hey M8 how are you.
I am not 100% sure if this will do the job But I assume you want to use a GPS to Sync a Boat speedo ?????
Most GPS's have a large enough display and options to show speed and say compass etc"have an older Garmin Etrax and the version after mine had extra features in bar form to show speed direction and things like that " it maybe easier just to use the GPS as the speedo.
Maybe some pics of the situation may help ??
Here is a link of a GPS display of a later unit
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