Exhaust vent

[Welti]

I'm trying to get Coast Guard to sign off on my boat, 25' Cal. Everything is good except the inspector is saying because I have a built in fuel tank (under the cockpit) I should have an exhaust fan. BTW this boat has an outboard only, but the fuel tank is in an enclosed area under the cockpit floor, just in front of where the tiller is. I have two existing round holes (6" or so with threaded insert) near the aft of the boat already. One is where I can deploy a rear anchor through it, the other has battery and fuel cable for the outboard coming out and running to the outboard. My thought was that somehow I could maybe get a smaller exhaust vent in that opening but still keep my fuel and power cable for the outboard also running through there. That seems like the simplest. I just need some sort of fitting that would port th air but also allow the cables through. I could also just add new a vent somewhere, but would love to not make any new holes in my boat. Any creative ideas?

[CarinaPDX]

Ventilation for boats with gasoline below decks has been a requirement for many decades. My guess is that your Cal was intended to be used with the gasoline tank in the cockpit, not down below, or otherwise there would have been a ventilation system in place from the builder. A 3" diameter vent hose will be more than enough, and 3" bilge fans are readily available. Generally the intake has a forward facing scoop and the exhaust faces back. Since you already have larger holes I think the best approach is to mount 3" scoops onto the 6" plates for the existing holes, and then you can cut out a second hole in one plate for the wire and hose. You must always run the bilge fan for 5 minutes before starting the motor. Or just use a tank in the cockpit and avoid the nuisance.

Normally the exhaust hose must draw from the lower third of the hull. I'm not sure how that fits into your situation but you should consider meeting that standard.

Greg

[rslifkin]

As far as I know, a compartment containing a gas tank but not engines only needs passive ventilation, not powered vents. Unless they've changed the rules very recently.

[Welti]

Thanks for replies. I'm not sure if I need an intake if the system is not passive. I think there is enough ways for air to get into the area in question (from the cabin for example) so with a decent sized exhaust fan I could just vent it out through the existing holes as suggested. I could also add another separate hole for vent but I'd have to cut into the hull and seal it up super tight, and just doesn't seem like a good idea.

[CarinaPDX]

Originally Posted by rslifkin

As far as I know, a compartment containing a gas tank but not engines only needs passive ventilation, not powered vents. Unless they've changed the rules very recently.

You are quite right.

It does appear that both an exhaust and intake are required, along with at least exhaust ducting from the lower 1/3 of the compartment.

See attached spec, section 2.6.4 Natural Ventilation.

Greg

[Welti]

Originally Posted by CarinaPDX

You are quite right.

It does appear that both an exhaust and intake are required, along with at least exhaust ducting from the lower 1/3 of the compartment.

See attached spec, section 2.6.4 Natural Ventilation.

Greg

Interesting. I'm not even sure if a ventilation system is required based on that. My tank IS metallic, and motor outboard. I do have batts under there so I should look at the referenced document as well. I'm gonna put in the ventilation regardless. The inspector said I could just have the blower near the bottom of the compartment but above any bilge water of course, and simple extract air from there to a vent on the exterior of the hull somewhere.

[AKA-None]

Originally Posted by Welti

Interesting. I'm not even sure if a ventilation system is required based on that. My tank IS metallic, and motor outboard. I do have batts under there so I should look at the referenced document as well. I'm gonna put in the ventilation regardless. The inspector said I could just have the blower near the bottom of the compartment but above any bilge water of course, and simple extract air from there to a vent on the exterior of the hull somewhere.

Air line from bottom
Blower
Outside

Outside
Air line to high in the space

Pulls any fumes from below and fresh air enters above

[Welti]

Originally Posted by AKA-None

Air line from bottom
Blower
Outside

Outside
Air line to high in the space

Pulls any fumes from below and fresh air enters above

Yes, that might be better. I had assumed that outside air would enter, from the cabin at a minimum, but adding a purposed vent would be good.

[AKA-None]

Originally Posted by Welti

Yes, that might be better. I had assumed that outside air would enter, from the cabin at a minimum, but adding a purposed vent would be good.

You want to minimize air circulation between the cabin and engine, fuel space