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Sail trim quiz question

Discussion in 'Sail Trim with Don Guillette' started by Jackdaw, Nov 29, 2017. Add this thread to a FAQ

  1. Jackdaw

    Jackdaw

    Joined Nov 8, 2010
    8,769 posts, 2,100 likes
    Beneteau First 36.7 & 260
    US Minneapolis MN & Bayfield WI
    what do you think??? ;^)
     


    Apex likes this.
  2. Jackdaw

    Jackdaw

    Joined Nov 8, 2010
    8,769 posts, 2,100 likes
    Beneteau First 36.7 & 260
    US Minneapolis MN & Bayfield WI
    OK, bridle systems like that are designed to as much as possible replicate the traveler's ability to bring the boom to centerline. They cannot quite get to centerline, because while the block at the top the the bridle will be on the c/l, the pressure of the breeze will always make the purchase between the bridle and the boom fall off somewhat.

    But this distance is much less then if the mainsheet was attached to the deck. So performance is better.

    Because it cannot be lowered, a vang is needed to vang sheet in breeze.

    In any case, in a boat like the Melges 20 the driver is also trimming main, and only having the mainsheet (just like a laser) makes perfect sense.
     


    Last edited: Dec 7, 2017
    Will Gilmore likes this.
  3. BobbyFunn

    BobbyFunn

    Joined Apr 16, 2017
    257 posts, 122 likes
    Hunter 170
    US Tampa
    Not exactly :biggrin:

    The bridle makes a triangle. The higher the triangle the longer the hypotenuse. The difference between the hypotnuse and half width is the amount one can cheat the boom across to windward.

    Maybe im an idiot and have that backwards. One thing is for sure, if i had that set up, i would arrange it so the each side of the yellow line could be shortened.

    Eventually, well have materials strong enough to replace the sheets like that with accuators that pivot boom up and down and another that pivots the boom port and starboard. Itll have a bluetooth contrller so everyone, even the skipper can be railmeat.
     


    Last edited: Dec 7, 2017
    Will Gilmore likes this.
  4. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    2,577 posts, 1,061 likes
    O'Day 19
    US Littleton, NH
    Actually, it would be the case for all bridle arrangements but, I am changing my song here. As the boom is hauled to center, the block rises with the steepening angle. This causes it to move CLOSER to center, as jackdaw said. The lateral force would always force it off center to some degree. But, as the sheet is shortened, the triangle of the bridle becomes more equilateral.
    I have been thinking about how my mariner sheet is setup and I will set it up initially the way it was previously, just to get it on the water but, this looks like a great system to change over to. I don't really care for the mid-boom sheeting.
    Thank you, jwing, for this idea and discussion.
    I can see that with a couple of cam cleats on either end of the bridle, I could even vang the boom with it.
    - Will (Dragonfly)
     


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  5. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    2,577 posts, 1,061 likes
    O'Day 19
    US Littleton, NH
    I see it and agree.
    To shorten the bridle on one side or the other, I said cam cleats but, I think people also call them snatch blocks?
    - Will (Dragonfly)
     


  6. jwing

    jwing

    Joined Jun 5, 2014
    399 posts, 150 likes
    ODay Mariner
    US Guntersville
    True dat. Assuming that the apex of the bridle is centered, then the height of the apex determines how close the boom can get to the centerplane. If the height of the bridle block is the same as the height of the boom block, then the boom's offset from the centerplane is just the dimensions of the blocks. That is, there will be no length of mainsheet between the blocks. If the vang is set to pull the boom down to the apex of the bridle, then easing the mainsheet affects exactly like easing a traveler.

    There are reasons to compromise of course. For more info, read the bridle height article I linked to in #114.

    In my particular boat, most of the time, the driver is also trimming the main and the jib and fetching beer.
     


    Will Gilmore likes this.
  7. BobbyFunn

    BobbyFunn

    Joined Apr 16, 2017
    257 posts, 122 likes
    Hunter 170
    US Tampa
    Man i was hoping this was going to be it solution to upwind sheeting. Looks like no matter what centerline is best that can happen. All roads lead to a traveler or a dual mainsheet, or compromise. I did see some examples of a rope traveler, but they look like a hassel versus a fixed track.
     


  8. Jackdaw

    Jackdaw

    Joined Nov 8, 2010
    8,769 posts, 2,100 likes
    Beneteau First 36.7 & 260
    US Minneapolis MN & Bayfield WI
    While it will never be a functional as a real traveler, a bridle is a good solution for small boats, in particular ones that are sailed 'dinghy style', with the driver sailing with tiller in one hand and mainsheeet in the other. Its popular on small high performance OD boats, where everyone is limited in the same way.

