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Rudder toe angle

Discussion in 'Post Yacht' started by Greg Page, Jun 24, 2022.

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  1. Greg Page

    Greg Page Active Member

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    Do your Post's rudders have toe-in? The ones on our 43 were rigged with zero toe-in angle. While I was replacing the sterring cylinder rod ends (old ones were very shot) I decided to try adding some toe-in toe see the effect. I put in 4 degrees toe-in (leading edges of rudders closer together to avoid ambiguity). It is less than half of the recommended 10 degrees I saw in some references. Going to 10 degrees would have resulted in less rod end thread engagement than I am confortable with so I started with a smaller change.

    It made a quite noticable effect in the boat feeling that it is running bow higher, and also higher out of the water overall. So far I've only run in in calm conditions. Ancious to see if it feels better or worse in cross and stern seas.

    -Greg
  2. mapism

    mapism Senior Member

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    Can't answer your specific question, but generally speaking 4 degrees is already a lot - let alone 10 deg!
    Did you experience any vibrations or "hunting" effect when on autopilot, with parallel rudders?
    These are the possible reasons for some toe-in, afaik.
    Never heard of other effects on boat's attitude, and neither of any rationale behind that.
    Was the difference you are reporting so noticeable?
  3. Capt Ralph

    Capt Ralph Senior Member

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    I assume during your adjustments you were out of the water and cleaned the bottom well.
    Could be the clean bottom be helping your bow angle?
    A propeller re-work? Trim tab adjustment? Cleaned some stuff from the bilges?

    Toe in / Toe out (pending how you look at it), helps keep the rudders from chattering, Maybe, maybe, maybe change the feel on a helms wheel..
    Not change the bow angle, IMO..

    One last thought; 10° on the rudders could have induced extra drag. Backing off of this may have helped pick up a fraction of speed.
  4. mapism

    mapism Senior Member

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    100% Agreed.
    But as I understood, the OP did not back off from 10 to 4, but went from zero to 4.
    He just mentioned that 10 is allegedly the builder's recommendation.
    Though that's unheard of, in my books.
  5. Capt Ralph

    Capt Ralph Senior Member

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    Yes, I miss read.
    0 to 4 is not going to change bow angle.
  6. Greg Page

    Greg Page Active Member

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    The rational for toe in is that it actually aligns the rudders to the flow coming off the bottom due to the V in the hull. Change was made between run home from winter storage (and a couple intervening weekend trips) and run back to the same marina for new head install last week (back home today) with no changes to the bottom in between. Adjustments all in the water, from the winter rudder R&R I had already verified the rudder keys and thus arms are dead align to the rudder blade so can measure with angle gauge inside the hull. No significant cruise speed change, both runs before and after within the same variation I see day to day, fraction of a knot on GPS.

    I don't remember what the toe on the outboards on my racing hull CC was but it was a very deep 26 degree V and was enough to be visually noticable. 4 degrees is about 3/4" over the long top chord of the rudders, 3/8" on each.

    I wanted to get the hull more bow up, an attribute I read the toe in/out affects, to see if it makes a difference in the steer and roll crossing waves at shallow angles. Conditions so far were very flat so not easy to say if there was any difference crossing the small waves and wakes on the two after trips. Tabs are full up in both cases, and most of the time I'm running. Bow down previoulsy made the turn-off effect more significant on shallow angle crossings thus the hope more bow up than full up tab provided would be better.

    The effect is more noticible than I expected, it feels much the same as when the boat was going from normal cruise to top speed previously, overall lighter on the water (same speed effect of my much facter CC and offshore sport boats). I haven't made a full throttle run to see if it feels to light then.
  7. Greg Page

    Greg Page Active Member

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    Note 4 degrees toe in is 2 degrees on each rudder.
  8. mapism

    mapism Senior Member

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    Never heard this theory, but it's patently wrong anyway.
    The water flow under any planing hull, aside obviously from going backward, also goes slightly outward, not inward.
    So, if any rudder toe should be driven by that logic (not that I'm agreeing it is, mind), it should be toe out, not in.

