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The final version of the Junk Rig Glossary is now available and can be found under the Junk Information menu, or directly here.  This Glossary lists all the terms related to the junk rig, its implementation and use.

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November 2018 - Mirror dinghy design

This project never proceeded beyond the design stage which was mostly carried out in 1990. At the time I had too many boats and not enough time, so it was put on the back burner. Now, I am 78 and probably my dinghy sailing days will be limited to my junk rigged sabot (8 ft) Ah Sup.

However I still think a junk-rigged Mirror would be wonderful, and I would be really pleased if someone else would use the design.

I thought at the time that a two masted junk rigged Mirror would be good for someone who wanted to sail longer distances or who liked to leave the boat rigged for longer periods. So I designed one of those as well. The sail area is approx the same as the single master, but with a lower centre of effort, and a more versatile rig for different wind conditions.

However I realise that most people would be interested in the single master,for the type of sailing that most Mirrors are used for.

The sail area of the single master is 8.74 sq metres (94 sq ft) which is 34.28% larger than a standard mirror of 70 sq ft. This may sound excessive to some people, but my junk rigged Sabot carries 38.8% more sail than the standard Sabot and it sails very well. Even with that sail area it doesn’t heel as much as the standard Sabot. To windward it matches the other Sabots and reaching and running it leaves them behind. And if the wind gets up I can reef it without moving from my position. Manageability is what should determine a boats sail area.

The centre of effort is 490 mm (19.29 ins) higher than the Mirror CE. This is partly due to the boom being raised so as to clear a mans head when he is sitting on the seat/buoyancy tank and give him clear view. He won’t have to duck. But again I remember the junk rigged Sabot with a considerably higher CE than the standard Sabot . Going to windward it doesn’t heel anywhere near as much as the standard Sabot.That is, of course, because it doesn’t  need to be pulled on as hard when going to windward. It doesn’t luff. There is very little load on the sheet,and therefore very little heeling. Wonderful. Going to windward I always have a big smile on my face.

In his classic "Junks and Sampans of the Yangtse" GRG Worcester points out that the trading junks which followed the trade winds had, generally, fewer battens than junks that worked the rivers and estuaries. Trading junks, that had to deliver their cargo into a river, had more battens than those that did not. He concluded that the more battens, the better the windward ability. I thought 8 battens would be a reasonable compromise for a boat that would do a lot of tacking and would be judged on its windward ability.

It may be noticed that the distance between the battens on the leading edge, reduces toward the top of the sail. This is to reduce what I call batten creep.That is, the tendency for each batten to land a little abaft the one below as the sail is dropped. In some cases the yard can end up aft of the mast. Not good.

In terms of scantlings, my untried design allowed for:

Yard. 40 mm OD , 2 mm wall thickness aluminium

Battens. 12 mm OD 1.2 mm wall thickness aluminium.

Boom. 25 mm OD , 1.6 mm wall thickness aluminium.

Mast. I guess that 8.74 sq metres could be safely carried by 60 mm dia 3.25 mm wall thickness.

The mast is free standing and is located on the forward face of the buoyancy tank bulkhead. Because of the difficulty of installing the mast socket in this location, it was my intention to remove a piece of the forward deck, to give me easy access, and then replace it on completion. The buoyancy tank bulkhead and the forward deck would provide good lateral strength.

Because of the shape of the sail and its location in relation to the stern of the boat, the best sheeting system has to be double sheeting. One set each side. At one stage, with my experiments with junk sails on Ah Sup, I had a sail with double sheets. It is quite common on Chinese junks and it works just fine.

The sheetlet system I show on my drawing is common for Chinese 8 batten sails. They, of course, use euphroes where I have shown little blocks. My reasons for doing so are that euphroes assist in keeping the sail twist and distortions to a minimum, by adding a little friction. Once the sailor has given the sheetlets a tug here and there, the sail tends to stay that way until a change of direction prompts him to do it again. In our case this is not practical, as the sheeting on a dinghy needs to be self adjusting.  I had to slightly modify the standard Chinese 8 batten sheetlet system to use little blocks instead of euphroes. The modification involves doubling the power of 3 of the sheetlets to account for the area of sail they support, and the angle of pull on the sheetlet. (The steeper the direction of pull, the less lateral force on the batten.) It works fine on my current boat, self adjusting as I change direction and sheeting.

I include a drawing showing the different stages of reefing.  As the sail is reduced, it will be necessary to shorten the lower sheetlets (shown by the longer tails). This just entails pulling them through their beckets, tying a stopper knot, and somehow tidying up the tails.

I hope one day someone will build this and tell me if it all works.

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