It seems relevant here to refer readers to Robin Blain's lovely photograph of Sesi, on page 49 of issue 69 of the JRA Magazine.  The accompanying text says that the boat,  "invited much comment on her unusual controls in spite of her well-balanced rig and light helm ...".  (Someone might insert that photograph in this thread).

I for one would love to read much, much more about Sesi's split-junk rig, how it is controlled and how it works!

James Hleba wrote:

Thanks for all the info so far. I will upload a picture and make a thread about the sail plan I have decided to go with. I landed on a balanced lug rig based pretty close off of the Van Loan drawing. I found that really interesting things happen when you play with the mast placement and balance with some dowels and strings. I wanted a low yard angle so I can get away with using a 30ft above the partners mast. I have a some really interesting drawings I will try and upload once I find the camera cord. With the mast balanced at 35% chord, and not using any lead, the mast is placed aft of where the current Sloop mast is! After all the research I really liked all the thing illustrated by the Split Rig documentation. I am going to have 6 battens, 375 sqft of sail area. I am still trying to decide how to shape the camber. I am thinking of just doing a straight 8% round and broad seem with the lower 5 panels. I am hoping that having the sail more balanced will allow me to avoid HK parrels, Yard haul, or any extra rigging. My goal is to try and build a camber panel system that only uses a halyard, down haul (I like the one Illustrated in the split rig docs) and sheet.  I will post some pictures for you guys to look at. Hope fully you will spot any mistakes I did not :)

Michael,

Actually these matters have been up here and there a number of times (use the new search faciliy and see for yourself). I am not a boat designer, so just have to draw on my practical experience. To sum up, here are seven issues I can think of around a mast:

1.      Windage when sailing.

2.      Windage when anchoring.

3.      Windage when doing harbour manoeuvres (under motor)

4.      Static moment sideways (stiff-tender)

5.      Static moment fore and aft (nose/tail-heaviness)

6.      Dynamic moment, inertia in rollplane.

7.      Dynamic moment, inertia in pitchplane (hobby-horsing)

#1: Of course we wish that our masts should have a tiny diameter to keep drag low. I have used thick wooden masts on my two first junks. On my 29’/3ton Johanna, the 10.6m mast had a “sail area” of 1.6m². That could definitely be felt when we were tacking with a deeply reefed sail. Still, I don’t think it ever widened the tacking angle with much more than about 10°. Head sea (and averse tides) does a lot more to slow down progress to windward.

#2: Honestly, I haven’t done much anchoring from the bow with my junks (..much easier to drop the hook over the stern here, since there is  hardly any tidal currents...). My Malena surely sailed around badly when being anchored at the bow. Still I think it should be possible to dampen the swing, for instance by adding an asymmetric bridle, as shown on the sketch below (Yawl rigs were popular on small gaffrigged yachts, as the mizzen could be used as a riding sail)

#3: Doing harbour manoeuvres, that is, backing out of the berth and heading in the preferred direction, in strong winds, surely can be a challenge: The thinner and shorter the masts, the smaller the problems. In addition, I find that having a steerable outboard engine, makes these critical manoeuvres a lot easier. At least there is no bowsprit around...

#4: The added weight of the mast robs a bit stability, but I have found that as long as the mast does not add more than 3% ( better with 2.5...) to the boat’s displacement, one needs not worry about its impact on stability.

#5: Putting a stout mast in the fore section of a boat surely will make her more nose-heavy. On Malena, Johanna and Ingeborg I either removed or just emptied the water tanks there, and this restored balance.

#6: The mast’s inertia in the roll plane simply slows down the roll rate (compared to with a lighter mast or no mast). This makes the boat more comfortable in some conditions (short inshore waves and swell from ferries etc) but tends to get the boat in resonance with bigger sea waves. This is the same for all sail rigs.

#7: Inertia in the pitch plane. Again, if the mast is kept at moderate length and weight, this seems to not be an overwhelming problem. After all, pitch plane inertia of the boat itself will be the main contributor here. What you can do (and which racing crews do) to minimise pitching (“pitch radius”), is to move heavy weights inside the central third of the boat:  Stuff like anchors, fuel and water. And remember; hundreds of sloop-rigged junks plus Bermuda- and Gaff-rigged cats are already sailing around and coping well, most of them.

In haste  -  hope some of this makes sense...

Arne

James,

there is no problem with choosing a lower yard angle. That lets you increase the balance in the sail (sail area before the mast), as in Van Loan’d sails, or in JRA-member Paul J Thompson’s La Chica . In fact, the yard angle could be said to be a function of how much balance you want in your sails. In my sails, with 70° yard, the balance should be somewhere between 5 and 15%. The reason why I prefer a moderate balance (around 10%) in my sails is that I want the mast to disturb the camber in the sail as little as possible. I use to put the max camber point about 35% from the luff, which by chance happens to be about where that vertical h-line from the peak, is drawn.

On the diagram below I have drawn in a mast in it most forward position on the sail, giving just 5% balance (the first had 18%). As you see the mast can be moved aft to about 10% balance and still clear the hatch.

Cheers, Arne

James, you wrote:

“PJR Camber sail- This will cost more, require more attention to stresses, more work, has developed a lot since its inception. Can be a seaworthy rig, but requires more fore thought, planning, and might not be as reliable or safe as the flat PJR if one is caught in extremely heavy weather. Pros- Windward performance, quicker then I can paddle a canoe. More power in the sails.”

Now I have made five Hasler-McLeod style sails with cambered panels, after first having sailed with a flat HM-sail.

I am not with you in some of your concerns about the cambered panel sails. The sails I have made, ranging between 10 and 48m², have taken me between about 30 to 50 man-hours to make. You will have a hard time cutting the production time with 50% by making your sail flat, and even if you do so, those saved 10 -20 hours will be nothing compared to all the hours you will spend on rigging and maintaining your boat over the next 15 years.

As for cost, you will spend some more canvas to produce the round in each panel, but again, these extras may well be paid back by sailing more and motoring less.

As for general handling and also the number of running control lines, they are the same as with the flat sails. I cannot see why cambered sails should stress the sailcloth more than flat sails do, as long as the cambered sails are put together correctly, that is, with a stout boltrope around it, as the Chinese did. The problems described in some fora here, appears to me to stem from either lack of proper boltrope, the use of metal grommets (high-stress points) or UV damage  -  or a combination of those.

Now I have, just for fun (..cold rain outside, today...) tried to sketch up a rig for a Columbia 26. I used my own info, found in Chapter 3 of  “The Cambered Panel Junk Rig” (TCPJR). Since I wanted to get the mast through the fore hatch and avoid the bunks in the fore-peak, I ended up giving the mast a 2° forward rake.

To get a more accurate drawing, I then scaled down a master sail with AR= 2.15 until B=4.77m (see chapter 4 of TCPJR). This resulted in SA=38.8sqm and a SA/Disp=20.5.

Open the  second diagram. If you look in the middle of the top panel, you will spot the original Bermuda masthead. The masthead of the JR appears to be around 10cm/4” lower.  

Hope some of this makes sense...

Arne