how much current for 12v fans

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Jools_of_Top_Cat

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Have been looking around the web for some oscillating fans to cool down the cabins and saloon and to keep air moving, should the sun ever rear its head this year.

But non of these sites mention the current draw of their fans. I am probably looking for 6" fans, which seem about the most common. Does anyone know what the specs are or better still actually measured them?

Thank you in advance.

<hr width=100% size=1>Julian

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More than you will like I'm sure Jools, definitely amps not milliamps! Have you thought of the green alternative like the spinnaker cloth windsail over the forehatch? We bought one last year and found it very effective

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>
 
Those little (3") caged fans that you get in instruments and computers, draw 190 mA at 12V. So anything useful is like to be 1A or so?

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An amp, a bloody amp. That is crazy..... 2 fans = 2 amps

hot day lets say six hours to keep it cool during the midday heat, 12 Ah out of my batteries.

It also makes running a fan above our bunk overnight to keep the air cool a real no no, 8 Ah for a good sleep.

That is nuts! Ok, maybe I will have to just try to catch the ambient air and pull it through the hatch as suggested.

<hr width=100% size=1>Julian

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No, they don't work very well either! There is the, hanging a tea towell just in bowl of water, trick! Do it under a hatch and you get refrigerated air coming in... It'd work on a Cat, even when sailing!

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Hi Julian

We considered fans at one stage but discarded the idea for the reasons Robin states when we added them to our other usual loads such as refrigeration, lighting, etc (we have over 500 AHr of batteries).

However, a fan that is frequently quoted as being efficient and good balance between price and quality and that we looked at is the Hella 3361 which can be found on Hella's marine site (hellamarine.com from memory). As far as I recall draw is quite a bit more than 1/2 amp on high speed and half that on low - but they are quite small at 6 inches dia so one would probably need a number going at once to get much air flow, so say a couple of amps minimum.

An alternative solution that I have seen is using computer fans. In the application I saw the vessel owner had a large specialist wood product business and he made up classy looking wooden mounts for them which matched the fine joinery in the boat. As far as I know they worked quite well in a reasonably large volumed boat (was around 60 foot) but I think that if one does the sums that they may use about the same current/volume of air as the Hella ones and probably at higher noise level - may be worth checking if interested.

If one only wants a small amount of local air movement a computer fan with its DC supply through an adjustable voltage DC supply (say using a 317 TO220 3 terminal regulator) slows them down so they are not too noisy. I have done this for ventilating lockers with thermoelectric refrigerator heatsinks in and it quietens the fans down alot - around 5-6 volts from memory and current draw seems small but I have never measured it. Obviously the air flow drops too. If you are interested I could measure the current on a slowed 6 inch one next weekend.

Along the lines of other solutions, our hard dinghy is cunningly (the boatbuilder's cunning, not mine) stowed over our forward accommodation hatch facing bow forward - the inner forestay halyard picks up the bow and turns it into a wind scoop.

John



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I was looking at computer cooling fans and solar panels on the maplin site last night, I was shocked how much you need to spend to get any decent power from a solar panel.

We have an aerogen 4, but the days we could do with fans to cool down the boat are the days that the windgen stays motionless.

This all started because I replaced the solar vent above the heads on Sunday. The old solar panel was ruined, but the fan still works when I connected it to a 9v battery. I went looking for a new solar panel so I could convert the vent over the galley, anyone know a source?

Then I got onto thinking that if I bought a larger panel and some small oscillating fans I could cool down the saloon on hot days. How wrong I was.

On the bigger cats, I notice in harbour they open their escape hatches, the cool air coming in off the water really helps to keep the hulls at a nice temperature. Unfortunately we do not have this option, we do not have the bridgedeck clearance to allow this. Damp tea towel sounds interesting, but I would imagine you would need a fair breeze to get any air to pass through.

<hr width=100% size=1>Julian

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the Hella turbo fan, reccommended by most blue water cruisers, draws 500mA on fast speed (which you won't often need)

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If you look in the right place there are solar operated fans for greenhouses and conservatories, which appear to be effective without drawing on the main battery.
I am sure you can rig one up on a pro tem basis

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190ma is reasonable I use a slightly larger one on my boat, the only snag with computer ones is that they make a bit of noise. I bought one the other day about four inches diameter for ninety nine pence at a computer fair. The biggest one I use is 300 ma. Not much current for a good nights sleep. If you can get hold of small speaker brackets you could fit them to those. I have bought a "proper" one but find the computer ones better. 99 pence is not a lot for a new fan is it.

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Fear not mon brave
when i scrap power supplies off computers i keep the 80 mm fans, as stated the draw is in mill amps at 12v. will bring some down this weekend FOC so you can experiment.
Denbighshire County Councillor Stuart Davies (yes I won)

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Hi Jools!

We use two of the bog standard 'lorry type' oscillating fans in the main cabin. Both draw 0.9amps but do make life bearable below in the Med / Caribbean and are used with a sensible eye on the total amps consumed.

