Sailboat with a heavy helm-rudder analysis

Discussion in 'Sailboats' started by Crazer, Aug 8, 2013.

  1. Crazer
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    Crazer Junior Member

    I own a 1967 Pearson Wanderer 30, and have discovered what many other Wanderer owners have discovered: that the boat has the heaviest helm of any boat I've ever sailed. She is difficult to handle in large gusts, a problem that is exacerbated (in my opinion) by the shoddy Edson wheel steering. Of course, removing the wheel will make handling easier but the loss of the mechanical advantage will exacerbate the heavy helm issue. Another sailor, who had sailed my boat, mentioned, in passing, that they had "not got a look at the rudder" and implied that doing so might explain why the boat required so much strength to handle. Of course, we are here discussing the actual effort required to move the rudder as opposed to weather or lee helm, or anything that might be affected by the rig.

    So my question to you, the fine gentleman of the forum, is two fold: A) Can the heaviness of the boat's helm be explained by the design of the rudder and if so B) what should be changed when designing a replacement? I'm a cruiser and occasional offshore sailor, not a racer, so I'm not concerned with speed, just improving the boat's handling.

    The rudder in question (not my boat):

    http://www.sailblogs.com/member/newp-wanderer/images/026_26_scale.jpg

    A profile of the boat:

    http://i648.photobucket.com/albums/uu207/ilikerust/Grizabella/Picture1.jpg
     
  2. JSL
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    JSL Senior Member

    So, not weather or lee helm. Is the steering 'heavy' in both directions while on a certain tack -port? stbd?... or running... or under power????
    I was on a boat with 'heavy' steering and the cable system was undersized and compromised. Sometimes a bent rudder stock can 'stiffen' things up but my favorite : An improperly machined plastic bearing which expanded by water absorption over a period and seized up the stock.
     
  3. Crazer
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    Crazer Junior Member

    I repeat: the problem is with the boat itself, as all other Wanderer owners I have spoken to have noted the same problem. You can also see it in the disproportionate number of Wanderers that have had their tillers replaced with wheels. Mechanical issues are not suspect here, although the wheel has plenty (including an alarming tendency to fail at critical moments.)
     
    Last edited: Aug 10, 2013
  4. Petros
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    Petros Senior Member

    presuming everything is working properly in the steering system, I would say that is a rudder that will always transmit large loads to the steering system. It is like a barn door with no way to counterbalance the lateral forces on it with area ahead of the hinge line. If it were my boat I would do a major redesign of the rudder and aft keel during other heavy maintenance during a haul out. If you do that better get some professional guidance.

    After making sure everything is working properly and it is still not to your satisfaction, there is something else you can try. The easiest way to deal with it is to change the mechanical advantage on the system so the forces transmitted to helm are smaller. longer lever or bell crank on the rudder shaft end, smaller levers or drum on the helm end (this will depend on the details of your steering system). this means it will require more turns of the helm to get the same rudder response, but it will greatly reduced the work load on the helmsman. This can likely be done without the help of a NA, but should be with the guidance of someone knowledgeable about maintaining and repairing steering systems on yachts.

    I would also say that you would be best to beef up the strength of everything in the steering system at the same time. When that large rudder gets hit by side forces it will transmit large loads to all of the system, I would want it as stout and safe as possible for the occasional unavoidable heavy seas.

    good luck.
     
  5. Crazer
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    Crazer Junior Member

    I won't ask you to design it for me, but I would like to know what kinds of changes you would make. Are we talking a structural rebuild (reshaping?) of the aft lower hull? That's too much for me. If there's not much I can do by modifying the rudder or designing a new one, I'll come up with a steering system that works better than the one I have. I am going to have a tiller, but there are ways of increasing the mechanical advantage, as you said.

    Edit: One thing that just occurred to me is that I plan on removing the inboard and filling in the prop aperture. Might that make a difference somehow?
     
  6. alan white
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    alan white Senior Member

    It really sounds like the rig CE is too far aft, possibly by design. An unbalanced rig/underbody (by design) would cause the helm problems and would consequently cause the wheel steering to react too slowly due to the increased mechanical advantage it has over tiller steering and the more turns it has to travel.
    If so, there is probably a lot of info available on the subject somewhere on the web.
    Various remedies are available, some simple and cheap, others complicated and expensive.
    Weather helm is going to be really hard on your wheel steering mechanism. No matter whether you use a tiller or a wheel, the boat will still be slower and more uncomfortable to sail.
    Simple causes could be old blown out sails or improper mast rake or badly set up rigging. While the boat may have been designed with a "healthy" weather helm, any of those factors could more easily make for an unhealthy helm on a boat that came off the design board with a strong weather helm.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Change the lower bearing and the rudder port. Then tune up the Edson setup, which I've found most have replaced on this particular yacht. The real issue with this rudder is its location and aperture, though the plan form and section could also use some upgrades. Filling in the aperture will make a huge improvement in the rudder's effectiveness.
     
