Blower motor venting seems all wrong!!

Hi,

Although I know that diesel engines don't need to be vented with a blower motor in the same way as gasoline engines, I'm nevertheless very puzzled by the routing of the vent hoses in our 1984 E30+. I will be replacing them, as they are getting old and cracked, so I have an opportunity to re-think how they are positioned.

Currently the blower motor is situated under the quarterberth where it draws air from the starboard side of the boat, low in the hull--presumably from under the fuel tank and to some extent from the engine compartment and exhausts it from a vent on top of the starboard side transom facing aft. The intake hose for fresh air has an intake vent on the port side of the transom top, also facing aft, and the 3" diameter plastic hose descends from there to an opening in the floor of the engine compartment, likely drawing air down low in the hull aft of the engine.

So my puzzlement: if the idea is to exhaust hot air to lower temperature in the engine compartment, then the blower and exhaust hose (not the engine exhaust) should be high up in the engine compartment because hot air rises and that's the air that should be discharged. The fresh air intake could then come in low in the engine compartment to replace the exhausted hotter air, creating a bit of a circular motion which could help to keep the engine compartment a bit cooler, which is good for the alternator, battery charger, etc..

Before I try to reconfigure it this way, is there any good reason for the current positioning with both the blower/exhaust hose and the fresh air intake hose openings being down below the floor aft of the engine compartment?

Thanks for shedding any light on this for me!

Frank

For gasoline fueled engines the pickup point for the blower has to be low in the engine area to exhaust possible fuel fumes.
For a Diesel engine I have always been told by our mechanic to put the hose pickup higher up inside and if possible near the alternator. This pulls the most heat out.
Also, run the exhaust blower all the time the engine is running.

As far as air intake, if there is an opening to the engine compartment from back aft, the voracious appetite of the engine for combustion air will pull that air into the engine area whether you provide a 3" hose or not.
We long ago removed the extra 3" hose from the intake ventilator aft. Only our exhaust hose is in place, and it was replaced some years ago when the old hose was found to be brittle and cracked.

That said, I have spoke to many sailboat owners that either do not have an exhaust blower or never use it. These are all diesel boats, BTW.

Thanks, Loren. That makes alot of sense.
These blower motors are pretty simple and cheaply made, I think--can they handle running full time when the engine is running? Have you had to replace your blower motor, and if so, did you upgrade to a more robust one to allow you to run it so much?
Thanks again for your reply.
Frank

Frank Langer said:

Thanks, Loren. That makes alot of sense.
These blower motors are pretty simple and cheaply made, I think--can they handle running full time when the engine is running? Have you had to replace your blower motor, and if so, did you upgrade to a more robust one to allow you to run it so much?
Thanks again for your reply.
Frank

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I recall replacing the original (?) axial flow fan about 8 or 10 years ago. It was, and is, an Atwood blower. They seem to be very long lived. Only complaint is that they are kind of noisy. I never noticed until the engine was replaced, and then the new Betamarine was so much quieter that the blower was really irritating.

Thanks, Loren. I don't know the make of our blower motor, but I'll crawl in there tomorrow and check. And then I'll try to figure out a way to get the exhaust hose closer to the alternator and engine heat.
I guess if I've got time to focus on this kind of stuff, it means my boat is in pretty good shape. It's running well, sailing well, no repairs or major projects underway. So I've got time to ponder these puzzling questions.
Thanks again!
Frank

Are our blowers in the wrong place?

Frank, You bring up a valid concern in that the way many of our boats were configured to move air with a blower, including ours, seemed ass backwards. It is for that reason that I set out to change that many years ago by fitting a bilge fan exhaust side to the under side of our port mushroom vent. It now draws hot engine room up and out. An untended benefit to this is that on night passages when the air temperature is cooler, no, downright cold, That warm air serves well as a hand warmer when sitting at the helm for hours on end. The vent is easily reachable without even having to leave the helm. I have another identical vent that I posited installing under the starboard bent but was dissuaded from doing about of concern that I would be somehow depriving the engine room and finally, the engine of sufficient breathing air. I've yet to install the second one for that reason but might try it anyhow to see if engine performance is affected. Photos of my port vent installation attached here. Maybe this will help, Glyn Judson, E31 hull #55, Marina del Rey CA

Thanks, Glyn. That gives me lots to think about. And as I sail year round on the BC coast, the idea of warm hands near the exhaust vent sounds good!
Frank

Before your reroute blower hoses, if there is a stove on your boat what fuel does it use? If it's propane you may want to leave the hoses in their "gasoline engine" configuration. Propane has similar properties to gasoline, the important one in this discussion being that it's vapors are heavier than air. A leak in the system will result in a volume of explosive vapors low in the boat waiting for the slightest ignition source. With the blower system in its original configuration you'll be able to exhaust those vapors. Changing them may leave vapors behind. Ask yourself, if a leak did occur, how would I get rid of the vapors?

Be safe my friend. Of course, any other cooking fuel and the above discussion does not apply.

