Forces on top of the mast

Discussion in 'Sailboats' started by Mast, Sep 2, 2013.

  1. Mast
    Joined: Sep 2013
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Euro

    Mast New Member

    Hi everyone!

    Let's say we got a sailboat with fractional mast and 2 spreaders, so unsupported top of the mast.

    What will happen if we hoist a spinnaker to a top of the mast?
    I know, it depends of the mast itself and how strong is it, let's assume that it is strong enough.

    I would like to know is there a difference in forces on the top of the mast if we hoist a spinnaker or if we hoist a assimetric spinnaker (genaker)?

    Is it possible that assimetric would produce less force on the top of the mast?

    In both ways lets assume that we are sailing beam reach or even closer to the wind if we can.

    Best regards
  2. MikeJohns
    Joined: Aug 2004
    Posts: 3,192
    Likes: 208, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    You'd better flesh out some details of that hypothetical 'sailboat' and it's hypothetical mast and stays before anyone can even start to think about answering your query.
  3. Mast
    Joined: Sep 2013
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Euro

    Mast New Member


    My question was general, not for one type of sailboat.

    I was thinking something like this on the picture:

    So fractional mast with V1, D1 and D2 and a backstay.

    This kind of mast clearly isn't dimensioned for top mast headsails.

    But often people hoist bigger spinnaker to a top mast in light winds.

    So that is why my question was is there any difference in the force on the top mast if you hoist large spinnaker or assymetric spinaker?

    Best regards
  4. gggGuest
    Joined: Feb 2005
    Posts: 857
    Likes: 34, Points: 28, Legacy Rep: 76
    Location: UK

    gggGuest ...

    Well there's the obvious one that the mast is being pulled forward by a damn great load on the halyard which at a guess is orders of magnitude greater than anything the mainsail can generate up there...
    Running/reaching deep you have a big forward load which you just don't get otherwise and hugepeak loads you are going to get if the bow is stuffed into a wave.
    Shy reaching you still have a big pull up there, but this time its sideways and forewards. Forward loads can be counteracted by vang tension of the mainsail in this case, and result in compression, but both are working together pullingthe mast head to leeward

  5. Richard Woods
    Joined: Jun 2006
    Posts: 2,209
    Likes: 172, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    The load on a spinnaker would be less than on a sail used close to the wind. A true genoa is a point load at the masthead and has lots of halyard tension (thus extra mast compression, a halyard lock helps). A conventional spinnaker is pretty much 30/30/30% load on each corner and downwind it isn't much. Often you can hand hold the spi sheet

    So an asymmetric will be between the two

    Richard Woods of Woods Designs
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.