You may be right concerning what you call the tabernacle and the length of the bury.

This plan from Montaubin (a french architect and builder of cat rig boats) is similar to what you say.

I would like to re-use the mast shortening it by about 2 meters. If necessary I may reinforce it with a 45°x45° polyester fabric  all long and another fabric layer (oriented in ?) from foot to 2m above deck. I did even think about filling it of polystyrene foam.

In a previous post Mark Thomasson also told me, as you do, that the present mast " is too far forwards and rakes to the stern, so a new location is required, mast vertical or slightly leaning to the bow"".

I hoped I could keep the mast as it is, the center of effort of the projected junk sail  being forward of the LjR rig' CE.

Regarding the aft rake, where's the problem ?

Claude

PS- I shall soon put a link to my JR sail design

Before discussing the mast question for Ar Vag Melen's conversion to junk rig, here under links to pictures of the once broken mast while motoring at 5 knots front of choppy 80 cm high waves. The mast is a tapered mast, 11 m high (10.1 above partners), with a 10° rake aft. Diameters are 110 mm at foot and 80 mm at top, wall is 3.5 mm thick. Mast is made of an epoxy-carbon-polyester composite (supposedly 50/50 for fibers, the volumic percentage of epoxy matrix being unknown by me).

From the pictures it looks like made of three layers, the internal and external ones applied by small angulated filament widing, the medium layer being manually applied with UD° / longitudinal.

As Arne wrote in a previous post "if the mast is weak for a LjR rig it will prove weak for a junk rig" so the question is why did this mast break : buckling, bending or shear forces ?

Are these forces significantly different between a LjR and a junk rig ?

The boat builder, the architect, the engineer who defined the mast scantling, the mast builder, all said the mast is not weak.

So ???

Tilapia's mast rotation system

Broken mast detail 1

Broken mast detail 2

Broken mast detail 3

Thank's Annie, looking at your (under construction) boat lines gives me an answer.

Concerning David's comment about the shallow draft of the twin keels ( "your boat may not have so much sail carrying power") I shall have to check how much more healing will result from an increased sail area.

As already said, the righting moment (calculated by the architect) is 882 kg.m at 50°.

Having modeled Ar Vag Melen with Delftship, I obtained a stability curve which confirms this figure (see full curve in illustrations folder). The only problem with this curve (othertwise quite classical with max moment around 50° and vanishing stability about 120°) is that it is not as steep as one should hope under 30°.

Ar Vag Melen then heals quite rapidly which explains reefing is needed from 4 Beaufort.

We'll have to discuss this with point 2 ("the mast") unless one has to make any more comment about the boat itself.

Claude

PS :I still dont know how to include a picture directly in the post; If anyone may help !

Claude, I've been having a look at the details of the Tilapia here, and it only seems extreme to me in one way - the twin keels are very shallow. Comparing my boat of similar size, with keels 0.9m deep, it seems that your boat may not have so much sail carrying power. Otherwise, all the dimensions do not seem extreme, and I can see no reason why you cannot use a junk rig. I must say, though that the rig will have to be light, so I would be thinking of carbon fibre yard and battens, and light sailcloth. Probably the existing mast can be shortened and used again, as is usually done when Freedom yachts are converted to JR.

Hello Arne,

As far as LjR rig is concerned I agree with your points 1, 4 and 5.

If converted to a junk rig "Ar Vag Melen" (that is the name of the boat which means 'the yellow boat" in britton) will certainly be equipped with a Windpilot.

Concerning your idea of having two sheets instead of one, each equipped with a barber hauler, it seems to me there is not much distance aft the clew to get correct angles of the sail sheets. 

Tacking and gybing are not a problem, even single handed, and it may become with two sheets and two barber haulers so, if keeping the rig as it is, I will probably look further on Gary Hoyt's genoa boom.

Controlling the sail shape to obtain the best performance is an issue but there are more important ones like safety issues.

Please have a look at this video  https://www.youtube.com/watch?time_continue=11&v=U7Nb88zhEPY

Neither the wind, neither the waves are unusual and yet boat's behavior is somewhat lunatic and screwy. She rolls more than usual due to it's low draft, she also has poor stifness so she heels quite quickly  and, as the hull has a (modern) wide, flat and V shape, buoyancy distorts and make's her turn windward.

Therefore reefing should be easy, which is not the case although one is supposed to reef by one mast rotation at 4 Beaufort and three at 5 Beaufort.

A junk rig would certainly solve the matter.

On this video one may also see how much flexible is the mast. When held in place by the sail under tension it is not a problem but when motoring sail completely rolled with short and choppy waves it induces great shear forces on the mast at deck level.

With a fixed and lower mast these forces shoud diminish.

And finally, being, as said before, mostly a summer sailor, more sail area would be appreciated under 3 Beaufort which is not possible with the present Ljr rig .

Did not you write yourself "Make the mast as short as you can and then ... pile on as much sail as you can " ?

Claude

Ps : May anyone tell me how can I include a picture directly in the post ? I did upload some in the illustrations folder but was unable to show them in my previous posts