    That aside, with outboards and outdrives there is a different rationale for (usually, but not always) some toe in, and it's that the props tend to push the legs outwards, so some toe in can contrast that.

    Lastly, I always followed the convention of calling whatever degree of toe in/out you've got as the angle of each rudder. In other words, when you said 4 degrees, I assumed 8 degrees in total between the two rudders.
    That's just semantic of course, but in light of this, the 10 degrees which you mentioned (i.e. 5 on each rudder), while still pretty high, isn't as crazy as it sounded.

    PS: Doh! Sorry, I just re-read your OP and noticed that by "toe in" you meant the opposite of what I have in mind.
    Again, just a matter of semantic, but you can forget my above objection to the water flow theory, of course.
    Though I still think it isn't the reason for toe in/out anyway, neither with shafts nor outboards/outdrives.
    Last edited: Jun 24, 2022
  9. Greg Page

    Greg Page Active Member

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    Water flowing out "is" toe (leading edge) in. I realize some people have said "toe" is the trailing edge of the rudder (which is why I said toe in is leading edge in on the first post) but that is opposite of all other uses of the term toe angle. I have never heard of toe measurement being a single surface on boats or any other vehicle, but again that may be some persons usage.
  10. mapism

    mapism Senior Member

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    Yup, that's the bit I missed at first, while writing my previous post. Sorry about that.
    But no worries, all clear now, including the angle you're referring to.
    According to that, what I wrote about the setting in outboards and outdrives for contrasting the outwards force of the props should be read as toe out, not toe in.

    I'd just be curious to hear from Capt Ralph, who said that o to 4 degrees ain't going to change the bow attitude, if he understood 4 degrees on each rudder, or 2. I would have agreed with him even if he meant the former, but even more so with the latter, of course!
  11. Capt Ralph

    Capt Ralph Senior Member

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    Facing forward, front of rudders in, back (after) edge out, as on cars, I call this Toe IN.
    There are other geometry figures on rudders but I do not believe your fine ole Post has the high tech rudders as on race boats.

    I have witnessed some wild tricks attempted on rudders. Including adding hotz tabs angled to help lift the stern.
    That owner said it worked. I'm happy for him.

    I've even added trailing and depth surfaces on my own rudders to help slow speed operation. I think it helps.

    I am also not going to argue with anybody if rudder toe in / out can raise a bow.

    I can only understand the potential of the stern going down if there is really any change at all.
    This is based on ole swamp logic, no formal training and nothing scientific at all.
    Just been walking boat yards most of my life. Even during that other bill paying career.

    Greg, if you are happy with your information and happy with your ships operation, then that is great and bless you.
  12. Greg Page

    Greg Page Active Member

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    Alas no Post owners with how their boat is set up. Not really surprising since most wouldn't know, I didn't know how ours was until I had to disassemble the steering. I do think some leading edge in would be normal for most boats.
  13. chesapeake46

    chesapeake46 Senior Member

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    If this thread was posted 2 weeks ago I could answer you about mine but during that short haul it did not occur to me to even look.
    I was just so happy the yard took time to clean my gear and bottom.
  14. Greg Page

    Greg Page Active Member

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    I actually thought about posting a couple weeks ago after the one run from my dock to the marina but wanted to wait till I had more time with the change and different water cases from the run back home on Friday.

    I have 45 years doing computational fluid dynamics for aircraft, but boat flow with the free water surface is not able to accuratly modeled in my codes and coupling in the propeller swirl wake effects is more work than I wanted to tackle.
  15. bayoubud

    bayoubud Senior Member

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    Makes more sense for leading edge in than out. Seems the toe in aft would create some pressure and drag.
  16. leeky

    leeky Senior Member

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    The toe is at the front, unless you have very unique feet. :D
    bayoubud and Capt Fred like this.