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Old 12-06-2012, 20:14   #16
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Re: Rigging tension???

Jeff,

I got it now, thanks. For anything to happen over the course of one crossing it would have to be almost tested to failure. No idea how.

But I actually wouldn't enclose a fitting with anything. The best way to keep stainless from corroding is to give it plenty of fresh air and fresh water. Any small amount of water that might have been underneath the wax would have quickly (as in months, not days) reacted with the available steel, and now that there is a low oxygen environment accellerated the deterioration of the steel.

This is exacally why coated lifelines are prohibited by ORC and other racing standards bodies. So long as everything is dry, the coating will keep it dry, but as soon as any small amount of moisture gets into the system, the coating holds the water against the steel and won't let it evaporate, accelerating crevice corrosion.

This is the same reason that tapeing, heat shrinking, or enclosing stainless is a bad idea. Because it is a guarantee that if water gets in, it can't get out. And this will lead to premature failure.
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Old 12-06-2012, 20:50   #17
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The vibrating might be reduced by adding some more pre-bend. More tension in the forward lowers. Less to no pre-tension in the aft lowers. Do all the rig alignment with the forward shrouds the just take the slack out of the aft ... Or whatever works.

Islander 30 hulls are likely a little softer than either newer boats or heavy tubs. So the rig slackens in a breeze as the hull bends. You don't want the lee shrouds slack enough to flop around ... As said by others here. The uppers can be as tight as necessary to "get the job done."

I wind the slack out of the lee uppers while on beat to windward at max typical heel angle. In a good breeze. The repeat on the other tack. Then play with the lowers to get the rig bent as I like.

I think a tension gauge is pretty useless in this situation. I use them in racing to set a rig to a previously determined condition. But for initial adjusting your original "by hand" technique is better.

(this is on boats like yours ... Not the SC 50 I have here. That's a real trick to set up)
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Old 12-06-2012, 20:57   #18
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Re: Rigging tension???

It's very common on 30 footers to have "mast pumping" issues. It's not a matter of rigging tune (AFAIK). Several T30 owners have installed a baby-stay to combat the vibrations with excellent results. Other owners have not complained....
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Old 12-06-2012, 21:18   #19
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A baby stay seems redundant on a rig with forward lowers. But in that vein the topping lift or some intermediate forward halyard can be tensioned to the deck.

Why would 30 footers be more prone to pumping? Seems to happen on 75 footers too.
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Old 12-06-2012, 21:27   #20
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Re: Rigging tension???

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Originally Posted by daddle View Post
A baby stay seems redundant on a rig with forward lowers. But in that vein the topping lift or some intermediate forward halyard can be tensioned to the deck.

Why would 30 footers be more prone to pumping? Seems to happen on 75 footers too.
I only know that it's common on T30's, which have single lowers. The c&c in the slip next to me has a baby stay (and for/aft lowers), and the Santana 28 next to me in my old marina had a baby stay, so I assume it was a common issue in this size range. (obviously a broad assumption, thanks )

I can only really speak of my tartan 30 experience, and other T30 owners have reported good results with installing a baby stay to counter mast pumping issues. It's something I'm considering on my own boat, because no matter how I tune the rig the mast still pumps....
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Old 12-06-2012, 21:40   #21
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Re: Rigging tension???

FWIW,

My old Yankee 30, a S&S design very similar to the T-30, had single lowers and a baby stay... and pumped happily away when the wind was from the right angle and at the right speed.

There have been previous discussions on CF about ways to combat pumping... some searching might help out here. IMO, the phenomena are related to vortex shedding from the mast tube and are not related to rig tensions. Thus, again IMO, one is better advised to tune the mast for lateral straightness and the desired prebend, not to attempt to reduce pumping. YMMV.

Cheers,

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Old 12-06-2012, 21:56   #22
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Re: Rigging tension???

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Originally Posted by Jim Cate View Post
FWIW,

My old Yankee 30, a S&S design very similar to the T-30, had single lowers and a baby stay... and pumped happily away when the wind was from the right angle and at the right speed.

There have been previous discussions on CF about ways to combat pumping... some searching might help out here. IMO, the phenomena are related to vortex shedding from the mast tube and are not related to rig tensions. Thus, again IMO, one is better advised to tune the mast for lateral straightness and the desired prebend, not to attempt to reduce pumping. YMMV.

Cheers,

Jim
Couldn't agree more, tune the rig... But, don't you think 'vortex shading' is effected by displacement in tension? (IE: a baby stay).

in other words, Doesn't a baby stay tune the mast (displace it) to a different frequency?

Meanwhile, "tuning" the mast is specific to keeping it perpendicular to the deck (port and starboard). "prebend" (I've never heard that term before) seems more about shaping the sail on the fore/aft bend of the mast (adjusted through tuning).

