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Thread: Rig & Sail Fine Tuning

  1. #1
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    Question Rig & Sail Fine Tuning

    After learning construction skills building two IACC 120’s under the expert guidance of ClaudioD, I have been happily sailing my creations alone for roughly 6 months now. I was happy with myself that I had a good set-up and confident in participating in my first competitive RC regatta.

    Over the two day competition, good ole mother nature threw everything at the fleet from high winds from 20+ knots and white caps to go, down to virtually glassy mirror conditions and everything in between.

    It was exciting changing mast rack, twist, sail draft, tightening & loosening up, down and out hauls, topping lifts, shrouds changing from flat to round sails to have the right rig settings and boat balance for the given conditions....that’s what sailing is all about.

    Then I put my boat in the water and sail next to other boats to see how I compare on speed and pointing ability and compare the look of other rigs and sail shapes to decide to tweak it or not which I was doing often...hmm my boats pointing was lower and speed not as fast as other boats....I could not figure out why ?!

    Ignorance is Bliss when you have confidence in your own knowledge which is inversely proportional to how much you know about a topic… I talk about myself here, after this regatta I quickly came to the conclusion, what I know about fine tuning, you can write on the back of a postage stamp, hence the reason for starting this thread, I would like to learn more and hope that newcomers (like me) to the sport will also find hints here when setting up their boats.

    Most are 'au fait' with the skills for “rough set-up” in finding helm balance by changing Center of Effort (C.E) mast position and boom angles etc. (good reference is Lester Gilberts IOM rough set-up http://onemetre.net/Race/Roughset/Roughset.htm)

    What I wish to learn more about is “Rig & Sail Fine Tuning”.

    The first topic I like to ask about is “mast bend” I am in the middle of constructing my next hull and changing the mast box structure as per attached drawing.

    When looking at other boats at this regatta they could set a flatter main than I could, the major difference between my boat and others was I had “deck mast step” while everyone else had “keel mast step” and were using a “mast ram”.

    Asking for opinions here about the pro’s & cons of changing before I go any further ?

    Cheers Alan
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    You can only create, what you can imagine

  2. #2
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    Default Re: Rig & Sail Fine Tuning

    Hi Alan, yes as you found out the hard way, fine tuning is the difference between being at the front or somewhere back in the bunch.
    It is an acquired skill which can be learnt by anyone although some will always be better at it, just like life really.

    In a yacht the size of an IACC 120 a keel stepped mast with a ram is a huge advantage.
    The ram controls the lower half of the mast fore & aft curve, which in turn controls the draft position and depth of the lower portion of the main.
    There is an alternative if you wish to retain the deck step and that is to fit a deck mounted ram.
    Either way, some method of controlling that section of mast is essential.

    The next question comes with the control of the top section of the mast.
    Should one use jumpers for this or are they simply adding windage and weight where it is not needed.
    I personally am a jumpers believer. They allow you the luxury of making the choice with the draft position and depth again.

    Next we come to mast material and the shroud set-up.
    I have just been away to check that any material may be used for the mast construction.
    That pretty well tells me that carbon fibre is the only way to go if you are serious about having the fastest 120 on the planet.
    How big a diameter, wall-thickness, section, taper, straight, groovy, round, aerofoil, luff wire, tie-on, etc, etc, these are some of the options a builder has to choose before the question of rigging is considered.

    Perhaps I should stop here and allow you to answer some of the questions I have posed here and to ask some more from the many thoughts that you must have.
    Others will also have much good advise on this most excellent forum.
    Best wishes from middle earth.
    Ian.
    Do it NOW before it`s too late.
    Add Lightness !
    MICRO MAGIC NZL 01 "TAHI"
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  3. #3
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    Default Re: Rig & Sail Fine Tuning

    Here is a link that you may find helpful, where the EC12 class have published a complete manual on the building and rigging of their class.
    Whilst the IACC 120 may be more advanced in their use of materials, the tried and true methods of controlling sail shape for larger area sails should not be discounted.
    You do not have to reinvent the wheel just because you want to move up to "mags"

    http://www.ec12.info/Rigs.htm
    Do it NOW before it`s too late.
    Add Lightness !
    MICRO MAGIC NZL 01 "TAHI"
    IOM V5 NZL99
    Canterbury J NZL 196
    RG65 in the build
    Four foot six vintage, launching soon
    10 R Phoenix NZL 20



  4. #4
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    Default Re: Rig & Sail Fine Tuning

    Hi Ian, One advantage at being on the tail end of fleet is that it can only get better from there ...and your right, it is all in the fine tuning.

    Currently I have upper and lower shrouds with one straight spreader just below hound position @ 60% mast height (no jumper strut at top section of the mast) I thought at the time I can use the shrouds and fore & back stay tension to control mast shape. Top shroud base is abreast the mast and lower shroud aft of the mast, but feel this is not right.

    Without a mast ram I now think the lower shroud should be more at 40-45% of mast height to better help mast shape control.

