A Question of Balance

  • 25 Aug 2019 06:53
    Reply # 7847920 on 7843011

    Thank you Arne and Paul for your suggestions. I think we might be onto something here based on your ideas, Arne. At the moment I'm flat out getting the boat in the water - been antifouling all day between the showers. I would like to draw a sail plan up in a few days time and come back to you on the forum.


    Thanks David for your suggestion about the mast rake. I am reluctant to do this now - crane costs, more spartite etc. but it could be done in the future, if required. We hope to be at the Tall Ships and look forward to seeing you there.



  • 24 Aug 2019 22:21
    Reply # 7847595 on 7843011

    Hi Rob,

    it looks as if you have installed the new mast vertically. Is there any possibility of adjusting it to give some forward rake? This would move the center of effort of the sail forward and would mean you would need less balance area. How tall is the mast? Can you make a higher aspect ratio sail that effectively increases the balance by reducing the area aft of the mast and consequently moves the center of effort further forward.

    All the best with the project and I hope to see her sailing in the Tall Ships in January!!

    David.

  • 24 Aug 2019 04:10
    Reply # 7846761 on 7843011

    Rob, if you change the yard angle to 60 deg as Arne has shown 25% balance will work. Don't worry about the maximum camber falling by the mast. My experience with LC's foresail suggests the wind/sail does not care, it may even be an asset that the mast is buried in the sail. It could well be that the loss of parasitic drag due to the mast not being fully exposed more than makes up for any inefficiencies in the sail shape. Certainly LC's fore sail performed well and it had 12% of camber.

    If you need assistance, feel free to contact me.

  • 23 Aug 2019 15:07
    Reply # 7845076 on 7844691
    Anonymous member (Administrator)
    Rob wrote:

    Thank you, Arne. As always you make some good points. We are tending towards a split junk rig with a balance of around 25%. Before we do so, could we use your rig with 25% balance and adjustable parrels? What happens if we have too much balance?

    Rob

    Rob,

    no, you will most probably run into problems if you try that. If you look at the diagram below, left, you will see that the slingpoint of the yard will have to be moved too far aft. To allow a mast balance of 25%, now I sketched up a new two-panel top section. With a yard angle of 60° or lower, that 25% balance should work.

    Note: I haven’t tried it hands on, so this must be armchair speculations:

    My guess is that the modified sail will behave and weathercock with the sheet released, but we are approaching a limit, here: What I don’t like is that the mast has now moved very close to the max camber points in the lower panels. That was my reason in the first place to keep the balance down to around 10-12%. Later, when Paul Thomson reported about good performance with 18 and 22% balance in La Chica’s sails, I have relaxed this ‘rule’ a bit.

    As can be seen on the same diagram, the original sail with 70° yard can be set with 15-17% balance. Maybe it will work to move the slingpoint on the yard from 5% to 10% aft of the middle. In that case, one can approach 20% balance in the sail without lowering the yard angle.

    On the diagram to the right I have tilted the modified sail until 40% balance at the boom. Who knows, maybe it will work. At least, the initial 10° boom rise helps to keep the boom from drooping.
    Personally, I would much rather take the trouble and make a big, powerful rudder, and save the trouble of canting the sail back and forth (in particular since I don’t sail for three days on the same leg...).

    Hope this makes sense...

     

    Arne

     
    Last modified: 24 Aug 2019 09:51 | Anonymous member (Administrator)
  • 23 Aug 2019 06:01
    Reply # 7844691 on 7843011

    Thank you, David for your reply. We have not had the opportunity to sail her with the Bermudian rig. From the Bermudian sailplan I see that the centre of effort is positioned where the Bermudian mast was. The boat has been sailing for 35 years with the Bermudian rig including sailing from England to New Zealand so it must have worked. We have placed the junk rig mast 1.2 metres forward of the old mast position and I'm not moving it! I know I should have started with my prefered rig but hopefully a split rig may work. I enjoyed looking at your photos on your profile and learnt quite a bit. Thank you.

    Thank you, Arne. As always you make some good points. We are tending towards a split junk rig with a balance of around 25%. Before we do so, could we use your rig with 25% balance and adjustable parrels? What happens if we have too much balance?

    By the way, I promise to fit an end plate to Blondie's rudder next time we come out of the water and we are still the proud owner.


    Rob




  • 22 Aug 2019 11:32
    Reply # 7843177 on 7843011
    Anonymous member (Administrator)

    Rob,

    The best sail for reaching and running, from a steering balance point of view, is no doubt the symmetric squaresail. Since this sail dominated for so long in Europe, the ships tended to be made with small rudders.

