Split Junk Rig on Westerly Windrush

  • 28 Mar 2013 17:10
    Reply # 1253842 on 1248976
    Deleted user
    Yes, looking at it again I think I've got the scale wrong. Batten length should be around 4.8m.

    Not sure about going for a taller rig - as Slieve pointed out, the hull is on the tender side because of it's beam/length ratio - might be better to go for a lower aspect ratio.

    However, I am sufficiently inexperienced in this to take a strong recommendation.
  • 28 Mar 2013 16:38
    Reply # 1253815 on 1248976
    Anonymous member (Administrator)

    Chris

    Er, could there be a scale confusion somewhere? It surprised me that the crimped Johanna sail could be 30sqm and still not have the CE further aft with an AR of just 1.87. Now I printed it out on a transparent to the same scale as my last drawing. Your Johanna sail is quite a bit smaller with a batten length of around 4.23m and a SA of only 25.7sqm. The LAP stops at 6.85m.

    The idea with my AR=2.0 sail was to hit the "old CE". One could even go up to an AR=2.05 and thus shorten the battens a bit while still keeping the SA= 30sqm and use your planned mast with LAP= 8.25m. This would move the CE a bit forward of "Old CE"

    Arne

     

  • 28 Mar 2013 13:13
    Reply # 1253662 on 1253627
    Deleted user
    Arne,

    Your eye is good. When I scaled Johanna's sail to 30 sq m and placed it on my sketch, positioning the mast 0.375m further forward than in my sketch gave a CE 5% of WL aft of the original Bermudan CE. I'm not convinced that the Windrush IS well-balanced, having rather a lot of weather helm. This is not just my experience - many other owners of this and it's 'little sister', the 22' Nomad, have reported the same. The mast certainly could be placed in or very near the ideal place for the interior layout.

    Chris
    Last modified: 28 Mar 2013 14:21 | Deleted user
  • 28 Mar 2013 12:26
    Reply # 1253627 on 1248976
    Anonymous member (Administrator)

    Stavanger, Thu

    Chris. Your situation illustrates that a forced position of a mast, far forward or far aft, may dictate the shape of sail plan (on a sloop). To my half-trained eye it appears that your sail sits very far forward. Experience with cambered panel junk sails have convinced me that the CE of the junk sail may well sit 5% of the WL aft of the BM rig‘s CE - that is if the balance was OK with the BM rig. Even if you used to have problems with weather helm, I doubt if you need to move the JR’s CE forward of its original position.

    If a mast is forced to sit far aft, then a sail with big balance would be needed to get the CE right. One then has the choice between the Van Loan style sail with a low yard, or the split junk. I certainly would go got the latter.

    If the mast is forced to sit far forward, a sail with little balance would be better, I think (or a little mizzen could be added). The choice is then between the high-peaked HM sail, like Johanna’s, or the high-peaked fanned sails like those on Fantail and Tystie.

    Now I have added a 30sqm HM sail to your last sail plan. I have in my pc a stack of standard sails with varying aspect ratios so could just pick one and quickly scale it to the needed area. The HM sail would actually need the mast even further forward (along that meter scale) and a LAP of 8.0m should do. An added asset with this sail is that the foredeck area will not be blocked by the overlapping sail bundle so anchor handling will be easier.

    One more thing: Even if you manage to balance your boat upwind, the weather helm will increase on a beam-to-broad reach when most of the sail will sit outside the boat. To cope with that I suggest you add a set of end-plates to the rudder, as shown on this Freedom.

    Whatever you go for, good luck!

    Arne

    PS: Idrafted this letter before your last posting  -  it seems that we think along the same lines.

  • 28 Mar 2013 10:33
    Reply # 1253593 on 1248976
    Deleted user
    Thinking aloud....
    My options seem to be:
    1. Forget the whole thing - not an option.
    2. Lose hatch & place mast there - don't want to lose hatch & fwd cabin access compromised.
    3. Mount mast just aft of hatch - fwd cabin access near impossible without redesigning & rebuilding whole interior.
    4. Reduce aspect ratio, & balance of sail to considerably less than 30% with mast fwd of hatch - would probably lose most of the advantages of Slieve's design.
    5. Mast fwd of hatch & choose one of the other cambered sail plans with less balance, such as that on 'Johanna' - which incidentally, scales nicely to 30 sq m and looks well on this hull diagram. Scaled batten & yard lengths very similar to the split rig I drew.

