This article written by Inventor and BCC member Anthony Warren, was published in Catalyst, Journal of the Amateur Yacht Research Society, early in 2003.

Snow shoe introduction

My wife Maureen and I have sailed a Halcyon 27 for the last few years. We were finding the big Genoa increasingly hard work with the passing years, and we planned to build something bigger and more comfortable. Also, easier to handle, especially in heavy weather. I spent a good deal of time thinking about the rig.

I read several of Marchaj’s books, and articles about Junk rig, and Hasler and MacLeod’s book Practical Junk Rig. I enjoyed a short trip on a two masted Junk-rigged boat through the auspices of the Junk Rig Association.

I was impressed with how easy Junk is to manage, especially when we were hit by a squall and reefing was accomplished very quickly by simply easing off a couple of halyards.

Equally impressive was the efficiency and performance of the Sail Wing reported by Marchaj (Aero-Hydrodynamics of Sailing, p606). This wing has a D section leading edge canted into the air-flow, with stretched double skin cloth abaft. Marchaj also made some very positive statements about parabolic leading edges in a similar role (Sail Performance, page 190). How then, to combine the ease of handling of Junk rig with real aerodynamic efficiency?

Answer: snow shoes! Well, that’s what we ended up calling the shaping foils which are the key feature of the Warren Parabolic Rig.

What is WaPRig?

The key features are: (see photos)

• Aero-dynamically shaped foils (the snow shoes) with circular cut-outs slightly ahead of mid-length through which passes the mast. There are a number of these spaced along the length of the leading edge.

• A sail. This passes right round the snowshoe and comes together at the downwind end of the snow shoe. Behind this is conventional single thickness cloth. So we have a thick foil part of which is ahead of and around the mast, tapering down into a conventional sail.

• Battens pivoting about the aft end of the snow show extending aft to the trailing edge of the sail, and forward into the frame of the snow shoe. The forward extension ensures that the snow show cannot over-articulate, and that the lee side of the thick foil merges smoothly with the single layer cloth abaft.

• A boom, with what is called a topping lift in Junk Rig parlance, or adjustable lazy jacks. This serves the double purpose of holding up the boom and catching the sail as it is lowered.

• A boom downhaul

• A yard, from which the top of the sail is hung

• A halyard for hauling up the yard, and a sheet, to haul in the sail.

There are many many open questions about what might be best to do within this overall design framework. Below I list some of the questions and some of the considerations which might suggest the answers.

Prototype Development

We bought a second-hand YW Dayboat (14ft centreboard dinghy, heavily built and stable by modern standards), and built a prototype. I fitted some additional woodwork to support the new unstayed mast. The mast was keel-stepped and about 9inches abaft the original deck stepped mast for the Bermudian rig for which the boat was designed.

The Mast and its support:

We elected to use an unstayed mast in line with Junk Rig practice. It might be possible to attach shrouds and forestay at or near the masthead, but there might be interference with the yard and foils.

The mast cross section can be relatively large, because most of it is within the sail and does not create drag.

There is the possibility of fitting a freely rotating streamlined fairing to the upper part of the mast to further reduce drag, and a similar fairing could be downhauled from the base of that upper fairing as the yard is lowered. We built the mast out of standard aluminium tubing.

The Snow Shoes:

The precise shape of the leading edge, the aspect ratio, and the chord are all open to experimentation and development. We opted for as near to a parabolic leading edge as my woodworking skills allowed. From about 6 inches aft of the leading edge the entire curve was drawn by eye simply to look fair.

The ring in the centre of the snow shoes is a very loose fit over the mast. This ensures there is no binding, neither in rotation, nor vertically during the process of raising and lowering sail.

We made the snow shoes by casting glass matting and polyester resin into a mould made from several layers of MDF board.

A very crude arrangement made from rectangular pultruded fibreglass section stuck to the aft point of the snow shoe allows the battens to pivot from side to side. Movement of the leading end of the batten is restricted by another piece of poltruded fibreglass screwed to the end of the batten. As the batten pivots, the batten stop comes up against the inner rim of the snow shoe.

We stuck heavy duty Velcro all round the outer rim of the snow shoes to attach the sail.

The Sail

What plan-form should the sail have? Somewhere or anywhere between a square and a triangle seems to be possible.

We opted for a basically rectangular shape with a fairly low aspect ratio (see picture). The aim was to more or less match the sail are of the original Bermudan rig.

We opted to angle the yard upwards toward the aft end, giving a triangular head above the top horizontal batten. I have no idea if this was a good thing to do or not, but it looked pretty. The sail was tied out to the ends of the yard, but not attached along the length of the yard.

