Raymarine forum
[DG] [DG11] calbration speedometer - Printable Version

+- Raymarine forum (http://forum.raymarine.com)
+-- Forum: Raymarine Forums (/forumdisplay.php?fid=1)
+--- Forum: Instruments (/forumdisplay.php?fid=117)
+--- Thread: [DG] [DG11] calbration speedometer (/showthread.php?tid=7745)

[DG11] calbration speedometer - PERSEUS - 03-25-19 12:24 PM

Hi, there is a difference of 1/1.5 knots between my speedometer and the GPS. Now I have the factory parameters, when I calibrate the sensor the difference with the GPS is double. How can I resolve this? .
I have installed a speed sensor DST800 in my sailboat, model DST200 with serial nÂș 1917885, software version 1.003- 1011 and two displays ST 70 with software version V3.04, hardware version 0590585, bootcode version V1.00 the first and the second: software version V3.04, hardware version 0590783, bootcode version v1.00

RE: [DG11] calbration speedometer - Derek - Raymarine - Moderator - 03-26-19 10:44 AM


Thank you for your enquiry.

The differences between GPS SOG and Speed through the water can be affected by many things, mostly external influences.

These factors can be described in this FAQ read here.

If the Speed transducer is more than 2 years old, it is possible the shaft and paddlewheel bearings are worn and a paddlewheel service kit can be used to change these components.

Check the speed comparison is carried out at slack water when there is no tide or current affecting the boat.

Water flow under the boat can also affect the calibration of boat speed, it is important the transducer is aligned accurately to the direction of water flow, underwater fittings of the boat can affect water flow, so can hull features such as bow thruster tunnels, sacrificial anodes, water inlets and outlets, keel and spray rails, all can create levels of turbulence or redirect water flow which can affect the accuracy of the speed transducer.

The two guides either side of the paddlwheel are intended to guide the water over the paddlewheel, however, if the transducer is misaligned, these guides can cavitate causing poor performance too.


RE: [DG11] calbration speedometer - PERSEUS - 03-27-19 05:52 AM

Hi Dereck,
Thanks for your answer. I checked the sensor and it's perfect, clean and in the correct position. I sail in an area without tides nor currents. It's very peculiar that when I calibrate it with the gps speed, according to the instructions, the result is always the same, half the speed of the gps. Could you tell me how to solve this problem? Thanks in advance.

RE: [DG11] calbration speedometer - Derek - Raymarine - Moderator - 03-27-19 08:44 AM

Hi Perseus,

Thank you for your feedback.

There are many other things that can affect performance,

Check the paddlewheel with a small steel screwdriver, you should feel a slight attraction to each lobe or 'tooth' of the paddlewheel, there is a small magnet in each 'tooth' which triggers the speed pulses, occasionally thes emagnets weaken and so cause the transducer to underread.

If the paddlewheel is more than 2 seasons old, replace the paddlewheel and the shaft using a speed transducer service kit.

Check the orientation of the paddlwheel, the flat face of the 'tooth' should be facing towards the bow of the boat.

Are there any obstructions or fouling on the hull of the boat which is impacting the water flow over the transducer?

Where is the transducer located, next to the keel, on the centreline, near the outboard chine of the boat?


RE: [DG11] calbration speedometer - PERSEUS - 04-01-19 09:42 AM

Hi Derek

Hi installed a new paddlewheel and I have the same problem and conclusion

Do you have any idea to solve the problem?

Many thanks


RE: [DG11] calbration speedometer - Derek - Raymarine - Moderator - 04-02-19 05:52 AM

Hi Perseus,

Please can you check the speed calibration factor in the speed instrument, can you increase the cal factor to equal the SOG reading when at slack tide or current? The speed transducer you are using is a smart transducer connected direct to the STng backbone?

It also looks like the software version of the transducer is very early, how old is the transducer? do you have the Raymarine serial number ( you have identified a serial number 1917885 but is there a different serial number too?)

You gave a software version for the DST200 of 1.003 for your transducer - the current version is 1.022 for that version . . . if you can confirmthe details of your existing DST200, then it will need a software update.


RE: [DG11] calbration speedometer - PERSEUS - 04-03-19 10:56 AM

Hi Derek

I will try to install the latest version. (1022)

I have downloaded the software update from Airmar.

How can I install it?, I have a display c120w

Many thanks


RE: [DG11] calbration speedometer - Derek - Raymarine - Moderator - 04-05-19 06:33 AM

Hi Perseus,

The Transducer really needs ot be sent to our service workshop or to Airmar to be updated, there is a piece of hardware that is used by Airmar to update their transducers and this is generally not available other than direct from them.


RE: [DG11] calbration speedometer - PERSEUS - 04-08-19 03:21 AM

Hi Derek

Many thanks for your help

kind regards