Bilge Blowers - Dangerous?

[generator12]

Prior to getting into my first I/O I thought that bilge blowers in these boats would either be "forced draft" (pushing air into the engine enclosure) or explosion proof (rated as able to retain the force of vapors ignited within and not cause ignition of vapors outside the body of the device).

Of course, they are neither. They are "induced draft" types made of plastic, which move the gases from the enclosure through the body of the fan as they exit the enclosure. And, being DC motors, they have armatures and brushes. In industry, these would be forbidden by the National Electric Code as hazardous devices since they are not of explosion-proof construction. It's interesting that the alternators in the 470 Mercs are open windings, but the Delco style with which these are often replaced must be "marine-rated" to avoid the likelihood of causing an explosion within the engine compartment.

I've read the earnest advice all across these forums to "run the blower before you start the engine". But I get nervous when I do it because these blowers appear to me to represent a hazard in themselves.

Does anyone have relevant knowledge on this apparent contradiction?

 

[NYBo]

Re: Bilge Blowers - Dangerous?

CG-certified blowers are indeed ignition protected. In good repair, they are only a hazard if you don't use them.

 

[kellmike626]

Re: Bilge Blowers - Dangerous?

I always think of it this way. If it was a real danger, why would they even have it there in the first place?
I always run my bilge blower before going out and at idle speeds. Haven't had any problems to be concerned about.

 

[cribber]

Re: Bilge Blowers - Dangerous?

CG approved blowers are required on all new i/o drive boats and mine pulls air out of the engine compartment and bilge. I turn it on a few minutes before I hit the ignition and turn it off at the end of that day out on the water. I look at it as bringing cool fresh air to help the engine run cooler and more efficient like a cold air induction system you'd install for a car.

 

[blifsey]

Re: Bilge Blowers - Dangerous?

Does anyone have relevant knowledge on this apparent contradiction?

If it is USCG and ABYC rated for ignition protection I don't see there being an apparent contradiction.

 

[Bob_VT]

Re: Bilge Blowers - Dangerous?

All the "marine rated" electrical parts are shielded from allowing sparks to escape. The blower's, alternator's and starter's are all in that category.

If you feel uncomfortable switching it on ..... you have a few choices. Open the engine cover and let it air out .....then start the blower and close the engine cover with the blower running....... to clear any heavier fumes that may have settled......... OR always have an enemy flip the switch while you stand far away!

Gas vapors explode when the air to gas ratio is 16:1 in the fumes........ the blower prevents/changes the ratio very quickly.

 

[scoutabout]

Re: Bilge Blowers - Dangerous?

My super-anal I/O start procedure was thus:

1. Turn on fume detector
2. If no fumes detected, turn on blower (...yeah, yeah....)
3. Sniff test on the outlet after three minutes or so
4. Start engine
5. Run blower at all times the engine is running

 

[shrew]

Re: Bilge Blowers - Dangerous?

Safe Practice says you always open the engine compartment and stick your head down low for a good sniff to see if there's fuel vapor present anyway. If you smell fuel, particularly after the boat has been sitting for a while, then there is the possibility (Good Possibility, unless you know you spilled fuel down there yourself) that you have a potential fuel leak. You most likely wouldn't start the boat in this situation.

The blower is most likely not mounted directly in the bottom of the bilge. It is most likely mounted halfway up the engine compartment, or higher. There is most likely some duct work that gets down into the bottom of the bilge and another that goes to the outboard vent. Since fuel is heavier than air, the fuel vapor would sit down low in the bilge, and the blower would sit higher than a small amount of vapor. If you have a large amount of vapor, then again, you would notice it if you did a sniff check prior to starting and wouldn't start the boat if you smelled fuel anyway.

I strongly recommend doing a sniff test first, then running the blower for 5 min. Then starting the engine. If you suspect your blower might have some issues, then replace it.

 

[25thmustang]

Re: Bilge Blowers - Dangerous?

I hit the blowers as soon as I step on the boat. Then I open the hatches to check the fluids on both motors prior to start up. Should I be opening the hatches before hitting the blowers, to check for fumes? I always assumed they were ignition protected, given what they are required for.

 

[shrew]

Re: Bilge Blowers - Dangerous?

I hit the blowers as soon as I step on the boat. Then I open the hatches to check the fluids on both motors prior to start up. Should I be opening the hatches before hitting the blowers, to check for fumes? I always assumed they were ignition protected, given what they are required for.

My thought on this (opinions will vary), is that the fuel leak is the problem. Fuel evaporates (into vapor), but vapor doesn't. Fuel vapor will just sit in the lowest part of the bilge. The smell from the fuel vapor is merely a symptom. If I had a small fuel leak and vented the vapor with the blower, then started my engine, I would still have a small fuel leak. I would prefer to be aware of an issue before my blower masked the symptoms. I certainly don't want to find out I have a fuel leak after I've gotten out on the water.

