Relocating rudder

Discussion in 'Boat Design' started by Vronsky, Apr 3, 2014.

  1. Vronsky
    Joined: Apr 2014
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    Vronsky Junior Member

    Dear all,
    Please be gentle, newbie here...
    I'm studying options for a 33' sailboat for solo circumnavigation.
    Since I'm 6'5" tall, boat options in this size with standing height headroom in the salon are VERY limited.
    I was looking at a Beneteau Oceanis 343 that seemed to fit my needs very nicely.
    But after seeing this YouTube clip, I changed my mind on having any boat for my big trip with a spade rudder >
    http://www.youtube.com/watch?v=Z7GYGlN_t2g&list=UUC5sAt5yfQtH4bYe-VmRztA&feature=share
    http://www.youtube.com/watch?v=E5xKM4y36-A&list=UUC5sAt5yfQtH4bYe-VmRztA&feature=share&index=1
    http://www.youtube.com/watch?v=KKBzu0geNvM&list=UUC5sAt5yfQtH4bYe-VmRztA&feature=share&index=2

    However, non-spade rudder boats with the required headroom are almost non-existant (discovered one, Bjorn Olsen's Nimbus 33: very hard to find).

    So I am wondering if it is perhaps possible -within reason- to replace the spade rudder of an Oceanis 343 by a transom hung rudder, like in the Beneteau First 27.7.
    Or is this a ludicrous idea ??

    Please share your thoughts.

    THANKS,
    V.
     
  2. FAST FRED
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    FAST FRED Senior Member

    Since I'm 6'5" tall, boat options in this size with standing height headroom in the salon are VERY limited.

    SO?

    Standing in very smooth water is OK to relieve oneself below and perhaps to wash dishes.

    Lots of boats have specifically designed SITTER interiors, but usually way smaller than 30+ft.

    Interior modification has little risk.

    A transom hung rudder conversion should be no problem , even if the transom needs to be beefed up.

    Building the new rudder put a tab on the trailing edge and power the tab with a wind vane , as well as an electric ram style auto pilot.

    These use tiny electric with the minor load of a trim tab.

    Biggest hassle is a pendulum style vane would be harder to fit , in a downwind cruise they work the best as the stern shifting by a wave is noticed (and proper correction to the helm made) before the air vane notices a shift..
     
  3. Vronsky
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    Vronsky Junior Member

    Insufficient headroom is indeed not so much an issue during sailing, but greatly at anchor/in the marina where some 75% of the time is spent during a world tour.
     
  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Modifying the cabin top to pop-up would be easier and cause less structural and balance problems.
     
  5. BertKu
    Joined: May 2009
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    BertKu Senior Member

    Indeed, like Gonzo suggested, a popping up cabin top as shown on the photo's could solve your problem.
    You may have to make a drastic decision on what for material to use between the existing cabin and the new pop up roof made from fiberglass. thick see through plastic or canvas or net. Bert
     

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  6. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    A pop-up cabin top on a boat which will be circumnavigating and almost certain to go through some major storms. Hmmm...... Might leaks be a problem? Structural integrity a concern?
     
  7. oceannavigator2

    oceannavigator2 Previous Member

    Or forget the pop up and do it for real.

    Check stability, but bumping the cabin roof up a few inches and re glassing would be easisr than building a rudder.
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    I agree a poptop isn't a reasonable course for an ocean going machine. You lose way too much strength by cutting the cabin roof this way. Build a doghouse to get the needed headroom, which, if well thought out will retain the strength and stiffness required for a passage maker. The Bene 343's deck structure isn't intended to take this level of compromise. Just "bump up" the main cabin "blister" the few more inches you need.

    As to making a transom hung rudder, well your boat isn't well suited to this modification and is a dubious idea at best. The spade offers the best performance and steering "bite" you can get. You can look a videos all day, but every arrangement will have someone complaining, about things they don't understand. A transom hung can be damaged as quickly as any other setup and you'll find an equal amount of videos, with self appointed rudder design experts, suggesting it's a design flaw, when in fact, they simply bashed into something or didn't perform the maintenance necessary to keep them in good shape. So, before you condemn all spade rudders as a "design flaw" consider that 90% of production boats have them, so if they where this fundamentally flawed, don't you think the insurance companies (at the very least) would insist on a different engineering approach?

    Simply put, a spade, if routinely maintained (just like anything else), will live for generations under the butt of your boat. Conversely, bash it into a coral head or rock and you'll tear it loose, just as easily as backing a transom hung down, into something that tears off it's gudgeons. If you want more protection for a spade, consider converting it to a skeg hung arrangement. Naturally, you'll lose any balance it might have (helm weight), but this can be compensated with skeg/rudder relocation and shapes.This isn't a small job and should be designed professionally, so it actually works and can take a shot, when you do find a hardheaded and wayward mermaid in your path.
     
  9. Vronsky
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    Vronsky Junior Member

    I'm not arguing the design, it's that these thin and delicate blades are inherently vulnerable to collisions. Here's an exmple of a (very) good boat that sunk when something hit their spade that ruptured their hull and flooded the boat >

    http://www.liveleak.com/view?i=3ac_1358107957&comments=1

    Of course, a transom hung rudder can be hit as much as a blade, but a fatal rupture of the hull will be far less likely (provided its properly mounted).

