This all comes down to the physics. To trim your main, you have to pull against a force (the lateral force on the main) through a distance (the angle the boom moves). The product of force times distance is work. When you pull on the end of the boom, you are pulling the same angle to achieve proper flow, but the point you are pulling on is moving a lot farther than if you have mid-boom sheeting. To do the same amount of work, you don't need to pull as hard. To put some rough numbers to it, if you pull at the mid span of the boom, you have to pull twice as hard for half the distance. To get back to a reasonable pull force, you can add purchase (8:1 vs. 4:1 pulley setup, for example) to trade back distance for force. Nothing is ever free, however, and each layer of purchase adds drag, which hurts in both directions (sheeting in and out). Big sheet tension hurts drag too, as the frictional force is directly proportional to the sheet tension. For this, and a bunch of other reasons, end boom sheeting is mechanically more efficient, but Sailboat Design, like life, is a series of compromises and imperfect solutions. There are a lot of practical advantages to mid-boom sheeting.
Keith Sneddon #4760, "Are We There Yet?" ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Tim Millar Sent: Thursday, June 11, 2009 10:49 AM To: [email protected] Subject: Re: [IC27A] Main sheet trim Jeff, I have the same original setup on our 1986 and agree that it can be difficult. Hope we can get an explanation and solution. Tim Sea Scout Ship 76 Spirit, #6254 On Jun 11, 2009, at 10:29 AM, jlenox225 wrote: I searched the forum and did not find any other posts regarding this issue. Does anyone else have trouble trimming and easing their main. I have mid boom sheeting to the original cabin top traveler. I find that the sheet binds up when I try to ease it under load and I need to assist it by feeding line from where the sheet enters the aft most block on the boom. When sailing to weather it seems like there is a significant load on the sheet when trimming which requires the use of the winch handle. I would even say that with the sails down, to fully sheet the boom amidships it feels a bit tight. It would seem that it binds somewhere in the turns from the winch to the turningblocks on deck to the 3 blocks which redirect the sheet to the traveler. I found that I had the same problem on my S2 27 which had a similar set up. It appears by looking at other C27s that this is the standard set up. I hope I explained this in a not too confusing manner. Thanks, Jeff ________________________________ This e-mail and any files transmitted with it may be proprietary and are intended solely for the use of the individual or entity to whom they are addressed. If you have received this e-mail in error please notify the sender. Please note that any views or opinions presented in this e-mail are solely those of the author and do not necessarily represent those of ITT Corporation. The recipient should check this e-mail and any attachments for the presence of viruses. ITT accepts no liability for any damage caused by any virus transmitted by this e-mail.
