Quiet 12v Galley Blower?

[Canibul]

Working our way through this boat I'm slowly improving things where I can. One real annoyance is a very noisy galley exhaust blower. It's so loud we have to shout to carry on a conversation over it. It came with the boat, and is one of those ducted fan type inline blowers, mostly advertised as bilge blowers. This one uses 4.8 amps and does a good job exhausting cooking fumes but dang it's deafening. It's hooked up with standar aluminum 4" dryer hose, and vents overhead through a screw-down mushroom cap kind of vent cover.

Does anyone here know of a good, quiet alternative to these jet engine things?

[JPA Cate]

Try mounting a computer cooling fan in there instead. You'll probably want to make a timber frame for it.

Another possibility might be to mount one of those vents with a solar powered fan to suck the air out. [I have never used one, and do not know how reliable they are.]

[Cheechako]

Yeah, it depends on how much you think you need. the bigger Computer fans are quiet. A small hatch over the stove area works exceedingly well also, especially if it opens aft side, the flow across it or thru the boat really evacuates a lot of air.. more than a fan.

[colemj]

Oh, I am watching this. We too suffer from loud exhaust fans in the galley. Here is what we know/tried so far:

1. A computer fan just isn't going to cut it. They are not designed for the flow necessary or the flow restriction in the application.

2. There are very quiet in-line blowers. Actually, all of them are pretty quiet when new. However, they gradually become loud as leaf blowers over time - let's say they are perfect for 4-6 months, then noticeably louder between 6-18 months, then they are screaming after that. The problem is the stuff that gets pulled into them. We have a filter that looks like course SS wool in our range hood (I'm calling it this for lack of a better term), but grease and moisture still get by it. The blowers start to look like crud on the inside after a while. If I put in a finer filter, the air flow lowers too much.

3. There is a variable speed control on our fan circuit. We can use this to change the "tone" of the fan so that it is a bit less annoying. It isn't that we even change the speed much - just a tweak around high speed changes the tone. This is minimally helpful.

4. A squirrel cage blower seems like it would be the best solution, but we cannot fit one in any way to work in our particular setup. The 90* intake/exhaust is a killer.

What we have settled on is buying cheap in-line blowers and changing them every 1.5-2yrs. They are really quiet when new, and if you buy the really cheap ones, the cost isn't too onerous. Here are the ones we currently favor: Very Good Marine Boat 12V Electric in Line Bilge Air Blower 130CFM 3" | eBay Ours is branded "TMC", but it looks like this one with the same specs. I think the same blower has several different brand labels slapped on it.

Anyway, if you get any good insights on this let me know! I don't think it is a "normal" problem here, because I don't think many boats have exhaust hoods over their galley.

Mark

[colemj]

Actually, it isn't clear to me what you need. Are you talking about a range hood like I describe as ours, or just an opened active vent in the side of the boat next to the galley?

If the latter, then a large computer fan or similar would work. I assumed you had a hood over the stove that needed a blower to pull air through and out.

Mark

[redsky49]

What type of noise are you experiencing? Is it fan noise, coming from the motor or the fan blades? Is it roar at the intake, perhaps due to the airflow exceeding the capacity of the intake (grille?).

Is it duct noise due to too small a duct, too many turns or a restriction in the line? Is it primarily at the discharge end?

Could it be vibration transmitted through the hull from the motor assembly?

[colemj]

For us, it is the fan. The other things also make some noise, but it is constant and known. The fan itself gets progressively louder over time. It could be the motor or the blades, but these things are pretty much a sealed one-piece molding. There really isn't the ability to suss out much about them.

The noise is both inside the boat and outside at the exhaust vent.

Mark

[Cheechako]

Those type of fans are always noisy. new or old. Never heard one that wasn't. I like the rheastat idea to find the least noisy RPM though.

[colemj]

Like I said, they actually are pretty quiet when new and get louder as they age (in this application). The Rule models are terrible from the start, but we have found most others to be very quiet. Another quiet one we had was a "Yellow Tail", or something like that. We put in two of those, but they are rather expensive. We later gravitated toward <$20 ones, and find they they last just as long as the more expensive ones before getting loud.

Mark

[redsky49]

Originally Posted by colemj

For us, it is the fan. The other things also make some noise, but it is constant and known. The fan itself gets progressively louder over time. It could be the motor or the blades, but these things are pretty much a sealed one-piece molding. There really isn't the ability to suss out much about them.

The noise is both inside the boat and outside at the exhaust vent.

