The "Sib-Lim" Challenge

  • 23 Jul 2015 17:15
    Reply # 3446280 on 3144241
    Anonymous member (Administrator)

    Ah, Annie,
    I see now that the displacement spec has always been at 3 tons. I haven't followed this thread for a while, so had forgotten. However, I am still worried that it will be difficult to make a 26' boat boat with 3 tons displacement and shoal draught sail well to windward. A coastal cruiser must sail well to windward unless one is willing to use the motor a good deal.

    Arne 

    Last modified: 23 Jul 2015 19:47 | Anonymous member (Administrator)
  • 23 Jul 2015 05:48
    Reply # 3445627 on 3441311
    Arne Kverneland wrote:

    Set the LOA free

    Now that the loaded displacement has been increased to 3000kg, it appears to me that the set LOA limit of 26’ or 8m is too short. Initially the displacement was set to 2500kg (right?) and that would be ok in an 8m boat.

    No, the displacement was always set at 3000 kg: I wanted the same length as I have now, but felt it should be designed to carry more weight than my existing boat.

    There are several good reasons for setting the LOA free, resulting in a 9m boat (or thereabouts):

    • ·         The boat will sail better, in particular to windward and in a seaway. Higher speed means less leeway. The result is more sailing and less motoring.
    • ·         The boat will be faster or use less fuel when motoring, even with the same engine as was planned for the 8m version.
    • ·         As a result, over time, the longer boat will save fuel costs.
    • ·         The sail area does not need to be increased and there will be better room for the JR sheeting, which will solve many of the problems seen on short junks with very steep sheeting angles.

    I don't think it's necessary to have a low aspect ratio rig on the boat, so there should be no real need for very steep sheeting angles.

    • ·         That extra meter of waterline length will make the interior less cramped. Adding a few inches here and there will make a lot of difference in use.
    • ·         Building the thing will probably be easier, as the planking will be straighter, as long as the beam is not increased as well. The extra material cost will add a minor percentage to the whole building budget. Remember, a 9m 3-tonner will not need more equipment (winces, anchors, radios etc) than an 8m 3-tonner.
    • ·         Since the Sib-Lim is mainly to live at anchor and not be using marinas, I cannot see that one extra meter of length will generate much extra costs of keeping, except for a few teacups of paint.

    As it is now, I can’t help feeling that the tight LOA limit tends to result in contenders that look a bit cramped inside and tubby outside, which probably will result in reduced comfort and sub-optimal performance.

    Cheers,
    Arne

    Arne, as ever, you speak much sense.  But my views, however odd they may seem to others, are what they are.  The dream is a boat that suits that strange woman called Annie Hill, and no-one has ever described her as the most rational creature on the planet.  My main reason for wanting a maximum of 8m is that it is the length of boat I have at present and I find it very handy.  The extra metre that you suggest I should have may not add to the displacement of the boat, but would add to the windage and, to be honest, I shouldn't be happy anchoring a 9m boat on a 10k anchor.  So I would have to upgrade to 15k.

    One of the things that has really surprised me, and continues to do so, is that my 8 metre boat really does seem to be able to shoehorn herself into anchorages where there would apparently be no room for a longer boat.

    If it were possible, I would wave a magic wand over Fantail, transforming her into a new wooden boat with bilge/leeboards and a transom stern.  I love her size, her accommodation, her manoevrability under sail.  I dislike her age, the fact that she's commercially built of GRP, her draught and her complex, inboard engine and would be a lot happier without those elements.
  • 23 Jul 2015 05:36
    Reply # 3445623 on 3144241
    To David (Thatcher).  I can see why Catboat 696 has caught your eye, David.  I'm sure she'd sail very well, but the fixed twin keels aren't what I really want.  However, I'll bet she'll be fast to build - as well as to sail!
  • 23 Jul 2015 05:30
    Reply # 3445622 on 3437801
    Iain Grigor wrote:

    Okay, what about the Tilikum 32' centreboard barge, from Tad Roberts Yacht Design?  Twin centreboards, draught 1'8" boards up, junk yawl, circa 33% ballast ratio, sa/dislacement 17 to 1.  From the profile drawing, this strikes me as a very sexy and versatile boat.  Perhaps she could be scaled down a bit, for Annie's needs?

    Well, apart from the minor details that she's too long, too heavy and that I don't want centreboards, I dare say she would be just fine for me!  The object of the exercise is to find a design of the right size, not to alter one that already exists, because scaling down (or up) is not a simple arithmetical exercise.
  • 23 Jul 2015 05:26
    Reply # 3445604 on 3439428
    Paul Thompson wrote:

    Talking about Tad Roberts designs, I'd say that this one the Harry 26, pretty much does everything Annie wants. Tad has even designed a junk rig for it.

