DAYBOAT KICKING STRAP SYSTEM by Andrew Cleare
The basic problem for the Dayboat is the small angle that the kicker makes with the boom. I calculate that it needs nearly twice (x 1.86) as much kicker tension to give the same downwards force compared with the Yawl.
I looked at my pulley system to see how effective it was. First I looked at the roving of the line. In some places the line rubbed against itself.
Much thought and doodling produced a scheme with no rubbing. Experiment then showed that the 6:1 purchase now gave a 3 fold increase in pull. I changed the 6mm line to 2mm and got up to a 4 fold increase. I was not impressed! The blocks are plain bearing, 25mm sheave Holt Allens. Something better is needed.
Research at Sailboat ’96 showed purchases of 6:1, 8:1, 12:1 and even 16:1 on some of the racing boats. The systems included combinations of multi-pulley blocks, cascades, and levers in various configurations. The Scorpion dinghy has two kicker systems, one conventional, and a second pulling vertically over a horizontal strut pivoted at deck level. This system gives an improved downward force of 20% compared with the Yawl and 122% compared for the Dayboat. This gave food for thought.
On a Dayboat a vertical pull could be achieved with a triangular frame as shown in the sketch on the left.
Tension would be applied via a purchase system. The compression force in the upper arm could be transferred to the mast via a second gooseneck, or to the front end of the boom with an eye. The tension in the lower arm at the foot of the tabernacle needs a substantial horizontal eye or lug. (I do not like the standard lug on my tabernacle as it is rather far away from the gooseneck axis and gets pulled sideways when the boom is swung out. It is showing signs of cracking at the weld.)
Alternatively a lever system like Alan Cole’s as seen on the right above can give a purchase of 4:1 or more, with few bearings to add friction. A cascade uses fewer pulleys than a comparable multi-block purchase so there should be less bearing friction. Having worked it all out I shall go for system 2 and add a pair of pulleys to bring the end of the line out to cleats by the aft ends of the handrails.