Rudder pulls sailboat leeward

Discussion in 'Boat Design' started by Keith Redfield, Jun 6, 2021.

  1. Keith Redfield
    Joined: Jun 2021
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    Location: Aptos, CA

    Keith Redfield Junior Member

    Hi all, I've an Islander 27 (NOT a Perry design https://sailboatdata.com/sailboat/islander-27 ), possibly the only 1 remaining and so no owners to collaborate with. Please excuse this long post, I'm not quite sure I'm describing the issue well.

    I bought the boat sitting on a trailer for 50+ years have never seen water (they were sold as kits, this one never quite completed). She's launched now and I'm pretty happy with the sailing performance so far (I just do coastal/daysailing) but one issue I have is that the rudder (see pic: a trapezoid, wider at bottom - pretty much opposite of usual) wants to pull the boat strongly to lee.

    I'm not speaking of the boat itself having lee helm - the boat will go properly (and slightly) to weather just fine if I keep helm centered, but if I relax my grip, the tiller quickly pulls to weather and the boat will go to lee if I let it - which feels, and probably is, dangerous.

    I don't have a huge amount of experience with tillers on larger boats, so maybe this is normal? but on a 24' transom-hung I used to own I never noticed or was the opposite behavior (where I'm pulling slightly on the tiller, to weather instead of having to constantly push it to lee).

    The rudder is 'semi-balanced' (I believe) with perhaps 10% of the chord in front of the post. It has a pretty thick cross-section (2.5+" at widest). The helm is *extremely* responsive - I can literally turn on a dime. Other observations is that the rudder is strongly influenced by my prop-wash - wanting to pull strongly when under power. Additionally, once it's over far, it's pretty hard to pull back to center. So I would describe it was having a tendency not to want to center - that's it's 'unstable' point and being to either side is more stable. My rudimentary take is that it's got excessive lift if that makes sense?..

    Any ideas on how to approach addressing this? Obviously a marine architect would be a good start, but impractical where I live. Intuitively it seems I might want to trim that wide trailing edge down and maybe even reverse the taper a bit - closer to what's shown on sailboatdata drawing
     

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    Last edited: Jun 6, 2021
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum Keith.

    That rudder of yours is quite an enigma for sure!
    When you are sailing hard on the wind, under full sail, and you are hit by a gust and she heels a bit more, do you get a bit more weather helm causing you to pull the tiller up to windward slightly(or some more)?
    Or does she just stay on the same course without any tendency to 'come up'?

    Re how the tiller quickly pulls to windward when you relax your grip, I was initially thinking that you have too much area forward of the rudder stock - but that cannot be, as from your photo you have very little counter balance effect there.

    What is her behaviour like when you are motoring astern - can you pretty much point the tiller in the direction that you want to go, and she goes there, or is she rather unpredictable as to what she wants to do?
    Is the helm very 'heavy' in reverse, needing a firm grip to ensure that the rudder does not 'spin around'?
    Have you checked the fore and aft alignment to see if the rudder and the tiller are both on the centreline ?
    I am wondering if perhaps the rudder stock is not vertical in the sideways plane, and if so, if this might have an effect?
     
    Last edited: Jun 6, 2021
  3. Keith Redfield
    Joined: Jun 2021
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    Location: Aptos, CA

    Keith Redfield Junior Member

    Thanks bajansailor, appreciate the kind response. Answers inline with >>

    I haven't fully tuned the rig (it's time-consuming now because I have to tabernacle and don't have a good backstay adjuster yet), and I think I may try that on next tests and induce a bit more weather helm w prebend (I singlehand a lot, so more prob better)

    I was thinking about this rudder in relation to the other surfaces -- lots of turbulent source at the 'skinny' part (prop, keel cutaway, hull) up top, so the wider bottom is doing yeomens work..
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Pulls the same way with no sail up, under engine power ? To one side only ? It should be possible to nut this out if that is the case.
     
  5. Keith Redfield
    Joined: Jun 2021
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    Location: Aptos, CA

    Keith Redfield Junior Member

    No, this seems to be mainly an issue under sail. For example if I motor up to say five knots and then kill the motor where I'm drifting it actually tracks fine and stable.

    But under power, it is definitely a fight because the prop wash is wanting to pull the the rudder into the wash mostly in one direction I think it's the same effect as prop walk.

    I'm going to try a test maybe tomorrow getting towed by a powerboat. This should eliminate a lot of variables in re my rig and prop wash and things like that. If it's stable under those conditions then I'm going to blame the rig. (Which I spent a lot of time tuning today so hopefully I'll be able to verify its behavior right after the tow test)

    Another variable is I'm heavy, I've got 500 lb of battery on board cuz I'm electric. And I may be heavy forward both because of that and because of the way the keel was poured.
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    What happens when sailing downwind ?
     
  7. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    You may have a Lee helm disguised by a balanced rudder.

    If your boat trims bow down, as you suggest, the Center of Area of your sails may have moved forward.

    Raking the mast back a bit may be an inexpensive way of finding out if this is so.
     
    bajansailor likes this.
  8. Keith Redfield
    Joined: Jun 2021
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    Location: Aptos, CA

    Keith Redfield Junior Member

    I spent some time tuning the rig and putting in more bend, and also moved batteries around (had been on my todo list for other reasons) which brought the bow up a couple of inches and should be be able to test today. Static tow test will be tomorrow.
     
  9. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    It looks too me like your rudder is hung upside down. Refer to the elevation drawing on sailboatdata, the link to which you included in your opening post.
     
  10. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    In taking a second look at the drawing compared to your photo, they do not look like the same boat. The drawing indicates a skeg-hung rudder, where your photo shows no skeg keel.
     

  11. Keith Redfield
    Joined: Jun 2021
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    Location: Aptos, CA

    Keith Redfield Junior Member

    @Will - I had the same thought actually. And yes I may actually have a prototype hull. Backstory is it a wayfarer employee bought the boat with the intention of finishing it.

    I think sharpii2 wins -I had to haul out for unrelated reasons (Don't ask) and one of the local boat builders as soon as he saw the rudder said "that's not going to work very well" - before I'd even told him I had a problem. Excess rudder in front of the post. So now I get to carve a new rudder! Luckily this guy has a lot of experience building rudders

    I'll post an update after she goes in the water and I have a chance to test.
     
    Will Gilmore and bajansailor like this.
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