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Nacra tiller crossbar ends  Bottom

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  • upwindhacker, that is absolutely 100% correct, and I agree its not the best design. The plus side is once you have it locked in its solid, but the downside is you have to drill that hole dead nuts on the first time!

    What I did to one of my Infusion crossbars that I kept, figuring somebody else would like adjustable down the road and my standard one was setup correctly, is take one of the Nacra 5508's mentioned above and shown in this photo here

    https://www.thebeachcats.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=130868&g2_serialNumber=4

    and pin that to the crossbar then insert the urethane tiller on the other side. It took a bit of fidgeting to get the diameters sorted and its heavy but it does work well.

    The right thing to do is probably install one of the Hobie 20 threaded crossbar endcaps into the aluminum crossbar (would need to double check the size) then machine a fitting with the correct threads for that endcap on one side and a hole for the urethane piece with its plastic housing on the other (this is where the pin goes through to remove the setup from the boat). Optionally, and probably smarter, is to effectively bond or screw a threaded stud into one end of the tiller crossbar and machine that same fitting but with a threaded hole for the stud. I say that as I could machine that fitting in a few hours on a lathe and use a 316 stainless fastener in the end of the tiller, where as machining external threads is painful. See the Hobie 20 kit here: https://www.murrays.com/product/07-1953/

    The alternative is to run the complete Hobie 20 style setup, which is similar to the Exploder setup. You would have to cut down the Nacra tillers and install pins, which isn't a trivial job but do-able. The big issue I see is the length of the tillers, there is a sort of minimum there in terms of force required to turn the rudders. On some of the boats you could order Nacra 20 tillers but its gets tricky as the ackerman angle is built into the tiller bars on a modern Nacra.

    And I have no clue how much that matters but I will say that if you can lower drag in a turn on a race boat it absolutely does matter. Keep in mind on an F18 in breeze tacking upwind you are looking at boat speeds from the top teams in the 12.5-13.5 kt range for an upwind VMG of 9.5 kts assuming a tacking angle of 90 degrees (we run tighter than that but only in flat water). In a tack you are probably down to half that in terms of VMG, and a very good tack is still a 20 second operation before you are coming back up to speed; we can take a minute to accelerate back to max speed. Lets call it 45 seconds at an average vmg of 4.5 kts during the tack. That translates into 360 feet or 20 boat lengths lost in what I would call an average tack. A top team can probably get it down to 5 or 6 boat lengths, but if you have additional drag from the rudder system that could impact that further with less ability to turn the boat easily. Add in some waves and any additional drag from +20 deg to -20deg head to wind could have you stopped dead which would spell disaster.

    This math also shows why tacking on high performance boats must be done smoothly and quickly, and why it should also be avoided whenever possible! The problem gets worse at higher speeds, if you watched Glenn Ashby at the last A-Cat Worlds fully airborne upwind he would go right for the layline and one tack it to the market at a boat speed in excess of 21 kts.

    All of this probably doesn't mean much to the OP's original issue or long term plans, or most folks sailing recreation ally though having a proper rudder system setup tends to be more enjoyable with less force on the tiller during long outings!
  • Thank you samc99us. That is what I was afraid of - no adjustment. I am going to have to make something up. I like being able to make adjustments if I don't get it right the first time (which is usual). I can't believe that the NACRA 17s use the same system. If anyone needs fine adjustments, they do.

    The Hobie 20 system looks good. I think I can make something like that.
  • upwindhackerThank you samc99us. That is what I was afraid of - no adjustment. I am going to have to make something up. I like being able to make adjustments if I don't get it right the first time (which is usual). I can't believe that the NACRA 17s use the same system. If anyone needs fine adjustments, they do.

    The Hobie 20 system looks good. I think I can make something like that.


    When you are dealing with boats off the showroom floor they can be pretty confident in the fit/alignment of parts. The rudder alignment isn’t really something anyone adjusts once it’s set so if it’s built correct then it’s one less thing to check. Also I’ve had my alignment screw come loose in a race so had to tighten it back down while underway. So them making it non adjustable also means it can’t mess up your day at the same time.

