The "Sib-Lim" Challenge

  • 10 Mar 2015 03:00
    Reply # 3245891 on 3244995
    Deleted user
    David Webb wrote:

    David T's,

    have you thought of a drop keel?


    Yes a drop keel and ballast bulb is certainly an option but introduces more complication in terms of a dagger board case intruding on the accommodation and some sort of lifting mechanism is needed. It would certainly get the ballast down where it is going to do the most good and this could result in less ballast being required. I think these keels don't necessarily need to be all that difficult to build in themselves based on some designs I have seen.

    Another option is twin keels as used by the French RM yacht designs, basically an updated version of the old bilge keels but of the fin and bulb configuration. This would have the disadvantage of increasing the draft but would allow the boat to sit upright when aground. If draft could be kept down to 800mm to 900mm that would be fine with me. I imagine that twin keels would be easier to engineer than one single center keel with all the righting moment acting on one part of the hull.

    Another option is a combination an external ballast shoe and also some internal water ballast. The water ballast could be under the cabin sole, or higher up on the hull in the space between the dagger board cases and the hull, because I think the dagger boards are canted inward at the top. Water ballast which could be dumped when not needed for stability would be one way of keeping the boat lighter.

  • 09 Mar 2015 02:16
    Reply # 3244995 on 3144241

    David T's,

    have you thought of a drop keel? I used one on a Warwick Stratus that I modified a few years ago. The original IOR type keel had a weight of half a ton, but the center of gravity was only 19 inches below the waterline. I took the tip of this keel and made a wing shape from it and hung it on the bottom of a wooden drop keel that went down to seven feet below the water when fully submerged. This meant that the 200 kilogram ballast weight had a greater righting moment than the half ton of the original keel, so much better sailing performance, lower overall weight and better righting moment. while still maintaining the shallow draft with the keel up. I also installed a sliding rudder blade to allow some rudder control when in the up position. I originally  installed a manual winch to raise and lower thr keel, but the subsequent owner installed an electric winch that made it much easier to raise and lower. She regularly exceeded ten knots and could be driven directly on to the beach and walk ashore in ankle deep water.

     I hope that this gives more food for thought.

    David Webb

    I still think this needs a new thread!!

    Last modified: 09 Mar 2015 02:17 | Anonymous member
  • 08 Mar 2015 22:34
    Reply # 3244921 on 3244650
    David Thatcher wrote:

    Thank you for that. It would be interesting to see the modified modelling. 

    Two views with the wider transom are now in my Sib-Lim album.

    More waterline length equates with a harder shape to build, with more twist in the sloping hull panels around the forefoot, and I wanted to make it as easy as possible for Annie. Also, the sloping forefoot rides over any obstructions that place themselves in your path, a feature that has saved my face on more than one occasion. It's better to slide gracefully onto the top of a rock than to butt it head-on!

    I think it's possible to reduce the displacement to 2 tonnes, if the interior is very simple - more of a camping cruiser than a home. But if you don't want a deep keel, I don't think that's an option, as I firmly believe that a shoal draught boat needs to be reasonably heavy. 

    For the deck, I'm thinking in terms of two strong deck stringers 4ft apart. Outboard of these, the deck to be flat, but angled at 20 degrees to horizontal. This makes the plane surface of the deck meet the sheerline very neatly, with no compound curvature. Between the two stringers, there are options: a curved crown, a flat horizontal surface forward of a wedge shaped companionway, a coachroof, or anything else you can think of.

  • 08 Mar 2015 07:05
    Reply # 3244650 on 3244484
    Deleted user
    David Tyler wrote:

    David T, (the other one, that is),

    I've tried widening Siblim's transom, following your remarks, and I think it improves both the looks and the cockpit space. I just moved the topsides apart a little, without touching the underwater shape, so performance would be unchanged. Whether Annie will be inclined to go that way, I don't know, but I see no reason that she shouldn't. 

    What I can't do is to both decrease the displacement and increase the headroom. Indeed, if the displacement is decreased, then then headroom should actually be decreased, to sitting headroom, not standing headroom, on this size of vessel. You want a sport-boat, and as such, it ought to have a deep fin keel with a lead torpedo, sitting headroom, minimal accomodation, etc - all the antithesis of Annie's needs. I can see how you could put a mini-coachroof on Siblim as drawn, for headroom, but still at 3 tonnes displacement. If you then add a deep fin, for stability, you can then add a big high rig, to power the three tonnes displacement more than Annie needs to do.


