sharpen your blades!?!

Discussion in 'Laser Talk' started by WestCoast, Apr 4, 2006.

  1. TimClark

    TimClark New Member

    Likes Received:
    0
    Trophy Points:
    0
    No I don't mean holding the line, I mean that it could hold the cleat.

    Tim
     
  2. TimClark

    TimClark New Member

    Likes Received:
    0
    Trophy Points:
    0
    Woops sorry, I meant holding the cunningham block.
     
  3. rock steady

    rock steady New Member

    Likes Received:
    0
    Trophy Points:
    0
    Ha ha, that would some strong tape to hold a cleat in place. Anyway, I'm going to try this set up over the weekend. I'm really hoping it will "ease off" better than it currently does.
     
  4. tomsinamerica

    tomsinamerica New Member

    Likes Received:
    0
    Trophy Points:
    0
    Is this thread about the finishing of foils or heading up? :-S

    I once tried to get my foils knife edge and managed to get them like that for a while but they blunted really easily and the daggerboard chipped a few times... yes repairing it was a b**ch....

    I looked into it in some hydrodynamics books i had from university and the important thing is to ensure that the flow leaves the foils cleanly. The thing to avoid is a rounded trailing edge as that causes the flow to be turbulent just after leaving the foil so you either need a knife edge or.... a sharp squared off edge about 1-2mm wide.

    So.. now, on the rudder, i have a sharp edge which i look after meticulously so that it doesn't get damaged and on the daggerboard I use a file to ensure that the trailing edge is square and true and about 1.5mm wide. This eliminates cavitation behind the foil so there is no "humming" while hacking offwind in a breeze.

    The other thing I would add is that I never ever sand along the length of the foil, especially on the rudder as this makes cavitation worse. Instead I use 220 grit paper and sand in the direction of water flow which helps the water flow across the foil rather than down the leading edge... obviously only sand in the areas the class rules allow. it's more work to sand with the flow rather than down the length but I stongly beleive that it makes a big difference? I guess it's personal preference though and we all have secrets... so long as at the start you beleive that you are in the fastest boat on the water then you're halfway there....
     
  5. rock steady

    rock steady New Member

    Likes Received:
    0
    Trophy Points:
    0
    I tried this set up by tieing off the block with a bowline, then wrapping it around the mast and under the vang, then back through the bowline. Taping the whole kit to stabilise it.

    The effect was that the system releases much more effectively when rounding the windward mark.
     
  6. glasky

    glasky Member

    Likes Received:
    0
    Trophy Points:
    16
    Aside from whether this set-up releases better at the windward mark I have noticed some differences in sail set-up by varying the downhaul angle. have not tried taking this forward, as shown in the pics on PR's set-up, but an old vang system I had I used to run the downhaul from the forward most bottom cleat block pin that engaged a max length swivel attached to the mast tang. The effect of this was to move the line of attachement of downhaul aft about 10mm (while ever the vang tension was such that it resisted lifting the block more skyward). - somehow this seemed to improve upwind set, possibly by pulling in a line from mast head to a point slightly aft of the tack grommet. i.e. like windsurfer sails set on a mast with substantial 'pre=bend'.

    A possible secondary effect might have been that when downhaul tension overode some of the vang tension the vang angle may have effectively been more acute (greater forewards vector than standard) assisting a lightweight in depowering upwind??

    Does PR's modification to the top block on the vang system alter the effective angle of pull for the vang??

    Not sure if the differences are worth pursuing, but the set-up with the old vang system, and slightly aft attachment point of the downhaul still felt 'sweeter' than with the new Harken vang and downhaul attached to the top fitting provided.

    Moving forward (like PR's setup) would on the surface seem to get further away from the setup described above - but possibly some other changes may compensate. Certainly, varing the angles of vang and downhaul can make differences to the rig.

    Any ideas in this direction ?? - need to look at the whole set-up as well as how set-up is managed in different windstrengths up to and beyond design wind for each sailor's weight.

    GL
     
  7. pirouette

    pirouette Member

    Likes Received:
    0
    Trophy Points:
    6
    I had Andy (gybetech) do my blades a few years ago and then 2 years ago had them awlgripped by a local autobody paint shop ($$). The bummer about AwlGrip is that is is very brittle and the leading edge of the daggerboard chips from going up and down in the trunk

    Once I went to a carbon fiber tiller, I encountered a lot of turbulence felt through the tiller extension when sailing downwind. Al Russell and Peter Follansbee both suggested "squaring off" the trailing edge even though Andy thought they were OK when he looked at them one day this winter when frostbiting in Newport. I squared off the trailing edge of the rudder only (2 mm width of the "squared edge") and voila! trubulence is gone.
     

Share This Page