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The difference in the between a prop fan and a centrifugal fan is huge. Prop fans have difficulty creating static pressure. Static pressure is need to push the air thru the tubing. The longer the tubing and bends in the the tubing, the more static pressure you need. Corrugated tubing creates a lot of static pressure, smooth PVC is much less.

You will commonly see prop fans in a window with no duct work. Centrifugal fans are used for almost every other application in HVAC.

And inline fan does not mean it is a prop fan. Most are Centrifugal fans.

As far as sound goes, hands down a Centrifugal is quieter. If a Centrifugal fan is noisy then it is out of balance from dirt or debris or the bearings are shot. Motors can be replaced.
 

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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.
 

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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.
 

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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.
 
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