    On my largest sail plan (78dm2) I have mast height from the deck of 1.7 meters, and mast shape is clearly critical on such a high mast, hence my search for mast shape control was first on my list, next size down sail plan is 74 dm2 with 1.6 meter mast height, these are my first sails and I know can change sail plan to have shorter mast height, and albeit a shorter mast would help mast shape control I’m more interested is what the effect of a lower sail plan C.E would be like for better heeling stability.

    The wind maybe free, but sails aren’t so I’ll come back to this later on when I have better understanding on what I have to work with for now.

    Reality check on mast bend: The backstay is tensioned so that the mast bend matches the mainsail luff curve. Fore and aft mast bend changes the shape of the mainsail in two ways. 1) the mast either pushes fullness into the body of the mainsail when it straightens, or pulls fullness out of the mainsail when it bends more 2) the head of the mainsail either twists off as the mast bends more, or twists off less as the mast is straightened.

    The mast ram is then necessary on a high mast for controlling lower section of the main, I’ve come across no negatives so far? I’m more convinced now why a mast ram is the way to go ! btw could not find anything on deck mounted ram you touched on, if anyone has any details, would be really appreciate to look at this arrangement.

    I sometimes think rigs on 120’s are designed to represent the real boats rigs rather than more suitable for best performance as a model. In particular the headboard does not hold the sail well and the main twists reducing power significantly maybe this brings us to your next point about of top mast control, using jumper struts.

    As said earlier, I have no jumpers, and only because no-one else has (sheep syndrome ... I know) are you saying the problem with a fractional rig where the forestay pull at the hounds creates a curve in the top of the mast with the pull from the backstay via head crane ?

    Further, often thought that a long head cranes create too much leverage (read mid mast bend) anyway, I remember looking closely at what I think are the two best sailing/rig tuning in Italy (Luca RSA 09 last years Cup winner & Gabriel USA 71 this years Cup winner) on what was different on their boats compared to others ... they both had jumpers, whereas others did not...never quite registered then, but now it is beginning to make some sense.

    Gabriel had traditional jumper strut each side of the mast using turnbuckles for tension adjustment, it looked mast top heavy and Luca has single jumper strut which is mounted on “front of the mast” (facing forward) with one threaded adjustment screw through the strut for adjustment, looked smart and much lighter with minimum windage....thinking about it, both were always top 3 fleet racing finishers, so that discounts the argument about jumper weight and windage for me ...it’s baloney and I’m now becoming a believer too.

    On jumper adjustment I’m I right in thinking:

    1) Jumpers too tight - mainsail too full in heavy air and can't be depowered with luff and foot tension ?

    2) Jumpers too loose - mainsail overly flat most of the time and you may get an "overbend wrinkle" mainsail crease that usually runs from the clew, diagonally up and toward the luff near the middle of the mast, especially when sailing up-wind and sheeted-in tight ?

    Btw: don’t know if you noted in the drawing posted, but I’m also changing to a telescopic Fairlead post, to keep fairlead sheeting point as close as possible to the main boom. I found when the gap was too large (mast forward tilt in heavy wind) I could not sail tight-hauled due to the widening gap between post and boom.

    Next you mentioned mast material oh la la ... until now I have only been using aluminium groovy mast (foil shape) and I was thinking this was the reason for no stability to help control mast shape, I think I was wrong, without a mast ram, would have the same problem no matter what mast material we're using, albeit the stiffer carbon mast would better than aluminium (without a mast ram)

    I have purchased a carbon groovy (airfoil shape) when I was in Italy and also a round carbon mast to try all possibilities, just out of interest.

    Ian we covered a lot here, thank you and really interested in what good advise other members have to say on this interesting topic also

    Next question, what is the best position to have your shroud base (chain plate) in front, beside or behind the mast and their relation to spreaders? (Straight or V shaped) particularly for supporting fore stay tension.?

    Cheers Alan

    P.S thanks for extra reading from ec12 site and middle earth is a good place to be ...weather forecast here saying first snow on mountains here this weekend
    You can only create, what you can imagine

  5. #5
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    Default Re: Rig & Sail Fine Tuning

    "if" the mast rotated, (like on a cat) it is an auto-function of mast bend to side, that when rotated will pull sail flatter. Keep in mind, we multihull guys use a forestay, side shrouds and if a tall mast, a single diamond wire. There is NO NEED for a backstay, jumpers, etc. - even when using an asymetrical spinnaker.
    Let the mast rotate, bend out of column depending on wind strength and diamond wire tightness, and instant (relatively) a flatter sail. Want a fuller sail? - reduce mast rotation.

    Ahhhh - this would be some of the "trickle-down" technology on loan to monohull sailors from us multihull guys.

    Didn't mean to hijack the thread - just introducing an option that we use to eliminate a lot of standing rigging. Is a rotating mast legal in your class?

    Cheers, Dick

    BTW - a rumor - some of us may show up with an IACC shape hull in the RG-65 Class next spring.