    I have a plan......
    Build mast, yard and battens as planned, but build cheap 'polytarp' version of the split rig as accurately as possible to evaluate it without having invested £100's in a solution which doesn't work. If balance & performance is OK then I'll build a proper sail. If not, I'd probably only have to make small adjustments to batten and yard length to adapt to a different cambered design.

    This plan has the added benefit that I get to practice sail building at not too much cost to my purse or to the rig. My kite is up! Let the shooting commence.
  • 28 Mar 2013 00:22
    Reply # 1253355 on 1253327
    Deleted user
    Slieve McGalliard wrote:Hi Chris On Edward's boat, with the later rig, I reckoned that the centre of area of the rig was at 50% of the chord from the jib luff to the main sail leech. This thinking may move the clr of your new sketch forward a little. Edward wasn't too worried about the fore hatch being availale for inshore sailing, and that may be a question for you too. Cheers Slieve
    Hi Slieve

    OK, but looks like the sail on Amiina is rather more rectangular than what I have drawn, so one would expect the CE to be around 50%. Taking account of the rig I drew being taller aft, and the gap in the forward part, one would expect the CE to be a little aft of centre.

    I have actually calculated my CE by filling the whole sail in black, on a white background, counting black pixels using a histogram, and then progressively removing columns of black pixels 'til only half the total was left. This gave me a longitudinal position for the CE of 54% of chord aft of the luff of the jib. I then repeated this top to bottom to get the vertical position of the CE as I've drawn it.

    Chris

    Edit: I've modified the diagram to show interior layout - it's not just the hatch - with the mast much further aft I start blocking access to the fwd cabin which is only 20" wide. I guess I have to weigh my priorities :)
    Last modified: 28 Mar 2013 00:49 | Deleted user
  • 27 Mar 2013 23:49
    Reply # 1253327 on 1248976
    Hi Chris On Edward's boat, with the later rig, I reckoned that the centre of area of the rig was at 50% of the chord from the jib luff to the main sail leech. This thinking may move the clr of your new sketch forward a little. Edward wasn't too worried about the fore hatch being availale for inshore sailing, and that may be a question for you too. Cheers Slieve
    Last modified: 27 Mar 2013 23:51 | Anonymous member
  • 27 Mar 2013 22:52
    Reply # 1253296 on 1253176
    Deleted user
    Chris Gallienne wrote:Edward,

    looking at pictures of the Splinter it looks like you might also have had to deal with an obtrusive fore hatch in moving the mast 12" forward?

    Chris
    Yes.  I got rid of the fore hatch, as the mast went straight through the middle of it.
    For better or for worse, I now have no fore hatch.
    Edward
  • 27 Mar 2013 20:57
    Reply # 1253176 on 1248976
    Deleted user
    Edward,

    looking at pictures of the Splinter it looks like you might also have had to deal with an obtrusive fore hatch in moving the mast 12" forward?

    Chris
  • 27 Mar 2013 20:46
    Reply # 1253163 on 1253143
    Deleted user
    Edward

    I suspect your eye is far less untutored than you claim - and yes, it is too far forward,but it's that damned fore hatch. When I drew it I believed the mast had to be some way forward of the current mast position, but after more thought, guided by slieve, I'm not so sure.

    I have now redrawn it between the hatch and the old mast position and it looks better, though it puts the CE aft of the old CE. I really need to go down to the boat and measure up, as that diagram (the best I can find) does not seem to represent the hatch position or size very well.

    Thank you for your very kind offer, and I would be delighted to take you up on it.... when the weather gets a bit less chilly I think. Your generosity is even more laudable given my threat to rob you of your title as the most westerly......

    Chris

    Edit: I have replaced the diagram with the modified version - sail area reduced and mast moved aft - also smaller section mast.
    Last modified: 27 Mar 2013 21:11 | Deleted user
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