Re: Looking for my first boat
1. Unless you're buying a wooden boat there's really not a lot to go bad when they're on the hard, structurally that is. You already realize that rubber can go bad in time so that's a good place to look. General condition of things is important.
2.You've obviously thought about some issues outweighing others. So-get out there and look at boats. Really look at them-climb around look inside all the places you can including lifting floorboards and cushions and moving stuff if you have to. Look with an inspection mirror. Take along a digital camera to photo those places you cant see like under engines or around the keel step(this is an invaluable method to find issues). Turn the wheel and wiggle the rudder and knock on it while you're at it. Dont be shy about it. Corrosion is red/brown on steel and puffy white on Aluminum so watch for it. Look close when you find it. You already know about sponginess in decks etc. Look for signs of leakage of any kind and investigate.
Surprising what you'll see and what you'll learn about boats. Eventually you'll get a feel for the type of boat you want and how the others like it you've looked at compare. Don't take anyones word for a boats condition- look for yourself. Dont be afraid to look at lots of boats and say no to all but one. Everyone has to look before buying a used boat. You'll develop feel for the conditon of boats fairly quickly. A survey of the one you pick will help determine structural issues. Make sure you point out all concerns to your surveyor-they can miss stuff too!
3. If you are serious about going open water you must have an inboard diesel IMHO! Size of at least 3 to 4 HP per ton of boat. More power is good but just eats more fuel. Gas in a boat is scary! 1 gallon of gas = two sticks of dynamite!
4. Dont hurry the buying and look at each one as long as you need to. Even if you find the right boat you can always find another one just like it another day. When it comes to used boats you will spend a lot of money on it so try to get what you really want. No sense spending a lot then finding you want something else very soon. Dont buy too small if you want others aboard.
Hope that helps!