On Fri, 04 Jul 2008 19:16:46 GMT, Short Wave Sportfishing
wrote:

On Fri, 04 Jul 2008 18:34:18 GMT, (Richard
Casady) wrote:

On Fri, 04 Jul 2008 13:49:02 GMT, Short Wave Sportfishing
wrote:

GPS has nothing to do with fuel usage.

No, it's just a tool used for management of fuel use.

I've given up trying to understand why. :)

Here's what I'm thinking.
You're traveling from A to B at what rpm and pitot speedo say is 20
knots.
The current is going from B to A, at five knots.
You don't have GPS, and are on a compass heading to Grand Cayman.
You didn't know about that current.
The engines start coughing as the fuel runs out.
It's hot as Hades, with not a cloud in sight.
For the first time you notice fins cutting through the water.
You look at the sky again. Damn, what are those vultures doing flying
so far from land?
You try to raise Wayne on the VHF, so he can get a fix on you with his
radar.
No luck. Wayne is taking photos of salt water pigs.
What do you do?
What do you do?
Oh, there's no conductor aboard to ask.
HTH

--Vic

On Fri, 4 Jul 2008 11:18:42 -0400, "Jim" wrote:


"Richard Casady" wrote in message
.. .
On Fri, 4 Jul 2008 06:29:26 -0400, "Jim" wrote:


"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.

It reports MPH everywhere equally well. It doesn't know sea from land
unless you get it wet. It reports speed over the land and if the land
is flooded, at sea or on a river,






THIS IS THE WHOLE POINT. If you are heading against a 5 kt current at 10
kts, what speed will the GPS report?

10 knots. But, without the current, you'd be making 15 knots all else being
equal.

"Vic Smith" wrote in message
...
On Fri, 04 Jul 2008 19:16:46 GMT, Short Wave Sportfishing
wrote:

On Fri, 04 Jul 2008 18:34:18 GMT, (Richard
Casady) wrote:

On Fri, 04 Jul 2008 13:49:02 GMT, Short Wave Sportfishing
wrote:

GPS has nothing to do with fuel usage.

No, it's just a tool used for management of fuel use.

I've given up trying to understand why. :)

Here's what I'm thinking.
You're traveling from A to B at what rpm and pitot speedo say is 20
knots.
The current is going from B to A, at five knots.
You don't have GPS, and are on a compass heading to Grand Cayman.
You didn't know about that current.
The engines start coughing as the fuel runs out.
It's hot as Hades, with not a cloud in sight.
For the first time you notice fins cutting through the water.
You look at the sky again. Damn, what are those vultures doing flying
so far from land?
You try to raise Wayne on the VHF, so he can get a fix on you with his
radar.
No luck. Wayne is taking photos of salt water pigs.
What do you do?
What do you do?
Oh, there's no conductor aboard to ask.
HTH

--Vic
Rewind to the beginning.
Plan your trip.
Use the rule of 3 for gas. 1/3 out 1/3 back 1/3 reserve. When you've used
1/3 of your fuel it's time do decide do I go forward or do I go back.
Use a chart or graph similar to what Gene has to get your performance data.
You probably already know your most comfortable and efficient cruise speed.
You can now estimate your trip time. and fuel usage. If you know that you
can refuel at your destination you can safely use 2/3 of your fuel and still
have your 1/3 tank in reserve.
Don't forget to bring human fuel too.
Plan for every situation you can think of. That way when something
unexpected happens you might already have a plan.
What not to plan for?
Don't plan on Wayne being there to save your bacon when you didn't do your
planning.

On Fri, 04 Jul 2008 15:26:45 -0400, Gene Kearns
wrote:

Wouldn't it be nice to be able to figure out the most efficient RPM
for covering a given distance? Say, I want to head 30 miles offshore
and use the least amount of that $4.759 liquid gold?

My boat specs, per the Grady site:

2000 RPM 8.5 MPH 3.8 GPH 2.22 MPG
3500 RPM 20.3 MPH 10.9 GPH 1.87 MPG
4000 RPM 27.5 MPH 12.8 GPH 2.16 MPG
4300 RPM 30.7 MPH 14.5 GPH 2.12 MPG
4500 RPM 33.1 MPH 15.7 GPH 2.12 MPG
5000 RPM 37.5 MPH 19.2 GPH 1.96 MPG

Well, I think we've entered tomato/TOMAHTOE stage. :)

I understand your points - they just don't make any sense to me.

Then again, I'm not exactly normal.

Check out that helicopter POH.... same thing there, too.....

Speaking of which, I solo next week and get my "official" license.

WHOO HOO!!!

On Fri, 4 Jul 2008 15:38:21 -0400, "Jim" wrote:


"Short Wave Sportfishing" wrote in message
.. .
On Fri, 04 Jul 2008 11:39:02 -0400, Gene Kearns
wrote:

GPH is pretty meaningless when one wants to determine fuel consumed
per distance traveled. Miles per gallon is really what we want to
know, since that is a better measure of fuel economy. (Least fuel
consumed, per mile, is my goal, anyway.)

Please take no offense, but that doesn't make any sense.