"Rake" is the degree of verticle alignment of the mast, adjusted at the mast step and has nothing to do with this conversation
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Old 12-06-2012, 22:09   #23
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Re: Rigging tension???

Quote:
Originally Posted by callmecrazy View Post
Couldn't agree more, tune the rig... But, don't you think 'vortex shading' is effected by displacement in tension? (IE: a baby stay).

in other words, Doesn't a baby stay tune the mast (displace it) to a different frequency?

Meanwhile, "tuning" the mast is specific to keeping it perpendicular to the deck (port and starboard). "prebend" (I've never heard that term before) seems more about shaping the sail on the fore/aft bend of the mast (adjusted through tuning).

"Rake" is the degree of verticle alignment of the mast, adjusted at the mast step and has nothing to do with this conversation
I dunno, mate! I was never able to really determine which plane the mast was pumping in -- fore and aft or athwartships. The vortex production is related to the aerodynamics of the tube, and I suspect that the frequency of the oscillation is determined by the stiffness of the tube. Hmmm... I suppose that the stiffness is modulated by rig tensions... well, I guess that I really don't know! All I can say is that I fooled around with various combinations of rig tune and could never affect the pumping very much if at all. (It was over thirty years ago!)

I do know that folks who build tall tubular chimneys often weld a spiral rib along its entire height. The purpose is to break up vortex shedding, which apparently can cause serious damage to such structures... even though they can withstand hurricane force winds otherwise.

Perhaps there is someone more knowledgeable here on CF who could shed some lite on shedding vortices.

Cheers,

Jim
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Old 12-06-2012, 22:19   #24
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Re: Rigging tension???

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Originally Posted by Jim Cate View Post
I dunno, mate! I was never able to really determine which plane the mast was pumping in -- fore and aft or athwartships. The vortex production is related to the aerodynamics of the tube, and I suspect that the frequency of the oscillation is determined by the stiffness of the tube. Hmmm... I suppose that the stiffness is modulated by rig tensions... well, I guess that I really don't know! All I can say is that I fooled around with various combinations of rig tune and could never affect the pumping very much if at all. (It was over thirty years ago!)

I do know that folks who build tall tubular chimneys often weld a spiral rib along its entire height. The purpose is to break up vortex shedding, which apparently can cause serious damage to such structures... even though they can withstand hurricane force winds otherwise.

Perhaps there is someone more knowledgeable here on CF who could shed some lite on shedding vortices.

Cheers,

Jim
Exactly. Mast pumping is not a tuning issue....

Creating a new point of tension on the mast creates a completely new dynamic. Adding a baby stay is very different than adjusting the tune on the existing stays.....

I don't know the physics of it, I just know several people have reported positive results in the T30 group. It's not uncommon at all and I suspect it's not uncommon among other boat owners....

Not sure how chimneys have anything in common with masts.... Last time I hired a chimney guy was to teardown and rebuild a brick chimney at my moms new house. I fired the guy because he was full of ****. He had no idea how to repair the rafters and subfloors..... I ended up finishing it myself.
But that is besides the point
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Old 13-06-2012, 07:18   #25
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Okay. Depends on what you mean by "tuning". But crank on the forward lowers. Run a line forward from somewhere up high to the foredeck. Tension everything up. Maybe even the vang against the boom topping lift. Wind everything on quite hard. Including the running backstays and check stays. (No runners or checks? Oops! Your designer goofed on the rig - too bendy and not enough support!) There will not be any more pumping. Maybe a hum in a blow.
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Old 13-06-2012, 07:37   #26
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Re: Rigging tension???

My boat has single lowers that are both fairly loose, even with the turnbuckles fully tightened. They each have some "play" even when I'm at the dock. The leeward lower shroud is quite loose when sailing. I'm not sure if the lower shrouds were made too long (they are fully tightened) by whoever re-rigged the boat before I purchased it, or if it's designed purposely so I can't put a lot of tension on the lower shroud. In any case, I haven't had a problem in the 4 years I've owned the boat, but the slack/flopping leeward lower does occassionally make me wonder.
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Old 13-06-2012, 08:01   #27
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Re: Rigging tension???

Some quick tuning tips to get a baseline for yourself...

Starting point Tension Settings
Headstay: ~1000lbs. You can go up to 15% of the breaking load. 7/32 is around 6300lbs?
Uppers and Forward lower shrouds: ~600-700lbs.
Aft Lowers should be only tight enough to prevent pumping: 200-400lbs

The above assumes you have centered your rig.

A mast of this size with one spreader?? should have pre-bend around 1-2 inches. You can check for this using the main halyard pulled tight down the aft of the mast to the gooseneck or deck step and look at the gap between the mast and halyard.

Cant advise on rake angles, you will have to see what type of wheather helm, etc. you have or ask another Islander?

