Is a blower needed?

Fudd · Mar 23, 2009

I have a 16' tri hull with an outboard motor. The rear compartment houses the battery and gas tank. When I open that up it always smells of gas fumes. Should I install a blower or just some vents?

lowkee · Mar 23, 2009

Re: Is a blower needed?

A blower is most definitely needed! Gas fumes are heavier than air, which means vents cannot move them out of the bilge. The blower forces the fumes out. One spark after your boat sits for a few hours and you may not have a boat anymore. There are plenty of stories on here of people losing their boats because of a bad or missing/unused blower. Please don't become the next one.

Fudd · Mar 23, 2009

Re: Is a blower needed?

Yeah I don't want to be another bad story. Are they difficult to install? I don't have any vents to push the fumes out of so I would have to cut holes and install all of that. Any advice would be great. Thanks

seabob4 · Mar 23, 2009

Re: Is a blower needed?

Since the spark source is at the motor, no blowers are required per ABYC and NMMA. But you probably would want to vent the compartment. Try a couple of these, from Marine East. They work great for us.

lowkee · Mar 23, 2009

Re: Is a blower needed?

It doesn't necessarily have to go through the hull. If you can port it out in to the air (say, behind a seat back), that will be enough. As long as it gets out of the boat, anything more is just detail. If you want to go the thru hull route, I'm sure there are a few kits around which will get you going, and likely come with a nice air scoop for the outside. The blower itself is simply a 12V fan which attaches to a hose of each side. You hook up a switch at the dashboard and you are golden.

Outboards are likely not required to have a blower, as the engine (and any sparks is may possibly create) are outside the bilge area. This is probably why your boat isn't pre-ducted for one, but if you have fumes settling, you are best to add one, as sparks don't only come from the engine. Just connect a battery lead to see what I mean.

Moody Blue · Mar 23, 2009

Re: Is a blower needed?

Have the same situation. Boat is 40 yrs old and no factory ventilation at all under the splashwell enclosure. Enclosed in the same space is the gas can (open vent), battery, trim pump and bilge pump. Can't help but think there will be gas fumes accumulating in there BUT, why is there no ventilation?

dingbat · Mar 23, 2009

Re: Is a blower needed?

Instead of installing a blower why not fix the source of the problem?

I have two tanks, 147 gallons of fuel in all. I don't have a gas smell below decks so its not normal.

Fudd · Mar 23, 2009

Re: Is a blower needed?

Seabob and lowkee thanks for the help. Dingbat its a six gallon plastic tank for my outboard and when I open the vent on the cap the only place the fumes can go is into the storage area. So aside from installing an inboard tank, ventilating the storage area is the easiest route. I do agree with your point of fixing the problem not putting a bandaid on it.

Boatist · Mar 23, 2009

Re: Is a blower needed?

Is there any way you could connect a Hose to the gas can vent and run it to a outside vent like a internal tank. You would need a disconnect so you could remove the tank for fueling.

Another option would be to install a Cowl Vent faceing the stern to suck air out while moving on the road or water. also when the wind is blowing. From the vent then need a 3 inch hose to low in area where your fuel is. Should go low in the bilge at least below the gas tank.

http://www.iboats.com/Boat_Parts_Ac...l--search_in_category.f--**********.504283929

On boats with internal tank and engines you would also have a cowl faceing foward high in the area to feed in fresh air. Also would have a bilge blower.

In your case unless the area is sealed pretty tight a exhaust vent may be enough. Air flowing into the open back of the boat would likely make it into that area and also help to force air out the stern facing cowl vent.

strokeoluck · Mar 24, 2009

Re: Is a blower needed?

seabob4 said:
Since the spark source is at the motor, no blowers are required per ABYC and NMMA. But you probably would want to vent the compartment. Try a couple of these, from Marine East. They work great for us.

I'm new to boating and am confused. First, let me say that I understand that gas fumes are heavier than air, and they can settle in the bilge. I also understand generally that you don't want gas fumes hanging around. BUT, what's the real risk of the engine/boat blowing up? How does a spark that is INSIDE the engine, possibly ignite gas fumes nearby?

Again, I'm not saying it's intelligent, and I have no intention of NOT using the bilge pump, but still my simple mind would like to better understand the connection & risk. Thanks.

jay_merrill · Mar 24, 2009

Re: Is a blower needed?

Because you have the fuel tank in an enclosed compartment and have electrical components in the same compartment, you could be required to have ventilation. The key is whether or not the electrical components are "protected." There mere fact that there isn't an engine located in the comparment, is not the deciding factor.

