[Public-List] Replace chainplate knees

[Don Campbell via Public-List]

Brent:
    I think you will find that the old  knee is plywood and that it has 
delaminated completely from moisture seeping in from above. The only thing 
that is holding your stay is the tabbing. If there is any space between the 
shelf and the base of the knee or tabbing, then that has let go as well.  I 
always look at what is safe first, and whatever you have is probably not 
safe, and I do not think you can do much to make what is there safe for 
extending the life of the current situation. A mast replacement will be more 
than the value of your boat and so the idea of safe includes not having to 
buy a new stick.
    You are correct to consider removing the shelf and cutting out the 
current knee and tabbing. Glass is not an easy cut and a diamond blade helps 
but is not essential with the small amount of cutting for removal of a knee. 
Even a 4" grinder will cut things out for you. You will find though. that 
there will be dust everywhere, right back to the icebox, regardless of the 
tools you use for cutting and smoothing. That means you should take 
everything you don't want to get glass dust on it out of the boat before you 
start. Check the outside of the hull to see if there is any dimpling from 
stress on the chainplate that has indented the hull. If there is, you may 
want to consider increasing the length of the knee so that the stress from 
the tension is over a greater area and so less of a dimple on the hull.
    The next consideration is material for a knee and its strength. I used 
white oak and went for much greater length so had to trim the shelf to 
accommodate that. I also added a piece of strap stainless from the lower two 
bolts on the knee to the bottom of the knee to take some stress right to the 
bottom of the knee. Do not use any less than 5/16" bolts and the shoulder 
goes through the chain plate.
    I used West epoxy but the placement of the knee requires some fitting 
before  you get things we so that the chainplate fits through the hole in 
the deck and is flat on the knee. Two people help when you are adding the 
epoxy, one to hold the chainplate from above and one to set the knee. It is 
not easy to hold the knee in place until the epoxy sets, so consider a 
method to support whatever you do use until the epoxy sets, and then you can 
glass in the knee as Whitby has done originally.
    As for the top of the deck and chainplate caulking, I have added a small 
pier above the deck with a stainless plate so put the caulk in with the 
pressure of two bolts on that plate.
    If you want any more details, e-mail me off list at 
dk.campbell at xplornet.ca
Don Campbell

-----Original Message----- 
From: Brent Higgins via Public-List
Sent: Tuesday, April 11, 2017 8:43 PM
To: via Public-List
Subject: [Public-List] Replace chainplate knees