Why no Air-Cooling; in light of water's issues

[SeaKaye12]

Hi all, I hope this isn't too "off-the-wall" a question...

I've been around small boats all my life and am recently educating myself about larger vessels and their associated systems.

I'm new to sterndrives and notice post after post regarding corroded manifolds and risers, freeeze-cracked blocks and manifolds...all sorts of ruined engines because of overheating issues.

Especially in a salt-water application; is there some basic reason why an automotive style air-cooled radiator can't be used????

I know that it would have to be designed into the boat somehow...but it doesn't seem that it would be all that hard.

I know that there's plenty of water available on a boat to use for cooling purposes; but there's a lot of air as well.......Wouldn't it solve a lot of problems?

OK....I'll sit back now and await your answers.

Chuck

 

[thunderroad]

Re: Why no Air-Cooling; in light of water's issues

great question...and one I can't answer.
If you're talking about true air-cooled engines with cowling and cooling fins on the block, after being around ones used by Deutz in agricultural applications, I'd say one possible drawback would be the fact that they give off a trememdous amount of heat. In a tractor or combine this heat escapes into the air, whereas on a boat it would be tougher to do.
The thought of an air cooled engine for a boat is intriguing. Just think....catch a nice 70 degree day in Dec or Feb and head for the lake with your I/O, instead of just looking at it's winterized self sitting in the garage.

 

[HT32BSX115]

Re: Why no Air-Cooling; in light of water's issues

Air cooled engines are far less fuel efficient than liquid cooled engines (at high power settings rich mixtures are used to prevent high exhaust temps). This is why aircraft engine designers are moving towards liquid cooled engines again.

Liquid-to-liquid heat exchangers are FAR more efficient than liquid-to-air heat exchangers. (Water is also a FAR more efficient heat transfer medium than air and you have a ready source right under the boat!)

Air flow requirements for cooling would be MUCH more demanding (the fan would be HUGE and would take a lot of HP to run) in an air cooled boat since the continuous power levels are MUCH higher than in a car or motorcycle. (by the way most motorcycles are liquid cooled nowadays)


There have been air cooled outboard motors though. Lauson comes to mind....(I had a 3hp Lauson 4cy air cooled OB in the 60's)

Today you can buy a new Briggs & Stratton 5hp air cooled OB motor.

The air cooling requirements for a 7.4L air cooled V-8 would require a great big squirrel-cage fan. It would probably rob at least 30hp to move enough air .

If you used a radiator (air to water) it would require at least a radiator as large as the one in a full size pickup. You'd need an air intake (and output) at least as big as the radiator. (my "fresh water" heat exchanger for my 7.4L V-8 is only about 4-5" dia x 24" long)

I'll stay with liquid cooling.



Cheers,

Rick

 

[Bondo]

Re: Why no Air-Cooling; in light of water's issues

is there some basic reason why an automotive style air-cooled radiator can't be used????

Ayuh,.......
So Where are you going to Mount it,+ How are you going to get enough Air to it to cool it,..??......

 

[freddyray21]

Re: Why no Air-Cooling; in light of water's issues

it would seem to me you could mount it in front of the motor with a cooling fan and a combination of a ram induction system.

 

[Chris1956]

Re: Why no Air-Cooling; in light of water's issues

Freddy, An automotive type radiator could be used to cool a boat engine, however you would need ducts in the side or front (and rear)of the boat that are as large as the grill on your car, or perhaps larger. All that salt laden air (and air noise) would be sucked into the bilge, and then expelled. The size of the radiator would also cause significant design changes to the boat. In addition, you still need to cool the exhaust, so it doesn't melt the rubber couplings, or have a dry exhaust and it's required boat design changes.

As it turns out, water-to-water heat exchangers are more efficient and compact than radiators, and solve the water cooled exhaust issue as well.

 

[Windykid]

Re: Why no Air-Cooling; in light of water's issues

Not to mention if you are able to get that much air in there, you have to assume you can get that much water in the bilge area as well. Not good for the boyancy factor.

