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Would some be able to explain TARGET BOAT SPEEDS ?

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existentialsailor
Master Marine Consultant

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USA
1180 Posts

Initially Posted - 10/04/2005 : 14:00:42

http://www.wyc.org/capri25/tips,%20target%20speed.htm

That link is to the target boat speeds for a Capri 25. I've yet to be able to figure out how it works. Anyone?

Rick

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aeckhart
Master Marine Consultant

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1709 Posts

Response Posted - 10/05/2005 : 18:29:09

"Target Boat Speed" is the maximum speed, upwind and down wind, a particular boat - Capri 25 in this case, should achieve given a specific wind speed and angle of attack. You use the chart as a guide to set your boat up (set sails, steer, etc) to obtain the speed listed for the wind conditions. If the boat isn't going as fast as is listed for a given set of conditions you need to tweek the rig or make a helm adjustment. I believe the charts are established using a combination of scientific calculation and trial and error. The tables are generally used in racing but cruisers use them as well. It would be nice if someone would work up a chart for the C25.

Edited by - aeckhart on 10/05/2005 18:41:33

Champipple
Master Marine Consultant

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6855 Posts

Response Posted - 10/05/2005 : 23:34:04

Okay Rick - Here it goes

They are just that - Targets. If you look at the very first line of that spreadsheet in the link. If in two kts of breeze, your target Boat speed should be 2.3 Kts. I basically don't buy it, regardless of the wind angle. the numbers after about 3 knots look more realistic. The concept is to give you a number to hit in any condition. Its basically the numeric version of a set of polar diagrams.

If I can get some verification of the data, I might be able to whip up a set of polar diagrams for your fleet.

dw

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Derek Crawford
Master Marine Consultant

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USA
3321 Posts

Response Posted - 10/06/2005 : 01:00:27

I'm one of the older fellows! Tweak the genoa and see how high you can get the knotmeter (which has the widest range possible!)
Derek

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aeckhart
Master Marine Consultant

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USA
1709 Posts

Response Posted - 10/06/2005 : 11:18:40

Derek,

Ditto on that. When racing, I sail the fastest I can as close as I can get to the rumb line without pinching the speed out of the boat. Once the course and sails are set for max efficiency/speed, I am constantly checking the speedo, tell tails/windex, and the boats around me. In this way I'm sailing the fastest the boat can go given existing conditions.The big questiion is when to tack, a decision I seldom make correctly. Since I am not a serious racer anyway, the outcome doesn't really matter. It's being on the water that counts and continually learning my and my boats capabilities and deficiencies.

Edited by - aeckhart on 10/06/2005 11:33:27

Derek Crawford
Master Marine Consultant

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3321 Posts

Response Posted - 10/06/2005 : 12:09:19

That's precisely my philosophy, Al!

Derek

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Pokey uh da LBC
1st Mate

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35 Posts

Response Posted - 10/06/2005 : 12:49:23

You can also use the TBS Chart to determine the downwind sailing angle that nets the best VMG.

If the leeward mark is dead down wind, use the TBS chart (or polars) to determine whether sailing the rhumb line (shortest distance) or a hotter angle (further and faster) will get you to there first.

Just follow the steps outlined below to determine the optimum sailing angle for the current wind conditions:

1. Start by sailing the angle you feel is best considering the wind conditions.

2. Note your boat speed.

3. Note the apparent wind angle from your masthead fly.

4. Find your current apparent wind angle on the TBS chart. Compare the target speed to your boat speed:

a. <b>If your boat speed is higher than the target speed, sail a lower course </b>(shorter and slower).

b. <b>If your boat speed is lower than the target speed, sail a hotter course </b>(longer and faster).

5. After adjusting your course, repeat Steps 1 through 4 until your boat speed matches the target indicated for the angle you're sailing.

Although the above method seems pretty clunky, once you've used it a couple of times, achieving target boat speed will come pretty quickly. Of course it will never work if your boat is not in-tune and trimmed well.

The following diagram combines the hull shape and mast location of the Capri 25 with the target angles and speeds from the chart. Note that estimating the apparent wind within 5 or even 10 degrees is pretty sketchy, especially in a chop. So this whole exercise becomes a little academic. I find that in the prevailing conditions off Long Beach, we almost always sail DDW anyway.

"Never get off the Boat."
-Chief

Edited by - Pokey uh da LBC on 10/06/2005 20:03:21

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