Do you suck or blow

[RaymondR]

Be careful of the sucker crown mate, they generally harbour ulterior motives.


After about fifteen years of living aboard, mainly in the tropics and just into the temperate zone, I have found that have both sucking and blowing is necessary.


The first thing I had to do when I moved to the tropics was design some hatches I could leave open in rain storms that were much bigger and had fold down side screens. I could not find any commercially available hatches to fit my requirements so I had some made from alloy and fitted the alloy side screens myself. I then discovered that a fold up louver assisted in keeping the rain out and although it decreased the exit cross section by about half it increased the drawing ability of the hatches.


The home made hatches have at least doubled the cross section of the through-deck ventilation cross section although they don't look half as pretty as the yachty ones they replaced (but then again I don't look half as pretty as I did when I installed the yachty hatches 27 years ago)


The side screened and louvered hatches do a very good job of drawing out the rising hot air down bellow whilst drawing in cool via the companionway when the boat swings to the wind in non tidal stream or river anchorages but on really still, sticky days does not do so well - sucking don't work bro.


To handle really hot humid weather when I am away from the cooling seas and not swinging to the breezes I have installed an 18" 12V auto radiator fan in a fold down sub-hatch in the bow hatch with a speed controller (The speed controller is necessary as even running at 6 volts it blew a gale under that thing) This is the blower configuration where outside air is forced into the bow of the vessel, picks up the hot humid air from inside and exhausts it out the companionway.


I also have a number of small, area specific fans in the boat to move and mix the introduced air.


My experience is that you need both sucking and blowing to meet the changing circumstances.

[Cadence]

Going back to my somewhat lewd reference. You can blow all the air in you want. Suck out the lowest part of your bilge with an explosion proof blower. Anything you want to get ride of is heavier than air. I'm not sure with diesel it is a concern?

[Sailor Doug]

I have air conditioning and a 4" sober vent blowing in through forward hatch.


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[Compass790]

After many years welding inside pipes, tanks & pressure vessels I can tell you from experience if you only have one pump/blower it is MUCH better to blow than to suck. Actually if you were smart you wouldnt ever do any welding inside but thats another story!

[Djarraluda]

Originally Posted by Compass790

After many years welding inside pipes, tanks & pressure vessels I can tell you from experience if you only have one pump/blower it is MUCH better to blow than to suck. Actually if you were smart you wouldnt ever do any welding inside but thats another story!

As I noted earlier - Blow means you direct the cool/fresh air somewhere, suck means you just encourage air movement towards that point.
To get a tad more technical, we can consider the "direct" area of influence of an exhaust is limited to a hemisphere with a radius equal to the diameter of the exhaust point. Technically, we call this "B... All"!

[Cadence]

Give it just a bit of thought. Anything in the way of vapors you wish to get rid of are heavier than air and thus in the bottom of your bilge. You can blow in all the air you wish, at the top of an engine room to no avail. You can blow it into the bottom and mix it up for ignition. Would it not make sense to evacuate from the bottom and let clean air in from the top? Just a thought we always called the blowers but in fact they were suckers turned on and hatches were opened for fresh air. JMHO