Mast thickness? for our new Proa... please guide us.

  • 07 May 2021 06:01
    Reply # 10450323 on 10445484

    David, 

    I assume 20 square meters would include your head sail?

    My 22 square meters are all Junk rig laying against the mast. Bending forces are greater.

    90x3 sounds reasonable I suppose....... 

    Much appreciated! Nice little Kohler u got there, Enjoy!

    All the best, 

    Rael

  • 06 May 2021 20:26
    Reply # 10448764 on 10445484
    Rael wrote:

    Hi all

    I'm building a new 25 foot cruising Proa.

    It will have a stayed mast, like I've been using for a few years now....

    So, the  question is  if I have 22 square meters of sail on a 7.5 meter alu mast, is a 75x2 mm pipe enough?

    I'm worried about mast bend between mast srep and mast head.

    I am also worried about weight....    

    Your opinions will be great, Thanks

    Rael

    On my 6 meter cruising catamaran I have a 6.7 meter mast with 20 square meters of sail. The mast is stayed from the top because it is a gaff rig. I have used 100 mm x 3 mm aluminum tube T5. I know I should have used T6 tube, but I could only find T5 tube locally. But even with T6 tube I think the best I could do would be to go down to 90 mm diameter, and by preference I would stay with the 100 x 3 mm tube size for mast rigidity. My mast seems Ok, but I would say that the size of tube I have used is the minimum which could be used. The mast does have quite a lot of wobble in it if I push against it, but when sailing the mast seems to stay very rigid. My all up rig weight for mast, gaff, boom, sails and fittings is just under 30 kg. I have used Dyneema standing rigging to save some weight, and which I am very happy with.


    1 file
    Last modified: 06 May 2021 20:41 | Anonymous member
  • 06 May 2021 17:32
    Reply # 10448377 on 10445484

    Thanks Ueli.

    Yes u understood well my concern.

    I'm worried about the spar that holds the sail, lightweight multihulls are the way to go, on Proas it's even more important since they have less displacement. Proa bows are even more sensitive to weight......

    So weight is a problem! windage too... 

    I would like to go as thin as possible.

    All the best

    Rael

  • 06 May 2021 08:47
    Reply # 10447089 on 10445484

    hi rael

    as i remember, your boats need an arrangement of two (more or less) vertical spars. one is fixed and one moves while shunting. the fixed one doesn't receive any real bending loads, while the moving spar needs to cope with the side load of the wind force on the sail and the (more serious) loads of the inertia of sail and mast when the proa has to fight steep waves.

    just by guessing (without any calculation) your 75/2 spar seems to be on the light side for the fixed spar and too weak for the moving one with the sail on it.

    i would increase the diameter of the moving spar. but hopefully someone will jump in with 'calculation based guesswork'…

    ueli

     

    Last modified: 06 May 2021 08:48 | Anonymous member
  • 05 May 2021 21:04
    Message # 10445484

    Hi all

    I'm building a new 25 foot cruising Proa.

    It will have a stayed mast, like I've been using for a few years now....

    So, the  question is  if I have 22 square meters of sail on a 7.5 meter alu mast, is a 75x2 mm pipe enough?

    I'm worried about mast bend between mast srep and mast head.

    I am also worried about weight....    

    Your opinions will be great, Thanks

    Rael

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

                                                              Site contents © the Junk Rig Association and/or individual authors

Powered by Wild Apricot Membership Software