Request Advice for Rudder Replacement

Discussion in 'Boat Design' started by HighFly_27, Nov 11, 2012.

  1. HighFly_27
    Joined: Nov 2012
    Posts: 8
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    Location: Bonifay, FL 32425

    HighFly_27 HighFly_27

    Ref: 1970 Islander 37 Motor Sailor (MS)

    Rudder has 2 ft. Busted Off (happened in storm, broke free of morring).

    Question # 1. Would you remake the rudder as it was made by -- Islander

    (no changes) in 1970 _____________________ ?

    Question # 2. Would you go to (proven) later design of this airfoil to

    reduce drag & reduce it's size (see below) ______________ ?

    Question # 3. The former owner, said that he was always at risk with the I 37, I 37 takes (nearly) 6 feet of water. The stock rudder was very effective; he was caught in gale (50 knt.) winds & rough sea and no problem. He recommended that 9 to 12 inches could be cut off the bottom with no loss ot rudder authority. He thought this 9/ 12 inches off would reduce the risk of getting it wacked all the time. Also, the boat yard mgr. had motor sailed the boat back from the accident (45 miles) site; did not notice a difference in the handling of the boat with (est.) 2 feet wacked off.

    Questions 2 & 3 (above) cont'd. Would you consider a later design airfoil shape but not as long in overall length to reduce the risk of hitting it ? Currently, the rudder length is even with the keel depth at >> 5' 10" inches << rudder depth.
     

    Attached Files:

  2. Frosty

    Frosty Previous Member

    You have an offset prop and shaft. If it works well as it is I would repair the one you have and leave well alone --dont fix it till its broke etc
     
  3. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    You can design the rudder bottom to snap off without damaging the remainder of the rudder. This may be how the original was done, looking at the pictures. I would recommend you do this if the rudder depth is the same as the keel draft.

    The ICW is shallow and a lot of the bottom is the consistency of yogurt. Plowing through a foot of muck with the keel is pretty common. But you want to keep the rudder out of it. When stuck in the mud, you will probably try to break loose using the wake of passing vessels. That is hard on the rudder if you are pitching onto it. So I would terminate the rudder post well shy of keel draft, say 18" shorter. And then design the tip to fail before the shaft bends. Another consideration is the ability to pull the rudder with the boat blocked on the hard. I can't. I have to make sure the *** of my boat is over dirt so I can dig a hole.

    I would match the old design. I has proven itself in that the boat could self recover after the accident. If the rudder shaft had bent, the moaning would be much louder. Don't make the new one any heavier or stronger than the old one. It looks like the right thing broke in the right way.
     
  4. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    This is a CRUISING boat , a "better " rudder profile might help create .01 of a K better speed.

    Is that worth any effort at all?

    Just purchase a replacement rudder and install it.

    If a .01K speed increase excites you get racing bottom paint.
     

  5. HighFly_27
    Joined: Nov 2012
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    Location: Bonifay, FL 32425

    HighFly_27 HighFly_27

    I just asked the question (your advice). This rudder has to be made up and not off the shelf (purchase).

    I repeated what I was told by the former owner " rudder sticks down there (nearly) (6) feet. " He thought he'd remake the new one a little shorter.. to cut down the risk of getting it hit again.

    I understand the term.. " if it ain't broke. don't fix it ? "' I've been a mechanic & maint. test pilot since the late 60's and don't fix anything that don't need fixing.

    The owner said the I 37's rudder was very effective but he'd cut off 9 to 12 inches; then, I had to ask question (above), so don't shoot the messenger.
     
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