Need guidance on bilge ventilation, please.
 

Can you help me correct this bilge blower ventilation situation? Blower sucks on the lower plenum box and blows into an upper plenum box which communicates with the outer vent termination…the upper plenum has 2 additional open ports which makes me believe should be plugged to prevent recirculating the same air..there is no duct to the bottom of the bilge area. Should some of the ports be plugged and should some be left passive? I appreciate this forum immensely! Thanks!
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Blower sucking from the lower plenum area. Should one of these ports be used to loop down to the bilge and the other be plugged or left passive?
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Point A to point B view.
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Upper plenum box…Again should either of these 2 unused ports be plugged or left passive?
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The outside of the upper plenum box.

Should I lay down 2 hoses to the front and back of the bilge?
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Generally, the system can be setup so it has an inlet side and an outlet side. So it flows as you move through the air, purging uoir bilge air.

You want your fan pumped air to be drawn from the lowest part of the bilge, and exit directly out of the hull.

Keep in mind...the engine is pumping a lot of the air into the intake. Cruise at say 250cfm to be conservative...that is evacuating an 8x6x5ft volume per minute.

If you ever have a serious fuel spill in the bilge, the mixture may too rich to ignite...using the fans to remove the fumes can put the bilge mixture into the explosive zone by adding air.

I’m not sure I understand…I guess I’m wondering how it would have been from the factory 34 years ago…(I think it’s missing a hose or two).

The blower draws air currently from the lower collector box with 2 open ports. I suspect the 2 open ports should have a length of 3” to the stern area of the bilge and between the motor and the fuel tank part of the bilge? What would you do?

The blower blows 130 cfm to the upper collector box with 2 open ports (doesn’t exit the boat all the way just reaches the box)…since the open intake grille is on the opposite side I kinda lean towards leaving those 2 ports open but on the other hand worry about recirculating….maybe I can place a divider/dam inside the box to discourage easier recirculating of blower exhaust air?… Again, what would you do?

I appreciate the help.

On my twin eng Fountain, the starboard side vent louvers face fwd, on the port side, they face rearward. This creates a cross flow when on plane. The bilge blower connects to a port on the port side plenum box. That box has 2 other spots where a vent hose could connect but there's only one hose. The 2 vent ports that aren't used have duct tape sealing them off. Otherwise, fumes (heavier than air) removed from bottom of bilge could re-enter the bilge. Pretty sure it came like that from the factory.

Duplicate post.

This is my concern, but aren’t those 2 unused ports used as the passive air exit when going for a rip?

Can you feel the air coming out of the vents outside the boat? If not, what about shoving that hose further in?

some yes out the vent and some back through the ports…the vent kind of meanders upwards around the molded fiberglass. The tubing will not reach.

What does the port side plenum box look like? One side faces the bow to let air in as you're moving. Creating slightly higher pressure in the bilge. The opposite side faces aft and as the air passes by the vent. It aids in sucking the bilge air out. Along with the slightly higher air pressure from the bilge. If the plenum box shown faces forward. Then you're going to have to find out where the two holes in the deck next to the vent fan go.