Thursday, April 7, 2011

Rig #6 from "100 Small Boat Rigs" ("103 Sailing Rigs")

One of my boys built himself a lapstrake (clinker) dinghy. At the time, we were working very long hours in the Brisbane workshop and I couldn't give him much of my time to help. But, he was surrounded by timber, glue, and tools, and with space in one corner and a ready-built strong-back he was on his way.

The boat turned out very well indeed, especially as the builder was only fourteen years old.

The owner-builder (Dave, in white) with Cousin Kevin lending a helping hand.
Hull nearing completion
After the building process, Dave was keen to get on the water, and he decided to purchase a carbon windsurfer mast to speed the launching, and a friend gave him an old Laser sail, which happened to be the same size as the designed sail.

Builder, carbon windsurfer mast, and Laser sail
The boat sailed reasonably well with the windsurfer mast, but it was too flexible down low and when sheeted on, the whole rig bent aft inducing weatherhelm and other handling problems - still it was fun.

Sailing nicely in light conditions...

...but in the gusts and sheeted hard, the rig bends aft, and you can see that the boat is becoming difficult to control
Eventually, Dave stashed away enough money to get the proper sail made. It had a fair amount of roach and leech battens which were too short. The leech would not stand as the flexible mast bent back, and it flapped uselessly. I don't have a photo to hand, but below is one of a boat we built earlier to the same design. This one had a nice, hollow timber mast which I made using the "Bird's Mouth" method. Although a lot stiffer than the windsurfer mast, the leech problem is still evident.

Stiff mast on an earlier boat, but still having problems with the floppy leech
We decided to do something drastic, so we cut the roach off Dave's new sail, removed the battens, and sewed on a new leech tabling (hem, I guess you would call it). This improved the set of the sail, as I had put a slight hollow in the leech and it worked well without battens. But the mast was still too whippy.

The final stage was to install a forestay and two shrouds (side stays). In order to retain the sail-shaping advantages of the bendy mast, we attached the stays at a point only a fraction above the half-height point on the mast (as per Rig 6 in Phil Bolger's book, "100 Small Boat Rigs", which is now published as "103 Sailing Rigs").

The improvement has been astounding. The handling issues have been resolved, and with the mast held at the half-height position, all sorts of sail shaping options are available by using the main sheet, the vang, the halyard, and the outhaul. We made the stays from 4mm Dyneema without an outer sheath as an experiment, and it has worked very well indeed. I couldn't work out the correct method for splicing the braided Dyneema core, so we ended up just doing plain bowline knots around the stainless thimbles - not very neat, but they work fine. I don't have sailing photos, but here is the boat on dry land as we set up the stays.

Stays attached halfway up the mast
Simple lashings
Mast far better controlled, and showing a little 11sq.ft. Heron jib set as well. The original boat carried quite a lot of weather helm and the jib helps to balance that out.
Sail plan in cat-rig form. The alloy sleeve around the lower part of the mast was an earlier attempt to stiffen things up.
All of this shows how much fun you can have messing around with rigs and layouts. A great source of satisfaction.


  1. Interesting saga. I'm guessing that having a mast that is too bendy in the Phoenix III lug rig could also have a substantial effect on balance of the boat.
    I have an oregon NS14 mast that I was hoping to trim down for the Phoenix, but it has quite a bit of lateral flexibility. If it becomes necessary, might timber strips glued up the sides stiffen it up or be a disaster waiting to happen?

  2. I don't know off-hand what the cross-sectional dimensions of the NS14 mast are, but given the stayed configuration, I'd guess that it is a pretty skinny mast. Yes, you can add some strips to the outer surface, and that is an excellent way to increase the stiffness of the mast. The other thing to consider (or do as well) is to add carbon fibre reinforcement to the external surfaces. However, the lug rig is far less sensitive to mast bend than is the leg-of-mutton rig on the boat in the article.