Thursday, June21, 2018

Boat Targets

This chart of target boat speeds is based on a model of target speed vs wind speed. The model does not hold for all boats but it was very close for boats from a Catalina 22 to a TP-52, a Farr 36, a Cal-40, and several other boats. I suspect it will not work for some exotic sports boats but I doubt that will be an issue for many readers.

You should gater two target boats speeds, one around 5 or 6 knots of true wind speed, the other in the 15 to 20 knot range.

If you have no idea what your target boat speeds are and want to just get started, use 0 knots boat speed at 2 knots wind and 1.2 times the squar root of your boat water line length at 99 knots as the upper target boat speed. This will enter reasonable numbers into the program. You can then update either or both of the numbers as you collect data.

Once you have the target boat speed chart, the next step is to select the table mode and print out the table of various apparent wind angles and boat speeds for the VMG implied by your entries. That will allow you to check and adjust your boat speed on the water. Every column in the table represents the same VMG to Wind. If you sail different speeds and sail trims, you will only be able to hit one of the speeds in the row for the true wind speed you have and for the apparent wind direction listed at the column heading. If you are faster than what you entered for your polars, you will be able to sail faster then one of the entries for that wind angle. The idea is to find the heading that gives you the greatest speed in excess of the table, or the speed closest to the table targets. The setting that gives you the best speed relative to the table entry is your true maximum VMG to Wind for the conditions you are in.

I suggest you write your actual boat speed in the corresponding table square for the wind speed and apparent wind direction so you can go back and refine your targets when you get off the water.

Finally, if you just want to have the program give you a list of targets for a variety of wind speeds, use mode euqal to short targets.

When you print this page, the text, forms, headers, and ads will not print.

Note, to find the true wind speed, sail at the reference apparent wind angle and read the apparent wind speed. You can then look up the true wind speed using the table.

Masthead Fly Dimensions:
Flag spacing:deg
Enter flag width: deg
Enter tail width: deg

Boat Speed Parameters:
LWL feet. Length Water Line (optional)
Base Use 1.35 unless you have reason to do otherwise.

Reference True Wind Angle:
Ref degrees. Reference true wind angle for apparent wind measurements.

Polar Data:
True Wind Speed Low (use 6 - 8 knots) knots.
Target Boat Speed Low knots.
True Wind Speed High (use 15 to 20 knots) knots.
Target Boat Speed High knots.

Apparent Wind Range:
Minimum apparent wind knots
Maximum apparent wind knots
Step size (@ 10 knots) knots


The maximum target speed is: 6.44 knots
The square root of your LWL is 5.32 Your maximum target speed is probably between 5.9 and 6.9 knots
The minimum wind speed factor is 2.2 knots. This is usually between 1 and 3 knots.
The speed over root waterline factor is 1.21 times. This is usually between 1.1 and 1.3

23 25 28 30 33 35 38 40
4 (6.6) 3.1 26 2.8 3 3.5
5 (8.2) 3.8 26 3.4 3.7 4.3
6 (9.7) 4.5 26 3.9 4.3 4.8
7 (11) 4.9 27 4.3 4.6 5.1 6.6
8 (12) 5.3 27 4.6 4.9 5.3 6.2
10 (15) 5.8 29 4.9 5.2 5.5 6.1 7.2
12 (17) 6.1 30 5.1 5.3 5.6 6 6.7 8
14 (19) 6.2 32 5.1 5.3 5.6 6 6.5 7.2
17 (22) 6.4 33 5.1 5.3 5.6 5.9 6.2 6.7 7.7 8.9
20 (25) 6.4 35 5.1 5.3 5.5 5.8 6.1 6.5 7.2 7.8

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