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Old 29-07-2009, 08:39 PM   #1
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speedometer

looking for somet to give me a good reading on speed for a speed power boat . what can you recommend looking for value for money
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Old 29-07-2009, 08:44 PM   #2
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Old 29-07-2009, 08:59 PM   #3
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GPS & I use this puppy
combines Speed ,Volt, RPM & compass all in the one unit - also has a gps output for any repeater if you wanted to run one

http://nordskogperformance.net/produ...&cat=22&page=1
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Old 29-07-2009, 09:27 PM   #4
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looking for somet to give me a good reading on speed for a speed power boat . what can you recommend looking for value for money
ive just got an old navman in mine (non-marine)..very accruate speed reading but city and town maps usless
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Old 29-07-2009, 09:51 PM   #5
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GPS is great, because you can run in a fast tide, then bullshit, but not bullshit about how fast ya boat is.

Buy a Gaffrig or Livorsi pitot and hold your head high when you tell people what speed ya boat does.
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Old 29-07-2009, 10:31 PM   #6
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Buy a Gaffrig or Livorsi pitot and hold your head high when you tell people what speed ya boat does.
How accurate are the Gaffrig/Livorsi pittot ones Jon?

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Old 29-07-2009, 10:56 PM   #7
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How accurate are the Gaffrig/Livorsi pittot ones Jon?

Alan
My experience is that they're excellent.

When we've been on Windermere, they're been absolutely bang on with the official speed. We indicated 79-1/2 mph in the yellow extreme (virtually full scale on a 80mph Gaffrig), and the official speed was 79.37mph.

When I've done very honest 2 way runs on southampton water with my boat, again it's been spot on. a 2-way gps average agrees within a gnats cock of the Gaffrig reading.

In both cases we've used the in-built pitot pickup in the Bravo drive, not a transom mounted pitot. The drive version is good and deep in the water away from the running surface.

It seems to be human (powerboater) nature to always quote the highest speed they've ever seen on their gps as their 'top' speed, which is rarely an accurate figure for the boat. When my Gaffrig says 70, I'm comfortable it's actually doing 70, or fecking close to it.
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Old 29-07-2009, 11:09 PM   #8
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GPS is great, because you can run in a fast tide, then bullshit, but not bullshit about how fast ya boat is.
Quite correct - more of a problem on a displacement hull
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Old 29-07-2009, 11:12 PM   #9
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Nuts Edit Time Out.

Pitot measures speed over/through the water - GPS over the Earth surface - each has it's shortcomings & advantages
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Old 29-07-2009, 11:31 PM   #10
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Quite correct - more of a problem on a displacement hull
a 4 mph following tide adds 4 mph to your gps speed, whether you're going at 5 mph, or 105 mph.

BTW, I was being facecious.
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Old 30-07-2009, 12:22 AM   #11
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a 4 mph following tide adds 4 mph to your gps speed, whether you're going at 5 mph, or 105 mph.

BTW, I was being facecious.
So was I
There are +ve & -ve to both. But interestingly when you make a record attempt it's between two fixed points on the surface of the earth (typical 1Km). They donít shorten or lengthen it because of the tide or wind & no correction is made in respect of that in the attempt unless it's athletics.
Time between two fixed points. You can play off the numbers one way or another depending on the perspective that the individual prefers, both work, both effective, both have error margins situation dependant.
It's only a bona fide timed run that counts for speed anything else it's just a ball park unverified number by an uncertified instrument that is only installed as an aid to navigation.

Gezz the guy only asked about speedos
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Old 30-07-2009, 12:24 AM   #12
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Buy a Gaffrig or Livorsi pitot and hold your head high when you tell people what speed ya boat does.
Oh thats speed through the water not between two fixed points
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Old 30-07-2009, 12:49 AM   #13
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OK, so carry on kiddin yaself. no skin off my nose.

There's some fast flowing water in the CI's, mebbe worth a trip for team wam for a fake speed claim. (47mph)

'Through the water' is the hard bit.

Records are always two way, within the hour to try to 'cover up' all the problems with measurement of speed over ground.

GPS is a superb tool, but what we're all trying to achieve is speed over water, not ground.
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Old 30-07-2009, 05:26 PM   #14
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But shirley as any good nav knows, if an alternative route exists that adds say 2 nm to a journey but gains a tidal stream advantage of 4 knots and the race period is likely an hour then the alternative route is the no brainer.

So we are actually interested in getting between two fixed points on the globe in the shortest time possible regardless of speed through the water QED.

Or am I thinking too hard
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Old 30-07-2009, 05:59 PM   #15
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Or am I thinking too hard
I think you should come out & show us.
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Old 30-07-2009, 06:18 PM   #16
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I think you should come out & show us.
I thought it was the distance travelled over the time taken to do the distance - forget speed through the water...
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Old 30-07-2009, 06:22 PM   #17
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But these are the thoughts of a simpleton not a racer... and as far as i know that has been the definition of "Speed" for time immoral

For what its worth and what do I know anyway ........
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Old 30-07-2009, 06:27 PM   #18
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and what do I know anyway ........
I think you can answer that.
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Old 30-07-2009, 06:38 PM   #19
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I think you should come out & show us.
Ok Ok I'd like to announce to the forum I'm a closet lesbian, but what on earth did you want me to show you?
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Old 30-07-2009, 07:23 PM   #20
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I think you can answer that.
I did its distance over time......
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