 

[25thmustang]

Re: Bilge Blowers - Dangerous?

Thats a good point. It would be simple enough to switch up my routine, I just always reach for that bilge blower switch while I'm unlocking the cabin and putting my keys/phone/wallet down below. If there is a cause for concern with that, I could always open the hatches, check fluids, and then hit the blowers and wait a bit longer.

The one time I filled the boat this season with fuel, I made sure to have the hatches open, and to continuosely poke around in the bilge for smells. Sounds like another procedure to add to my pre-castoff routine.

 

[rwidman]

Re: Bilge Blowers - Dangerous?

Prior to getting into my first I/O I thought that bilge blowers in these boats would either be "forced draft" (pushing air into the engine enclosure) or explosion proof (rated as able to retain the force of vapors ignited within and not cause ignition of vapors outside the body of the device).

Of course, they are neither. They are "induced draft" types made of plastic, which move the gases from the enclosure through the body of the fan as they exit the enclosure. And, being DC motors, they have armatures and brushes. In industry, these would be forbidden by the National Electric Code as hazardous devices since they are not of explosion-proof construction. It's interesting that the alternators in the 470 Mercs are open windings, but the Delco style with which these are often replaced must be "marine-rated" to avoid the likelihood of causing an explosion within the engine compartment.

I've read the earnest advice all across these forums to "run the blower before you start the engine". But I get nervous when I do it because these blowers appear to me to represent a hazard in themselves.

Does anyone have relevant knowledge on this apparent contradiction?

The USCG and ABYC require bilge blowers on all new inboard and I/O boats with gasoline powered engines. They have done the research.

You would be a fool to ignore their recommendations to have a bilge blower and run it before starting your engine(s).

 

[642mx]

Re: Bilge Blowers - Dangerous?

I flip mine on before we start it and anytime its running. I also leave it on for 10 or 15 minutes after a long/hard run to help get the heat out of the engine compartment. Its amazing how much hot air those things will suck out!

 

[Kaplooi]

Re: Bilge Blowers - Dangerous?

IMO blowers mask the underlying engineering shortcomings of carburetors. I'd like to think stern drive boating will continue to get safer as more and more people migrate to true multi-port fuel injected configurations (i.e. injectors on a rail as opposed to TBI). A properly operating EFI setup should produce no fuel vapors out of the intake either when it's at rest or in use at any RPM. Whereas the smell of raw gas is accepted as normal on carbed engines at rest (to an extent), if you smell raw gas on an EFI motor something is leaking and needs to be fixed asap given it'll likely be leaking under pressure. Discussions about incorporating evaporative emissions on boats is a different matter, but even now tanks vent to the atmosphere outside of the engine compartment so you shouldn't have vapors from the tank either. Obviously on carbureted boats having an intake tube with an integrated flame arrestor connected to the carb throat and routed to an exterior intake vent would help prevent vapor build up, but that would probably affect performance or something. Or maybe it's just too costly for manufacturers to install. Whatever the reason I hope it's a damn good one because it's always been interesting to me how the USCG requirements for blower and flame arrestor seems to miss the point. Requiring a blower, to me says that it's acceptable to design an engine such that a potentially explosive buildup of fuel vapors can exist so long as you have the option of blowing in a little fresh air before 'ignition'. I'd rather there not be vapors in the first place but I guess that's not possible on carbed boats.

All of this assumes nothing has failed on its own that could be leaking fuel, so a little healthy paranoia before every firing is probably just as well, but allowing fuel vapors 'by design' has always bugged me some.

 

[blifsey]

Re: Bilge Blowers - Dangerous?

IMO blowers mask the underlying engineering shortcomings of carburetors.

No...they mask the underlying engineering shortcomings of closed bilges. If mfrs would build boats with open bottom bilges we would not need blowers

(Note all the smilees! Post was made in jest.)

 

[Beefer]

Re: Bilge Blowers - Dangerous?

I personally don't sweat it that much. Think of this; there are thousands of boats that are wet-slipped, that has electric automatic bilge pumps in the bottom of the bilge, as well as the non-automatic bilge pumps. Some of those boats will go weeks without the blowers being used, but the bilge pumps will come on almost everyday. I don't think there is an instance of a boat blowing up because the bilge pump came on before fumes were removed from the bilge. Granted, most of the time, the components of the bilge pump system is submerged at the time of start-up, but that's also assuming that 100% of the bilge pumps are installed 100% properly. I know there are many pumps that will kick on when the switch is submerged, but the pump is in a slightly higher section of the bilge.

