Nick, the last time Byrd151 posted was January of 2011. He may not be monitoring the boards any longer. Similarly, BrentPD has only two posts -- he may have gotten what he needed and moved on. He last posted only two months ago, though, so he might still be monitoring. But let's talk about chain plates.
Good for you! Inspecting the chain plates on a boat of that age is wise. Stainless is subject to crevice corrosion where it is oxygen deprived, and that slowly eats away at the metal. Less metal, less strength. Important stainless steel items on a boat that can suffer from crevice corrosion include chain plates and keel bolts. If chain plates fail, you can lose your mast. If the keel bolts fail, you will probably lose your entire boat. Your model of Islander 30 was designed by McGlassen himself and differs from mine so I don't know how your keel is attached. I hope it is the encapsulated type, in which case there are no keel bolts.
While I can't help you with your specific year and model of Islander, I can point to some good posts that address the general subject. Here's one
that leads to blog about how the owner did it. This posting
contains some great advice from Sailingdog, who was one of the most highly respected contributors on the board while he was here. Here's some more insight
on the chain plate setup.
Finally, I wanted to include some how-to posts on rebedding your chain plates to guard against crevice corrosion. There is not universal consensus on what to use for the rebedding, but butyl tape has worked for me and is recommended by senior members of these boards. Take a look at this one
. Just so you know, not all butyl tape is created equal. The stuff you can buy at hardware stores isn't very stretchy or sticky, traits you really need in abundance for pieces that move around some, such as chain plates. You can buy the best butyl tape from Mainesail here on this board at a very reasonable price. Use this Mainesail posting
to do so. Mainesail is also one of the most respected people on this site and does boat maintenance professionally. Be sure to read through his maintenance articles
. There's also one for rebedding deck hardware using butyl tape.