Bilge Fans - independent or ganged

[Alanna Mo Cree]

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Source of the post My 360SS has all four bilge blowers going to the vents outside the hull, two on port and two on starboard. ...

Curious what the vents look like on that model.

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The two blowers on each side are mounted right next to each other, so even if one was sucking and one was blowing it would seem like the air would be pretty localized.

They are very loud and I can put my hand over the screens on either side to feel the air being blown out.

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So, if I understand you correctly there are two hoses on each side port and starboard connected to blowers which are evacuating air from the compartment and one hose allowing air back in on each side ? Yes

Is there any other fresh air venting for the engine compartment, just curious. Not saying you have an issue, would be nice to hear from someone that has the same boat as you.

Engines need fresh air to be efficient....fun fact, a running carbureted 454 will need around 75 CFM air at idle depending on the engine build ( efficiency)...up from there 1500rpm- 158 Cfm......3600rpm-378 Cfm....you can double that for two engines....all that air will to be pulled into the compartment and out the exhaust pipe by the engines alone.

The third hose on each side goes from the battery boxes forward to a point aft in the engine room, but I don't remember exactly where now. I'm pretty sure they end near the blowers.

The vent area is pretty large, as you can see in the pictures, with only one of the three sections taken up by the blower outlets.

[Jskhome62]

Sorry for being a bit late back on this thread. Haven’t been back out to the boat since posting my original question. Finally got back out and did some more tracing/troubleshooting. Here’s what I found.

I have 4 breakers on my bridge dc panel, one for each of the bilge blowers. The number 1 has to be on for any of the others to work but if number 1 is on, the rest will work in any combination. I’m guessing this is what the relays at each blower do. Maybe they’re also tied into the fire suppression system too but I have no way to test (nor do I hope to ever find out). And I confirmed again that once the main breaker for the dc bridge panel is on, I can start the blowers, with or without turning on the ignition (rotating the key, not turning over the engine) from either my main panel in the salon or from the switch at the helm. Which ever switch I use first, it is the only one that will work to turn them off again.

As for the blowers and hoses, I was wrong before and both blowers on either side of the boat are connected to the vents on the outside of the boat. The open hoses I was confused about before are connected to small vents on the face of my stairs and do just drop open in the front of the engine compartment. This would get fresh air from outside and away from the exhaust into the front of the engine compartment. I think the main make up air comes in through the larger part of the same vent panel where the bilge hose output connects. Guessing (hoping) the size of the opening vs the size of the output is what keeps any fumes from just being sucked back in.

Lastly, in the initial troubleshooting of the bad fans, I was able to press lightly on the center of the blade hub to get the fan spinning. This is how I knew it was a bad fan (warped housing, bad fan bearing, etc) and not an electrical problem.

Appreciate all the help and prompting that got me digging a bit deeper. With this better understanding, I think everything is configured as it should be.

[Alanna Mo Cree]

Source of the post Which ever switch I use first, it is the only one that will work to turn them off again.

It should be that if either switch is on then the blowers will run. Both switches have to be off for the blowers to be off. They are independent of the ignition to allow use with the generator and should be tied into the fire suppression system. I typically turn a blower switch on before flipping each blower breaker independently. This lets me hear each blower come on to confirm all four are working.

I just had the fire suppression system inspected last week and part of the test is to simulate a discharge. This will stop both engines and the blowers. On my boat it didn't stop the generator. The inspector said that doesn't fail the inspection, but it isn't a good idea to have any engines continuing to run in the space when the fire suppression is triggered.

Nice pic from the inside. How did you manage to get that one? I've been thinking about replacing my blower hoses and haven't been looking forward to the contortionism it will likely take to make that happen. I'm assuming the vent covers can be removed from the outside allowing access to the hose mounts and then I can use gravity to drop the hoses in to the engine room, but assumptions and boats seem to rarely work out.