A sea trial can be anything you want it to be depending upon the agreement between buyer and seller. In that regard why can't it be a test drive? Maybe it's conventionally just an extension of the survey, but if buyer is willing to pay for a test drive, and the seller agrees, then why not?
In fact it makes some sense to me ... how are you supposed to know how a boat feels under sail if you don't have an opportunity to sail it before committing?
Scott... that is a sensible question. What you're really wanting to know is if you even like the boat you're thinking about buying. You want a demonstration, or test ride. But that's not what a sea trial is for...
Rather than a home inspection, as I mentioned before, the sea trial is akin to a final walkthrough inspection. It's to verify that all repairs have been made and that the boat hasn't been damaged since the survey and still has all the equipment agreed to in the contract... i.e. that you're getting what you paid for. It's also the time that the owner/broker goes through the boat and explains all the systems, spare parts locations, operating procedures, etc...
If you're looking for a demonstration ride.... you do that before you submit an offer. Not after the contract has been signed and the boat taken off the market.... losing any potential buyers during that time...
If your were really keen on selling your boat, would you take potential buyers out for an hour's sail to show them what your boat is all about? I would.... because I'm in sales... and the demo would be like a sales presentation...and that's when you close.
As a seller, though, I would qualify my prospect before I took him out. Getting his financial and motivational data to determine if it's worth your time to make the presentation..... so you have to ask some tough questions... and if they aren't willing to answer or show proof of financial ability... they aren't serious.
The bottom line is this... if you are a serious buyer you should have no problem getting a demonstration ride. If you're just looking around at different boats you may want to purchase some day.... go to a boat show.