Need for blower on an outboard?

In the process of setting up my first real boat. Its an older boat with an outboard but the hull, floor and transom are in fantastic condition. Redoing the complete interior, plus all new wiring, adding power trim and bilge pump as well.

While installing the bilge pump a concern came to mind and thought I'd ask the members opinions here.

The gas tank, battery, power tim pump and bilge pump are all located under the splash well, as is typical of most all outboards I'm assuming. This area is closed off from the passenger area by a vinyl barrier that is snapped in place. This effectively creates a closed area.

Is there danger of gas fumes accumulating in the bilge area?

Should I install a blower like is used on I/O's? Am I concerned over nothing? What is typically done with outboard setups regarding venting this storage area?

Re: Need for blower on an outboard?

Most were designed that way, when new.

I would just make sure your battery is in a box.

Re: Need for blower on an outboard?

With an I/O you have an internal combustion engine running in a same small enclosed area at you store your fuel supply. The motor spews a lot of noxious and combustible flumes and at the saem time provides numerous points of ignition to these fumes. Something about storing the dynamite and the matches in the same room come to mind.

An outboard is mounted outside the confines of the bilge. The only way for combustible flumes to accumulate under the floor with an outboard is to have a leak in your fuel system. A blower will not do any good should your tank start leaking

Re: Need for blower on an outboard?

All good points, BUT, the thing that concerns me is that I have a fuel tank (with an open vent) stored in an enclosed space along with the battery and bilge pump.

The battery won't pose any problems because there are no make/break contacts occurring that would create a spark. The bilge pump, being the lowest point in the boat, could create a spark when operated. Don't gas vapors seek the lowest spot to settle?

The space is relatively small, about 6 1/2ft x 18" x 18" and for all intent and purpose is completely sealed up.

Am I being paranoid or should I be concerned?

Re: Need for blower on an outboard?

Cautious yes paranoid no. Think about this. If the need arises for the use of the bilge pump it is likely under water so the chance for a spark is nill. Just put your rig in the water and have some fun. The battery in a box is a good idea though.

Re: Need for blower on an outboard?

Bilge pump motors are sealed, thus they can run underwater. There is no difference in an I/O bilge pump and an outboard one.

I/O's require a blower, outboards don't.

Re: Need for blower on an outboard?

Do you have any of those clam shell vents?

Any boat with a fuel tank mounted in it needs ventilation. I don't remember the exact wording but yeah you should have some type of ventilation.

My boat has two clam/ scoops one facing forward one facing back to force air through the fuel tank area and that's even with a external vent.

Re: Need for blower on an outboard?

Yeh, I've seen those clam shell vents and may install a pair for piece of mind. Can't ignore the fact I have an open gas container (vent open) in a closed space with electrical components.

There is virtually no ventilation now. Where the cabling and controls go thru the splashwell, the openings are sealed with rubber boots. The front of the storage space is closed to the floor and gunnel to gunnel with the vinyl snap on cover.

Re: Need for blower on an outboard?

Only vent I have on my outboard's inboard tank is the overflow. No need for a blower when the motor isnt with the fumes.

Rock on

Re: Need for blower on an outboard?

I have a Hurricane Midships. It was made to accommodate either an IO or OB; mine is the OB version.

I have a deck hatch that gains access to an 80 gallon gas tank, oil reservoir, and battery. I have no vents. Prior to starting up or during refueling, I always open the hatch, go down into the area, and do a sniff test to see if I have any fuel leaking.

I really never thought much about any venting, but at least for me, I have no good area to install one.

Re: Need for blower on an outboard?

OK I went by the boat shop yesterday and picked up one of the federal requirements brochures.

All boats that use gasoline for electrical generation, mechanical power or propulsion are required to be equiped with a ventilation system.

A natural ventilation system is required for each compartment in a boat that:
1. contains a permanently installed gas engine.

2. has openings between it and a compartment that requires ventilation

3. contains a permanetly installed fuel tank and an electrical component that is not ignition protected

4. contains a fuel tank that vents into that compartment ( including a portable tank)

5. contains a non-metallic fuel tank


A natural ventilation system consists of:

A supply opening (duct/cowl) from the atmosphere ( located on the exterior surface of boat) or from a ventilated compartment or from a compartment that is open to the atmosphere.

and a exhaust opening into another ventilated compartment or an exhaust duct to the atmosphere.


Yes your boat requires a ventilation system of some kind!

Don't be stupid and not use one.

The rest of you either have 70's or earlier boats built before the coastguard started requiring all boats be built with one or don't see them. BUT YES you need to vent that compartment. Use one vent facing forward and backwards and all will be right.

Hey guys I don't want to be a jerk or anything but don't give out advice on things that could be incredibly dangerous if you don't know what your talking about.

It is VERY important that you follow the coastguard regs on safety you guys might want to pick up a copy of the Federal Requirements & Safety Tips brochure it's at every boat shop or check USCGBoating.org but please no bad advice.

Re: Need for blower on an outboard?

