[Brewgyver]

FYI, a fan running and not moving air will over amp. Draw more power than when under proper load.

It will also overheat, as most have the motor in the airflow to cool the motor.

+1 on the noise issue. The squirrel cage itself can get incredibly loaded up. Remove the cage from the motor shaft and soak it. Sometimes you can get them clean with a simple stream of water (preferably hot) directed at the blades, making them spin. You won't believe how much you can get out of them, and they'll move much more air, with less noice, once clean.

 

[krazzz]

If I thought my squirrel cage was salvageable I would probably look at tearing it apart and giving it a good cleaning but it appears to be a relic and is likely as old as the boat (43 years.) Maybe I shouldn't have been so quick to condem this old blower but I can probably replace it in half the time of tearing it apart, inspecting and cleaning it. I'd rather spend my limited free time sailing My inline blower was delivered today and I purchased the PVC pipe and fittings. Looks like I will be into the whole project for under $60. I'll be sure to post pictures of the final project. If it turns out good enough to show off I will add it to the "Low Bucks Projects" thread. Now to find the time...

 

[Delta-T]

Don't throw out the old blower. You will find that the 43 year old one, rebuilt will last you another 43 years and the cheap setup you just bought, you will be replacing in a few years.

Our boats are almost the same age, and I am in the same boat on this blower. I should have fixed it this year, but had to do the centerboard. Everything I replace with new, lasts a fraction the time the original does.

 

[Delta-T]

FYI, you do know these blowers, the motors are out of the air stream...in other word explosion proof. One spark from a fan being used to exhaust flammable fumes will be a problem. I'm not going to take my time to look it up, but I am sure there is a safety code here.

 

[deniseO30]

Let's not forget, these things are pretty small blowers.

 

[ThirdCoastSailor]

PCV sounds like it would work fine but honestly since my engine is diesel I never bothered to run the blower and eventually ripped out the vent tubing.

 

[krazzz]

FYI, you do know these blowers, the motors are out of the air stream...in other word explosion proof. One spark from a fan being used to exhaust flammable fumes will be a problem. I'm not going to take my time to look it up, but I am sure there is a safety code here.

Yes all blowers must meet USCG codes to be use with flammable gases. The inline blowers used for this type of application have sealed motors.

 

[krazzz]

Don't throw out the old blower. You will find that the 43 year old one, rebuilt will last you another 43 years and the cheap setup you just bought, you will be replacing in a few years.

I never throw out anything if there is a chance it could be useful in the future.

 

[Brewgyver]

FYI, you do know these blowers, the motors are out of the air stream...in other word explosion proof. One spark from a fan being used to exhaust flammable fumes will be a problem. (snip)

The actual term is "ignition protected," not explosion proof. An explosion proof fan would also be considered ignition protected, but not the other way round, and explosion proof motors are MUCH more expensive than standard duty.

In normal working condition fan motors don't spark, they have induction motors. No commutator, no brushes.

 

[hellosailor]

I'm told that PVC doesn't like continued high heat. It is also combustible.

Why not use plain metal ducting? Not corrugated flex hose, but plain metal vent ducting, available 3", 4", 6", etc. and much lighter than PVC too? Either you buy whatever corners you need to fit it up, or use the corrugated stuff just for the bends.

You'll also find that the shape and fairness of the actual fan blades can affect noise greatly. Rotron, the folks who make genuine "Muffin" fans? Used to have several lines of "identical" fans in their catalogue. Except, one line could be twice the noise level of the next, because of more expensive fans blades, with a better finish on them. Look for a decibel noise rating on the new fan, as well as the air volume it moves. Expect the quieter ones to be more expensive.

 

[gptyk]

Isn't standard HVAC metal ducting galvanized steel? Wouldn't that turn to rust quite quickly (assuming salt environment)?

I'd guess (as mentioned before) that the rigid PVC is no more flammable than the "dryer hose" stuff from west marine.

 

[hellosailor]

Good point. I suppose that would depend on the quality of the tubing, and whether you added some protection like a cold galvanize spray or paint.

