Forgot password

New (cambered) sail for Footprints

  • 22 Mar 2012 03:33
    Quote
    Reply # 865503 on 858946
    Anonymous member
    Gary Pick wrote:I had a look at your sail designs David and I must say you have an eye for form. Beautiful shape.
    Thanks, Gary. My aim has been to make something that both looks good and works well. And working well, to me, is not quite synonymous with sailing fastest to windward, but means sailing fast to windward and on all other points, at the same time as being entirely manageable on all points of sail. We'll see tomorrow how well I've succeeded with this sail. We know it's working well on Fantail, and this is just a scaled-up version.
  • 22 Mar 2012 03:26
    Quote
    Reply # 865499 on 829776
    Anonymous member

    The two Ds have spent an energetic morning rigging Footprints' sail, albeit with makeshift lines and blocks in places, and now have only the boom to finish off tomorrow morning. Then she'll be ready to drop the mooring, and we'll see if she sails or not.
  • 14 Mar 2012 20:58
    Quote
    Reply # 858946 on 829776
    Anonymous member
    I had a look at your sail designs David and I must say you have an eye for form. Beautiful shape.
  • 14 Mar 2012 20:01
    Quote
    Reply # 858894 on 829776
    Anonymous member
    Well done David - I am really looking forward to seeing the sail in action!
  • 12 Mar 2012 04:58
    Quote
    Reply # 855840 on 829776
    Anonymous member
    This is to certify that

    David Thatcher

    has graduated with honours from the Tyler School of Junk Sailmaking.

    Footprints sail is now complete, with sailcatchers added fore and aft.
  • 06 Mar 2012 22:52
    Quote
    Reply # 849568 on 829776
    Anonymous member
    Arne is right in saying that the behaviour in bending of tubes of different spec, but the same size depends only on the modulus of elasticity, so long as the stress is kept within safe limits. My Machinery's Handbook says that the modulus doesn't vary by more than 10%, for all the aluminium alloys. But I have my doubts as to whether the 6060T5 tube available here is good enough for Footprints' 6.6m battens, going on my experiences with it.

    Paul is right in saying that the drawn, T8, tube will take a higher load before it deforms permanently. But I wonder whether the sudden, catastophic collapse of a hard tube would be more difficult to deal with, offshore, then the gradual bend of a soft tube? 

    David is right in saying that consideration of replacement battens should wait for phase 2 of Footprints' rig upgrade. The cedar battens are serviceable, even if heavy and flexible. There is more important expenditure on new rope and blocks to be made before considering upgrading the battens.
  • 06 Mar 2012 09:27
    Quote
    Reply # 848969 on 848677
    Anonymous member (Administrator)
    Paul Thompson wrote:
    Arne, I'm sorry but I have to disagree with you here. The modulus of elasticity is the same as you say but there is a big difference in hardness and behaviour under bending loads as well as in recovery.

    While all grades (T5,T6 and H8/T8) will ultimately fail at the same point, how they fail is quite different. The soft tubes will gradually deform (take a bend) as the load is applied. The hard tubes will resist bending until close to their failure point, then collapse suddenly.

    As long as we are working with in the load limits of the tube, the harder tube will resist bending to a much greater degree than the soft tube. I have 50x1.5 tube in all three grades in my workshop and I double checked before I wrote this post. The hard drawn tube was very much more resistant to bending than both the T5 and the T6 tubes.

                                                                              Stavanger, Tuesday

    Paul,

    your practical tests surely beat theory! Still, the "soft" tubes don’t take permanent bend unless one passes a certain stress limit. My point is that to get a tube stiff enough to not flex more than will add 1 - 2 % to the camber, it has to be quite over-dimensioned, so will resist deformation or breaking even in hard gybes. Malena’s 25mm battens clearly were on the thin side so have been bent here and there. Johanna’s 50mm thin-walled battens (not tempered) have stood up perfectly well (ok, the long batten no 2 has 3.2mm wall). Surely they haven’t seen long distance offshore cruising, but they still have taken some blows and many gybes.

    If the tempered battens are available and not too expensive, they may be worth the extra cost. If they are not available, the ordinary aluminium is still good enough and probably better than wood.

    "Cheap, available and good enough" - that’s me.

    Arne


    Last modified: 06 Mar 2012 13:54 | Anonymous member (Administrator)
  • 06 Mar 2012 07:04
    Quote
    Reply # 848934 on 829776
    Deleted user

    Thanks for your interest Gents. I did actually get a price today for the T8 alloy for battens but the cost was quite high, plus the batten pockets are made now for the profile of my tmber battens, so the die is cast - timber battens and the new Alloy tube yard. I am confident it will all work out well and regardless of some of these details I am going to have a much better rig than in the past.

    I have today though been dreaming up all sorts of fancy schemes for modifying my cedar battens sometime in the future by hollowing out the sides and adding carbon fibre unidirectionals to create a sort of an I beam. But once I have the boat sailing again I will probably stop worrying about these things and just enjoy the sailing with the new rig.

     Watch these pages over the next 2 weeks as the current project reaches completion - reports will follow.
  • 06 Mar 2012 01:04
    Quote
    Reply # 848677 on 848501
    Anonymous member
    Arne Kverneland wrote:I would not bother with paying extra for the tempered aluminium for battens since its flexibility (modulus of elasticity) is the same as for un-tempered aluminium. 

    Arne, I'm sorry but I have to disagree with you here. The modulus of elasticity is the same as you say but there is a big difference in hardness and behaviour under bending loads as well as in recovery.

    While all grades (T5,T6 and H8/T8) will ultimately fail at the same point, how they fail is quite different. The soft tubes will gradually deform (take a bend) as the load is applied. The hard tubes will resist bending until close to their failure point, then collapse suddenly.

    As long as we are working with in the load limits of the tube, the harder tube will resist bending to a much greater degree than the soft tube. I have 50x1.5 tube in all three grades in my workshop and I double checked before I wrote this post. The hard drawn tube was very much more resistant to bending than both the T5 and the T6 tubes.
    Last modified: 06 Mar 2012 01:05 | Anonymous member
  • 05 Mar 2012 22:46
    Quote
    Reply # 848501 on 829776
    Anonymous member (Administrator)

                                                                             Stavanger, Monday

    David Th, that 100mm tube sounds big enough with respect to strength. It could be that it will bend (..see PS...) a bit, but in that case you can beef it up later with a bracing rod like that on Fantail’s yard. The thing to remember is that aluminium is a lot more flexible than wood so one has to dimension for stiffness rather than breaking (or yield) strength.

    I would not bother with paying extra for the tempered aluminium for battens since its flexibility (modulus of elasticity) is the same as for un-tempered aluminium. If you can afford it, I therefore suggest that you for new battens go for ordinary un-tempered aluminium tubes which can be welded without any loss of strength. By using big section and thin walls (say 50mm and 1.5mm) you get good stiffness to weight and with some useful spare strength: I think that this combination of strength, lightness and flexibility make the aluminium battens less prone to breaking in a gybe than wooden battens seem to be.

    In my view, the only natural material which can compete with aluminium tube in this respect, is bamboo. I have tried it once and its strength/weight ratio was amazing.

    Good luck; that batten issue can maybe rest a bit!

    Arne

    PS: With bending, I actually mean flexing, not taking a permanent bend as when crossing the yield strength limit.
       " ...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