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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

downwind performance

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treuland
Deckhand

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USA
17 Posts

Initially Posted - 11/15/2005 : 12:41:30

Has anyone seen polar diagrams for the Catalina 25? Are there conditions in which other than direct (almost) downwind is better. Are there PHRF corrections for spinaker v nonspinaker?

Edited by - on

Steve Milby
Past Commodore

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USA
5909 Posts

Response Posted - 11/15/2005 : 20:20:21

Welcome to the forum! Several people have asked about polars in past years, and I don't recall anyone ever finding them for the C25. But, the design of the C25 isn't all that unique. A lot of masthead-rigged trailer sailors of that era have an 8 ft. beam, 25' length, and approximately the same weight, sail area and hull shape as the C25. If you can find them for a similar boat, they won't be exact, but they would give you some food for thought.

A sailboat race is not a speed contest. It's a time contest. It's a contest to get around the racecourse in the shortest period of time. When racing downwind, the object is not to get to the leeward mark at the highest rate of speed. The object is to get there in the shortest period of time.

Let me explain the process of downwind sailing by comparing it with the way we all sail to windward. When you're racing toward the windward mark, you want to gain ground to windward by sailing the shortest possible distance at the fastest possible speed. When you tack in phase with the windshifts, you are sailing the shortest distance possible. Likewise, to maximize your boatspeed to windward, you head up in the puffs and bear off slightly in the lulls. Most racers understand these principles fairly well, but they completely forget about them on the downwind leg.

On the downwind leg, most sailors just point the boat more-or-less at the leeward mark and trim the sails for that course. Their course might be a run straight at the mark, or it might be a broad reach at a diagonal to the mark. But the same principles that you use on the windward leg to maximize your speed and minimize the distance also apply to the downwind leg. As the wind shifts back and forth and as it gusts and lulls, an enormous advantage in terms of speed and distance can be gained by "tacking" downwind.

When you're on a downwind leg, it's rare that the windstrength and direction are the same all along the leg. The wind blows in gusts and lulls, and it shifts back and forth. In order to cover the downwind leg in the shortest period of time, the general rule is that you should bear off in the gusts (even though that would actually put your course to the left or to the right of the leeward mark), and broad reach in the lulls. (Generally, you should broad reach on the tack (port or starboard) that makes the fastest speed and takes you the closest to the leeward mark). In order to do so, you might even have to gybe the sails back and forth as the wind shifts back and forth.

When your opponents are heading straight for the mark, they'll cover the shortest distance, but they'll make progress towards it at a fairly uniform speed all along the leg. By tacking downwind in phase with the shifts and puffs, you'll gain ground to leeward more quickly than them. The sooner you get to leeward, the sooner you can head up toward the mark on a much faster beam reach. While they're covering the last distance on the same, slow, broad reach, you'll be covering a slightly longer distance, but you'll be on a beam reach and going much faster.

In short, you want to go downwind in the puffs, when it's fast to go downwind, and you want to broad reach in the lulls, when it's fast to broad reach. And then, when the wind shifts, you want to "tack" the boat downwind in phase with the shifts.

I'm sure there are PHRF corrections for spinnaker /non-spinnaker C25s, but don't know what they are for any given locale. They differ from place to place.

Edited by - Steve Milby on 11/15/2005 20:27:03

Bruce Baker
Captain

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USA
402 Posts

Response Posted - 11/22/2005 : 16:15:23

I'm taking an advanced piloting course with the Power Squadron, and we had a short discussion of velocity made good, a standard readout from a GPS. It occurs to me that we can make our own polar diagrams.
Do a test where you sail all the angles, and see which ones are fastest to the mark.

Edited by - on

weluvlife
Navigator

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166 Posts

Response Posted - 11/23/2005 : 08:07:28

Thanks for the great explanation Steve. You've
touched on ideas that I've had for some time.

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.