Well, I am sure others will likely dissagree with me... but I have to side with the broker. In my opinion, Sea Trials are a joke and really nothing more than show. I worked with a broker some years ago that told me that in 20+ years in the business he had NEVER had an buyer walk away from a deal on a sea trial. The critical piece (and negotiating piece) is the survey. That is where the deals fall apart.
If I was the seller, I would not accept your offer. If the sea trial is critical to you, walk away from the deal and wait until you can sail it. If you think a sea trial is going to magically expose a boats problems... well, it better be a really long sea trial.
Again, others may dissagree. Just my opinion.