All the parts diagrams for the Nacra show a mast spreader assembly that uses 4 bars that attach to brackets on the outside of the mast. My Nacra 5.0 has a simple tube that passes through the mast via holes in the sides of the mast. Mine is badly damaged and needs to be replaced. Is there are replacement for this type of spreader, or should I retrofit a 4 bar spreader assembly shown in the parts catalog?

Thanks



edited by: dhibberd, Nov 14, 2009 - 09:09 PM

I have the same system on my 5.2 and am also interested in the answer to this. How hard is it to retrofit with a 4 bar system? Where can I get one?

--
Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
--

when they changed the diamond wire spread from straight to adjustable swept they also changed the mast head system and the sail construction. the big Q is, did they also change the mast extrusion???

with the old straight spreader mast, pre1983?, downhaul was only for removing the wrinkles from the sail luff

the swept spreader system came in with a different way of hooking the main sail on the mast top and different hardware at the top of the mast to allow this

with the swept spreader system to tension on the diamond wires was increased greatly to induce fore/aft mast bend before the sail was raised

the reinforced sail was then raised and by wailing on 10:1? downhaul the mast could be bent on it's for/aft axis to flatten the sail and so de-power it

if you change just the spreaders from straight to swept what will happen???

not much if you stick with the 3:1 downhaul!

but if you also replace that with something more powerful what will happen?

perhaps you will pull your unreinforced sail apart, it was never designed for 10:1 downhaul and it's now probably over 20 years old so....

ok so you've got a new swept spreaders, uprated downhaul and a new sail.......what will happen now???

well it depends on the mast section, did nacra change mast section when they changed sail, sail head and downhaul or not?

i don't know, please tell if you do

erice

if you change just the spreaders from straight to swept what will happen???

not much if you stick with the 3:1 downhaul!

That's probably what I will try to do. Do you know if I will need to replace the diamond wires? Or will my current wires work with the new spreader?

Thanks.

I would think you can use the same ones since the turnbuckles give you some play for length, and the distance from the mast should be roughly the same.

--
Rob
OKC
Pile of Nacra parts..
--

but if the spreaders have even slightly different dimensions.. i would expect to need to change the wires. even with turnbuckles.. you dont have more than an inch (or so) of adjustment range ...

IMHO... change them out anyway.. if they are as old as the rest of the mast.. they probably could use replacement. they are subject to the same conditions as regular stays (exposure, repeated loading/unloading)

Quote

ok so you've got a new swept spreaders, uprated downhaul and a new sail.......what will happen now???

well it depends on the mast section, did nacra change mast section when they changed sail, sail head and downhaul or not?

i don't know, please tell if you do

This is a question where you call the factory and speak to one of their tech support folks. I have found them to be most helpful. I also might suggest your local dealer. Sounds like the physics of the whole rig are in question here.

If it helps you, here is a picture of the spreader assembly on a 5.7
I undid one side of the spreader assembly to gain enough clearance to get the mast inside for the winter. They come apart simply by removing the locking ring
& pulling the pins.
It appears that the sleeve the spreaders attach to are simply riveted onto the mast.[][/img]

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
--

I'm not sure who's picture of who's mast that is, but you might want to tell him that it WILL fail sooner or later. It's not a matter of "if", but "when". The starboard adjustable spreader has been bent, it has been significantly weakened, and will fail, causing the mast to fold. I've seen it a dozen times.

Replace that one piece. More than likely, if it hasn't been adjusted in a while, the threaded part is seized due to corrosion, and will not adjust. In that case you might need to replace both sides. An ounce of prevention . . .

--
Philip
--

Quote

The starboard adjustable spreader has been bent,

Hey, good eyes there Philip.. i didnt see that, even after reading your post i had to go back and examine.

Quote

The starboard adjustable spreader has been bent, it has been significantly weakened, and will fail, causing the mast to fold. I've seen it a dozen times.

How exactly does it fail when that happens? Does the spreader bar fold up vertically at the pin?

--
Rob
OKC
Pile of Nacra parts..
--

Quote

How exactly does it fail when that happens? Does the spreader bar fold up vertically at the pin?

yes.. it slides up or down (often the result of capsizing or when sliding the mast in the trailer)

andrewscott

Quote

How exactly does it fail when that happens? Does the spreader bar fold up vertically at the pin?

yes.. it slides up or down (often the result of capsizing or when sliding the mast in the trailer)

No, not necessarily, but as you described this can cause perfectly healthy hardware to fail.

