SibLim 4 metre dinghy

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  • 30 Jul 2021 23:41
    Reply # 10785206 on 10741742

    David Tyler not sailing doesn't quite compute. You have done more than most though David,  so maybe a bit of hiking and kayaking is not so bad.

  • 30 Jul 2021 03:35
    Reply # 10783374 on 10741742
    Anonymous member (Administrator)

    Best wishes for an enjoyable retirement from boat building/ownership David. Hiking and kayaking sounds pretty good, and I trust that your valuable contributions on the forum will continue.

    The 4m SibLim remains an exciting concept and it would be great if you can find time to progress the design, anyway.


  • 30 Jul 2021 01:38
    Reply # 10783160 on 10741742

    Oh dear, David, that is terrible news.  I can't imagine your being a couch potato, but I can't imagine you not having a boat to work on, to try out ideas and to experiment with.  I hope you will stay active on forum: so many people rely on your input.

    Take care and I send you my love.

  • 29 Jul 2021 07:53
    Reply # 10781455 on 10741742

    David T,

    Sorry to hear that you are having to curtail your boating activity on medical advice.

    But glad to hear that you can still keep active in other ways.


    You have been a great source of information and inspiration down the years for so many, for so many years, through this website, and hopefully that will continue for many more years to come.


    Best wishes, and keep safe.


    David D.


    Last modified: 29 Jul 2021 07:54 | Anonymous member
  • 28 Jul 2021 19:37
    Reply # 10780342 on 10741742

    Turns out that it would be unwise of me to start to build this boat. After a session with my medical consultant this afternoon, my feeling is that I should retire from boat ownership at this point, quitting while I'm ahead, rather than starting something that I couldn't finish. Had to come, sometime.

    But I won't become a complete couch potato. I can still do a bit of hiking, biking and kayaking.

  • 14 Jul 2021 01:03
    Reply # 10749590 on 10741742
    Anonymous member (Administrator)

    I didn't think about that either (the bendy battens potentially affecting sail balance).

    My battens bend a little downwards (due to tweaking a  bit too hard on the downhauls sometimes). So there are now two good reasons to give a SJR stout, rigid battens.

    In reply to Dave D I would agree it is important to be very clear exactly what is meant by "balance" on a SJR. I believe for the purpose of calculating balance, the sail and its perimeter should be considered as a single entity, including slot, and I do not like to calculate "area of sail in front of mast" etc. In the case of SJR with vertical luffs and leeches, it is sufficient to consider the balance axis as a vertical line which divides the lower battens in the required balance ratio. Period. I see no reason why a dinghy sail should not balance in the same way as a larger sail (I guess we will find out) but you are certainly right to look closely at sheeting systems with a view to keeping sheet friction to an absolute minimum.

    On the smallish sail of Serendipity sheeting forces are low but I never had a problem letting fly in a gust. I am wondering now if this is an unexpected benefit of the double sheeting system I use, rather than a single long mainsheet going through many blocks. This leads me to contemplate, for Little Dipper, to try tiny dyneema sheetlets, no more than 4 sheeting points, and paired mainsheets made of soft and very moderate diameter rope, which I have found works very well on Serendipity (the only difference being 5 sheeting points).

    Rather than lose some of the advantage of SJR (and also in order to test the limits at small scale) I will certainly go for 33% balance on Little Dipper, and try to reduce sheeting friction - rather than reduce sail balance.

    Last modified: 14 Jul 2021 02:35 | Anonymous member (Administrator)
  • 13 Jul 2021 19:21
    Reply # 10749034 on 10741742

    With that sheet system, you're pretty much using the running spanline and euphroes that Tom Colvin used, aren't you?

    Thanks for the info on geometry, David. I'm right on the limit, as drawn, which is where I want to be for investigative purposes.

    Thanks, too, for the caveat on the battens. I hadn't really taken on board that with a SJR, both ends tend to bend to leeward, putting more incidence on the jiblets, less on the main. This would very likely explain any bad behaviour. I am planning to use 22mm x 20mm x 2000mm carbon fibre battens which should be OK, I think.

  • 13 Jul 2021 16:37
    Reply # 10748653 on 10741742

    For quicker sheeting, you might consider the "Ahs-up" style of sheeting mentioned in one of the magazines a few years ago.


    It used a split system with a single sheet for the helm, attached via a turning block on the transom, to a triple block, through which the conventional Junk style of sheeting was attached to the battens.

    The author used it on his Sabot dinghy and when he reefed, he tied off the excess Junk sheeting line at the batten end.


    I modified it slightly and brought the end of the line forward to the mast, through a turning block and down to a cleat on my tabernacle.


    It worked well enough and meant that, in a gust, the helm sheet only had to run through a single turning block on the transom, and not through multiple turning blocks on the batten ends and triple block.  Giving a much quicker response to release of the sheet.


    Disadvantage is having to make a further adjustment of the Junk line each time you reef, to get the twist out of the sail.


    I would be careful about the amount of SJR sail area you put in front of the mast on an unballasted dinghy.

    Too much and it definitely will not feather.  Certainly no more than about 25% of total sail area maybe less in an unballasted dinghy, with the luff not more than 33% ahead of the mast centre line.

    I misunderstood Slieve's original instructions, put 33% of sail area in front of the mast, plus the split, and in one particularly heavy gust, the sail didn't feather and I powered along, basically out of control,  until the gust passed. Lighter gusts, fine. The heavy one, NO!.

    The fact the Wayfarer has a lot of stability for an unballasted dinghy and I hiked like crazy is what saved me from a bath. 

    Apart from that one incident, it was great. Went upwind and uptide, fast downwind and easy to reef or drop completely. Ideal for a solo sailor.  

    Having battens which were too small (19mm) and possibly bending in that bigger gust, simulating sheeting in, as the luff of the jiblet got pushed to leeward, but the leech stayed where it was, may also have contributed to the problem in the large gust. Feathered no problem in smaller gusts, despite the wrong dimensions.


    Unfortunately, I still haven't got to sail it since 2017 due to lack of time, family circumstances and now Covid, but have a new set of jiblets with larger dia battens ready to go, whenever circumstances change.


    Anyway, have a look at "Ah-sup's" sheeting arrangement for a potentially quicker sail response in a gust.

    Dave




    Last modified: 13 Jul 2021 16:46 | Anonymous member
  • 13 Jul 2021 16:37
    Reply # 10748651 on 10741742
    Anonymous member (Administrator)

    I like David’s 4-panel Halibut-SibLim sail.
    My original 3-panel ‘Halibut Special’ rig was a half-hearted go on making an aux. rig for Halibut. Requirement No. 1 was quick reefing, and thereafter stowing along the mast within 60 seconds.
    By adding a fourth panel and generally increasing its seize, David has made a much more useful sail, which still can be stowed along a mast  -   and which btw. is not longer than the boat.

    I think little balance is better on a JR which is smaller than 10-15sqm. Apart from the discussed ability to spill the wind in a gust, there is the problem of sheeting out the sail in very light winds. If the sheet has to run over three sheaves, a high-balance sail will struggle. The 10sqm sail of my Broremann had only 10% balance, but was still easy to sheet, and the sail swung out just fine in any wind when I let the sheet go  -  even though the mast had a little aft rake.

    Arne


    Last modified: 13 Jul 2021 16:38 | Anonymous member (Administrator)
  • 13 Jul 2021 12:00
    Reply # 10748097 on 10741742

    Yes, Graeme, I think you're right. A maximum of four sheeted points, preferably three.


    Last modified: 13 Jul 2021 12:38 | Anonymous member
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