Depends, are you kids at hart? Then it may take longer lol. 2-3 hrs should be sufficient. But if you have more time check out the Reiman Aquarium and the schooner "The Dennis Sullivan". Both will be added cost, however both are very interesting.
There are lots of activities to do. If you juat want to see around then maybe half a day. If you are like me where i like to do the activities then you can spend the entire day there. There is a sail boat that starts right next to museum. You will need separate tickets for those but it's an interesting and fun way to learn about sail boats.
2 adults did it in 2hours. If you have kids, I'd be their longer.
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