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Hi everyone, I am fitting a new engine this winter and a new (good fitting) deck above the engine room

boat is a semi trad.

 

For the first time ever I have to consider air intakes.

 

The manufactures specification sheet concerning air intake is nothing to do with running of the engine air

intake but all about the 'Engine block ambient air temperature'. It states upon my calculations that it requires

two 6 inch pipes leading to the engine room from the outside air.

 

That's fine with me I will fit to the spec , but I lack info on the following ;-

 

1. Do I leave as two pipes or use forced air (i.e small fan , and then push or pull ? ) ?

 

2. Where do the pipes end in the engine room ? ( hot air rises , so Im thinking above the engine

but cold air sinks , floor of the engine room )

 

3. How do I terminate at roof level do large domes exist , I have to stop rain etc ?

 

4. What do I use ? (thinking of using bathroom duct pipe , but will it last )

 

My boat at times will find itself out on the Humber river so the deck floor will be sealed hence my

focus on getting the air intakes right as on river/sea passages.

 

Thanks in advance for any comments and info from those out there

who know more than me about air intakes.

 

cheers

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IIRC there was some discussion around this issue on the Tuesday Night Club website when they were fitting out their new semi trad. Unfortunately that website isn't operating at the moment but the gist of it was they wanted a boat that was safe to use on tidal waters but in order to comply with the RCD they had to have air intakes to the engine room. This is to do with fire safety BTW. I've never heard of the "engine block ambient air temperature" being an issue, so I may learn something here.

 

I'm fairly sure they compromised by having vents in the side of the hull, with blanking plates made so they could close off the intakes when the boat was "at sea", which made me think getting air into the engine room can't be that important. I'll be interested to hear what others think about this.

 

 

 

 

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Hi everyone, I am fitting a new engine this winter and a new (good fitting) deck above the engine room

boat is a semi trad.

 

For the first time ever I have to consider air intakes.

 

The manufactures specification sheet concerning air intake is nothing to do with running of the engine air

intake but all about the 'Engine block ambient air temperature'. It states upon my calculations that it requires

two 6 inch pipes leading to the engine room from the outside air.

 

That's fine with me I will fit to the spec , but I lack info on the following ;-

 

1. Do I leave as two pipes or use forced air (i.e small fan , and then push or pull ? ) ?

 

2. Where do the pipes end in the engine room ? ( hot air rises , so Im thinking above the engine

but cold air sinks , floor of the engine room )

 

3. How do I terminate at roof level do large domes exist , I have to stop rain etc ?

 

4. What do I use ? (thinking of using bathroom duct pipe , but will it last )

 

My boat at times will find itself out on the Humber river so the deck floor will be sealed hence my

focus on getting the air intakes right as on river/sea passages.

 

Thanks in advance for any comments and info from those out there

who know more than me about air intakes.

 

cheers

Fabricate two vertical rectangular trunkings using the inside aft corners of your semi trad, place the grills high up and facing aft. You can add hinged or removable covers to suit. The trunking can end just below deck level. This should minimise any noise nuisance when stood at the steering position.

Edited to add:

Yes airflow to the alternators is important, but this is far more ventilation than is commonly found on narrowboats. Ducting directly to the alternators can if needed be achieved by adding a length of flexible duct between the fixed duct and alternators; which can be easily removed for maintenance.

Edited by Eeyore
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Yes good point , 50 Hp Shire Barrus, water cooled using side tank keel tank.

Am guessing that the reference to ambient temperature is referring to "hot soak" which is the condition where the engine compartment temp. will rise after the engine is shut off.

 

Good practise is to install 2 roof vents with ducting down to the engine bay,one terminating at bilge level and the other at the top of the comparment

 

This setup encourages warm air to flow out of the area,inducing cold air in through the lower duct

 

CT

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Neil2 - thanks , air intakes on the side with shutters interesting , but like you said shut when running makes no sense for me , as when running against the tide , the engine will be working much harder than

on the canal and my deck will be sealed against the elements salt water etc. So this is just when I need air into the engine room. Aread2 - Yes your prob right although current will be minimal

when I do runs across the Humber I run a minimum boat 12V Nav lights and engine ignition only, but your right the alternators are another large heat source.

Eeyore - sounds a good design, think I would prefer over side vents , Cereal tiller - Yes I am thinking of one bilge level near engine block/alternators and one at the top- hot air exhaust , just read someone

added a 12v fan on the exhaust pipe to add air pressure (but dont want to make complex if I dont have too + another thing to worry about if the fan stops mid Humber)

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I've never considered this before, but I wonder to what extent skin tank cooling has on the temperature of the engine compartment.

 

What made me think about this is the number of cruiser/yacht engine installations I've seen where the power unit is shoehorned into a tiny space and you would think it would get very hot in there, but these are raw water cooled, so is that the difference?

 

I got concerned about the heat in the engine bay on my trad so fixed up a vent with a SV pipe into a mushroom vent in the roof. The problem is it is surprisingly noisy. If I was the OP I would carefully consider the position of these air intakes, rear facing sounds like a good idea, but I suspect if they are anywhere near ear level the sound is going to be irritating.

