Rules changed recently??
We bought a used Canadian registered boat in B.C., transferred the registry and only paid PST. This was several years ago. We likely paid PST because it was through a broker and the sale went through his books.
If you buy privately, then you won't get dinged with the tax until you transfer the "K" number licence. Since any boat under 30' and under 10hp does not require licencing, you can avoid the PST on such boats.
Our latest boat is licenced, foreign built and bought in the US so we were subject to PST, GST and duty. Yet it was still a reasonably good deal.