Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 06-01-2006, 10:04   #1
Registered User
 
Catamount's Avatar

Join Date: Jul 2005
Location: Keene, NH
Boat: Island Yachts Peterson 34 GREYHAWK
Posts: 370
Aluminum Chainplates

A week ago I had my mast pulled for a thorough rig survey by Chesapeake Rigging. I'm now waiting for their report and recommendations, and I have my own list of things I would like to do with the mast and rig now that it is on the ground. I just hope we can get it put back in the boat for less than what I paid for the boat in the first place!

With the mast out, I extracted my shroud chainplates. Here's how they are installed in the boat:



The longitudinal bulkhead (setee back) is a cored-fiberglass structure strongly tabbed to the hull -- it is an integral part of the boat's structure. The chainplate is secured with sixteen 3/8" stainless steel machine screws through the cored-fiberglass bulkhead and an aluminum backing plate.

And here are the chainplates extracted from the boat. They are 45.5" long by 10" wide by 3/8" thick:



And the backing plates:



Here's what it looks like where the chainplates pass through the deck:



The deck in this area is cored with plywood.


Despite a little bit of corrosion here and there, there's still plenty of metal. My main concern has to do with the elongation of the pin holes (mainly for the cap shrouds and the lowers):

Port:


Starboard:


What do you guys think?
__________________

__________________
Tim Allen
My Boat Projects and Sailing Stories
Sailors for the Sea, a new voice for ocean conservation
Catamount is offline   Reply With Quote
Old 06-01-2006, 10:32   #2
Senior Cruiser
 
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Now in Blaine, WA
Boat: Modified Choate 40
Posts: 10,702
Images: 122
The only down fall to elongated holes is more backlash. BUT, I would have them all DPTed or X-rayed for cracks. Alum. is fairly forgiving up to a point, then the mushroom effect starts cracks, and that you don't want.

I'd recommend replacing them with a 5052 or better aluminum plate. SS would be nice but that size would be costly and heavy.

I'll stop here and let others add their comments..................._/)
__________________

__________________
delmarrey is offline   Reply With Quote
Old 06-01-2006, 10:44   #3
Senior Cruiser
 
Jeff H's Avatar

Cruisers Forum Supporter

Join Date: May 2003
Location: Annapolis, Maryland
Boat: Farr 11.6 (AKA Farr 38) Synergy
Posts: 543
Images: 13
That looks much better than I expected after seeing them in place. You might talk to Chesapeake rigging about doing filler welds in the area where the bolt holes have distorted and then welding doubler plates over the area to beef up the fatiqued aluminum around the bolt holes. You can also use bushings to spread the loads and reduce abrasion between the clevis pin and the chainplate a bit.

Regards,

Jeff
__________________
Jeff H is offline   Reply With Quote
Old 06-01-2006, 11:32   #4
Registered User
 
Catamount's Avatar

Join Date: Jul 2005
Location: Keene, NH
Boat: Island Yachts Peterson 34 GREYHAWK
Posts: 370
delmarrey, there's definitely some mushrooming of the Alumnim above the clevis pin holes. An inspection with my 10x handlens didn't reveal any cracking, but there's a enough Aluminum Oxide covering everthing so it's kind of hard to tell for sure.

As for SS plates, some sisterships do have them, but they've separated the lowers from the caps and intermediates so that you've got two approx. 3" wide plates coming down instead of one big 10" wide plate.

Jeff, I haven't even taken a wire wheel to them to really clean them up yet! I like the idea of drilling them out and inserting some bushings. At least that might hold me for next summer's delivery and cruising...

Thanks,

Tim
__________________
Tim Allen
My Boat Projects and Sailing Stories
Sailors for the Sea, a new voice for ocean conservation
Catamount is offline   Reply With Quote
Old 06-01-2006, 12:17   #5
Registered User
 
Catamount's Avatar

Join Date: Jul 2005
Location: Keene, NH
Boat: Island Yachts Peterson 34 GREYHAWK
Posts: 370
Hmm .... here are some "back of the envelope" engineering calculations:

My boat has -10 rod rigging, with an ultimate tensile strength of 10300 lbs. If loaded to 50% (e.g. racing margins) that's about 5000 lbs of force being exerted on the clevis pins. A 1/2" diameter pin in a 3/8" thick chainplate presents an effective cross sectional area at the hole of about 0.1875 square inches. That works out to an elongating pressure on the pin hole of about 26,667 pounds per square inch!