Mark

An issue with all kitchen exhaust fans is the loading of the fan blades with grease/dirt/yuch. Once this occurs, the fan typically increases in noise due to the reduced aerodynamic qualities of the blades, the fan starts to go out of balance, and it just goes downhill from there.

Inlet grease traps can go a long way to deferring this problem. If unable to access the innards of the fan, you are likely facing replacement. Spraying some sort of degreaser or solvent into the intake, in order to clean the blades, is strongly discouraged. You are more likely to destroy the bearing or the motor than to fix the problem.

[Canibul]

Originally Posted by colemj

Actually, it isn't clear to me what you need. Are you talking about a range hood like I describe as ours, or just an opened active vent in the side of the boat next to the galley?

If the latter, then a large computer fan or similar would work. I assumed you had a hood over the stove that needed a blower to pull air through and out.

Mark

It's a, uh, sort of range hood approach. Without the hood. Basically one of those 4" diameter inline bilge blower type fans held by 2 #10 screws to a bulkhead in the galley. There is standard, hardware store type aluminum 4" flexible round duct extending downward about a meter to it's open end which is secured over the top of the Force 10 stove. The outlet goes up through a galvanized flex elbow through the cabin roof. It's got one of those screw-down-to secure aluminum mushroom caps on top to close it up in weather. There's really no restriction in it. The blades are clean. Not much grease buildup. I don't think the fan has been used much. Last owner told us he never used the stove. |

The fan works fine. It exhausts a lot of cooking/frying odors right up and out of the boat. It's just deafening.

So far the only thing I've done to it is remove it and drill the mounting holes out and put it back up with longer screws so that I could put rubber grommets between the screw head and the flange, and between the flange and the bulkhead plywood. To dampen the mechanical connection to the plywood. Helped a bit.

I've got some sound deadening coating I could paint onto it. Or build a box around it with insulation. no issues with cooling because the motor is in the flow.

An externally mounted exhaust blower on the deck would be good, but I can't find a good one on the internet. yet.

[colemj]

When our fans get noisy, they are also working just fine. The amount of air blown is as good as ever.

If you disconnect the fan from everything else and run it, is it still noisy? Maybe your particular setup is like a trumpet or something, and you need to install a bend or baffle to stop it from resonating?

Or just get another cheap blower and see if that works better. This is what works for us - the blower becomes loud by itself and we replace it.

Mark

[GordMay]

Because fans operate at a low frequency, and are light in weight, vibration isolators must be soft and flexible. A common error with the use of these pads is for the bolt to ”short-circuit” the pad, resulting in little isolation. Installing an additional pad between the screw head (& washer) and the fan mounting foot will reduce this short circuiting, and greatly improve isolation.

Ideally, for maximum fan efficiency and minimum noise, make sure there is at least 2 - 3 duct diameters of straight (not corrugated) duct between any feature that may disturb the air flow and the fan itself.

Fan noise is roughly proportional to the 5th power of fan speed. So in many cases it is possible to achieve a large noise reduction from a small drop in fan speed.

[GordMay]

Originally Posted by GordMay

... Installing an additional pad between the screw head (& washer) and the fan mounting foot will reduce this short circuiting, and greatly improve isolation ...

Edit:
I should have noted that the hole in the mounting foot must be larger than the screw diameter, so that the screw never comes into contact with the fan mounting (remains "isolated").

[Canibul]

Originally Posted by Canibul

So far the only thing I've done to it is remove it and drill the mounting holes out and put it back up with longer screws so that I could put rubber grommets between the screw head and the flange, and between the flange and the bulkhead plywood. To dampen the mechanical connection to the plywood. Helped a bit.

Yep. Drilled it out so that the flange isn't touching any part of the screw.
There are two grommets per screw, one on each side of the flange.

I've been thinking of trying "squishier" material for the dampeners. Had good luck in the past punching round washers out of the tops of old Crocs. Can stack em to play with durometer, but they last forever. There are still some Croc isolation dampeners riding around this island under the air-cleaner on a Land Rover. Mounted a macerator pump under a live well with Croc rubber. It's really good stuff, actually. UV doesn't hurt it and it's impervious to most stuff.

All of the noise is fan noise. And this is now a new fan just installed last night.
http://www.amazon.com/gp/product/B00...ilpage_o06_s00

Same installation, and only slightly quieter than the old one.

I can handle a 90 deg. installation, so now am thinking maybe squirrel cage is the way to go if I can find one small enough. And with 4" intake and outlet fittings.