Engine cooling water turbulence

Discussion in 'Inboards' started by tranmkp, Mar 9, 2022.

  1. tranmkp
    Joined: May 2002
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    Location: Texas

    tranmkp "wherever you go. there you are"

    This has been on my mind for years - the boat has the clamshell intake midships. Since this is a semi planing boat that intake is smack in the middle of the boundry between out of water to turbulent water. The idea behind this is that the water is not solid and instead is full of air. Ive had two semi displacement trawlers with proper cooling system - all sorted out and when pushed to max speed ran close to hot - when backed off - to displacement speed - cooled instantly -
     
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Is this a boat that you are intending to buy?
    Or is this your current boat, and you are worried about a 'what if' situation?
     
  3. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Bet the cooling pick-up/systems where undersized in terms of K factor. Right angle clamshells are notorious for having very high losses (large K) at high flow, and too many tight radius fittings also drive down flow at high velocities. While there are ways to make sure that proper inflow is achieved at the inlet, usually more care needs to be taken on the inboard side. Also consider the wet stack exhaust pressure if relevant.
     
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  4. tranmkp
    Joined: May 2002
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    Location: Texas

    tranmkp "wherever you go. there you are"

    Bajansailor - its my current boat.. if you own a boat its ALWAYS a "what if" situation. I am just a little frustrated at higher temps at higher speeds. I never experienced higher temps in my sailboat when (foolishly) pushed to max engine RPM

    Jehardiman - no idea about what your saying - is a flush thru hull leading to a properly sized sea chest/manifold - to the engine so the engine is getting undisturbed water a way to correct this?

    cheers
     
  5. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Before assuming that it is an air/water mixture causing you issues. I would find the spot where the intake hose enters the engine. Purchase say one foot of clear, same inside diameter SUCTION( so it does not collapse) plastic tubing and two
    unions, plastic would be fine. Insert this tubing in line and see if you have bubbles. If so you may be on the right track.

    The other issue could be that when you push the throttle to max, that the existing cooling system is inadequate to dissipate the extra heat caused by running the engine at higher horsepower levels. The higher the engine output horsepower
    the more heat it will produce. ( within normal operating parameters)

    Also check the condition of the rubber impeller on the cooling pump. Perhaps the issue can be resolved with a $60 dollar impellor
     
    Last edited: Mar 10, 2022
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  6. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    There is a lot more going on than the inlet type. For a given flow, there is a pressure loss for each length of pipe and every fitting including the inlet and outlet. This loss is sometimes expressed as del pressure = K*u^2 where K is the equivalent length of pipe at a flow velocity of u. There is also a pressure at the inlet, a pressure increase at the pump, and a pressure at the outlet. It is therefore possible to calculate the flow and associated pressure at any point in the system. If there is too much negative pressure (i.e. suction) at the pump, or too much back pressure (i.e. head) at the pump, it ceases to function properly. Since the pump speed (i.e. flow velocity) and waste heat are directly linked to the engine speed, it is possible that the system has too much head loss to support the flow needed at maximum engine RPM.
     
  7. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    Yep, check the simple most obvious things first. Always a good idea. When I installed a raw water strainer years ago I never thought about air in the raw water. A lot of those strainers have a clear plastic housing. You can see the water pass into the strainer (and any debris that's in there). I don't recall ever seeing much in the way of bubbles/turbulence but if it were happening I certainly would. It's always a good idea to have one on an inboard engine.
     
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  8. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Raw water intakes properly mounted well under the hull will still take in some air, especially in rough conditions, or when driven fast, but that shouldn’t be enough to actually cause overheating.
    Are you certain that the entire raw water system from intake screen to exhaust outlet is installed to specs, clean, and operating correctly?
    Barnacles, rust, scale, deteriorating impeller, collapsing hoses, etc can cause coolers to partially or completely fail.
    Air pockets can also develop on the coolant side, and cause similar overheating symptoms.
     
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