    But on our old beaters with half the rudder system replaced and bent up it’s nice to be able to fine tune things.

    --
    '82 NACRA 18 Square "Bangarang"
    '85 Hobie 18 "Honey Badger Don't Care"
    '86 Hobie 18 "The Rippin & The Tearin"
    Jacksonville, FL
    --
  • Haha you must be joking right? The build quality has come up on newer boats sure (Hobie is pretty high, Nacra is good as are others) but there is still enough mis-alignment in the beam bolts between boats and slop in the system that if you take your boat apart and store it or ship it then re-assemble it there is no guarantee you will be back to zero, and you could have 1mm of toe-in/toe-out which is impossible to fix with a standard tiller crossbar from Nacra.

    The other note is the N17's (c-board boats) played with toe-in/out on the rudders plus boards to get to an optimal foiling configuration. It is also an important thing to dial in for proper helm balance, and it would be nice to tune it on the water to get a clean exit angle off your rudders.
  • tamumpower1Sounds like you are thinking of toe in.


    Toe in as a general steering setup has nothing to do with the Ackermann theory/concept. However, Ackermann does add/subtract differential toe in when the steering is at any position other than centered (steering straight ahead).

    tamumpower1Ackerman steering does not add toe in or any extra drag to the rudder system when it's going straight....


    (SP, Ackernmann NOT Ackerman) True, but it does add/subtract differential toe in at any other position and as previously stated it is only at the theoretically correct amount of differential for one predetermined turning radius, all other positions are off.

    tamumpower1Beyond that and any other technical discussion, lets just go look at the top level A class boat, the DNA F1, and we notice that it has ackerman bend in their rudder arms... so I'll trust the class still throwing seeming unlimited money every year at trying to gain 0.0001% on the competition.


    I personally couldn't care less about what other folks do. No one has ever gained an advantage at anything being a me too. Further, before I buy in to any theory (and that's all it really is relative to boats) show me the tank testing with strain gauges etc. where it has been proven. My experience is that perhaps 90% of everything you will ever be told about how to make a boat "fast" is nothing more than theory and opinion based on nothing more than what an individual "thinks is right" urban mythesk.

    tamumpower1This is all in reference to the most important "radius" and that's the one the boat takes when tacking.


    Why is the turning radius at tacking the most important? Steering to climb the wind and change gears etc. is equally important to the turning radius during tacking and generally a much more gentle turn, larger radius. Further, my turning rate/radius in a tack varies substantially depending on wind speed, waves, weight, trapping and the part of the tack I'm in beginning/end.

    tamumpower1Since the boat mostly rotates around one hull due to the boat slowing down, there is a formula for each beam width to add in the ackerman angle so that when it matters most you have minimal rudder drag.


    The boat does indeed not "rotate." With two hulls in the water it's being shoved sideways through a very non-circular arc, think French curve.

    tamumpower1 I think you'll find that speeding up a tack and minimizing the time you are head to wind will gain you far more than the half a second you spent at speed making a minor steering correction with different turning radius' present.


    Not exactly sure what the last half of this comment is about? I roll tack my boat when possible with all weight in the old side rear corner until through the eye.

    --
    Hobie 16 (3 formerly)
    MacGregor 25 (formerly)
    Chrysler Dagger 14 (formerly)
    NACRA 5.0 (currently)
    High Point, NC
    --
  • Then run parallel rudder arms and don’t complain about it...? You remind me of a guy I heard going off about how “that stuff about lift is all bull, the sail just redirects the wind”

    I suggest removing all copy cat items on your boat since they must not work. Bendy mast, high aspect sail, actually the sail all together, dagger boards, smooth hulls in general. Actually all that stuff about saving weight must be bs too since everyone does it.

    Just because you don’t understand the theory behind something doesn’t mean you should go fake news on it.

