On Fri, 04 Jul 2008 08:25:15 -0400, Gene Kearns
wrote:

On Fri, 4 Jul 2008 06:29:26 -0400, Jim penned the following well
considered thoughts to the readers of rec.boats:


"Graham" wrote in message
news:ypjbk.54744$Jx.31786@pd7urf1no...
Does anyone know if these gauges display miles per gallon (or litres per
km) or just miles travelled and gallons consumed?

Do they need any special interface to work with standard GPS's like a
Raytheon chart plotter?

Thanks, Graham

The GPS reports miles per hour over land. It would be useless to use those
calculations in determining real miles per gallon over the surface of the
water.

Au contraire, mon ami!

The Yamaha fuel management gages must receive a fuel flow and GPS (or
speedometer... IMHO,useless) input. You must provide the GPS. I'm not
sure what format(s) of in/output are acceptable, but I suspect it is
configurable to standard formats IOW.... I don't think any special
interface is necessary (since you are likely using the Command Link
interface, already), if the GPS unit outputs a format recognizable to
the FMM..

http://www.yamaha-motor.com/outboard...nk/page05.aspx

No, I think Jim is right.

The link doesn't really give you any information on what data sets are
actually being shared and what format - I would assume NEMA 183.X
which is the defacto standard. The major issue would be connectors on
that harness they supply and how compatiable it is with other units.
However, being NEMA 183 systems, the connector to the hub has to be
something standard - maybe like a N connector or RCA jack.

To the point though, what purpose would having a fuel flow meter do a
calculation based on GPS? The calculation would be simpler and more
efficient to take the fuel flow data in GPH and base the rest of the
calculation on that - position has nothing to do with fuel usage. GPH
has a direct correlation to RPM and MPG - why complicate things?

For instance, if the metering system does the calculations and you
select MPG, then you know if you are using more or less fuel to reach
your destination - X miles equals Y fuel (or the inverse - Y fuel
equals X miles). Same with GPH - X miles equals Y operating time
equals Z available miles.

GPS has nothing to do with fuel usage.