Category Archives: sail

The Spitfire sail

I’ve spent most of my limited wakeful time in the past few days reading books by Czesław Antony Marchaj:

  • Seaworthiness: the forgotten factor
  • Sail performance: techniques to maximize sail power
  • Aero-hydrodynamics of sailing.

These are all fantastic books. Not only is Marchaj one of the few writers to present actual hard evidence for his assertions, he writes with a dry wit that implies a great deal of criticism for the rumours and fashions that dominate sailing design. (The junk rig community seems somewhat exceptional in this regard.)

He presents evidence that elliptical foils produce more lift than rectangular or triangular, especially at low aspect ratios. (I’m summarizing here.) This is rather interesting given my earlier drawing of an enlarged sail for Tammy Norie. I think this evidence gives some clues to why the top triangle on junk rig sails is important: it approximates a curved top.

With this in mind I drew this sail plan based on the elliptical Spitfire wing.

The “Spitfire Junk” sail plan, based on research by C A Marchaj, which showed that elliptical sails generate more lift, especially at low aspect ratios.

This plan is based on 4.5m battens, but has a 3.2m second batten and a yard of only 1.9m at a steep angle of 65°. The yard forms the leading edge of the approximately elliptical wingtip.

Given Marchaj’s other results showing the critical nature of the leading edge of foils, the yard shape could be quite critical, but fortunately this suggests shaping it in a way similar to that suggested by Hasler and McLeod to provide strength. In this case it would be arched to fill in the ellipse and have a thin top.

If this plan works, the centre of lift will be shifted forward considerably, hopefully correcting the Coromandel’s balance problems.

I also can’t believe it’s a coincidence that Paul McKay’s Aerojunk looks like a Spitfire wing.


Fantail even resembles it.

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Filed under A New Rig, 2017-2018, sail

Sail art

Curved 4.5x1x40 sail

18 Comments

2017-09-26 · 20:14

A New Rig

It’s been three years since I first wrote about making new sails for Tammy Norie. Since then I’ve been delayed by illness and injury, and have been getting along quite well with her existing sail, but now I’m planning to make a move.

Seeing Emmelène with a split junk rig was inspiring, because of improved light wind performance and especially the significant improvement in boat balance.

There has also been some very interesting (and sometimes fierce) debate about sail position and balance on the Junk Rig Association forums. This prompted me to experiment with my own sail position and geometry, with some very encouraging results.

But mostly, of course, I want to play around with the rigging.

Currently I’m doing several things simultaneously, as my health allows:

  • Designing a new mast step that will allow me to adjust the rake of the mast up to about 5° forward.
  • Making sketches of sail plans to see how they might fit.
  • Sailing Tammy with the sail tied in various odd positions to see what happens.
  • Experimenting with materials for making short-lived experimental sails and sail battens.
  • Shoving Tammy around with a boathook to discover her centre of lateral resistance.
  • Reading about Roger Taylor’s experience with his “Triple H TB” rig on Mingming II.

I hope to write more about all these activities and cover the actual construction and testing of a new rig, so I’m starting a new blog series called “A New Rig”.

Be warned that what I do is going to be experimental. This won’t be a step-by-step guide on how to build a junk rig written by an experienced constructor. (You can find that information at the Junk Rig Association.) As usual this will be me trying out ideas, making mistakes, and possibly discovering some new and useful stuff.

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Filed under A New Rig, 2017-2018, mast, Plans, sail

Presenting the Tied Hybrid system: can it work?

I’ve been pondering new sails for Tammy Norie for some time. My goals are to increase performance in light winds and improve upwind performance while keeping things simple, strong, and maintainable. I believe that I’ll need to increase sail area and add camber to my sails to achieve this. I’ve briefly described various methods in my earlier post New Sails for Tammy Norie . I had more-or-less settled on an HHH system for simplicity and maintainability.

On Friday I was looking at figure 10.2 from Practical Junk Rig showing how to attach the sail to the yard.

Figure 10.2 from Practical Junk Rig

Figure 10.2 from Practical Junk Rig

Then it struck me: why not attach all the panels to the battens with string? One weekend-long brainstorm later, and I present to you the Tied Hybrid system for Junk Rigs.

