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Thread: Corrosion Protection for an OB Prop

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  1. #1
    Join Date
    Nov 2001
    Location
    McHenry, IL, but sail out of Racine WI
    Posts
    626

    Corrosion Protection for an OB Prop

    My Yamaha OB is always in the water, and the lower unit, including the prop, encounters a significant corrosion problem. Yes, I do have a sacrificial plate above the prop and the Ariel is used in fresh water. The prop is an aluminim alloy.

    The problem of the disappearing propellor (and lower unit) is commonly recognized (The Yamaha prop is about $100, so, being cheap, I don't like to replace it annually).

    I have painted the prop with TRI-Lux II which seems to work well as protection. Tempo did not work. But the prop has to be repainted each year, with a significant buildup. My motor mechanic has told me that the rough surface of the paint on the propellor is responsible for loss of thrust I have been experiencing.

    The question is, what have others found best to protect the prop? Or is sanding it every year and refinishing it the only or the best solution?

  2. #2
    Join Date
    Sep 2001
    Location
    Orinda, California
    Posts
    2,311
    A Plastic prop?

  3. #3
    Join Date
    Nov 2001
    Location
    McHenry, IL, but sail out of Racine WI
    Posts
    626
    Do you know if they make such a thing, or is that just an idea (although a good one). My recollection is that the plastic was not rigit enough for a larger horsepower motor (They do have them for the 2 HP for example). Has something new come on the market?

  4. #4
    Join Date
    Sep 2001
    Location
    Hampton Roads Va.
    Posts
    821
    Sounds like a 'hot slip' or a wiring problem on the boat.
    1- Get a heavy cable and attach a bunch of zincs to one end , the other to your ground . Hang in the water at the slip. Or go to West Marine and buy a 'Guppy Zinc' .
    2- Pull the motor out the well , thats what I do . $100 buys a lot of BenGay ointment.
    4- Is that the right prop , pitch wise ? Cavitation can cause your prop to erode too , and too much pitch will cause cavitation .

  5. #5
    Join Date
    Sep 2001
    Location
    Hampton Roads Va.
    Posts
    821

    Exclamation

    Just re-read your post;
    If your motor is elec start , I'm betting on wiring problem .
    I left a motor in salt water for the same time and only got marine growth , no corrosion .

    Are you slipped anywhere close to some big powerboats , 1 or 2 slips away, thay could have a leaking electrical system.

    I had a home made 'slip meter' to measure stray current in marinas. Basic VOM with special leads and 3' long probes . Works great in salt water.
    Found an old Egg Harbour with enough stray current to shock a diver !

  6. #6
    Join Date
    Nov 2001
    Location
    McHenry, IL, but sail out of Racine WI
    Posts
    626
    Thanks Mike for your comments. I can not pull the 85 lb motor out of the well. Further, I have concluded (be it right or wrong) that to try to remount a motor in a heavy sea is very dangerous. I don't know how others do it safely. And as for pulling the motor out when leaving the boat, that is a big hassle, and I don't have a couple young turks standing nearby to help.

    Yes the pitch is correct for a heavy load - minimum pitch, pitched for almost no forward motion at all. Actually, the pitch issue and cavitation, I think, would only arise with a low pitched prop used on a high speed/light boat. With a high pitch prop on a low speed hull, the prop would not cavitate, but, instead, the motor would not get up to speed and there would be no power. The engine appears to reach the right rpm.

    The problem I don''t think is wiring (I do not hook up to the AC when in port) The entire electrical system is tied into a large copper grounding plate in the water near the keel. The zinc anode on the outboard just above the prop should discharge any currents relevant to the motor (and yes, it is eaten away). As for powerboats nearby in the marina, yes there are tons of the floating kitchens. However, I can't really control other people's wiring. Further, I visit various marinas during the summer.

    Keep in mind that this problem is not just related to my set-up but is related to all outboards. The problem is discussed in the Interlux brochure, and outboard motor instruction manuals. It appears to be universal. Everyone says that if the motor is left in the water, the lower unit and the prop must be protected by some sort of supplementary finish. It may not be electrolysis but simply corrosion of the aluminum. It may be that the movement of the prop, or the motor through the water creates a static charge that eats up the prop. I don't know.

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