Gardners badly 'clagged up'. It may have been satisfactory to use raw water cooling years ago but much better to modifiy systems so that modern cooling additives can be used.

 

Gardners don't even recommend fitting calorifiers as the sudden injection od cold water into the block can cause excess wear - this may be a case of being overcautious though as my 2LW happily runs well with a keel cooler and a calorifier.

 

Kelvins are massively over-engineered and may be happy with the injection of cold water but it would be fun to experiment with a sealed cooling system incorporating a calorifier ( I hate to think of all that hot water going to waste).

 

KK ( another Kelvin owner) was considering trying to develop a system using a heat exchanger on the exhaust pipe.

 

Also if a sealed system can be used one overcomes a possible problem in having a 'through hull' hole and possible overheating problems if you forget to open up the seacock to allow cool water into the boat/engine.

 

Sealed systems also make it much simpler to protect the engine during the frost.

 

The mere fact you have a vintage engine does not preclude one from trying to incorporate changing ideas/technology if it prolongs the life of the engine - I often try to explain to my wife that 'I don't actually own a Gardner but am merely it's custodian'.

 

Leo

[Gibbo]

Gardners don't even recommend fitting calorifiers as the sudden injection od cold water into the block can cause excess wear...............

 

I too have heard this from several people though never from a Gardner engineer. I have a gut feeling it is complete b*ll*x. If it was true, how on earth would the engine be able to cope with raw water cooling? Further, a properly designed system doesn't suddenly produce cold water into the engine from a calorifier.

 

My 4LW was designed for raw water cooling and uses a ram pump. It was (still is) skin tank cooled when I got it but with manual temperature control. Useless! I've converted it to a thermostat and it works like a dream. It's not as easy as it sounds but it can be done. I don't see why the same couldn't apply to any other ram pump raw water cooled engine.

 

I totally agree that raw water cooling is madness on the canals and I wouldn't touch it with someone else's barge pole.

 

Gibbo

[LEO]

I too have heard this from several people though never from a Gardner engineer. I have a gut feeling it is complete b*ll*x. If it was true, how on earth would the engine be able to cope with raw water cooling? Further, a properly designed system doesn't suddenly produce cold water into the engine from a calorifier.

 

Gibbo

 

Hi,

 

I tend to agree with you, but page 21 of the 'Operations and maintenance' manual produced by Gardners for diesel engines types LW.HLW.LW20 & HLW20 covers this point.

 

As I said my system works happily so let it be.

 

Gardners may have felt that plant/lorry users did not need heating in cabs when they developed their engines.

 

Leo.

[Tony Brooks]

I too have heard this from several people though never from a Gardner engineer. I have a gut feeling it is complete b*ll*x. If it was true, how on earth would the engine be able to cope with raw water cooling? Further, a properly designed system doesn't suddenly produce cold water into the engine from a calorifier.

 

My 4LW was designed for raw water cooling and uses a ram pump. It was (still is) skin tank cooled when I got it but with manual temperature control. Useless! I've converted it to a thermostat and it works like a dream. It's not as easy as it sounds but it can be done. I don't see why the same couldn't apply to any other ram pump raw water cooled engine.

 

I totally agree that raw water cooling is madness on the canals and I wouldn't touch it with someone else's barge pole.

 

Gibbo

 

 

I will add to that heat exchanger cooling unless you want a more complicated system and insist on using the raw water side of the heat exchanger system as a feed through a skin tank (of correct size).

[nb Innisfree]

Hi,

 

We have a 4 cylinder lister canalstar, which we need to figure out a cooling method for. The boat previously had a 1.5 BMC (before it was stretched to be a 70ft boat!) The skin tank for that is about 2ft by 1.5ft by 6" thick.

 

Now in searching google for info on how to determine skin tank size, there is not a lot of clear information, but some calculations suggets it would need to be about 11 square feet!!!! There is no way any boat I can think of could possibly have a skin tank that big is there????

 

It also seems to be that they need to be thin as well, further limiting the size they can be. Does anyone know how to calculate the size of a skin tank? Or does anyone have a similar engine with a skin tank they could say what size it is?

 

Any other advice would be welcome, as we are not having much luck in finding plausible answers!

