The "Sib-Lim" Challenge

  • 20 Aug 2015 23:30
    Reply # 3489832 on 3144241
    I have been doing a lot of thinking, calculating, pondering, and agonising over the three fantastic designs that have been suggested to me.  It's cost me more than a few sleepless nights, in truth.  I am fully aware of the fact that I could use a design already available, or, for that matter, buy a centre-boarder and achieve more than a few of my desiderata.  However, as time has gone by I've found myself more and more attracted to the idea of creating a boat that ticks as many boxes as possible, to end up with a new boat to see me out, and to have something simple and pleasing to my own personal ethos and aesthetic.

    In the end, I've decided to go with David Tyler's design.  I love its jauntiness and its 'feel'.  The two other contenders also had a huge amount going for them: they both had wonderful accommodation and I found the overall appearance of David Webb's design very appealing.  The fact that David Tyler has just come back to New Zealand for six months and is offering to help me build his design is a great bonus, but if I hadn't preferred his design overall, I really don't believe that it would have swung the decision.  But thank you so much, David (W) and Hampus, for all the work you have put in to your designs.  I very much hope that you will complete them (although David Webb's is just about there) and that some other JRA member will build one.  They are both intriguing and clever designs that deserve to be translated into three dimensions.

    So now I start haemorrhaging money and the project is underway as David creates a 5:1 model to see if his ideas work and so that I can visualise what the Real Thing will look like.  I suspect we'll see a few changes to the design on the way, but  I hope it will be enormous fun and tremendously satisfying for both of us.

  • 03 Aug 2015 22:39
    Reply # 3463307 on 3144241

    Hi Annie,

    have you looked at the leeboards on my Rodark design on my page in Box. This type of board could be a good alternative for Puffin. They would clear the interior of the boat from the complexity and intrusion of the bilge boards, and the main stresses from the leeboard hinges would be transferred to the bulkhead forward of the head. The hinge is made from a very robust "T" made from stainless rod, a salvaged 1 1/2 inch prop shaft would be good as a source of material. This would be held to the board by a pair of stainless straps bolted to the solid hardwood boards. The inboard end would pass through a strong angle bracket bolted to the hull and bulkhead. The hole through the hull would be a section of 2 inch stainless pipe welded to the inner bracket with a nylon bearing inside. The friction at the hull would be mitigated by a 1/2 inch nylon bearing plate screwed to the hull with a corresponding stainless steel plate on the leeboard. High density rubber sealing washers would be installed inside and out to prevent water ingress.

      The solid hardwood boards should deploy without additional ballast, however if needed a steel shoe could be bolted to the leading edge at the base. This would then allow you to use the board as a depth sounder in shallow water, without damaging the board. A lifting tackle at the back would be easily accessible from the cockpit for raising and lowering the boards.

       Anyway have a look at Rodark and let me know if you think they would be a better alternative for Puffin.

    David.

    Last modified: 04 Aug 2015 21:56 | Anonymous member
  • 03 Aug 2015 13:26
    Reply # 3462553 on 3144241

    Having had to re-build 4 timber foils on a catamaran - 2 daggers boards & 2 rudders, with hindsight I wished I had built complete new ones out of grp.  They take a bashing so anything that can eventually rot is not so good.

    The method would be to make a half mould which can make each side of the foil, then stick together and foam fill.  The rudders would use the same mould, modified to be less wide.

    Dagger boards where fine, though good dense foam crash-blocks at the rear of the trunk should be incorporated.