You have to have a base calculation which would be gallons per hour
(actually I've been told that the true base is per minute) because
it's the only true way to measure fuel usage.

Thus, you use X fuel over Y time.

So what can be the variable in the equation - RPM. At low RPM,
G(used)PH goes down and when RPM rises, G(used)PH goes up.

Thus, at A revolutions you use X Fuel over Y time.

That cannot change - it's the base calculation.

Now from there, you can make whatever calculation you want - furlongs
per fortnight or miles per gallon - it doesn't matter because it's all
based on GPH. It can't be any other way.

Feed distance, time, and gallons consumed into the computer and out
comes MPG.

That's fine, but it's still the same number as GPH. You have still
used a certain amount of Gallons Per Hour.

You asked a question in another post:

Heading upstream in a 10 MPH current at 8 MPH would give what
sort of MPG???? Sooner or later the fuel tank would overflow...!

That's exactly the point of GPH - you have a known figure.

If your not making headway, you are still using fuel - GPH again.

There are simply too many variables to calculate MPH over water. You can use
a GPS log of total miles traveled to calculate MPG of a particular trip.
That won't necessarily compare to the same trip on a different day. You can
collect data and come up with averages if you want. That might be useful.
You can reliably chart GPH at given throttle positions and then convert
throttle position to approximate MPH(over water, not land). You and I are on
the same page but the other folks don't buy into what we are saying. No big
deal.

You've wrapped it up much more clearly that I did. :)

It's actually a tomato/TOMAHTOE thing - I'm comfortable with GPH and
others are comfortable with MPG.

No worries.

On Fri, 04 Jul 2008 14:52:22 -0500, Vic Smith
wrote:

On Fri, 04 Jul 2008 19:16:46 GMT, Short Wave Sportfishing
wrote:

On Fri, 04 Jul 2008 18:34:18 GMT, (Richard
Casady) wrote:

On Fri, 04 Jul 2008 13:49:02 GMT, Short Wave Sportfishing
wrote:

GPS has nothing to do with fuel usage.

No, it's just a tool used for management of fuel use.

I've given up trying to understand why. :)

Here's what I'm thinking.
You're traveling from A to B at what rpm and pitot speedo say is 20
knots.
The current is going from B to A, at five knots.
You don't have GPS, and are on a compass heading to Grand Cayman.
You didn't know about that current.
The engines start coughing as the fuel runs out.
It's hot as Hades, with not a cloud in sight.
For the first time you notice fins cutting through the water.
You look at the sky again. Damn, what are those vultures doing flying
so far from land?
You try to raise Wayne on the VHF, so he can get a fix on you with his
radar.
No luck. Wayne is taking photos of salt water pigs.
What do you do?
What do you do?
Oh, there's no conductor aboard to ask.

Um....

Ok.... :)

"John H." wrote in message
...
On Fri, 4 Jul 2008 11:18:42 -0400, "Jim" wrote:


"Richard Casady" wrote in message
. ..
On Fri, 4 Jul 2008 06:29:26 -0400, "Jim" wrote:


"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.

It reports MPH everywhere equally well. It doesn't know sea from land
unless you get it wet. It reports speed over the land and if the land
is flooded, at sea or on a river,






THIS IS THE WHOLE POINT. If you are heading against a 5 kt current at
10
kts, what speed will the GPS report?

10 knots. But, without the current, you'd be making 15 knots all else
being
equal.
Wrongo old bonged one. The GPS sees you doing 5MPH over ground. What matters
on a boat is your speed thru the water. Speed thru the water is determined
by your throttle position which has a relationship to RPM and GPM. These
things are predictable and repeatable. When you want to know ground speed
toward destination you need to take into consideration current and drift.
Same thing in an airplane. There is ground speed and air speed. They're
different.
Sorry you got bonged. I wonder why Harry got less jail time for a more
flagrant rule violation?

On Fri, 4 Jul 2008 16:47:55 -0400, "Jim" wrote:

Don't forget to bring human fuel too.

Cannibalism?

EEEEWWWWWWW......

On Fri, 4 Jul 2008 16:47:55 -0400, "Jim" wrote:



Rewind to the beginning.
Plan your trip.
Use the rule of 3 for gas. 1/3 out 1/3 back 1/3 reserve. When you've used
1/3 of your fuel it's time do decide do I go forward or do I go back.
Use a chart or graph similar to what Gene has to get your performance data.
You probably already know your most comfortable and efficient cruise speed.
You can now estimate your trip time. and fuel usage. If you know that you
can refuel at your destination you can safely use 2/3 of your fuel and still
have your 1/3 tank in reserve.
Don't forget to bring human fuel too.
Plan for every situation you can think of. That way when something
unexpected happens you might already have a plan.
What not to plan for?
Don't plan on Wayne being there to save your bacon when you didn't do your
planning.

Sounds good (-:

--Vic

"Wayne.B" wrote in message
...
On Fri, 4 Jul 2008 10:14:30 -0700, "Calif Bill"
wrote:

And how many people in lakes and ocean are running against large currents
for a long time?

Heh, ever been near the Gulf Stream?


Nope, but returning you got the same current with you.