[Public-List] Polar Plot

[Meinhold, Michael J.]

I would like to have both knotmeter and GPS, and compass too.
Traditionally, the knotmeter and the compass were all you had, so you
had to infer leeway and true velocity.
I would base the VMG on the GPS mean velocity, and use the knotmeter to
estimate the current.

We can't derive a zero-current polar from a 2-knot current polar  or
vice-versa, unless we develop a full velocity prediction method for the
A30.
Mike

-----Original Message-----
From: public-list-bounces at lists.alberg30.org
[mailto:public-list-bounces at lists.alberg30.org] On Behalf Of Lawrence
Morris
Sent: Monday, January 13, 2014 9:48 AM
To: Alberg 30 Public List -- open to all
Cc: Alberg 30 Public List -- open to all
Subject: Re: [Public-List] Polar Plot

I would guess the difference is due to instrumentation.  

If the knot meter sending is off centerline( stb on my boat) the
measured velocity will be different on each tack. 

Correct me if I'm wrong but to develop polars you need a calibrated knot
meter, not a GPS.  Using the GPS will bring current into the equation
and skew the data.





Larry 

Sent from my iPad

> On Jan 13, 2014, at 9:21 AM, Dominic Amann <dominic.amann at gmail.com>
wrote:
> 
> Gord - I note that the windspeed was quoted in Mph, whereas hull speed

> was in knots, so the results might not be so far off. I am curious why

> reaching to port is faster than starboard.
> 
> 
> On Mon, Jan 13, 2014 at 9:11 AM, Meinhold, Michael J. < 
> MICHAEL.J.MEINHOLD at leidos.com> wrote:
> 
>> That's something we should be able to do this summer!
>> One of the racing boats with a good wind instrument, GPS and logger 
>> could collect,  note the wave conditions and what sails are in use 
>> and I volunteer to compile it.
>> 
>> J Bergquist did some of this before he took his boat to Lake Superior

>> but I don't think  he had a lot of data.
>> 
>> Of course, racers may not be willing to divulge their actual 
>> performance......
>> 
>> Mike
>> Rinn Duin #272
>> 
>> -----Original Message-----
>> From: public-list-bounces at lists.alberg30.org
>> [mailto:public-list-bounces at lists.alberg30.org] On Behalf Of Gordon 
>> Laco
>> Sent: Monday, January 13, 2014 8:35 AM
>> To: Alberg 30 Public List -- open to all
>> Subject: Re: [Public-List] Polar Plot
>> 
>> I reckon he figured the A30 was towing an inverted dinghy to be doing

>> only 5knts in 18knts of wind!
>> 
>> Gord #426 Surprise
>> 
>> 
>>> On 13/01/14 3:14 AM, "gregr at nethere.com" <gregr at nethere.com> wrote:
>>> 
>>> Hi Folks,
>>> 
>>> I'm looking for the polars for our boats.
>>> I found one done by a gent by the name of Jack Hornor. It only 
>>> covers wind speeds up to 18mph and tops out for boat speed at less 
>>> than 5
>> knots.
>>> 
>>> Any ideas where I might find them?
>>> 
>>> 
>>> Regards,
>>> 
>>> Greg
>>> _______________________________________________
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>> 
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> 
> 
> 
> --
> 
> 
> Dominic Amann
> M 416-270-4587
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