    Last modified: 03 Aug 2015 13:27 | Anonymous member
  • 03 Aug 2015 01:06
    Reply # 3461909 on 3144241
    I don't think I said I had anything against leeboards.  Just as long as they are sufficiently stout and don't go 'clunk, clunk' all the time at anchor!  In all other respects, I find their essential simplicity very appealing. 
  • 31 Jul 2015 05:44
    Reply # 3458528 on 3144241

    Reading through Grahams comments on centerboards and dagger boards reminded me of the boats I have owned which had such arrangements, and also reminded me that each time I have had a boat with such an arrangement I have said; 'Never again!" My Searunner trimaran had a hinged centerboard which had positive buoyancy. It had to be winched down but when raising popped up very quickly by releasing the downhaul line. I always had to haul it up the last bit with an up haul line but it was no effort because of the buoyancy in the board. But there came a time when the fiberglass wore away completely from the inside of the centerboard trunk allowing toredo worm in, which eventually resulted in a bilge full of water and some very unpleasant experiences trying to repair the inside of the trunk.

    Another trimaran had a dagger board, quite large, which was a less complex system but it was forever getting jammed in the case unless it went up and down at exactly the right angle. If I was doing a dagger board again I think I would make sure that all the contact points on the board, or the case, had polysuperslippery plastic on them to encourage easy raising and lowering. 

    Although the idea of a centerboard or daggerboard appeals for the shallow draft they sometimes seem more trouble than they are worth. That is why I think I would be more content with a fixed keel provided the draft was under 1m, or as has also been discussed exploring the idea of a modern interpretation of a leeboard. I have seen them on a couple of yachts where they worked quite well.

  • 30 Jul 2015 09:32
    Reply # 3457295 on 3144241

    I don't think the boards need to be ballasted, or heavy enough to sink.  That would be true with a centreboard that needs to sink under its own weight, but you can use one tackle to push the board down and another to pull it up.  When you release the "down" tackle, if the board is not under load, then it will come up easily.  I've seen them pop up on their own!  But usually they need a little tug.  With the lever arm provided by a 5:1 tackle, and the directional effect of the case - the pressure from the tackle can only go in one direction, either up or down - the boards should go up and down easily.

    Especially if you put the windward board down just before you tack, when it will have minimal load on it, then haul up the board that was previously to leeward after the tack is complete.  If you were willing to cant the boards inboard at the top by 15 - 20 degrees - whatever the optimal heel of the vessel to windward in 15-20 knots of wind - then the leeward board would be vertical, and you could leave both boards down when short-tacking as the windward board would be canted out at 30-40 degrees and would be providing some righting moment, if it was doing anything.  The top of the cases would take up a bit more space, of course, but you could always stow your wine bottles behind them!

    If the boards are built from appropriate structural closed cell foam, with splines, rather like a surfboard, maybe even 6mm thick carbon fibre splines, with some exotics in the epoxy layup, it will be massively strong.

    I'm not saying this is the only way to do it, just the way I would.  I might even be wrong, since my daggerboard experience has all been on multihulls. Even though these boards are going on a monohull, though, it is a small boat and the boards are proportionately small as well.

    Annie, you said you wanted some lively debate about the Sib Lim challenge, and you are getting it!

    PS: (just added this)  Ballasted leeboards may well be the easiest solution here, which can be raised and lowered effortlessly from the cockpit with a single tackle on each board.  I sailed with this set up on Grace Ellen in 2014 and was impressed.  If the hinge pins and their brackets are strong enough, they are structurally very robust.  My experience of daggerboards is that you may well have to step up onto the deck at times to "encourage" them to go up or down, due to pressure on the boards in the case. Since the boat is moving, there will always be some pressure, and no amount of ballast will overcome this.

    Last modified: 30 Jul 2015 23:55 | Anonymous member
  • 30 Jul 2015 09:01
    Reply # 3457286 on 3144241

    Hi Annie,

    my figures for the board were displacement of water, not the board weight. In order for a four inch thick board to sink to the depth indicated on my design, a fully enclosed board would have to weigh at least 200 pounds, otherwise it will float back up the slot!! When fully raised then all of this weight has to be lifted. Most of the boards on catamarans etc have a very short chord length so their thickness is much less so they need much less weight to submerge them. Puffin needs a much bigger area because of her slower normal speed and large sail area, and to make the boards a reasonable length so that the draft is reasonable when they are deployed. The fully flooding and draining boards appear to be the best solution. unless you change to a leeboard solution, but you have shown some reticence about using these.

