It pays to read the instructions.
I just received the rudder for my Sparrow. It comes with a support tube to go through the hull, I thought to myself, that seems on the large side. Needless to say I drilled out the pilot hole I already made. Because the stern rises up slightly the outer part didn't sit flush with the hull, so I countersunk it to make it fit flush.
Excellent job I though, but when I looked inside the hole was almost at the edge of the balsa brace inside the hull.
I looked at the plans in the book and it showed just the rudder stem going through the hull.
I guess that's lack of experience for you. Anyway to remedy it, I just filled the hole back up with resin and redrilled the pilot hole. Hopefully that'll do the job.
As a footnote, would I be right in thinking that just a spot of grease oo the stern tube will stop the water coming in. It is a snug fit.
Nigel.