Association Forum - Flying by instruments (and instinct)

Assn Members Area · Join

Home.

Association Forum

Ships Store

Cruising

Racing

Technical Tips

Photo Gallery - New

Boat Search - Updated

Manuals & Brochures

Swap Meet

Links

Officer Flag Line & Staff

Bylaws & Constitution

Members Area

Join the Association

Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
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.

Association Forum

Username:	Password:
Save Password
Forgot your Password?

All Forums

Catalina/Capri 25/250 Sailor's Forums

Capri 25 Specific Forum

Flying by instruments (and instinct)

New Topic

Topic Locked

Printer Friendly

Author

Topic

leebitts
Navigator

Member Avatar

USA
122 Posts

Initially Posted - 10/20/2009 : 17:34:56

I found a polar diagram for the Capri 25. They describe pretty specific optimal true wind angles when going to windward as well as down wind. I'm playing with buying a good knotmeter and wind indicator to make effective use of this tool. Anyone have any insight or experience with that? I understand that wind and wave conditions can play havoc, as can flakey winds on a lake.

Boats out of the water, looking forward to next year already.

LeeBitts
1981 Capri 25 Hull # 142
Sailing in NH and Maine

Edited by - on

Ericson33
Admiral

Members Avatar

USA
892 Posts

Response Posted - 10/20/2009 : 20:37:58

I have a full line of standard marine, but would look into a device that gives VMG like Velotec, look on SA

http://www.mauriprosailing.com/Velocitek/velocitek.htm

Edited by - Ericson33 on 10/21/2009 05:24:17

Fleet
Navigator

Members Avatar

USA
151 Posts

Response Posted - 10/21/2009 : 04:26:29

I have a Raymarine ST40 Wind system with a Rotavecta transducer. The wind speed appears to be accurate but the wind direction always diagrees with my windex. Error varies but can be as much as 20 degrees. The Rotavecta has an unusual way of detecting wind direction and I think it is inaccurate. I don't recommend the ST40 system. My paddle wheel speed transducer was dead when I bought the Capri so I replaced it with a Northstar 550 marine GPS. Nice GPS but I made the mistake of buying the unit with the built in antenna. To keep a good signal, I have to mount it just above the top of the cabin. Now it gets in the way. Also I think the signal sometimes gets masked by the boom. If you go with a GPS like a 550 then I recommend an external antenna. Another option is to run a handheld GPS like a Garmin 60csx on your stern pulpit. I run this unit also, never lose the signal and it's portable. Hope this helps.

Edited by - on

leebitts
Navigator

Members Avatar

USA
122 Posts

Response Posted - 10/21/2009 : 04:53:27

Thanks, I had wondered about the ST40 Wind, as the price is great and it shows a digital number for wind angle. At that price I was concerned it might not be real accurate. What is SA in reference to "Velotec, look on SA"

Thanks again

Edited by - on

Steve Milby
Past Commodore

Members Avatar

USA
5909 Posts

Response Posted - 10/21/2009 : 05:49:18

Polars provide useful information, but instruments on a small racing boat create unexpected problems. Usually, the skipper is the only person who really knows how to use the instruments and the information they provide. Therefore, in addition to the gazillion other things the skipper has to think about, he has extra instruments that he has to program (e.g., gps), information that he has to gather from the instruments, and then he has to translate that information into an action plan.

On a small racing boat, the skipper has so many things to think about (sail choice, sail trim, helmsmanship, wave action, other boats, clear air, etc., etc.) that it is easy for him to suffer overload. In an important race, I was once so busy thinking about so many different things that I actually lost track of where I was in relation to the windward mark, and had to ask my crew to keep track of the layline and not let me sail past it. I frequently crew for one of the most skilled and winningest small boat racers in one of the most competitive classes in the Annapolis area, and have seen him focus on his gps, instead of focusing on sailing the boat, and lose a terrible amount of time and position. Now, when I see him wander off course while messing with the gps, I alert him to it.

IMHO, the information provided by polars should be regarded as a useful guide, but not as an absolute, because those numbers are generated in an ideal environment, and not on a real race course under actual racing conditions.

I would suggest that you commit the general information contained in your polar plot to memory. (Not every detail - just the general parameters.) If you have a working knowledge of the information provided by the polars, you can use that information to help you make choices along the way.

If you have enough knowledgeable crew to assign one of them to devote his time and attention to programming, reading and interpreting the instruments, then the instruments might be useful, but if the skipper will have to do it all himself, I wouldn't do it.

I'm a firm believer that racing success usually depends more on how well and how consistently you do the basics than on whether you use more sophisticated instruments and techniques. You can actually lose time and distance by misdirecting your focus to instruments.

Edited by - on

joearcht
Navigator

Members Avatar

USA
243 Posts

Response Posted - 10/21/2009 : 06:59:04

I'm sort of in agreement with Steve. I have an old set of Nexus instrument and server that is pretty comprehensive, including VMG calculation. It is a very complex set of instruments and about the only use I obtain from it while racing is occasionally looking at the wind speed and hull speed. My sailing conditions are fickle and I've never been able to make good use of the VMG readings. The wind heading readings are all but worthless (compared to looking at the sail telltales and mast windvane). I would love to see that polar diagram you located. Where did you get it from? Is a polar diagram specific to a certain sail type/configuration? I've seen places you can purchase them or have them developed. I wonder if the association would consider buying/posting something on this website for the memberships use? I would contribute to such an effort.

