Time to make a Yacht!
Following on from appearing to have (temporarily at least) sorted the steam plant, it’s time to get on with fitting Befur with her Junk-Rig sails, so that she can truly be the Steam Yacht that she was always intended to be. The embarrassment of having to be towed home on three occasions also sharpened our desire to get this job done.
The Rig Choice
Having decided on a Chinese Junk rig for Befur, the Junk Rig Association (aka “JRA”) has been a considerable help, with advice from members, and loads of technical, design and use information on their site – I can thoroughly recommend this very friendly and international organisation.
Along side this, the junk rig bible is a book written by Hasler and McLeod called “Practical Junk Rig” (aka “PJR”) is a must have. Copies become available on-line from time to time, but I think it is out of print at the moment, but it is indispensable.
Also one of the JRA’s most prolific writers and designers is Arne Kverneland. He has developed a bunch of how-to guides for people making their own sails, and has been responsible for much (perhaps all) of the development of producing sail camber by the use of sewn-in “shelves” for each panel, causing the up-wind performance of the rig to be much improved.
We should perhaps just say that we chose the Junk Rig as it is reputedly much easier to handle (especially single handed) and is much easier for DIY sail makers – read all about the benefits on the JRA Site here.
Befur’s Rig Design
Using Arne’s and PJR we developed a rig plan with the following parameters:
- An tapered (un-stayed) aluminium mast 6.4 metres long (177mm dia at the base and 90mm at the mast head).
- The mast can be folded down for trailering, as it is secured in a “mast partners”, constructed of galvanised steel. The construction of the pivot is covered below. This will be fitted to the top of the existing cabin, and mated to an internal support structure transferring the strains to the Keel (Hog) and Deck Clamp. (Pictures of this internal support can be seen here).
- The sail has 6 panels and is following Arne’s design, with an area of 18.5sqM. The picture below below is the CAD drawing, also showing the supporting steel-work and partners.
The Mast is of 4mm walled tube, the Battens (and “boom”) are also aluminium tube, 22mm diameter and 3.2mm wall thickness, the Yard is 2-inch 10SWG (50.8mm x 3.2mm).
The Battens and Yard are just under four metres long, and as noted above the mast is 6.4M from foot (in the partners) to tip.
The sail cloth is about 160gm/sqM (4.4-oz/sqYard) polyester. Each of the lower panels is 3.9M long and ~800mm high.
Junk rigs do not need the weight of cloth used in traditional (Bermuda) rigs, as the battens and bolt rope (webbing around the edge of the sail) take most of the strain. We will probably make it in two colours, as the construction from separate panels make this really easy.
The Mast Partners
Originally we were intending to organise the mast pivot with a single hinge bolt through the mast. While this might have been OK for a wooden mast, I did not think this was a good idea for a aluminium tube mast, due to the concentration of load.
So the final solution was to make a 50mm high aluminium collar in two halves to grip the mast, machine a pair of 50mm diameter “stub axles” (Trunions?) on this collar to pivot in the galvanised partners, and then fit a 15mm stainless bolt through the entire assembly – quite literally a bolt-and-bracing approach!!!
Machining the collar from a 55mm thick slice of 10-inch bar was quite a game, and boring the new holes in the partners took a careful set-up to provide the rigidity needed.
The following photographs and videos provide a guided tour to this job…
First (noisy) cut boring the mast collar centre:
Boring the partners for the new mast collar:
The Finished Partners: