Some tips, as we have no idea what kind of rudder, or for what boat & application you're building it for.
You can directly bond fiberglass cloth
to a stainless steel
, or aluminum
rudder shaft. And to this, you can bond various types of internal rudder structures.
The methodology, as well as things to watch out for are well documented in many places on the WEST System site, in addition to multiple other composite resources.
But,... regardless, do yourself a BIG favor & download the (free) classic book, On Boat Construction
via the WEST System site, along with their user guides. Also, their other resource is Epoxyworks
magazine. Again, free for download, with searchable archives
, describing various project
builds, just like on the main WEST System site.
Pretty much every composite supplier, & manufacturer have how to publications, as well as videos, & tech help lines. That, & if you get stuck at some part in the process of rebuilding things. You can come here for some answers, or better yet, go to BoatDesign.net Forums
They're all about building, & fixing things which float.
As far as wood, if you're fixed on using it, you're best bet in terms of making sure that it survives for a while, is to use thing stuff. Like thin sheets
of BS 1088 Okume plywood. Say 3-4mm, and use a vacuum system to pull the epoxy through each piece, so that there's no air space left in the wood.
Then, laminate them together (under pressure or vacuum) to get whatever thickness it is which you desire.
You can use things like a clear penetrating epoxy sealer, this one for example Clear Penetrating Epoxy Sealer
but as long as there are spaces in the wood that water & air can get to, then things can rot.
That's just reality.
To get some ideas as to how some of the "pro's" build/rebuild rudders, take a bit of time looking around on this site. CCI Marine composite fabrication | Competition Composites Inc.
They've been around/playing this game
for a few decades, & a good bit of their stuff is pretty decent. I say a good bit, as in/for some applications, you really need to be an experienced engineer
to say how well X will work for a specific job.
But being a business, it's in their best interest to keep their customers satisfied, so have a look at some of their techniques.
Albeit, IMO, there are far better ways of building a rudder than to "secure" a stainless steel
blade structure in between 2 glass skins, using only high density foam as the "structural attaching" component. Meaning that which is the primary attachment between the rudder stock & blade skeleton, & the skins.
Frankly, there's a LOT which goes into designing & building a quality rudder, but no one here wants to read a (technical) book on the subject, so... that said, I'll shut up, & wish you well on your project.