Pre bent masts

Discussion in 'Multihulls' started by ChrisVJ, Nov 29, 2021.

  1. ChrisVJ
    Joined: Nov 2021
    Posts: 21
    Likes: 1, Points: 3
    Location: Kelowna

    ChrisVJ Junior Member

    I am in a harbour with a buch of new catamarans awaiting delivery and a few others on passage. The new ones all have pre bent masts. Why?

    These are not performance boats, more like floating condos, some of them destined for the charter business. It can't possibly be about speed or modifying sail shape. These are beefy masts, I doubt they would flex under normal loads but it has to cost to pre bend them like this.

    Can anyone tell my why the manufacturers would go to the trouble and expense?
     
  2. patzefran
    Joined: Feb 2011
    Posts: 362
    Likes: 46, Points: 28, Legacy Rep: 10
    Location: france

    patzefran patzefran

    If these are rotating masts, it could make sense !
     
  3. Doug Halsey
    Joined: Feb 2007
    Posts: 640
    Likes: 210, Points: 53, Legacy Rep: 160
    Location: California, USA

    Doug Halsey Senior Member

    Can you elaborate?
     
  4. Blueknarr
    Joined: Aug 2017
    Posts: 1,369
    Likes: 357, Points: 83
    Location: Colorado

    Blueknarr Senior Member

    To make a fashion statement.

    The appearance of performance
     
  5. patzefran
    Joined: Feb 2011
    Posts: 362
    Likes: 46, Points: 28, Legacy Rep: 10
    Location: france

    patzefran patzefran

    The pre-bent is in the plane of the longitudinal axis of the mast , if your mast is turned along this axis , the luff is along the curved track, the draft of the sail is minimum.
    if you rotate the mast on the opposite, toward the transverse axis, the track becomes rectilinear, the draft of the sail increase. This used currently on beach cats to manage the power of the sail.
     
  6. ChrisVJ
    Joined: Nov 2021
    Posts: 21
    Likes: 1, Points: 3
    Location: Kelowna

    ChrisVJ Junior Member

    I get the usual reasons for having a bendy, or even pre bent mast but it has to cost and, with the greatest admiration for the builders, these are far more floating condos ( actually more like split level town houses!) than they are peformance boats or even blue water cruisers. (They are well designed and built for the market and use for which they are intended.)

    Given that I can see no real purpose for pre bent masts.
     
  7. patzefran
    Joined: Feb 2011
    Posts: 362
    Likes: 46, Points: 28, Legacy Rep: 10
    Location: france

    patzefran patzefran

    Marketing !
     
  8. Will Gilmore
    Joined: Aug 2017
    Posts: 793
    Likes: 327, Points: 63
    Location: Littleton, nh

    Will Gilmore Senior Member

    Flattening the sail, although that can be done by the sailmaker instead of pre bending, allows for a little better windward performance.

    I never saw the point of prebending for the purpose of depowering. Why put all that sail area up if you just take its power out of it? Get an adjustable backstay and have more power to use off the wind.
     
  9. patzefran
    Joined: Feb 2011
    Posts: 362
    Likes: 46, Points: 28, Legacy Rep: 10
    Location: france

    patzefran patzefran

    Tell this to A class cat sailors !
     
  10. Will Gilmore
    Joined: Aug 2017
    Posts: 793
    Likes: 327, Points: 63
    Location: Littleton, nh

    Will Gilmore Senior Member

    Are you saying it makes sense to pre-bend the mast if it does rotate or if it doesn't rotate?

    Bending the mast is used to flatten the luff to allow the boat to point a little higher. As you say, it reduces draft that can produce more heeling than drive on a close reach. It prevents the sail from stalling out early. I can see, if you are saying, that by swinging the boom out when off the wind, more draft can be regained because the mast is now bent in the direction of lift. But if the mast rotates with the boom, no more depth to the draft would be introduced.

    I'm beginning to see the wisdom of pre-bending.
     
  11. patzefran
    Joined: Feb 2011
    Posts: 362
    Likes: 46, Points: 28, Legacy Rep: 10
    Location: france

    patzefran patzefran

    Pre bending is useful to windward on rotating masts. It allows powering / depowering of the sail by rotating the mast relating to the boom. The sails are designed with corresponding luff roach to allow managing the power . It is equivalent to reefing but is much better as it increase the fineness ratio of the rig instead of decreasing it. It looks bending the mast for depowering was first used upwind by Star sailors together with a non rotating very slim mast.
     
  12. Erwan
    Joined: Oct 2005
    Posts: 442
    Likes: 25, Points: 28, Legacy Rep: 97
    Location: France

    Erwan Senior Member

    Pre-bending provides the cunningham (downhaul) with some leverage, otherwise with a straight mast, the luff tension induced by the cunningham would just create compression on the mast and would not create mast bending , or at least not as much as with a pre-bend one.
     
  13. ChrisVJ
    Joined: Nov 2021
    Posts: 21
    Likes: 1, Points: 3
    Location: Kelowna

    ChrisVJ Junior Member

    These are floating condos so this can't really be about sail performance as in a racing boat. I notice that, like a lot of boats these days the spreaders are raked back too. I was questioning that the point about a beam flange is that it has to be perpendicular to the web to be strong. Raked spreaders would appear to be far, far weaker than laterally square spreaders. However if there is lateral bending pressure on the raked spreader the load would result in longitudinal bending moment. I speculate that in a straight mast this might result in sudden point failure whereas in a pre bent mast it might result in a spread flexing.

    It might also be that someone has a new bending machine and wants to get their money's worth out of it!
     

  14. Blueknarr
    Joined: Aug 2017
    Posts: 1,369
    Likes: 357, Points: 83
    Location: Colorado

    Blueknarr Senior Member

    You are absolutely correct it is NOT performance related.

    It is perception related. A marketing ploy. Has visual display of performance thereby it can be charted at a greater price. Guests who don't know better will think they are having a performance experience.
     
Loading...
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.