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Your engine needs a fair bit of air for combustion, as well as cooling alternators etc.

 

A 2 litre engine running at 1000 rpm will need 500 litres of air per minute! At 2000 rpm, 1000 litres.

 

The tripboat I skipper with the engine hidden away below decks and fairly sealed in has a bilge blower, to suck in more, cooler air and ventilate the space, which makes a difference when working hard.

 

I'd go with ducting down from the back corners of the semi trad cabinsides. You can then have ventilation grilles on the outside, facing the stern of the boat, and have removable tops on the ducts if you wanted to really increase airflow when you wanted. A bilge blower to suck in cooler air as it'll naturally be wanting to rise out would help too, I think.

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I've never considered this before, but I wonder to what extent skin tank cooling has on the temperature of the engine compartment.

 

What made me think about this is the number of cruiser/yacht engine installations I've seen where the power unit is shoehorned into a tiny space and you would think it would get very hot in there, but these are raw water cooled, so is that the difference?

 

I got concerned about the heat in the engine bay on my trad so fixed up a vent with a SV pipe into a mushroom vent in the roof. The problem is it is surprisingly noisy. If I was the OP I would carefully consider the position of these air intakes, rear facing sounds like a good idea, but I suspect if they are anywhere near ear level the sound is going to be irritating.

Bilge blowers in the trunking seem to reduce the Engine noise significantly

 

Have in blowing in and one blowing out via Mushroom vents which will keep running after engine is shut down,switched by a digital roomstat

 

CY

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Your engine needs a fair bit of air for combustion, as well as cooling alternators etc.

 

A 2 litre engine running at 1000 rpm will need 500 litres of air per minute! At 2000 rpm, 1000 litres.

 

The tripboat I skipper with the engine hidden away below decks and fairly sealed in has a bilge blower, to suck in more, cooler air and ventilate the space, which makes a difference when working hard.

 

I'd go with ducting down from the back corners of the semi trad cabinsides. You can then have ventilation grilles on the outside, facing the stern of the boat, and have removable tops on the ducts if you wanted to really increase airflow when you wanted. A bilge blower to suck in cooler air as it'll naturally be wanting to rise out would help too, I think.

 

I think noise wise that's the best option, assuming you steer the boat from the correct position ie within the stern doors. Here we go again...

Edited by Neil2
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Thanks for the comments above, Looks to me like I need to fit a fan to pressure the air into the bilge section and then let natural convection lift heat from the top. Noise - Never considered this ! , but now I think, any conduit that conducts air will conduct noise , hence when it comes to the inlet/outlet tube I will have to consider carefully the postion. A fan lowering the noise makes sense, as itl puts pressure on the sound waves leaving the engine trying to travel up the tube.

cheers

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Some useful links:

http://betamarine.co.uk/wp-content/uploads/downloads/operators_manuals/Engine_Installation_Guide.pdf

http://www.proboat.com/2015/06/venting-the-engineroom/

http://www.passagemaker.com/articles/technical/engines/the-holy-place-let-it-breathe-engine-compartment-ventilation/

 

Any fan should be an exhaust fan on the outlet side (sucking), not on the inlet side (blowing). Then the engine pulls cool air for combustion in (which goes out of the exhaust pipe) and the fan pulls hot air out to keep the compartment cool. Inlet vent should end low down in the engine bay, preferably near alternators and engine air intake. Outlet vent should start at the top of the engine bay, and preferably and up as high as possible to get the maximum chimney effect.

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My original engine was a Perkins MC42 and it didn't seem to need any extra air but when we changed it for a Beta 43 it was apparent that more air was needed. The general air temperature under the deck was very high and there was plenty of dust being shed from the alternator belts which Beta say is a sign of excessive temperature. When we had the exhaust system re-routed afterwards, instead of having the original hole blocked we took the opportunity to fit some ducting and a bilge blower which blows cold air to the front of the engine. At everything up to 90% of max revs it is possible to feel air being blown out of the original inlet vents. The result is that the air in the engine compartment is at least 20 degrees cooler (an estimate, I haven't got round to measuring it properly) and I presume that the alternators run considerably cooler.

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It occurs to me that the old "wet bilge" boats have a distinct advantage here, in that all you would need to do is fit a high level vent with a blower (acting as a "sucker") and nice cool air would be drawn through the bilge into the engine compartment. That would be good for the cabin bilge too.

 

 

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Have a look at Vetus "Round air suction vent" ERV110. It includes a dorade box which is ducted upwards to reduce risk of water entering the vent.

 

I built two into steel boxes (ducts) installed the corners and about 500mm above the rear deck of a semi trad.

 

Scares me seeing open vents in the hull just above water level even on canals and rivers.

  • Greenie 1
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This is why I was perplexed by the TNC account - the reason they chose a semi trad was to avoid the stern deck being swamped in rough water, then they have side vents in the engine room - which have to be blanked off in rough water... The rear facing ducts sounds eminently sensible to me.

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