Which to choose - in line fan or snail cam blower type?

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West Coast

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Hi, I am fitting a powered vent extractor to the heads (natural ventilation is not well designed!).

I have fitted a passive dorade vent into the heads, but going to also fit a powered extract fan. Thinking of a 76mm id hose, which will be ducted approx 6M from the heads to the stern lazerette where there will be a 12V fan to suck the air approx 6M and then to push air through the last 1M of pipe then through a vent fitting at the stern

My option is either for a in-line fan eg SHURflo In-line Blower, YellowTail 12V (76mm Hose)

Or a snail cam type eg Vetus VENT7612 Flange Mounted Ventilation Blower (12V)

For this application, which is the better type of fan to go for?

Thanks
 
I really cannot think you need a high spec solution ... but ... you might want a low amp solution.

To improve, fresh, airflow for our fridge and freezer we did something similar to what you are suggesting and ducted, 100mm i.d., from the anchor locker to the fridge and then another duct to the engine bay which had a vent right at the transom. We used 100mm computer fans which were wired to the compressor fan. Computer fans are cheap and even cheaper if the computer has been 'discarded'.

One fan sucked from the bow, located at the fridge, and another sucked into the engine bay. As the air was coming from the bow the flow was augmented by 'natural' airflow.

Ducting was in excess of 11m.

Jonathan
 
West Coast said:
Hi, I am fitting a powered vent extractor to the heads (natural ventilation is not well designed!).

I have fitted a passive dorade vent into the heads, but going to also fit a powered extract fan. Thinking of a 76mm id hose, which will be ducted approx 6M from the heads to the stern lazerette where there will be a 12V fan to suck the air approx 6M and then to push air through the last 1M of pipe then through a vent fitting at the stern

My option is either for a in-line fan eg SHURflo In-line Blower, YellowTail 12V (76mm Hose)

Or a snail cam type eg Vetus VENT7612 Flange Mounted Ventilation Blower (12V)

For this application, which is the better type of fan to go for?

Thanks
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Both fans will use quite a bit of power. The scroll fan will deal with pressure drop better than the inline fan, so better in this application with your long duct run. It may be worth looking to see if you can use a speed controller with these fans that will cut the amps used. Maybe a ormal and boost mode
 
I'd second using a computer fan - I'm FT liveaboard with a separator loo, have a 12v computer fan on 24/7, works very well, uses next to no power and virtually silent. There was an existing vent out for the holding tank that's no longer in use so I cobbled together ducting the computer fan to that...
 
Thanks all. I will be fitting a timer on the fan switch so it only comes on for say 3 - 5 mins. So I am not so worried re current consumption.

I was more thinking which fan type would be better for this application, snail cam or in line, or if it makes any difference?
 
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The flange mounted fans seem more durable.

Keep in mind both types of fans are very noisy. Normally they are mounted in an engine room with sound insulation. It is unpleasant to be in the same room as these fans when they are operating and if someone uses the fan at night it may wake up others who are sleeping.

A lower volume, quieter fan may be a better choice.
 
Your idea is a good one. I would use the in line fan if fitting in ducting just to reduce space. On my own boat the in line fans are built into the mushroom style vents, large motors with cowlings that protrude below the head lining to hold the fan motor (I believe they are the same as Series III Landrover wiper motors). I have looked on line but cant see any, except the ones that are powered by solar panels. If you can get such fans, fit them, because they work well.

Like you, I agree with the high flow rate and low running time. I use mine predominantly to shift orders and maybe mask noises from the heads. I removed the shower head, but used to use them with the shower as well, which was the longest they would run for. I think either of your options would do the same job as mine, rapid movement of air, at a reasonable flow rate.

One of my heads is between the fore cabin and saloon. One of the doors is louvred and when I leave the boat, the fore deck hatch is left in the vent position and I never get any condensation issues. In the aft heads, which is a dedicated compartment in the aft cabin, no louvred door, and if I leave that heads door closed, I get condensation in there.

Good luck with your installation.
 
Not in my two
Refueler said:
Also my two boats don't have hatch in the heads dept. But one boat has a variable mushroom vent ... while other has a fixed cowl mushroom vent.
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Both mine have mushroom vents with built in extraction fans. The fans are 24v, 2 speed, suction, or blow. A hatch would be a good idea and the deck is thick enough to not warrant much thought.
 
Thanks all for helpful comments

Fwd heads has a decent hatch, the aft one has only a very small hatch in the side coachroof which is not well designed. I have fitted a coachroof mounted dorade vent to the aft heads, but this fan extract is supplement this.
 
I would suggest the scroll type fan where you have a lot of ducting. (so resistance to air flow) This is known as a centrifugal fan the other type is axial fan. Now axial are very good in low pressure load situations like fan to cool you face but even in a duct can not produce much pressure gradient. So you will find centrifugal fans in vacuum cleaners and smaller gas turbine (jet) engines. In both these cases producing a lot of pressure in one or 2 stages. (large jet engines use axial compressors but with 14 stages of fan to get the pressure needed) ol'will
 
West Coast said:
Thanks all for helpful comments

Fwd heads has a decent hatch, the aft one has only a very small hatch in the side coachroof which is not well designed. I have fitted a coachroof mounted dorade vent to the aft heads, but this fan extract is supplement this.
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Think of what you have in your Bathroom/toilet at home. You don't need a howling gale drawn through to extract condensation / odours.
 
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