Kemah here. The marina where I am requires the boat to be at least 41'!
I hear good things about Waterford Harbor Marina. The rates are on the high side though. Waterford Harbor Marina Rates
Also, check with Legend Point. Legend Point Marina & Condominium Community
Then, there's the Kemah Boardwalk Marina Untitled Document
Nice, clean marina, with access to the boardwalk resturants. A bit noisy for my liking, but depends on the person.
Many more to choose from.