With the mushrooming, the width of the chainplates in the area of the hole has increased, let's say to 1/2", so the effective cross sectional area is maybe .25 square inches, and the elongating pressure has dropped to 20,000 psi.

If I drill the pin holes out to 3/4" (and thus bring the chainplates back to 3/8" thick), and put an 1/8" thick bushing around my 1/2" clevis pins, then the effective cross-sectional area at the hole in the aluminum goes to about 0.28 square inches, and the elongating pressure on the pin hole decreases to about 17,778 psi (assuming 5000 lbs tension in the rigging).

Ted Brewer wrote an article in Good Old Boat about metal boats that had some data on the ultimate tensile strength and yield strengths of several metals, including the Aluminum alloys 5086 (hull plating) and 6061 (mast extrusion). The yield strength of 6061 alloy was given as 35,000 psi, but that reduces to only 19,000 psi if welded. (Ultimate tensile strengths were 42,000 psi or 30,000 psi if welded.) The 5086 alloy does a bit better.

Regards,

Tim
__________________
Tim Allen
My Boat Projects and Sailing Stories
Sailors for the Sea, a new voice for ocean conservation
Catamount is offline   Reply With Quote
Old 06-01-2006, 12:57   #6
Senior Cruiser
 
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Now in Blaine, WA
Boat: Modified Choate 40
Posts: 10,702
Images: 122
I would agree with the bushing method providing there is not cracking!

One can buy the DPT spray cans at a welding supply. The problem with welding on corroded alum. is the weld will have porosity and you may not even get a good weld.

Defiantly, the wider the pin area the less wear to the plate.

I was going to suggest splicing a SS upper plate to the lower alum. but one just adds more fasteners to create more maintenance inspections. That's up to the individual, I guess.

It sounds like you’re on top of the engineering! So, I guess, we're here to confirm you thoughts and keep you out of trouble, if needed.

5086 is the best alum. for marine app's but a little more expensive.

.................................................. ...._/)
__________________
delmarrey is offline   Reply With Quote
Old 06-01-2006, 14:13   #7
Registered User

Join Date: May 2005
Location: Pennsylvania
Boat: Tayana 37, M-20/I-20 Scow
Posts: 250
If you can correctly identify the alloy, I'd suggest contacting the foundry,etc. and get the 'fatigue endurance' values of the material, then do your stress analysis by reverse enginering from the 'next weakest link' to ensure that plate is stronger than the next weakest member. For any correction I'd base all my engineering/strength calcs. based on the ** fatigue endurance limit** rather than Ultimate Yield Strength
or other tensile values. When/If you contact the alloy supplier also get the 'creep rate' (plastic deformation rate versus applied stress) as the 'mushrooming' that you observe may be other than simple yield failure, etc.
Ive not specifically worked with Aluminum but metals installed in cyclical stress applications should be designed for endurance rather than UTS/UYS. Without tech values based from test the fatigue endurance values for plain vanilla aluminums probably should be approximately 1/3 (or less) of the Ultmate tensile values. That equates to a Safety Factor of about 3 and would probably be consistent with a 'coastal design'.
__________________
Richhh is offline   Reply With Quote
Old 07-01-2006, 23:45   #8
Senior Cruiser
 
Alan Wheeler's Avatar

Cruisers Forum Supporter

Join Date: Dec 2003
Location: Marlborough Sounds. New Zealand
Boat: Hartley Tahitian 45ft. Leisure Lady
Posts: 8,038
Images: 102
Another thought is to bush with a high density high strength engineering plastic. Not sure what type, but there ar several that would take this type of loading. The added benifit is anti-wear of the hole in the future. The hole would have to drilled out to take the bush. This would result in the loading being taken over a larger surface area and the elongation in the alloy should not accur again. I would also suggest you get those plates anodised. They would come up real smart and be protected from corrosion for a lot longer. Or another method is to etch them and put on a good epoxy paint system.
__________________
Wheels

For God so loved the world..........He didn't send a committee.
Alan Wheeler is offline   Reply With Quote
Old 01-02-2006, 20:07   #9
Registered User
 
Catamount's Avatar

Join Date: Jul 2005
Location: Keene, NH
Boat: Island Yachts Peterson 34 GREYHAWK
Posts: 370
Well, my rigger has quoted $1600 to supply and fabricate new chainplates. Given the overall bill to get my mast put back in the boat, I'm somewhat inclined to try getting some Dye Penetrant Testing done on my old ones first, and if there are no cracks, drill them out and bush the pins. (At my suggestion, the rigger would bush the pins on the new chain plates from the get go).