In the forecabin (which on our little boat is the sleeping cabin) I installed two 85mm computer fans each fitted to the flexible arm of a red/white chart light. They are virtually inaudible. We therefore have extremely low (circa 80milliamps) current draw on each, and maximum orientation. The fans cost less than £2.00 each, brand new in Spain and have been used for the last five years. They are frequently left on all night if the wind is zero and there's nothing for the Windscoop to funnel below.

As we anchor virtually everywhere, we would rate the Windscoop the 'best buy', and this is very often enough to keep the whole boat cool. It does seem that our friends with aft cabins suffer much more because of the difficulty in feeding cool air through the aft hatch, even with a Windscoop fitted.

Hope this helps.

Good sailing!



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Alternative approaches

One thing that increases the heat load in the cabin is if the cabin top is not insulated (some constructions such as foam sandwich are naturally insulators too, of course).

If you find that you get much radiated heat from the inside of the overhead lining in the cabin from conduction from the outside deck with the sun beating down on it, then insulation can help. Also keeping the sun off the deck with an awning or cooling it with evaporative cooling by keeping the deck wet all help to some extent. A light coloured deck is obviously a help.

In the end fans basically only circulate the already hot air in the cabin around and only cool the body by evaporating sweat ( that probably increases the humidity in small cabins and adds to the discomfort) - getting an air flow through the boat and reducing the heat load in it by means of insulation are, in my opinion, the best objectives. If the cabin is hotter than the outside ambient, as it usually will be, then having a hatch(s) in the cabin top will also encourage air flow through the boat by convection flow out through it and thus draw air in from bow and companionway hatches.

As mentioned our boat is set up so the dinghy can be used as a scoop (assuming it is on deck), central hatches on the deck/cabin top and a hard dodger over the companionway producing a venturi - it is also fully insulated. I mention those things just as what we have found helps alleviate the problem and not to say that they are all necessary or the best. We have only cruised in up to the low 30 C's temperature wise but spend weeks at a time away (as I think you do, going by your web site) so require to be comfortable - I cannot recall ever having a significant temperature problem in the cabin even on still days. Obviously, one is always stuck with the temperature, at best, being the same as outside with cooling being from sweat evaporation from moving air but blasts from fans are not necessary to achieve that in my opinion.

John

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Re: Alternative approaches

100% agree with the need for ventilation and deck insulation.

there is however an extra benefit of fans which never occurs to you till you've got one: as white noise generators.... when you are still awake at 4am because of reggae blasting from the shore you can shut the hatches, put the fan on high and drown it out enough to get some kip!

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Hi Jools....Each forward cabin on my 10 metre Dean cat has two roof hatches, one facing forward, the other aft. Especially when at anchor, (ie, facing into wind) the slightest movement of air generates a turbulent air-conditioning effect in the cabin. The problem is more often reducing the throughput to get a good night's sleep, and we're in the Aegean!.
I once was looking at a French Piana plywood cat, which had a floor grill into the 'tween hull tunnel which generated a fabulous up-draught, although not exactly where one really wanted it. One might have ducted it through some of that light spring/plastic ventillator stuff used in domestic ventillation.
There's good possibilities for this sort of static solution on a cat.
I reckon the fan solution is a bit mickey mouse.
Happy experimentation!.....Cheers...R

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Some great advice posted here thank you. I am totally on board re. more ventilation and have plans for dorade vents at the front of the saloon and small opening hatches at the rear.

Problem is mainly that I am a tight git. I know, and I do know that as soon as I finally do spend the money and increase the ventilation I will wonder why I did not do it much sooner. It is just being prepared to part with the best part of £400.00 for essentially 4 pieces of molded plastic. I know there is more to it, the hatches need to seal in a marine environment etc.

I will do it, but I just wanted to explore moving the air with some fans first, while we are still in this climate!

<hr width=100% size=1>Julian

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a few tips on increasing ventilation...

dorade type vents are ok in british waters but totally inadequate for hot climates. plastimo make one that automatically seals when water comes down the cowl. it really works, you can pour a bucket down the cowl and not a drop comes in though they aren't that strong and could be broken off in extreme conditions.

rear-hinged hatches do the job but of course not at sea. a small tent-shaped awning over a hatch will keep the rain out but still allow ventilation - easier to rig on a mono than a cat.

tannoy vents leak if immersed (green water on deck)

our best investment was to set opening portlights into cutouts in the front windows. we also have small (10" x 15") hatches, aft hinged, in the cabin top which deliver lots of air but have to be closed when sailing as the mainsheet catches on them (or in your case the genoa sheet)

windscoops do the business but are a pain to rig over hatches in the side deck. there is a type with a spring hoop which is self-supporting.

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+1 for Calframo, we are also in the tropics and have 2 in the aft cabin, one of which runs 24/7, they last about 12 - 18 months with continuous use and cost about US$50 each

On low speed each draw about 0.25 of an amp
 
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