We made the sail in two parts. Both parts were made from PE cloth (incredibly cheap) and were cut completely flat.

The first part goes round the snow shoes. It has horizontal Velcro strips on what is to be the inside for attaching the sail to the snow shows. Both trailing edges have Velcro stitched along the entire length, on the inside, for attaching the second part of the sail.

The second part of the sail is effectively a big flat sheet, with batten pockets along the whole depth. Velcro is sewn the whole length of the leading edge on both sides, and attaches to the other part of the sail.

How should the upper and lower ends of the tube formed by the snow shoes and surrounding sail be shaped? I don’t know. We left them open to the air, and tied the leading edges of the upper and lower snow shoes to the end of the yard and boom respectively. This seemed to work OK, and may contribute to keeping pressure high within the tubular space: that would help resist collapse of the shape between snow shoes.

The battens all run horizontally, and the line of the top batten extended forward meets the yard ahead of the mast.

The bottom batten is a couple of inches above the foot of the sail. Clew and tack are tied to the boom, but the rest is loose.

The Battens

These are full length, and have a stop fitting on the forward end to prevent over-articulation within the snow shoe. They are made of pultruded fibreglass.

The Boom

The boom is mainly there to hold up the sail when lowered. The bottom batten can fulfil all the aerodynamic requirements, bearing in mind the sheeting arrangements described below.

The boom should be symmetrical and form a wishbone round the mast. No gooseneck fitting is required as the boom is free to slide up and down the mast. However we made a crude wooden rectangular box which fitted round the mast, and screwed the boom to it on one (arbitrary) side.

We made the boom out of pultruded glassfibre section.

The boom uphaul (lazy jacks) runs from the masthead, under the boom, back to the masthead and down to a cleat. This enables the rig to be held up out of the cockpit when the sail is lowered. When the boat is to be covered up the whole rig can be dropped down to deck level.

The Boom Downhaul

This enables the luff tension to be adjusted. For reefing, it might be necessary to attach further downhauls to some of the snow shoes, one for each reef. We have not experimented that far.

The Yard

All the same remarks apply as for the boom, except the yard, obviously enough, is to hold the sail UP. The sail with its snow shoes, battens and boom all hang from the yard when under sail, exactly as with Junk rig.

Halyard and Sheet

The halyard is led from the cockpit to the masthead and down to the yard. The point of attachment to the yard needs to be made such that the yard is more or less in balance as the sail is hauled up and down.

From the masthead the halyard is passed down inside the frames of the snow shoes but not through the ring through which the mast passes. The same route is used for the boom uphaul and flag hoist.

The sheeting arrangements are typically junk. Sheeting lines are attached to the sail at the point where each and every batten emerges from the trailing edge. We played with a variety of spans and ephroes. What we ended up with is (I think) a six point ephroe span. We used alloy Inglefield clips as ephroe blocks and they work well. The net purchase on the mainsheet in hand is 3:1.

In order to obtain a sheeting point far enough aft, we built a wood frame extending about 18 inches behind the transom, and attached to it.

Does it Work?

I’ve done a lot of dinghy sailing in the past. It was a wonderful and entirely new experience to be sailing downwind onto a marina pontoon and be able to stop! You just drop the sail, anywhere, anytime, any point of sailing. And it doesn’t fall on your head.

We’ve only sailed the rig twice, and both times in light winds. We had no similar boats against which to measure performance, and the strong tide running made it difficult to estimate just how close to the wind we could sail. What we do know is that the sail sets fair, with the lee side forming a smooth join between the foil-supported section and the aft part. There was minimal caving in of the leading edge between foils. The rig handled as we had hoped.

The boat remained well balanced, in spite of our new mast being well abaft the designed position, and our having only the one sail set on it, no jib. This could be some indication the foil is generating real lift near the leading edge.

• Plus Points:

• Very easy to handle
• Low stress in sail and rig
• Boat can be left rigged
• Performance? Maybe?

• Minus points

• Getting rigged: all that Velcro! All those battens!

Further Developments

I have seen enough to convince myself the rig will work on a yacht. We need to develop a snow shoe design where the snow shoes can be fitted round the mast at deck level, rather than being dropped over the top. This means a two piece snow shoe that can be taken apart.

Apart from that there is endless opportunity for further experimentation with foil shapes, aspect ratios etc etc. I am leaving that to others.

We are rebuilding a 40 foot Cornish Lugger. This type of boat could have been designed for our rig. The mizzen lug sail of old was sheeted onto an outrigger (bowsprit on the stern), and so will ours be. The mainmast was and will be right forward in the boat.

Don’t hold your breath for further news. The project will take several years at least.

 

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