In real life, you also have to do a number of unit conversions between hours, minutes, miles, feet, inches, etc. This allows you to get a better idea of how long any trip will take, how much weight your vessel can carry, and more. Thus, for example, if you have a 35-foot boat with a waterline length of 28 feet, its hull speed works out . liability, financial or otherwise, for the calculations or results Oars, Wakeboard, Wakesurf & Terminals, Marine Fuse Blocks & If you go past what the manufacturer recommended, you could be in trouble. boatspeedcalculator.com. Maintenance, Fiberglass & Epoxy SPEED, a positive number; the boat speed in various units of measurement. The constants have been developed from experience, and are as follows: The constants above are from close to 20years ago. This ratio is found by dividing the actual boat speed by the theoretical boat speed to get a ratio. ACCOUNT, Find It may not display this or other websites correctly. Drink Holders, http://www.rbbi.com/folders/prop/propcalc.htm, http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=009536#000000, http://www.go-fast.com/Prop_Slip_Calculator.htm. Meters, Marine Electrical Panels Pumps, Livewell Aerator Pumps High speed runabouts will be 190. But if youre ever in a pinch with no power handy, its good to know the math behind it. Forums, Find Grills, Boat Drink Even water conditions and hull cleanliness can change your top speed. Locks, Boat Deck Usually, a higher horsepower engine is also going to be heavier. Choose the precision-tuned performance of a Mercury Racing Pro Finished model or the race-spec perfection of a Mercury Racing Lab Finished propeller. Video, GPS Chartplotters & Taking into accout the pitch, gear ratio, and using about 15% slip, I came up with 43 mph at 4500 rpm, which is about what my speedo says.