500+ hours on the Merc puts you near the rebuild window. If you use the boat reasonably heavily, you should expect to have to rebuild or repower within 3 years.

Same for the outdrive, especially since you may not have any idea what the service/usage history has been.

Either of these will be on the order of the purchas price.

Outside of those major items, there will be a constant litany of little things that you will want to do. $50 here, $100 there, etc., etc.

Not to scare you off, but realize that with an older boat, purchase price is only the beginning. Very rarely do you find a well-cared-for older boat that the owner is willing to sell.

Open up the motor box and get into the bilge. Is it a toxic waste site, or is it clean? Is the bilge pump a teeny, dirty, rusted pitiful thing? How is the wiring -- Nicely arranged, or rat's nest? Get into the floorboards. If they are spongy, there is a decent chance that the stringers and transom need work, which will get you into some serious coin.

Lastly, 17.5' is better than 16', but still on the small side for all but the good weather days on the Sound. My 20' Maxum is fine until the seas get over 3', at which point I need to be careful about how I'm taking the waves, and keeping the boat on plane without thrashing the passengers. a 17.5' boat is not necessarily dangerous, but it will definitely get tossed around by waves and wakes.

Regards.

Mike
Woodinville