 

Thanks a lot

 

Ronie

 

We have a 40 hp 4 cyl Canalstar with a 6.5 sq. ft, skin tank (approx 1.5" thick) I don't know if it is baffled but we have had no problem belting up the Thames. One thing I have done is de-pressurise the cooling system and connected it to the CH/calorifier circuit via a diverter valve, works a treat and it is handy as extra emergency cooling though we haven't needed it yet.

[Tony Brooks]

We have a 40 hp 4 cyl Canalstar with a 6.5 sq. ft, skin tank (approx 1.5" thick) I don't know if it is baffled but we have had no problem belting up the Thames. One thing I have done is de-pressurise the cooling system and connected it to the CH/calorifier circuit via a diverter valve, works a treat and it is handy as extra emergency cooling though we haven't needed it yet.

 

 

Warning to others thinking about running a pressurised sys ten without any pressure.

 

Modern engines are pressurised for a reason and that is to prevent hotter places in the engine boiling when under high speed & load. If the engine is run without pressure you MIGHT (not will) get the symptoms of boiling whilst, initially, the temperature gauge will read normal.

[nb Innisfree]

Warning to others thinking about running a pressurised sys ten without any pressure.

 

Modern engines are pressurised for a reason and that is to prevent hotter places in the engine boiling when under high speed & load. If the engine is run without pressure you MIGHT (not will) get the symptoms of boiling whilst, initially, the temperature gauge will read normal.

 

I always thought that pressurising car engines was to prevent boiling at high altitudes (lower air pressure - mountain passes?) but never thought about engine hotspots. Definitely something to consider

[david and julie]

Does anyone know how to calculate the size of a skin tank? Or does anyone have a similar engine with a skin tank they could say what size it is?

 

Any other advice would be welcome, as we are not having much luck in finding plausible answers!

There's some interesting reading on the Beta marine site about skin tanks.

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

[nb Innisfree]

There's some interesting reading on the Beta marine site about skin tanks.

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

 

Interesting info, but, maximum power for 1.5 hrs?

 

Arrrggghhh!

[david and julie]

Interesting info, but, maximum power for 1.5 hrs?

 

Arrrggghhh!

They have to cover every eventuality - including their a***s.

[Tony Brooks]

I always thought that pressurising car engines was to prevent boiling at high altitudes (lower air pressure - mountain passes?) but never thought about engine hotspots. Definitely something to consider

 

 

Probably was when they first did it, but as powers increased so the heat requiring taking away got more without a corresponding increase in surface area inside the engine, in fact I suspect the area go smaller. I can remember 4psi caps then it went to 6 until now we regularly use 15 psi. Its the exhaust valve seats we mainly think about and possibly around the injector tip.

 

A diesel will use more of its heat in useful work so compared with petrol the cooling load may be lower but when you compare a Beta 42 and a BMC 1.5 the Beta engine looks smaller than one that develops less power so I would be unwilling to risk my engine by running it unpressurised, but it could easily be OK, thats the trouble, we just do not know. (Actually mine does run unpressurised but then it was designed as a raw water system.

 

I have not heard of BMCs causing problems when run unpressurised or the Perkins 4-xxx range but I would be very wary of anything more modern.

[Mike C]

Tempest (30 years ago) were working with 3.5 BHP to the sq foot of surface area with a maximum water capacity per square foot of 0.5 gl (ie approximately ONE inch of thickness per square foot of surface area) this is a calculation that is still used today by some Japanese engine marinisers.

 

Whilst some threads on this post have been alarmed by the size requires, the calculation takes into account that the accumulated heat needs to be lost even if the external water flow reduces. - Imagine running hard in deep water on a warm day and then tying up to say wait for a lock, or at a water point, suddenly the water through the tank is reduced (engine revs reduced) and the water passing the external surface has also significantly reduced or stopped.

 

I hope this helps

[alan_fincher]

I have not heard of BMCs causing problems when run unpressurised or the Perkins 4-xxx range but I would be very wary of anything more modern.

Typically BMC pressure caps are only intended to be 7 PSI. I've a feeling my old Perkins was the same.

 

That's not a lot, and a lot less than modern car cooling systems.

 

As Tony implies, it seems reasonable that the higher the pressure an engine is intended to run at, the more problems you might cause by running it completely unpressurised.

 

Based on actual experience I have seen, the example of a 6.5 sq ft tank on a 40 HP engine doesn't sound that generous. However I know a lot are no bigger than that, and regularly people get away with it, even on rivers. If I were adding a new one, I'd certainly go significantly larger than that, though.