    Anyway it is all a compromise, just about choosing the best one for you.

    David.

  • 30 Jul 2015 08:04
    Reply # 3457255 on 3457069
    Anonymous member (Administrator)
    Dear Arne

    Your insistence on my lack of sanity here is wearing me down.  I don't believe that I'm asking for the impossible.  Surely, the point is that when the boards are down, the boat isn't shoal draught?  And my design criteria are not producing a lightweight boat.  There is a trailer sailer, called the Noelex 25 that is very popular in New Zealand and they are not only sailed in open water, but regularly raced: and we get a fair bit of wind in this country.  If a trailer sailer, equally limited by design constraints, can be persuaded to go to windward, why can't my Sib-Lim concept?



    Annie,
    I hate to be the naysayer (or the devil’s solicitor ) here.

    I am sure (as said before) that the Sib-Lim contenders will stand up to quite some offshore conditions, better than that Noelex 25. With really big bilge- or leeboards (Noelex draws 1.4m with c.b. down) there may also be enough leeway resistance.
    It is just that the 3 ton Sib-Lims have 2.5times the displacement of the Noelex 25 on about the same waterline length. My fear is that this last factor, heavy displacement for the wl. length, will make the Sib-Lims slow, since there is little room for increasing the sail area.

    But enough grumbling from me on this thread,

    Good luck!

    Arne

  • 30 Jul 2015 06:05
    Reply # 3457158 on 3144241

    Displacement is not the only defining criterion for performance, of course.  One thinks of the gaff-cutter rigged, Falmouth Quay Punt,Curlew, which, at 28ft LOA and 10 tons displacement, regularly licked the racing fleet in various ports of the world.  She was a very different type of boat to Sib Lim, but if you have enough sail area and efficiently shaped bilge boards of sufficient depth, plus nice buttock lines (not too steep), then the boat will perform adequately for a cruising boat.  As Annie says, when the boards are down the boat is not a shallow draft vessel, as a bilge-keeler would be (Annie don't do it!).  Also, it is perfectly possible to design strong, light boards, the multihull crowd do it all the time.  Use a few exotics just in this place, foam, epoxy and kevlar!

  • 30 Jul 2015 02:07
    Reply # 3457070 on 3455587
    David Webb wrote:

    Arnie, David,

     at four inches thick and without holes in the bottom, the bilge boards, when fully immersed will displace about 200 pounds of water, my original two inch thick solid hardwood boards weighed in at about 130 pounds, still very heavy for Annie to lift. They will need to weigh well over 200 pounds if they are to deploy under their own weight. They will also need this much lift to fully raise them and I think that this will be too heavy for Annie to manage, correct me if I am wrong Annie. This is with no allowance for friction of the board in the case. If there are holes in the bottom then the structure of the board will weigh about 60 to 70 pounds and this is all that Annie will have to lift plus friction, but this is still marginal for her strength I would imagine. With a two to one tackle and a small winch I would see it as  quite possible. This would need a sheave embedded in the top of the board and a sheave with becket at deck level,  with the tail led back to the cockpit and a small winch on each side. If the boards are open at top and bottom then ant stones or mud could easily be dislodged with a stick poked down from deck level.  What are your thoughts Arnie, David, Annie.

    Hi David

    You are quite right: 200 lbs is way too heavy and a fair bit of the overall displacement.  However, if they are made of wood, surely a good portion of this weight will be supported by water?  There do seem, she said somewhat plaintively, do be other boats of this size sailing around with boards of manageable weight.  I assumed that there would be some sort of purchase to raise and lower the board; however, I don't think a winch would be acceptable: too slow and, equally to the point, too expensive.  I want to be able to rattle the boards up and down fairly smartly.

    I think I might just saw off Fantail's keel and add twin keels.

       " ...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