I would rather go for West 406 colloidal silica in this case of rudder repair.

406 gives a tougher resin compound with more abrasion resistance. It's a fraction heavier but that plays in your case no part. Only disadvantage is that it tends to be a bit more stiffer when applying. But if you use less, you can make it butter-like.

So be sure to fill the gaps and tears fully!