Make sure during the tensioning process that the mast stays centered, also look up the mast track periodically during the tensioning of the lowers to make sure you arent inducing bend athwartships.

Very basic tips - dont know your rig but this should work for a boat of your size and wire thickness.

Start around here and then go sailing and see what it looks like and tune as needed. You dont want your rig falling off to leeward as a whole as it will create additional downward pressure and heel.

hope that helps.

also in this threaad there is a link to the selden manual on mast tuning which is a good guide

Rig Tension
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Old 13-06-2012, 09:27   #28
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Re: Rigging tension???

Quote:
Originally Posted by Stumble View Post
So long as everything is dry, the coating will keep it dry, but as soon as any small amount of moisture gets into the system, the coating holds the water against the steel and won't let it evaporate, accelerating crevice corrosion.
So in a way you do not recommend the use of stainless steel under water?

Quote:
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This is exacally why coated lifelines are prohibited by ORC and other racing standards bodies.
I got told that it was because it was not possible to inspect the internal cable.
I mostly attribute crevice corrosion to pollutant and the depletion of chromium.
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Old 13-06-2012, 10:41   #29
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Re: Rigging tension???

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So in a way you do not recommend the use of stainless steel under water?
Honestly I don't, but for other reasons. If stainless is on the bottom then the water near it doesn't get oxygen depleted, so the chromium can constantly self heal, then crevice corrosion isn't a problem. The concern with stainless below the water line is it become significantly more prone to electrolysis because stainless becomes less cathodic when under water. However if it is properly bonded to a zinc then it is fine.

So a stainless shaft is typically fine, since the zinc is mounted right there, but stainless through hulls could be a problem.


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I got told that it was because it was not possible to inspect the internal cable.
I mostly attribute crevice corrosion to pollutant and the depletion of chromium.
The coating does two things. First it holds water against the steel which accelerates corrosion, then as you point out it prevents you from seeing the corrosion as it occurs. It's really two sides of the same coin.

Crevice corrosion is a very complicated subject, but for boaters it can be simplified down to a couple of details. The reason stainless is, well, stainless, is that the chromium in the presence of oxygen will create a barrier to further corrosion. This process is the same thing that allows aluminium and titanium to prevent corrosion, where a very thin (a few molecules thick) barrier of oxidized metal reacts very quickly, but once this barrier is formed no further oxygen penetrates the deeper metal.

But for this process to occur there has to be free oxygen available for the metal to react with. In closed environments where the water, or air, cant be exchanged for fresh, the oxygen gets depleted, and the chromium can't form the protective coating necessary to shield the steel from attack. So the water attacks the steel causing rust, and the chromium doesn't help. From what has been described to me by metallurgists the metal starts to look like Swiss cheese, with tunnels bored into the structure as the steel grains rust away.

What makes this process isidious is that it happens fastest inside the body of the part. So a small scratch can deepen before it spreads across the surface. It is only right at the end of the parts life that the crack will rupture and the corrosion becomes visible.

In lifelines particularly this is problematic because the coating helps to create a low oxygen environment against the metal, and can hide the presence of broken strands at the same time. So the first time anyone might be aware of a failure is when they hit the lifelines and they part. I have unconfirmed stories of coated wire failing in as little as a year, and confirmed in three or less.

This is why dye testing is recommended for stainless parts (rigging after about 8 years depending on the manufacturer). The dye penetrates the cracks, and then the developer makes the cracks very visible, either to the naked eye or under black light. It can be a little tricky to confirm a failure with these tests since there is an art to reading the dye (determaning a true crack vs a scratch), but you can pretty easily confirm a good part since after the developer goes on there won't be any dye marks.

For further reading:
http://www.corrosionist.com/Pitting_..._Corrosion.htm
http://www.azom.com/article.aspx?ArticleID=1177
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Old 15-06-2012, 10:39   #30
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Re: Rigging tension???

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But for this process to occur there has to be free oxygen available for the metal to react with. In closed environments where the water, or air, cant be exchanged for fresh, the oxygen gets depleted, and the chromium can't form the protective coating necessary to shield the steel from attack.
My understanding is that the protective coating would have been produced long before the oxygen is depleted and so long the protective coating is not damaged stainless steel does not require oxygen.
Both link state that high concentration of chloride can lead to pitting. Trying to protect stainless steel by the use of a sealant make more sens to me than regular washing with seawater.
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Any small amount of water that might have been underneath the wax would have quickly (as in months, not days) reacted with the available steel,
The problem with seawater is when it evaporates it leaves behind some residue.
I may not use beeswax but if I had the choice between having a hollow fill with seawater residue or with beeswax I use beeswax.
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From what has been described to me by metallurgists the metal starts to look like Swiss cheese, with tunnels bored into the structure as the steel grains rust away.
Swiss cheese (Emmenthaler variety) has holes, no tunnels. Your’s metallurgists should keep to metallurgy.
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