Air blower for engine installation

[MalcolmK]

I'm planning the installation of a Beta 25 in our Westerly Fulmar. The installation guide states that an air blower system is required in order to keep engine bay temperature down. The boat doesn't have one now and many other owners report that they have no problems without one.

Is a blower really necessary on a boat where the engine compartment is not a sealed box but has openings into the cockpit locker and from there to the outside world? Is the engine air consumption enough to draw air in, realising, of course, that pre-heating intake air is not a great idea?

If this has been discussed before a link to the previous thread would be welcome.

[Lepke]

It depends on how restrictive the air path is. The cooler the incoming air is, the more efficient the engine runs. On large engines the difference is measurable. Also incoming air helps cool the the engine top end.

[Sailmonkey]

We’ve got a wide open engine bay as well, I’ve put an extraction fan into the space primarily to pull heat out after the engine is off. It runs when the engine runs and stays on 10 mins after the engine is off. It was done for the people, not the engine.

[tkeithlu]

Consider: Go ahead with your installation without an evacuation fan/blower. Run an ordinary meat thermometer probe into the compartment through a tiny hole. Monitor your compartment temperature for awhile and see if you need to go back and install an exhaust fan.

https://www.amazon.com/Thermometer-F...s%2C209&sr=8-8

I've got two of them in the space that carries my dry exhaust, just to make sure that there's not a leak in there that will start a fire.

[GordMay]

Greetings and welcome aboard the CF, Malcolm.


➥ https://www.cruisersforum.com/forums...-it-37561.html

➥ https://www.cruisersforum.com/forums...-245777-3.html

➥ https://www.cruisersforum.com/forums...n-85829-2.html

➥ https://www.cruisersforum.com/forums...wer-42656.html

Engine Room Ventilation - Caterpillar ➥ http://s7d2.scene7.com/is/content/Ca...13-53120-44971

[Pete7]

Malcolm, welcome to CF

If you chose a blower rather than an extractor, you might aim it at the alternator to keep that cool first.

Do you have any batteries in the engine space. They also prefer to be kept cool.

Pete

[skipperpete]

Thanks for the Caterpillar link gordmay, very informative. Here’s the similar considerations from the Yanmar installation manual and if an electronic common rail engine is fitted, these guidelines need to be observed by the installer......less so for non electronic.

[MalcolmK]

Originally Posted by Pete7

Malcolm, welcome to CF

If you chose a blower rather than an extractor, you might aim it at the alternator to keep that cool first.

Do you have any batteries in the engine space. They also prefer to be kept cool.

Pete

Thanks for that. Fortunately, the batteries are outside the engine compartment, under a bunk.

[MalcolmK]

Thank you all for the replies. I'm now settled that due to the large engine space, and the lack of problems over the previous 40 years of the boat's life, I will not be installing a fan when I change the engine. However, I will check on temperature in the engine compartment and review this decision if necessary. Your comments have also helped in resolving the sucker/blower question. It is clearly a mistake to suck air out of the engine compartment without forcibly blowing air in at the same time as this would reduce the air pressure at the engine inlet. The engine and the sucker fan would be competing for the same air, meaning that there would be a risk of low air intake to the engine and over-fuelling of the mix. I well understand the comments about keeping the engine compartment pressure lower than the cabin as this would stop fumes from migrating into the living space but the engine intake volume should take care of that, if a blower fan is suitably sized and not excessive. If I think forced ventilation is required I'll look carefully at the likely engine air intake volume and size the blower to just about match it.

[tkeithlu]

Your engine sucks up 1,600 liters of air per minute running wide open. You're going to have a hard time finding a fan that big. Don't worry about it. The fact that the box is negative pressure is perfectly OK. If you run your air inlet by your alternator, you will cool it as well.

Of course, it's a bit less than that because you have a naturally aspirated engine - the cylinders fill in a slight vacuum, and then you can halve it if you run at 1,800 RPM.

[tkeithlu]

The 4 cycle Beta displaces 900 cc. Each cylinder fills on every two rotations, so you suck half your displacement per revolution. 450 cc times 3,600 revolutions per minute is 1,620,000 cc per minute or 1,620 liters per minute. Yeah, that's a lot of air.