[C320-list] Speed Increase by Installing App on Smart Phone - How to calibrate knotmeter?

[Scott Thompson]

True enough, at least for true wind, which is calculated using the 
knotmeter reading. True wind is the sum of the apparent wind vector 
(from the wind instrument and compass heading) and the motion vector 
(from compass heading and knotmeter speed). If you only need the true 
wind angle relative to your heading then the compass data isn't needed. 
For a good explanation see 
http://www.sailingworld.com/how-to/instruments-and-real-angles.

A work-around for a faulty or inaccurate knotmeter is to use ground wind 
instead of true wind. Ground wind is the sum of the apparent wind vector 
and the ground motion vector (SOG/COG), which instruments can obtain 
from networked GPS. It is similar to true wind unless there is 
substantial current or leeway. In principle it gives the motion of the 
air relative to the ground rather than relative to the water, which is 
what "true" wind measures. On my boat with two-year old Raymarine 
instruments the wind indicator will not display ground wind, but you can 
pull this up on the chartplotter's data display. It does NOT require 
accurate speed reading from the knotmeter.  You can use this to 
approximate true wind if the knotmeter isn't working, or is 
miscalibrated, and you know there isn't much current.

Scott Thompson

On 8/4/2015 2:15 PM, Dean Vermeire wrote:
> Good info, Jeff.
>
> I am thinking I want the knotmeter properly calibrated because I would 
> expect the true/apparent wind speed and angle functionality to be more 
> accurate.  True?
>
> Thanks,
> Dean Vermeire
> Moonstruck II (#847)
>
> On 8/4/2015 12:45 PM, Jeff Hare wrote:
>> Hi,
>>
>> On a lake without current, I agree you should just calibrate it so 
>> that you
>> can go faster and kick everyone's butt.  :)
>>
>> If you sail where there are tides and currents and have a chart
>> plotter/depth/speed/wind instruments tied together, then properly 
>> calibrated
>> knot meter and wind instrument can make quite a bit of difference in 
>> showing
>> the strength and direction of currents you're sailing against (or with).
>> Without calibrated gear you miss out on some helpful data, mostly 
>> because
>> the chart plotter calculates current vectors based on GPS course/speed
>> combined with knot meter speed through the water and compass heading.
>>
>> Specifically, you might opt to run with the current or tide now to make
>> better speed over ground even if it takes you off your line, 
>> especially if
>> you can plan for a reversing current to help pull you back in line 
>> later.
>> In our area there are times when I need to head more into a current 
>> early
>> knowing that it will increase or change direction later along my route.
>> Sailing a direct line might force me to point to close to the wind to
>> counter the increased tidal current and stay off the shore.  Can make 
>> the
>> difference between being able to sail and having to motor. Around 
>> here if
>> you don't take advantage of the current, you're missing a lot.
>>
>> -Jeff
>>
>> -----Original Message-----
>> From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On 
>> Behalf
>> Of Bill Lowe
>> Sent: Monday, August 3, 2015 9:49 AM
>> To: C320-List at Catalina320.com
>> Subject: Re: [C320-list] Speed Increase by Installing App on Smart 
>> Phone -
>> How to calibrate knotmeter?
>>
>>   Dean,
>> I have the manual and have calibrated my speed readout several times.
>> Recently, I have been sailing to your marina fairly frequently to 
>> help some
>> friends who recently bought "Sunlower" a hunter 28.5 there. I would 
>> be glad
>> to loan you my manual if you don't have one.
>>
>>
>> Bill
>> Papillon
>> #1146
>>
>>
>> -----Original Message-----
>> From: Dean Vermeire <dean at vermeire.us>
>> To: Catalina 320 List <C320-List at Catalina320.com>
>> Sent: Mon, Aug 3, 2015 8:00 am
>> Subject: [C320-list] Speed Increase by Installing App on Smart Phone 
>> - How
>> to calibrate knotmeter?
>>
>>       First of all, I should point out that after 40 years of 
>> sailing, our
>> Catalina 320 (which we have had for 4 years) is our first boat with 
>> speed
>> and wind instruments.  Electronics aren't all that necessary on a 
>> lake in
>> Kansas.
>>   So, when I see that I am doing about 2.2 knots in 6-10 knots of 
>> breeze on a
>> beam reach, or motoring at 2.5 knots with the yanmar humming along at 
>> 2500
>> RPM, I really don't have anything to compare to.  And then, some of you
>> folks talk about motoring at 6-7 knots, so I just figure that I should
>> switch out the 2-blade prop for a 3-blade.  But when you talk about 
>> sailing
>> at 6-7 knots or more, and the most I have been able to get out of her 
>> is 5
>> knots with the Asym flying in a good breeze, I start thinking one of two
>> things - either the knotmeter is lying to me, or I suck.
>>   Yesterday, I downloaded a simple GPS app, "SailDroid", to my phone. My
>> knotmeter says 2.2 knots.  The phone says 4.5!  This is not definitive
>> proof, but I'm going to say that I do not suck!
>>   It is amazing how it feels like you are going faster, just because 
>> some
>> widget thinks you are.  :)
>>   The paddlewheel sending unit is only 2 years old.  Is there a way to
>> calibrate the knotmeter (ST-60)?
>>   Thanks,
>> Dean Vermeire
>> Moonstruck II (#847)
>>
>>
>>
>>
>>
>