Back to my point. That alloy is weakened and will fail. It will just freakin' fail, then the mast will not be supported by the designed truss (the spreader/diamond wire), the spreader will collapse, and the mast will fold, then tear and break in two, usually around the spreaders, the rig will come down, the sail will tear or cut at the luff, everybody will be screaming (oh sheet!) as they are teabagged off the wire into the drink.

So no, it will not slide up or down, it will break, it will just plain ol' friggin' break, starting a microcosm-oh-craptastic chain reaction of exponentially expensive, untimely and undesirable perils. Your arse will be towed home, and you will foolishly be wishin' that you would have replaced the $4 part.



edited by: mummp, Dec 18, 2009 - 06:10 PM

--
Philip
--

I understand all the potential things to go wrong after a spreader fails, and I have to assume that the same forces that cause the spreader to fail will insure that the rest of the rig doesn't get totally spared, but 'It will just freakin' fail' may be too technical for me. I'm really curious as to how. I understand that aluminum loses lots of strength after being bent, but from that picture the only way I imagine it failing is that bend just going further in the same direction and the spreader bar bending straight up.

Quote

So no, it will not slide up or down, it will break, it will just plain ol' friggin' break, starting a microcosm-oh-crapomistic chain reaction of exponentially expensive, untimely and undesirable perils. Your arse will be towed home, and you will foolishly be wishin' that you would have replaced the $4 part.

Don't forget - you'd get to throw in an 'I told you so.'

--
Rob
OKC
Pile of Nacra parts..
--

Yurdle,
I really don't know how to articulate to you the techno-babble of what is happening, 'cause I ain't good at it, but, I will try.

I'm not talking about it bending up further, as that will surely kill it.

Is this a loose rig or tight rig? If it is a loose rig it is very easy to bend this piece, and that is one way it happens, and then you run the risk of further bending and failure. Not Good. If it is a tight rig it is less likely to accidentally move up or down. But, let's not focus on if or if not it is going to move up or down, because that should not be your concern. Your concern should be this weak chain in the link, which can cause catastrophic failure as described above. The day that piece bent it was weakened and fatigued. At some point there will be that unwelcome significant load (either compression or tension, without the spreader bar moving) that will do it in.

If you run a tight rig, (we run 600-900 lbs. on each of our diamonds) you put pretty significant loads on that tiny shoulder of alloy. That area is further and constantly being loaded and unloaded in copious ways, i.e. downhaul cycles, mainsheet tension, on and off the trapeze, stuffing waves, etc. It is further complicated by the fact that one ear could carry more load that the other due to the bend, and/or the holes being out of alignment while sharing the same clevis pin. The problem is further enhanced with a loose rig. Picture this, your sailing in heavy air traveler out, hard mainsheet, tight wave sets, and two large adults on the wire. The leeward spreader/diamond is under a tremendous load. Skipper screws up, drops the mainsheet because he lost balance while stuffing a wave, both skipper and crew teabag hard, and the boat luffs up. So what do you think the loads were on the weak link in the chain? Thats right, they were all over the place. What do you think the loads would be on that leeward spreader when double trapped upwind, downhauled, and hard sheeted main and jib? That piece, depending on rake, can also cycle between tension and compression. I can describe plenty more situations that exercise forces on that little piece, and you can hardly imagine what it has gone through over 20-25 years. I'm willing to bet there is also corrosion/pitting where the stainless steel clevis pin contacts the hole in this piece. Conclusively the bent and weakened piece is further compromised by age.

So, to satisfy your curiosity of why, I'm not sure I know the answer, or if any of the above is any help. What I can tell you is through time and experience, I have learned these things, and they tell me to replace things like this or replace your standing rigging every x# years, etc. The real issue is that there is an obvious problem that can lead to a bigger problem, and my experience is that it will cause rig failure, sooner or later.

I wouldn't add an "I told you so". I've lost rigs and it is a sickening feeling, and you can get hurt. Got that t-shirt also.

--
Philip
--

I'm not too concerned about this rig in particular. I'm pretty sure Ed knows its bent.

I'm not concerned about mine either. I try to keep all my standing rigging (during the summer) as tight as possible, although my diamond wires definitely get the least attention.

I just asked out of curiosity, since you'd seen it before. Sorry for the confusion.

How do you measure the 660-900#?

--
Rob
OKC
Pile of Nacra parts..
--

Loos Gauge. We usually check/adjust tension before every race according to conditions/crew weight.

--
Philip
--

Quote

The leeward spreader/diamond is under a tremendous load.

