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S2 6.7 Junk Rig Conversion

  • 01 Apr 2019 15:34
    Quote
    Reply # 7254811 on 6872873
    Anonymous member

    Thank you all for the responses. Graeme, the thread you started about mast height is very useful. I understood that halyard 'drift' was what I needed to consider but I was not sure exactly how to quantify it.

    I found a local metal supplier with a price that seems more reasonable. I am just about to commit some boat budget money to 1.5" OD 0.065" wall 6061-T6 aluminium tube.

    I think I am calculating the yield strength (is that the right term?) properly thanks to the newest chapter of TCPJR. But my formal education is in volts and amps and bits and bytes so there is a good chance I did something wrong. If someone could double check I would appreciate it.

    Yield of Arne's proposed 25mm OD and 2mm wall battens: 21.68 kpm

    Yield of the 1.5" (38.1mm) OD and 0.065" (1.651mm) wall tube: 46.48 kpm

    The sales person said they weigh about 5 lbs each.

    I think I am good to go. Any other thoughts?

    Last modified: 02 Apr 2019 14:37 | Anonymous member
  • 29 Mar 2019 16:16
    Quote
    Reply # 7251229 on 7251156
    Anonymous member
    Scott wrote:
    Phil wrote:

    [...] I wouldn’t consider pipe. Strength to weight is most often much too low compared to tubing. I’d stick with 6061 T6 for it’s strength. [...]

    I think I am missing something fundamental. I see pipe listed as 6061-T6. How is 6061-T6 Pipe different than 6061-T6 Tube?
    Pipe is intended for carrying fluids, and is sized by its internal diameter. Tube is intended more for structural applications, and is sized by its external diameter. Pipe is also designated by its wall thickness (eg schedule 40, schedule 80), and the higher the pressure they are to handle, the thicker and heavier they are. Otherwise, size for size, they will be of the same strength, if the material and temper are the same.
  • 29 Mar 2019 15:24
    Quote
    Reply # 7251156 on 7245846
    Anonymous member
    Anonymous wrote:

    [...] I wouldn’t consider pipe. Strength to weight is most often much too low compared to tubing. I’d stick with 6061 T6 for it’s strength. [...]

    I think I am missing something fundamental. I see pipe listed as 6061-T6. How is 6061-T6 Pipe different than 6061-T6 Tube?
  • 29 Mar 2019 15:22
    Quote
    Reply # 7251155 on 7245275
    Anonymous member
    Anonymous wrote:
    Scott wrote:

    Does anyone have reason to expect 6061-T6 with a 1" OD and a wall thickness of 0.065" is not strong enough for my rig?

    I would question the need to go to the expense of T6 aluminium. I had three aluminium battens on the sail we made for Footprints, (and 4 x carbon battens). The sail was 53 square metres, batten length of 6.5 meters  and a boat weight of just under 6 tonnes. The battens were T5, 65 mm in diameter and 1.5mm wall thickness. Despite numerous heavy gybes and thousands of miles of sailing, up until the time I sold Footprints just recently the battens never gave any trouble, and have performed equally as well as the carbon fiber battens. I think larger diameter with thinner wall thickness is the secret.

    Thank you for the response. The only tube I seem to be able to find here is 6061-T6 or 6063-T5. The strength of 6063 seems to be significantly less.

    I expect the 65mm battens on Footprints are very strong. That is about 2.6 inches using local measurements. I have not been able to find anything around that size with a 0.059" (1.5mm) wall. All the wall sizes are much larger.
  • 26 Mar 2019 22:35
    Quote
    Reply # 7246665 on 6872873
    Anonymous member (Administrator)

    I have been following this thread with great interest, as it has drawn out a lot of very good information and much food for thought, from our experienced commentators.

