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 Post subject: Sailing Speed based on angle
PostPosted: 17 Apr 2019 15:31 
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Able Bodied Seaman

Joined: 22 Jul 2015 12:33
Posts: 30
Location: Stuart, Florida
Hey Folks,

Does anyone have any information about average expected speeds based on sail angle? I think it may be called a Polar Chart but I'm not sure. Thanks.

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Jesse
s/v Sailsman


 
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 Post subject: Re: Sailing Speed based on angle
PostPosted: 17 Apr 2019 16:59 
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Skipper

Joined: 16 May 2009 08:06
Posts: 179
Either a polar plot or polar chart. If you do find it, please post on the website (I guess in the specifications section?). Iím sure there is one published somewhere.


 
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 Post subject: Re: Sailing Speed based on angle
PostPosted: 17 Apr 2019 23:25 
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Skipper

Joined: 13 Feb 2011 21:19
Posts: 257
Location: Canyon Lake, TX
I'll be dammed if I can remember where I found them but here is a spreadsheet with the T-37 polars.


Attachments:
File comment: TWA = True Wind Angle
Speeds in Knots

polars.xls [7 KB]
Downloaded 67 times

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Wayne
Master and Commander of the Sailing Vessel Impetuous
Rider of Waleli Honda 1800 VTX
Subservient to no man except SWMBO
Any day without dock lines is a GOOD day!
 
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 Post subject: Re: Sailing Speed based on angle
PostPosted: 19 Apr 2019 17:17 
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Midshipman

Joined: 31 May 2017 22:18
Posts: 66
Location: Gulf of Mexico
WayneH wrote:
I'll be dammed if I can remember where I found them but here is a spreadsheet with the T-37 polars.


This is awesome! I was literally just looking for this last week as we were preparing for our crossing from the Keys to the Bahamas. We got a subscription to a fancy new weather routing software, and couldn't find a polar chart so I made some educated guesses....

Based on my experience these numbers feel a bit high, but it may just be that we're fully loaded for cruising and so Soulianis is a little more sluggish now. But these feel close enough to start playing with, anyone else have an opinion/data?

Thanks again for sharing!


 
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 Post subject: Re: Sailing Speed based on angle
PostPosted: 12 May 2019 15:40 
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Able Bodied Seaman

Joined: 22 Jul 2015 12:33
Posts: 30
Location: Stuart, Florida
Thank you for the quick response Wayne. I thought I would get a notification if someone responded so Iím just seeing this now. Now I need to decipher what Iím looking at. Very Happy

Jesse

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Jesse
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 Post subject: Re: Sailing Speed based on angle
PostPosted: 17 Dec 2020 13:57 
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Rail Meat

Joined: 01 Nov 2020 18:02
Posts: 4
Wayne,
Thanks for posting the spreadsheet. I needed these to input into PredictWind.
I found another set of numbers, with a polar plot, at:
https://jieter.github.io/orc-data/site/?#GRE/GRE1495
These are ORC numbers for Cristel, a Condor 37 (British-built version of the T37, I believe).
These numbers seem a little more conservative than in the spreadsheet, so looking forward to comparing with Island Pearl.
Happy holidays, all

BJ
Island Pearl, Hull #27 (1977)
Vero Beach, FL


 
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 Post subject: Re: Sailing Speed based on angle
PostPosted: 18 Dec 2020 19:06 
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Midshipman

Joined: 06 Aug 2020 09:02
Posts: 72
I would not use either of those files for routing purposes. Based on my experience with race boats and polar generation, I believe those numbers to be significantly high. In addition, these polars assume sail selection that cruisers do not normally have access to (how many of us are cruising with symmetrical kites, 150% genoas, and other smaller headsail combination that aren't roller furlers?). For that matter, how many of us are trimming our sails precisely 100% of the time? If that isn't enough, anecdotal evidence from travel lift load cells suggests most T-37s are MUCH heavier than the design weight (like 3,000 to 7,000 pounds).

Polars are generated with velocity prediction programs. Some are very advanced (designer's in-house VPPs and the IMS/ORC VPPs are particularly rigorous), while some are not (there are basic parametric VPPs that give you ballpark numbers). Inputs include, among other things, hullform or hullform coefficients, sail selection for different true wind angles, displacement, ballast, spar data, and sometimes weight distribution. The numbers are truly supposed to be "best case". They don't account for a particularly nasty sea state for instance. They probably have a feathering prop factored in. They assume a clean, smooth, and fair bottom.

Personally, if you want data for real word conditions, generate the polars yourself. Not hard to do really with good calibrated wind instruments (BTW, TWA is pretty hard to get right). That way you will have real numbers tailored to your boat. Each time you go sailing, if the conditions are steady, try taking a few data points. Hone in a TWA and get your sails trimmed, then get a good average speed. I wouldn't use maximum speed because that's not how you will sail your boat. Your sail selection and specific boat condition is now "baked into the cake". For that matter, use your speed while motoring for TWAs that you won't sail in (e.g. 6 knots TWS dead downwind).

Anyway, that's how I would do it for a cruising boat. Racing boats are a very different story.


 
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