Thanks for pointing that out. I did notice the slight bend, but did not think it that serious. I think for the small cost I will change it before spring. Is it worthwhile to look for a used one, or is that merely replacing old with old? Where to get a new one, Murrays or the manufacturer? The boat was never in salt water, I had a quick look at the adjusters, no visible corrosion, so it MIGHT undo easily. Thanks for pointing that out to me. You are right about an ounce of prevention, plus I might loose a big part of the summer waiting for pars, & the cost of a new sail or mast would definitely gobble up the beer budget!
I'm not a racer, & I think I read not to leave the diamonds tight for long periods. I will probably tension to a setting that I can leave. I believe I read in the manual about measuring tension by deflection of the wire under slight load, ie pressing with your thumb. Not nearly as accurate as what you do. What tension would you recommend for a new guy, who won't be going out in big wind the first year?
With regards to the quote, am I missing something? I can't visualize the LEEWARD wire being under load. As the mast tries to bend to leeward, doesn't that wire go slack, and the windward wire coming under greater tension? It would then act like a truss, stiffening the mast. I noticed on a Hobie Wave that the lee shroud would slack right off, to the point of flopping around.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
--

A used one should work fine, as long as it hasn't been bent. Check with Dan Berger, who has a pile of parts for sale for a 5.7 on the classified adds. He may be able to help you with all the bits and pieces you need (he sure helped me with mine!). Send him an e-mail he hasn't listed everything he has. I have used Murrays with good success but if you have a Nacra dealer close by it may be more convenient and they may be able to give you some good advice.

You can simply tension the diamond wires by deflection as they say in the manual no need for anything fancy.

The diamond wires try to keep the mast straight (side to side anyway). So the force on the sail tries to bow the mast toward the lee and the leeward diamond wire resists this. The windward shroud takes the load (so the leeward shroud goes slack) and the leeward diamond wire keeps the mast from bowing out (at least too much there is always some bow).

D.

--
Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
--

Quote

The diamond wires try to keep the mast straight (side to side anyway). So the force on the sail tries to bow the mast toward the lee and the leeward diamond wire resists this. The windward shroud takes the load (so the leeward shroud goes slack) and the leeward diamond wire keeps the mast from bowing out (at least too much there is always some bow).

Thank you Dave. Let me add that the weight of the windward hull, and the crew weight on the windward hull or wire, also act to increase the load on the leeward diamond. So will mainsheet and jib tension, all forces adding compression on the mast and increased loads on the leeward spreader/diamond.



edited by: mummp, Dec 21, 2009 - 12:03 AM

--
Philip
--

Yeah, basically all the load that pulls against the windward shroud (sail forces and weight of the boat/people) want to make the mast bow out and the diamond wire resists that. Some cats don't bother with diamond wires (hobie 16 for example) and they have to live with the bowing or put stronger (heavier) masts on thier boats. The mast on most Nacra boats is pretty light and tall.

--
Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
--

Here's a diamond wire question thats relevant here. Do you or should you take the pressure off your diamond wires in the off season?

Thankyou gentlemen, that now makes perfect sense. I had not thought of the mast bowing, I only thought of the mast being tipped to lee, pivoting at the base, hence transferring the load only to the shroud. The hulls, trap etc contributing to bend also makes sense now.
Sometimes the obvious isn't!
I did find the tension directions in the assembly manual.


--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
--

I ran my diamonds at 450 lbs. on the gauge and the spreaders swept to 1.75 inches on my 5.5 SL. This gave me about .5 inch of prebend. This was not a great setting for light air but worked well in 10-15 at a crew weight of about 290 lbs.

That was a class Mylar sail. Not a Dacron like he has on the 5.7.

No way would I go with that much on a dacron sail that was not cut for prebend.


--
Ron
Nacra F18
Reservoir Sailing Assn.
Brandon, Mississippi
--

In the post-1985 manual it talks about tensioning the wires until you are not able to push the diamond wires against the mast 20" above the bottom of the wires but are still able to push the diamond wires against the mast 12" above the bottom. That is the rule of thumb I use.

--
Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
--

Quote

No way would I go with that much on a dacron sail that was not cut for prebend.

without getting over technical, and this is much more important for racing and maximizing your speed...

Ron brings up a good point here... diamond tension, sweep of the spreaders and especially pre-bend..are VERY dependant on the cut of your sail.

AS i understand it... the pre-bend should match your luff cut curve (with down/outhaul and some main sheet



edited by: andrewscott, Dec 22, 2009 - 09:49 AM