Raw water cooling vs. fresh...basics, please

[Greenheart]

Running waterheated radiators in a small boat is a nightmare, although possible in larger boats.

I believe you, but why is it difficult in little boats?

Having hot water available transforms boat life and the water stays hot overnight for a shave in the morning.

Just my way of thinking...so I'm guessing the issue is space, to house enough hot water, plus thick insulation to keep it hot. I'd sacrifice some sail-locker space for a big h/w tank.

I confess again, how little I know. It just seems perverse to be working hard to throw heat overboard with one hand, whilst struggling with the other hand to keep the cabin/domestic water supply warm enough.

(Calorifier) ...heats up really quickly, within minutes of starting the engine, and stays hot seemingly for ever.

That sounds terrific - but (bear with me) isn't it connected to the exhaust? If it isn't a central part of the cooling process, it must only use a small percentage of the waste heat.

I'd like to see a miniature steam-engine making use of all the waste-heat, but realistically, doesn't it make sense to find room for biggest possible calorifiers each boat can fit?

 

[prv]

That sounds terrific - but (bear with me) isn't it connected to the exhaust? If it isn't a central part of the cooling process, it must only use a small percentage of the waste heat.

Not to the exhaust, no. It's connected to the freshwater circuit that goes round the engine. The engine water goes through a coil in the middle of the domestic hotwater tank, and heats it up. So it's pretty central (the reason it heats up so fast) but I imagine that once the tank is up to temperature it's not pulling all that much heat out of the engine system, no.

The calorifier we have is about the biggest one that could be fitted, but with a large aft cabin we have little "dead" space and not enough locker capacity as it is.

Bear in mind also, that most of the time we're sailing, we don't want to heat the cabin because it's summer. Designing the whole engine installation and space layout around an ultra-efficient heating system makes no sense unless your boat is destined for the Arctic.

Pete

 

[Tranona]

I believe you, but why is it difficult in little boats?

Simple. Lots of things in the way such as bulkheads, tanks, batteries etc for pipe runs. You would need a positive pump to circulate the water. Fitting panel type radiators would be difficult because there is nowhere big enough and flat enough to attach them. Blown matrix heaters are possible but they are bulky, take up valuable storage space and require a fan to make them work. On top of all this you still have the problem of storing enough water to keep them hot. Therefore they would only work when the engine is running which on a sailboat is not when you need the heat.

Suggest you try and fit even a 30l calorifier into a boat less than 30' in length just to appreciate what the constraints are. Then you will understand why blown air diesel fired heaters such as Ebers etc are the only practical form of heating on a small boat except for those who like the traditional fire types - diesel, paraffin, charcoal fueled that sit on the bulkhead.

 

[Greenheart]

Thanks for the replies, gents. I'm unexpectedly busy right now, I'll give it all a close re-read later/soon.

 

[cryan]

In George Orwell's terms. Sea water Cooling Bad! Fresh Water Cooling Good!
Sea Water is a very corrosive fluid so minimising its contact with components is the goal to aim for. FW cooling allows you to keep the cooling water in the optimum condition for cooling the water and reduces the build up of contaminants that reduce heat transfer. In the long run this will save you a considerable amount of time and money.
Keel cooling is required for ships lifeboats to prevent someone forgetting to open the cooling valve in the chaos of abandoning ship. They are usually set up as a series of bronze pipes mounted next to the bilge keel.

 

[wipe_out]

It's actually an interesting question, specifically in sail boats, why use sea water at all other than because its there and is the easy option??

The sail boat engines are typically in the 8-40hp range.. The excess heat that would need to be disposed of would only need a relatively small radiator and some air movement.. Thinking back to my Motocross bike riding days with engines producing similar power the radiators were pretty small and the amount of air flow they needed wasn't that great.. There is easily enough space in most sail boats to accommodate what's needed..

So a simple fan assisted radiator with access to outside air , possibly through ducts with an inlet and exhaust, would mean no issues dealing with sea water at all.. It would have to be designed at boat build time to cater for the ducts etc. but it seems feasible..

