Mast Rake

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  • #6021
    heymacaulay
    Keymaster

    Hi Sabre Techs! I thought I saw a measurement in one of the forums for the distance from masthead to transom. Can’t find it now. Does anyone know?

    Cheers, Don.

    #7146
    liamedleston
    Keymaster

    To some extent the position of the mast step will affect rake.
    My mast step is 20mm forward of the most aft position allowed by the rules. I use a Loos guage on the shrouds to repeat settings. Wayne Bates moved his mast step back to the same position and has similar mast rake.

    Every 5 units of measure on the Loos guage translates to 10mm of rake.
    The following measures are top black band to the top of the transom (outside).

    Loos Measure Rake mm
    0 5750
    5 5760
    10 5770
    15 5780
    20 5795

    hope this helps

    Barry Eastgate

    #7147
    Meryl Todd
    Participant

    Barry, I fully agree the mast step positions impact on rake. I moved mine maximum aft to reduce rake simply to give me more headroom on tacking; however could please you expand on what is happening as you tighten your rig?

    As I tighten my shrouds the mast bends allowing the mast tip to go aft shortening the black band:transom distance. I have the shroud and forestay attachments maximum tolerance apart to promote bend as most of my sailing is light wind, thus easing the leech. The result is my rake: Loos gauge distances appear to move opposite to your results.

    As for optimal rake, I suggest adjusting the shrouds until the boat is balanced with about 2 degrees of helm going to windward. My new Irwin requires one-two shroud holes longer than the old sail to get the same balance due to sail shape differences.

    #7148
    heymacaulay
    Keymaster

    Hi guys,

    For us numpties, who just wing it most of the time.

    Can someone please explain Loos guage?

    Regards . . .

    #7149
    syreetanajera
    Participant

    It’s for measuring tension in a wire. see e.g. :
    http://www.landfallnavigation.com/hlpt2.html

    A cheaper version is also available from Superspars:

    http://www.sailboats.co.uk/product~Superspar_Tension_Gauge_254mm_wire_SU-RTGS.html

    or the harken alternative…….(better be sitting before you look at the price of this one!!_

    http://www.purplemarine.com/Product.aspx?ProductCode=H7850

    All work by bending the wire & converting the force used to bend the wire a known amount into the load being carried by the wire.

    #7150
    Paul Matthews
    Participant

    OMG

    I knew they meaured this stuff south of the border … BUT

    … i am an insensitive bitch .. no feel for balance in the boat
    … where do I start?
    … no Loos guage up here!

    What’s a good starting point .. I’m running a training session in a few
    weeks!

    If u have a secret to success email me at [email protected]
    [Those who help will be rewarded at Safety Beach]

    Slowest Hand

    #7151
    heymacaulay
    Keymaster

    Damn,

    I’ve seen people use them, never new they were named after a toilet.

    I always just use Mk1 finger tension gauge when I rig Fiona’s boat and just ask SHMBO (She who must be obeyed) if she is happy.

    Regards . . .

    #7152
    Meryl Todd
    Participant

    The advantage of a rig tension measurement tool is that it helps you repeat the tension that won you the last race, or sneak up to the winning boat and find out her secret.

    Regardless of the make, they are all basically a spring which measures the pressure needed to pull the wire out of line. The more rig tension in the wire, the stronger the pressure to obtain the standard distortion. The stronger the wire the more pressure required, this is why the calibration figure differs for the diameter of wire. For example on a Loos model A pulling out to the 32 mark indicates 181 kg in a 2.5 wire, 136 kg in 3.0mm but only 91 kg in 4.0 m wire. That is 1x 19 wire, the equivalent tension in 1×7 dyform wire would be different as it’s a stiffer wire.

    In many more complex rigs the sailmaker will give you a crib sheet of major numbers for tensions, rakes and spreader angles. For example I have a 10 page Int. Dragon tuning guide from a sail maker. It certainly helps when they are some 10,000 possible combinations.

    The Sabre is extremely simple, and any guitar player can tune one with a MK1 RTG but they may not always be singing your song.

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