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Boat Motor Skeg/Cavitation Plate Welding

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  • Boat Motor Skeg/Cavitation Plate Welding

    I have started repairing Cavitation plates and Skegs on Stern drives and have learned a lot from reading this forum. I appreciate the wealth of knowledge members have generously shared.
    I am considering buying some weld on skegs from Skeg Depot, but I am concerned a little about their casting alloy ALMAG 35 (they call it 535). On several sites they give it a 4 on weldability on a 1-5 scale, 1 being most weldable.

    Also I have seen posts here state that these jobs run around $300 and I wanted to know is that just the weld portion or does that also include repainting the unit? One I just did seemed like the painting process took as long or longer than the welding and blending.

    Finally, I would appreciate what paints (primers and top coats) folks are using that they feel are quality products and any tips on the finishing process.

    In an effort to give back to this forum I have uploaded some pictures of a cavitation plate repair where I machined a Trillium Copper disk that i used as a positive mold for the Anode cavity. The missing portion of the Cavitation plate was built up using Fusion King's favorite alloy 4943 and I was very pleased with the final result.

    After prepping the joint I followed the advice given here and directly to me by Fusion King to "dance" the A/C arc gently over the cast joint surface to bring any impurities to the surface and then use a stainless brush to clean them off before beginning to add the 4943 3/32 filler rod. I did have some porosity issues as you can see from the pictures that I tried to eliminate with a secondary operation, adding just a small amount of filler after melting the porous areas and slowly reducing the foot pedal control to try and let the Hydrogen gas escape. I did my initial grinding / shaping of the build up with Walter grinding disc from their ALUM line. They cut very quickly and don't load up. I finished up with a belt sander and air die grinder equiped with a drum sander in the fillet areas. In the future I will be using a self etching primer before applying a filler primer. Any suggestions on those products would be appreciated.

    Dynasty 300 with Foot control, Liquid cooled Diamond Back Torch
    Diamond Ground Brand 1/8 2% Lanthanated Tungsten
    AC Balance Varied: 65% initial pass then 70%
    AC Freq: 40 initial pass, then 50
    Filler: 3/32 Hobart Maxal 4943
    100% Argon
    Ambient Shop Temp 80° Note: In the future I will be welding these in an Air Conditioned room to lower the humidity in an effort to reduce the porosity caused by hydrogen gas.
    I used a Temperature Gun to monitor the lower unit temperature and let it cool when the gear drive / Bullet area approached 150°.
    I oriented the cavitation plate Fin vertically so I was adding filler metal in a flat position. The Trillium copper disk was 3/8" thick. This material melts at 1900° versus the 4943 at 1065-1170°. I didn't have any issues with melting the copper or the aluminum filler sticking to it.

    I hope this information is of some value to someone.

  • #2
    I hate painting. I'd rather trim my finger nails with my plasma cutter than paint. <br />
    <br />
    Good luck painting your skeg/cavafloppy whatchacall, I will be of zero help to you.


    • #3
      I love fixing alum boat motor parts. Been doing it for more than 39 years. But i don't paint them either...Bob
      Bob Wright