Ventilation

[amarosa]

Hi there. I have a 35 foot Hartley powerboat that have had for a year. It has a 165 volvo turbo. I recently got a new prop as the other one was too big so now slightly smaller. The issue now is that the turbo can't get enough air so have to open up the engine bay and is sweet. The original set up was that someone had taken a drain pipe and run it under the bilge and popped out some random space and then made it a car filter so was rubbish. I am now just trying to get the proper air filter set up. There is no other ventilation in the engine box and was thinking of putting vents on the side but thought that would open up a whole lot of noise into the cabin. So am stuck with how to get enough air into it. With enough air she hits 20knots and hits WOT but with not enough she only hits 12 knots at 2500rpm. Any ideas would be great as is first boat and really enjoying getting out most weeks and getting some great ideas from old PBO magazines

 

[snooks]

Most Motorboats have cowlings on the hull with baffles inside to stop water getting into the engine room.

Imagine sound as water, any holes in the engine compartment and the sound will come out.

So you want the holes in the engine compartment to be outside the living accommodation (if you when the engine is running). And any pipe work carrying air (and sound) to be substantial unless you won't be in their vicinity with the engine going.

Also if your engine is in a confined space the air will heat up in there causing belts to wear faster and a reduction in power (diesels like cool air because it expands more than warm air).

So ideally you want a way of sucking cold air in and blowing the warm air out.

I hope that helps...

 

[PCUK]

High powered fans blowing the air in is one option.

 

[sarabande]

I find it hard to understand how the boat has survived without breathing properly till now. Are you sure

1 an existing air inlet has not been blocked by something as simple as a cushion or plastic bag

2 the existing air filter is clean and not bunged up

3 any rubber tubing in the inlets is not collapsing under suction.


It would be unusual to filter air that goes into the engine room, as filtration normally takes place just before the engine.

 

[amarosa]

I find it hard to understand how the boat has survived without breathing properly till now. Are you sure

1 an existing air inlet has not been blocked by something as simple as a cushion or plastic bag

2 the existing air filter is clean and not bunged up

3 any rubber tubing in the inlets is not collapsing under suction.


It would be unusual to filter air that goes into the engine room, as filtration normally takes place just before the engine.

I think in the past the air has just sucked through the air filter in the cupboard which is clearly why it was there but as I replaced the prop with the right size and gave her a good clean it is clearly performing beautifully now. I was looking at a fan but not sure where I would put the outlet and inlet without drilling some big holes. The engine bay is at the stern in front of the transom. There is about a meter between the side of the enclosure and the side of the boat in either side.

 

[oldsaltoz]

We have twin engines and both have bulkheads each side so fully enclosed, air is fed in through an 8 inch hose that connects to dorade vent on deck and the air enters close to the bilge.

Have you looked at installing a vent on deck and running a hose to the intake/engine compartment?

Good luck and fair winds.

 

[amarosa]

We have twin engines and both have bulkheads each side so fully enclosed, air is fed in through an 8 inch hose that connects to dorade vent on deck and the air enters close to the bilge.

Have you looked at installing a vent on deck and running a hose to the intake/engine compartment?

Good luck and fair winds.

Did you need a fan to pump the air in or was it sweet?

 

[oldsaltoz]

Did you need a fan to pump the air in or was it sweet?

No pumps fans or blowers of any type, however if you work out how much air the engine actually needs, it helps to size the vent/s.

Good luck and fair winds.

 

[amarosa]

No pumps fans or blowers of any type, however if you work out how much air the engine actually needs, it helps to size the vent/s.

Good luck and fair winds.

Great thanks for that. Think with all that info I have now worked out that I can attach a hose to the turbo and put ventilation on the transom as is space there. From reading looks like 1inch squared per hp so would need to be 165inch squared?

 

[sarabande]

possibly 165 square inches (say roughly 8x20 - which seems inordinately large BTW) but definitely NOT 165 inches squared. That would be a hole measuring roughly 14 feet by 14 ft.

 

[amarosa]

possibly 165 square inches (say roughly 8x20 - which seems inordinately large BTW) but definitely NOT 165 inches squared. That would be a hole measuring roughly 14 feet by 14 ft.

Whoops!

 

[oldsaltoz]

Not a good idea to attach the intake direct to engine for a number of reasons.

Try one of these to calculate the flow required.

https://www.google.com.au/search?q=...hannel=sb&gfe_rd=cr&ei=ogloU_vuIaqN8Qf8hYCgAQ

Good luck and fair winds.

 

[rob2]

It's a good idea to ensure the air intakes are of the correct size and they should not be connected direct to the intake as the air has a critically important role to play in cooling everything in the engine bay before it is ingested. Incorrect air flow can happen even in automotive designs where you'd think everything was bathed in air, but certain models of Range Rover with the underbonnet crammed with every optional extra used to spontaneously ignite!

Rob.