Mmmmm..... yes, I do have a propane stove which gets used quite frequently, and a propane furnace which is only used occasionally, but the hoses and valves for both are there continuously of course. So yes, food for thought...
But if I did have a significant propane leak, wouldn't starting the blower motor create a spark and blow up the boat?? :0
Frank

I ripped out 25 feet of exhaust hose and three in-line blowers and all the wiring. I determined that this enormous complicated mess, with hoses drooping all over the engine, hid from view everything I wanted to see and evacuated very little air.

I discussed it with the surveyor, who shrugged. He is unimpressed with most blower systems.

My engine compartment ventilation is passive--two big cowl vents on the counter and one on the coaming behind the starboard winch. BY merely opening the lazarette lid, more hot air comes out than any blower could accomplish in x minutes. As it happens, my 5432 run not very hot at all, even for long periods.

I am also entirely blase about propane. It is the commonist of commodities, heating homes across the land. My propane tanks are vented at bottom. I have an operating sniffer and solenoid. I do not descend into the cabin smoking a cigar. Photos posted about yachts blown to bits by propane exist, yes. One is more likely to be hit by a fish dropped by an Eagle than to fall victim to the probability.

I am cautious by nature and probably pathologically in fear of being snickered at postmortum, e.g., "what an idiot not to have known that would happen."

Even so, I trade simplicity for complication when possible, and I would rather have an uncluttered engine room than a maze of hoses, as I feel a great need to see what is going on and have access to it unimpeded.

Not recommending any of this to anybody; just another report of differing practice. What the forum is for.

In general, I think the majority wisdom is usually right, and when in doubt don't deviate. But do think it through your own way.

The blower motors are sealed. No spark.

Thanks for the additional food for thought, Christian. Lots to ponder as I spend today at the boat. Actually, the weather and winds are looking pretty nice out - - maybe I'll go sailing instead to give me more time to ponder.

Frank

Yeah, Bob, I guess the blower motors would have to be spark free to be at all effective for gasoline engines. Makes sense!
Frank

FWIW, the intake and out-draw vent hoses were both just laying in the bilge behind my A4 motor. I spent a couple of dollars and bought screw-on flange terminators to seal them both to the two holes in the engine compartment that appeared to be made for them. Well, that means the rest of the bilges now have no direct venting. Wrong or right, I don't know. Anyway, I replaced the plywood bilge hatches with grates, so most of the bilge remains dry and airy. Except from the companionway aft the nether spaces still have no direct ventilation. And the refrigeration unit is in there.

Also I have this nagging feeling that those engine vents ought to have dorade boxes...

The blower motor on our boat made quite a racket, so we never used it. It never would have occurred to me to keep it running the whole time the engine was on. Should I be embarrassed?

I'm a newbie but my understanding is the blower only served a direct purpose in Atomic 4 / gas-powered boats so as to prevent possible explosions from fume build-up. As such, I've completely written off the need to ever turn the blower on, which works nicely for me as mine seems to be dying with a veritable SCREAMING noise every time I accidentally flip the switch on. I'll more than likely follow suit to Christian and pull all the wires and hoses and whatever else out when I redo the engine panel, if not sooner. I don't think I'll miss it.

Sati said:

I'm a newbie but my understanding is the blower only served a direct purpose in Atomic 4 / gas-powered boats so as to prevent possible explosions from fume build-up. As such, I've completely written off the need to ever turn the blower on, which works nicely for me as mine seems to be dying with a veritable SCREAMING noise every time I accidentally flip the switch on. I'll more than likely follow suit to Christian and pull all the wires and hoses and whatever else out when I redo the engine panel, if not sooner. I don't think I'll miss it.

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My blower must be the same as Geoff's. The squealing when I turn it on (which only happens accidentally) is startling. My mechanic said, "You don't need it unless the weather gets really hot." I should have asked him how hot that is. This thread has reminded me of the blower's existence. Now, it's on the to-do list. Since my engine is a diesel, I'll focus on warm air removal.

Well, on the other hand an in-line or coaxial replacement blower is one of the cheapest and most painless boat repairs there is. The original squirrel-cage blower on my boat seized up and died early-on in my ownership, which made me suspect that the previous owner never used it.

Oh yeah, that reminds me of the state of the wiring at the time. There was a fuse and a switch for the blower on the old "main" panel, and a second switch on the cockpit engine panel. You had to make sure that both switches were turned on, though you could stop it by turning off either of them, which seemed weird and stupid to me. During the re-wire, I wired it through the engine fuse-box and kept the switch in the cockpit.

I read or heard somewhere an opinion that on a diesel boat the blower should pull outside air in to provide adequate oxygen to the engine. I suspect its not an issue on these smaller diesels, but it kind of made sense to me. And in fact that is the way my blower was pointing, so I didn't change it. But now I wonder if I should.

Bigd14,
Our boats were built in the same year, yours being 14 hulls after mine. Is there any way to tell if your blower arrangement is factory original, or was changed by a previous owner?
I'm pretty sure mine is original, because the blower is mounted quite nicely on a separate board under the quarter berth, and the hoses are placed in openings clearly designed for that purpose. Also, the starboard hose is almost impossible to access because it rises up behind the propane locker in a very narrow space.
If you think yours is also factory original, it would be interesting to know what changed their thinking regarding the orientation of the blower motor if yours really is blowing air into the engine compartment rather than exhausting it out.
Frank