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10 degrees of leeway?

Aug 2, 2010
434
J-Boat J/88 Cobourg
Was out for a nice sail in 10 knots of breeze and a fairly lumpy sea state and decided to trim and trim to get the best VMG I could upwind. Using my learnings about speed then point I was getting her to sail well at 47-43 TWA and really feeling in the groove. When I had her going well I turned on the track feature on my chartplotter and after a few minutes tacked over and got her in the same groove on starboard but was shocked to see the angle on the plotter. I took a photo and then measured it with a protractor to show 110 degrees actual from a tacking angle of 90 degrees. 5' keel I know is not as good as the deep keel but I think 10 degrees leeway is a lot.
Thoughts?
 
May 1, 2011
2,270
Pearson 37 Lusby MD
Dan, when I'm sailing close hauled (about 40 degrees off the wind) and using the autopilot to steer, I have learned that a 90 degree turn doesn't cut it. I have to do a 110 degree turn. Not surprised with your observation.
 
Aug 2, 2010
434
J-Boat J/88 Cobourg
I was under 30 degrees AWA and settling about 45 TWA according to my chartplotter that does the calculation. By compass my tacking angle was 90 degrees so I know I was ok on all elements of this. I also know I wasn't getting to my polars either but I am sailing with a furling main while I am sure the polars were set with a battened main with some roach.
According to the polar plot I should be able to hit 6 knots at 10 knots true pointing a little higher than I was and the best I could get to was about 4.5 knots which matches what I would expect so close hauled. Basically I was working to find the best VMG on the beat and this was where I landed though I could have pointed higher or footed and gone faster.
So in summary, I was happy with the performance (though you always want to go faster) but surprised by the track. I believe the lumpy seas contributed as the top of the mast was carving a pretty big arc and of course that upsets sail trim as she pitches.
Dan
 
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Apex

.
Jun 19, 2013
1,025
Oday 28 Traverse City
vectors victor! or nice wind instruments can calculate that out for your.
Use simple examples to start and confirm your calcs, then move up to the actual answer you seek. TWA at 0degrees, 5kts. Boat at 0degrees, 6kts. Apparent wind = 0degrees, 11kts. Turn the boat to 180degrees, at 6kts, and AWA = 180degrees at 1kt.
 
Mar 13, 2011
175
Islander Freeport 41 Longmont
Start with Rig tuning. Is everything exactly the same, Then look at sail trim and of course don’t forget the affects of current and waves. Sometimes our boats favor on tack over another. Just some ideas.
 
May 17, 2004
3,380
Beneteau Oceanis 37 LE Havre de Grace
My course from tack to tack is a bit less than yours, usually closer to 100 degrees. Could there have been any amount of unfavorable current? Also, is your speed transducer properly calibrated? Our chart plotter uses that by default for the true wind calculation, so if it’s out of adjustment, as often happens later in the season with fouling growth, the TWA will be a bit off. There is a setting in our plotter to use GPS speed instead for the calculations. I’d be surprised if you could really point much higher than 30 apparent; I know that’s about the limit for me.
 
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Nov 8, 2010
11,385
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
This does not surprise me at all.

First ALL boats sideslip (leeway) to a certain degree, they have to for their keels to generate lift. The amount is a function of design. Hull, heel, and rudder design all factor. As you found out, it can be more a couple of degrees. 10 is not atypical for a cruiser. Good polar charts will tell you what designer predicts. Here is what Farr has to say about the deep keel First 36.7.

Screenshot 2019-10-03 08.09.08.png


It's the bottom line. In 10 knots the 367 slips 3.91 degrees, so on a 41.8 degree optimum (8 lines up) upwind angle for 10 knots true, the boat tacks through 91.42 degrees. It's one if the reasons the 35 footer rates 72 in PHRF. She's a witch upwind. Note she REALLY finds her feet in 16 knots TW. Accounting for slip, she tack through 88.08 degrees. Nothing touches a 367 in that breeze. Due to angle and speed she's making 5 knots of pure VMG upwind.
 
Last edited:
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Mikem

.
Dec 20, 2009
752
Hunter 466 Bremerton
Dan, when I'm sailing close hauled (about 40 degrees off the wind) and using the autopilot to steer, I have learned that a 90 degree turn doesn't cut it. I have to do a 110 degree turn. Not surprised with your observation.
Same observations with my boat.
 
Aug 2, 2010
434
J-Boat J/88 Cobourg
This does not surprise me at all.

It's the bottom line. In 10 knots the 367 slips 3.91 degrees, so on a 41.8 degree optimum (8 lines up) upwind angle for 10 knots true, the boat tacks through 91.42 degrees. It's one if the reasons the 35 footer rates 72 in PHRF. She's a witch upwind. Note she REALLY finds her feet in 16 knots TW. Accounting for slip, she tack through 88.08 degrees. Nothing touches a 367 in that breeze. Due to angle and speed she's making 5 knots of pure VMG upwind.
Thanks Jackdaw, that makes me feel a lot better. I had noticed the TP52 tracks on the video coverage as being sometimes less than 90 and thinking I was tacking through 90 was shocked to see how far off I was. Pretty happy that I was managing a solid 45 to the true wind on both tacks as I have been below that many times.
Dan
 

Apex

.
Jun 19, 2013
1,025
Oday 28 Traverse City
It's the bottom line. In 10 knots the 367 slips 3.91 degrees, so on a 41.8 degree optimum (8 lines up) upwind angle for 10 knots true, the boat tacks through 91.42 degrees. It's one if the reasons the 35 footer rates 72 in PHRF. She's a witch upwind. Note she REALLY finds her feet in 16 knots TW. Accounting for slip, she tack through 88.08 degrees. Nothing touches a 367 in that breeze. Due to angle and speed she's making 5 knots of pure VMG upwind.
Welcome back JD. Always the encyclopedia of good racing information! Do you have the same charts for BlueJ? The 36.7 and 40.7 have a big race following, probably not so much for your smaller Benny? So perhaps you have created your own?
 
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Nov 8, 2010
11,385
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Thanks Jackdaw, that makes me feel a lot better. I had noticed the TP52 tracks on the video coverage as being sometimes less than 90 and thinking I was tacking through 90 was shocked to see how far off I was. Pretty happy that I was managing a solid 45 to the true wind on both tacks as I have been below that many times.
Dan
Besides deep high-aspect keels, one of the things that make modern boats like the TP52s so weatherly is the tight sheeting angle. With non-overlapping rigs, the sheeting angle is no longer the limitation of windward angle. And this is cracked off a bit!

yysw214300.jpg
 
Nov 8, 2010
11,385
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Welcome back JD. Always the encyclopedia of good racing information! Do you have the same charts for BlueJ? The 36.7 and 40.7 have a big race following, probably not so much for your smaller Benny? So perhaps you have created your own?
Thanks. Needed a break.

Finot produced a decent set of polars for the First260, they do that for all the First boats they design for Beneteau. But sadly it omits slip. So we have to figure it out on our own.

Screenshot 2019-10-04 06.30.49.png


Looking at Up.Bt (upwind angle) you can see we have two modes, below 8 knots TWS, and above. Below we have to foot to keep the boat moving and flow attached to the narrow keel. Headsail is eased the the lifelines, and we tack tru almost 100 degrees.

Above 8 knots, the keel works, trim on, and the boat takes off - the narrow sheeting angle product some crazy upwind angles. 37 degrees! I sight down the traveler, and when I see the mark we can safely go.

Our RaceGeek D10 will display both course and heading, the difference is slip. In slack water thats leeway. I'm trying to get the team at racegeek to make that delta an optional display!