I recently stumbled across two new tools that I cannot recommend highly enough.
First is a alternator belt tensioner. I have planned on getting one of these for a while, but never seemed to get around to it. A post on another blog finally prompted me to order it. Despite the purchase of a giant screwdriver to use as a lever, I could never get the proper tension on my alternator belt before purchasing this tensioner. Huge mistake to not do it earlier. One of the best tool purchases ever.
The second is a set of flare nut wrenches. I have had a major problem trying to loosen nuts on my 25 year-old boat. I have often stripped them trying to loosen them. These wrenches make putting serious torque on a nut much safer since they grip all 6 sides at once (instead of the two sides a normal wrench grips). If you have a diesel engine on your boat, these are a must have item. They will be my first choice wrench from now on for almost all applications where a socket is not an option.