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Inboard engine on GRP cruiser - cooling options


Philip

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Basically I'm on the lookout for a new or well maintained used engine because my current one has seemingly had enough (suspected broken crank shaft). I currently have a Volvo MD11c model with 110 saildrive, which uses raw water cooling. 

 

I'm award that Beta custom-build engines to replace old Volvo md11s, such that through an adapter they can still fit to the old saildrive. However, I've read that all Beta engines use a closed system of cooling (fresh water). So my main question is, is it easy or possible to fit an engine with a fresh water cooling system into a fibreglass cruiser? I'm aware that I'll need a heat exchanger.

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1 hour ago, Philip said:

Basically I'm on the lookout for a new or well maintained used engine because my current one has seemingly had enough (suspected broken crank shaft). I currently have a Volvo MD11c model with 110 saildrive, which uses raw water cooling. 

 

I'm award that Beta custom-build engines to replace old Volvo md11s, such that through an adapter they can still fit to the old saildrive. However, I've read that all Beta engines use a closed system of cooling (fresh water). So my main question is, is it easy or possible to fit an engine with a fresh water cooling system into a fibreglass cruiser? I'm aware that I'll need a heat exchanger.

The Beta engines use a closed circuit cooling system as used in motor vehicles and a heat exchanger stack which fits over the exhaust manifold. A fresh water pump then feeds from the canal / river / sea into the heat exchanger and then overboard. That's what I have on my B50 engine and it's common practice on more modern units used in salty water boats. AFAIK that's what most fibreglass cruisers use - whether they're Ford, BMC, or whatever.  

 

If you look at their 16Hp seagoing engine here -

http://betamarine.co.uk/portfolio-item/beta-16/

you'll see at the rear a block with Bata MArine written on it - that the integral heat exchanger - sea water and exhaust gasses are discharged through it through rubber pipes - overboard. Seawater is pumped up through a skin fitting (or preferably a 'mud box' on inland waters) by an additional pump which you can see on the far left of the photo.

Does that help?

 

 

Edited by OldGoat
more clarity (??)
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There is no reason an engine that uses indirect raw water cooling (what Old Goat described) can not be easily modified for keel cooling but I ma not so sure about the wisdom of doing than for canal as opposed to river use. However if you have a sail drive without impact damage problems keel cooling shoudl be fine.

The heat exchanger should come as part of the engine as supplied. The only thing I am unsure about is if the raw water is drawn up through the sail drive leg if the pipework etc could support the volume required for heat exchanger indirect cooling.

.

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2 hours ago, Tony Brooks said:

There is no reason an engine that uses indirect raw water cooling (what Old Goat described) can not be easily modified for keel cooling but I ma not so sure about the wisdom of doing than for canal as opposed to river use. However if you have a sail drive without impact damage problems keel cooling shoudl be fine.

The heat exchanger should come as part of the engine as supplied. The only thing I am unsure about is if the raw water is drawn up through the sail drive leg if the pipework etc could support the volume required for heat exchanger indirect cooling.

.

Aha - I didn't consider that last point. Not being used to salty stuff, I didn't realise that sail drive dealt with water inlet as well.. Interesting. 

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Thanks for the help. It seems the heat exchange system should work fine, the saildrive currently does draw water in from the canal. The main things to consider are special feet for the engine mounts if needed and also the fact that the saildrive and prop on mine are configured the opposite way round compared to the normal Beta design 9and most designs by the looks of it). The prop is located directly under the engine on mine.

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10 hours ago, OldGoat said:

Aha - I didn't consider that last point. Not being used to salty stuff, I didn't realise that sail drive dealt with water inlet as well.. Interesting. 

I am not sure, I just think some may to save another hole in the hull seeing it has an enormous one already. I thought it best to warn it MIGHT be the case. If so just using the raw water for the exhaust shoudl be fine but that implies a keel cooling system. If I am right I would try it with the heat exchanger first before doing anything else.

 

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1 minute ago, Philip said:

Thanks for the help. It seems the heat exchange system should work fine, the saildrive currently does draw water in from the canal. The main things to consider are special feet for the engine mounts if needed and also the fact that the saildrive and prop on mine are configured the opposite way round compared to the normal Beta design 9and most designs by the looks of it). The prop is located directly under the engine on mine.

I have no experience of sail drives but I would have thought there was a  good chance the led is secured to the bevel box (the bit behind the flywheel housing)  by studs and nuts so it MIGHT be possible to take the leg off, twist it through 180 degrees & refit.

