Fiberglass Chain Plates - Paging Minaret

[Sam Plan B]

Consider the enormous tension forces developed when a heeled boat slides down a steep sea to plant itself in the trough between waves. The shrouds and the chain plates must withstand these forces. All must resist the same forces as must the hull where the chainplates are fixed. Clearly, the GRP chain plates would be the weakest link. I cannot imagine going with anything other than stainless steel (how the chain plates are fixed to the hull is another question). Consider the outcome if your GRP chain plates do fail. Yes, I am old school and especially so with things like this. It is not all that uncommon these days for a new high tech boat coming to a bad end, dismasted or worse. Better to be safe and go with materials of know properties (tension and torsion strength). If you do that you will have the added benefit of sleeping better.

[minaret]

Originally Posted by Pauls

Something you should be aware of here. The chainplates need to be strong enough to to have a fatigue strength sufficient for a really large number of cycle. Every wave the boat sees is going to add a stress cycle to your plates. Gougeon Bros did some fatigue strength testing on polyester glass and measured an 83% reduction in strength from a fairly small number of cycles, as I recall they estimated it was what a boat would see in about 3 months.

So, a few points:
#1, the chain plates need to be a lot stronger than just the loads they will see. Typically they'd be designed to fail at maybe 1.5X the breaking strength of the wire. With glass, make that number a lot bigger. I'll give you a comparison - on homebuilt aircraft, using metal construction, the typical safety factor over the max load the aircraft is rated for is 1.5. That is a really low safety factor which works because of careful engineering, design and maintenance. On homebuilt fiberglass planes the safety factor is commonly 5x to 10x the designed load on something like the wing spars. Partly because it is very hard, at a built at home level, to make a fiberglass layup that is anywhere near as consistent in strength as is metal. So make them really strong. And as Minaret said, forget the recessed bolts.
#2, make the layup with epoxy. And not just any epoxy, a high strength, structural grade. This is NOT WEST, etc, they are designed for glueing up wood. If you don't use the good stuff, and you can't buy the good stuff at local retailers, then again make them bigger to compensate.
#3, the moral of all the above is that there are a lot of variable which are not practical to determine. So you do what engineers do - the larger the unknown factor, the larger the safety factor. The less you know about what you're working with, the more you overbuild it.

Some research is required here. My understanding is that the move to integral glass chainplates is in part because a fiberglass laminate is MUCH more resistant to load cycling and overall fatigue than SS, exactly the opposite of what is being said here. Perhaps I'm wrong, but I have built these, and the design is by Carl Schumacher. The plates end up not much thicker than a SS plate when fanned out. They have a ridiculous load rating, and are built carefully this way at great expense. I have to think Schumacher knows what hes talking about. I doubt he'd design them this way at great expense if they were just going to fail due to load cycling.
Totally agree on resin quality for this application. I would use Proset laminating resin only, with a careful post-cure.

[Nicholson58]

Originally Posted by s/v 'Faith'

Would love to buy some titanium chain plates if someone were to figure out how to tool them for a reasonable price...

Found the reference in Practical Sailor Dec 2011 page 24-25. The listed source is Alied Titanium. Allied Titanium - Home Page They made the new chainplates from the guy's old ones. Great stuff in this magazine. Ita a good one to join. Its the only paper I keep. Also a great bit on keeping SS shiny.


http://www.cruisersforum.com/forums/...reply&p=887448


I may be replacing ours.

[Pauls]

A response to Minaret's points above, the designs he's describing are uni-directional carbon, laminated with a good grade of epoxy, cured in a compression mold, and built by pros with experience in doing all this well.

This is light years away from glass fiber, polyester resin, and lay up by someone who is learning how to do all this.

In addition, Minaret's design is a really nice, elegant approach that takes the chainplate stress and distributes it across a large area of the hull. As contrasted with bolt mounting, which concentrates the stress at the bolt holes (just putting a hole in a stressed part triples the stress around the perimeter of the hole).

My point is, if you want to do this, without the engineering background that Schumacher has, just overbuild it. Make it beefy. Use a big safety factor. It'll definitely work, if you build it strong enough to take all the loads it will ever see.

