Exhaust/extractor fan

drcoastline · 03:40 AM

I can't think of a better place to come to for good ole' Mercan engineering and problem solving than here.

So I own a big old wooden boat which is subject to mold and dry rot if not looked after. While this boat is now sixty years old and does not have any major issues. Mold is ever present. Controlling humidity/moisture and adequate ventilation will greatly reduce the chances of mold growth. Humidity is controlled by the AC units and we have an onboard dehumidifier when necessary. There are areas deep in the bilge below the floors and water line that are stagnant. They have no air movement can have high temps when the engines or generator are running and don't get any relief from the AC systems or the dehumidifier. So I am going to devise a ventilation system to move air around down below.

I am looking for a medium to high volume in line exhaust fan, 12V, 36V or 110 power low noise that I can attach a flexible ductwork or PVC pipe to say 3" to either end. One end in the engine room the other out a port hole to exhaust the air. The fan will run 24/7 when the boat is not underway. The fan and most ductwork will be permanently mounted below the floor. The exhaust side of the duct work will be able to be disconnected and stored. the hatch closed when needed.

Any ideas on a fan?

dad911 · 04-04-2018, 06:34 PM

if you want 110v A/C, you can get a radon fan, they run about 100 bucks.

for 12v, don't they make bilge blowers?

Tobra · Tobra's Garage

Maybe a cooling fan for a computer?

island911 · 04-04-2018, 09:01 PM

E-Ram - Moment of truth?

Seriously, One thing to think about is make-up air. --a path for air to come into the space easily.

look 171 · 04-04-2018, 11:31 PM

Ventilation Products for Residential and Commercial Applications | www.fantech.net

We use their fans often. Inline mount in attic and they are ultra quiet. Use insulted flex duct to further reduce wind noise if necessary. A silencer or muffler can be added for even quieter operation. The inline fan by itself is plenty quiet and you have to stop talking and really pay attention to hear this fan. Great stuff

id10t · 04-05-2018, 02:54 AM

Quote:

Originally Posted by Tobra

Maybe a cooling fan for a computer?

This, plenty of sizes to choose from, cheap.

KFC911 · 04-05-2018, 03:01 AM

Methinks the link Look171 provided is the solution. Inline and designed for that purpose....my dad has one simlar in his ductwork in the basement for a woodstove.

onewhippedpuppy · 04:47 AM

You guys are overthinking this. A bilge blower, or multiple bilge blowers, are exactly what he is asking for. Available in multiple airflows and diameters, designed to exhaust air out of a bilge, designed for a marine environment, designed to be attached to a flexible duct on either end, available in 12 VDC for easy connection to the boat electrical system (also available in AC), and cheap. All of my boats have had them, I think the current one has one that is connected to a 3" flexible duct (think dryer vent) to suck flammable vapors out of the engine bay prior to starting. I'd be willing to bet that a household exhaust fan wouldn't last very long in a damp marine environment.

If you keep the boat sealed up, you could also add a desiccant designed for a marine environment to your dehumidifier. I've always taken the approach of trying to promote airflow, but my boats are probably smaller too. For winter storage we have a top with vents and take everything out of the boat. We also keep it in dry storage so that helps too.

drcoastline · 04:35 AM

Hey guys, thanks for the input. A bilge blower is exactly the design I am looking for and was my first choice as it provides excellent air movement through the bilge because that is what was designed to do. Unfortunately it won't work in my application for several reasons. First they are designed to run for short periods of time. Five to ten minutes to clear a bilge of fumes prior to starting a gasoline engine then they are shut off. They are not designed to run 24/7 for days at a time. Second they draw a lot of power, I am looking for something that has a low power draw. First to keep my electric bill down if on shore power and second to keep a low draw on the batteries. If for some reason there is a power failure and my battery charger can not keep the batteries topped off, the fan will run the batteries down pretty quickly leaving the boat vulnerable as I won't have power for the bilge pumps in the event they are needed. Lastly is noise. Bilge blowers are noisy. No big deal during the day but at 3AM it might present a problem.

Island911- Make up air isn't an issue the engine vents will provide more than adequate air supply. Not to mention the construction of the boat is designed to allow air from above to be pulled down between the ribs into the bilge. What I am attempting to do is devise a system that will pull fresh air through the engine vents and from above down into the bilge and then vent out of the boat. Keeping a constant flow of fresh air through the bilge.

