Re: Grand Haven Michigan
I think Rotary beat me to it...
A 20 footer is fine for the big lake on most days. We spent alot of time on the big lake in a 21 foot SeaRay. Rolling 3 footers is about the most we (The Admiral

) will put up with.
Are you looking to tow to Grand Haven? If so, there are many options for more sheltered waters when the big lake gets nasty. As mentioned earlier, Muskegon, Holland, Saugatuk, and the Grand River all offer sheltered waters when the big lake isn't safe for small craft. Many "inland" lakes are also available.
All of those ports are great places to visit!