Back in the days when there were less maps we played every map back to back
Ooh a little higher, now a bit to the left, a little more, a little more, just a bit more. Oooh yes, that's the spot!
One thing we used to do was to let the boats lapse and then build them fresh. It cost more then just maintaining them. It is a limited solution, but Merric already had the more obvious one.But it is an excellent solution for tweaking your treasury. Having four ships and scrapping 1-4 of them and rebuilding them is very, very useful at times.