Strange aluminum shaft strut?

Discussion in 'Inboards' started by bigkahuna, Feb 12, 2017.

  1. bigkahuna
    Joined: Jun 2008
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    Location: USA

    bigkahuna Junior Member

    I'm looking at buying a boat (sailboat built by Dehler during the 80's) and have run into something I've never seen before. This boat has an aluminum shaft strut. At some point the owner picked up a crab trap line in his prop which bent the shaft and loosened the strut. They replaced the shaft and to repair the loose strut they did what you see in the attached photos. One photo is before the work where you can see the crack where the aluminum alloy strut is loose in the slot in the hull. The second and third photos show the aluminum "wings" that they welded onto the strut and what looks like wedges from aluminum pipe that were welded on for support. They also added a tab in front of the strut for a zinc anode. Strange, huh?

    Four questions:

    1. Have you ever encountered an aluminum shaft strut on a fiberglass boat before? Obviously if they can build boats out of aluminum it should be possible, right?

    2. What are your thoughts on the repair?

    3. Will that repair cause as much additional drag as I fear it will?

    4. Assuming this repair wasn't an ideal fix, what method(s) would have been better? I think I probably would have pulled the shaft, pulled out the strut, reinforced the glass, and re-install the old strut or replaced it with a suitable replacement (in bronze or stainless steel). Thoughts?
     

    Attached Files:

  2. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    bigkahuna

    Not a pretty repair at all.

    If the p-bracket is a casting, then it is much weaker now, if it was originally plate and tube welded together..then it will be "ok".

    But before doing any repairs from cracks, one needs to understand the root cause of the crack to begin with. Was it from a grounding or vibration etc?

    It will cause drag, but, it wont slowly you down 5knots, if that's what you're thinking. Just make sure the leading and trailing edges fore/aft are smooth and gradual too.

    It's a bodged job...but will probably work. Depending upon the grades of ally they used and the quality of the welds and whether they left any voids inside their 'wing's, which woudl quickly propagate as cracks under any loading.

    Nowt wrong with the ally p-bracket...but if you were going to replace a S/S casting is better.
     
  3. bigkahuna
    Joined: Jun 2008
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    bigkahuna Junior Member

    Yup, it's about the ugliest repair I think I've ever seen. And if the strut wasn't cracked or bent, I think it was probably unnecessary. Maybe they figured this repair would be cheaper than pulling the shaft and having to align it later?

    The story I was told was that the previous owner snagged (the line from) a crab pot in the prop and it bent the shaft. They replaced the shaft but during a later survey found that the strut was loose.

    I can't tell if the strut was welded or cast, there's paint in the corners of the strut in the photos so there's almost no way of knowing.

    The more I look at these photos the less I like this repair. Imagine the reaction by a surveyor if I owned this boat and was trying to sell it?

    I've been searching the 'net for a ballpark cost on replacing the strut and I"m guessing around $1,500 ($500-$700 for the strut and $700-$1000 for the installation). Sound about right?
     
  4. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    Exactly...if you as the owner are unhappy with it..then why keep it? It is an eyesore for sure, and most likely wont last that long if repaired badly!

    No idea about prices in the US...im in Japan. But worth shopping about and then get one that is suited to your shaft diameter and power of engine.
     

  5. bigkahuna
    Joined: Jun 2008
    Posts: 53
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    Location: USA

    bigkahuna Junior Member

    Thanks again Ad Hoc. Although I have no doubt this issue could be fixed, I have neither the time nor interest to take on this project. I've decided to walk way from the deal. Over the years I've found that if you find one or two really poorly done repairs / modifications, chances are the deeper you look the more you'll find wrong. This P-bracket / shaft strut was one of two weird "improvements" on this boat. That's usually a very bad sign and I've decided to spend my effort finding something else. Thanks very much for your help!
     
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