    What I had in mind was this transom solution applied on a 27.7 , ideally in a kickup version >
    [​IMG]

    This rudder would be some 2 feet from the original position in the hull. Could someone explain why this would cause serious unbalance ?
    Such a conversion doesnt look like a big technical challenge for a professional builder, although certainly not a DIY weekend job. Connecting it to the steering wheel mechanisms of a 343 is another story. And that the rudder function will be affected is clear but an acceptable compromise.

    THANKS,
    V.
     
  10. BertKu
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    BertKu Senior Member

    I have seen yachts having such pop up cabin roofs overseas on seagoing yachts. If one can build a hatch which can withstand storms, I have difficulty in believing that a good yacht builder cannot make a bigger "hatch" on a yacht, acting as a cabin roof. Where I do agree with both of you, not all yachts cabins designs are suitable for a modification. Bert
     
  11. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The Bene 343 has a 30 degree transom rake, the 27.7 is dead plumb, so rigging a transom hung on a 343 will require considerably more, then just a new rudder and some gudgeons. Moving it aft will also change the CE/CLP lead relationship and not for the better. The Bene 343 has a balanced rudder blade. If it was skeg hung, you can't employ a balanced blade. These are all fairly simple concepts the average sailor understands. If you're having difficulty with why moving a rudder 10% of it's LWL farther aft might affect balance, than you probable shouldn't be considering these changes, without serious professional design help.

    As to the poptop on a balsa cored deck, well again, you'll need professional help getting that sorted out and you'll still have a big hole in the top of the boat, if you get knocked down, unexpectedly swept, etc., which isn't good if farther from shore than you'd care to swim back. A doghouse or increasing the blister side heights are much better/stronger options.

    As to spade vulnerability, well the fin will hit first, which should give you a clue about draft concerns, if it hasn't brought he boat to a sudden stop, most of it's momentum will be gone. Lastly a transom hung is considerably less efficient than a spade and certainly more vulnerable. It's just as vulnerable under the boat and much more so backing down of if someone bumps your stern. The Bene has 6' 4" of draft and about a 4' rudder. You got to try pretty hard to beat this up, without not also having a bashed in fin.

    What is you fear of belly hung rudders? The spade could be made kickup if you're really that concerned, without some sort of rigged up contrivance to hold up a transom hung on a 30 degree reversed Bene 343 stern. I work on a lot of boats and see far more issues with transom hung rudders, then spades or skeg mounts.
     
  12. BertKu
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    BertKu Senior Member

    PAR, I have high respect for a couple of forum members and you are one of them. You could design it strong enough. I assume you would design it with a couple of air pockets in the roof , when there is a serious problem, the upward pressure will close the roof. Thereby reducing water inflow. Also with today's modern technology, it could be solved with hydraulics or electrical. The sensors would sense a dangerous situation and the poptop would close, with minimizing the inflow of water. Or better, if the sensors are positioned in such a way, that it could be prevented any influx of water in total, even better. Attached an example of a ÔÇťocean" going speedboat (they claim) with hydraulics roof. Bert
     

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  13. gonzo
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    gonzo Senior Member

    A pop-top is simply a hatch with curtains. If it fails, so will the other hatches.
     
  14. oceannavigator2

    oceannavigator2 Previous Member

    Was just about to make this exact post. This is the answer. I would stress:

    1) Your boat may end up very annoying to steer and slow with the loss of balance.

    2) Raise the whole roof.

    3) The rudder isn't what hits first. The keel does. You're all set on collisions. If you are picturing hitting flotsam in the middle of the night, get working on watertight bulkheads, not rudders.

    If I were in your exact situation, satisfied with a small boat's space for circumnavigation, I would do the following:

    a) Buy a much bigger boat. Something with performance. An ex racing boat without a home.

    b) Wall off the entire forward V berth area, creating a watertight compartment.

    c) Wall off whatever you can aft in the same way, living in the center section amidships where the motion is most kind.

    d) Enjoy the greater speed, greater stability and greater weather handing capability of a longer waterline.

    You are going to spend a lot of days at sea in all conditions. Might as well have the safest, fastest boat you can afford. The Beneteau isn't it.

     

  15. PAR
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    PAR Yacht Designer/Builder

    Bert, I wouldn't consider that boat (pictured) anything close to "ocean going" - it's likely Cat. C, possibly B, though I'd question this, without spec's. Electrics, sensors, etc. are the type of thing you'd probably not want to rely on in deep water. A simple, robust, fool proof system, with a minimum of parts, is the way to go. Poptops work on small trailer sailers, but not Cat. A vessels. Especially when a raised deck blister will retain the integrity of the deck and offer the headroom desired, without big holes in the cabin top, failed sensors or closing mechanisms, gumming up the works.

    As to the rudder concerns, well I think (as might be imagined by now) I'm not as concerned as the original poster in this regard. I've quite a few miles under many keels, most with spades or skeg hungs and though I've run around plenty (a natural function of living in Florida a working the USVI for a few years), I've yet managed to tear one off, though I've damaged a few, though the most serious, was after bouncing over a coral head and coming down on the shaft and rudder, bending both badly. They were repaired in Honduras easily enough (delivery job) and I was on my way. This isn't a common event, though does happen. You can't prepare for everything and lastly a transom hung rudder, would have suffered just as badly (if not worse) if it had it's fin bounce over a coral head and dropped down on it. I think the Original poster is hoping to prevent an uncommon circumstance. It would be nice if a design could be bullet proof and if you really want something like this, looking at a used production boat isn't the way to go.
     
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