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Old 07-05-2017, 01:33   #1
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Bilge blowers set up for Petrol Engines

Hi,

I'm in the process of a refit of two 350 mercruiser gas/petrol powered mercruoser engines.

Currently there is only a single blower on the starboard side but there is provision for one on either side.

I'm not quite sure how these work. I've read varying posts with some saying all should be set to exhaust the air from the bilge woke others say one should suck and one blow and one post where a member was adamant that the purpose of the blowers was to blow Siri to the bilge to push the air out.

Can someone in the know explain the correct process for venting the bilge?

I've attached a photo which shows the existing pipes coming from the external vents. There are four of these in total. Is there a reason each vent has two outlets ? See the two hoses? I'm confused. The other photo shows the location of the vents from outside.

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Old 07-05-2017, 02:04   #2
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Re: Bilge blowers set up for Petrol Engines

The blower exhausts the air from the lower area of each engine compartment. Fortunately we have the Coast Guard that has standardized the regulations with calculations, some handy references for resistance in ductwork and more.
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Old 07-05-2017, 03:22   #3
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Re: Bilge blowers set up for Petrol Engines

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The blower exhausts the air from the lower area of each engine compartment. Fortunately we have the Coast Guard that has standardized the regulations with calculations, some handy references for resistance in ductwork and more.


Any chance you can point me towards that info? I'm in Melbourne Australia.

Thanks for the reply.
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Old 07-05-2017, 03:27   #4
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Re: Bilge blowers set up for Petrol Engines

This will show you how to do it ....
Safe Ventilation of Gas Powered Boats
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Old 07-05-2017, 10:52   #5
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Re: Bilge blowers set up for Petrol Engines

Your probably good with one exhaust blower. Let fresh air in through the other opening, the exhaust blower it not worth a damn if trying to pulling a vacuum.
Open your engine room hatches prior to stating.
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Old 07-05-2017, 14:18   #6
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Re: Bilge blowers set up for Petrol Engines

I use radiator cooling 12 volt fans. They cost about seventy dollars each. They are axial compressors and although a bit noisy, they blow a hell of a lot more air INTO the compartment--and the exit intakes I mount low in the bilge and take them to outlets at the stern using ordinary splash-proof ventilators. You can have as many outlets as you like--but with two engines at least two would be advisable.

The reason I like to blow a lot of air INTO the engine compartments, since when the engines are running the power used is not a problem, is that there is no risk of a spark in an explosive atmosphere from the fan itself as there would be if sucking any fume-filled air out, and if fuel does become spilled, the more air flow taking it away the better.

I am told that petrol, mixed in the right proportions with oxygen, has about eight times the energy of nitroglycerine..

If the engines are not being used the bilges still need to be ventilated, a small snail-shell or axial turbine blower will draw about five amps or less and shift a lot of air in a day. They are supposed to be spark-proof, but I still believe in pushing air into these spaces and displacing the foul air out through ducted piping to deck outlets.. A solar panel is enough to keep this and a small back-up battery for night time use charged, if the boat is to be left unattended.

Then you also need a gas detector, with one element sampling the out-going air. If there is a developing source of fumes--you need to know about it.
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Old 07-05-2017, 14:26   #7
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Re: Bilge blowers set up for Petrol Engines

Any chance you can point me towards that info? I'm in Melbourne Australia.

Thanks for the reply.


Your Welcome.

The pdf. file is too large to attach here, and can be found at the following locations

https://www.uscgboating.org/regulati...ENTILATION.pdf

Boatbuilder's Handbook

Boat Building Regulations | Engine Compartment Ventilation

Was trying to recognize the manufacturer in your photos. Looks a little Burnscraft or early Bertram. If the bilge is any indication of the final outcome, I'd wager that things are going to be better than new by a wide margin.
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Old 07-05-2017, 14:38   #8
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Re: Bilge blowers set up for Petrol Engines

The pickup tube going to the outward blowing fan in ended low in the bilge to extract any gas fumes. The other tube is to let fresh air in so the fan works well.
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Old 07-05-2017, 23:36   #9
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Re: Bilge blowers set up for Petrol Engines

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Originally Posted by Three Sisters View Post
Any chance you can point me towards that info? I'm in Melbourne Australia.

Thanks for the reply.


Your Welcome.

The pdf. file is too large to attach here, and can be found at the following locations

https://www.uscgboating.org/regulati...ENTILATION.pdf

Boatbuilder's Handbook

Boat Building Regulations | Engine Compartment Ventilation

Was trying to recognize the manufacturer in your photos. Looks a little Burnscraft or early Bertram. If the bilge is any indication of the final outcome, I'd wager that things are going to be better than new by a wide margin.


Thanks so much. Really good links you've provided. Very Handy and just what the Dr ordered.

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