I see boats all of the time with enclosed areas under the splashwell. Many times, those areas are used to located both gas tanks and batteries. To me that is a bad idea. At a minimum, if I had a boat with such an arrangement, I would either remove the covering, or install at least a passive ventilation system. This might consist of a forward facing air intake and a rearward facing exhaust. An even better arrangement would include a spark safe blower.

Here are the USCG rules:

Boats built after 4/1/1940

At least two ventilator ducts fitted with cowls or their equivalent for the purpose of properly and efficiently ventilating the bilges of every closed engine and fuel tank compartment of boats constructed or decked over after April 25, 1940, using gasoline as fuel and other fuels having a flashpoint of 110? F or less.

Boats built after 8/1/1980

At least two ventilator ducts for the purpose of efficiently ventilating every closed compartment that contains a gasoline engine and every closed compartment containing a gasoline tank, except those having permanently installed tanks vented outside the boat and containing no unprotected electrical devices. Also, engine compartments containing a gasoline engine with a cranking motor must contain power-operated exhaust blowers controllable from the instrument panel.

Fudd · Mar 24, 2009

Re: Is a blower needed?

Boatist I think a few well placed vents will get the air moving in there to solve the problem.

Strokeoluck the sparks don't occur just inside an engine. Under the distributor cap, which is not air tight, sparks occur. If your spark plug wires are going bad they can start to ground to surrounding metal and create sparks. Almost any kind of electronic device, when activated, a small spark occurs. It doesn't take much to ignite fuel vapors when the proper conditions are there. Inboards have a greater risk because they are in an enclosed space inside the boat. The blowers are there to vent the vapors before the conditions allow them to ignite.

Having an outboard my risk of the engine causing the fumes to ignite is almost none, but the battery can still spark at times and I thought I would ask if I should take the steps to vent the area. People on this forum have been boating for longer than I've been alive so why not learn from their experiences. Know what I mean?

oops! · Mar 24, 2009

Re: Is a blower needed?

your battery is in that compartment where the gas fumes are........thats good enough of a spark source.

vent the area well........

NSBCraig · Mar 24, 2009

Re: Is a blower needed?

Are your trim/tilt relays mounted down there?

They can spark too.

180shabah · Mar 24, 2009

Re: Is a blower needed?

strokeoluck said:
I'm new to boating and am confused. First, let me say that I understand that gas fumes are heavier than air, and they can settle in the bilge. I also understand generally that you don't want gas fumes hanging around. BUT, what's the real risk of the engine/boat blowing up? How does a spark that is INSIDE the engine, possibly ignite gas fumes nearby?

Again, I'm not saying it's intelligent, and I have no intention of NOT using the bilge pump, but still my simple mind would like to better understand the connection & risk. Thanks.

In a car when fuel vapors are present the just fall to the ground and dissipate. In a boat, the engine compartment is enclosed and the vapors can't escape, so they collect in the bilge. For this reason there are significant differences between regular and marine electrical components. All of the changes have one goal, contain the spark inside the unit.

The flame arrestor on your engine serves the same purpose, except it is there to contain a backfire instead of an electrical spark. The bilge blower is there to remove the accumulated fumes in case there is a an "unplanned" ignition event.

How often do boats go boom - several every year. In most cases either incorrect parts, or incorrect procedures(or both) were used and the results can be catastrophoc.

Utahboatnut · Mar 24, 2009

Re: Is a blower needed?

There is probably a bilge pump down there as well what happens when you turn any electric motor on even a 12 volt motor. Take a cordless drill into a dark room and hit the trigger it will only take a second to see all the sparks going on. Post a picture of your boat I'm sure someone can help out with an Idea. Even a couple of clam shells would help if you could get some way to feed air into the area. Post a pic.

180shabah · Mar 24, 2009

Re: Is a blower needed?

Yup, pics are always helpful.

Fudd · Mar 24, 2009

Re: Is a blower needed?

No pics available broke the digital camera last week. There was two links posted higher up on the thread for some vents. I like the looks of them and know right where they can go and how I can install a blower fan to work with them as well. Thanks for all the help.

cbavier · Mar 24, 2009

Re: Is a blower needed?

One point I didn't see in this post and I was always taught with an I/O was.

Every morning before turning anything on, lift the engine cover and do a sniff test. If no vapors are present then turn the blower on and let it run at least four minuets before attempting to start the engine. Obviously an outbord procedure might be different, but I still think the sniff test might be a good idea for enclosed fuel compartments. My vote is to add a blower for any enclosed fuel compartment. Just my .02

180shabah · Mar 24, 2009

Re: Is a blower needed?

Fudd said:
and how I can install a blower fan to work with them as well. Thanks for all the help.

Just remember, the blower "sucks" from the bilge and "blows" overboard, not the other way around.

Is a blower needed?

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