Hi Clare
I haven’t had my boat long and initially just set the mast up to marks left on the rigging screws by the previous owner. Generally it seemed OK, the mast was about straight sideways but the forestay seemed a bit saggy and I appeared to get better main sail shape on a Port tack than on STBD, so some tweaking was in order, but I needed to start from a known point so decided to re-tune from scratch – this is what I did.
http://www.seldenmast.co...?id=6740&randnum=4379830 gives some good tips on the tensioning by measurement method. However you do need a couple of bits of information on the set up to get you started.
The first is mast rake, the sail and rig tuning book suggests a figure of 2-3 deg. Literature for the SS27 suggests setting the mast so it’s almost vertical with a slight aft rake but I haven’t been able to find an actual figure. There is limited info on other fractional rig boats to compare with but that I have found seems to suggest 2 degs is the norm. On the SS26 2 degs gives a distance of 317 mm along the boom (distance b in the sail and rig tuning book). On ‘Calypso’ with the shrouds hand tight and the backstay off the measured distance was about 320 mm, so I didn’t need to adjust this.
Using a tape measure and a short rule I tuned the cap (upper) shrouds first to 20%. At this the forestay still seemed a little saggy so decided to increase to 25%.
The second input is pre-bend, the sail and rig tuning book suggests 30 – 50 mm, info for other fractional rigged boats is in the range of 60 – 80 mm and literature for the SS27 suggests a pre-bend of 2-3 inches (50 – 75 mm). Before starting the re-tune, with the shrouds still tight and the back stay hand tight, the pre-bend on ‘Calypso’ was about 2 inches, so again in the right ball park.
After I had tensioned the cap shrouds during the re-tune I measured the bend at about 4 – 5 inches, I then tuned back to 2 inches using the lowers.
I have yet to check the tuning under sail as I ran out of time, but I will update when I can.
Jon Foreman
Calypso
Jon Foreman
Calypso SS26, no.96