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Old 23-04-2013, 09:48   #16
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Evans,

Does loctite isolate the two metals? Part of the reason steel pulls out of a mast is that the threads have turned to dust.
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Old 23-04-2013, 09:51   #17
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Re: Stripped Threads on Mast

Agree with the clutch. Also provides safety when hoisting people.

On the inserts: I think Monel is the best choice, then stainless steel. Monel might not be available. Red (permanent) threadlocker to keep it in place plus provide isolation like estarzinger wrote.
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Old 23-04-2013, 10:09   #18
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Re: Stripped Threads on Mast

The question on whether a clutch or a winch is stronger actually got me thinking. I responded based on what I know - but thought maybe I should look at the math to make sure I wasn't just parroting bad advice.

A simple calculation can demonstrate the difference in force applied to the lower screws and the difference or Mechanical Advantage could then be divided by the number of fasteners. This is obviously crude but at least a basis for discussion:

MA = D2/D1

D1 = Height of pull from mast for clutch - 15mm
D2 = Height of pull from mast for winch - 75mm

MA = 5

This of course also doesnt take into account the change in angle of pull from almost full shear to about 45degrees.
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Old 23-04-2013, 10:13   #19
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Re: Stripped Threads on Mast

Quote:
Originally Posted by foolishsailor View Post
Evans,

Does loctite isolate the two metals? Part of the reason steel pulls out of a mast is that the threads have turned to dust.
It does the job.

I would guess that "seal" is more technical than "isolate". It certainly seals against oxygen and salt water. It is thin and an excellent thread lubricant, and it may also isolate the aluminum and steel as well, but I am not sure - that will probably depend on how the threads are cut.

I agree with Jedi that monel would probably be terrific. I use monel rivets. I have never seen monel threaded inserts, but they probably exist somewhere.

If you truly want to completely isolate you can use G10 plugs. That's done on some carbon masts to separate the stainless fasteners from the carbon. You buy G10 tubes, and cut threads on both the inside and outside. But that's over the top for the OP's application.
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Old 23-04-2013, 10:34   #20
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Re: Stripped Threads on Mast

Thanks for the many responses. Not surpisingly, many opinions on this subject...

Additional info: To the best of my knowledge, the other halyard winch is the original, a Barient 10 chrome-plated bronze unit. I learned that the unit which failed, and Arco alloy winch. was a replacement done by the previous owner. He said that the bolt pattern was off just a bit from the original unit, and he had to do a tiny bit of modification on that unit's base to get it to fit the existing holes. On that Arco unit, the base piece (the piece that has the mounting flange) is made out of some sort of high strength plastic (!!?!?). I'm thinking that the modifications made to make it fit might have comprimised the unit and caused it to fail. Once the mounting flange was broken, addtional stress was put on the mounting screws. Hard to say.

Anyway, can't really rotate unit and put 4 new holes in, unless the new holes are quite close to the edge. This is because the current holes are at located at NE/SE/SW/NW positions. Rotating 45 degress to N/E/S/W positions won't work because flat part of the mast's side isn't quite wide enough...only about 25% of the screw would be in the flat area, the other 75% of the screw woul be in the area that's curving away to the front and rear of the mast, leaving the screw threads exposed.

Could move it up an inch or so and drill all new holes...of course then it would quite match the axis of the other winch...cosmetic, I know, but still. Plus I don't care for the idea of srilling so many new holes.

The rivnuts were interesting. One thing I didn't care for with them is the flange...this would mean the the winch's mounting plate wouldn't be flush against the side of the mast, but would effectively be offset by the thickness of the flange section.

So I think I'm going with inserts (and as 2 of the existing holes are fine, I only need to do this work on the other two); just need to decide exactly which inserts to go with.
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Old 23-04-2013, 11:42   #21
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Re: Stripped Threads on Mast

Btw, I'm a bit of a newbie..could someone send me a link to a webpage that shows the type of clutch mentioned, and how it works in conjunction with the winch? Thnx.
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Old 23-04-2013, 11:45   #22
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Re: Stripped Threads on Mast

Quote:
Originally Posted by estarzinger View Post
I disagree with the use of aluminum inserts.

First, the stainless insert will be stronger, because the you will have a bigger diameter of stainless threads, essentially just as if you had used a bigger bolt. With an aluminum insert and stainless bolt you are just back to the original strength, which we know either stripped or corroded.


Second, If you use a stainless insert you will always be able to remove the stainless bolt. It will never freeze or corrode in a stainless insert. And since you don't need to remove the stainless insert, so it does not matter if it freezes (but as a note the heli-coils are the easiest to remove from any corrosion because you can 'unwind' the spring, which you can not do with the more solid inserts). If you use an aluminum insert the stainless bolt may cause corrosion and freeze in it.

