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We're searching for a good 45' bluewater cruiser and the Liberty is on our short list. the layout, quality and offshore capability make her our ideal boat. One concern we have is the chain plate design. The chain plates appear to be built into the hull and there doesn't seem to be any access. how do you get comfortable with the integrity of the plates when you can't see them? Any info would be greatly appreciated!
Can the chainplates be moved outboard and fixed to the outside of the hull? On a cruising boat that doesn't point too high to begin with, moving them outboard can offer a number of advantages. While you lose a bit of the sheeting angle, you gain in other areas. You can make very strong and inexpensive chainplates out of stock SS (even make a reserve set while you're at it). They are easy to inspect and re-bed when necessary. They tend not to have corrosion issues because they are exposed to air and freshwater rinses. They free up your side decks, making movement on board safer and easier.
Thanks for the posts. I like the idea of the xray, very interesting article. I believe the cost of the xray a small price to pay for peace of mind. Moving the chain plates outboard seems to be a great idea and would take it under consideration if the situation arises.
Chainplates should be 'visualized' for fatigue cracking either by 'dye penetrant' techniques or by 'magnetic flux' analysis via specialized equipment. Therefore the plates must be removed to inspect. Xray is only 'incidental' in such analysis as it cannot define the small micro-cracks, etc. that are a stark 'forewarning' of imminent catastrophic failure. Cyclically loaded 300 series stainless steel that goes beyond 1 million load cycles of loading at beyond 30% of maximum design strength .... will usually be 'ready' for sudden catastrophic brittle/fatigue failure .... well beyond 'worn out' and 'exhausted/tired' metal'.
Those chainplates 'must' be removed and visualized, etc. ... for 'safety sake'.
I have a Starratt & Jenks 45' sloop with the chainplates fiberglassed into the hull. I dont trust them and will be fabricating and installing external ones. I have found a few pieces of stainless on the boat that had very small rust lines on them, when I tested them with a lever, they snapped very easy on the line. I want to make new ones out of 7075 T6 Aluminum alloy .75" X 2.5" flat bar. The 7075 T6 alloy is not your average aluminum with a yield strength of over 53,000 lbs. Thoughts and input would be greatly helpful.
IMHO, you'd be better off with 316L stainless steel for chainplates. First, IIRC aluminum is far less fatigue resistant. Second, aluminum is less noble and you'd probably be using stainless steel fasteners with them. Using stainless steel and aluminum together with fairly large stainless steel fasteners is generally a bad idea, since the galvanic corrosion issues are far more likely because of the size of the fasteners.
I have a Starratt & Jenks 45' sloop with the chainplates fiberglassed into the hull. I dont trust them and will be fabricating and installing external ones. I have found a few pieces of stainless on the boat that had very small rust lines on them, when I tested them with a lever, they snapped very easy on the line. I want to make new ones out of 7075 T6 Aluminum alloy .75" X 2.5" flat bar. The 7075 T6 alloy is not your average aluminum with a yield strength of over 53,000 lbs. Thoughts and input would be greatly helpful.
Aluminum7075 T6 in contact with halides (NaCl > 0.5% wt.) similar to seawater has a very low nominal "Fatigue Endurance Limit" .... about 15,000 psi. Chainplates and other components that are subject to repetitive cyclic stress loads will typically fail in fatigue/brittle failure mode and not in 'ductile failure'.
The nominal Fatigue Endurance Limit FEL for 7075 T6, depending on post treatment, can be as high as 25-30,000 psi; but, when in contact with chlorides, etc. can be 1/2 that value 12-15ksi. Assuming a design Safety Factor for this boat at FS=3 and a UTS of 60ksi, UYS of 53ksi, FEL of 15ksi ... ... ... ... I'd be selecting stainless 316 for the plates and would be mechanical mirror polishing (followed by electropolishing if possible) the 316 to retard both fatigue and crevice corrosion potential and would be selecting 30ksi as the FEL for that material.
So stainless it is, 316L sounds to be the bees knees for this application. Can I also purchase 316L hardware? What size hardware? What length should I make the chainplates? What size stainless stock do I use to make them out of? How far apart do I drill the mounting holes? Can I use aluminum for backing plates or should I use stainless for that too?
Mabey I need to go buy a book on rigging... I still cant figure out how much tension to adjust the shrouds to either. I'm not a racer, just a cruiser. Thank you so much for all your help. Any answers you can give are much appreciated!
If the plates are simple 'bar' and have no welding alterations, etc. then plain 316 will perform to the same level as 316L.
wkeenan - Just imitate the same shape and size of the OEM plates just change the materials and surface finish. If you have had 'failure' then of course you can increase the 'cross section' of the OEM plates. Dont totally reinvent the wheel, just make the old wheel 'better' - small steps of improvement.
You have just joined a large group of concerned sailors who are in the same situation. Early versions of the Island Packet yachts were plagued with corrosion problems in their chain plates as was a lot of the older Hinkleys. Many manufacturers use this method of fiberglassing the chain plate weldment into the laminate of the hull. Contact the owners association of these boats. I am sure there will be plenty of interesting solutions to chose from. I prefer being able to inspect them visually, either through external mounting to the hull or bulkhead mounted chain plates. Also consider hull liner/tie rod installations, ie: Beneteau, Catalina, Hunter and other manufacturers using interior grid/liner construction. Consider and get quotes for the repair before making an offer. Your surveyor will advise you to the extent these repairs may take.
Interesting little story about stainless steels. This week we got back a wastewater RO filtration unit from a customer. All the stainless on this unit was 316. The sch 40 piping was welded and not subsequently finished in any way. It was all quite corroded at all the welds. The filter canister was a bead blasted finish, and eaten completely through in several places! The high pressure Can pump had an electropolish finish, and was still bright and shiny everywhere. Interestingly, the hot dip galvanized frame still looked great! I don't know what they were processing, but it sure raised hell with stainless steel.
Not surprised the bead blasted portion and welds got eaten up. Not surprised the electropolished stuff was in good shape. The irregular surface of the bead blasted areas encourage crevice corrosion and that's why it got eaten away so badly. IIRC, the welds tend to be more prone to corrosion because the alloy composition changes due to the high temperatures of the welding process, since the various components of the stainless steel alloy have different melting points. The increased corrosion can be reduced by using low carbon versions of the alloy, 316L, rather than 316.
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