Need catamaran rudder head advice

Discussion in 'Multihulls' started by jdory, Apr 11, 2017.

  1. jdory
    Joined: Aug 2015
    Posts: 122
    Likes: 2, Points: 18, Legacy Rep: 10
    Location: Nome, Alaska

    jdory Senior Member

    I'm rebuilding a 30' cruising cat
    and have 1.5" round bar rudder shafts in 316L stainless. Living in very rural Alaska no one here has a mill that can cut keyways. My old rudder heads were aluminum with keyways so I had to protect against corrosion with goop as well as have keys. To get keyways cut into these new shafts I would need to ship to Anchorage where I can get the keyways cut for $200 for two shafts, but also would take a couple hundred to ship down and back.

    Design isn't specific on this point but looks like a detail shows something not much more than a small section of pipe slipped over the shaft with a through bolt. I could do that myself - got the cobalt drill bits. Also a guy in town is good at tig welding stainless if I need to beef up any straps from head to tillers. I'll include a pic or two of old jury rigged system that worked under motor (never had it rigged for sail). I could still use this head without a key and just run a bolt or roll pin through it. It would clamp tight.

    So looking for advice/pics of folks' rudder heads.

    Second question - If I cut keyways or drill a through bolt, should I put ackermann geometry into that keyway/hole in relation to centerline of the rudder blade or just plan on bending inward each tiller, if that works?

    Here's old head and tiller attachment, and a pic of James's boat steering system I'm shooting for similar:

    Attached Files:

  2. PAR
    Joined: Nov 2003
    Posts: 19,126
    Likes: 498, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    What is the shaft head fitting made of, Aluminum? I sure don't like the cast in key, but if it's aluminum, it's understandable from an engineering point of view. If the shaft head fitting can clamp down pretty good, you might just consider a couple of (bigass) set screws, which I'd install in some stainless "helicoils" to insure they don't strip with adjustment and loading. This you could do yourself, assuming some good bits and reasonably careful work. In short, if that cast (aluminum) key can do the job, a couple, maybe three setscrews can too.

    Yeah, you'll have to keep ackermann angles in mind when you put the steering back together. The way most do this is by "clocking" the shaft head fitting, so both sides land on the crossbar with similar angles. I wouldn't be surprised if the key and slot are clocked, which solves the problem. You can bend the tiller brackets, but I don't like this as much as you're introducing an additional "moment" to the assembly, though this isn't all that uncommon either.
  3. jdory
    Joined: Aug 2015
    Posts: 122
    Likes: 2, Points: 18, Legacy Rep: 10
    Location: Nome, Alaska

    jdory Senior Member

    Thanks Par, some good advice.

    The head pictured is aluminum but I think it is just milled out of thick stock, not cast. The key is stainless and removable. Not "clocked" to ackermann.

    The more I think about it the more sense to just reuse what I have. I like the idea of set screws - I assume one would divot the shaft somewhat where the set screw bears against it.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.