adding more ventilation

[James Francis]

I have a 22 center console with a 350 marine power inboard. The existing ventilation to the engine is two front facing air scoops and two facing aft. The port scoop facing aft has the power blower connected to it. I want to add some more natural ventilation to the compartment because it is incredibly tight and gets very hot when trolling. I would like to put a vent in the front of the CC hatch right but I think that might be problematic given the potential of water spray entering the vent and being sucked into the flame arrestor/carb. My other thought was vents on the port side and starboard side of the CC which should draw some hot air out. Any thoughts on what might work best and what to avoid would be helpful.

Thanks

[gonzo]

You can run the blower.

[James Francis]

I do run the blower and it helps - but this engine seems as though it wants more air when it goes throttle up...

[Ike]

You have identified the problem with a lot of boats. Simply not enough air to the engine. The old trick to tell if this is so, is to simply open the engine hatch while the engine is running. If it speeds up you need more air. The Coast Guard regulations on ventilation are designed for one thing, to remove any gas fumes from the bilge. If the boat was built to the regulations or ABYC Standards it will do this, but they are not designed to provide enough air for the engine to run right or cool the engine compartment.

You are on the right track. WHat you need to do is provide more air while keeping the water out. This can be done using a manifold behind the vent that lets air pass up and over and drains water out, or you can simply put a hose on the vent that goes up 6 inches and then loops back down (like an upside down p trap) Water that enters the vent will drain back out and air will go up and over and down to the engine. The other thing is you don't need exteror cowls pointing forward or back. Research has shown that with natural ventilation, what is in and what is out is dependent on what way the wind is blowing and how fast the boat is moving.


Running the blower without providing more air will just create a low pressure system in your engine room and it will actually move less air.

[marshmat]

The blower's only real purpose is to get all the flammable/explosive fumes out of the bilge before any machinery is started, so that you don't blow the engine room across the lake. Its intakes are low in the bilge where fuel vapours collect. It doesn't bring much more air into your engine bay, it just clears out what's there.
Your problem sounds like a plain old lack of airflow. The solution is more vents, baffled as Peter describes to direct any incoming water away from the engine. Indeed, on some custom jet-skis the baffles on these vents are good enough that the entire boat can be submerged and resurfaced with the engine running, no problems. Basically, just make sure you give the water somewhere to go when it gets into the vent, and give the air somewhere different to go.