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Engine Room Air intakes

Discussion in 'Technical Discussion' started by Fortunate One, Sep 6, 2008.

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  1. Fortunate One

    Fortunate One New Member

    Joined:
    May 14, 2006
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    Location:
    New England
    We are dealing with requirements to get air into the engine room of my one- off custom 48' express tournament sportfishing boat. We've installed tow Yanmar 8y-STP 900 hp twin turbo "V" 8's and one Norpro 12.5Kgen set.

    Now I've seen the typical side louvers and the side panels that are used by Cabo on the 52 Express.

    I've also noticed boats that don’t' have any vents on the side that must be getting air into the engine room from vents under the gunnels or vents that lead into the cockpit via some other means.

    But what I'm looking for is experience and thoughts on engine room ventilation.

    The air box was built on the 2 sides of the engine room with the thought of cutting in and making louvers.

    I think it will take a lot of time to make these custom louvers contoured to the hull. I'd prefer to spend my money on something other than having the crew mold the hull and then painstakingly build the custom louver area. I told them I think the panel with the perimeter cut out would be fine if we rout in some recessed detail to it.

    It would certainly be easier to keep clean than louvers.

    I was told that it might not be able to be done as a result of the air flow requirements. But my answer to that is Cabo is doing it.

    I also like the clean look of no louver so that would mean concealing the air intakes in the cockpit and that could be done easy enough since we haven't started building the cabinets yet. I could mount them on the sides of the cabinets between the gunnels and the cabinet sides. And I have plenty of cabinet space back aft so I'm not concerned about that resulting in lost cabinet space.

    So my questions are.

    Are any of you running boats with concealed air vents?
    If so where are they ducting to?
    What’s the end result with regard to engine room noise being transmitted through the vents?

    To the builders:
    The boat is a plank on frame with 2 layers of bi-directional plywood on the outer skins. How many hours should it take to make louvers to fit the shape of the hull? Keep in mind that the air boxes are built on the interior. Are there standard components available to build these?
  2. NYCAP123

    NYCAP123 Senior Member

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    Four concerns come to mind:
    First make absolutely sure you're getting enough airflow (especially at slow speeds) or you'll have a nighmare boat.
    Second, venting to the cockpit will bring with it engineroom noise and heat. Are you sure you want that?
    Third, I've seen several vent designs that look good, but suck saltspray and water in with the air leaving you with a daily cleaning chore and not being great for your motors.
    Fourth: If you're going custom make a second set of vents.
  3. AMG

    AMG YF Moderator

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    I am calculating vents on a boat right now and to start with, the air used by the engines represents an area in cm2 of 1,9 x total kW. Then the ventilation should be an area of 1,65 x kW in, and the same area out. Add all three.

    Having the vents high on the hull sides gives the best airflow and with a drained water trap and another sound trap it should work pretty well. The inlet side should come low inside and the outgoing higher on the other side of the engines to get the right circulation, if you are not using fans for evacuation.
  4. Capt J

    Capt J Senior Member

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    I've run the 52' Cabo on a long trip and feel it is underventilated. When you are at cruise the engine room door stays sucked shut and takes a little force to open. Telling me it's trying to suck air in from anywhere or negative vaccuum in the ER. The 52' also relies on intake and out-take blowers to properly vent the ER. I like large vents that keep plenty of air flowing in the engine room and heat dissipation in there. Especially if you have to fix something at sea. Each engine manufacturer has a formula of how much airflow each model needs. I also do not like venting it in the cockpit underneath the gunnels as it puts heat in places I don't want it to be. You can find a nice set of vents that do look good on the hull.
  5. AMG

    AMG YF Moderator

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    May I just add that a little negative pressure is desired in an engine room, so you don´t get any fumes into the boats interior.
  6. C4ENG

    C4ENG Senior Member

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    Location:
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    A salvage worker was once telling me a story about how his company had to go clean up a Carribean island harbor littered with smaller sunken vessels (sailboats and sport fishers mainly) after a hurricane came through. All the vessel where left anchored in the harbor and they all sank the same way. The wind blew them over to a list, then the water poured in through the ER vent system. The good thing was it made it easier for them to recover the vessels becuase there was no repair work before refloating.
  7. Capt J

    Capt J Senior Member

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    This is a little more then a little negative pressure. You have to pull fairly hard on the latch for the door to open. Like ten lbs of force.
  8. Innomare

    Innomare Senior Member

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    The Netherlands
    My 2 cts.:
    - Consider installing a mist eliminator on the air intake. It will more than pay for itself in the long run.
    - Make sure the intake is high enough above the main deck (or let the ventilation line goose-neck high enough) to eliminate the flooding point.
    - If you have closed bulwarks and low-positioned air grilles, the bulwark may reflect the engine room noise towards the cockpit.

    Bruno
  9. infvoyager

    infvoyager New Member

    Joined:
    Oct 27, 2007
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    Location:
    tacoma
    If you can afford the ac pwr budget I would take a look at Delta T systems
    and run two tube plenums fr cockpit or FB airboxs. Think old Westport Charter boat designs (43'-50') . Be sure your Sq.in's get you your Cu.Ft of air , air starving is a really efficiency killer.
    In large yacht construction the Delta T's are set to Neg 2-3 lbs No whistling or dust-dirt tracks leading to leakage areas.