south pacific columbia 30´

[Blue Knight]

Hi everyone:

I have a 1974 Columbia 30 sailing in Lima Perú. I have an Atomic 4, with God only knows how many hours. But since last major overhaul a year ago,(including cylinder liners, valves, rings, etc ,.pistons were ok) and after the trial and error process of tuning it. (Recently discovered the forum)I think I now have a very strong little engine purring along the peruvian coast, when ever needed.

A question regarding blowers. Must the suction be near the bottom of the engine room or at the top ? will a bigger blower sucking air from top of engine room be more efficient than suction at bottom ? any info will be appreciated.

regards,

Manuel

[bputney]

Where to locate blower intake...

Hello,

I think you're supposed to locate the intake for the blower near the bottom of the engine compartment,mainly because that is where the gas is likely to be sitting. I guess closer to the source. I don't know if gas fumes are light or heavier than air. I put mine as low as I could.

Hey, do you know if you're supposed to run your blower any time the engine is on, or just the 5 minutes prior to start?

Thanks,

brett

[Blue Knight]

Hi Brett:

Thanks for your reply. Yes, I remained with suction close to engine, carb area. Regarding using blower, I used to, for a couple of minutes, whenever cruising long hours, since oil filler cap is also a breather on gearbox vent, all smoke gets to the cabin. I solved this problem extending a hose from the vent tube (without the cap) and connecting it to the suction hose that delivers gases at the side of the cockpit, via the blower. It works beatifully, no more smoke in the cabin when running long hours with the engine. If wind is strong enough, sometimes natural aspiration pulls smoke without using blower.

Manuel

[Windsinger]

Blower hose locations

Hi folks. I've had a bit of experience with the location of blowers and hoses. Gas fumes are heavier than air. That's why I installed a blower in my bilge, at the lowest point in my engine room and one actually blowing in. It's always a good idea to use a fume detector also. I see that Moyer has a good selection. The one I have blowing in I put close to the carb intake so as to get the freshest air to it. Heat and any smoke wont affect it that way. It's also a good Idea to have your intake and exhaust cowlings on a swival base. In rough seas you can turn the intake around and assure yourself that you will get not water in. Hope this info helps. That's what we are here for. Hope the winds are good for all of you.

[Baltimore Sailor]

I'm pretty sure they're called "blowers" because they don't provide suction. If one is trying to get rid of potentially explosive fumes, I think pulling them into an electric motor is contraindicated.

The blower should force air INTO the engine compartment so that the hypothetical fumes will be pushed OUT of a conveniently-provided exit path.

[Baltimore Sailor]

Hello,

I think you're supposed to locate the intake for the blower near the bottom of the engine compartment,mainly because that is where the gas is likely to be sitting. I guess closer to the source. I don't know if gas fumes are light or heavier than air. I put mine as low as I could.

Hey, do you know if you're supposed to run your blower any time the engine is on, or just the 5 minutes prior to start?

Thanks,

brett

We had a poll on that a while back, and it pops up every so often still. Personally, I run my blower the entire time the engine is on. It helps provide fresh air to the intake and clears out any smelly engine outputs. I also have the PCV modification to the carb, and now my boat smells like "boat" and not "engine." (Actually is smells more like my air freshener; those car pine tree dangly things are STRONG!)

Also, the blower should not suck, but blow. (Low humor not intended.) You don't want to pull potentially explosive fumes into an electric motor.

[ndutton]

Oooh Balty, gotta disagree w'you on this one.

Blowers, aka exhaust blowers, are intended to suck and the motors are supposed to be sealed from dangerous vapors the same as our battery switches although how well they are I can't say. If fresh air is positively blown into the engine/fuel space it will disperse the nastiness all over the place. In agreement with your motor-in-a-possible-vapor-environment concern, the blower should be mounted as high as possible.

I bit my tongue on Windsinger's post because he was exhausting air as well as supplying it, a 2 blower system if I read it correctly. I don't think his blower in the bilge is a good location though because that's where the fumes collect.

Sorry, guys.

[roadnsky]

Gotta go with Neil on this one...

Fresh air is supplied by a vent (PORT on my Vessel) with appropriate hose.
The removal of any possible fumes is accomplished with an Exhaust Fan that is mounted NEAR a vent (SBD on mine)
with the hose located as close to the bottom of the engine room as you can get it.

The idea is to SUCK the fumes out and create a FLOW of fresh air in the engine compartment.

[Baltimore Sailor]

Interesting. In my boat the fan pulls air into the engine compartment. It is mounted high in the compartment and has a vent hose connected to an outside air source. The vent hose (it looks like small dryer vent hose) is lying on the deck right behind the engine and is attached to an exhaust vent. When the blower is running air flows strongly out of the exhaust vent. The installation looks original, so I assumed it was designed that way. It seemed logical to me for the reasons I said before.

Of course, the fix is simple: reverse the polarity of the connection. Then my fan will suck instead of blow.

[sastanley]

suck & blow

BS,
Mine sucks too. - It pulls air out from the bilge.

I plan to add some length to my blower hose to get it lower in the bilge where the fumes would reside (if there are any)...on my C-30 the hose doesn't make it much past the fuel tank right now.

[ndutton]

I'm so confused.

Is there only 1 vent hose attached to the blower? What is the outside air source mentioned? Different from the exhaust vent? How many vents do you have?

Thought I'd ask before replying to your post and embarrassing myself.

I will offer this, though. Reversing the polarity to the blower will result in a very inefficient flow. The design of the squirrel cage is efficient in only 1 direction.

[CalebD]

Suck or blow???

I never thought that the nuances of this subject would garner such interest. There are some subtleties to be considered though.
To answer Neal though, the 'outside air source' on our boat are 2 cowl vents that are mounted on deck aft of our rudder. And yes, only 1 vent has a blower in it; the one that sucks the air out of the engine compartment. The blower is located just below the cowl vent. The other vent provides fresh air to the engine compartment and we usually orient this vent pointing forward with the exhaust vent facing aft. Fresh air is forced into the supply vent by the exhaust vent sucking and passively by the cowl.
The only problem I can think of with having 2 fans (one for each supply and exhaust - suck/blow) is if the intake fan overtakes the exhaust fan then the exhaust gases could be forced out of the engine compartment into the cabin.

As far as squirrel cages go I am all up a tree!

[Marian Claire]

On the MC the intake for the blower/sucker is below the tank, carb, oil pan basically at the lowest point in the engine compartment. The fan is located outside of the engine compartment and above the carb level. The exit for the blower/sucker is in the cockpit. There is no dedicated supply of air to the engine compartment but just general vents. One from the cabin space and one over the lazeret. I will be back on the boat Wed and will check the type of blower/sucker I have. How do you tell if it is “sealed from dangerous vapors”? Dan S/V Marian Claire

[ndutton]

To clarify, my confusion was with Baltimore's setup and my questions were directed there.

No issues with my system, flange mounted blower under a cowl vent, ducted to a point at the bottom of the engine space. Supply air provided by another duct running from a second cowl vent to the fuel tank area. Fuel tank and engine areas communicate atmospherically. Good air flow, system works well.

10-4, Roger, Out.