Do you think the typical small town machine shop would be able to do the DPT? Or is this a job that one can DIY?

Thanks,
__________________
Tim Allen
My Boat Projects and Sailing Stories
Sailors for the Sea, a new voice for ocean conservation
Catamount is offline   Reply With Quote
Old 02-02-2006, 01:46   #10
Senior Cruiser
 
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Now in Blaine, WA
Boat: Modified Choate 40
Posts: 10,702
Images: 122
Thumbs up You can DIY.

The DPT spray cans you can get at a welding supply or machine tooling supply.

There is the developer, dye and cleaner. First, file off the mushroom and smooth with fine sandpaper. Then you'll want to sandblast the rest with a glass or garnet medium.
Use the cleaner to get out any excess oils/dirt. Then heat the part up to around 100º. This makes the dye soak in better. Let it set for a couple minutes, wipe off the dye with a cotton rag. Then spray on the developer (white powder) and let it sit for a while.

If there are any cracks they'll show up as red lines. If you don't see any after an hour, get out a magnifier and look real close. If they are that small, you should be able to drill/ream them out by going to a larger hole, but not too big.

And the bushings should be pressed into the aluminum, that way there is only one wear surface........................._/)

P.S. The DPT stuff is made by Crown.
__________________
delmarrey is offline   Reply With Quote
Old 03-02-2006, 12:15   #11
Registered User
 
Catamount's Avatar

Join Date: Jul 2005
Location: Keene, NH
Boat: Island Yachts Peterson 34 GREYHAWK
Posts: 370
I would really like to thank everyone for their comments and advice. Given the role of these chainplates in the overall structure of my boat, and the loading my rig has to support, I've decided that in the end, the rig is just not a place to mess around.

So I'm going to go with the "complete package" in the Rigger's proposal. This will include new chainplates, as well as repairing the crack in my mast, replacing all of my rod-rigging (including turnbuckles), servicing the hydraulic cylinders for both backstay and vang, replacing the hydraulic system pressure gauge, adding a shiv-box to the front of the boom for single-line reefing, adding tangs and halyard blocks for a removable inner fore-stay and running back stays, fixing the check stays, installing a Shaefer System 2100 roller furler, replacing two halyards, installing lazy jacks, replacing all of the electrical wiring and installing a new masthead tricolor/anchor light, and prep and painting (Awlgrip) of both spars. Oh, and they're going to put the mast back into the boat and set it all up, too.

(In case you're wondering, although wire is less expensive than rod, and making up wire stays and shrouds is a DIY proposition, switching my rig from rod to wire would have required re-doing all the spreader bases, among other things, which meant that wire rigging would have cost more than new rods. Rod rigging does have the advantages of less weight and windage aloft, less stretch, and the potential for longer life than wire.)

All of this adds up to quite a few pretty pennies (several more than I paid for the boat itself, in fact) -- I'm really going to be scraping the bottom of the barrel to pay for this now (anyone want to buy some sails?). But it is all work that I anticipated would need to be done sooner or later -- I just didn't anticipate doing it all at once! Much of it is work that I could not (and/or would not want to) do myself: welding aluminum, cold-heading the rod rigging, rebuilding hydraulic cylinders... Certainly some of the work I could do myself, including the painting and prep, electical wiring, etc..., but I don't have the mast sitting at home -- it's 450 miles away! Plus, I do have a full-time job, and as my wife points out, she's the one who does all the painting around our house. That, and I really do want to go sailing this summer !-)

Thanks again,
__________________
Tim Allen
My Boat Projects and Sailing Stories
Sailors for the Sea, a new voice for ocean conservation
Catamount is offline   Reply With Quote
Old 09-03-2010, 16:15   #12
Registered User
 
tager's Avatar

Join Date: Apr 2009
Location: Vashon, WA
Boat: Haida 26', 18' Sea Kayak, 15' kayak, 6.5' skiff, shorts
Posts: 837
You can make new chainplates waaay cheaper than that. Onlinemetals.com
__________________

__________________
tager is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Corroding Engine mounts ccannan Engines and Propulsion Systems 6 29-09-2015 00:13
Spade Anchor jim Anchoring & Mooring 12 25-02-2008 01:26
Aluminum spar damage. irwinsailor Construction, Maintenance & Refit 2 01-05-2004 21:52
Repairing an aluminum spar Sonosailor Construction, Maintenance & Refit 6 12-12-2003 03:46



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 02:14.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.