    Thank you for that. It would be interesting to see the modified modelling. I basically like very much the shape you have come up with. I have been studying some hull profiles for the more modern style down wind and reaching flyers. They all still have reasonably narrow sterns at the waterline. I would still like to see more waterline length, only because I have always thought that the longer the waterline the greater the speed potential of the boat. A deep fin and bulb would certainly add power and sail carrying ability but compromise the ability to get into shallow water anchorages. Maybe the answer for me would be to go with the basics of your design, add a bigger rig for lots of reaching and downwind power, because being a junk rig it is easy to get rid of sail quickly when needed. I have been looking at mini transat designs and other box rule boats which basically seem get their speed from light construction using high tech materials, which does not equate to the honest wood construction that Annie and I both favor, canting keels for forced stability, and big rigs. I don't want a canting keel or even a deep keel, way too complicated so I still like the idea of minimal draft with asymmetric dagger boards to add upwind capability. Every boat is a compromise.

    In terms of extra headroom the only place that is required is where you need to stand to do things, so the galley and maybe the head. So a raised coach roof style set up at the aft end of the cabin which could form part of the companionway is probably all that is needed. In areas of the interior where all you are going to do is sit full headroom is not required.

    I very much love Footprints and she is a great boat for family cruising, but the idea of a smaller lighter boat with lighter gear certainly appeals. 

    Last modified: 08 Mar 2015 19:04 | Deleted user
  • 07 Mar 2015 22:56
    Reply # 3244484 on 3144241

    David T, (the other one, that is),

    I've tried widening Siblim's transom, following your remarks, and I think it improves both the looks and the cockpit space. I just moved the topsides apart a little, without touching the underwater shape, so performance would be unchanged. Whether Annie will be inclined to go that way, I don't know, but I see no reason that she shouldn't. 

    What I can't do is to both decrease the displacement and increase the headroom. Indeed, if the displacement is decreased, then then headroom should actually be decreased, to sitting headroom, not standing headroom, on this size of vessel. You want a sport-boat, and as such, it ought to have a deep fin keel with a lead torpedo, sitting headroom, minimal accomodation, etc - all the antithesis of Annie's needs. I can see how you could put a mini-coachroof on Siblim as drawn, for headroom, but still at 3 tonnes displacement. If you then add a deep fin, for stability, you can then add a big high rig, to power the three tonnes displacement more than Annie needs to do.

  • 03 Mar 2015 18:41
    Reply # 3241063 on 3240351
    Deleted user
    David Webb wrote:

    David Thatcher, I have added two photographs of my Webb 18 design to thw Illustrations section of the Technical Forum. They are from Danny Greens book Cruising Sailboat Kinetics which is all the information I have available to hand at the moment. The original drawings are in storage until the new room is completed. I hope there is sufficient information for you to judge whether a 26 foot version may suit your needs, Junk rigged of course!

    I look forward to your feedback and maybe this subject should be moved to a new topic.

    David Webb 


    Yes, that is more the hull shape I am after, maximizing waterline length and quite beamy in the stern. The raised deck hull form work well for maximized interior space. I have a few days off work next week so I am going to try and put down my own concept on paper. I also like what David Tyler has done in his design re making the boat look a bit 'Chinese junk' which was to Annie's request. Just about all yachts look the same so it is nice when you own something a bit different as is the case with 'Footprints', it is a great conversation starter!
  • 03 Mar 2015 07:19
    Reply # 3240351 on 3144241

    David Thatcher, I have added two photographs of my Webb 18 design to thw Illustrations section of the Technical Forum. They are from Danny Greens book Cruising Sailboat Kinetics which is all the information I have available to hand at the moment. The original drawings are in storage until the new room is completed. I hope there is sufficient information for you to judge whether a 26 foot version may suit your needs, Junk rigged of course!

    I look forward to your feedback and maybe this subject should be moved to a new topic.

    David Webb 

    Last modified: 03 Mar 2015 07:21 | Anonymous member
  • 24 Feb 2015 22:18
    Reply # 3234317 on 3144241
    Deleted user

    OK, interior layout is here.

    Last modified: 24 Feb 2015 22:19 | Deleted user
  • 21 Feb 2015 18:40
    Reply # 3231491 on 3231041
    Annie Hill wrote:
     
    My plan, if you could call it such a thing,


    It sounds like a plan to me!

    And the great thing about your Challenge, I suggest, is that you do appear to be in earnest ... and that there is money available ... and your boat might just get built.  (Sorry I will rephrase that from passive to active!)  you might just build your boat. 

    I hope that this will encourage all who might feel that they have something to offer on the design.

    There is of course something missing in the equation which would appear to be a number of years of 'blood, toil, tears and ... "

    I couldn't do it! Personally I like to buy my boats ready made. 

  • 20 Feb 2015 23:29
    Reply # 3231117 on 3144241
    Deleted user

    Hmmmm. Galley is kinda' cramped. Can you do with one pot, one pan and one mug? ;)

    Last modified: 20 Feb 2015 23:29 | Deleted user
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