First of all, good luck with the purchase!
For boat purchases, they really aren't much different than any used vehicle purchase, a boat is not much different. In the end make sure you are comfortable with the mechanical operation of the engines and other systems (fuel, steering, electrical, etc.), and the overall condition of the boat (interior in good clean shape, all cushions in place, all cockpit features are operational, etc).
Being the dead of winter around here (I'm in MN too), obviously a water test won't be happening. If everything else checks out, maybe see if they will agree to the final sale being contingent on a successful water test? If that's not possible for whatever reason, there is no reason why you shouldn't ask for each engine to be run on the hose for a 5-10 mins each. That should show any potential problems and ensure that at least the engines are in good running condition and sound good when running. If any issue are found/heard a compression test is probably a smart next step, or just walk away from it and find another boat. In general, this year/model boat is very popular, so really any issues you run into will have been addressed by someone on this forum, so support is out there when you need it.
Overall some specific things to look for on that model that I can think of off the top of my head:
- Check the scupper in the rear of the hull, if it's plastic, that likely will need to be replaced with a new one (stainless steel preferably) as they are prone to cracking and leaking.
- Check all cushions top/bottom/sides for damage or wear. Repairs aren't all that difficult for any vinyl shop to do, but they can be costly.
- Check the steering to make sure it's functioning without any sort of binding when turning the steering wheel, a few people have had to replace steering cables and I think this age might be in range for needing that at some point.
- Since the marina is not a Yamaha shop, they might not have the ability to pull the hours from the engine. This year boat does not have engine hour meters, so the only way to verify the hours is to get a YDS cable and diagnostic software to pull the info from the ECU. Some have put on aftermarket hour meters, so the accuracy might not be 100% depending on when they were installed. Do some searching here for details, I personally have never used one.
Maybe someone else with a 21' 2008 can chime in to offer advice of specific things to look for...
