Island Packet question

[a64pilot]

I used to be of the opinion that 304 was much stronger than 316, but lost out severely in the corrosion perspective.
You built out of 304 when strength was the most important, and 316 when corrosion resistance was most important.
However I had an aircraft structural engineer at work pull out his manual and show me that there was almost no significant difference between the two, where I thought there was.
From a rusting perspective the most important thing is to ensure that the steel isn’t contaminated by being worked with regular steel tools and has been correctly passivated. Very good high grade 316 if contaminated will rust like the dickens, cause it’s not rusting, the contamination is.

However if your going to bury chainplates so that it takes $9,000 in labor to R&R them, then for goodness sake spend another grand to make them from Titanium and never have to worry about it.
I think if not mistaken, the actual cost difference was less than $1,000, maybe some of that was cause I supplied them myself, sort of.
What I did was asked Mack Sails to send Allied Titanium a set of chainplates they had removed, and Allied just duplicated them in Titanium and sent them back.
They fit perfectly, angles were perfect. I saved some by not having them polished as I didn’t want my Ti plates to look like SS, and the “frosted” finish from being bead blasted makes for an excellent adhesive bond, especially for the sealant.

[geoleo]

Why not just make them in T6061 aluminum and 30% thicker ? if they are 3/8 thick go to 1/2 thick.

[a64pilot]

It’s my opinion that our SS chainplates fail from both crevice corrosion and stress corrosion.
It’s why I think my relatively unused boat that had had leaks for years had very little corrosion, cause it hadn’t been used much.
However other boats at half it’s age have had chainplate failures, likely cause their chainplates were regularly load cycled and that sets up stress corrosion. Those boats weren’t Marina Queens, they had been regularly sailed.

I guess I push the Ti plate thing, cause I’m tired of hearing about how IP’s chainplates fail, I wouldn’t have an IP cause their chain plate design is crap.
I figure if a few of us go the TI route, we can turn that opinion around, and that might matter one day if I go to sell my boat.
Yes, the chainplate is an Achilles heel for an IP, however it’s a solved issue, and in fact you can increase strength by more than 300% and make it so that they will never fail.
A chainplate with an infinite life limit and one that will never fail it’s so over strong is a plus in my opinion, not many boats can make that boast. Maybe Carbon plates can, but Carbon is so easily damaged by impact.

[a64pilot]

Originally Posted by geoleo

Why not just make them in T6061 aluminum and 30% thicker ? if they are 3/8 thick go to 1/2 thick.

Probably go with 5000 series aluminum if you wanted to go with aluminum, but why when you can go with Ti and not have to reengineer anything, every thing fits cause it’s dimensionally identical.
6000 aluminum isn’t all that good for corrosion I don’t think and it’s resistance to fatigue isn’t all that good either, I don’t think. Not sure about that though.

[panamadean]

I broke my aft lower port chainplate on my 1989 Island Packet 35 hull #50 last month while anchored north of the Marquesas Keys in the Gulf of Mexico. It broke just below the teak cap rail in the hull to deck joint. It was a rough place to anchor and the boat was bounced around a lot. The stainless steel was corroded. I feel lucky this happened while the sails were down and I didn't lose the mast. I have read a lot about chainplates since this happened. The stainless corrosion is not unique to Island Packets. I intend to replace all the chainplates with grade 5 titanium and live happily ever after. I can't see using stainless again for this application and wondering when it will fail.

[robert sailor]

Originally Posted by panamadean

I broke my aft lower port chainplate on my 1989 Island Packet 35 hull #50 last month while anchored north of the Marquesas Keys in the Gulf of Mexico. It broke just below the teak cap rail in the hull to deck joint. It was a rough place to anchor and the boat was bounced around a lot. The stainless steel was corroded. I feel lucky this happened while the sails were down and I didn't lose the mast. I have read a lot about chainplates since this happened. The stainless corrosion is not unique to Island Packets. I intend to replace all the chainplates with grade 5 titanium and live happily ever after. I can't see using stainless again for this application and wondering when it will fail.

Your absolutely correct in the crevice corrosion comments but the really big and costly issue as A64 points out is that the boat has to be taken apart to replace the chain plates and there is no way to inspect them without tearing things apart so if I was an IP owner I wouldn't consider going to all that work and expense and not replace it with titanium especially for resale. Owners of boats with chain plates that can be easily gotten to can make different choices so really big difference.

[GordMay]

Greetings and welcome aboard the CF, panamadean.

[missourisailor]

True in an ideal situation Ti would be the better choice. Even with the cost increase.

But the SS chain plates have lasted for25+ years. Really, how many glass boats will last for 50 years?

And the true unknown is what new "issues" will crop up with Ti chain plates?
No one knows.

I don't and won't talk anyone out of using Ti. But for me (and I have already bought my SS ones, so I'm a bit bias)... the devil you know...