Third, you can actually isolate a stainless insert from the aluminum mast better than you can isolate a stainless bolt. Because you don't need to remove the insert, you can use 'permanent' stuff like red locktite, which seals the insert and will not wash out. You want to be able to remove the bolt so you can 'only' use temporary stuff like tuff-gel, which does wash out over time.
I think we're reinventing the wheel here. Aluminum inserts will supply more threads than the original thickness of the mast did. The Aluminum inserts will not corrode around the mast as Stainless would do. As far as removing Stainless from Stainless being easier...not necessarily. It can gaul quite easily. Telflon coating on either Aluminum or Stainless helps. Besides...how many times will the new winch come off once installed. Probably never.
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Old 23-04-2013, 17:26   #23
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Re: Stripped Threads on Mast

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Originally Posted by Celestialsailor View Post

The Aluminum inserts will not corrode around the mast as Stainless would do.

Agreed, but the stainless bolts will (possibly) corrode the aluminum inserts. You are going to have an aluminum/stainless interface here no matter how you do this. So one objective is to create that interface in a way that is as sealed and isolated and corrosion proof as possible. My experience is that is to create the interface at the outside of the insert (between the insert and the mast), rather than at the inside on the insert (between the insert and the bolt) - for two reasons, because you can use 'permanent type insulator/sealant on the insert which you typically don't want to do on the bolt, and because the loads are spread move on the outside of the insert so there is less force working to break the corrosion barrier there.

As far as removing Stainless from Stainless being easier...not necessarily. It can gaul quite easily.

That seems like a red herring re the OP's question. I have never had a helicoil gaul. And never had stainless on stainless gaul if I used any sort of decent thread lubricant.

Besides...how many times will the new winch come off once installed. Probably never.

My hard won lesson . . . every thing needs to come apart at sometime, and its best to design/make it so its easy. Otherwise someone is going to be there with a torch and impact wrench at some point. Particularity with winches, it is very nice to be able to inspect behind them - often you can stop some early stage corrosion before it causes any real damage if you can occasionally look behind them.
.......
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Old 23-04-2013, 18:43   #24
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Re: Stripped Threads on Mast

I think I started the controversy by suggesting the aluminum insert. I stand by that recommendation and have some experience in dissimilar metals. The aluminum insert will not corrode the mast which everyone agrees. Monel and 316 stainless steel are nearly identical in the galvanic series thus monel offers little or nothing in terms of galvanic corrosion resistance when in contact with aluminum.

Using loctite or some other goop between the insert and the mast seems risky to me. The insert is designed to grip the aluminum inside and out. With goop in there it might interfere with the clamping function and not stay tight over time and temperature variations. Having an insert spin free when trying to remove the screw is maddening because about the only thing you can do is try to cut the screw. And if the insert is installed correctly there very likely will still be metal to metal contact no matter what you do with goop. So the stainless insert will likely further corrode the mast which is then weakened more. And there is more risk of galling when a stainless bolt is inserted into stainless threads even with lubrication.

There is a chance that the steel screw will corrode the aluminum insert threads. As someone else pointed out there will be many more threads in the insert than the mast skin. But Tef-Gel or lanolin will help prevent or slow corrosion and the insert can be easily replaced if it does corrode. A stainless insert is a real pain to drill out and replace but aluminum is easy. Of all the options this is the best compromise in my view.

I still believe the aluminum insert is a superior solution compared to tapping or inserting a helicoil into a thin mast skin. One should follow the insert manufacturer's instructions to the letter.
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Old 24-04-2013, 09:33   #25
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Re: Stripped Threads on Mast

^^

To the theoretical concerns about helicoils . . . all I can say is I have an aluminum hull and an aluminum mast and I have dozens of helicoils installed. I now use them whenever I want to be able to remove the bolt later (which is pretty much always). They have all been installed with red Loctite and none have any problem at all - there is no corrosion, the bolts are easy to remove, and several have proved stronger installations (because of the bigger steel thread diameter) than the previous direct into the aluminum installation.

On the other hand I still also have dozens that are tapped directly into the aluminum, installed (by several different 'professionals') with a mix of tufgel and duralac, and about 1/3 of those are frozen/corroded when I try to remove them.

As to the aluminum inserts . . . I was looking at datasheets and many of them are 5052 aluminum (which has copper in it) rather than the 6061 the mast is probably made of. I have never used 5052 inserts but I have used 5052 machine screws and the copper in them does appear to cause some incompatibility problem with the 6061 aluminum, and they are quite weak (it is very easy to twist off their heads).
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Old 24-04-2013, 10:23   #26
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Re: Stripped Threads on Mast

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Monel and 316 stainless steel are nearly identical in the galvanic series thus monel offers little or nothing in terms of galvanic corrosion resistance when in contact with aluminum.
Is that your opinion or from a technical paper/report ? The Monel rivets in our masts do not cause any corrosion at all (19 years old) while every stainless steel fastener has major corrosion around it. This leads me to believe that Monel is much better in aluminium than stainless steel. It must also be the reason that mast manufacturers use Monel.
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Old 24-04-2013, 10:32   #27
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Re: Stripped Threads on Mast

