How do you use your blower?

[ButchPetty]

Thanks man. That is the knowledge I was looking for.

Happy Luffs

[rigspelt]

When adding new engine or fuel tank air exhaust ports to an existing boat design, there is code about the proximity of the new exhaust port to places where fumes can re-enter the boat.

This thread has has me thinking about three reasons to vent the engine space:
1. To remove gasoline fumes (draw from the lowest spot).
2. Supply engine with fresh air for combustion at an appropriate rate.
3. Vent out hot air and replace with cool air for thermal control (draw from highest spot).

Not a simple engineering feat on small sailboats, really.

[ButchPetty]

When adding new engine or fuel tank air exhaust ports to an existing boat design, there is code about the proximity of the new exhaust port to places where fumes can re-enter the boat.

This thread has has me thinking about three reasons to vent the engine space:
1. To remove gasoline fumes (draw from the lowest spot).
2. Supply engine with fresh air for combustion at an appropriate rate.
3. Vent out hot air and replace with cool air for thermal control (draw from highest spot).

Not a simple engineering feat on small sailboats, really.

Thanks. That project is fast approaching.

[Bobgrif]

I use the sniff test every time I go aboard and run the blower a few minutes before I fire up the A4. Someone made the point that if a substantial gas leak occurred such as a fuel line break, it is unlikely that the bilge blower would cope. I checked the blow capacity of my blower and it's only around 200 cubic feet per minute, so I decided not to rely only on the blower. I now have a gasoline vapour detector with the detector located within 12 inches of the carb, filter and fuel pump (I test often with a paper towel containing a few drops of gasoline), with the guage located next to the engine instrument panel. I also installed an automatic fire extinguisher, the biggest I could fit.

Bob
s/v Dovetale (C&C Corvette)

[hnygren]

Blower

Several years ago this was worried to death on another forum, and one math minded owner compared the volume of air exhausted by the blower to the amount of air pulled in by the running engine. His conclusion, once she starts the air flow into the running engine dwarfs the blower output anyhow. I shut mine off. The advice on sniffing is well worth taking in addition.

[ILikeRust]

Several years ago this was worried to death on another forum, and one math minded owner compared the volume of air exhausted by the blower to the amount of air pulled in by the running engine. His conclusion, once she starts the air flow into the running engine dwarfs the blower output anyhow. I shut mine off. The advice on sniffing is well worth taking in addition.

This is what I've always figured. Let's do the math - feel free to check me here and keep me on the straight and narrow if I make a mistake along the way...

The A4 displaces about 65 cubic inches. Each cylinder takes in its volume of air once every 2 revolutions, so it takes 2 full revolutions of the crank to suck in the full displacement of the engine. So if it's running at, say (to make things easy) 1,000 RPM, it's inhaling 65 cubic inches every two revolutions, or about 32,500 cubic inches of air per minute.

Since cubic inches divided by (12 x 12 x 12) = cubic feet, that's about 19 CFM (actually 18.80787...).

So if your blower is 200 CFM, the blower dwarfs the engine's air ingestion. By the same token, I always figure if it didn't blow up when I started the engine, and now the engine is merrily running away down there, it is sucking air in, and I also typically keep the companionway wide open while motoring, so it's well ventilated, so I turn the blower off.

Is there an ABYC standard regarding running the blower while the engine is running?

[ILikeRust]

And I now see the same math was done upstream in this thread...

[edwardc]

But at 1000 RPM, there's some non-zero amount of vacuum present at the manifold. This means that the 65 cubic inches of air every 2 revolutions is actually air at a lower pressure, and is the equivelent of a somewhat smaller amount of air at normal atmospheric pressure.

Which makes your point even more!

I usually like running the blower while the engine's on in the summer to help evacuate some of the engine heat out of the boat!

[domenic]

Normal first time starting procedure on the MC. Check the bilge. This puts my nose at the lowest point in the boat. Sniff. Open the main hatch to the engine and open thru hull and gas cutoff, check oil level and general visual check of engine. Sniff. Run blower for 1 minute or so. Sniff. With hatch open I start her up. The man who built the MC gave her a large engine compartment with good ventilation. While motoring I often open the main hatch, in the cockpit sole, and give a good look/see. I always run the blower before restarting after sailing but do not do all the other steps. So yes I use the blower before each start but not constantly while the engine is running. Dan S/V Marian Claire

I agree 100%. Bilge is the lowest part. Gas fumes are heavy. I open the engine hatch, cabin door, and foward hatch. let the wind clean it out.

Don't like gas fumes, sharks, and spiders.

Domenic

[Dave Neptune]

Fyi

For the A-4 to move 200 CFM it would have to be at WOT and turnig just over 10,600 RPM right where I run mine, outside the marina of course.

At 2,000 rpm cruise and about 6" of manifold will not move much air as far as ventilation standards are concerned.

Dave Neptune

[hanleyclifford]

I agree 100%. Bilge is the lowest part. Gas fumes are heavy. I open the engine hatch, cabin door, and foward hatch. let the wind clean it out.

Don't like gas fumes, sharks, and spiders.

Domenic

I'll agree on the gas fumes and sharks (except on the menu), but I like the spiders in the bilge - I think they eat the no see-ums.

[jpian0923]

I hate the noise from the blower "and" from the engine, but not from the sails.
I guess the question I have is, Is it a blower or a sucker?
Mine is a sucker. And, I know if it's sucking air/fumes from the bilge that that air/fumes has to be replaced by something.
I'm guessing it's replaced by hot air from the engine compartment (or it's replaced by cool air from outside which displaces the hot air faster).

So, it cools my engine compartment, alot.

[Dave Neptune]

Good fortune!

My engine sits right on the keel the lowest spot in the boat. My exhaust (fan side) hose sits under the engine inside the engine box and the inlet hose from the transom goes to the top side of the box at the exhaust end of the engine. This works well at venting the engine box as well as any fumes in the bottom of the bilge.

Dave Neptune

[gary gerber]

My standard proceedure is to run the blower for five minutes before starting the engine then remove the engine access cover, open water valve when starting the engine, when engine is running I immediately go to look for exhaust water discharge. Then I check all engine hose connections and the stuffing box for leaks. Then I shut down the blower and replace the access cover. This has been my routine for forty years.

[Mo]

Need a system...saves problems.

I never start the boat without going aboard...never. I don't always check the bilge unless it rained ( have a keel stepped mast and water sometimes runs down the inside). I will smell gas if it's there.

Usually, I'll be on the boat 20 minutes or so before my wife and kids show up. I go through my routine, check oil, turn my little grease cap for the pump, check position of by-valve, autopilot switch on, power on.

Then sail cover off, main halyard on, most main sail ties off, furler ready to deploy the jib, some dock lines off. Then open lazarette; open fuel valve, stow sail cover and binnacle cover in that lazarette.

I usually run the blower for a minute, but there are times I have forgotten...as long as I stick to my system I should avoid a fire / explosion. We have to remember the SYSTEM. Your nose is a good detector if you can smell, don't enter the boat with a cigarette in your mouth, and use your fuel shut off when away from the boat.

I put an entry in the below thread a while back. Had I been smoking I'd be playing a harp.

http://www.moyermarine.com/forums/showthread.php?t=1802