The "Sib-Lim" Challenge

  • 09 Jan 2015 02:07
    Reply # 3185542 on 3144241
    I did consider long and thin over short and fat, but feel that a slim hull is inherently more tender.  Due to my wish for shoal draught this could be difficult to counteract, although I might be wrong here.  And, ridiculous though this might sound, the extra 6 feet of length is surprisingly noticeable when attempting to wriggle into a crowded anchorage and find a space.  Again, my wish for shoal draught is to get to the head of the bay where fewer boats dare go. 


    It's very kind of David to say that I am being rational and logical in my list of desiderata.  They all make sense to me, but I'm sure that there's as much prejudice as sound sense in my reasoning.  And I confess that I rather like short fat boats, even though I'm only too aware of the fact that the performance may be less than a long thin one.  At the end of the day, however, I spend far more time not sailing than I do sailing (and that was the case even when I voyaged).  The sense of space in a beamier boat is important to me and I'm prepared to make sacrifices to achieve a more satisfactory home.

    David and I have been discussing his design off forum and I'm very impressed at how he has been able to tweak his boat better to suit my requirements: at the end of the day, however, the family resemblance to Tystie is still there.  I'm also terribly impressed by all the calculations that he has been able to make - even if I don't understand them all!  It is very interesting to compare them with Gary Underwood's Shoehorn, which is where this all started.  At the first NZ junket, in fact! 

  • 08 Jan 2015 04:12
    Reply # 3183945 on 3144241

    We're in danger of straying rather a long way from the point. With a sea mileage somewhere in excess of six figures (gallantry prevents me from saying how many decades this has been spread over), Annie has a very clear concept of what kind of boat she is happy to live on, and what kind of boat she can build, and afford to build, and she has laid down a clear list of her requirements.  The task she has set us is to design a boat that covers as many of those requirements as we can manage. 3 tons of displacement, on a LOA of 26ft and a LWL of say 22ft 6in, gives a very wholesome and live-able D/L ratio of around 260. A longer boat at this weight would be more lively than is desirable, as a permanent home, and would require a higher tech structure than Annie wishes to build and than she wishes to afford.

    Now that I have Freeship to work with, I've been able to model the hull and deck, and check some of the figures for my design:

    Length over all : 7.958 [m]
    Beam over all : 2.962 [m]
    Design draft : 0.510 [m]
    Midship location : 3.980 [m]
    Volume properties:
    Displaced volume : 2.968 [m3]
    Displacement : 3.042 [tonnes]
    Total length of submerged body : 6.950 [m]
    Total beam of submerged body : 2.502 [m]
    Block coefficient : 0.3346
    Prismatic coefficient : 0.5733
    Vert. prismatic coefficient : 0.4931
    Wetted surface area : 13.501 [m2]
    Longitudinal center of buoyancy : 3.938 [m]
    Longitudinal center of buoyancy : -0.610 [%]
    Vertical center of buoyancy : 0.336 [m]
    Midship properties:
    Midship section area : 0.745 [m2]
    Midship coefficient : 0.5837
    Waterplane properties:
    Length on waterline : 6.950 [m]
    Beam on waterline : 2.502 [m]
    Waterplane area : 11.802 [m2]
    Waterplane coefficient : 0.6786
    Waterplane center of floatation : 3.708 [m]
    Entrance angle : 7.579 [degr.]
    Transverse moment of inertia : 4.148 [m4]
    Longitudinal moment of inertia : 30.165 [m4]
    Initial stability:
    Transverse metacentric height : 1.734 [m]
    Longitudinal metacentric height : 10.499 [m]
    Lateral plane:
    Lateral area : 2.558 [m2]
    Longitudinal center of effort : 4.230 [m]
    Vertical center of effort : 0.296 [m]
    Approximate weight of hull and deck 0.851 tonnes

    Sectional areas:
    | Location | Area |
    | [m] | [m2] |
    |-----------+----------|
    | 0.950 | 0.096 |
    | 1.900 | 0.371 |
    | 2.850 | 0.622 |
    | 3.800 | 0.747 |
    | 4.750 | 0.671 |
    | 5.700 | 0.473 |
    | 6.650 | 0.161 |
    | 7.600 | 0.000 |
    |-----------+----------|

  • 07 Jan 2015 13:58
    Reply # 3182819 on 3144241

    Is considering the length as (the most) important governing factor a mistake?  Is the cost of a boat more related to the displacement.  A longer / thinner boat may serve the other criteria as well and certainly sail better.  It is only the need to pay marina fees that dictate short fat caravan-yacht.


