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A 6 hp outboard will go about fast enough to plane a 10 ft. aluminum boat, with one passenger aboard.
5mph or less
Speed is dependant on a number of factors. Most importantly the size, type and weight of the boat that it is on and the number of people on board. A 50 HP outboard will push a small aluminum fishing boat a lot fast than it will a 20 ft fiberglass boat. I have a 50 HP 2 stroke that will push a 16 foot aluminum boat 35 MPH.
246 knots
About 240 MPH
About 10 to 12 on plane
First, it needs to be mounted on the boat. And the boat determines how fast the attached motor will go. If the boat is wood, then it will likely float deeper in the water, and not be particularly fast. If the boat is a smaller fiberglas one, then the motor and boat will go faster. Based on much boating experience, I would say that most boats could go 30 to 35 mph with the 40hp Merc.
My Water Skimmer 10 ft boat can go 27 mph. Probably the fastest hull design ever for a small boat. Boat is rated for a 15 hp and that can push the boat well over 30 mph. Unsinkable, glass bottom, replace your dinghy or jet ski. www.WaterSkimmerBoats.com
the 50 ft AMG model with twin 1350 hp motors will probably do about 135 mph