Obviously wouldn't work with power boats as the waste heat generated by the large engines would be too much and so the radiator and venting system would be quite large..

Anyway, just thinking outside the box (or engine bay as the case may be)..

 

[fisherman]

Consider this: I want to run the engine for a short while when the boat is on the beach. I am looking into inter-inter cooling, running fresh water where there would normally be salt, through a keel cooler. One thought is to make the bilge keels from 3" steel pipe and run the raw circuit through them, but it would be simpler to fit external keel cooling pipework. Problems? Well if I get a leak there will be salt water where there would usually be....salt water, and it would quickly become evident when hauled out. Only question is capacity. About 50hp, calcs suggest about 22ft of 3" pipe. Not sure the engine would stay cool for long after a long run and immediate hauling out.
Many years ago there was a boat with gardner bus engine complete with radiator and fan, ran OK.

 

[Plevier]

As for the water boiling, I believe the Lister D series engines worked this way - an open trough of water around the cylinder head and you would pour buckets of water into it while running to keep the level up as it boiled off! There's a brass tap at the bottom, presumably to empty the remaining water at the end of a run but perhaps you could pour it straight into a teapot while running...

http://www.antiques-atlas.com/antique/lister_a_stationary_engine/as172a187

Saw one at a fair years ago simmering gently!

 

[rob2]

It should be possible to mount a smallish car radiatorand a bank of computer fans under a bunk with a diverter to select either radiator or normal heat exchanger. Of course, you lose the stowage beneath the bunk as you must not obstruct the airflow - perhaps if you fit a lockable diverter, the space could stil be used in summer. It would have the advantage that it would only be of use with the engine running, so the current to run the fans shouldn't impact on your battery capacity. Just a thought...

Rob.

 

[prv]

So a simple fan assisted radiator with access to outside air , possibly through ducts with an inlet and exhaust, would mean no issues dealing with sea water at all..

True, but would introduce the rather significant issue of two big holes in the boat

It is done on some canal boats, because the water for them is always flat and the boat is always upright. But a sailing boat on the sea needs to be properly waterproof from all directions - most of the time the main hatch stays open, but even that should be capable of being closed against major flooding (they're rarely fully watertight) in very rough conditions.

Pete

 

[vyv_cox]

So a simple fan assisted radiator with access to outside air , possibly through ducts with an inlet and exhaust, would mean no issues dealing with sea water at all.. It would have to be designed at boat build time to cater for the ducts etc. but it seems feasible..

You would still need to cool the exhaust hose and manifold with seawater. There are boats around with uncooled exhausts but they need special precautions to overcome the high temperatures involved. They often tend to be noisy.

 

[ghostlymoron]

It should be possible to mount a smallish car radiatorand a bank of computer fans under a bunk with a diverter to select either radiator or normal heat exchanger. Of course, you lose the stowage beneath the bunk as you must not obstruct the airflow - perhaps if you fit a lockable diverter, the space could stil be used in summer. It would have the advantage that it would only be of use with the engine running, so the current to run the fans shouldn't impact on your battery capacity. Just a thought...

Rob.

This is precisely why such a system is impractical on a small boat where storage space is at a premium. On a larger boat there's plenty of locker space.

 

[fisherman]

You would still need to cool the exhaust hose and manifold with seawater. There are boats around with uncooled exhausts but they need special precautions to overcome the high temperatures involved. They often tend to be noisy.

I wouldn't change my dry exhaust: I know exactly how my cooling water is flowing, no worries about syphoning and melting boxes, it isn't noisy, it is 2" pipe lagged with preformed pipe cladding, to a lorry silencer above deck in a stack with a venturi extractor at the top. Not ideal for most leisure boats though.

 

[Greenheart]

How impractical would it be to have a sort of tubing coil, like the steel hoops that keep fishing nets open, which you could drop over the stern when motoring, and through which fresh-water coolant could be pumped to keep an on-board coolant reservoir, cool?