For what it's worth, I've used the simple buy-a-slightly-bigger-tap-and-use- bigger-bolts-method. It worked fine and has held up in gale conditions. By the way, gale conditions were not what worked the original bolts loose. It was the slatting caused by motoring through a calm.
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Old 24-04-2013, 10:49   #28
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Re: Stripped Threads on Mast

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Originally Posted by Tia Bu View Post
For what it's worth, I've used the simple buy-a-slightly-bigger-tap-and-use- bigger-bolts-method. It worked fine and has held up in gale conditions. By the way, gale conditions were not what worked the original bolts loose. It was the slatting caused by motoring through a calm.
You might even be able to use a M7 tap (7mm) in the hole as it is. My results with Tefgel (exactly that product, no "similar" ones) are very good too.

p.s. for strength in thin-walled materials, use a course thread.
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Old 24-04-2013, 10:55   #29
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Re: Stripped Threads on Mast

See below for the Galvanic series. Most screws unless specifically requested otherwise are 304 not 316.
  1. Magnesium
  2. Mg alloy AZ-31B
  3. Mg alloy HK-31A
  4. Zinc (hot-dip, die cast, or plated)
  5. Beryllium (hot pressed)
  6. Al 7072 clad on 7075
  7. Al 2014-T3
  8. Al 1160-H14
  9. Al 7079-T6
  10. Cadmium (plated)
  11. Uranium
  12. Al 218 (die cast)
  13. Al 5052-0
  14. Al 5052-H12
  15. Al 5456-0, H353
  16. Al 5052-H32
  17. Al 1100-0
  18. Al 3003-H25
  19. Al 6061-T6
  20. Al A360 (die cast)
  21. Al 7075-T6
  22. Al 6061-0
  23. Indium
  24. Al 2014-0
  25. Al 2024-T4
  26. Al 5052-H16
  27. Tin (plated)
  28. Stainless steel 430 (active)
  29. Lead
  30. Steel 1010
  31. Iron (cast)
  32. Stainless steel 410 (active)
  33. Copper (plated, cast, or wrought)
  34. Nickel (plated)
  35. Chromium (Plated)
  36. Tantalum
  37. AM350 (active)
  38. Stainless steel 310 (active)
  39. Stainless steel 301 (active)
  40. Stainless steel 304 (active)
  41. Stainless steel 430 (active)
  42. Stainless steel 410 (active)
  43. Stainless steel 17-7PH (active)
  44. Tungsten
  45. Niobium (columbium) 1% Zr
  46. Brass, Yellow, 268
  47. Uranium 8% Mo
  48. Brass, Naval, 464
  49. Yellow Brass
  50. Muntz Metal 280
  51. Brass (plated)
  52. Nickel-silver (18% Ni)
  53. Stainless steel 316L (active)
  54. Bronze 220
  55. Copper 110
  56. Red Brass
  57. Stainless steel 347 (active)
  58. Molybdenum, Commercial pure
  59. Copper-nickel 715
  60. Admiralty brass
  61. Stainless steel 202 (active)
  62. Bronze, Phosphor 534 (B-1)
  63. Monel 400
  64. Stainless steel 201 (active)
  65. Carpenter 20 (active)
  66. Stainless steel 321 (active)
  67. Stainless steel 316 (active)
  68. Stainless steel 309 (active)
  69. Stainless steel 17-7PH (passive)
  70. Silicone Bronze 655
  71. Stainless steel 304 (passive)
  72. Stainless steel 301 (passive)
  73. Stainless steel 321 (passive)
  74. Stainless steel 201 (passive)
  75. Stainless steel 286 (passive)
  76. Stainless steel 316L (passive)
  77. AM355 (active)
  78. Stainless steel 202 (passive)
  79. Carpenter 20 (passive)
  80. AM355 (passive)
  81. A286 (passive)
  82. Titanium 5A1, 2.5 Sn
  83. Titanium 13V, 11Cr, 3Al (annealed)
  84. Titanium 6Al, 4V (solution treated and aged)
  85. Titanium 6Al, 4V (anneal)
  86. Titanium 8Mn
  87. Titanium 13V, 11Cr 3Al (solution heat treated and aged)
  88. Titanium 75A
  89. AM350 (passive)
  90. Silver
  91. Gold
  92. Graphite
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Old 24-04-2013, 11:30   #30
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Re: Stripped Threads on Mast

Quote:
Originally Posted by transmitterdan View Post
... Monel and 316 stainless steel are nearly identical in the galvanic series thus monel offers little or nothing in terms of galvanic corrosion resistance when in contact with aluminum ...
Anodic Index Potential (Volts) vs Saturated Calumel Half-Cell Electrode (or Standard Calomel Electrode - SCE):
Aluminum Alloys -0.70 to -0.90V
Monel -0.04 to -0.14V (-0.08V)
300 Series Stainless Steels -0.00 to -0.18V
Type 316 Stainless Steel (Passive) -0.05V
Type 304 Stainless Steel (Passive) -0.08V
Type 316 Stainless Steel (Active) -0.18V
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