 

[the_abuse]

I like the idea of rigid tubing you can have it go where you want im gonna do that to my boat thanks for the idea. My only question is do you only need a fan to pump air out or can you have 2 fans one to blow in and one to blow out

 

[krazzz]

My only question is do you only need a fan to pump air out or can you have 2 fans one to blow in and one to blow out

You only need one fan. I don't think two fans would hurt anything but it wouldn't be necessary.

 

[Capt Len]

The largest household downspout may be big enough for your purpose. Square aluminium tubing. Bendable elbows too.

 

[deniseO30]

the big box stores have alum 4" pipe and elbows. Most HVAC supply has it also. I'd go with abs black plastic.

 

[Delta-T]

I like the idea of rigid tubing you can have it go where you want im gonna do that to my boat thanks for the idea. My only question is do you only need a fan to pump air out or can you have 2 fans one to blow in and one to blow out

It is called pressure equalization and is required for commercial applications. This means you have to have a way for air to enter into a space to allow air to be removed. You can't remove air/fumes without having a way to replace that air. And, you want cross ventilation to evacuate all air/fumes at least five times. It can be done with two fans, one exhaust and one supply. But with two fans, you now have a second point of possible failure. KISS! This is not normally done on a boat, but would be the best. Boats use a passive intake, usually by the means of openings. My boat has two clam shell openings, high at the stern. The exhaust is piping is in the lowest point in the bilge. The fumes you want to exhaust are heavier than air. This setup lets all the compartments from the lazarette, under the cockpit, engine compartment and bilge get vented. The air intakes, if passive, need to have the free area to allow the same CFM (cubic feet per minute) as the fan is drawing out. 4 to 6 times the size of the powered exhaust. If you use a powered intake, it can be the same fan and size as the exhaust.

Using any metal ducting will not last long. I used the bendable alum. duct for my air cooled Ref system. It denigrated in less than 5 years. You might think that is a long time, I beg to differ. My 45 year old Bristol has the original fan and flexible ducting. This ducting is not dryer vent, it is much heavier hose made for this purpose. Using PVC would be okay, I have only a few concerns. One the OP has taken into consideration, vibration of the fan sound boarding the pipe and transferring and amplifying the fan noise. I would use the flex marine grade hose for this application, not rubber, the rubber might degrade from the fumes. Another concern would be vibration from the engine. The engine will shake the boat and if PVC if not mounted/secured it might rattle around. Another would be the route from the bilge to the exhaust opening. This is not going to be a straight run and will involve, in my case, many turns, not all 90 or 45 deg. And last, PVC is not rated for hazardous exhaust, but assuming you are venting nothing flammable, and we all hope we are not, and this is just a life safety item for just in case there are flammable gasses present, PVC should be okay. I do allot of lab. fume hood exhaust setup designs and we specify stainless or

.

Someone here said they do not use ventilation because they have a diesel engine. I don't understand this. Is diesel not a flammable liquid? Gas is not flammable in a liquid form, but is very explosive in a gaseous form, is diesel not? Do you have white cooking fuel? CNG? Propane? Charging batteries creating hydrogen? Bathroom, methane? Gas can for an outboard, etc?

Boat ventilation is a life safety item and should not be DIY redesigned. This is an engineering thing and should be left to the professionals. Location of inlets and outlets, fan selection and static pressures needed. The amount of air exchange needed and how long you need to run the system are all mission critical here. Even if this is proceed as a small fan system. And if that all does not convince you, then talk to your insurance company and see if your boat is still covered after you alter the OEM without a system designed and engineer approved.

 

[the_abuse]

My own ventilation is degraded to the point of being near inoperable so I think I surface wouldn't mind if I rebuilt it to a better spec than what was issued

 

[hellosailor]

The only drawback to flex hose of any sort, is that it radically slows down the airflow. I don't recall the numbers but was taught this a long time ago, in connection with exhaust pipe systems. Corrugated hose creates a lot of drag and turbulence in the hose, you are better off not using it. That turbulence will create extra noise and vibration, and demand a more powerful fan (more noise and vibration and energy used) as well, to move the same amount of air.