    My preferred layout:

    Stern locker, 0 to 2ft.

    Full waterproof bulkhead.

    Cockpit, 4 to 5ft.

    Entrance, 3 to 4ft - This is a key area when sailing, it is a transition between the dry interior and wet cockpit. In colder climates it is where you wish to be.  Everything is to hand and the main cabin stays dry.  Contains: Navigation & emergency equipment,  Toilet, Hanging space for oilies,  reclining seat for catnapping.

    Full waterproof bulkhead.

    Kitchen 3 to 4ft - a semi dry space.  The kettle should be reachable from the entrance.   Wood stove one side.

    Half bulkhead, in emergency / storm could be infilled to above the waterline.

    Sitting 6 to 7ft.  Removable dining table,  visitor bunks.

    Full waterproof bulkhead.

    Bedroom, 6 to 7ft. 

    Full waterproof bulkhead.

    Locker 3 to 5ft.  For lightweight objects - fenders, ropes.  Anchor locker, if full chain, one bulkhead back.

    O/A length 25 to 34ft  Beam,  say 6ft. 


    cheers Mark


  • 06 Jan 2015 20:28
    Reply # 3182166 on 3182044
    Robert Biegler wrote:
    Annie Hill wrote:I like to be able to tack instantly when I'm headed in a confined area and there is no way I want to play with a balance jib.  I can see the appeal of a proa, but not for me.

    Well of course, make a suggestion of your own: this is what the Sib-Lim Challenge is all about!!
    I find it doesn't meet your requirements.  I was thinking of a monohull proa, stabilised by a foil to windward instead of a hull.
    That's certainly an interesting idea. It could have buoyancy as well instead of "just being a foil". Although maybe not. The amount of buoyancy to make a difference while under way would uncomfortably make the hull heel the other way when not sailing. Thinking aloud, sorry! Have you tried your model in rough weather? I suspect you'd still want ballast with just the fin which would mean we're probably better off with an ama. 

    PS. Yey, finally the WA editor  works with Chrome/Android! 

  • 06 Jan 2015 17:33
    Reply # 3182044 on 3179718
    Annie Hill wrote:I like to be able to tack instantly when I'm headed in a confined area and there is no way I want to play with a balance jib.  I can see the appeal of a proa, but not for me.

    Well of course, make a suggestion of your own: this is what the Sib-Lim Challenge is all about!!
    I find it doesn't meet your requirements.  I was thinking of a monohull proa, stabilised by a foil to windward instead of a hull.  My aim is good average speed without either having to babysit the boat every moment in strong wind or relying on a deep keel.  But the boat would have to shunt.  It couldn't be tacked by simply putting the helm down.  I tried the foil idea on a tacking model boat, but although it had greater stability, it was slower than its equivalent with a keel (perhaps more wave drag from two more things breaking the surface), and tacking was slower.
  • 05 Jan 2015 12:10
    Reply # 3181065 on 3144241

    I received this as part of a Christmas message from a Dutch friend:

    All my best thoughts were stolen by the ancients. (Ralph Waldo Emerson)

    That might just be appropriate for JR design. 

     

     

  • 03 Jan 2015 18:43
    Reply # 3180105 on 3144241

    I've used a small bow transom, above a sharper stem. This gives more room for anchor handling.  I wouldn't want to use a deeper transom unless it was very well angled, which detracts from the waterline length.

  • 03 Jan 2015 10:55
    Reply # 3180017 on 3179615
    David Tyler wrote:

    There are the hydrostatic calculations to do, and the bow needs to be modelled, virtually or as a hard model, as I can't be sure of exactly how the shape should be, on the basis of the 2D drawing.


    David

    Have you considered a 'pram' bow?  Makes for easier construction and fits nicely with the 'Chinese' aesthetic.

    Peter S

     

  • 02 Jan 2015 21:14
    Reply # 3179803 on 3179784
    Shemaya Laurel wrote:

    Copper on the bottom is not in the running? Expensive initially, but then no more buying bottom paint… And the five panel hull would make copper sheathing so easy!

    Shemaya

    Wouldn't that be nice, Shemaya? I would choose that option, on a high budget, but a quick look at prices indicates that enough 1/4" hard copper plate to make a grounding protection plate alone would cost $1500 USD.
  • 02 Jan 2015 20:42
    Reply # 3179784 on 3144241

    Copper on the bottom is not in the running? Expensive initially, but then no more buying bottom paint… And the five panel hull would make copper sheathing so easy!

    Shemaya

       " ...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