If a bilge pump won't cause a boat to explode, and it isn't designed as a 'fume safety device', I couldn't imagine there ever being an issue with a blower, which is designed to deal with the fumes.

I agree you can never be too safe, but sometimes there is such a thing as obsessive-compulsive.

Get on your boat, open the engine access, turn on the blower, wait about 5 minutes, start the motor, and enjoy boating.

 

[rwidman]

Re: Bilge Blowers - Dangerous?

I personally don't sweat it that much. Think of this; there are thousands of boats that are wet-slipped, that has electric automatic bilge pumps in the bottom of the bilge, as well as the non-automatic bilge pumps. Some of those boats will go weeks without the blowers being used, but the bilge pumps will come on almost everyday. I don't think there is an instance of a boat blowing up because the bilge pump came on before fumes were removed from the bilge. Granted, most of the time, the components of the bilge pump system is submerged at the time of start-up, but that's also assuming that 100% of the bilge pumps are installed 100% properly. I know there are many pumps that will kick on when the switch is submerged, but the pump is in a slightly higher section of the bilge.

......

I think you'll find that marine bilge pumps and bilge blowers are "ignition protected" (designed and ertified to be safely operated in an explosive atmosphere). Also, most bilge pumps begin pumping when the water level reaches about three inches.

The ABYC and USCG have done the research and designed and mandated safety equipment to make gasoline powered boats as safe as possible. I really don't understand how and why a boater might come to the conclusion that the equipment itself makes operating the boat more, not less dangerous. It's like arguing that wearing seat belts increases your risk of injury or death in an automobile accident

 

[rw99]

Re: Bilge Blowers - Dangerous?

IMO blowers mask the underlying engineering shortcomings of carburetors. I'd like to think stern drive boating will continue to get safer as more and more people migrate to true multi-port fuel injected configurations (i.e. injectors on a rail as opposed to TBI). A properly operating EFI setup should produce no fuel vapors out of the intake either when it's at rest or in use at any RPM. Whereas the smell of raw gas is accepted as normal on carbed engines at rest (to an extent), if you smell raw gas on an EFI motor something is leaking and needs to be fixed asap given it'll likely be leaking under pressure. Discussions about incorporating evaporative emissions on boats is a different matter, but even now tanks vent to the atmosphere outside of the engine compartment so you shouldn't have vapors from the tank either. Obviously on carbureted boats having an intake tube with an integrated flame arrestor connected to the carb throat and routed to an exterior intake vent would help prevent vapor build up, but that would probably affect performance or something. Or maybe it's just too costly for manufacturers to install. Whatever the reason I hope it's a damn good one because it's always been interesting to me how the USCG requirements for blower and flame arrestor seems to miss the point. Requiring a blower, to me says that it's acceptable to design an engine such that a potentially explosive buildup of fuel vapors can exist so long as you have the option of blowing in a little fresh air before 'ignition'. I'd rather there not be vapors in the first place but I guess that's not possible on carbed boats.

All of this assumes nothing has failed on its own that could be leaking fuel, so a little healthy paranoia before every firing is probably just as well, but allowing fuel vapors 'by design' has always bugged me some.

I've been curious about this point, as well. In a modern EFI application (closed system fuel delivery) the bilge blower seems to be a bit anachronistic. Don't get me wrong, on my I/O I still run the blower before starting up and open up my cover after fueling... but to me it seems like carbed motors are 10x more likely to generate fuel vapor problems.

Anyone have relevant data on this subject?

 

[DianneB]

Re: Bilge Blowers - Dangerous?

It's like arguing that wearing seat belts increases your risk of injury or death in an automobile accident

Totally an unfair comparison!

I have worked as a designer in the petroleum industry, design equipment for use in hazardous locations. I am familiar with the regulations as well as the science and engineering behind them.

Having recently returned to boating and having replaced a couple of blowers, I was struck by the cheap style of motors used. I would not have considered them explosion proof - they certainly would not pass any CSA or UL test for hazardous locations! I would have expected a sealed case rather than an open frame.

However, the saving grace MAY BE in the voltage/current required to achieve ignition of an explosive vapour and the low current at which these motors run. The current may be limited enough that ignition can't be achieved. The problem is that to meet UL criteria, ignition can not be achieved even with one fault introduced and I KNOW these motors would fail on that basis.

I have seen LOTS of products marked claiming to "meet code" when in fact they have never been formally tested and none have blown up yet! I have even seen products marked "UL Approved" that do not meet code!

You are justified in being skeptical

 

[Brewman61]

Re: Bilge Blowers - Dangerous?

Perhaps it comes down to real world experiences? Are there any documented instances of bilge blowers causing fires/explosions, etc?
Certainly there are enough of these out there now that if this was a real risk, perhaps a pattern would have emerged?