TOPIC: Bilge Blower Question

Should the blower suck the dirty air out of the bilge, or blow clean air into the bilge?

Suck ass it vents the gas fumes.

Robby321 wrote:

Suck ass it vents the gas fumes.

Loud and clear! Suck the fumes and blow out the back of the boat. Thanks for answering my question.

Yes, you want to suck the fumes out (using a proper blower), but you also need to have the same size (usually 3") intake for fresh air to properly evacuate the fumes. The fresh air hose should go as low as possible in the bilge, as fumes are heavier than air.

Cheers
Bill

Thanks Bill! Have you or anyone ever used a timer of some kind for a blower? It would be nice to turn it on and it shut off automatically after several minutes.

Andrew, a rule of thumb, at least when I had my inboard (Century) was to run the blower for at least a minute BEFORE you even think of turning the key. Fumes accumulate under the engine and under the fuel tank. The person I bought my century from said the boat was a replacement for one he lost that "popped" and caught fire while turning the engine over. Not only did he lose his boat and get seriously burned but another boat along side of it got totaled. Even if you shut down for just a few minutes I would still run the blower. A problem I did have was forgetting to turn the darned thing off

www.bing.com/videos/search?q=youtube+fires+aboard+small+boats&FORM=VIRE5#view=detail&mid=3F871B477996C142C9E83F871B477996C142C9E8

I would not recommend using a timer. I always ran the blower anytime the boat was not at cruising speed, particularly when coming in through a no wake zone and up to the dock (or ramp). You may have to sit out in the water idling waiting your turn. I would rather it ran needlessly than shut itself off at a time when it should be running. You can't be too cautious when it comes to gas fumes in an enclosed area. Gasoline vapors, when in it's optimum fuel/air ratio is ten times more volatile than dynamite. I'll err on the side of caution thanks.

Cheers
Bill

Don't worry, I'm installing 2 blowers. one pulling in clean and the other sucking out the bad. What I'm hoping to do is have the blowers on a switch that I turn on manually and another circuit that turns the blower on automatically for 10 minutes after the engine is shut down.

The important one is the 5 mins BEFORE starting and before starting after fueling.

Good point firstfibre, I was assuming that was a given, running it before starting. I was focusing on the time when I thought a timer would be detrimental.
Cheers
Bill

All great points and wonderful advise, I want to be as safe as possible out there.

I will run the blower while fueling up,takes the risk out of any sort of spark that might occur while turning it on after fueling.

I always open the engine cover, run the blower for a minute and then hit the starter. It's important to have an ample supply of air coming into the engine compartment via vents or as you mentioned, force-feeding with another blower. On one of my boats, I installed a red dash light that was on whenever the blower was on...an idiot light, if you will, to remind me to turn the damned thing off!

I use an egg timer when i crab, it would be nice to have a blower on a twist timer with a chime at the end, turn to 5 or 10 mins, when it chimes turn the key

Thanks everyone for all the valuable info. Being new to the world of I/O, and not able to get my new purchase on the water till spring this is great info. I'll be sure to take advantage of this . Thanks again. madbohunk safe boating

Nautilus wrote:

I always open the engine cover, run the blower for a minute and then hit the starter. It's important to have an ample supply of air coming into the engine compartment via vents or as you mentioned, force-feeding with another blower. On one of my boats, I installed a red dash light that was on whenever the blower was on...an idiot light, if you will, to remind me to turn the damned thing off!

Great advice Jan! I always value your input. I may need an idiot light to remind to turn the darn thing ON! haha

I sold my I/O, but the proper way to ventilate is the 4 hose system. Notice any I/O as vent one side (opposite the blower) the vent fins pointed forward and inside 2 hoses. One to lower bilge, other to vent the engine box. Blower side (vent fins pointed back) is that hose bottom bilge, other open for exhaust box fumes at speed, air exchange. I would NOT use 2 blowers, one in, one out as simple gas fumes sink when parked, and simple running the blower out 3 minutes is fine. A blower in would BLOCK air flow when off. And as fumes sink, a blower in would mix up the concentrated fumes, and thats not proper way to first fire the motor. And I never seen a 2 blower system anyway, but not a I/O expert either.
The best way is before a start, sniff test. Use a length of small hose and stick it down the bilge and take a whiff in your nose. If powerful smell, find the cause FIRST. You will get some engine smell, but should not over power you. Ya should do this at first a new boat, and after satisfied all buttoned up and no leaks, just run the blower before start, and turn it off it speed. If ya leave it on so what. Blowers last a long time. Its ALWAYS to be run BEFORE START THOUGH!

Actually the USCG regulations (and ABYC and ISO standards, and Canadian Standards) all require two means of ventilation. One is a natural ventilation system, that is a hole for air in and a hole for air out. This applies to any compartment (not just the engine compartment) that can have gasoline fumes accumulate and has electrical equipment that is not ignition protected (that is can create a spark)

On any inboard engine that has a cranking motor you must also have a blower on the exhaust ventilation duct.

It is nice to have cowls or louvers on the outboard end of the holes but it is not required. In the mid 80's the USCG and ABYC did a study of ventilation and found that the flow of natural ventilation depended more on which way the wind was blowing rather than have cowls that pointed one way or the other. So at one point your exhaust vent could be an exhaust and at another time an intake. Powered ventilation eliminates this ambiguity.

The exhaust duct should extend down to the bilge but not so far that it will in water in the bilge.

The USCG also requires a blower warning label placed near the start or ignition switch that says


You can make your own. Just print it on paper and laminate it in plastic.

There is a formula for determining the size of the ducts or holes and the blower based on the cubic foot volume of the compartment. However it is far easier to use the graph (see newboatbuilders.com/pages/vent.html

One simple rule is that a 3 inch diameter hole is 7 sq inches and is adequate for a 20 cubic foot compartment. Increasing the size to 4 inch diameter doubles the air flow. Most small boats (under 20 feet) use 3 inch ducts. Also, bends and obstructions reduce the air flow. Look carefully at the blower. If the duct is 3 inches, the tube on the blower is less than three inches and reduces the air flow.

One last thing. Think about where you put the louvers or cowls. You don't want them where they will take in water, or suck in exhaust.

Great post, and two means of ventilation is why the 4 hose system. Also its a good idea to do a "loop" the blower hose and the fan mounted higher. If its straight down to the blower and ya get a good splash water (salt me) into the blower its not gonna last long. And check the loop once in awhile to make sure not fulla water (will block the air flow out also!). A ventilation system is more involved than some think. Not you guys, but the clueless, and I see many at our marina.