    My guess is that its better than the Catalina 22 traveler, which is too short (vs the vertical run of the mainsheet) to get the boom to centerline.
     


    Last edited: Dec 8, 2017
    Will Gilmore likes this.
  9. Apex

    Apex

    Joined Jun 19, 2013
    739 posts, 79 likes
    Oday 28
    US Traverse City
    My take on bridle is same as Will, a design necessity to allow the tiller and mainsheet to occupy the same space.
     


  10. Jackdaw

    Jackdaw

    Joined Nov 8, 2010
    8,769 posts, 2,100 likes
    Beneteau First 36.7 & 260
    US Minneapolis MN & Bayfield WI
    That's a nice knock-on effect; allowing the mainsheeting to be centered straight over where the tiller wants to be!
     


  11. Slick

    Slick

    Joined Jun 17, 2016
    11 posts, 3 likes
    Ericson 35 3
    Us Paris Landing Tn
    yikes! This all reminds me of learning trig. It was like a foreign language
    until one day it just "clicked". At least I hope sail trim will "click" at some point.
    Thanks for the thread guys, it helps even if I don't quite get it all yet.
     


  12. Jackdaw

    Jackdaw

    Joined Nov 8, 2010
    8,769 posts, 2,100 likes
    Beneteau First 36.7 & 260
    US Minneapolis MN & Bayfield WI
    If you want, we can work some trig into this discussion.... ;^)

    1) I'm sailing upwind at 44 degrees true, making 5.2 knots
    2) I'm sailing upwind at 47 degrees true, making 5.4 knots

    Which is faster to windward??
     


  13. Meriachee

    Meriachee

    Joined Aug 1, 2011
    2,523 posts, 669 likes
    Catalina 270
    CA Wabamun - on the orange ball
    Depends where the mark is and who is in the way. :)
     


  14. Jackdaw

    Jackdaw

    Joined Nov 8, 2010
    8,769 posts, 2,100 likes
    Beneteau First 36.7 & 260
    US Minneapolis MN & Bayfield WI
    Which is faster to windward??
     


  15. Apex

    Apex

    Joined Jun 19, 2013
    739 posts, 79 likes
    Oday 28
    US Traverse City
    1) cos(44)5.2 = 3.74knots VMG
    2) cos(47)5.4 = 3.68knots VMG

    mariachee has a much better answer though: esp who is in the way. lol
     


  16. Jackdaw

    Jackdaw

    Joined Nov 8, 2010
    8,769 posts, 2,100 likes
    Beneteau First 36.7 & 260
    US Minneapolis MN & Bayfield WI
    Sail racing questions always assume the absence of other boats and wind/tide being equal. Else you could not even pose questions. But even so:

    As long as you are going to windward and inside the laylines, it does not matter where the mark is.
    We are talking about a 3 degree heading change. Not likely someone's going to be in or out of your way based on that!
     


  17. BobbyFunn

    BobbyFunn

    Joined Apr 16, 2017
    257 posts, 122 likes
    Hunter 170
    US Tampa
    Why you folks using cosine, and where's your proof?
     

    Attached Files:



  18. Apex

    Apex

    Joined Jun 19, 2013
    739 posts, 79 likes
    Oday 28
    US Traverse City
    yes, correct Jackdaw. AND I find Meriachee's answer entertaining, which I assume the smiley indicated as humor.

    What is also interesting is a small heading change of 3degrees to gain boat speed really doesn't offer advantage, rather a disadvantage. I have not paid enough attention to VMG, rather trying to point as high as possible without pinching. It might be fun to play out some more scenarios when sailing.
     


  19. Apex

    Apex

    Joined Jun 19, 2013
    739 posts, 79 likes
    Oday 28
    US Traverse City
    perahps I am looking at it wrong? BobbyFunn, wind direction is x-axis, so angle off wind is between x-axis and speed vector. Thus the windward (x) component is ADJ/HYP = cosine
    ???? yes/no ????
    OH, and I was on starboard tack, so opposite of your sketch....
     


    Last edited: Dec 18, 2017
  20. BobbyFunn

    BobbyFunn

    Joined Apr 16, 2017
    257 posts, 122 likes
    Hunter 170
    US Tampa
    Awesome, thanks. For the sketch i have, i should have subtracted each angle from 90 degrees since i have the angles upside down
     



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