Venting Fuel Vapors under rear decking

Per Ky Fish and Wildlife boating laws ( located at https://fw.ky.gov/pdf/08fishboat6.pdf?lid=2032&NavPath=C102C682 )

Quote "
VENTILATION
Most fires on a boat are due to ig-
nition of fuel vapors. Gasoline is heavier
than air. It can collect in the bilge or engine
compartment and any spark can ignite it.
Therefore, Kentucky law requires boats to
have adequate ventilation of areas where
flammable vapors can accumulate.
Most boats are equipped with ad-
equate ventilation systems when they
come from the factory. Usually,
this is a combination of active and
passive systems. Active systems
use electrical blowers to exhaust
flammable vapors from the bilge
and other areas. Passive systems
are ducts and cowls that ventilate
areas when the boat is moving.
Almost all inboards will have an
electrical blower installed in the
engine compartment. Operators
should run the blower for several
minutes before starting the engine. If
the blower is inoperable it should be
repaired or replaced immediately.
"

I guess I've got to add some sort of vent to the rear decking, any thoughts?

I'm thinking louvers and maybe small 5 inch fan.

I would probably forego the fan, and just put the louvers. That is all that most boats are equipped with. You face one forward, and one astern, and it circulates air while running. In my Yazoo, I am putting my batteries up near the bow, and all my wiring will be in a separate chase above the deck, so the fuel fumes will hopefully remain separate from sources of ignition.

Crap, I just remembered that I had forgotten about my bilge pump.

This really only applied to boats with inboard engines. But even with an outboard, you shoudl take care around potential gas vapor spots, especially if you use a portable fuel tank

Thats exactly why I left the middle of my rear deck open. I don't want to take any chances.

you should be fine with adding a pair of vents. better safe then sorry

Wayne

I installed some vents because the gas smell in my lockers was so bad. I put one of these on each side under the seats.

I am currently designing a rear compartment system for a 14ft deep V I purchased. 90% of the floor is decked and carpeted and the side are carpeted to the gunwales. The last 18 inches are open to the stern in the bilge area.

What I want to do is enclose this area by building out a rear bench to sit on when underway. This bench will lift up and give access to a battery, fuel tank, bilge pump, oil.. basically the mechanical stuff.

The way my boat is designed (A 14ft 1975 SmokerCraft) is with the shallow transom and wash tray which drains to the rear. Under the wash tray is open to the bilge. I would probably design the compartments so that the fuel tank is on the starboard side of the boat and the battery, bilge, bank chargers are at the port.

I would assume the best way for me to vent this rear area is to first diamond plate, silicon and completely separate the fuel tank compartment from the electrical compartment. I am using a 6.5 gallon tank so about 40 lbs worth of fuel. This weight will be offset by battery and me sitting on the port side to operate the engine.

Once the compartment is 100% sealed from the electrical, I will add a front vent at the deck level for air inlet. I will also add a side vent for air outlet. I believe I have enough freeboard to do this. If I do smell fumes, I can vent the fill cap with a line to the side vent.

I will probably visit some marine show rooms to see different designs to get more ideas.

Here is a scetch, The lines in red represent the new framing

You do not have to fully compartmentalize your electrical from your fuel. Many times this is impossible anyway because of the bilge pump.

It actually may be beneficial to have the areas open to one another so that you are gauranteed that fuel fumes do not collect in an unvented electrical compartment.

Put one of these on either corner, one facing forward and one aft, and you will be fine.

Captain Ahab said:

This really only applied to boats with inboard engines. But even with an outboard, you shoudl take care around potential gas vapor spots, especially if you use a portable fuel tank

Click to expand...

Bingo.The inboards that I have been around have a bilge or motor well fan.This fan sucks air from bilge level and blows it over board.The fan housing is sealed to prevent fumes from entering.The ignition and starter solenoid switch is what usually sparks bilge fires on inboard boats.Rarely it's the alternator.With and outboard you should be fine with hatch vents.Just make sure there is no electrical parts or wiring running through the fuel tank bay.