Edited by - on

leebitts
Navigator

Members Avatar

USA
122 Posts

Response Posted - 10/21/2009 : 10:26:40

It took me a while surfing to find the polar I'll get a chance tonight to find it again. If I can't I'll scan what I had printed out and post that.

Edited by - on

Ericson33
Admiral

Members Avatar

USA
892 Posts

Response Posted - 10/21/2009 : 10:45:50

http://www.wyc.org/SailingTips/TargetBoatSpeeds/tabid/510/Default.aspx

Edited by - on

Ericson33
Admiral

Members Avatar

USA
892 Posts

Response Posted - 10/21/2009 : 10:47:57

Data Supplied by Craig Swanson, our new best friend.

True
Wind
Angle Apparent
Wind
Angle Windward
Target
Boat Speed Windward
Target
VMG True
Wind
Speed   Downwind
Target
Boat Speed Target
Apparent
Wind
Angle Target
Boat Speed
@ 45º
Apparent   Target
Boat Speed
@ 90°
Apparent
47 35 2.3 .6 2.0 2.1 135
2.6 .9 2.5 2.4
2.9 1.2 3.0 2.6 138
3.2 1.5 3.5 2.8
47 3.5 1.8 4.0 3.0 4.2
3.8 2.0 4.5 3.2 142 4.5
3.9 2.3 5.0 3.5 4.9
4.2 2.6 6.5 3.7 5.1
46 34 4.4 2.8 6.0 3.8 146 3.7 5.4
4.5 3.0 6.5 3.9 150 4.2 5.6
4.6 3.2 7.0 4.0 155 4.5 5.8
4.8 3.3 7.5 4.1 159 4.7 5.9
45 33 5.0 3.5 8.0 4.2 162 5.0 6.1
5.1 3.7 8.5 4.2 165
5.2

6.2
5.1 3.8 9.0 4.3 167 5.3 6.3
5.2 3.9 9.5 4.6 170 5.4 6.5
42 30 5.2 4.0 10 4.8 5.5 6.6
5.4 4.1 11 5.0 5.6 6.7
40 5.5 4.2 12 5.4 173 5.8 6.9
5.5 12 5.4 173
39 5.6 14 5.9
38 5.6 15 6.1
.

    Wally Upwind    Wally Downwind
5° Lift = +.1 5° Lift = -.5
10° Lift = +.2 10° Lift = -1.1
5° Header = -.13 5° Header = .3
10° Header = -.25 10° Header = .45

Edited by - on

leebitts
Navigator

Members Avatar

USA
122 Posts

Response Posted - 10/21/2009 : 16:18:43

Great, that is exactly the polar that I had found. Hence my question about instruments. As I sail on a lake with pretty flukey winds I'd think the accuracy of instruments could be important. What fun!

Edited by - on

Ericson33
Admiral

Members Avatar

USA
892 Posts

Response Posted - 10/21/2009 : 16:37:13

I have more, will upload soon.

Edited by - on

joearcht
Navigator

Members Avatar

USA
243 Posts

Response Posted - 10/22/2009 : 07:00:23

Thanks guys, I'll study this and see where it leads.
I was expecting something a little different however. The polars that I've seen in the past were actual diagrams with curves and radials, but I suppose this can be converted to that format and vice versa. With information like this I may make better use of my instruments, just don't know yet.

Edited by - on

SailCO26
Captain

Members Avatar

USA
457 Posts

Response Posted - 10/27/2009 : 06:46:58

I'm in agreement with several of the posts above - the polar knowledge is great stuff, but dont get caught up in it. Keep your boat clean and tuned, watch your trim and strategy/tactics, and you'll be competitive in the CP25.

If you're already in the top 5-10% and looking for that next step up, polars and good instruments MIGHT get you there eventually - but expect to pay a penalty for a while as you get used to the "system" before you start to realize the benefits.

As far as racing instruments go, I have a bulkhead compass and that's it. I'll use it to check against the start line, and on occasion to measure lifts/headers tho that's usually fairly apparent where I race. There is an analog speed installed, but it hasnt worked since I bought the boat.

I *do* have a GPS I have on the boat when racing, BUT it's only used to record the track for post-race analysis (which I rarely ever get around to, for some reason...). For grins, I'll usually check the max speed after the race, but I do NOT watch the speed during the race.

Remember that a GPS tells you what you just DID, not what you're DOING. If you use a GPS and polars you will spend a lot of time focusing on chasing what just happened rather than what you're doing until you get used to that.

That being said, polars are also great for reality checks/tuning. For a given condition, am I making the speeds I should be or falling short? Without the polars everything might LOOK good, but you could actually be slower than you should be.

Oh, and the "Velocitek on SA" comment probably referred to searching the SailingAnarchy.com site. Do yourself a favor, use the SEARCH function and dont post another "what's the best instrument for..." thread unless you have really thick skin...

Jim

Edited by - on

Topic

New Topic

Topic Locked

Printer Friendly

Jump To:

Association Forum

Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
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.