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The manual for my engine says I need a skin tank area of 1.25msq for 50hp it also says “the engine is unlikely to work hard on the canal” which seems like they’re saying this figure is too small. 
 

I presume that I can’t have too much cooling.  My question is does it  make a difference if the skin tank is inside or outside the hull? I guess yes but how much?

 

And what would be a good size to allow for river work for 50 hp?

 

or am I better off sticking with a heat exchanger - it’s struggling at the moment with an electic pump? A Johnson 3itres per minute (yeah, ha ha) 

 

My choices seem to be add an engine driven larger jabasco pump or rework the cooling system with a skin tank.
 

There’s no straightforward way of adding a raw water pump so this solution is likely to involve some expensive engineering. 

 

Advice please?

Edited by Pierre Thomas
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18 minutes ago, Pierre Thomas said:

I presume that I can’t have too much cooking.

Correct. The engine thermostat will restrict flow if the coolant gets too cool. You can have too little, but not too much. A bigger skin tank may make the difference between not needing a separate expansion vessel, or a larger expansion vessel if it has one already. More volume of coolant and therefore more expansion as it heats up, so that is something to consider.

18 minutes ago, Pierre Thomas said:

My question is does it  make a difference if the skin tank is inside or outside the hull? I guess yes but how much?

Whatever makes up the side of the tank in contact with the canal, or river water is by definition the outside of the hull. Building a new tank on the outside of the existing hull is easier to do, but may interfere with water flow to the prop. Building one inside the existing hull will likely mean the engine has to be removed to get enough access to weld.

 

18 minutes ago, Pierre Thomas said:

And what would be a good size to allow for river work for 50 hp?

Don't know. Others here will be able to say. Must be able to cope with the engine at full load for hours on end. The manufacturers recommendation (which engine maker?) is a good start.

 

18 minutes ago, Pierre Thomas said:

or am I better off sticking with a heat exchanger - it’s struggling at the moment with an electic pump? A Johnson 3itres per minute (yeah, ha ha) 

What is your cooling system at the moment? Isn't clear from this description.

 

Jen

Edited by Jen-in-Wellies
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It’s currently a water intake to a heat exchanger and a separate circuit for the engine. With an electric Johnson intercooler pump. It’s barely adequate at canal cruising revs when the intake is clear. 
 

im also considering external tubing but i’d prefer no holes in the hull if possible 

 

 

19 minutes ago, Jen-in-Wellies said:

The manufacturers recommendation

Is in my post and, like the rest of the manual does not inspire confidence. 
 

it’s a yanmar tn88 marinised by Barrus 

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23 minutes ago, Pierre Thomas said:

It’s currently a water intake to a heat exchanger and a separate circuit for the engine. With an electric Johnson intercooler pump. It’s barely adequate at canal cruising revs when the intake is clear. 

 

My engine is a tad bigger but my water pump is around 2.6 litres PER SECOND. (158 litres/min (2100 gal/hr).

You are never going to get proper cooling with 3 litres PER MINUTE

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14 minutes ago, Alan de Enfield said:

 

My engine is a tad bigger but my water pump is around 2.6 litres PER SECOND. (158 litres/min (2100 gal/hr).

You are never going to get proper cooling with 3 litres PER MINUTE

Did I say I say 3 ? It’s actually 30 ( though really it’s nearer 3 ) but I take your point. 

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1 hour ago, Jen-in-Wellies said:

Building one inside the existing hull will likely mean the engine has to be removed to get enough access to weld.

 

Cut a hole the size of the required skin tank through the hull from outside, fabricate the inner tank and the baffles through the hole, reattach the hull plate cut out previously.

 

This job is best done out of the water ...

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55 bhp and using the generally accepted 1 sq ft of tank area one face) per 4 bhp gives 13.75 sq ft of skin tank area.

 

An inter cooler pump is more likely designed for the engine coolant circuit, not to pump raw water with bits in it. I  expect it's centrifugal so not self priming and also subject to loss of output as the impeller clogs. I say centrifugal because a normal Johnson/Jabsco rubber impeller would not take kindly to engine running temperatures.

 

If this is a steel boat  don't see the difference between a pipe welded into the hull and a hull seam. If its GRP we operated a large GRP Thames hire fleet using keel cooling a sour preferred option because it was so much more reliable compared with indirect raw water cooling (heat exchanger).

Edited by Tony Brooks
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15 minutes ago, Pierre Thomas said:

Did I say I say 3 ? It’s actually 30 ( though really it’s nearer 3 ) but I take your point. 

 

1 hour ago, Pierre Thomas said:

it’s struggling at the moment with an electic pump? A Johnson 3itres per minute (yeah, ha ha) 

 

Mine is a Johnson F7B-9 Flange Mounted Engine Cooling Pump (1" BSPF)

 

It is actually driven by the crankshaft using the fixing for the air-brake pump,

It is also available as a belt driven version but NOT electric.

 

 

b2.jpg

IMG_20151219_084410.jpg

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I run a Beta 50hp in a narrowboat, you will struggle to get the correct ammount of cooling with one skin tank as it will need to be about 8-9ft long.

Staying with HE cooling you could ditch the electric pump and fit a belt driven pump at the front of the engine similar to the one AdE has or you may be lucky and find there is a PTO on the engine designed for an external water pump.

