The Boat Shop allows you to buy your own Boats which you can spawn at anytime using the F2 menu. There are 2 Boat Shops on the map which are shown as 
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There are 9 boats to buy at various prices. When buying a Boat you can change the colors, though if you wish to customise a boat that you already own you will have to go to the Vehicle Shop.
Note that you need to be in the water if you wish to spawn a boat.