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Engine room air intake blower replacement 2001 34 convertable

Discussion in 'Luhrs Yacht' started by Aquavit, Mar 17, 2020.

  1. PacBlue

    PacBlue Senior Member

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    Since you are monitoring temps, roll the dice, see what you get. You can always remove it. I would rely on the heat probe closest to the engine air intake.
  2. Bucksh0t

    Bucksh0t Member

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  3. boatpoor

    boatpoor Member

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    You can install a cheap magnahelic guage in the engine room to monitor the pressure/ vacuum.
  4. Beau

    Beau Senior Member

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    I wouldn't roll the dice on my "iron".... Start cutting engineered compartment air flow, you'd better be down there with an infrared heat sensor monitoring all your engine surfaces. That little "sears" temp gauge ain't gonna tell you nuthin' but the temperature around it. You could have a nice comfortable 125 degree forward while the back of your your exhaust manifolds and mixer are charring their paint.

    This started with replacing an exhaust fan - now we are reducing air flow? Hmmmm.
    Last edited: Mar 20, 2020
  5. Bucksh0t

    Bucksh0t Member

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    I am not the OP,
    Different question but same topic, sort of.
    I probably should have started another thread.
    I do not have fans , only large vents that allow quite a bit of the engine room noise to enter the cockpit.
  6. mapism

    mapism Senior Member

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    That's irrelevant, sort of.
    It's just the vents size that matters, to allow the engines breathing as much as they need.
    Fans are usually added just to cool down - or better said, to avoid warming up further - the e/r temp upon arrival.
    Or when cruising at low rpm, which conterintuitively is when the e/r temp gets higher.

    So, assuming that your vents are correctly sized for the needs of your engines, restricting them is a very bad idea indeed.
    Routing e/r vents through some kind of labyrinth-like path is the correct way to reduce noise, minimizing in turn also salt water and rain ingress.
    But that's something that must be dealt with at drawing board stage, and if this was not addressed satisfactorily by the builder of your boat, achieving a much better result now with any kind of afterthought is bound to be a sort of mission impossible, I'm afraid.

    There's just one thing that you might consider.
    By definition, the vents size must be able to cope with the max air demand of the engines, which is at WOT.
    So, since this airflow is a linear function of rpm, if you know that you never cruise at more than say 70% of the max RPM, restricting by up to 30% the air passage shouldn't have any practical drawbacks.
    Not something I would fancy trying on my own boat, though.
  7. Capt J

    Capt J Senior Member

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    You're noise is not coming from the air vents. Your engines are sucking air in through the vents when running at cruise and keeping the noise in. The noise is coming from the deck itself directly under your feet and the hatch seal of that deck, as well as the exhaust. I did a lot of this testing with Cabo back in the day. Ironically, the new Cabo 41' with the Volvo's are super quiet as far as engine noise goes, but the exhaust itself is noisy and you hear that at the helm, BUT it's clearly a different sound and totally different than the earlier 40's with man's or cats.
  8. mapism

    mapism Senior Member

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    Good point in principle, but noise path can indeed be weird enough to find its way resonating back through e/r vents.
    I've been on some boats where that was clearly the case.
    But if you know that this isn't what happens with Cabos, I take your word for it.
  9. Bucksh0t

    Bucksh0t Member

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    J, Yes there is a lot of turbo and engine noise coming out of the vents, easy to hear it while engines are running. The vents are quite large I am sure there was an elaborate set attached at one time. There are the " boxes " behind the vents. They are open on 2 sides.
    I have moved the remote temp sensors around in the engine room and my temps seem to be fine.
    I may experiment with a couple of simple ideas , if I find a simple idea that helps I will share it.
  10. Beau

    Beau Senior Member

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    Start with applying quality acoustical material? If you can find the material that had a thin lead sheet in the middle those work very well. Start with the sides of two sides of the vents as you describe and any other surface that could transmit the sound wave via vibration to the cockpit. Not a fan of reducing that air flow. You have no outboard hull vents? Diesels?
  11. Capt J

    Capt J Senior Member

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    As an experiment, you can put several layers of moving blankets from China Freight (Harbor Freight) on the helm deck floor and run the boat at cruise to experiment. From what I've found, A lot of noise come from the exhaust due to the flat transoms on SF and the 3 sided shape of the helm window area and tends to suck the noise back (station wagon effect).

    The 41' Cabo is almost erie in this situation, if you've run a lot of the old ones. At cruise, you hear almost zero engine noise from the engine room. The Volvo's are very very quiet (and really smooth,fuel efficient, and fast engines in that boat, REALLY good match), but you hear the exhaust from the transom clear as day, like driving a sportscar with loud exhaust.
  12. PacBlue

    PacBlue Senior Member

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    Did Hatteras add a Cockpit engine room intake/exhaust vent to the Cabo 41 Express? They typically have them on their SF’s.
  13. Capt J

    Capt J Senior Member

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    I never paid any attention, but think so.
  14. Bucksh0t

    Bucksh0t Member

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    Capt J- "As an experiment, you can put several layers of moving blankets from China Freight (Harbor Freight) on the helm deck floor and run the boat at cruise to experiment. From what I've found, A lot of noise come from the exhaust due to the flat transoms on SF and the 3 sided shape of the helm window area and tends to suck the noise back (station wagon effect)."

    Why? I already told you that I am addressing the noise coming from the vents. My deck is already insulated with Aqua Traction.

    Thanks, I will try a few quick experiments and get back to everyone.
  15. Beau

    Beau Senior Member

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    Sorry for repeating myself, try to absorb that noise before it gets to the vents with good acoustical materials made for that purpose. Placement is also important so I've read. There are a number of good articles on the internet about attenuating noise.

    Good luck and let us know ....
  16. Capt J

    Capt J Senior Member

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    How is the gasket where the hinged deck meets the deck?
  17. Bucksh0t

    Bucksh0t Member

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    The gasket was crappy, fixed that. I also made a huge difference.