Is it normal to get speed spikes, I seem to everytime I use my navi, I have the latest firmware installed from Mt Best and use Realspeed 1.92. some are easy to spot and I just delete that run in the lower window of Realspeed and let it recalulate my data. Is that what I'm supposed to do? Others are not so clear cut for instance yesterdays Breakwater to Beacon race the navi showed a max speed of 22.45 but realspeed showed up 2 max 2 sec 1 at 27.17 and 1 at 24.05 What is the general rule when analizing and deleting the data. Ive started uploading onto the GPSSS site so I would like to think my data is accurate, not that I am going to break any records I apologise if this has been covered before.

Jerry, when you are sailing do you cover the GPS with your wetsuit or anything that can absorb water. This is usually the cause of trouble. The best solution recommended by Tom Chalko is to put the GPS unit(s) in your helmet. This way it gets full visibility to all satellites and less inclined to be submerged when you fall off.

Generally you should not need to delete anything in RealSpeed. RealSpeed will not produce a result that contains an identified spike. First take a look at the results in the results pane. Click each result and only if one of the results contains a spike do you need to mark the spike invalid or delete it. Tehre is more info on my website at http://www.intellimass.com/RealSpeed/RealSpeed_FAQ.htm.

Mal, Thankyou for the feed back, I wear my navi in an aqua pack on my upper arm, I have noticed that sometimes it might rotate around my arm maybe that is an issue I can adjust. Ok Im looking at the graph on Realspeed the green is doppler the black is track points, what dose the red represent? The green seems to be the accurate graph? I click on the suspect result in the top results pane, which is the 1st listed, the blue line appears on the graph if I delete that blue line with the right button it dosn't fix up all my results just seems to adjust them a bit. I know I just have to learn how to use the program

Every now and then I get a run between 2 spikes which looks ok on realspeed and even the acceration looks fine too but what ive been told its actualy a loss of signal from the gps which then has to catch up to your current location and so you get nice speeds.
Of coarse when calc using doppler its ignors that run
Ive attached a pic for what to look out for.

Here is Vando's track with the dopper (green line) showing the difference and what to look for.
This graph perfectly illustrates the value of having the Doppler speed from a GPS as well as the track points. In this case the track points have been affected by a spike and give a highly inflated speed. We can prove this has happened because the Doppler differs and remains at the speed we would expect at that time and place. Doppler is not affected by locational calculation errors.

What doppler is affected by on the NAVi are filters that smooth out readings. If the sats drop below a threshold level that shows up as lost satellites in the trackpoint data the unit reverts to a dead reckoning algorithm that uses speed over ground (SOG) and course over ground (COG) to estimate what the speed should be until satellites are re-acquired. The unit also use a track smoothing filter to clean up the data stream.