  8. Petros
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    Petros Senior Member

    Alan, he did not say it has weather helm, but was heavy. which I take to mean that it takes a lot of effort at the helm to operate the rudder.

    I could be wrong but it appears to me that by having a large "barn door" like rudder hinged at the leading edge, that the center of pressure (the dynamic center) on the rudder face would be a long way from the hinge line. meaning that the rudder forces would be quite large. A longer and narrower rudder would not take as much effort to deflect it, but the hull and aft keel design does not allow for that. Another idea might be to run the rudder below the keel, and have a portion of it ahead of the hinge line uder the keel. this would to move the center of pressure closer to the hinge line. this would make the rudder vunerable to damage, and catching weeds, so this is not really a good solution either. If the rudder was replaced with a spade type rudder, moving the hinge line further back on the rudder, the area of the rudder ahead of the hinge line would greatly reduce the force required to turn the rudder. this means building new structure in the hull to handle the large cantilever loads transmitted through the the shaft (rather than through hinges on the keel trailing edge). professional design guidance would be required, but it should not only reduced the forces at the helm, it will also increase the effectiveness of the rudder since you can use a NACA 00XX foil profile on the rudder. I would also taper the trailing edge of the keel to a near point to improve the flow over the new rudder. You can further strengthen this kind of rudder installation by putting a bar or brace from the bottom of the keel back to the tip of the rudder. This will also protect it and reduced the tendency to collect weeds on it.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Petros, you've hit on a few of the other problems with this particular design. The "built down" sections of the keel aren't very tapered as they approach the aperture and the blade itself isn't well shaped either.

    I know of a few that have converted to a spade and many more that have just reshaped the plan form and section. Naturally, the spade conversion has more effectiveness, but the reshaped plan form and section option will help and without the aperture, a much better working rudder.

    Personally, I've worked on a few of these and similar builds of this era and the rudder ports and bears are almost always shot. Fixing these issues, with a new apertureness blade profile and section will make a huge improvement.

    Making the rudder deeper than the keel, wouldn't be my recommendation on a shoal draft boat. You're just asking to break it, though the balance this could offer would be helpful.
     
  10. michael pierzga
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    michael pierzga Senior Member

    Disconnect the steering gear and turn the rudder. If its Heavy..friction...your bearings are shot. Plastic bearings are notoriuos for swelling
     
  11. Eric Sponberg
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    Eric Sponberg Senior Member

    Crazer, In my opinion, most of the other opinions are valid and should be checked, but there are two things, taken together, that are really causing the problem. First is the incline of the rudder stock. By design, it is angled down and forward, and so when the helmsman turns the wheel, the flow across the rudder is actually trying to pull the hull down deeper in the water. He is fighting the displacement of the boat that wants to keep it afloat. The other thing, as others have mentioned, is the shape of the rudder--it is too "barn door" shaped. The best rudder shape for inclined rudder stocks is more of a "half Heart" profile shape, with a larger bulge or loop up near the waterline, and tapered to very narrow at the bottom. Modifying the rudder to that sort of planform would be a readily made improvement.

    Eric
     
  12. tomas
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    tomas Senior Member

    What would the motivation behind this design choice in the first place?
     
  13. Eric Sponberg
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    Eric Sponberg Senior Member

    Such a rudder design was kind of the norm for the period, which was the CCA rule era from about the between war years into the 1960s. There was still very little numerical or analytical effort done to figure out what worked. It was the evolution of experience. It continues to this day, but with many more analytical tools available to us.

    Eric
     
  14. DCockey
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    DCockey Senior Member

    Probably tradition. I don't recall seeing a boat with the rudder on the keel which didn't have the rudder post raked aft (top aft / bottom forward). Raked aft rudder posts go back centuries to boats which didn't have overhanging counters. The rudder was attached to the stern post as was the transom, and the stern post and transom was always raked aft. As keels became shorter the rudder post continued to be raked aft.
     

  15. Petros
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    Petros Senior Member

    IOW, it was the look of a traditional boat that results in a poor design. raking the rudder hinge line looks nice, but results in a rudder difficult to control.
     
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