Tim, I did not see a response from a 35-3 owner so here is how we approach backstay pressure on Calypso. Calypso has Dyform wire fore and back stays rated equal to the rod that was replaced. We have a Harken roller furler. Typically we experience the most forestay sag in 17 to 20 TWS with the heavy #1 up. By downshifting to the #3 we are again able to meet our target forestay sag. The 70’s era 43’s have fore/aft bulkheads that run from the foreward bulkhead to about 6’ aft the mast to stiffen the hull from bending forces.
A good visual is the backstay adjuster is attempting to force the mast through the keel. As you add tension (represented as pump PSI) there will be a point where you risk damage to the rig or hull. When we purchased Calypso the hull had some fractures just forward of the mast step / leading edge of keel. The fractures were discovered when looking for the source of water seepage. During the repair process the best theory we developed was during the decades of hard racing with over use of the backstay adjuster the hull laminate was stressed causing the athwart ships fractures. A few years later we had several guys on board who had crewed on the boat when it was raced hard up and down the east coast in the 70’s (then known as Arieto). Both indicated they “cranked the s#*t out of the backstay adjuster to gain a straighter forestay. On Calypso we also use 2,000 psi as a upper limit. As we approach that limit I sight up the mast to be sure it is still in column. If the mast head is sagging off to leeward or there is excessive mast bend the forestay “looks” longer to the rig. I have yet to determine a good way to measure hull deflection/bend when at max backstay pressure. The 2,000 psi upper limit is based on the feel of the rig and past experience with other hydraulic systems. I do expect the psi gauge is representing only the internal pressure of the pump. If a more scientific calculation of actual force being added to the rig was desired I recommend obtaining a copy of Brion Toss’s rigging book, the owner’s manual for your hydraulic pump, and a friend good a math. On several fancier race boats I have sailed we used running back stays to straighten the mast reducing the forestay sag. We would set the backstay adjuster close to max then crank up the running back until the mast and or the forestay was straight enough. To be clear, I was not the boat owner nor responsible for the repair bills. As the saying goes “nothing performs like a loaner”. If you are confident the mast/rig is correctly set up and in column, all the fore and aft stay components are in good shape, and you are not using too large of a head sail for the TWS it may be worth adding a little more pressure to the adjuster and look for an improvement. If there is no change to the forestay sag I would assume the boat is bending or something else is giving way. Martin Calypso 1971 C&C 43 Seattle [cid:D1BF9853-22F7-47FB-86F2-4115CE0BAF2F] From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Tim Goodyear via CnC-List Sent: Thursday, June 12, 2014 9:16 AM To: cnc-list@cnc-list.com Subject: Stus-List Backstay Tension 35/3 Hi all 35-3 racers (and others with hydraulics), how much do you tension your backstay to get an acceptably straight forestay in 20-25kts? We were racing in that last night and our forestay was way looser than I wanted with the backstay at 2000psi (2 on the hydraulic panel). I have never gone above this before (1.8 seemed to be plenty for most conditions last year), but wondered what others maxed out at. I think the backstay is -10 rod with associated cylinder and we have a navtec panel that manages both backstay and vang. Thanks, Tim Mojito C&C 35-3 Branford, CT
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