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  #21  
Old 10-07-2013
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Re: Mast Life and When to Replace It ?

Quote:
Originally Posted by Omatako View Post
Are you sure that is "bare"? Mostly when mast sections are aluminium colored, they are clear anodised. Raw aluminium will corrode like billy-o.

If the anodising gets scratched it corrodes as badly as scratched paint.
Anodized.

However, with anodized masts the corrosion is right there, in the open, not under paint that holds water and salt. Though corrosion is possible, way up in the air is generally a pretty dry place washed free of salt by the rain. While some surface corrosion is certain where the coating wears away, pitting of structural importance is unlikely. Even bare aluminum (depending on the alloy) can do quite well up in the air.

I don't agree that bare aluminum corrodes like billy-o. I have had numerous aluminum components on these boats, deck and boom, that were not anodized. If isolated apropriatly and mounted apropriatly they did just fine. Mounted poorly or coupled badly they can pit; the builders made tha mistake a few places.
No, in my experince anodized aluminum (booms and masts) does NOT corrode as badly as scratched paint. If that has happened, there is certainly a disimilar metals issue or something equivalent (in that case, you're in touble either way).

I didn't say anodized Al couldn't corrode, I said "I've had 3 boats, 1 with a painted mast and 2 bare. Guess which one had corrosion issues?" Those are my facts.
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Last edited by pdqaltair; 10-07-2013 at 07:30 AM.
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  #22  
Old 10-07-2013
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Re: Mast Life and When to Replace It ?

I have never heard of a mast failing due to fatigue or just being old. I would suspect that a mast could last well over a 100 years as long as corrosion is dealt with and not allowed to run wild.

Has anyone ever heard of mast corrosion causing a catastrophic failure?
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Old 10-07-2013
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Re: Mast Life and When to Replace It ?

SS 304 is stronger than 316 - that comes at a price; and that price is more carbon.

316 is sufficiently strong enough for chain plates if you use the same size as before (there is a safety factor built in that is larger than the difference in 304/316 by a multitudes).

Aluminum of the proper grade for a mast should have a sufficient magnesium percentage to produce it's own anodizing coating (i.e. just leave it bare).

If you are going to talk chain plates you should also consider checking the deck step as it's under compression for years and could use a checkup.
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Old 10-07-2013
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Re: Mast Life and When to Replace It ?

Quote:
Originally Posted by HighFly_27 View Post
Boat Info: 1970 Islander 37 M S

I've searched for information but did not find a lot about the method used to evaluate a mast and when to replace it.

My mast has some (2 inches) corrosion at the base but nothing visible up the tube.

I read where racing boats have their mast's replaced due to.... cumulative stress loading. I'm a airplane mechanic and understand why a alum. mast is stain hardened and becomes brittle & fails under heavy load... specifically in a raced boat.

My question is geared against a non raced boat but 43 years old. Logic may dictate.. it may/ should be at the end of it's service life. If I was inspecting it in the airplane world... I'd strip the paint and inspect it for cracks and return it to service if found A Ok. I have the mast off the I-37 and did not see a bending set in the mast.

My reason for asking this question is receive advice, & what others have learned over the years. I understand the saying... if it ain't broke, don't fix it. I'm concerned about sailing in higher wind conditions and my mast fails. I could address the 42 year old mast now and save a much higher $$ expense, should it fail at sea. I was pricing new masts, they run about $ 4 K.

Note, the hull is in good shape, blister/ defect free. A lot of money has been spent on this boat. If I bought a new mast... it would not be throwing money away against a boat that need's everything else to be seaworthy.


Avery
I see you are an air plane mechanic. Have a question for you. Can air frames last "forever" if they are inspected regularly (and cracks and defects repaired). I know fatigue in a salt envivronment can be devastating on aluminum:



From above link:

"Investigation by the United States National Transportation Safety Board (NTSB) concluded that the accident was caused by metal fatigue exacerbated by crevice corrosion. The plane was 19 years old and operated in a coastal environment, with exposure to salt and humidity.[6][7]
According to the official NTSB report of the investigation, Gayle Yamamoto, a passenger, noticed a crack in the fuselage upon boarding the aircraft prior to the ill-fated flight but did not notify anyone.[8]"


Also, I understand some planes use wire to move control surfaces. Is this wire and the fittings stainless steel? If so, would you know the type (316 or 303). How does an airplane mechanic inspect the aircraft cable and fittings? Do you pass the cable as good on a visual inspection, or does it need to be replaced based on age?

