Blower for engine

Hi Wild,

The Jabsco 35400 is a centrifugal blower which I believe is the best option in this application. The manufacturer lists the maximum motor life as 1000 hours, so you have been very lucky if it is running already for 2500 hours. Nominally it is designed for intermittent duty.

Cheers, DJ

The problem with your suggestion is that the fan is sucking air out of the engine  room which is quite small on these boats. The fans are not blowing fresh air into the engine room.

The engine itself is a high flow air pump, which creates but better suction than any small axial air blower/fan, and transfers enough volume too. If the engine is running the electric fan proves nothing but a lower pressure in the engine room, and it is fighting the engine for air supply.

It could be that the engine running will increase rhe pressure drop across the electric fan enough to overload it electrically.

That is an excellent blower you have, continuous rated. Interesting that you have 4" ducting. On my 400 ( l2007 build) I have only 3" duct, and only an extraction duct, no fresh air duct. There are various openings between engine room and the lazarette area which is where the engine draws it's air, as well as through the extraction duct in the reverse direction if the fan isn't running.

It looks like you have a generator tucked in the engine room too. Is that to power the 11 amp draw from the fan? 😉 Fisher-Panda?

I won't run my fan continuously as I see no need to it for the reasons I stated,  but if you want to run yours continuously that's fine too. I have seen the odd yacht which the OEM  has configured one fan blowing into the engine room, and another extracting air from it. I can't remember if they ran continuously or not.

Cheers

DJ

Blowers were originally fitted to boats to clear fumes or dangerous vapours from gas appliances and petrol engines (which use to be all carburettor fuelled and off gassed at shut down) and the blower was run for a while to clear the bilges of potential explosive gases before starting the engine. This was done to minimise the risk of fire or explosion when activating the starter and the associated electrical spark risk. With the move away from inboard Petrol engines blowers were still fitted and then in general became a regulatory requirement. 

While not having one on my boat, I have considered fitting one as I still have gas onboard for cooking and a small amount of petrol. Having said that I feel it is more important to properly maintain the gas system and store the petrol correctly than go to the grief of fitting a blower. However if you already have a blower maintain it properly, but don’t get hung up if it stops working, add it to the end of season maintenance list, but at all times look after your gas system and how you store any petrol onboard.

Simon 

From the various contributions  it appears that Hanse didn't even fit engine room fans in 2005, 2006, then fitted a fan in 2007/2008 but didn't include the fan in wiring schematics, and then a year or two after they stopped fitting them again.   In 2007 they used 3 inch fan and a single duct, but at some later stage it seems from posts they used 4 inch and two ducts. Clearly Hanse had trouble coming to a firm conclusion about what was needed.

I agree with previous two posts on a couple of points.

Firstly the fan should be run before starting the engine  to remove any combustible fumes which could ignite from starter motor/solenoid operation. Just a safety precaution.

Secondly running the fan immediately after stopping the engine to remove any hot air, diesel fumes etc. A matter of comfort.

During running the engine itself does create a slight under-pressure in the engine room as it is an effective pump,  which should prevent fumes and smells escaping into main cabin area. The fan is thus not necessary while the engine is running.  

While the engine is drawing in significant amounts of air, it is not as much as some might think. The 3JH4E Yanmar is just 1.6 litre, so at 2400 rpm it is only drawing 1920 litres of air per minute (67 cfm). A 3 inch Jabsco 36740 is nominally 150 cfm for comparison. As the engine room is less than 2 cubic metres the engine will effectively draw in all the engine room air in under 30 seconds  when running. The Jabsco will nominally do it in less than15 seconds.

My own personal opinion (as a retired engineer) is that a fan is a good idea, but that it only needs to run before starting and after stopping the engine. If you want to fit one then either axial flow or centrifugal fans will work, but a centrifugal offers superior characteristics for this application.

Cheers

DJ