Kurt - thanks for the encouragement.  After a few false starts I have developed a method by which I can build the tapered hinges in polyester resin with layers of chopped strand mat and woven rovings, with reasonably accurate internal dimensions.

The prototype hinge is nearly complete, and gives the full range of movement of batten parts within the hinge, whereas some of the old hinges do not allow the batten parts to move to the full extent theory would suggest.  Calculating the geometry the maximum deflection on the main battens should be 534 mm, but setting up a full batten on the bench with the old hinges (all randomly chosen) gives 435 mm and 415 mm on the two tacks.  The geometry is more complex in reality as the sail is on one side of the battens, so is inside or outside the centreline on different tacks.  However this indicates that the variability of the shape and size of the hinges as made is limiting the camber experienced.  I understand the camber aimed for with the original hinges was 9%.  My calculations give the theoretical camber as 12.3%, and the average of the two measurements I made as 9.7%.

Calculating the geometry for the tapered hinges indicates a maximum deflection of 359 mm giving 8.3% camber.  However, with the more consistent shape and dimensions I think I can achieve with my manufacturing method, this figure would be more reliably achieved in practice.

David Tyler's write-up in the Junkmaster pages on Badger's sail quotes a camber of 6%, while Arne Kverneland in his Junkmaster write-up calls for 10% or 12% on a heavier boat.  Being roughly half way between the two I think my tapered hinges are in the right ball-park.  What does the panel think?

Hi David,

Thanks for your interesting response.  My first reaction is not to like reducing the section of the timber, both by tapering and introducing a drill hole, both in the same locality, just where it comes under a lot of force.  I imagine the drill hole might act as a crack inducer to start splitting along the grain.  The battens which I have broken already show a split which goes at an angle to the length of the wood, and a slightly wavy break surface, showing the difficulty of getting straight grained timber with the grain parallel to the edges, and that only adds to my first impression.  Of course GRP and aluminium are more homogeneous and would lend themselves more to your suggestion.

Each batten has two hinges, apart from the top one which has one, so the total deflected angle will be 36 degrees, reducing to 24 degrees with my internally tapered hinges.

Crossing Liverpool Bay last year I broke a couple of battens.  One of the hinges, which are tied onto tabs which hold the battens to the sails, fell overboard as the tab stitching tore, setting it free. Thus I need to make a new hinge (plus a few spares) (or a whole new set).

The hinges that came with the boat are formed in (I think) epoxy and woven rovings, wrapped round a former to create a rectangular(ish) hollow section inside which the wooden batten parts abut each other (via a stainless steel bar set into the hinge) and achieve articulation in the horizontal plane.  There are some photos on my profile page of the hinges, plus a couple of drawings, if someone knowledgeable would care to look.  These hinges show a degree of variation in shape and size, which I hope to improve on.

I was wracking my brains to think of a way to build a jig which could be re-used several times, to build several hinges, when I had the inspiration to use pieces of expanded polystyrene, which can be broken or disolved out after the resin has set.  This can be cut accurately to size and squareness, thus making a more uniform product.  One photo shows a first trial at making a former with a constant cross section to replicate the existing configuration.  It would also have the advantage of being able to work on several hinges at once, instead of only one at a time if a high-tech jig were made.

My next thought was to develop the design a bit.  The batten parts are made of wood with rounded edges, and this lets the batten parts rotate inside the hinges, which is not desireable.  To overcome this some of the battens have had square corners formed over the rounding off with epoxy locally at the ends where they enter the hinges.  Some do not have these squarings (which is how I know they rotate in the hinges) and maybe these are later replacements of broken battens.  I thought the extra work of squaring off could be avoided by forming the hinge with an internal taper.  This would deny the battens the space to rotate, and might allow a greater spread of loads at the hinge mouth.  The downside is that the articulation at each hinge will be reduced.  I calculate the angle between the hinge and the batten to be 9 degrees for the existing hinge, and 6 degrees for the tapered version (see the second drawing).  These double up to 18 and 12 degrees between adjacent batten parts.

Here is the request for opinion - will this loss of articulation reduce the power of the rig too much?  Are there downsides to the tapered hinges I have failed to spot?  Robin tells me his hinges supply 3 or 4 degrees each end, doubling to 6 or 8 degrees over the hinge.  Would a reduction from 18 degrees perhaps be desireable?  Any thoughts are welcome before I commit to resin.

Is anyone still interested in hinged battens?

Roy.