Seems planes and sail boats have a lot in common.

When I had my boat surveyed, I asked him how long the mast should last. His answer was forever, as long as I don't bend it.

Regards

Last edited by casey1999; 10-07-2013 at 03:58 PM.
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Old 10-07-2013
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Re: Mast Life and When to Replace It ?

Casey,

I found out from one of the folks here that the Mast is supported and Not Subject to the ... unsupported loads that a aircraft would endure.

If the Mast is rigged properly with Zero loading... mast life or failure is Not a Problem.

*** I will answer the question about the 737 that blew the cabin top off. This 737 is pressurized and the aircraft skin is flexed time & time again as it cycles from being pressurized to not pressurized. You can visualize how many times (19 years) the thin metal fuselage will be expanded outward and then de-pressurized (contracted). The metal becomes strain hardened and metal fatigue results with cracks forming. After this accident... all the 737's were inspected per the manufactures (new) Airworthiness Directive (AD).

All aircraft manufactures have A D's on their aircraft.. no aircraft is fault free, some are critical and reoccurring. The wings are very critical... the old Beech 18 had a reoccurring wing inspection... x-ray or install a added strap fix to beef up the wing.

Aircraft and Sailboats have some similarities i.e. sail & wing, etc. are airfoils, the hull is hydrodynamic (airfoil shape). The materials are similar i.e. high strength alum., rigging cables set to proper tension. Inspection & Care is very critical for a aircraft, you can't coast to a stop and call for road service. A sailboat requires a critical eye to prevent catastrophic part or (correct) assembly failure while under way.


Avery



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Last edited by HighFly_27; 10-07-2013 at 04:58 PM.
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Old 10-10-2013
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Re: Mast Life and When to Replace It ?

The mast is much different than an aircraft in that most or all of the loads it experiences are in compression. The stays take loads in tension. When a mast fails, it is due to buckling or a stay failure. So, I suspect that the chances of a mast experiencing metal fatigue is extremely low.

Quote:
Originally Posted by HighFly_27 View Post
Casey,

I found out from one of the folks here that the Mast is supported and Not Subject to the ... unsupported loads that a aircraft would endure.

If the Mast is rigged properly with Zero loading... mast life or failure is Not a Problem.

*** I will answer the question about the 737 that blew the cabin top off. This 737 is pressurized and the aircraft skin is flexed time & time again as it cycles from being pressurized to not pressurized. You can visualize how many times (19 years) the thin metal fuselage will be expanded outward and then de-pressurized (contracted). The metal becomes strain hardened and metal fatigue results with cracks forming. After this accident... all the 737's were inspected per the manufactures (new) Airworthiness Directive (AD).

All aircraft manufactures have A D's on their aircraft.. no aircraft is fault free, some are critical and reoccurring. The wings are very critical... the old Beech 18 had a reoccurring wing inspection... x-ray or install a added strap fix to beef up the wing.

Aircraft and Sailboats have some similarities i.e. sail & wing, etc. are airfoils, the hull is hydrodynamic (airfoil shape). The materials are similar i.e. high strength alum., rigging cables set to proper tension. Inspection & Care is very critical for a aircraft, you can't coast to a stop and call for road service. A sailboat requires a critical eye to prevent catastrophic part or (correct) assembly failure while under way.


Avery



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Old 10-10-2013
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Re: Mast Life and When to Replace It ?

One thing I was questioning is how often control cables on air planes are replaced and are they replaced based on just inspection or time in service (or both). I know small planes like piper cubs use cables to move control surfaces, I did not realize a 747 also does:

"The B747 has a mechanically actuated flight control system. This means that there are cables running from the control column / wheel to the servo-valves on the actuators. These cables will pass over a myriad of pulleys, levers, bell-cranks and other assorted mechanical devices."

Seems these aircraft cables would be somewhat equal to standing rigging on a sailboat. Generall concensus is standing rigging on boat should be replaced every 10 years. What about an airplane?
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Re: Mast Life and When to Replace It ?

Control Cables are inspected per the Manufactures Service Manual. Control cables are always checked during the annual inspection. Visual Inspection for Wear or Broken Strands and Correct Tension per Cable Size and Temperature. You have a Cable Replacement Life that is beyond inspection Criteria, specified by the manufacture.

Fly by Wire is the latest technology, it's been around for 20 years or so. The fly by wire is a double or triple redundant system. I remember when it first came out... everyone had a mistrust for the system. You can't survive the lost of control system in a aircraft.....guaranteed to crash in a heart beat or two.
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