On his website Lester Gilbert suggests a jib sheeting radius of around 10% greater than the main sheeting radius. Martin Roberts works on around 15% and Graham Bantock works on 20%.
When close hauled with the main boom at 5 degress off centreline the jib boom needs to be between 12 and 13 degrees off centreline as the jib "Bends" the wind flow to the mainsail. As both sails are sheeted out this effect reduces and then on a reach no longer exists. Therefore - ideally - on a reach the two booms are best parallel to each other like two wings on a biplane.
The difference in sheeting radii dictates how quickly the main boom catches up with the angle of the jib boom as we sheet out.
We have 3 identical Widgets and when the wind dictates that we have a long reach on one leg of our course the one Widget always seemed to reach better than the other two.
Yesterday was one such day and I checked the faster Widget's sheeting radius difference and it was 20% (Graham Bantock's setting). We then increased the jib sheeting radius on one of the other Widgets from about 12% to 20% and lo and behold, the Widget began to maintain a similar reaching speed to the previously faster one.
Martin Roberts made the comment to me the other day that with the new style course not as much reaching is done as before with "triangle and sausage" courses. He maintains that that is why he uses a sheeting radius difference of around 15%.
As the IOM class does not allow for a jib twitcher you only get one shot at this setting. It would be interesting to hear other opinions, and wouldn't the addition of a jib twitcher to the IOM class rules be an exciting development ???
All it would cost is a standard servo a short piece of cord and a PTFE ring to go around the jib sheeting between bulkhead eyebolt and jib sheet eyebolt. Most of us sail on at least 3 channel sets and with the modern 2.4 radios you could use heli mode so that the twitcher responded proportionately as you sheet in or out.
Joined: Wed Feb 06 2008, 06:11AM Location: Burton on Trent Posts: 277
Slow Coach wrote ... As the IOM class does not allow for a jib twitcher you only get one shot at this setting. It would be interesting to hear other opinions, and wouldn't the addition of a jib twitcher to the IOM class rules be an exciting development ???
Something else to fiddle with
I struggle with two thumbs, add another dimension and I'd be completely stuffed!
The issue of sheeting radii is something that I have recently being looking at, it seems obvious to me that the slot must change when you ease the sheets, which in turn must make a speed difference if you bear away to pass a boat when racing from the startline, something that Brad did very well with his widget was to have good boat speed when bearing off the wind. The thing is when does the slot effect disappear, or does it work all the way through the sheeting range?
I am hoping to find out more from Martin, Brad and Rob at the MYA seminar next weekend. Darin
It would be very interesting if you could share your findings with us after the seminar, Darin. I can still remember the old Swiss engineer who taught me to sail full size dinghys yelling at me to watch the luff of the main which showed clearly whether the Jib was backwinding the main or too far out which you could also tell from the luff of the main.
When we set our sails with the main in at 5 degress to the centreline of the boat we can get the two sails interacting to work as one. The minute we start slackening the sails, because of the luff radius difference that relatiohship changes and the slot changes. Depending on the difference between the radii, there will only be one point that the sails get to where the booms are exactly parallel. Let the sails out a bit further than that point and main boom will overtake the jib boom's angle to the centreline of the boat. The greater the % variable between the radii of the two booms, the sooner the main boom will catch up to the jib boom i.e. become parallel to the jib boom. The question is one of give and take - very difficult, and could make a hell of a difference depending on the angle of reach a particular course is dictating.
Joined: Tue Dec 29 2009, 03:02PM Location: PETERBOROUGH Posts: 80
David
Why don't you come along yourself and get the questions you may have answered by Brad, Martin, Robby, Mike and Tony E in person. I have only a couple of ticket still available.
If you or anyone is interested is in these tickets for the Manor Park seminar please email me now before they are all gone.
Thanks for the suggestion, Graham, afraid I won't be able to make it. If they do one at Woodspring sometime I may be able to attend.I'm not all that mobile (traveling wise) so I use the forum in the hope that some of the guys in the know will share their views.When you look at the number of views the forum gets I often wish the pros would participate more - I think it would be a good way of them getting better known and boost their sales too.One can only wait and hope.
When, on Thursday I conducted the experiment of changing my mate's boat to 20%, it was amazing how it suddenly became as fast on the reach as the other Widget which had always been using Graham Bantock's suggested 20%.
