No – not the guts of a chicken. The jiblets in a Split Junk Rig are the small jib sections in front of the mast. Since they are in clean air in front of the mast they should be more efficient than the main sections (mainlets?). hence they can provide a critical part of the drive of the sail. So their design is important.

I’ve been playing with some prototypes. The established thinking is that an angled shelf foot design is best, with the caveat that the actual sail shape will be different to the shape you think you’ll get. This tends to make me think ‘why?’ and try to understand how to get a predictable shape, when I should probably get on, make the thing and go sailing.

Ok – so first I tried a barrel cut jiblet. This was built into a panel with batten pockets and tapes to see how it all worked.

I’ve finally got the cleat board painted and assembled:

With the mast nearing completion it is time to finalise the sail plan. I’ve been using a scaled-down copy of the Poppy plan for the preliminary design. I’ve now followed through to make sure everything works ok.

As recommended I built a string and stick model of the sail. This is the first attempt – a copy of the Poppy rig. With old garden bamboo it looks pleasingly authentic!

I’ve got the deck reinforcement in. Horrible job, working in a tight space with no room to move my arms and epoxy dropping on me. But it is in. Phew.

I thought I’d describe my current junk rigged boat and show some of the design features. The boat is called Owl because it is green (as per The Owl and the Pussycat).

The boat is a 11′ GRP clinker-style boat originally built in the early 1980s for a gentleman to take his kids out in. I suspect it was adapted from a standard hull – probably designed for rowing or fishing. It had:

• A flat centreboard that is a bit far aft;
• A rudder that only just touched the water;
• A standing lug rig that wouldn’t go upwind, with heavy yard and boom that reduced stability and threatened to hit heads.

However it did have a free-standing mast and, without the lug-rig up, was extremely stable. A perfect candidate for a junk rig!

Real progress. Got the turning block fixed to the tabernacle:

I’ve made a (rather rough – don’t look too closely) pivot. This has threaded holes so that bolts can be screwed in from either side to avoid making a big hole in the back of the mast

I want a cambered sail for the advantages it gives us – better performance particularly close to the wind. There are disadvantages for ocean travellers – the sail can flap about in light winds and swell – but these don’t affect a dinghy (hopefully!).

This is my approach to calculating how to make the sail. There are others, and there may be errors in my calculations – if you spot any please let me know.

If you want to skip the maths there is a spreadsheet that you can plug the basic figures into. The maths is just to explain what the spreadsheet is doing – for me as much as anyone!

Update: before you build anything from this please read subsequent posts:

• Jiblet design
• Jiblet design – update

These cover tweaking the edges of the cloth to get good shape in the forward part of the panel.