Replacing a damaged rudder

Discussion in 'Props' started by missinginaction, Mar 9, 2019.

  1. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    254.JPG
    Last summer I was cruising on the kicker. Speed was only 4 knots or so. Main engine (I'm a single v-drive) was not even running. The autopilot was set and I was keeping an eye on things but drifted a little out of the channel and.......yep, I hit part of a submerged tree. Completely my fault. I guess I'd be better off with two eyes on things from now on.

    When it happened I felt a scraping then a small bump and then heard a loud crack as I apparently broke off a branch of this submerged tree. The boat never stopped just slowed for a second. I stopped and dove underneath. Strangely, the prop and shaft showed no damage but the rudder shaft was bent where it entered the hull. When I turned the wheel hard over the steering would "stick" so it was obvious there was some binding between the shaft and hull.

    Near as I can figure, because the main engine was not running and the prop was freewheeling the obstruction skipped over the prop and got caught forward of the rudder bending the shaft back. It's the original bronze shaft, 1.25 inch and must be pretty soft. I realize I can straighten it but I've decided to replace it. The saving grace is that since the shaft bent so easily I can see no hull damage or issues with the rudder port.

    The existing rudder is 10.5 inches wide at the top, 13.5 inches deep (top to bottom) and 7.5 inches wide at the bottom. This rudder is designed for planing but I never, ever plane this boat off. I typically run at displacement or semi displacement speeds, never faster than about 8 or 9 knots.

    My steering going forward is fine but in reverse I have very little control, especially when backing. I can just replace this rudder with one of the same size. If I increase the depth of the rudder a few inches or the width (or both), would I improve my steering when backing and maneuvering?

    Thanks in advance for any thoughts, MIA
     
  2. gonzo
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    gonzo Senior Member

    Is the bottom of the rudder as low as the lower blade in the propeller?
     
  3. missinginaction
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    missinginaction Senior Member

    232.JPG I'll get a precise measurement Gonz, next time I'm down at the the club. Based on this photo I'd say that the bottom of the rudder is slightly above the lower blade of the prop.
     
  4. gonzo
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    gonzo Senior Member

    The propwash is a cone. I think you will get more steering force if the blade goes a bit lower.
     
  5. kapnD
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    kapnD Senior Member

    The existing rudder design could be improved for slow speed use by squaring it out and possibly adding a horizontal plate at the top.
    Looks like there’s probably no keel on the vessel, so there’s not much hope of adding further protection without extensive modifications.
    Deep vee hulls are often outfitted with twin engines due to the severe running gear exposure necessitated by having the singl edrive on the centerline.
    I had a similar vessel that I wound up cutting a large triangular chunk out of the vee in the stern in order to raise the propeller.
    It worked amazingly well at displacement speeds, significantly reducing wake and fuel consumption, but it did reduce high speed capabilities, a trade off that I found quite acceptable.
     
  6. TANSL
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    TANSL Senior Member

    If the blade goes lower or if the blade has more area?. What should do the OP, lower the blade or adding surface to the blade?
     
  7. missinginaction
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    missinginaction Senior Member

    Thanks for the replies. I'll be contacting some running gear vendors over the next few days. Based on Gonzos comment and stock rudders I can find online, it looks like I can go 2 or 3 inches deeper and a bit wider as well. I'm curious as to the different shapes of some of these rudders. From left to right these are called Standard, Spade and Special Rudders. If anyone can shed any light on the advantages of these different designs I'm all ears. It looks like my existing rudder is a Special Rudder. I'm assuming it's for planing boats. There are a number of stock rudders in each of these three categories that look like they would work. I'll have to do some more homework.
    KapnD, you're right about the running gear hanging out there. The only saving grace is that she draws well under three feet of water with the current set up and even with a little deeper rudder will be under three feet. I've been running her on the Erie canal system (pretty shoal in many spots) out to the Great Lakes without incident until last year. The mishap was completely avoidable and entirely my fault. :rolleyes:
    BTW, I was fortunate to spend three weeks over last summer in your beautiful state. Especially liked Kauai and the Napali Coast. You're lucky that you live out there.


    standard.jpeg spade.jpeg special.jpeg
     
  8. Blueknarr
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    Blueknarr Senior Member

    On my screen they appear one over the other.

    Standard-- with its round bottom allows submerged objects to be deflected instead of a hard snag.
    View attachment 145948

    Spade-- gives greater surface area but is more easily snagged or damaged
    View attachment 145949

    Specials-- are spades with a portion of the trailing edge removed. This would increase the "balancing function of the portion ahead of the pivot. It could also provide clearance for something hanging below the hull aft of the rudder such as a boarding ladder or wake shaper.
    (Edit) notch could also allow clearance for sides of tunnel
    View attachment 145950
     
    Last edited: Mar 11, 2019
  9. missinginaction
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    missinginaction Senior Member

    Thanks Blueknarr.
     

  10. missinginaction
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    missinginaction Senior Member

    Thanks again to all who weighed in with this. I did some research and made some phone calls. Getting information was difficult. Calculating the surface area of a spade rudder is easy but the curved standard style rudders, not so much. I even called Hydrasearch/Buck Algonquin thinking "they must have area specs for the rudders they sell." but struck out there too. Vendors wouldn't stick their necks out at all. Even general questions were met with "You need to contract with an engineering firm."
    Thankfully there is some information out there (thanks Dave Gerr). In the end I decided on a standard rudder from Buck Algonquin that I estimate to be about 25% larger in surface area than the rudder it is replacing. The stock is long enough that I can drop the blade down an inch or two and get it even with the lowest point on the propeller arc.
    As Bluenarr pointed out the standard style rudder is less likely to snag and with my running gear completely unprotected, the standard style will be more forgiving.
    I could have gone one step larger with a blade that had about 50% more surface area but decided on a more conservative approach.
    In the end I'll either have roughly the performance I always had or somewhat better low speed handling. Either way will be fine.

    Thanks as always for the responses,

    MIA
     
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