non-pole polars for an asym E38

This is a question for Seth and anyone else who wants to chime in. Can anyone hazard a guess as to the optimum downwind sailing angle for an A sail tacked to the forestay? I was attempting to race my E38 last weekend and it seemed to me that deeper than, say, 110-120 degrees true the boat slowed down so markedly that it probably doesnt pay. Wind speed was about 10 knots. Didnt try to measure VMG though, although I could probably try with the GPS. Of course, at that angle to the true wind, you are not making much VMG, hence my confusion.

Cheers, Roger

E38 200 Kingston, ON

sounds about right...

I'd love to see polars for the boat with a poleless asym, although the range on ours is pretty narrow- so I guess it's pretty elementary. We get much better vmg going wing-on-wing in 15kts of breeze than we'd ever get with our cruising kite.
I don't drive much or well, so I don't pay much attention to true wind- but I'd say that if I'm trimming in light air, apparent just aft of the beam (say 100 degrees) would be about right. As it builds, the tack could be eased for better windward rotation and you could get deeper (down to the 120-130 apparent range), but sailing the angles is key with the asym. Ours is cut pretty narrow on Sequoia, but even with the monster running kite on the 395 I used to race on, 140-150 was as deep as you'd want to go- and that was in 12+. Anything deeper and you got run over by the symetrical crowd. Heck, in 10 kts true, I become a fussy trimmer on the symetrical kite if the apparent hits the tabs:baby:
I've become a "vmg nazi" racing phrf... Unless there is some major tactical or strategic advantage, go to the mark!:headb:

Tip for Rog

In about 8 or under, your best VMG will be around 95-110 degrees app-ROUGHLY (no polars avail.). As the breeze comes up, the angle gets bigger and bigger (you can sail deeper with same VMG in more breeze).

The best way for you to calculate the optimal angles for a given wind speed(unless you have this function on your sailing instruments) is to set a mark in your GPS that is dead downwind, and set the GPS to show VMG to waypoint.

Now you can experiment. If your first attempt is in 8-10 knots of True Wind, start at about 90 app. and work in 10 degree app. increments. You will probaly see better numbers near 100 app, than you will at 130 or 90 degrees.

Note the best angle, and try and do this every chance you get so you can develop a table for 8-10 knots, 10-12, 12-14, 14-18, and 18+ TWS. Then you can simply note the wind speed and the best VMG angle and sail it (laminate this table and tape it to the cockpit bulkhead). Of course, when you are sailing these angles, remember to work the puffs-these are opportunities to dig a bit deeper, and conversely, up in the lulls.

This should get you very close. With the A-sail, you will need more than 15-18 TWS to sail deeper than about 135 app. with reasonable VMG-

These are best guess numbers of course, but I bet they will be close.

Go get em!

S

Thanks, Seth and Chris, but ...

What about Chris' point, that in 10 knots or below, is your VMG much better by just sailing dead downwind (wing on wing?) to the mark WITHOUT the A sail? Plus you save the hoist/drop time.

Roger

Not really.....

Because I think he said that happened in 15+ knots of breeze. And I would buy that-the boatspeed is nearing the top end where whatever you gain with the better angle is not worth the distance. BELOW 10, I think you must sail the angles, especially if you have any kind of spinnaker..make sense?
S

From an old Sailnet Article????

I put together a word document for myself in which I copied a number of different articles and emails in which advice was given concerning the rigging, dowsing, and trimming of asymmetrical spinnakers before I even began to look into buying one. Attached is an article that I think I copied from the old Sailnet site...my apologies to the author(s) and the site if I don't have the citation correct.

A note of caution, just because it appeared in an article doesn't make it absolutely valid & the suggestion that one try different angles for one's boat seems to make better sense...the graph in the article is probably a pretty good "shoot from the hip" guide.

Regards,

Ed

FWIW,

There is a software program out there called "Sailfish Yacht Analyzer", which will take input of hull, rig and sail data and plot polars for you. Within the program, you can change the variables, such as the dimensions of your a-sail, which the program will then calculate new polars based on the new data.

I bought the program because there are no polars for a 32-2 in any database I can find. I'm still working with it so I don't have an opinion as to its accuracy but I'll update as I become more familiar with it.

Jim McCone
Voice of Reason E-32-2 Hull #134

Software

Jim,

I am quite anxious to see how this works-how are you able to give freeboards, lwl at various stations, bow shape (flat, V, rounded, etc) that affect speed. IMS does (or simulates) a full hull shape measurement and takes freeboards to generate the polars..Will you have to haul the boat and take some detailed measurements? Or will this be more of a ballpark polar chart???

Inquiring minds want to know, so please keep us posted!:nerd:

Corrected for too much coffee at 11:33 CST

Hey Seth,

This is the program that I was trying to convert all of the IOR numbers to IMS numbers to generate a polor. The program is supposed to do everything that the IMS / Americap numbers.

The numbers that it generated seemed to me to be approximately correct for my E-46.

Here is a photo of the input page. There are about 4 more input pages for rigging etc.....

I am still trying to figure out what all the old IOR numbers have to do with these numbers......

Apparently my boat was rated under Americap, although I don't have a copy of the polars that they generated. Paying $200+ dollars to get them out of the folks at US sailing seems way way beyond absurd to me.

(Rant deleted here about US Sailing and the pay pay pay aproach to being a "Support Org.)

Thanks,
Guy

eyeball approach

Guy,

Thats the page. I guess at $49,95 its a better deal than buying the perf. pack from US Sailing. Unfortunately, US Sailing doesn't have a perf. pack for the 32-2.
I've had to continually go back to the glossary to figure out what some of those terms on the various pages mean so I can compute the numbers.

Seth,

There are fore and aft freeboard numbers, along with all kinds of other measurements, such as the width and depth of the mast at the headboard and at the deck. There's even a measurement for the size of the headboard.
I've taken what I can from our phrf cert. and other docs, like sail dimensions, etc. for input. I'm going to go down to the boat this weekend and take what measurements I can with tape measure, ruler, whatever I need. I want the info as accurate as possible because I'm then taking the polars generated by the program and entering them into the Deckman software. The more accurate the data I input, the more accurate the Deckman will be able to do routing strategy. We'll also go out and test on the water to see how close we are to the theoretical polars.
What I didn't see in the Sailfish program were things like "sheeting angles" or the variables such as exterior-run halyards and radar dome. Ah well.

Jim McCone
Voice of Reason E-32-2 Hull #134

I'd be interested in the numbers

If you would like I would be happy to input the numbers for your boat and make a polar for it. I have wanted to play with some of the numbers on the E boats for a while.

I need some help from Seth though, and am worried that I may have hacked him off when I was trying to tease him about a ride on my boat. I know better than trying to do scarasim as a form of humor on a board, but I slipped....

Anyway, if we can figure out your ior numbers and figure out how they relate to the numbers the program figures out,then we can put them in.

From the cert that I have aboard I am sure that most of the numbers are in some way applicable, but they changed the names...

Guy

What, me worry?

Guy,

I have thicker skin than that! No problem here-let me know what I can do for you!

Jim, these things assume conventional sheeting angles-which you have (for the style of boat), and assume nothing like radar or extra gear. They do a fair job at predicting performance for the boat in racing trim, but are not too focused on the effects of extras that slow you down..6you just have to make whatever allowance you can for that..

I am sure you can dig up an example IOR cert-and I guess a tall tig 32 will come in around 20-22 as an IOR rating-with old age allownace figured in-which it should be on the cert..

Guy-what do you need?

S