[DeepFrz]

I didn't read all of this but carbon fiber is what you want to use. Poke around this site and you should be able to find out how one guy did it very nicely.
Fram sailing & building pages, home building a F-39 trimaran

[44'cruisingcat]

Originally Posted by Sam Plan B

Consider the enormous tension forces developed when a heeled boat slides down a steep sea to plant itself in the trough between waves. The shrouds and the chain plates must withstand these forces. All must resist the same forces as must the hull where the chainplates are fixed. Clearly, the GRP chain plates would be the weakest link. I cannot imagine going with anything other than stainless steel (how the chain plates are fixed to the hull is another question). Consider the outcome if your GRP chain plates do fail. Yes, I am old school and especially so with things like this. It is not all that uncommon these days for a new high tech boat coming to a bad end, dismasted or worse. Better to be safe and go with materials of know properties (tension and torsion strength). If you do that you will have the added benefit of sleeping better.

I have fibreglass chainplates and I sleep better than if they were stainless.

I know they'll never corrode, or fatigue, the bolts won't leak (there aren't any), and they are massively overbuilt, so I'll never need to replace them, unlike the SS ones the OP is replacing.

They look better too:

100 6328 - Cruisers & Sailing Photo Gallery

[cat man do]

Worth looking through these for some ideas

composite chainplates - Google images
Interesting to see the massive amount of glass, down and around as in the Orams



Vs a bit of spread out black as in the DD55

[downunder]

Building a vessel in 2012 why consider else anything else but composite chainplates.

Many of modern designs are using it.

As 44'crusing cat says QUOTE

"I know they'll never corrode, or fatigue, the bolts won't leak (there aren't any), and they are massively overbuilt, so I'll never need to replace them, unlike the SS ones the OP is replacing.

They look better too: "

[pressuredrop]

Originally Posted by Pauls

A response to Minaret's points above, the designs he's describing are uni-directional carbon, laminated with a good grade of epoxy, cured in a compression mold, and built by pros with experience in doing all this well.

This is light years away from glass fiber, polyester resin, and lay up by someone who is learning how to do all this.

In addition, Minaret's design is a really nice, elegant approach that takes the chainplate stress and distributes it across a large area of the hull. As contrasted with bolt mounting, which concentrates the stress at the bolt holes (just putting a hole in a stressed part triples the stress around the perimeter of the hole).

My point is, if you want to do this, without the engineering background that Schumacher has, just overbuild it. Make it beefy. Use a big safety factor. It'll definitely work, if you build it strong enough to take all the loads it will ever see.

did you only read minarets post and not mine? beacuse i mentioned epoxy and uni fibers numerous times, (i did ask about over doing all uni to avoid the cost of carbon...) i am not "learning" and the bolts are really just for pieces of mind, it will be glassed onto the outside of the hull as well, i need to paint the hull anyways, might as well get this out of the way, soo thanks?

[pressuredrop]

Originally Posted by 44'cruisingcat

I have fibreglass chainplates and I sleep better than if they were stainless.

I know they'll never corrode, or fatigue, the bolts won't leak (there aren't any), and they are massively overbuilt, so I'll never need to replace them, unlike the SS ones the OP is replacing.

They look better too:

100 6328 - Cruisers & Sailing Photo Gallery

cruising cat - i just found a thread from 09' where you say that your chain plates are all uni and no carbon, can you specify the lamination schedule?

[44'cruisingcat]

Originally Posted by cat man do

Worth looking through these for some ideas

composite chainplates - Google images
Interesting to see the massive amount of glass, down and around as in the Orams



Vs a bit of spread out black as in the DD55

Yeah, on Scrumble they have gone a fair way beyond what the plans describe. There's probably about 4 times as much glass as the design calls for. It won't break!

[44'cruisingcat]

Originally Posted by pressuredrop

cruising cat - i just found a thread from 09' where you say that your chain plates are all uni and no carbon, can you specify the lamination schedule?

I'm not carrying the plans on board, so can only go from memory. IIRC there was 2x 440 gsm double bias, then about 10x 1000 gsm uni tape, another 2x 440 db, then 10 more 1000 gsm uni, then the whole lot filleted in and glassed over with 2x 440 db for around 200mm either side of the taping.

The chainplate tapes extend about 500mm down the bulkhead.

I remember reading the specs on the 1000 gsm uni tape at the time, and the chainplates are immensely strong. We lifted the boat by them and IIRC they are able to handle about 5x that amount...