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3 hours ago, Tony Brooks said:

I have no experience of sail drives but I would have thought there was a  good chance the led is secured to the bevel box (the bit behind the flywheel housing)  by studs and nuts so it MIGHT be possible to take the leg off, twist it through 180 degrees & refit.

Unless its got an odd number of studs...

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Beta do replacement feet to fit the spacing of the old Volvo engine as part of their package. Whether or not that will work for the saildrive, I know not.

They're very approachable - give 'em a bell! 

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I've spoken to Beta and they have pointed me towards their 20 engine as the best replacement for the Volvo whilst keeping the original saildrive and leg. Is it correct that the Beta 20 is slightly shorter and shallower than the Vovlo MD11C, despite having an extra cylinder? I have found the dimnsions for the Beta 20 but struggling to find online dimensions for the MD11c. The Beta is 3600rpm, compared to the MD11c being 2500. So it would have to be rev limited to that point if I kept the same prop. That would still give around 15hp which I gather is still plenty for a cruiser? The only possible issues might be whether there is clearance for the weedhatch (it is located on the right edge of the engine bay on my boat) and the water pump is located on the rear side of the engine (the alternator end), so access to it might be difficult if there's not much room between the engine and the stern.

Edited by Philip
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Not so sure about having to be rev limited. It all depends upon the maximum torque the engine will supply at what speed and hence prop size. I suspect it may limit itself by refusing to accelerate after a certain point but what that speed will be is open to question without the two torque curves and the prop curve.

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  • 3 weeks later...

Well to update things...I've now ordered a Beta 20 engine as a replacement for the MD11c. So far Beta have been very good; the existing saildrive and prop arrangement can remain in situ by use of an adapter to connect to the Kubota; heat exchanger to combine raw water cooling with fresh water; and they can fit the water pump on the more convenient side. I have a question regarding the control panel which comes with the package, I've gone for the standard 'ABV' panel which has warning lights and alarm buzzers for high water temperature, low oil pressure and no alternator charge, but no actual gauges for these. Are these lights and alarms generally reliable and do they give reasonable notice before the situation gets to a critical stage?

Edited by Philip
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This implies that it will be a wet exhaust boat so you need to  find out what the water temperature light is monitoring. If its the actual engine temperature then a raw water failure will take a short while to show and there will be enough time to burn the inside of the exhaust hose or I have known burn right through "rubber" silencers. If it were my boat I would want the temperature of the exhaust mixing elbow monitoring by either the existing light or an add on sensor and light/buzzer.

The oil pressure switch is probably not as reliable as one would hope but most times you get a low oil pressure warning its the switch that is at fault. Ditto the temperature switch.

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  • 2 weeks later...

I've upgraded the panel to the 'B' version, this includes a water temperature gauge which seems a sensible thing to have. I've read a few reports about these engines being prone to overheating, even when the water pump is working properly and that it's to do with a lack of ventilation. Is this common? One of the reports I've seen dates from as long ago as 2007 to be fair.

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9 minutes ago, Philip said:

I've upgraded the panel to the 'B' version, this includes a water temperature gauge which seems a sensible thing to have. I've read a few reports about these engines being prone to overheating, even when the water pump is working properly and that it's to do with a lack of ventilation. Is this common? One of the reports I've seen dates from as long ago as 2007 to be fair.

Not as far as I am aware. However ANY engine with cooling that relies on raw water requires far more vigilance than a tank or keel cooled one because, even at sea, its all too easy to get a blockage in the raw water system and that inevitably leads to an overheat if it is not noticed.

Then there is a question about how well owners maintain their raw water pumps. My experience suggests far too many only think about it once it has failed and caused an overheat when annual inspections of the impeller are vital in my view.

I am far from clear what the sea strainer/weed trap/mud box arrangement is on a system drawing water up a leg, it might just be a perforated cover over the inlet hole. That is not the best idea in my view, especially when plastic bags are floating in the water.

I do not see that a Beta engine will be any more susceptible to overheating than the Volvo although the degree of damage resulting from prolonged overheating may be more. Ventilation is down to whoever did the installation, not the base engine. lack of ventilation is likely to cause loss of power and black smoke long before an overheat.

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Philip,

I've had a BD722 (20hp) in 'Kingsbridge', a 35ft Liverpool boat, since 1998. It's got 3800 hours on it and hasn't, up to now, shown any tendency to overheat. I have to admit it got up to about 88C indicated when I opened it up a bit on the Weaver on a very warm day, but for normal canal speeds it varies between 65C and 80C depending on the prevailing weather. It's keel cooled with a slightly undersized tank on the swim.