 

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2 hours ago, Loddon said:

.

Staying with HE cooling you could ditch the electric pump and fit a belt driven pump at the front of the engine similar to the one AdE has or you may be lucky and find there is a PTO on the engine designed for an external water pump.

 

That would be my favourite but it’s complicated 🙂 it’s a yanmar tn88 and although it has a PTO I can’t find a pump coupling to fit. I thought about a belt drive on the engine alternator and water pump but I’m worried about losing wrap. Lancing Marine suggested fitting the pump through a bracket on the face of existing pulley but a mounting bracket would be a bit tricky. 
 

I’ll post a diagram of the extra pulley arrangement tomorrow because I’d welcome an opinion on that.

 

thanks to everyone so far. 
 

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13 minutes ago, Pierre Thomas said:

Just as a curiosity, why do boats never use radiator and fan cooling? 
 

 

A car has a flow of air 'forced' thru the radiator (also assisted by the fan sucking)  In a boat the engine is caccooned in a box not much bigger that the engine itself and there is no airflow to cool - it would boil-up in minutes. 

Using the river / sea / canal cold water to cool the engine is much more reliable and consistent 

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If you can find a way of mounting a bracket for a foot mounted pump you may be able to drive a pump on the back of a wide poly-V belt. It would also increase the wrap on the alternator and crank pulley. You may have to have a flat pulley made for the pump.

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4 hours ago, Tony Brooks said:

If you can find a way of mounting a bracket for a foot mounted pump you may be able to drive a pump on the back of a wide poly-V belt. It would also increase the wrap on the alternator and crank pulley. You may have to have a flat pulley made for the pump.

Good thought

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16 hours ago, Pierre Thomas said:

Just as a curiosity, why do boats never use radiator and fan cooling? 

 

I've always wondered this too. Silenced 10-20kva generators often have similar sized diesel engines, cocooned in a box barely bigger than the engine and are radiator/forced air cooled. They have to deal with cooling a bloody great alternator too, at full output at 1500rpm continuously.

 

Guessing it's because you'd need a fairly big vent for the intake/exhaust air, which takes up a lot of space on a narrowboat and is difficult to duct into a cruiser stern. The radiator is also quite big and flat which is hard to hide on a small boat. Without baffling, the fans can be loud, and would need to be electric rather than engine driven due to the location. Adding complexity, you could even have a couple of smaller radiators, one each side on a trad stern but you'd have to have vents on the outside and would lose internal space.

Edited by cheesegas
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17 hours ago, Pierre Thomas said:

Just as a curiosity, why do boats never use radiator and fan cooling?

 

Some did/do. I think the IWA chap had a radiator cooled engine on Cressy. Used to be common when people were fitting old car engine into boats an modifying the car gearbox for the gears.  I also knew of a steel yacht hull a chap built and fitted radiator cooling, but they need vast amounts of air blown through them and that is difficult in engine rooms.

 

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17 hours ago, Pierre Thomas said:

Just as a curiosity, why do boats never use radiator and fan cooling? 

Still a lot of direct air cooled Lister engines on boats with no water/radiator circuit. They need ducting to get the volume of air required to cool them. It just makes sense to use the water that the boat sits in to dump the excess heat. The heat capacity of water is much much better than air.

Edited by Jen-in-Wellies
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so. I’m trying to find a way to make a pump like Alan’s or the jabasco equivalent work but not getting very far. I thought there would be a PTO underneath the cover on the left but there’s not, or anywhere else I can find so my alternatives now are the skin tank(s) - probably around £1,500 - £2,000 with the docking or something off off one of these pulleys. Opinions please.  It seems to me that putting a pulley on the water pump shaft risks causing side loading and wear but a third crankshaft pulley could also cause issues. What do you think?

 

image.jpeg.d5bb34752ffd4e652c70dc81e5eaf674.jpeg

 

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I would look to run a  flat water pump pulley on the back of the poly V belt driving the large alternator.  It looks like there is some structure to support a pump  and if you position it right you will get enough extra belt wrap on both existing pulleys to counterbalance the extra load on the belt.  You will need a longer belt and the layout will need to be accurate, so a certain amount of scale drawing is needed once you have worked out the right size pump pulley to give the flow rate needed.

 

A ritzy solution would use a double sided belt and a poly v pulley on the new pump.

N

 

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1 minute ago, BEngo said:

I would look to run a  flat water pump pulley on the back of the poly V belt driving the large alternator.  It looks like there is some structure to support a pump  and if you position it right you will get enough extra belt wrap on both existing pulleys to counterbalance the extra load on the belt.  You will need a longer belt and the layout will need to be accurate, so a certain amount of scale drawing is needed once you have worked out the right size pump pulley to give the flow rate needed.

 

A ritzy solution would use a double sided belt and a poly v pulley on the new pump.

N

 

 

I agree but would he get enough wrap on the new pump pulley? Just a thought. I think this may be the easiest way of doing it. Otherwise as even a large Jabsco pump takes a comparatively modest load I think those three allen screws could be used to drive an extra crankshaft pulley without issue. It would need a land to centralise it on the existing pulley I suspect. seeing the size of the crankshaft pulley on the 1.5s with a Jabsco pump (very small) I don't think here would be much load at all

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