IMHP a correct answere is hard because we are NOT aware of the machinery that is installed in the bilge

As outboards are now installed in GIANT boats there can be A/c units ,Gen Sets ect that were never installed in outboard powered in the past

Re: Need for blower on an outboard?

If he's storing an open container of fuel below deck then yes he needs ventilation. I'm actually quite surprised that there are not regulations against storing open fuel containers below deck in the first place.

Looking at your criteria, generally speaking it appears that all outboard powered boat (with the exception of those with internal generators and such) would be exempt from this regulation unless they had plastic fuel tanks installed.

Re: Need for blower on an outboard?

NSB you're talking about a natural venting system and that's what's in the coast guard regs, the topic of this post is a manual power blower.

I would assume 99% of boats have a natural venting system, which is basically just an open vent on the front of the boat that runs from a duct through the enclosed area and then out through another vent in the back.

Moody blue do you have a NATURAL vent?

Re: Need for blower on an outboard?

dingbat said:

Looking at your criteria, generally speaking it appears that all outboard powered boat (with the exception of those with internal generators and such) would be exempt from this regulation unless they had plastic fuel tanks installed.

Click to expand...

Huh??? It's not my criteria it's the coastguards and I guess you didn't read it right it only has to be one of the list to need a ventilation system.

I don't see what's so hard to figure he fits the bill in a couple of ways and yes he should be concerned and yes he should correct it.

Fratalia17 oh I know I got tired of typing it all but the requirements are wether you need a ventilation system or not. The next page of the brochure goes into blowers. I mentioned to him earlier that all he need was a set of clam shell vents, so I was just providing the basic info he need not spending my whole morning typing.

Again if there is confusion on the subject then please check with the Federally mandated safety requirements.

Re: Need for blower on an outboard?

The simple answer is that the space needs to be vented. If you don't use vinyl to close in the space, then you may have sufficient natural venting. If not, you need to install something. If you use the clam shell scoops, one should be pointed forward and one should be pointed backward. This will give you the best chance to actually circulate air through the space. Connect inexpensive white air vent hose to the scoops and route those to the bottom of the space.

Gas fumes are heavier than air. They will settle to the lowest point of the boat and stay there unless vented.

Keep your fuel vent (on the tank cap) closed when you are not using the boat.

Re: Need for blower on an outboard?

NSBCraig said:

Huh??? It's not my criteria it's the coastguards and I guess you didn't read it right it only has to be one of the list to need a ventilation system.

Click to expand...

I?m not questioning the requirements. They all make sense. I?m only questioning if any of the prerequisites actually exist on your typical outboard powered boat. None of them would apply in my case and my boat?s configuration would certainly represent the norm in modern outboard construction.

As stated earlier, I would be more concerned as to the legality of storing an open container of fuel on the boat.

Re: Need for blower on an outboard?

All boats manufactured after 1980 are supposed to be made in compliance with the regulations. ( so the brochure says )

So yes Dingbat your Grady is built from day one to be right. But then most people on here don't own a boat as new as the late 90's.

The question is wether his boat was built before then or has been modified to not comply.

He seems to be asking because his doesn't and it definitely needs to.

I don't think his little whaler type boat as I think he describes it in his profile has a below deck space to worry about open gas cans stored below. Which is something that I'm not sure why anybody would do?

Re: Need for blower on an outboard?

Interesting reading. Didn't mean to open a can of worms but glad I asked. Thanks for all the great input, lots of valuable information to digest. Let me clarify a couple things about my situation.

Boat is a 1970 fiberglass 16ft deep V hull powered by an 80hp OUTBOARD motor. Rear of boat has the "typical" enclosure below the splashwell across the back of the boat. This space is used to house the portable fuel tank (open vent), battery, power trim pump and bilge pump.

The whole space is for all intent and purpose completely enclosed. Even the openings thru the splashwell for electrical cables and steering cable are sealed with rubber boots. The full width of the enclosure is closed up to the passenger area with a heavy vinyl cover to the floor and is secured in place with a number of dome snap fasteners.

Here is my concern to be clear. Boat is sitting out on the lake on a hot sunny day (maybe fishing, swimming, etc). Vent to fuel tank is open since boat is in use. Heat in storage area is high because it is enclosed. Gas vapors escape from fuel tank and accumulate in the bilge area and generally within the enclosed area. IF, I operate either the power trim pump or the bilge pump, is there any danger of blowing myself up? My gut tells me yes and I will be installing "natural ventilation" for my own piece of mind.

Here is a question? By simply adding clam shell vents on the top deck or louvered vents on the side gunnels, will that be sufficient?

The thing that puzzles me is I'm certain I'm not the only one with this situation? Am I missing something? Maybe I am way to worried about nothing.

Re: Need for blower on an outboard?

In your scenario, you are sitting still and the fuel vapors are going to just sit in the bottom of the bilge unless there is a powered ventilation system.

If I was as worried about it as you seem to be, I would get an extra cap for my fuel tank, modify it by adding a hose barb to it and vent the tank through the hull. You would have the extra cap for when you need to take the tank out to fill it. If you wanted to get fancy, you could use a self sealing quick connect fitting instead of the hose barb. Then you wouldn't need the extra cap.