 

[SeaKaye12]

Re: Why no Air-Cooling; in light of water's issues

My mental (imaginary) design team puts the radiator (wide as the boat; maybe 6 or 8 inches high) across the stern of the boat.

The highest portion of the transom isn't used for much else anyway; is it?

Designers can do wonders when they start with a clean sheet and are given some $$$ to spend.

I wonder if anyone has even attempted this????

Just think...no salt water going anywhere in the engine bay....just nice soft, anti-freeze protected water flowing through your engine. Think of the minimal service that your auto's cooling system requires...over decades of use...

Thanks for reading, Chuck

 

[Haut Medoc]

Re: Why no Air-Cooling; in light of water's issues

My mental (imaginary) design team puts the radiator (wide as the boat; maybe 6 or 8 inches high) across the stern of the boat.

The highest portion of the transom isn't used for much else anyway; is it?

Designers can do wonders when they start with a clean sheet and are given some $$$ to spend.

I wonder if anyone has even attempted this????

Just think...no salt water going anywhere in the engine bay....just nice soft, anti-freeze protected water flowing through your engine. Think of the minimal service that your auto's cooling system requires...over decades of use...

Thanks for reading, Chuck

It sounds good, but the heat exchange is just to inefficient......
& with a closed cooled system you get years out of the exchanger 7 manifolds.......
The risers aree the only thing that need to be replaced with any frequency......

 

[erikgreen]

Re: Why no Air-Cooling; in light of water's issues

Like many good ideas, there are probably designs for this that would work. However, you're going to basically end up with 1-2 good designs that function as well as the water cooled engines, and they'll be more expensive to produce and more mechanically finicky than the water cooled versions, and because of the design changes needed they won't work for all uses.

You can't just drive the fan off the motor - it has to run on an electric motor like in a car, so you have airflow for cooling when the boat's not moving fast.

The transom is used for a lot by a lot of people... diver access, downriggers for fishing, etc... it's the most stable (least moving) part of the boat in any waves. You can't block it completely for most uses. You can assume you could for your design if you like... again, you can't build an air-cooled boat for all uses anyway.

So now in addition to all the current mechanical hardware and associated maintenance for a boat you want to add bulky ducting, fans, electricals to power it, more temperature monitors... it adds up in cost, complexity, and weight.

You should know that someone did figure out that you could submerge a radiator in the water under the boat and not pump water inside to a heat exchanger, that works well. Look up "keel cooling". Only works for hulls with their keel always in the water though.

Finally, remember that many boats don't have a lot of problems with cooling....mostly it's planing hulls. Displacement hulls can use a smaller motor in the same length hull and run cooler. Really large boats and ships can use an exhaust stack to get rid of the hot gases, and may well use an air cooling system, but they have the space... the volume of the hull increases as the cube of its length.

In short, you can make an air cooled boat, but I think most people would consider it far more cost and trouble than it's worth. Just spend the cash on preventative maintenance or switch to lake boating and call it good

Erik

Edit: PS: For another alternative you could build a big swamp boat/air boat... they're air cooled. Hmmm... deep vee swamp boat about 35 feet long... that would look cool..

 

[orion25]

Re: Why no Air-Cooling; in light of water's issues

Keep in mind that a car (mine does anyway) cruises at a good bit less than the 4800 RPM my 5.0 MPI hits when moving my boat at 50 MPH. My Jeep GC at 50 mph, about 1500RPM.

 

[whywhyzed]

Re: Why no Air-Cooling; in light of water's issues

no radiator because it all costs money and manufacturers make boat stuff cheap and nasty... changes in design are made to save 10 or 15 cents a unit... they aren't going to put radiators and fans in any time soon... they're still taking a brand new hull and cutting a huge hole in the transom to use shafts and gears to drive it...

 

[SeaKaye12]

Re: Why no Air-Cooling; in light of water's issues

Thanks for all the insight; thanks to ErikGreen for the Keel Cooling reference; that's something new to me; I've been enjoying reading about that...

Off to work now, Chuck