    One rather crucial point seems to have been a little glossed over, and that is, choice of mast length. It seems that Scott has chosen Arne’s planform over other alternatives on offer, partly for the reason that it is important to him to keep mast length as low as possible. This is a question that I think would be of interest to anyone designing a new conversion and I would be grateful if it could be re-visited. So as not to distract from the current discussion which is ongoing in this thread, I have started a new one in the hopes of focusing on mast length.
  • 26 Mar 2019 21:37
    Quote
    Reply # 7246545 on 7245846
    Deleted user

    Anonymous wrote:

    For me figuring the yard was more of a challenge. I end up with 2” x.125 tubing, same grade. I screwed up my order for  2x.065. I’d planned to laminate a 1“ tube to the lighter 2 in. similar to what was done and shown elsewhere here. The single .125 tube is a bit heavier up high than I wanted but I was suprised to calculate that it was not by all that much. 

    https://www.onlinemetals.com/merchant.cfm?id=71&step=2&top_cat=60 

    This site lists tubing weights by size, inches and lbs., and should be helpful in making comparisons.

    I went back and looked at that. “Not all that much” ain’t very specific. The difference between the heavier single 2x.125 tube and the 2x.065 combined with 1x.065 is 26%  Which in Brenda B’s case was 2lbs not counting a few ounces of glue and fasteners. While that did not seem like much to me the reality is that at 9.57 lbs. the yard is heavier than it needs to be.  I could have cut that weight up high with better planning by going with a single tube 2 1/4x.065 in. at 5.83 lbs which I think would be stout enough.
  • 26 Mar 2019 14:56
    Quote
    Reply # 7245846 on 6872873
    Deleted user

    Scott, the battens on Brenda B are 11 ft.  The long one is probably about 12ft.. They all are 1 inch X .65in., 6061 T6. While the longer batten might have been one size up is has been fine over these past three sailing seasons.  While displacements are close, your boat is a a foot beamier, and at 22 ft is likely to carry more weight than my 19 footer. I think 1 1/4 inch  X .065 inch would give more stiffness and less weight than the 1 inch x .125.   I wouldn’t consider pipe. Strength to weight is most often much too low compared to tubing. I’d stick with 6061 T6 for it’s strength. It seems that 6061 T6 and 6063 are the most easily available grades of tubing in the US. 

    For me figuring the yard was more of a challenge. I end up with 2” x.125 tubing, same grade. I screwed up my order for  2x.065. I’d planned to laminate a 1“ tube to the lighter 2 in. similar to what was done and shown elsewhere here. The single .125 tube is a bit heavier up high than I wanted but I was suprised to calculate that it was not by all that much. 

    https://www.onlinemetals.com/merchant.cfm?id=71&step=2&top_cat=60 

    This site lists tubing weights by size, inches and lbs., and should be helpful in making comparisons.
  • 26 Mar 2019 04:33
    Quote
    Reply # 7245275 on 7243174
    Deleted user
    Scott wrote:

    Does anyone have reason to expect 6061-T6 with a 1" OD and a wall thickness of 0.065" is not strong enough for my rig?

    I would question the need to go to the expense of T6 aluminium. I had three aluminium battens on the sail we made for Footprints, (and 4 x carbon battens). The sail was 53 square metres, batten length of 6.5 meters  and a boat weight of just under 6 tonnes. The battens were T5, 65 mm in diameter and 1.5mm wall thickness. Despite numerous heavy gybes and thousands of miles of sailing, up until the time I sold Footprints just recently the battens never gave any trouble, and have performed equally as well as the carbon fiber battens. I think larger diameter with thinner wall thickness is the secret.
    Last modified: 26 Mar 2019 05:22 | Deleted user
  • 25 Mar 2019 21:20
    Quote
    Reply # 7244567 on 6872873
    Anonymous member

    Arne,

    At a 70% increase in cost and 82% increase in weight I can get 1" OD x .125" wall.

    I have been looking here and here. I hope to make a stock 12' length work for all battens except the top sheeted batten. For the 'long' batten I would buy a single 20' or 24' length and cut it down.

    Maybe the 6061-T6 0.840" OD x 0.109" ID (OD 21.336mm x wall 2.7686mm) T312 is a better option. Smaller OD but thicker wall?

    1 file
    Last modified: 25 Mar 2019 21:31 | Anonymous member
  • 25 Mar 2019 19:47
    Quote
    Reply # 7243911 on 6872873
    Anonymous member (Administrator)

    Scott,

    what other sizes are available near the one you mention?

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

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