blower CFM needed for proper ventilation

[ScottinAZ]

Boat was a basket case when purchased, blower motor was there, but no specs really on what it would push. Ducting is 3".

I have two vent ports on the rear deck of the boat, one facing forward, the other aft. What is the "proper" routing for the hoses, or does it not really make a lick of difference which hose goes where? Keep in mind none of this was installed when I got this project started, so I dont have a real starting point to go from

Is there a basic guideline on how many CFM the blower needs to be capable off to properly ventilate the engine bay on an I/O boat? Hull is a little 16 footer with a 2.5 Mercruiser engine. Its not a large space, but it is enclosed and I really dont want to turn it into a bomb.

 

[dwco5051]

Found this on a boat insurance site;

A Rough Guide to Selecting Blower Sizes​

For engine spaces up to:

• 70 cu. ft - 100 c.f.m. blower
• 71 to 100 cu. ft. - 150 c.f.m. blower
• 101 to 300 cu. ft. - 250 c.f.m. blower

 

[mr 88]

Air comes in through the bow facing vent and stern facing is for air out . Exhaust hose should be as close to the lowest point near engine that it will fit . Vapor fumes are heavier than air and will settle at the lowest point possible. After fueling up with a small doghouse,open it up aftering filling and smell with your nose as well as having the blower running.

 

[ScottinAZ]

Air comes in through the bow facing vent and stern facing is for air out . Exhaust hose should be as close to the lowest point near engine that it will fit . Vapor fumes are heavier than air and will settle at the lowest point possible. After fueling up with a small doghouse,open it up aftering filling and smell with your nose as well as having the blower running.

perfect. thats what I needed to know

 

[ScottinAZ]

Found this on a boat insurance site;

A Rough Guide to Selecting Blower Sizes​

For engine spaces up to:

• 70 cu. ft - 100 c.f.m. blower
• 71 to 100 cu. ft. - 150 c.f.m. blower
• 101 to 300 cu. ft. - 250 c.f.m. blower

great info. I will likely go bigger on the blower, as they arent really any more money for a bigger one. Mostly didnt want to go too small

 

[airshot]

great info. I will likely go bigger on the blower, as they arent really any more money for a bigger one. Mostly didnt want to go too small

Correct...I always made a habbit of smelling the air comming out the rear facing outlet checking for fuel odors. Get a piece of hose and get it down under the motor if you can but keep it out of any water in the bilge

 

[Kla]

Don't wanna hijack your thread, but I have a 19ft bowrider I/O with a 350ci Chevy smallblock and Alpha One outdrive. Should I run the blower while fueling up? The fuel vent for the gas tank works great but don't want fuel vapor to collect in the engine bay. Or is this not a concern?

 

[mr 88]

I always turn my blower on before I start fueling . My theory is if there is any sort of electrical issue with the blower that might cause a spark , the spark would happen when you turn on the blower , not while it's running . Not sure if I am correct but I feel better doing it that way.

 

[Kla]

Don't wanna hijack your thread, but I have a 19ft bowrider I/O with a 350ci Chevy smallblock and Alpha One outdrive. Should I run the blower while fueling up? The fuel vent for the gas tank works great but don't want fuel vapor to collect in the engine bay. Or is this not a concern?

I also mean while the boat is on the trailer. I don't fuel up at the marina, it's too expensive. Always fuel up the boat before I get to the dock.

 

[Comogene]

Hose from forward facing vent is for natural flow of air into the engine compartment. It can end anywhere. Aft facing vent should have blower attached to it (really a "sucker") and the hose attached to the suction side of the blower should run to near the bottom of the bilge to remove any fumes but out of any bilge water. If the hose is 3", any 3" blower will be more than sufficient.