S2 6.7 Junk Rig Conversion

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  • 03 Apr 2020 22:54
    Reply # 8878063 on 6872873

    I am still not sure why the sign at the store says '0.703" actual' if the nominal is 18mm (0.709") for this plywood. It seems like the 'actual' on the sign would be the nominal value.

    There are clearly bigger problems in the world right now.

    Evaluating risk of normal activities has become complex. For now, since our Governor has ordered everyone to 'Stay Home, Stay Safe' I am going to avoid going over to the boat storage.

    I will be working on cutting and shaping plywood for the mast partners here at home today. I am not sure what I am going to do when I eventually need a tool that I left on the boat.

    But yet the supplier for my mast, on the other side of the Lake Michigan, in Wisconsin, sent me an email. They claim to be able to keep up with any existing or new orders as normal. They gave me an expected ship date that is just about a week earlier than what I expected.

    Daily life is paradoxical right now.

    Last modified: 03 Apr 2020 22:54 | Anonymous member
  • 23 Mar 2020 14:05
    Reply # 8849569 on 6872873

    Even high quality sanded plywood can have a tolerance of +/- 0.2mm to 0.4mm (or 0.008" to 0.016") and your plywood is well within that, at only 0.006" from the nominal thickness.

  • 23 Mar 2020 13:37
    Reply # 8849548 on 6872873

    Thanks, David. I read a few of your other responses again. I think I now understand what you are recommending regarding thick disks bonded around the tabernacle.

    I would expect 18mm plywood to be 0.709" actual thickness (0.708661").

    Is 18mm plywood actually a little less than 18mm thick?

  • 23 Mar 2020 08:12
    Reply # 8849306 on 6872873

    What you have is 18mm plywood, Scott! [25.4mm = 1 inch] It's good to see N America taking steps to catch up with the rest of the world ;-)

    I don't think you need another piece of the same, across the entire hatch aperture. You have joined to the GRP deck satisfactorily, and further thickness won't add further strength at this point. Discs of plywood to build up thickness where the mast bears against the partners are what you need now.

  • 22 Mar 2020 18:20
    Reply # 8848358 on 6872873

    I have one layer of 23/32 CAT (0.703" actual thickness) dry fitted with bolts where the fore-hatch was previously located. Was it not confusing enough to sell plywood in fractional inches? Now we use a strange fraction like 23/32 and even that is only an approximation of the actual thickness? I think someone is trying to make this intentionally difficult.

    Anyway for my mental accounting I am considering this one 3/4" layer above deck for the partners. I have twelve 1/4" stainless steel bolts as mechanical fasteners. I imagine they are 304 SS. Six of them run through the deck and new plywood core. The other six are through the new plywood only. I plan to use plenty of thickened epoxy to fill in any gaps in this entire assembly. I plan to add one more layer of approximately 3/4" plywood and call it done.

    It did not come together exactly as I wanted but I am convinced that it will be strong.

    I would greatly appreciate a review of this description and the attached photos. If possible, please let me know if you see anything that looks 'wrong' enough that you would not personally trust it.

    One of the photos was taken through the plastic sheeting that I am using to keep the mess from my boat off of other people's boats in storage. Please excuse the blurry image.

    4 files
    Last modified: 22 Mar 2020 18:31 | Anonymous member
  • 09 Mar 2020 20:56
    Reply # 8815690 on 6872873

    I suppose my wording was not precise. I will look for 38mm x 34mm tube locally. Thank you.

    Last modified: 09 Mar 2020 21:08 | Anonymous member
  • 09 Mar 2020 19:56
    Reply # 8814660 on 6872873

    Much depends on the construction. Just to say "fiberglass tubes" says nothing about how the fibres have been oriented, what the fibre/resin content is, etc. Just as you have to choose the right spec of aluminum, you have to choose the right spec of FRP tube.

    PJR says that GRP tube is "too flexible unless used in large diameters", which is not at all the same as saying "not strong enough". The spec is not mentioned, and we have to remember that PJR was written in 1988, when pultrusion technology was not well advanced.

    The JRA, as an association, cannot and does not voice an opinion on the matter; its members can and do, though.

    I have been using GRP battens successfully for many years, and much prefer them to aluminum. If you were in the UK, I would immediately point you towards my current source, but unfortunately I have no direct knowledge of products available in the USA. All I can say for sure is that in Weaverbird's JR sail, the same size as yours, I found 30mm OD x 27mm ID GRP from this supplier to be just a little too flexible for my taste, though they were strong enough; whereas 38mm OD x 34mm ID is amply stiff and strong. I cannot say, though, whether any tubes that you can buy would match up to this performance. You would have to obtain and test a sample tube.

  • 09 Mar 2020 19:19
    Reply # 8813597 on 6872873

    Do you have any FRP tube dimensions to recommend? I recall PJR and the JRA some specific people on this forum expressing their personal opinions suggesting that fiberglass/polyester tubes were not strong enough adequate for use as battens.

    My sail is 237 sq ft and I will need battens just a little more than 12 feet long.

    Last modified: 09 Mar 2020 20:44 | Anonymous member
  • 09 Mar 2020 18:52
    Reply # 8812447 on 6872873

    You might also do a search for "pultruded FRP tubes" to see how they compare with aluminum tubes where you are. Here's one such source.

  • 09 Mar 2020 18:31
    Reply # 8812247 on 8810273
    David wrote:
    Scott wrote:

    David can you tell me, please, is your advice on making carbon fiber tubes still "Don't do it" ?

    It's more like "Don't Do It!" Yes, CFRP tubes are great, when made with the correct resin, tooling and methods, and with an autoclave to post-cure, but it's too hard to do all that reliably at home.

    OK. I will try to get myself mentally prepared to make at least one more aluminum purchase. After so many years of saving money 'for the boat' I find it hard to spend money, even on the boat.

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