    I think you are in the camp of “if my boat still sails without it then clearly it’s not needed”. Reality is small changes add up. I have no doubt it’s not a massive change to the rudder drag so if it makes you feel smart to buck the trend then be my guest. But my guess is if that’s your mind set then you’ll probably be admiring everyone else’s copy cat improvements quite well from behind them as they pull away

    --
    '82 NACRA 18 Square "Bangarang"
    '85 Hobie 18 "Honey Badger Don't Care"
    '86 Hobie 18 "The Rippin & The Tearin"
    Jacksonville, FL
    --
  • If Hobie can make adjustable till crossbar fittings, why can't NACRA? The fact that if I don't get it right the first time on a NACRA (that screw in the urethane tendon), I am stuck buying new tendons. I should be able to fine tune my rudders in and out. NACRA designs are good, but this part of the system on new NACRAs is poorly designed.
  • upwind, no argument from me that it isn't the best (or lowest cost) system; they would be better to make the tiller arms straight or with only one bend for the ackerman (cheaper than multiple bent tubes) and going to a Hobie or Goodall style setup. Of course the Goodall and Scorpion setup can bind, I don't think Hobie has that problem.

    Anyway, if you mess up on a Nacra urethane install you can flip it 180 degrees and try again. Its a two person plus lots of e-tape job for sure.
  • I have this on one of my tillers
    i like it (mine is black which is much faster)

    https://i.ebayimg.com/images/g/dmoAAMXQHO9Re4zX/s-l640.jpg
    https://www.ebay.com/i/151045562707?chn=ps
  • MN3I have this on one of my tillers
    i like it (mine is black which is much faster)

    https://i.ebayimg.com/images/g/dmoAAMXQHO9Re4zX/s-l640.jpg
    https://www.ebay.com/i/151045562707?chn=ps


    I think that would work quite well. Off to the machine shop.
  • That is a prindle end

    --
    Captain Chris Holley
    Fulshear, TX
    '87 Prindle 19 "Cat in the Hat"
    '74 sunfish "1fish"
    --
  • I find it a touch ironic that Nacra developed solutions for both the Prindle and older Nacra 5.2/5.5/5.8 line back in the day but neglected to implement one on their new boats. I guess the reality there is they have probably sold 1000+ new gen Nacra's since 1997 when the i20 arrived and I'm guessing they haven't had enough customer complaints to warrant a factory solution.
  • MN3I have this on one of my tillers
    i like it (mine is black which is much faster)

    https://i.ebayimg.com/images/g/dmoAAMXQHO9Re4zX/s-l640.jpg
    https://www.ebay.com/i/151045562707?chn=ps


    Well you may have the preferred black one, but just shut it down buddy. I've got the Ackermann version which is the ultimate "go fast" part to have.

    https://www.thebeachcats.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=130883&g2_serialNumber=4

    How do I know it's fast, well because I said so, nuff said.

    I'm selling these for $10,000 each and don't delay as demand will instantly outrun supply. PM me to place your order. I lamented for years as to whether or not to share this with everyone, but here it is alas...

    --
    Hobie 16 (3 formerly)
    MacGregor 25 (formerly)
    Chrysler Dagger 14 (formerly)
    NACRA 5.0 (currently)
    High Point, NC
    --
  • The previous owner of my boat replaced one of the bent tiller arms with a straight one, i sailed like that for years until i broke the other one, which i replaced with a straight one, as well as replacing the cross bar with a longer one. I was too lazy to find a workshop to bend the tubes. My impression is that it is harder to turn the boat now, particularly at the first half of the turn, at higher speed. I’m tempted to fiix it but i’m still too lazy. Perhaps i could add 90 deg. elbows each side with a short length of tube, instead of bending the tubes, but i doubt the end result will be elegant enough.



    Edited by Andinista on Mar 03, 2019 - 04:33 PM.
  • QuoteWell you may have the preferred black one, but just shut it down buddy. I've got the Ackermann version which is the ultimate "go fast" part to have.


    SWEEET!

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