This is the Go Cart of the sea, and it is something I wouldn’t hesitate to buy at the right price. From their website, it seems that the ultra light Marine Cart (55KG only) is good enough for cruising, fishing, and even water sports. I’m not sure if it can cope with the average tide height of the Gulf, but looks like the tide factor adds to the action.
You can install an engine of up to 10 hp on the marine cart, and could comfortably accomodate 2 adults although the product’s manual states 4 people. More photos and specs on their website here.