A computer fan has been mentioned to me before but I don't know anything about them or the amount of air flow they provide. If you can help educate me that would be great.

Look171 your suggestion may be what I am looking for and the flex duct is what I intend to use to exhaust the air.

onewhippedpuppy- In my boat sealing it up tight would be a death sentence for the boat. Keeping air flow is the prudent way to go as you suggest. That's why I am trying to devise a system to increase the airflow through the boat.

john70t · 05:44 PM

Assumed covered...
Perhaps use some type of miniature space heater powered by a little solar panel?
Mount it on a cinder block.

The small amount of heat will create upwards air pressure and movement by itself.
And the tub sides + cover will make the space inside warmer by just a degree which might help drive out moisture.
Maybe...
Or would it just bring in more humid air to condense on the cold walls?

VincentVega · 04-05-2018, 06:13 PM

I like the solar vent fan but they don't move a ton of air and might not look might. There are a bunch of options, maybe one matches other ports. If so you can add a few for not much $$. If you want a wired fan check out caframo. Very low power consumption and several options.

dad911 · 04-05-2018, 07:40 PM

Did you look at radon fans? Quiet, made to run 100% duty cycle.....

drcoastline · 04-06-2018, 02:33 AM

DAD911- I am sorry I didn't reply to your suggestion previously. No I have not. I will look into them.

Afterburn you can see it here. GM 671N Marine Diesel

onewhippedpuppy · 04-06-2018, 03:56 AM

That's actually not true with regards to bilge blowers, you just need to search specifically for continuous duty blowers, not intermittent. Here's an example that I found in about 5 seconds: https://www.hodgesmarine.com/Jabsco-4-Flexmount-Continuous-Duty-Blower-p/jab35770-0094.htm

As for sound, you just need to match the ducting and fan accordingly. Bigger ducting will cut down on the negative pressure but also make it quieter. You can also pick a lower speed fan to cut down on sound. Another option related to the above fan that is 24 VDC, if you run it at 12 VDC but keep the same current it should cut the RPM in approximately half. There are an abundance of options and they are designed for this exact application, I don't think you should rule it out.

If you want to go in a different direction, maybe a household bathroom exhaust fan would work? They are designed for continuous duty and would be quiet. I would just be concerned about how they would hold up on a boat, and you have to have AC power available.

greglepore · 04-06-2018, 05:33 AM

I can second the recommendation for fantech if you're ok with 110. I have several in the house, use a big one (like 1000 cfm as a kitchen exhaust that pulls air down one story and out, and others as bathroom vents. Excellent products, and they make a "muffler" that works really well and doesn't affect airflow.

drcoastline · 04-08-2018, 03:54 AM

Quote:

Originally Posted by onewhippedpuppy

That's actually not true with regards to bilge blowers, you just need to search specifically for continuous duty blowers, not intermittent. Here's an example that I found in about 5 seconds: https://www.hodgesmarine.com/Jabsco-4-Flexmount-Continuous-Duty-Blower-p/jab35770-0094.htm

As for sound, you just need to match the ducting and fan accordingly. Bigger ducting will cut down on the negative pressure but also make it quieter. You can also pick a lower speed fan to cut down on sound. Another option related to the above fan that is 24 VDC, if you run it at 12 VDC but keep the same current it should cut the RPM in approximately half. There are an abundance of options and they are designed for this exact application, I don't think you should rule it out.

If you want to go in a different direction, maybe a household bathroom exhaust fan would work? They are designed for continuous duty and would be quiet. I would just be concerned about how they would hold up on a boat, and you have to have AC power available.

I'll look into the bilge blowers further. If I can get a bilge blower to work I think that is the path of least resistance. My concern is not the sound of the air movement but the actual motor sound which in my experience are very noisy. I would also be concerned about the amount of power they use. Again, if we lose power when I am not around to turn the fan off I would be concerned that the fan would quickly drain the batteries leaving the boat vulnerable. I am not opposed to a bathroom exhaust fan, computer fan, etc. again if I can make a clean install, low power and quiet. If I need to replace a fan every few years no big deal. Still far cheaper and less work than repairing rot damage that could easily run in the tens of thousands of dollars.

Greglepore- I am OK with 110. My main concern with 110 would be cost to operate. If efficient it would be fine.

There are a lot of ways I can create air movement in the bilge. Again I am looking for a more or less permanent install that is essentially hidden in the bilge, is quiet, with a low operating cost.