Boat ventilation using fans

[orangemikey]

Hi All,
When ventilating my boat using small computer fans do i want to be blowing fresh air into the boat or do i want to be blowing the stale air out of the boat.
Many Thanks
Mike

 

[mattnj]

both, assuming you have more than 1, run them opposite, so you create flow through the boat

 

[orangemikey]

thanks for the reply but i am only putting in one fan (in the washboard) however i do have small normal vents up the front so should i be blowing out and assume that this will then suck in air through the normal vents to create the through flow?
Mike

 

[Pye_End]

When moored, what is the usual direction of flow of air? Worth not trying to fight it.

If you are using whilst on board then I would extract the one that is nearest the cooker, unless you have something else for this.

 

[alahol2]

Logically you want to create positive pressure inside the boat, so blow air in like a car. On the other hand I don't think a computer fan is likely to create any positive pressure so it probably doesn't matter whether it sucks or blows.

 

[prv]

Logically you want to create positive pressure inside the boat

Do you? Why?

For what it's worth, the computer fan I fitted to cool my metal shed in summer is run as an extractor, sucking warm air out to be replaced with cool air through the gaps round the doors etc. On a sunny day you can feel a plume of hot air coming out of it on the outside.

I can't really see why it would matter either way, as long as the air is moving.

Pete

 

[Searush]

Thread hijack approaching

I bought a solar powered vent to put in my forehatch but another forumite said that his got splashed on its first trip out & died. Any better (or worse!) experiences please?

I have a "powered vent" factory fitted 37 years ago & that still works, but it ain't solar & I'll bet it cost a small - no, make that medium - fortune at the time.

 

[mikemonty]

Do you? Why?

For what it's worth, the computer fan I fitted to cool my metal shed in summer is run as an extractor, sucking warm air out to be replaced with cool air through the gaps round the doors etc. On a sunny day you can feel a plume of hot air coming out of it on the outside.

I can't really see why it would matter either way, as long as the air is moving.

Pete

There is a reason but it has little to do with logic and more to do with physics.
A fan will not work as efficiently if it is "sucking", there is a natural throttling effect as the suction side pressure drops.
For that reason a fan should blow into the cabin so that there is an inexhaustable supply of air at atmospheric pressure and therefore no throttling.

However I doubt that a computer fan would make draw sufficient air to depress the cabin pressure and so in this case the subject is moot...

 

[alahol2]

Do you? Why?

Pete

Well, theoretically, logically, positive pressure should prevent liquid (as opposed to vapour) water from entering. As I said later it probably doesn't make any difference with a computer fan, as you said it's only moving the air about a bit.

Edit: AND as mikemonty explained while I was typing... but then I didn't know that.

 

[Wunja]

Hi All,
When ventilating my boat using small computer fans do i want to be blowing fresh air into the boat or do i want to be blowing the stale air out of the boat.
Many Thanks
Mike

My view is that the boat is a long way from sealed, especially around the hatch and that pumping air in at this point, most of the fresh air would leak out at these points. So I installed the fan under one of the vents in the bow, working as an extractor.

Thread hijack approaching
I bought a solar powered vent to put in my forehatch but another forumite said that his got splashed on its first trip out & died. Any better (or worse!) experiences please?

I have a "powered vent" factory fitted 37 years ago & that still works, but it ain't solar & I'll bet it cost a small - no, make that medium - fortune at the time.

Similar experience. One wave over the bow and the inside got flooded and both motors seized. That said, I suspect quality makes a big difference. Mine were sold as caravan and boating, so probably not the full marine spec or price.

 

[Quandary]

Searush
My boat has two which perform well (3 yrs) but they are either side of the companionway so sheltered by the sprayhood which, off course, reduces the amount of sunlight they get for charging, they run busily on bright days but do not keep going all night. They are Marinco. made in USA they come with a 2 yr. warranty. The forward passive vent in front of the forehatch is a straightforward screw up and down mushroom and there is another of these below the main hatch garage. When the sun is out we get a good flow through for cooling but I suspect that on their own they would not give enough thorough through ventilation in the middle of a typical UK winter.
The 3" Minivent size (7" overall) is claimed to move 20cu.m. per hour in daytime, 160cu.m. in 24 hrs and one is supposed to be adequate for an up to 24' boat but they only offer passive night ventilation, the 3" Day and Night 2000 works at the same rate but keeps going for longer claiming 480cu.m. per day.

 

[Bobobolinsky]

I have two fans in my Mobo transom and the boat is always fresh and dry. They are 220v units from industrial chillers. They have been in semi continuous operation as far as I know for five years. They both extract and of course they don't pull any rain in