    My ability to convert from pounds to kilos isn't all it could be, but I would reckon that 10,715 lbs is approximately 1.8 tons too heavy!
  • 23 Jul 2015 05:17
    Reply # 3445601 on 3441311
    Arne Kverneland wrote:

    Set the LOA free

    Now that the loaded displacement has been increased to 3000kg,

    If I may quote from my original challenge:

    The boat has to be simple to build and inexpensive

    About 3 ton(ne)s displacement.

    Hull: 26ft (8m) or less, wood of some sort.



  • 22 Jul 2015 02:57
    Reply # 3444093 on 3144241

    Arnie you are correct, it would free up the accommodation no end and cost usually goes by the weight rather than the length so if the displacement is fixed then the cost varies very little if the length is changed, as long as you stay within moderate parameters.

    David Tyler. With regard to your comment about the bilge board thickness on my Puffin design. Does the thickness you suggest of 12% apply to fully asymmetrical boards or is it for symmetrical foils? I am not an expert on this subject but my experience has been that an asymmetrical foil can be quite a lot thinner without stalling, is this correct? I could increase the thickness to three inches, about 8% chord thickness, with little change to the accommodation but the weight of the board would increase and may be beyond Annie's capacity to manage if constructed of hardwood as I suggest. It could be built of lighter material but then the strength  and ability to absorb knocks could suffer. Also the displaced volume would increase and require a greater weight to make the board drop. As with all things in boat design it is a matter of compromise.

     


  • 20 Jul 2015 10:07
    Reply # 3441311 on 3144241
    Anonymous member (Administrator)

    Set the LOA free

    Now that the loaded displacement has been increased to 3000kg, it appears to me that the set LOA limit of 26’ or 8m is too short. Initially the displacement was set to 2500kg (right?) and that would be ok in an 8m boat.

    There are several good reasons for setting the LOA free, resulting in a 9m boat (or thereabouts):

    • ·         The boat will sail better, in particular to windward and in a seaway. Higher speed means less leeway. The result is more sailing and less motoring.
    • ·         The boat will be faster or use less fuel when motoring, even with the same engine as was planned for the 8m version.
    • ·         As a result, over time, the longer boat will save fuel costs.
    • ·         The sail area does not need to be increased and there will be better room for the JR sheeting, which will solve many of the problems seen on short junks with very steep sheeting angles.
    • ·         That extra meter of waterline length will make the interior less cramped. Adding a few inches here and there will make a lot of difference in use.
    • ·         Building the thing will probably be easier, as the planking will be straighter, as long as the beam is not increased as well. The extra material cost will add a minor percentage to the whole building budget. Remember, a 9m 3-tonner will not need more equipment (winces, anchors, radios etc) than an 8m 3-tonner.
    • ·         Since the Sib-Lim is mainly to live at anchor and not be using marinas, I cannot see that one extra meter of length will generate much extra costs of keeping, except for a few teacups of paint.

    As it is now, I can’t help feeling that the tight LOA limit tends to result in contenders that look a bit cramped inside and tubby outside, which probably will result in reduced comfort and sub-optimal performance.

    Cheers,
    Arne

     

    Last modified: 21 Jul 2015 08:27 | Anonymous member (Administrator)
  • 18 Jul 2015 01:07
    Reply # 3439432 on 3439428
    Paul Thompson wrote:

    Talking about Tad Roberts designs, I'd say that this one the Harry 26, pretty much does everything Annie wants. Tad has even designed a junk rig for it.


    It looks like a lot of boat for the length but I don't know about that flat bottom and pram bow for bashing up and down our northern coast in adverse weather and sea conditions. Just goes to show how difficult it is to get everything you want in a small boat - there is going to be compromise somewhere.

    There is another website here with some interesting multi-chine small cruisers, many of which I like the look of.

     https://chantiermer.wordpress.com/productions/144-2/

    The boats all look as if they could easily be converted to junk rig and all have shoal draft hulls. None of the designs seem to be load carriers though so would be more suited to casual use rather than as live aboard boats.

    Last modified: 19 Jul 2015 04:36 | Anonymous member
  • 18 Jul 2015 00:45
    Reply # 3439428 on 3144241

    Talking about Tad Roberts designs, I'd say that this one the Harry 26, pretty much does everything Annie wants. Tad has even designed a junk rig for it.

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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