Originally Posted by zboss
What do you have in mind?
A while back, in a couple of different threads, I think it was Nicholson58 who chimed in with some great thoughts on, & a recipe for fillers for rudders & other items/areas which have a realtively high volume of fill. But need it to be both high strength, as well as fully waterproof.
One or two of said threads was specifically on rebuilding rudders, & the other I believe, was on what to back fill the core of a deck
with. When beefing up it's core, in order to mount highly loaded jib
That one, specifically, was when Dockhead was trying to figure out how to mount conventional, new tracks, for his new headsails.
IIRC, the mix was a very slow curing epoxy & microballoons. With a ratio of somewhere around 2 gallons of resin to 3-5 buckets of microballons. But it'd need looking up/contacting him in order to get it right. Especially as with the mixture & resin which he uses, it allows for a thick pour (several inches deep) without any exothermic problems. A key thing.
And it cures up, hard, & watertight.
One might, in addition to using a core such as this, bond glass cloth to as much of the surface area of the rudder shaft as is possible. Using standard practices for such. As when done right, not only is the glass, chemically bonded to the shaft, it's bonded to it in several mechanical ways also.
- Via the mechanical abrasions put onto the shaft, during sanding
, as part of the standard bonding process. Which creates a "toothed" surface on the shaft for the glass to grip onto. No too much unlike Velcro.
- And via the contraction of the glass & epoxy, as the epoxy shrinks slightly when it cures. Thus locking it in place.
If this is done, then anything, subsequently attached to these skins on the shaft, have a far higher chance of staying well attached. In addition to being bonded on in a leak free manner.
One of the other critical things, which is (sadly) often missing in production rudders, is a structural frame work made out of materials which are more corrosion
resistant than standard stainless.
And components that, structurally speaking, are mechanically fitted & locked together. So as to not be dependent upon welds in order to remain attached to the shaft. And to stay on there in the shape of a blade. Or a structure akin there to.
For example, taking the shaft, & machining slots into it for plates which fully protrude through it on both sides. And having the slots cut with a taper to them, so that the plates can only move in one direction. Regardless of how they're attached.
Also, in such a design, the ends of the slots in the shaft would be rounded, in order to avoid stress concentrations.
After which, the plates would be welded to the shaft, & the welds fully passivated.
Basically, I'm just advocating for having redundant systems in a rudder that, each, are designed to keep it together. Not too tough a thing, from an engineering perspective, but... in the real world, not necessarily all that common either.