CARAVELINA - New JR scow minicruiser

  • 25 Oct 2019 13:32
    Reply # 8076918 on 7917477

    PJR suggests 5.2 oz/sq yd or 177 gsm for this size of sail, when conventional sailcloth is used. This is plenty strong enough for the whole sail.

    I have found that the cloth breaks down in three main areas:

    1. At the throat of the sail, due to cyclical loadings, first on one diagonal, then on the other. The answer is not heavier cloth, but patches that put the threadlines at an angle to the panels. Sailcloth can withstand a pull along the line of the threads, but is not so good at withstanding diagonal pulls.

    2. Down the leech, fluttering and flapping will cause breakdown. This happens more in the lower two panels than in the upper panels, because there is little or no tension in the cloth. The answer is to add a doubler all down the leech, about 300mm wide, if you want to make an ocean-going sail. Again, there is no point in using over-heavy cloth throughout the whole panel, and for cambered panels, lighter cloth will take shape better in light airs.

    3. Threadlines should be close to parallel or perpendicular to the edge of the sail, where the loads are concentrated, or the cloth gets distorted and will break down.

    I have never seen cloth breakdown in the top panels, once the peak and throat have been reinforced with patches, in the conventional sailmaker's fashion. So I don't think there's any need to use heavier cloth here.

  • 25 Oct 2019 12:36
    Reply # 8076837 on 7917477
    Anonymous member (Administrator)


    for those small sails, I think you could better use 100-130g/sqm in the lower panels, and 160-200g on the upper three panels. Even this is close to over-strong. The light forces in the sailcloth of a junk sail have to be experienced to be believed.
    A boltrope around the whole sail is very useful, though.


  • 25 Oct 2019 09:09
    Reply # 8076725 on 7917477

    Hi David,

    many thanks for your opinion, I think I will make both sails same with area of  12,5 - 13m2.

    The other idea about sails that bothers me - how if making the lower romb panels of lighter fabric (say 220g/m2)  and three or two top ones, which often work as a storm sails, of heavier - like 340g/m2 ? I think it is quite logical...

  • 24 Oct 2019 15:35
    Reply # 8075260 on 7917477

    I think this will be OK with the two sails at 12.5 sq m ...

    ... but adding the extra panel to the after sail is getting a little bit too greedy for maximum area, and I think it will be difficult to sheet it in enough.

  • 23 Oct 2019 17:55
    Reply # 8073632 on 7917477

    Hi everybody, I think I made my homework - see attached - and my new sail plan that includes suggestions (many thanks :) ) is more proper. Basically, the main and the foresail are the same and of 12,5 m2 each. However, despite quite high AR 2,7, having seen the Badger sail plan I drew additional panel making the main 14,6 m2 with AR as high as 3.1.  Assuming total displacement of loaded boat of 1.600  ton this will result with 17 m2/ton. With such a factor I hope for being able to plan downwind. Please comment, ;) 

    4 files
    Last modified: 23 Oct 2019 18:05 | Anonymous member
  • 14 Oct 2019 10:29
    Reply # 7959014 on 7917477

    I don’t think I can answer that numerically - so many variables. Just (in my opinion) schooner good enough, ketch better, single sail best.  

  • 12 Oct 2019 12:56
    Reply # 7956904 on 7917477

    Thanks David for your opinion. Yes, I have good few reasons on my list to keep two masts, so I definitely will give it a try. But I'm going to plan carefully the rigging and go down with the chord to some 2.4m, as you have suggested. What, in the terms of degrees, would be in your opinion the difference in performance between one and two mast rig? 

  • 11 Oct 2019 09:47
    Reply # 7928012 on 7917477

    I'm seeing a hull shape similar to some of the mini transat boats, and I'm wondering whether that is what you have in mind? I see that you've completed an Atlantic circuit already, so you know what's involved with this. Two sails are not so good to windward as one sail, but this hull is optimised for downwind sailing as well, so they may match. 28 sq m would be more than enough for me, I'd prefer 26 sq m and a 2.4m chord, so that there's room for the sheets. With two sails, I found that the foresail was better with a single sheet, but the after sail needed port and starboard sheets to trim it close enough. Still, unless there's a very good reason for having two sails, I'd go for one sail on this boat, with upper and lower sheets, for better performance, better reefing and easier handling. If I scale up my Weaverbird sail to 26 sq m, the batten length is 4m. If I add another panel to the original 22 sq m sail, the area is also 26 sq m but the batten length stays at 3.375m. If the hull can stand up to a high AR like this, it would give the best upwind performance, and the downwind performance would be no worse than with the two sails.

  • 11 Oct 2019 07:22
    Reply # 7927865 on 7917477

    Thank you very much for your comments and advise. Sail plan as shown is in a very initial state. Certainly it requires some play  with Chord - now 2750mm, and the mast height. Definitely, I prefer single sheets on both sails.

    With displacement between 1.2 - 1.6 tons fully loaded for a long range cruise I'd love to have enough sail area to take advantage of hull shape and go planning in the trades. Will a 28 - 30 square meters be enough? 

  • 11 Oct 2019 00:33
    Reply # 7927478 on 7917477
    Anonymous wrote:

    After some 10 years of sailing my 24' Colvic Springtide I decided to build new quite different boat. With the help of professional naval architect I have basics ready. Now I need guidance from JRA regarding the sail plan details. After reading and seeing most of what available on the JRA website, I chose she (my new Dream Boat) will be a two mast schooner with similar sails on both masts. Alike Alouette or Badger. Rather flat with hinged battens. Please see the haul data and my idea regarding rig.

    A very interesting shallow draft boat.  Two masts with sails of similar size are also interesting, though it introduces some complexity for such a small boat.  For one thing, with the rig as drawn you will need to use double sheets for each sail, that is a sheet on either side of the sail, which is a lot more fiddly than single sheets.  I think two masts make a lot of sense for offshore cruising but for inshore work, or coastal cruising on a small boat, I prefer a single sail with one sheet.  It is so simple.  You only have one sheet and one halyard, so easy to adjust.  There will also probably be a yard hauling parrel and a luff hauling parrel but these lines are just for minor adjustments.
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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