Bilge Ventilation using Nicro Solar Vents

[PeteHalstedc]

Thanks for all the replies so far. A few of the replies talked about cabin ventilation, and that has been one of my issues trying to research ventilation. Most of it refers to venting the cabin, especially when unattended.

In our case, it will be a liveaboard, on the gulf coast. So Cabin will have A/C going 8-9 months out of the year. So I am not looking for info on venting the cabin itself, just trying to see what would be best to keep the build from becoming a science experiment.

Yes right now there are 4 vents, 2 facing forward, and 2 facing aft, about 10 feet apart, all with 4" ducts running to the bottom of the bilge.

There are 2 separate 3" ducts running to louvers on the sides, that have the bilge blowers in them for clearing fumes before starting.

I am sure the front two provide fresh air for engines when running as well, but I am guessing the design with the 2 facing aft is to provide passive ventilation when not running as well.

I am thinking that adding the solar vents to the two aft ones, in exhaust mode is probably my best option, that was they can draw fresh air in from the front vents down across the bilge and exhaust it out, but while under way the two front vents will not not have any restrictions that will keep them from pulling in enough air to keep the engines happy.

Please keep the comments, and experiences coming.

No matter what I do I have to pull these vents up and beef up/repair the core in those areas and then rebed them. "Surpisely" a couple tubes of 5200 around the vent over the years, instead of someone rebedding them properly, did not do the core any favors in those areas, and they are a bit soft when my 375 pound farm fed frame goes up to the bow!

[Lepke]

Bilge vents will stop the "boat" smell. As mentioned earlier, make sure you're drawing from the bilge so the smells don't pass thru the cabin. Also, people create much of the moisture inside a hull (cooking, showers, breathing, etc.) Properly venting cooking and shower moisture will keep the boat drier.
I have a wood boat and force vent my bilges. Power isn't an issue, but I use square, computer style 12v fans to remove the air and in some places to move the air around. I also vent below deck cabinets and closets to keep things dry.
If you use a biocide in your paints and varnishes, you won't have a mold problem.

[Kiwi.]

".......these are simply for bilge ventilation....." Sorry, but I think you're wrong.

Two 350ci gas motors running at 3000rpm need about one million (1,050,000) cubic inches of fresh air per minute to feed them. This air does not go out through your extractor vents, it goes out through the engine exhausts. The calculation is quite simple:
350ci times 2 motors times 3000rpm equals 2,100,000
Divide by 2 for four stroke motors equals 1,050,000.
A solar vent, or any other type of active vent, that delivers less than 1,050,000ci of air per minute will simply get in the way of this massive required airflow. Putting in Nicros would rob your engines of horsepower and, particularly if they are still original carburettor models, cause them to lean-out and blow-up.
A 4 inch Nicro gives 28,800 ci per minute so you would need 36 of them to feed your motors at 3000rpm!

[Uncle Bob]

Just a further comment regarding my distain for the modern nicro vents, when purchased my boat came with three old nicro vents, still working but the clear plastic had deteriorated to the extent that it was disintegrating, age unknown though obviously old so I replaced with new of the same. Yes I had to replace a couple of batteries, no problem, but they still were lackluster and then died, no solar panel output, no part available from manufacturer, recommended purchase of new unit. The old ones lasted just past the warranty!! At A$300.00 each. I still think it's a crap shoot if you get a good one.

[Nicholson58]

Originally Posted by Canibul

just open them up and replace the battery with a better C-cell rechargable, they actually work just fine.

This is also what we have found. I think they have a limited shelf life and may sit in their box on the shelf way too long. I have two installed over heads. New NiCad batteries - no problem. Does anyone know if LI battery replacements are available and will they work?

[PeteHalstedc]

Originally Posted by Kiwi.

".......these are simply for bilge ventilation....." Sorry, but I think you're wrong.

Two 350ci gas motors running at 3000rpm need about one million (1,050,000) cubic inches of fresh air per minute to feed them.

Ok, I believe you, and that is why I think the front two that are facing forward, provide that function and why I was thinking that they should not get solar vents.

I don't think those engines need all four 4" ducts to feed them air, my reasoning being go open the hood on a 1975 Chevy and you will find that factory breather attaches to a duct that is probably 2 to 2 1/2 inches. So I would think that 4" duct facing forward can feed one engine.

Just not sure, Would love to keep air moving in the bilge and hopefully keep it dryer and better smelling. But as you say I sure don't want to starve the engines either.