Choosing the right block

Discussion in 'Sailboats' started by rd.sail, May 7, 2007.

  1. rd.sail
    Joined: May 2007
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    rd.sail Junior Member

    I have a Bristol 29.9 and I need to replace my mainsheet blocks. I have being looking for options and I have narrow it down to eather Harken or Lewmar. The system right now is a 4-1 mid boom. I was going to upagrade it to a 5-1 for my wife. Right now the main systems has and very old harkens and at some point the previouse owner replaced some of the block with ronstan.

    I can use: Harken airblocks 57mm: 1 single, 1 Double and 1 double with becket. and 2 extra singles to lead the line aft. I could also use 75mm but that might be over kill.

    For the lewmar, I would be the same set up but 60mm.

    Here is my question. Which one should I used? Which is is a better block? I have being traing to find information only but I have not had many lock.

    I would greatly appreciate any direction you can give me?
     
  2. SeaSpark
    Joined: Mar 2006
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    SeaSpark -

    Harken

    Harken considered superior to Lewmar by most experts, the term Harkenizing (upgrading hardware on a production boat to harken) exists.
     
  3. rd.sail
    Joined: May 2007
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    rd.sail Junior Member

    Thanks you for the comment. I thought the same thing. I just need to check before a order all the parts.
     
  4. LP
    Joined: Jul 2005
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    LP Flying Boatman

    Increasing the purchase ratio is also going to increase the sail pressure needed to move the boom, it will also increase the length of your sheet and also the weight of the sheets. (light airs consideration)

    Just some thoughts.
     
  5. rd.sail
    Joined: May 2007
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    rd.sail Junior Member

    Last year I replaced the main sheet, I was thinking then to increase the the ratio so I purchased a longer line and lighter sheet.

    Question on you first part of your comment.(increasing sail pressure) Does this mean that there would be a larger force on the connection points on the sail (boom and traveller) so I would need to go to larger blocks?

    I thought the force on the boom and traveller would be the same but it would take more line to sheet the boom. The effort should be less but longer.

    One other thing I was thinking of doing is to rig it so when there is light air I can change the ratio to 4-1 instead of 5-1 by just reattaching the end of the line. I would deattached from the the traveller block (Double with becket) to a boom fitting.
     
  6. SeaSpark
    Joined: Mar 2006
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    SeaSpark -

    sail pressure

    LP must have been talking about the force needed to pull the sheet through the blocks. In light winds sometimes the sail does not deliver enough force to do this after a tack.

    I think reattaching the mainsheet may prove a bit cumbersome when the wind increases.
     
  7. LP
    Joined: Jul 2005
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    Location: 26 36.9 N, 82 07.3 W

    LP Flying Boatman

    SeaSpark was right. By increasing the purchase ratio, you increase the mechanical advantage of the sheet, but you are also decreasing the mechcanical advantage of the mainsail/boom. With free running blocks you may not see a difference or it may be negligible. Sounds like it's an easy switch so you can always go back if it doesn't work.
     
  8. rd.sail
    Joined: May 2007
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    rd.sail Junior Member

    Thanks for all the comments. I'm not too worry about very light air becuase that's when my engine comes on. My boat does not like light air anyway.

    It also would be very easy to go back to 4-1 with the same blocks I just need to change the placement.

    I guess my last concern is if the Hark carbon 57mm will handle the load. From comparing the stats they will. Does anyone think I should go to the 75mm?
     
  9. jim lee
    Joined: Feb 2007
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    jim lee Senior Member

    Different approach here..

    On my machine I run a Ronstan (sp?) 4/8:1 It has a double line coming through a double camcleat. Pull both and you have 4:1 drop one and you get 8:1.

    The mainsheet is actually a big loop. When you install it you have to splice the line togather. (I had mine done professonally 'cause I don't know how to do fancy splices like that.)

    I really love it though.

    -jim lee
     

  10. rd.sail
    Joined: May 2007
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    rd.sail Junior Member

    Jim,
    I'm trying to use the same set up that I had before. My line goes to a dedicated winch. So the cam cleat will just add another level of difficulty for my wife. We have a 5 year old so keeping the systems on the simple is a must for us.

    On another note, I contact a techitian at Harken. He recomended to go with the 75mm carbo blocks instead of the 57mm. The blocks will have a greater life that way. I'm going to follow his advice.
     
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