[nb Innisfree]

Typically BMC pressure caps are only intended to be 7 PSI. I've a feeling my old Perkins was the same.

 

That's not a lot, and a lot less than modern car cooling systems.

 

As Tony implies, it seems reasonable that the higher the pressure an engine is intended to run at, the more problems you might cause by running it completely unpressurised.

 

Based on actual experience I have seen, the example of a 6.5 sq ft tank on a 40 HP engine doesn't sound that generous. However I know a lot are no bigger than that, and regularly people get away with it, even on rivers. If I were adding a new one, I'd certainly go significantly larger than that, though.

 

Yes if I was doing it all again I would go bigger but on a standard cruiser stern (18" swim) 6.5 sq ft is near the limit without extending beyond the rear bulkhead, otherwise a second one 't'other side I suppose

[NB Alnwick]

Beta say 0.25 sq ft per hp and a TVU physicist did some calculations for me that came up with about 0.33 sq. ft per hp, I may have overstated the temperature of the canal water which might explain the difference. Ignore the Beta name because the physics are the same for all engines.

 

I get fed up to the back teeth with people warning that overlarge skin tanks will over-cool the engine. I have yet to see any engine in serious production since about 1960 that does not have a thermostat. This is the common "excuse" given by hull & boat builders who do not want to rectify undersized tanks or do anything other than they always do.

 

My DV36 is a proper marine engine and it uses a thermostat. It is also direct cooled but is perfectly happy running the direct cooling system through a skin tank OF THE PROPER SIZE.

 

George Bergius, the son of Walter (Kelvin's founder), and a member of the team that designed the Kelvin 'K' and 'J' series engines, advised Phil Trotter, the builder of our boat, regarding the style and size of the cooling system. Nevertheless, in practice, whereas it is ideal for sustained running at canal speeds and bursts of around two hours at full speed, the cooling system is clearly too small for sustained high speed running. Conventional thermostats were not originally fitted to Kelvin 'K' and 'J' series engines and, as far as I know, they were not fitted as standard on many other contemporary marine engines. The operating manual for Kelvin 'K' and 'J' series engines includes a warning that although the engine may be run at low speed (out of gear) all day, it should not be allowed to do so at high speed because this may cause "the cylinders to cool and cause excessive wear" I therefore concluded that 'over-cooling' the cylinders would do the same but if I am wrong, I am always willing to learn from someone who knows better.

 

Seaward Engineering of Glasgow have retro-fitted thermostats to 'K' and 'J' series engines but I do not know how successful these have been.

 

I do agree with alan_fincher, in that the capacity of a cooling system needs to be as large as possible and I accept that ours may not be large enough to cope when the engine is called upon to deliver maximum power for long periods. What I cannot decide is how best to remedy the situation given that our existing system is perfectly adequate for more than 95% of our cruising . . .

[nb Innisfree]

George Bergius, the son of Walter (Kelvin's founder), and a member of the team that designed the Kelvin 'K' and 'J' series engines, advised Phil Trotter, the builder of our boat, regarding the style and size of the cooling system. Nevertheless, in practice, whereas it is ideal for sustained running at canal speeds and bursts of around two hours at full speed, the cooling system is clearly too small for sustained high speed running. Conventional thermostats were not originally fitted to Kelvin 'K' and 'J' series engines and, as far as I know, they were not fitted as standard on many other contemporary marine engines. The operating manual for Kelvin 'K' and 'J' series engines includes a warning that although the engine may be run at low speed (out of gear) all day, it should not be allowed to do so at high speed because this may cause "the cylinders to cool and cause excessive wear" I therefore concluded that 'over-cooling' the cylinders would do the same but if I am wrong, I am always willing to learn from someone who knows better.

 

Seaward Engineering of Glasgow have retro-fitted thermostats to 'K' and 'J' series engines but I do not know how successful these have been.

 

I do agree with alan_fincher, in that the capacity of a cooling system needs to be as large as possible and I accept that ours may not be large enough to cope when the engine is called upon to deliver maximum power for long periods. What I cannot decide is how best to remedy the situation given that our existing system is perfectly adequate for more than 95% of our cruising . . .

 

Perhaps you could fit a car type fan cooled radiator matrix to which you could divert cooling water through when needed?