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Old 06-08-2013, 13:00   #1
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Speed Over Ground Data Collection

Hello Sailors,

I am continuing a spreadsheet that i found with data for cats. Technical (size etc), price by age, and would like to add SOG for the difference sailing angels by boat by different windspeeds. This information is then available to anyone (just ask) to help them making buying decisions (this is why i am doing this). I hope that you will add with your info. I appreciate loads etc make a difference, but its helps giving an indication of performance in covering distance.

Can you give it in following format foryour cat: angle///SOG(close hauled/close reach/beam reach/broad reach/running///speed). Average wind speed is assumed as 6 meters per second or 21.6km ph.

Thank you
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Old 06-08-2013, 14:51   #2
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Re: Speed over ground data collection

I commend you on your research project but don't you think the results are biased from the start by the competency (sail trimming ability) of the different persons suppling the data?
Because this bias, I could not personally use your data to help me pick a new boat.
Of course there will be the extremes but that is probably obvious from the start........sorry
I have met many cruising sailors with deep pockets and "fast boats" who are oblivious to the basic fundamentals of trimming sails or driving a boat for that matter. And yes on the other hand there are cruisers out there who squeeze every knot out of their craft.
Please let us know how you will account for this discrepancy in your data.
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Old 06-08-2013, 14:58   #3
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Re: Speed over ground data collection

Isn't that sort of data already available in the polars?
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Old 06-08-2013, 14:59   #4
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Re: Speed over ground data collection

11 knots?
45/6
60/6.5
90/6
135/5.5
180/5
lagoon 380
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Old 06-08-2013, 15:31   #5
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Re: Speed Over Ground Data Collection

STW would be more appropriate than SOG.
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Old 06-08-2013, 16:16   #6
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Re: Speed over ground data collection

Quote:
Originally Posted by caradow View Post
the results are biased from the start by the competency (sail trimming ability) of the different persons suppling the data?
We agree with caradow...and sailmonkey preferring the published polar diagrams instead; the latter may suffer the same bias as well, but at least there should be a roughly comparable group...and they provide a great deal more information.

Currents and sea state are also relevant, extremely so for the latter in our experience because wave impact on SOG is considerable (both positive and negative) over the large wetted areas of catamarans.
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Old 08-08-2013, 08:55   #7
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Re: Speed over ground data collection

Quote:
Originally Posted by caradow View Post
I commend you on your research project but don't you think the results are biased from the start by the competency (sail trimming ability) of the different persons suppling the data?
Because this bias, I could not personally use your data to help me pick a new boat.
Of course there will be the extremes but that is probably obvious from the start........sorry
I have met many cruising sailors with deep pockets and "fast boats" who are oblivious to the basic fundamentals of trimming sails or driving a boat for that matter. And yes on the other hand there are cruisers out there who squeeze every knot out of their craft.
Please let us know how you will account for this discrepancy in your data.
You are of course absolutely right. There is no way to allow for a difference in skill set or type of sailor, which affects the performance of the boat. However, as with most things in life, statistically averages filter out outliers in a string of outcomes. Hope that meets your question. Thank you for answering and bringing up a good point.
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Old 08-08-2013, 09:02   #8
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Re: Speed over ground data collection

Quote:
Originally Posted by Sailmonkey View Post
Isn't that sort of data already available in the polars?
Yes, but these numbers are subjective too depending on ability and goal when sailing. Great point. Thank you
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Old 08-08-2013, 09:43   #9
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Re: Speed Over Ground Data Collection

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Originally Posted by noelex 77 View Post
STW would be more appropriate than SOG.
Thank you. You may be right. I have chosen this because it is what most sailor see on their displays and therefor easy to recall from memory.
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Old 08-08-2013, 10:17   #10
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Re: Speed Over Ground Data Collection

you will need a lot of numbers for your statistics to have value when one speaks of "filters".
the other variables I could also interject is quality of sails on these boats you want to rate.
old boats with new sails can make a big difference.
also sea state will be a big factor. for example speed in the lee of an island will be faster than in unprotected waters for the same given wind speed.
anyway "not trying to bust your chops" so please don't take my comments personal.
when I buy a boat I have a pretty good idea how it will perform without this type of data so even if your numbers are valid the differences are bound to be insignificant when one considers "cruising boats" with the obvious difference in designs that should be apparent from the dock.
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Old 08-08-2013, 17:01   #11
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Re: Speed Over Ground Data Collection

Quote:
Originally Posted by noelex 77 View Post
STW would be more appropriate than SOG.
+1.

There are already too many variables in what you are trying to do without adding in currents.
Two identical boats, sailed equally well on a close reach, one in the Gulf Stream going north and one in the Gulf Stream going south, could have a difference in SOG of 8 knots or so.

As for me, when I want to know how fast my boat is going I look at the knotmeter, not the gps. That gives me quicker and more accurate information for trimming sails, etc. The reason I say more accurate is because I can relate STW to previous STW history in the same wind/sea conditions without having to account for current variables.
When plotting landfalls, etc., I use SOG.
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Old 08-08-2013, 17:21   #12
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Quote:
Originally Posted by FSMike View Post

+1.

There are already too many variables in what you are trying to do without adding in currents.
Two identical boats, sailed equally well on a close reach, one in the Gulf Stream going north and one in the Gulf Stream going south, could have a difference in SOG of 8 knots or so.

As for me, when I want to know how fast my boat is going I look at the knotmeter, not the gps. That gives me quicker and more accurate information for trimming sails, etc. The reason I say more accurate is because I can relate STW to previous STW history in the same wind/sea conditions without having to account for current variables.
When plotting landfalls, etc., I use SOG.
I know stw has historically been used to trim against , because that was all that was available. But in reality we trim to apparent wind and that wind is in effect SOG referenced. In your example with the Gulf Stream , the boats are most definitely not trimmed the same even though STW is the same

Why do we persist with stw then ?

Dave
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Old 08-08-2013, 17:38   #13
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Re: Speed Over Ground Data Collection

STW is the bottom line!!!
I do not understand why you trim to AW......not near as accurate.
AW is not an important part of trimming other than the obvious.
To get the most out of any boat you must always be cognizant of STW!!
Then after that is maximized I would turn to SOG in my strategy planning.
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Old 11-08-2013, 00:04   #14
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Re: Speed Over Ground Data Collection

No you are right. But I believe that overall most differences wash out (sea state, correct sail setting, sailing angle etc)
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Old 11-08-2013, 08:38   #15
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Already done and then some. See http://www.multihulldynamics.com/
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