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Hi. Just a quickie for you clever bods. The boat we are looking at is 40bhp with aquadrive and using the Beta calc from previous cooling posts (although it actually has a Barrus Shire) the skin tank area needed is 1sqft/4 bhp, ie 10sqft plus an extra 30% for the hydraulic drive. The tank is much smaller than this and the boat will be based on the Trent so will have to cope with river flow. How crazy an idea is it to fit an automotive radiator and fan to cope with the surplus heat when the engine is working hard? I recognise this would involve creating inlet and exhaust ducts for the radiator air flow. TIA and apologies if this has already been covered on the forum.

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2 minutes ago, MrsM said:

Hi. Just a quickie for you clever bods. The boat we are looking at is 40bhp with aquadrive and using the Beta calc from previous cooling posts (although it actually has a Barrus Shire) the skin tank area needed is 1sqft/4 bhp, ie 10sqft plus an extra 30% for the hydraulic drive. The tank is much smaller than this and the boat will be based on the Trent so will have to cope with river flow. How crazy an idea is it to fit an automotive radiator and fan to cope with the surplus heat when the engine is working hard? I recognise this would involve creating inlet and exhaust ducts for the radiator air flow. TIA and apologies if this has already been covered on the forum.

Far less complicated to have second skin tank plumbed in, either on the baseplate or other swim

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2 minutes ago, MrsM said:

Hi. Just a quickie for you clever bods. The boat we are looking at is 40bhp with aquadrive and using the Beta calc from previous cooling posts (although it actually has a Barrus Shire) the skin tank area needed is 1sqft/4 bhp, ie 10sqft plus an extra 30% for the hydraulic drive. The tank is much smaller than this and the boat will be based on the Trent so will have to cope with river flow. How crazy an idea is it to fit an automotive radiator and fan to cope with the surplus heat when the engine is working hard? I recognise this would involve creating inlet and exhaust ducts for the radiator air flow. TIA and apologies if this has already been covered on the forum.

@Tony Brooks best placed to advise but I would have thought  better option would be to make the skin tank larger.

 

Is it internal or external?

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5 minutes ago, MrsM said:

Hi. Just a quickie for you clever bods. The boat we are looking at is 40bhp with aquadrive and using the Beta calc from previous cooling posts (although it actually has a Barrus Shire) the skin tank area needed is 1sqft/4 bhp, ie 10sqft plus an extra 30% for the hydraulic drive. The tank is much smaller than this and the boat will be based on the Trent so will have to cope with river flow. How crazy an idea is it to fit an automotive radiator and fan to cope with the surplus heat when the engine is working hard? I recognise this would involve creating inlet and exhaust ducts for the radiator air flow. TIA and apologies if this has already been covered on the forum.

Why not have a large external skin tank on the other side?

 

added - as said above 🤪

Edited by Chewbacka

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1 minute ago, matty40s said:

Far less complicated to have second skin tank plumbed in, either on the baseplate or other swim

But wouldn't this mean taking the engine out?

2 minutes ago, The Happy Nomad said:

@Tony Brooks best placed to advise but I would have thought  better option would be to make the skin tank larger.

 

Is it internal or external?

It's an internal tank. Probably daft but I would be concerned about damaging an external tank - being a newbie and all that. Also wouldn't an external tank have an effect on flow?

Thanks so much guys. Having out of water survey tomorrow so I'll ask.

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External tank is made of steel, and would be on the opposite swim, protected by the boat side and counter.

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4 minutes ago, matty40s said:

External tank is made of steel, and would be on the opposite swim, protected by the boat side and counter.

Thanks Matty40s. I suppose NBs aren't the most aerodynamic at the best of times so not a major concern! 😂

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15 minutes ago, MrsM said:

But wouldn't this mean taking the engine out?

It's an internal tank. Probably daft but I would be concerned about damaging an external tank - being a newbie and all that. Also wouldn't an external tank have an effect on flow?

Thanks so much guys. Having out of water survey tomorrow so I'll ask.

See Matty's answer above.

