Calculating Drag

In order to get a better feel for the performance of your design, it is possible to conduct some mathematical computations to determine the drag on the hull. Generally, this will estimate the force that must be overcome before you can go anywhere. KAPER is a mathematical performance prediction program designed for the evaluation of small lightweight human powered water craft. It is highly emperical but is found to give reasonable results.

Resources

KAPER Analysis Spreadsheet
KAPER by John Winters
1 knots = 1.15078 miles/hour see www.onlineconversion.com

I strongly suggest that you read the article written by John Winters, referenced above. It is quite comprehensive and clearly explains the limitations and assumptions made in KAPER. The input parameters can all be found from the Hull Coefficient spreadsheet discussed in the 'Computing Hydrostatics' section.

The drag.xls sheet is poorly formatted, but seems to work all right. Try to ignore the highlighting. Input the parameters as required on line 9. Read the results for total resistance on line 15. Note the conversion to miles per hour, above. The plot of resistance vs. speed is also quite useful.

As far as I can tell, frictional resistance is strictly derived from the water-hull interface, while residiual resistance relates to an empirical computation that accounts for vortexing effects and what not.