Tied Hybrid sketch

Tied Hybrid sketch

The idea is simple: cut the main panels flat with reinforced seams with eyelets. Then tie the panels to the battens with loops of cord. By adjusting the lengths of the loops you can adjust the camber of the sail in pretty much any way you like. Sprung cord locks allow you to do this easily, but you can of course use stopper knots. If the battens are smooth stainless steel tubes then the loops will slip round easily when tacking, flipping the sail camber to the other side.

In addition, it’s a simple matter to make split panels and get a split junk rig with jiblets. It wouldn’t even be very hard to carry both split and full-length panels on a voyage for different conditions. Since all the panels are the same you can get a lot of flexibility.

This is so simple that I have trouble believing that it hasn’t been tried and somehow failed. I’ll be interested in feedback from the members of the Junk Rig Association about that. If it hasn’t been done then I’ll definitely be giving it a go. It should be easy and cheap to construct, and allow for a lot of research into sail trim.

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Filed under Plans, Repairs and Modifications, sail

Autumn plans

The summer was fantastic. I have gained so many experiences in the past few months that it surprises me to look back on them. Did I really do all that?

And now everything must seem very quiet to regular followers of this blog. This is something of an illusion. Two things are happening. I’m having to get on with some work. But also I’m quietly planning all the things I want to do with Tammy Norie before spring.

The next goal on my long term plan is the Jester Baltimore Challenge 2015: solo sailing from Plymouth to Baltimore in June. While not yet a true ocean crossing, it’s a significant bit of offshore solo sailing, and I need to prepare.

The most important item on the list is mechanical self-steering gear. Tammy Norie’s electronic tiller pilot has done well over the summer, but it sometimes plays up, fails to keep a course in some conditions, and I’ve managed to break it once already. I want a reliable wind vane, and I’ll keep the tiller pilot as backup.

I plan to build a Hebridean. Building my own self-steering will not only be interesting, it’ll give me a thorough understanding, and a much better chance of being able to repair or adapt the gear. It’s also a cheap option. If the Hebridean doesn’t work out, I will have lost only a little money and learned a great deal.

The second item on my list is to either make Tammy Norie unsinkable or repair the liferaft. My plans for making her unsinkable involve lining her with foam and that includes fixing up the headlining, so it might be a good move in any case.

I would like to have a Jordan series drogue ready. I’ve had various opinions on this. Most people think I’m unlikely to need one for the Baltimore challenge, but several have also said that I really should have one in general, given Tammy’s small size. So I’m going to see if I can get this done too.

I would also like to build a new sail, so that I have more flexibility in adverse conditions. This is quite a big job, probably involving re-engineering the mast step, so it may not get done this winter. The current sail is good enough, and it’s not a safety issue.

There are, of course, various bits of kit I need: a simple reliable GPS, an SSB radio receiver, a distress beacon (though I may just rent an EPIRB for the Baltimore challenge). I have a much longer list of things I’d like to have, but those are the only ones I think I ought to have before going offshore.

And of course, sailing! I’ll get Tammy on a mooring in Portsmouth Harbour as soon as I can for some autumn and winter sailing.

I’ll be writing about each of these projects in time, so watch this space!

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Filed under drogue, Plans, sail

Fan-tailed Tammy Norie?

I made this post on the Junk Rig Association technical forums. I’m quoting it here for the record, and so that anyone interested can follow the discussion.

I’m inexperienced with junk rig but (I hope) learning fast. So far I find the flat-sailed HR rig on Tammy Norie lacking drive below F4 and unable to make progress to windward in light airs in a chop. This may just be poor technique on my part, but when I bought her I was definitely thinking about making a more up-to-date sail. I have offshore ambitions. The fantail rig just looks right.

I admit that I have not done any homework yet, but I made this crude overlay by matching the waterlines of Tammy Norie and this fantail, just to get an idea if it’s at all feasible.

It quickly raises one question: does the mast position of the Coromandel rule out the fantail (at least, the standard one). If so, what can be done? But also, what homework should I be doing?

Coromandel on fantail overlay

Coromandel on fantail overlay

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Filed under Repairs and Modifications, sail