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Old 15-02-2014, 21:42   #1
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Inboard Engine cover question

Hello,

I'm building a new "engine cover" (technical name for a plywood box really). It will cover my raw water cooled inboard 2qm15 Yanmar engine and thought I'd better get some expert advice before I get too carried away.

My boat doesn't have dedicated air vents or blowers to circulate air through the bilge and around the engine and the old cover had a couple of small louvre vents but the amount of air they'd let through makes me wonder if I would need them in the new cover at all?

I am going to use some kind of soundproofing inside the cover to quiet things down and I'm thinking if I have to cut holes for air vents then that will reduce the effectiveness of the soundproofing.

Of course it's better to have a noisy, cool engine than one that is quietly boiling it's guts out, but I'd prefer to have no vents in the cover if it is safe to do so.

What are your opinions please? Perhaps you know better method?

Thanks,
bony.
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Old 16-02-2014, 01:08   #2
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Re: Inboard Engine cover question

You will need air for combustion of the diesel. Not sure if there is enough air for combustion entering the engine cover to cool the oil in the pan and alternator. Maybe air for combustion circulating in the engine cover is enough. Some heat will be lost through the hull. However, you do know that the original cover and hull let enough heat out as the engine did not burn up. Much of the heat will be removed anyway from the raw water circulating through the engine.
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Old 16-02-2014, 07:12   #3
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Re: Inboard Engine cover question

The maximum temperature of the engine room/compartment should never exceed 60 degrees C (1400 F) within 20mm (3/4") of any electrical equipment and 450 C (1130 F) at the air intake.

Ventilation Requirements for Yanmar Diesel Engines:
Duct Sizes (2 Required - 1 Supply In & 1 Exhaust Out)
Yanmar Engine - Square cm - Square inch - Diameter
2GM20 - 39cm sq or 6"sq - 75mm or 3" dia
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Old 16-02-2014, 10:24   #4
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Re: Inboard Engine cover question

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Originally Posted by GordMay View Post
The maximum temperature of the engine room/compartment should never exceed 60 degrees C (1400 F) within 20mm (3/4") of any electrical equipment and 450 C (1130 F) at the air intake.

Somethings wrong with those numbers?
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Old 16-02-2014, 16:49   #5
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Re: Inboard Engine cover question

Hello gents,

The old cover was a home made job and previous owner might not have bothered too much about air circulation, so I guess it's not a good guide to go by.

I'll take your advice and fit a couple of vents into the new cover. Thanks for the replies.

bony.
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Old 16-02-2014, 17:15   #6
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Re: Inboard Engine cover question

Quote:
Originally Posted by GordMay View Post
The maximum temperature of the engine room/compartment should never exceed 60 degrees C (1400 F) within 20mm (3/4") of any electrical equipment and 450 C (1130 F) at the air intake.

Ventilation Requirements for Yanmar Diesel Engines:
Duct Sizes (2 Required - 1 Supply In & 1 Exhaust Out)
Yanmar Engine - Square cm - Square inch - Diameter
2GM20 - 39cm sq or 6"sq - 75mm or 3" dia
well... he wont have to worry about that! It'll be charcoal by 1400F!
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Old 16-02-2014, 17:18   #7
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Re: Inboard Engine cover question

Quote:
Originally Posted by bony View Post
Hello gents,

The old cover was a home made job and previous owner might not have bothered too much about air circulation, so I guess it's not a good guide to go by.

I'll take your advice and fit a couple of vents into the new cover. Thanks for the replies.

bony.
I guess I'm not understanding... doesnt the engine sit over the bilge? Are you saying the engine sits over a floor that is totally sealed from the bilge or other boat underdeck compartments? If it isnt sealed like this... then just put an inflow vent to the entire compartment and and outflow also...like on the stern coaming of the boat...the air ingress and egress doesnt need to be near the engine....
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Old 16-02-2014, 18:08   #8
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Re: Inboard Engine cover question

Just fitted 3" blower fans to engine boxs on my cat to provide more air for breathing, vent & cooling 2X1GMS. Yet to be ran for a long period.

Regards Bill
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Old 16-02-2014, 18:31   #9
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Re: Inboard Engine cover question

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Just fitted 3" blower fans to engine boxs on my cat to provide more air for breathing, vent & cooling 2X1GMS. Yet to be ran for a long period.

Regards Bill

Are these intake, exhaust, or both? A intake and exhaust for each compartment?
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Old 16-02-2014, 18:41   #10
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Re: Inboard Engine cover question

Added to inlet. Outlet has various holes & vent. Might add the heat soak would last for hours before this mod. (Overheat warning used to come on when restarted until the water cooled) The idea was not to clear the fumes but to add air. Noise from fans not an issue.
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