You really don't need a professional tension gauge for your diamonds. Just follow the instruction in the Nacra manual (very difficult to pinch to the mast 12" above the bottom connection and make sure they are in good repair. As long as they are tight they will pick up the required tension. Boats are expensive enough to maintain without adding more complexity to it.
D.
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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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Recently bought 2002 Nacra 570 - Mast Collapsed in Corpus Christi Bay
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Posted: Dec 12, 2013 - 05:01 PM
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Posted: Dec 12, 2013 - 07:38 PM
racers and people who are trying to squeeze every last drop of speed out of boat will adjust diamond and shroud tension for crew weight, wind and wave variables every day along with jib halyard tension
even non racers can better isolate variables by having a gauge handy so you know shroud tension every time you rig
Lastly, the nacra manual that quoted those weights gave terribly vague directions on how much tension is needed - "Diamond wire
tension should be tight initially."
Edited by MN3 on Dec 12, 2013 - 07:44 PM. -
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Posted: Dec 13, 2013 - 04:07 AM
Does the 570 have a wing mast?
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Greenville SC
Offering sails and other go fast parts for A-class catamarans
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Posted: Dec 13, 2013 - 12:59 PM
I was actually mistaking the 570 for the 580, the latter is a little closer to the F-18 Infusion I do believe. You will need to refer to dealer specifications on the mast as it's not available online; it honestly wouldn't surprise me if it was a wing mast, since they use the same section on the F18, F16 and were using it on the Nacra 17 before the switch to carbon masts.
The tension I quoted was for a F18 Infusion mast and comes with no warranty or liability. Smaller boats will use less tension.
The days of leaving the beach without a wrench are over my friend, we adjust the diamond wire tension between races when it is blowing over 12 kts; if you think that is crazy, many teams carry heavy air battens in their boom and do a main sail batten swap between races. -
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Posted: Dec 20, 2013 - 06:47 AM
Yes you can use the book but a cheap gauge is really the way to go and a local cat sailor will probably have one you can borrow for a few minutes. They do make a big difference in performance But like the man said,, if you race you want to own your own
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2007 Nacra F18 Infusion
www.fleet250.org
Facebook: Sandy Hook Bay Catamaran Club
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Posted: Dec 20, 2013 - 08:21 AM
probably wouldn't be to hard to build your own device
just need a real one 1 time to calibrate it -
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Posted: Dec 23, 2013 - 01:31 AM
At last, I have posted some before and after pics of the mast collapse incident. I also did an additional inspection of the boat and rigging, and I confirmed that the diamond wires and attachment points are still intact. Only the fore-side spreader bolts failed, leading to the mast collapse. The aft-side spreaders are still attached to the mast, but the mounting bracket is bent downwards. Here are some pics:
• Before the fateful sail (does anything look wrong with the rigging?):
• Dead mast
• Broken spreader bolt
• Remnants of spreader bolts still attached to mast
• Remnants of spreader bolt attachments shown bent downwards next to fracture
• Aft side of spreaders still attached to mast, but are bent downwards
• Diamond wires are still intact and neither attachment point has been compromised
What I find most interesting is that the end failure mode was the spreader adjustment bolt breaking—not the diamond wires, or mounting hardware, or shroud lines, or forestay…. Instead, a bolt that should only be loaded in compression, primarily from the diamond wires, is what actually failed, leading to the mast collapse (I believe this is the “pop” we heard before the mast started to buckle). I would have thought one of these other items would have failed—or pulled the shroud anchors out of the hulls. I still think these aluminum bolts are under-designed for heavier sailing, and I would have much rather had a shroud line snap or disconnect to save the mast and sail. I will probably have custom stainless steel bolts made for the new rigging on this next round.
On a better note, my insurance finally came through on my claim after 2 long months of debating and negotiating. Let’s just say not all insurance policies are created equal—especially for boats. I would strongly advise anyone who has insurance to carefully read the fine print and exclusions to make sure you are ok with the limitations. I got very lucky with my claim, but a lot of things aren’t covered. As we all know, sailboats are not cars, and sometimes crazy s@?! just happens.
Anyway, I’m looking forward to getting the boat repaired to “like new” condition. Please let me know if there are any good upgrades you think I should consider, since I’m getting a new mast, spreader, diamond wires, and mainsail (probably mylar).
Thanks for everyone’s tips and ideas!
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Doug
2002 Nacra 570
Austin, TX
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Posted: Dec 23, 2013 - 06:41 AM
looks like corrosion was not the issue, just age and metal fatigue
if your wires were not set correctly, they could add lots of stress (anywhere) on the system leading to the metal fatigue
the rust at the base of your wires is an indicator you should closely inspect or replace then
the rigging tape MAY have hidden a small crack that MAY or maynot have been viable and should be removed from time to time for inspection (my tape has been on my mast for years .. .maybe today a good day to remove it and inspect)
this is an expensive post - Thank you for posting and sharing all the pics -
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Posted: Dec 23, 2013 - 09:19 AM
Thanks for posting the photos and the results of your investigation! I can't really say anything was at fault with your setup, looks like a bit of bad luck and finding the weak point in a design. It is possible you had some dynamic loading on the spreaders that could cause that sort of failure, but really your diamond wires would have to be loose and the spreaders at an angle, none of that seems to be the case.
Be warned however that moving to stainless steel on these bolts will be very expensive; you don't want a weld at the eye between the bolt and the attachment prong, rather a one piece bolt/prong fitting. I'd guesstimate that a competent shop would charge you $500 for those bolts, but maybe it can be done for less by simply cutting a slot in a threaded rod. You also have corrosion issues to contend with (two different metals), and a minor weight penalty.
I can't say any of the rust in the photos would cause me worry. I replaced the diamond wires on my last N20 from a reputable rigging company and within 2 weeks that level of rust was apparent. It's also pretty common on the staymasters we all use on the race boats. Simply surface rust that has no real effect on structural integrity. I will say my latest rigging from Rick Bliss at New England Catamarans has held up much better.
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