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27 minutes ago, MrsM said:

Hi. Just a quickie for you clever bods. The boat we are looking at is 40bhp with aquadrive and using the Beta calc from previous cooling posts (although it actually has a Barrus Shire) the skin tank area needed is 1sqft/4 bhp, ie 10sqft plus an extra 30% for the hydraulic drive. The tank is much smaller than this and the boat will be based on the Trent so will have to cope with river flow. How crazy an idea is it to fit an automotive radiator and fan to cope with the surplus heat when the engine is working hard? I recognise this would involve creating inlet and exhaust ducts for the radiator air flow. TIA and apologies if this has already been covered on the forum.

Are you confusing a hydraulic gearbox with an actual hydraulic drive?  Although a hydraulic gearbox produces a little extra heat its nothing like a hydraulic drive. If it is  a hydraulic box you may not need more cooling.

 

In my view trying to duct the heat out of the hull  so the engine room ambient temperature remains reasonable may require holes that could present more of danger from flooding when idiots pass at high speed than slowing down to match power output to the cooling capacity. I think an new, correctly sized, external skin tank would be the most satisfactory way forward. It is well protected by the boat's structure as Matty said.

 

Experience shows they normally do not affect the way the boat swims or handles.

Edited by Tony Brooks

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7 minutes ago, MrsM said:

Thanks Matty40s. I suppose NBs aren't the most aerodynamic at the best of times so not a major concern! 😂

Has understatement always been one of your strengths ?

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15 minutes ago, Tony Brooks said:

Are you confusing a hydraulic gearbox with an actual hydraulic drive?  Although a hydraulic gearbox produces a little extra heat its nothing like a hydraulic drive. If it is  a hydraulic box you may not need more cooling.

 

In my view trying to duct the heat out of the hull  so the engine room ambient temperature remains reasonable may require holes that could present more of danger from flooding when idiots pass at high speed than slowing down to match power output to the cooling capacity. I think an new, correctly sized, external skin tank would be the most satisfactory way forward. It is well protected by the boat's structure as Matty said.

 

Experience shows they normally do not affect the way the boat swims or handles.

Yes I probably am getting confused between the two and misunderstood what an Aquadrive is. Thank you for clarifying this, Tony What a massive learning curve this all is! A second skin tank sounds like the way ahead. My next question is what ballpark figure will I need to set aside for this work? I cannot risk losing power on the Trent so it's something I will need to get done sooner rather than later I guess. Thanks again for the advice.

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22 minutes ago, Alan de Enfield said:

Has understatement always been one of your strengths ?

Haha 😄. I was asked today by a marine insurance lady whether I would be going faster than 17 knots. I answered "probably not" - was that me being a bit understated again 😂

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10 minutes ago, MrsM said:

Yes I probably am getting confused between the two and misunderstood what an Aquadrive is. Thank you for clarifying this, Tony What a massive learning curve this all is! A second skin tank sounds like the way ahead. My next question is what ballpark figure will I need to set aside for this work? I cannot risk losing power on the Trent so it's something I will need to get done sooner rather than later I guess. Thanks again for the advice.

 

The Aquadrive is a sophisticated propeller shaft coupling that has many advantages over what is usually fitted.

 

No idea about the costs of an external tank but you will need to discuss this with whoever is to do the job. In fact some yards may suggest a pipe or pipes on the outside of the swim rather than a tank. That usually works just as well.

Edited by Tony Brooks

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27 minutes ago, Tony Brooks said:

 

The Aquadrive is a sophisticated propeller shaft coupling that has many advantages over what is usually fitted.

 

No idea about the costs of an external tank but you will need to discuss this with whoever is to do the job. In fact some yards may suggest a pipe or pipes on the outside of the swim rather than a tank. That usually works just as well.

Thanks again Tony. I will make some calls to yards tomorrow.

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8 hours ago, ditchcrawler said:

I have posted this link several times before http://boatbuildblog.blogspot.com/search?q=skin+tank

Thank you Ditchvrawler that is a great blog. As we will clearly need a second tank can you advise the approximate cost of this job? We have yet to hand over our pennies for the boat so do you think it is reasonable for us to use this job as part of our negotiation? The boat needs a full repaint so we are already looking at a big outlay after purchase. 

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9 hours ago, Chewbacka said:

Why not have a large external skin tank on the other side?

