Air Cooled Gas Engines????

[CaptPPan]

I have a 27' boat powered by a 330hp freshwater cooled Crusader Inboard. I use the boat year round in the North East to commute to work. In the summer I'm constantly cleaning the strainer of eelgrass and debree and in the winter I'm plagued with ice jams and freezeups. Why can't I just but a radiator and some electric fans in place of the entire raw water part of the cooling system??

[yipster]

RITE, i know what you mean!
boats dont have drivewind cooling like cars, salt water spray etc. recently did see a heckdrive with closed big radiator cooling system on the engine, whats holding that system?

[TheFisher]

It's almost impossible to get enough airflow with electric fans in that situation.

[BVI Jon]

How about bilge or keel coolers?

Keel coolers are a common thing and can be installed with ease. Check with your local yard. There maybe a trashed wooden work boat hull, with one for your needs.

[8knots]

If your hull is of the planing style, Make sure you will have the keel coolers in the water at all times. Your engine puts off a lot of BTU's in heat it needs to get rid of! I study slow displacement style hulls and see them installed all the time. I can't remember seeing them on a smaller fast boat. I may be all washed up so do keep asking these guys. You may be concerned with drag issues also. single engine will usually only require one cooler mounted port or starboard. Not sure what that would do to you performance wise!
8Knots

[yipster]

thanks 8knots, planing is planing and even bilgewater cooling isnt than such a great idea.
the problems capt p pan describes are very real, i blew an engine in seaweed not so long ago just becouse the audio alarm wire was lose.

yipster

[CaptPPan]

Thanks guys,

The boat does better then thirty so why would'nt I be able to get enought air flow?

The other problems I just thought of are. How do I cool the Risers? Right now there raw water cooled. I'm also force feeding the stuffing box with raw water to keep it from overheating but i guess I can install one of those dripless packings.

[Buck]

CaptPPan, we've got a lot in common. I've been wondering about a radiator system as well. You have also commented on my thread about shafts thru the transom. As far a getting enough air, I've been wondering about cowling intakes (like on a jet) on the hull toward the bow that run back to the engine area thru ducts that divert inside between the hull liner and hull. I'm not a boat designer or engineer (found my true love too late in life to prusue) but maybe some members can comment.

[8knots]

Buck
I might put those up say... on the side of the top house, I would worry about water getting in there when your at speed in a chop!
You might figure out some kind of baffeled box inside the hull so the intake draws from the top and the bottom would be self bailing. you would have to have fan fed so at low speed she does nnot overheat. Glad to see somebody from home. My family lives just up the road in Urbanna!
8Knots

[mmd]

Yes you can run an air-cooled engine, but you had best do a bunch of investigation and a bit of calculation before you commit to something that can easily become an very expensive failed experiment. You will have to address the following:

1.) Calculate how much radiator surface area is required to cool the engine coolant to the engine manufacturer's parameters.
2.) Calculate how much air flow is required over the radiator to achieve the required heat loss of the coolant.
3.) Arrange the radiator so that air flow can be maintained without ingress of water, be it rain or seawater. This usually means a separate, watertight radiator compartment with water trap and drain system.
4.) Refit the engine with a dry exhaust system, complete with silencer and adequate thermal insulation & lagging.
5.) Refit the engine with a higher capacity coolant water pump.
6.) Design a forced-air supply system with thermostatic control so that adequate air flow can be maintained over the radiator when the engine is still hot but boatspeed/natural airflow is low, such as motoring through marina approaches after a high-speed romp across the bay.

Keep in mind that the cooling system will have to be larger capacity than for that size motor in an automobile. In a car, the engine is open to the surrounding atmosphere underneath the car, so a lot of heat is radiated into the atmosphere; in a boat you have basically placed it in an insulated box, so all cooling has to be done through heat transfer to the coolant. Because of this, you need to beef up the radiator size and the coolant flow rate.

[gonzo]

Another problem to solve is the higher temperature in the engine room created by dry exhaust pipes. The HP of the engine would drop considerably. Also, it would probably be illegal.

[mmd]

Gonzo, I agree that higher engine space temps would rob horsepower (making engine compartment ventilation a priority), but why would it be illegal?

[Corpus Skipper]

Under the assumption you have a freshwater heat exchanger, you could cure the icing problem by tapping the engine cooling circuit by running a hose off the block circulating pump, routing the hose along the raw water intake, coiling around the strainer, and returning through the intake manifold fitting near the thermostat housing, much the same as if adding a cabin heater fed by engine coolant. As far as the fouled strainer, we have the same problem here with shallow water and sea grass. Not sure who, (Groco, I think) makes a self cleaning strainer, but it's EXPENSIVE!!! I've had better luck not using a strainer. The grass is fine enough to pass through the heat exchangers and out the exhaust. I just pull the exchanger and exhaust elbows annually and clean them. How thick is eel grass? Since it's making it past the coarse strainer of your through hull fitting, I assume it's similar to our sea grass. Hope this helps!

[gonzo]

A dry exhaust is hot. Because it is in the same compartment as fuel lines, fuel tank and other combustibles, it becomes a fire hazard. That is what probably will make it illegal. It is possible to design a dry exhaust, but retrofitting is more difficult. Also, the law requires a muffler within three miles from shore.