Doesn't matter who the bank is, loans on a used boat are going to be tougher than a new boat. Even new boats can be difficult due to options that you may add that add significantly to the purchase price, but not necessarily to the boat's value (in banks eyes). We just went through this on a new boat purchase and we shopped several banks, big nationals and some local. We ended up where we started, with BECU. They have the best rates and easiest approval process since we bank personally and our biz with them.
Good luck and hope it works out for you.