[omc-boats] Excel Spreadsheet for top Speed calculation

Hi,

I discovered my web page that I posted isn't very friendly unless you have installed a special Microsoft Office plug-in.

So here's the actual Excel file, for those of you who have the ability to read *.xls spreadsheets. If anyone out ther can write a javascript or perlscript version of the calculator, please let me know?

Also, here's a draft of a detailed expalnation of the calculation and some example data:
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CALCULATING SPEED POTENTIAL

Boat speed is ultimately a function of weight and horsepower. Over many years of observation, some general approximations of speed potential versus weight and horsepower have been developed. Here is one such relationship, provided by Clark Roberts, a long-time Boston Whaler owner and performance enthusiast.

Clark Robert's Formula

Based on many years of experience, Clark Roberts has developed this approximation to determine the ultimate speed potential of a particular combination of horsepower, weight, and hull design.

        Engine Power (HP) Hull

[ SQRT(-------------------) ] X ( Factor ) = Maximum Speed (MPH)

        Boat Weight (LB) Constant

The value of the Hull Factor Constant depends on the type of hull. Clark's suggested values are:

    Evinrude Gull-Wing = 168 to 180 (hull performs better under load)

    Moderate Vee Bottom = 180

    Tri-Hull = 200 <---Use this for Classic Whaler

    Flat Bottom = 220

The Boat Weight must be the total weight, including fuel and passengers. The horsepower must be the true horsepower at the propeller shaft. This includes correcting for air density at altitudes that are 1000 - 8000 ft above sea level. (Horsepower is reduced an additional 4 % per every 10000 ft ASL.) The propeller must be an efficient design that effectively converts the available horsepower into thrust, and the hull must be clean and free of drag inducing anomalies.

Example

I have some accurate data for my boat regarding speed and weight, so let's test Clark's formula. First, since we can't hang the whole boat on a scale, the boat weight must be calculated:

ESTIMATED WEIGHT: 1965 Sweet-16 Outboard powered by Evinrude 75-hp V4 Selectric

   Boat Hull 900 lbs (advertised bare hull weight of Sweet 16, add 20# for Sport-16)

   Gear/Battery 120 # (anchor, line, electronics, bimini, battery)

   Engine 290 # (1965 Evinrude 75 hp V4 Selectric shift)

   Fuel 50 # (7 lbs/gal)

   _______________________

   Total Boat 1340 lbs

   Crew @... 170 lbs (per person)

  GROSS BOAT WT 1530 lbs with 1 person crew

Next, the horsepower must be established. Although my engine is rated as a "75-HP" motor, I am going to derate it 15 percent (4-stroke sterndrives de-rate at close to double that due to camshaft, valve train, oil pumps, and 90-degree bevel gearing) because it is from an era of crankshaft rated-horsepower, and the formula really wants prop-shaft rated horsepower. Also, the engine is 25 years old and may not be as strong as it was when new. Instead of 75-HP, I'll use 64-HP for the engine's propshaft power. Filling in the equation:

 [ SQRT (64/1530) ] X 170 = 34.7 MPH

Accuracy - Evinrude Power Station Report of 1965

In a series of speed and load tests conducted by Evinrude technicians, the Sweet - 16 boat topped out at 34 MPH. By comparing the data shown in their graph, using various levels of outboard power, it is possible to verify and calculate the Sweet-16/Sport 16 hull's performance factor constant. Still, the observed speed is fairly close to the predicted speed, less than 10% deviation. Thus, the formula in this case seems to be quite good as a predictor of speed potential. I am sure with the right prop, engine height, and some other tweaking there could be another mile-per-hour of speed to be had from the boat and engine

Re-Powering

Predicted performance data for Sport-16 & Sportsman sterndrives with various engine combinations as computed by Lee Shuster following the formula suggested by Clark Roberts. See http://

ESTIMATED WEIGHT: 1965 Sweet-16 Outboard powered by Evinrude 75-hp V4 Selectric

   Boat Hull 900 lbs (advertised bare hull weight of Sweet 16, add 20# for Sport-16)

   Gear/Battery 120 # (anchor, line, electronics, bimini, battery)

   Engine 290 # (1965 Evinrude 75 hp V4 Selectric shift)

   Fuel 50 # (7 lbs/gal)

   _______________________

   Total Boat 1340 lbs

   Crew @... 170 lbs (per person)

  GROSS BOAT WT 1530 lbs with 1 person crew

MAKE/HP/CYCLE MOTOR WT TOTAL WT MPH (@... sea level)

---------------------------------------------

Evinrude 40 2 200 1440 25

Evinrude 60 2 270 1510 32

Evinrude 75 2 290 1530 34

Evinrude 90 2 290 1530 37

Evinrude 100 2 322 1562 40

Honda 50 4 212 1452 29

Honda 90 4 373 1613 37

Yamaha 50 4 233 1473 29

Yamaha 60 4 244 1584 32

Yamaha 100 4 356 1874 39

Yamaha 50 2 194 1434 29

Yamaha 60 2 228 1468 32

Yamaha 70 2 228 1468 34

Yamaha 90 2 261 1501 38

Merc 50 4 236 1476 29

Merc 60 4 236 1476 32

Merc 90 4 386 1626 37

Merc 50 2 199 1439 29

Merc 60 2 219 1459 32

Merc 75 2 303 1543 35

Merc 90 2 303 1543 38

Suzuki 50 4 243 1761 34

Suzuki 70 4 359 1877 39

Lee Shuster

Salt Lake City

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