If the coil in the water was damaged or dislodged, there'd still be the reservoir of coolant on the yacht, so there wouldn't be an instant overheating problem.

Isn't it often the case that the sea in winter/spring is warmer than the air? Wouldn't it be worth having a small manifold of coolant-cooling pipes on deck, where the heat would encounter a greater temperature contrast?

Is there a reason not to have a variety of methods aboard for cooling fresh-water coolant? If one fails there'd be another and their combined efforts could be better than one alone.

 

[wipe_out]

True, but would introduce the rather significant issue of two big holes in the boat

It is done on some canal boats, because the water for them is always flat and the boat is always upright. But a sailing boat on the sea needs to be properly waterproof from all directions - most of the time the main hatch stays open, but even that should be capable of being closed against major flooding (they're rarely fully watertight) in very rough conditions.

Pete

A minor hurdle to over come..

I initially envisaged two ducts vertically from the general engine area, perhaps coming out somewhere around the spray hood although that wouldn't be nice from a noise or comfort perspective.. One for intake of cool air and one for exhaust of the hot air.. The exhaust could be diverted into the cabin for additional heating while under way if required.. As for water ingress, some "mushroom" type vent would solve that..

Alternatively the radiator and fan assembly would probably be relatively small so could even be mounted in on of the aft quarters with vents that don't allow water to enter.. Problem there is the lengths of plumbing that would be needed..

I am sure if clever engineer types thought about it they could come up with a freshwater/air cooled arrangement but it's easier (and cheaper probably) to just suck in some sea water and spit out out again.. One the manufacturers warranty is up the damage cause by the sea water is the owners problem..

 

[wipe_out]

You would still need to cool the exhaust hose and manifold with seawater. There are boats around with uncooled exhausts but they need special precautions to overcome the high temperatures involved. They often tend to be noisy.

I really don't see that as an issue.. A thermal shield of some kind and a silencer is all that would be needed..

 

[vyv_cox]

I really don't see that as an issue.. A thermal shield of some kind and a silencer is all that would be needed..

On most boats the exhaust hose runs for a significant proportion of the boat's length, because the engine is placed well forward. Taking mine as an example, it runs along the tunnel, through a bulkhead into the lazarette, along its floor then up to a silencer and back down to the skin fitting. This would all need to be insulated (very well) and supported on flexible mounts to cater for engine movement. Seems a very complex requirement as an alternative to a system that works perfectly well in millions of boats worldwide.

 

[fisherman]

On most boats the exhaust hose runs for a significant proportion of the boat's length, because the engine is placed well forward. Taking mine as an example, it runs along the tunnel, through a bulkhead into the lazarette, along its floor then up to a silencer and back down to the skin fitting. This would all need to be insulated (very well) and supported on flexible mounts to cater for engine movement. Seems a very complex requirement as an alternative to a system that works perfectly well in millions of boats worldwide.

One of my boats had an aircooled engine with water cooled exhaust. My dry exhaust has a flexible S/S bellows nearest the manifold, necessary not to apply weight/strain to the studs.
Deutz do aircooled up to 500+HP:
http://www.deutzuk.com/file/8a85818a1840a9160118504688fd135b.en.0/luftgekuehlte_motoren_e.pdf

 

[wipe_out]

Seems a very complex requirement as an alternative to a system that works perfectly well in millions of boats worldwide.

At the end of the day it's all hypothetical anyway but yes there would obviously be issues to overcome..

 

[wipe_out]

One of my boats had an aircooled engine with water cooled exhaust. My dry exhaust has a flexible S/S bellows nearest the manifold, necessary not to apply weight/strain to the studs.
Deutz do aircooled up to 500+HP:
http://www.deutzuk.com/file/8a85818a1840a9160118504688fd135b.en.0/luftgekuehlte_motoren_e.pdf

Some interesting designs there.. Would mean no water cooling at all.. Very good ventilation in the engine bay needed though to extract the warm air..