I'd like an engine that runs at a lower rpm when cruising (1800 - 2200 for 2.8 - 3.2 mph, and I wouldn't like to spend much time with it at 3000+) but it's been a very smooth and reliable engine. I suppose that having said that I'll need to call  RCR the next time we leave the moorings.

Mike.

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IME heat exchanger cooled engines run cooler than conventional engines in a NB (at least). That's because there's no hot exhaust manifold or silencer to heat the engine space - it's all in the fresh water....

If the fresh water inlet gets blocked - then you soon notice it by the large amount of water vapour in the exhaust as well as a change in pitch.

I expect it's similar for a fibreglass boat - except that the exhaust is usually nearer the waterline and to the rear.

My concern is that these don't have an adequate mud box as they're designed for clear waters and not muddy ditches. If not fitted, I'd be inclined to fit a large Vetus water filter - certainly larger boats have at least one per engine. 

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On 2017-6-5 at 17:52, OldGoat said:

IME heat exchanger cooled engines run cooler than conventional engines in a NB (at least). That's because there's no hot exhaust manifold or silencer to heat the engine space - it's all in the fresh water....

If the fresh water inlet gets blocked - then you soon notice it by the large amount of water vapour in the exhaust as well as a change in pitch.

I expect it's similar for a fibreglass boat - except that the exhaust is usually nearer the waterline and to the rear.

My concern is that these don't have an adequate mud box as they're designed for clear waters and not muddy ditches. If not fitted, I'd be inclined to fit a large Vetus water filter - certainly larger boats have at least one per engine. 

Do you mean a strainer? If so my boat already has one, although it's not enough to filter fine particles like sediment, just big things like plastic bags.

Unfortunately heat exchanged engine is the only option other than a petrol outboard or air cooled. Keel cooling is no good for shallow canals with all their obstructions. I guess the heat exchanger cooling system is slightly more fascinating due to its hybrid nature, although I know only too well how important it is to check the water pump and impeller regularly for signs of wear. On the Volvo the impeller broke up which caused a blockage and the inevitable furnace. 

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  • 2 weeks later...

All being well and providing no issues with installation my boat should have a brand new Kubota/Beta in it this time in two weeks. Am I right in thinking the saildrive leg is a more reliable means of drawing raw cooling water in to the system than the seacock? The leg has six small inlet holes to draw water in, I'm assuming with a seacock there's just the one opening?

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Yes and its a fair big larger although some bots have a perforated strainer over the sea-inlet hole. Problem is it tends to such polythene or paper over the strainer and you can't shove a mooring spike down the hole to clear it. I suspect the prop will keep your inlet holes free of such problems.

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  • 1 month later...

Well the engine is in and having given it a 'wearing in' session, it seems very sound. Biggest difference compared to the Volvo is the lack of exhaust smoke!

 

However a new prop with a smaller pitch is needed because of the higher higher rpm. I've gone for a 14x7 2-blade propeller. Are there any differences between a 2-blade and a 3-blade in terms of performance, handling, prop wash etc? 

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If it's not been covered before, IMO it's essential to have a 'sensible' filter that can easily be accessed above the waterline - of the Vetus type. The sail drive leg may prevent anything large getting through, but smaller bit will het through and that will quickly demolish the rubber impeller in the sea water pump.

If you raise the saildrive leg - how then will you charge the batteries. To my mind a hole on the hull with a seacock and filter is better on the canals.

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6 minutes ago, OldGoat said:

If it's not been covered before, IMO it's essential to have a 'sensible' filter that can easily be accessed above the waterline - of the Vetus type. The sail drive leg may prevent anything large getting through, but smaller bit will het through and that will quickly demolish the rubber impeller in the sea water pump.

If you raise the saildrive leg - how then will you charge the batteries. To my mind a hole on the hull with a seacock and filter is better on the canals.

Even better than 1 Seacock is to have 2  of them Branching into a Tee or Y connector.if a single Intake becomes partially blocked it will suck all the Detritus into the Cooling Pump.if there is a second Path for it to draw from the Detritus will often drop back out next time the Engine is stopped.

Sounds like a strange way to do it but it works,most Thames/Broads Hire Craft are arranged this way.

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5 minutes ago, cereal tiller said:

Even better than 1 Seacock is to have 2  of them Branching into a Tee or Y connector.if a single Intake becomes partially blocked it will suck all the Detritus into the Cooling Pump.if there is a second Path for it to draw from the Detritus will often drop back out next time the Engine is stopped.

Sounds like a strange way to do it but it works,most Thames/Broads Hire Craft are arranged this way.

That's neat -self clearing weed traps - save having to rely on the hirer doing something....

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