    The Chinese started rigging their sails fore-and-aft fashion very early. In addition, since they didn’t make their boats with fixed keels, they soon developed centreboards and (in our eyes) oversize rudders. This way they managed to control their boats and ships downwind, with their offset rigs.

    During my years in JRA, I have seen many examples of boats that struggle downwind with their sloop JR. This is mostly because the rudders have been small and in-efficient. I keep nagging on this: Choose boats with a big, efficient rudder, or be prepared to fit one.
    There are other methods:

    ·         Go for a (sloop) JR with plenty of balance. My Johanna-style sail can hardly be set with much more than 17% balance. Paul Thompson’s sails with lower yard angle, have been used with 22% balance, as far as I remember. Slieve McGalliard’s Split JR can have 30-35% balance, which offloads the rudder a lot on a reach (and have light sheet-loads)

    ·         Make the sail with long Batten Parrels and a running Tack Parrel, so the sail can be centered somewhat when reaching and running. I’ve never used it, but they say it works.

    ·         Rig the boat as a yawl, with the CE of the (short-chord) mainsail far enough forward to cause a lee helm alone, and with a little mizzen way aft to balance the rig. When falling off to a reach or run, the mizzen sheet can be eased and thus help keeping the  steering easy. This method was in use on some elegant little gaff-rigged yachts, over hundred years ago (Albert Strange).

    ·         Reef!

    For my own part, I have decided to live with my sails with moderate balance in them (10-17%). As long as I can easily control the boat at speeds up to about 10% above the hullspeed before reefing, that is good enough for me. Actually, for my sailing, in and out among islands, it makes little sense to carry more sail downwind than my boat can carry when close-hauled.

    Arne

    PS:  When having a closer look at photos of Blondie on the hard, it strikes me that her rudder is begging for an endplate, both at the lower and upper end. I would go for a ‘wingspan' of 60% or thereabouts of the rudder’s chord. I bet that will make Blondie cope better on a screaming reach.


    Last modified: 23 Aug 2019 08:21 | Anonymous member (Administrator)
  • 22 Aug 2019 07:49
    Reply # 7843065 on 7843011

    Hi, Rob, 

    From what I understand, ideally you should decide first, what type of Junk sail you want to install.  The C of E of that sail should then determine the placement of the mast in the hull.  If the mast placement in the hull then doesn't work with your preferred sail-plan, you'll have to choose another type of rig.  

    If I am reading it correctly, you have already inserted your mast in your new boat.  

    If so, then the type of Rig and how much sail (the balance) to be placed forward of your mast  will depend on obtaining a similar C of E to the Bermudan Rig, provided that the Bermudan rig provided you with satisfactory sailing characteristics in the 1st place, i.e. an acceptable amount of lee or weather helm and good tacking.

    I think, if your mast is already fixed in place, you will need to find out where the C of E of the original Bermudan rig is (on a drawing or photo) and then see what type of sailplan, (Arne, Aero or Split-Rig or other) will allow you to place the Junk C of E, in as close a position as possible to the Bermudan position. 

    Remember, with the Split-Rig (and the Aero?), to include the split between main and jiblet panel in the area forward of the mast.  35% (from centreline of mast to luff incl. split) seems to be the practical maximum for the Split-Junk.  And that figure can be smaller than 35%.  How much smaller and still work effectively, I don't know.


    Others will be along shortly with much better advice than the above, but the above is a starting point, I think. 

    Cheers.  Dave D.  

    Last modified: 22 Aug 2019 07:56 | Anonymous member
  • 22 Aug 2019 06:30
    Message # 7843011

    I am having problems getting my head around how much balance a sail or a boat could handle? In PJR they suggest a balance of between 5% and 30% but favour 10%. Arne also opts for 10% but thinks between 5% and 15% is acceptable for his style of sailplan. We have an Arne sail on our boat Blondie and the balance is around 15%. We are very happy with the sail but there is some weather helm when heavy reaching. Maybe more balance would solve this?

    Our new boat is a Robert Tucker Beagle design. I have attached a photo. We have placed the junk rig mast 1.2 metres forward of where the Bermudian mast was stepped, which is 1.2 metres forward of Bermudian sailplan's centre of effort. We couldn't go much further forward because of the forward berth and the foredeck hatch.

    We were thinking about an aero junk rig with a balance of 25%, which would fit the new mast position perfectly. All the local JRA members want us to have a split-junk rig. Slieve favours a balance of 35% on the split junk rig. How can all these balances be so different?  Am I missing something? Would an Arne sail with more balance work?

    Rob

       " ...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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