Forgot password

Pacific Spray - Booms, Battens and Sheeting

<< First  < Prev   1   2   3   4   Next >  Last >> 
  • 05 Dec 2011 00:10
    Quote
    Reply # 765717 on 765598
    Anonymous member
    Hi Rob,

    As David has already said, it's likely that most of your problems come from 22 tons of very stiff boat. I must say however that IMHO your battens are way undersized. I used 50 x 3 6063 T6 aluminum for Aphrodite's battens. Aphrodite is approximately 38 tons but per ton, not as stiff as you are, Her battens are 6 300 in length.

    Given what I do know about the Spray (I have built and sailed one) I'd suggest that you go for the same. That may be a little heaver than you need but rather a little heavy than to light.

    As David as mentioned, getting the right grade of aluminum (6063 T6) can be a challenge in NZ but it is possible. In the case of Aphrodite I had to have a custom run done. The downside of that is that there is a minimum order of 150Kg. However I did manage to sell off the excess over 4 months and Carl only paid for what we actually used.

    The other way of getting the right grade stuff is to buy blank dinghy masts and cut the rope luff track off. This is what I have done for some of LC's battens. The other option, Carbin fibre tube is readly available and while pricey is not crazily so. Let me know if you need a contact for suppliers.

    As for sheeting, David has already replied to that one.
  • 04 Dec 2011 23:15
    Quote
    Reply # 765686 on 765598
    Anonymous member
    For your mainsheet, I think you need to introduce an anti-twist element into the system. I wouldn't add any more parts to the sheet, but you could try a 3 point span to the boom and lower two battens (Fig 4.25, 4.27), moving the two 2 point spans up by one batten.
  • 04 Dec 2011 22:54
    Quote
    Reply # 765671 on 765598
    Anonymous member
    I think some of your problems derive from having 22 tonnes of very stiff boat, that will not relieve stresses on the rig by heeling or accelerating. Pacific Spray, it seems, is going to need spars to scantlings somewhat in excess of PJR recommendations. 
    There isn't a great deal of recent big-boat experience to quote from - not that I can recall, anyway. Bernard Holland, in his article on Planesong (another Spray) in the last e-supplement, reported GRP pultruded tubular battens failing by being squashed elliptical against the mast, but there's no mention of tube size. Perhaps you could contact him and ask.
    I like David Thatcher's method of using light, straight-grained wood with uni-directional fibre reinforcement. In view of my experience with the too-soft aluminium alloy tube locally available, this might be the best way to get robust battens, more resistant to crushing and to unfair loadings.
  • 04 Dec 2011 22:13
    Quote
    Reply # 765644 on 765598
    Deleted user

    Hello Rob,

    When I needed new battens for the sail on Footprints several years ago I looked at all the options ranging from timber to alloy to pulltruded fibreglass and even carbon fibre. In the end I built my battens from 65mmx 38mm cedar with a layer of unidirectional fiberglass on either side but with a double layer of unidirectionals on the top batten. The battens are 6.3metres in length and have proven to be very stiff. I chose the cedar for a variety of reasons: relatively low cost; I could build them myself as I understood and was experienced in the technology (wood & fibreglass); relatively light weight; I would have needed to have alloy welded to get the required lenghts; easy repair or replacement in out of the way places. According to Hasler cedar would not have the strength or stiffness because of it's low density so that is why I added the unidirectionals. Three years on I would have to say they have been very successful. David  
  • 04 Dec 2011 21:03
    Quote
    Message # 765598
    Anonymous member

    We have just broken an oregon foresail boom that was 4.8 metres long and was 47mm in diameter, sized according to PJR. Thinking of an alloy replacement. Any ideas on diameter and wall thickness?

    We have just broken 4 foresail battens and 6 mainsail battens. All were 38mm outside diameter high strength alloy tubes ranging from 4.7 metres to 5.7 metres in length. Wall thickness was probably too thin. Any ideas on what the wall thickness should be?

    Whilst the mainsail is off we thought we would add a sheeting position to one batten higher up the sail to improve the sail shape. At the moment we are sheeting the boom and 5 battens as per PJR page 66, being a six part sheeting system. Any ideas how we can have a 7 sheet system?

    Hope you can help.

    Rob and Maren  
<< First  < Prev   1   2   3   4   Next >  Last >> 
       " ...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