 

added - as said above 🤪

This is the way to go. Have a second external tank fitted to the opposite side. Then link both taks together and plumb to engine. This will not affect boat performance in any way. 

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The question must be asked whether 40 hp is useable. How big is the boat? I've got 38 hp in my 15.5m nb and have never gone over 2200 rpm for more than a minute or two out of a max rpm of 3000 (and I've been on plenty of rivers in conditions which were marginal). At some point the hull just pulls down and the wash goes up. The advantage of an oversized engine is that it can run with less stress if the prop is matched. So, how big is the boat and how big is the current skin tank?

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4 minutes ago, Onewheeler said:

The question must be asked whether 40 hp is useable. How big is the boat? I've got 38 hp in my 15.5m nb and have never gone over 2200 rpm for more than a minute or two out of a max rpm of 3000 (and I've been on plenty of rivers in conditions which were marginal). At some point the hull just pulls down and the wash goes up. The advantage of an oversized engine is that it can run with less stress if the prop is matched. So, how big is the boat and how big is the current skin tank?

There is a lot of truth in that. personally I would do a prolonged high speed trial to see if it really does overheat. My own 35HP engine in a 54ft narrowboat ran at over 2000 RPM from Keadby to West Stockwith without overheating. I never measured it but I suspect the skin tank was a little undersized according to the Beta figures.

 

Mrs M should learn when the boat reaches its hull design speed on the Trent so she never tries to exceed that speed. That seed will be less or a lot less on canals. If she has a satnav she could use that to find the throttle position after which the boat speed refuses to rise although the engaging  speed does.After that point  you just waste fuel in making waves and trying to lift the boat out of the water.

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I've got a Barrus Shire 45 in a 52 foot narrowboat. If I do the calcs my single internal skin tank is nowhere near big enough. However I've done extensive cruising on the Thames, sometimes against quite strong flow, and I've never had an over-heating issue. A lot of the time, once the first thermostat opens and engine cooling water flows through the calorifier, that provides sufficient cooling. Why not try it for a while and see how it goes?

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8 minutes ago, RichLech said:

I've got a Barrus Shire 45 in a 52 foot narrowboat. If I do the calcs my single internal skin tank is nowhere near big enough. However I've done extensive cruising on the Thames, sometimes against quite strong flow, and I've never had an over-heating issue. A lot of the time, once the first thermostat opens and engine cooling water flows through the calorifier, that provides sufficient cooling. Why not try it for a while and see how it goes?

 

Only until the calorifier has heated up then it adds no extra cooling unless you run domestic hot water off. That action gives the Mrs M a safety procedure to use if the skin tank turns out to be too small and the engine overheats.

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Yes, worth trying it out and characterising it thoroughly before committing to a fairly expensive modification. The area of the skin tank isn't the full story: the baffles and tank thickness have a big influence on the thermal performance. My tank is a bit undersized according to the Beta estimate, but I've had no overheating problems since fitting a well-matched prop.

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As a long term solution a bigger skin tank is the answer but I have seen car / van engines installed pretty much straight out of the vehicle complete with fans and rads and they worked sort of OK. Nowadays most car rads are complete with electric fans and shrouds so I reckon a bit of basic plumbing and bodged wiring would assist the cooling just fine. Might make the engine compartment a bit warm though.

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1 minute ago, Bee said:

As a long term solution a bigger skin tank is the answer but I have seen car / van engines installed pretty much straight out of the vehicle complete with fans and rads and they worked sort of OK. Nowadays most car rads are complete with electric fans and shrouds so I reckon a bit of basic plumbing and bodged wiring would assist the cooling just fine. Might make the engine compartment a bit warm though.

The prime method of cooling a car radiator is air flow surely? The fan is just for assistance, usually when stationary. The fan would be running permanently and the heat would not dissipate.

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Most boats with skin tank are under cooled when you measure the area. Very few boats can use the full power of the engine before the hull and water interaction limit the speed.

Most owners don't worry about it and just enjoy their boating without ever realising it.

 

Consider adding a plate heat exchanger to the calorimeter circuit to heat the radiators in the boat, you can dump a lot of heat that way without dumping your hot water overboard. And in winter you have a toasty boat even with the doors open.

TD'

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