  6. #6
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    Default Re: Rig & Sail Fine Tuning

    Hi Alan,

    Here are some examples of a deck mount mast ram.
    https://www.radioyachtsuppliesaustra...ngs/Mast-rams/

    The ram does one additional service than shaping the lower portion of the main. It also resists the forward thrust of the goose neck. Try this. With your boat rigged and set to close hauled, lift the end of the main boom (to simulate a gust hitting the main). Watch the mast bend forward at the goose neck, and see that the upper main leach opens up.

    IOMs (similar fractional rig) try to get the mast ram as close to 'in line' with the goose neck as possible. Now, the boom cannot force the mast forward, and so the boom cannot lift, so the leach remains in control.

    This is one main reason that modern IOMs use a raised foredeck and a 'skiff' after deck. This allows the goose neck/vang to be lowered, and the ram to be raised.

    If you have a skiff style aft deck that extends to the mast, you could lower the goose neck/vang a bit and install a foredeck level mast ram, and get a bit closer than in your diagram.

    You would also get a stiffer mast if you went with the half inch high tensile round alloy mast than the same sized groovey. CF tubing has various degrees of stiffness, stiffer the better.

    Yes, get the adjustable sheeting post (that's what they are called) and set is as high as possible yet still to clear the boom. Raise and lower it as necessary with changing mast bend/vang tension. The sheeting post allows you to bring the main in closer to centre line without generating a downward pull (that closes the upper leach).

    It is also important to control mid and upper mast bend. Most IOMs use forward pre-bend, and then tighten the back stay to bring the mast straight. Even though you have hounds higher than an IOM, this should still work. A jumper strut will also help the top portion. Also don't be afraid to bend the spreaders to pull (or push) the mid section of the mast.

    With upper and lower shrouds, the normal set up would be to set the lower chain plate aft of the uppers. That way the lowers can limit and tendency to forward bend in mid mast. So the uppers would be in line or just aft of the mast step (20 to 30 mm), and the lowers a bit further aft again. Don't go too far aft as that will restrict the boom from going full out down wind.

    John
    Last edited by hiljoball; 10-14-2010 at 10:46 PM.
    John Ball
    CRYA #895
    IOM CAN 307 V8

  7. #7
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    Default Re: Rig & Sail Fine Tuning

    Hi Dick ...Yes rotating mast is within the rules, can you fit a mast ram to it ? The idea of eliminating the backstay sounds appealing, can you post illustration or photo of how it looks?

    Trickle down from multi’s uh...about time something comes back our way

    Hey like to see IACC shape RG 65 hull, when the rumours surface into reality....cool

    John thanks for the link with examples of deck mast ram. Your point on a ram also resisting the forward thrust of the goose neck rang a bell with me, I have had goose necks jam on me a couple times & once the bottom joint on one on my 120's was forced off its rotating ball joint & could not figure out why!? also remembered one of the Italian boats goose neck blew off in last years regatta and the skipper tied it back with plastic tie down (photo attached) and you can see albeit he has mast through the deck, no mast ram. ...very very interesting explanation on latest IOM developments in this area.

    Adjustable sheeting post on order ... thanks John great stuff !!!

    Cheers Alan
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    Last edited by K1W120; 10-14-2010 at 02:17 PM.
    You can only create, what you can imagine

  8. #8
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    Default Re: Rig & Sail Fine Tuning

    Will see if I can find/get some photos of a beach cat (5.5 meter or thereabouts as it is easier to see. In the meantime, I will try a sketch to perhaps explain the concept. We still use outhaul, inhaul and downhaul controls plus sheet tension at boom end (not middle) and a wide traveller for offwind broad reaching.

    I have a break coming up soon here at work, so maybe can get it posted before tonite.

    Dick

  9. #9
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    Default Re: Rig & Sail Fine Tuning

    Click image for larger version

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    Here is an example of a deck stepped mast ram as we use them on EC12`s in NZL.
    We call this a "Stubby" and it remains on the boat when you change rigs.
    If you would like to call me on Skype (captainbit) cos I can talk far better than I can type.
    So much to say it just takes me so long to type. Cheers.
    Do it NOW before it`s too late.
    Add Lightness !
    MICRO MAGIC NZL 01 "TAHI"
    IOM V5 NZL99
    Canterbury J NZL 196
    RG65 in the build
    Four foot six vintage, launching soon
    10 R Phoenix NZL 20



  10. #10
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    Default Re: Rig & Sail Fine Tuning

    "DO NOT" I repeat, Do Not, consider eliminating the backstay.
    IMHO it is a necessity on a rig such as yours.
    There is no way you will keep a tight forestay without a backstay.
    Loose forestay = can not point.
    No backstay = cannot set mast curve for varying wind strengths.
    Do it NOW before it`s too late.
    Add Lightness !
    MICRO MAGIC NZL 01 "TAHI"
    IOM V5 NZL99
    Canterbury J NZL 196
    RG65 in the build
    Four foot six vintage, launching soon
    10 R Phoenix NZL 20



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