We've got to assume you're talking about your header subject GPH vs MPG
- not miles per hour as you probably mis-typed above.

GPH is irrelevant, even with a trawler, hull speed type boat (of course
in mho). What does it tell you? How many hours of fuel you've burned,
how many hours you might have left? You'll still need to know how fast
you have gone or expect to go to determine where you can get to with
the fuel you have.

The ONLY reason I can guess that GPH is even used is that it has been
the only thing that could be measured with a normally available,
affordable gauge up til now. Fuel flow meters are common technology and
have been in use for ages. They can only tell GPH and that is why
people have been using that measurement. Everyone I've boated with
whether in a planing hull or displacement hull has a GPH flow meter,
but uses that info to mentally convert to MPG using their GPS or
speedometer reading. Yes, if the boat is a pretty steady traveler,
they could short cut by just looking at GPH, but when push comes to
shove (e.g., can we make it "there"), it is MPG which will tell you
what you need to know.

My only reason to have a flow meter on my boat (GPH) is to ultimately -
through a mental calculation- determine the most efficient speed, in
other words, the speed that maximizes MPG.

Nowadays, it becoming more common have the flowmeter GPH input to the
GPS's MPH measurement to give you an MPG reading on your GPS screen.
If I could afford a new unit, I would definitely get that feature -
because again, that's the only reason to measure GPH in the first place.

Both terms can be useful, especially for planning purposes, and when
used together.
If you have an engine with known GPH at specific rpm's (+/- a small
percentage) you can easily plan ahead for consumption and reserves for a
specific distance at various speeds or for days of operation (where
mileage isn't a consideration) before needing to "watch for a gas station".
Although MPG/MPH is great for planning, it doesn't take into
consideration that it's "through the water", so that even when connected
to a GPS, the number will vary up and down.
In the end, a lot depends on type of boat, type of operation, and route
to be traveled.
To be honest, I'd use both for comparison. Most ships use B/M
(barrel/mi) with a reserve of 2-3 days .... always calculate some degree
of reserve.

otn

On Thu, 12 May 2005 00:08:02 GMT, otnmbrd
wrote:

Both terms can be useful, especially for planning purposes, and when
used together.
If you have an engine with known GPH at specific rpm's (+/- a small
percentage) you can easily plan ahead for consumption and reserves for a
specific distance at various speeds or for days of operation (where
mileage isn't a consideration) before needing to "watch for a gas station".
Although MPG/MPH is great for planning, it doesn't take into
consideration that it's "through the water", so that even when connected
to a GPS, the number will vary up and down.
In the end, a lot depends on type of boat, type of operation, and route
to be traveled.
To be honest, I'd use both for comparison. Most ships use B/M
(barrel/mi) with a reserve of 2-3 days .... always calculate some degree
of reserve.

Good points.

Later,

Tom

On 11 May 2005 12:56:41 -0700, "Camilo" wrote:

~~ snippage ~~

My only reason to have a flow meter on my boat (GPH) is to ultimately -
through a mental calculation- determine the most efficient speed, in
other words, the speed that maximizes MPG.

Nowadays, it becoming more common have the flowmeter GPH input to the
GPS's MPH measurement to give you an MPG reading on your GPS screen.
If I could afford a new unit, I would definitely get that feature -
because again, that's the only reason to measure GPH in the first place.

I mean no offense here. Don't get upset - just follow me through
this.

To do a MPG calculation you basically need to know how many miles you
have traveled. Which means that you either need to know that by
experience or stop to use a chart or take a measurement with a GPS.

Now, you already know how many gallons you are using per hour. So all
you need to do is know how much gas is in your boat and how many hours
you have been traveling.

That seems a hell of a lot easier than doing arithmetical calculations
on the fly.

And just to add a complication, let's say that your GPS is kaput for
some reason. You have no idea how many miles you have traveled, but
you have a good idea of how many gallons you have left and how much
time it takes to return. That's a GPH calculation, yes?

Later,

Tom

Actually it is neither in this particular case.
If I am so stupid as to head out on a lake/river that I don't know without a
chart or gps and I did not fill up my gas tank before leaving but I kept up
w/ my time at various rpms then GPH at each of these rpms would mean
something.
On the other hand, assuming I at least filled the gas tank, as long as I
have over 1/2 tank left (not what the needle says but actually 1/2 tank) I
should be able to get back as long as I don't run any harder than I did
getting to where I am.

I use MPG as an overall average but GPH as an overall average works out to
be the same thing.
MPG I know I can run for 2.5 miles per gallon of fuel on average (averaging
40 miles per hour). This of course changes if I run wide open for long
periods of time or idle along.
GPH I know I can run one hour on 16 gallons of fuel on average (averaging 40
miles per hour). This of course changes if I run wide open for long periods
of time or idle along.

Both work just as good.
--
Tony
my boats and cars at http://t.thomas.home.mchsi.com

-
"Shortwave Sportfishing" wrote in message
...
On 11 May 2005 12:56:41 -0700, "Camilo" wrote:

~~ snippage ~~

My only reason to have a flow meter on my boat (GPH) is to ultimately -
through a mental calculation- determine the most efficient speed, in
other words, the speed that maximizes MPG.

Nowadays, it becoming more common have the flowmeter GPH input to the
GPS's MPH measurement to give you an MPG reading on your GPS screen.
If I could afford a new unit, I would definitely get that feature -
because again, that's the only reason to measure GPH in the first place.

I mean no offense here. Don't get upset - just follow me through
this.

To do a MPG calculation you basically need to know how many miles you
have traveled. Which means that you either need to know that by
experience or stop to use a chart or take a measurement with a GPS.

Now, you already know how many gallons you are using per hour. So all
you need to do is know how much gas is in your boat and how many hours
you have been traveling.

That seems a hell of a lot easier than doing arithmetical calculations
on the fly.

And just to add a complication, let's say that your GPS is kaput for
some reason. You have no idea how many miles you have traveled, but
you have a good idea of how many gallons you have left and how much
time it takes to return. That's a GPH calculation, yes?

Later,

Tom

On Thu, 12 May 2005 01:15:25 GMT, "tony thomas"
wrote:

Both work just as good.

True, but one relies more on technology rather than seat of the pants
reckin' :)

Later,

Tom

I know when the gas guage stops bouncing, I need to be near a gas station.

"Shortwave Sportfishing" wrote in message
...
On 11 May 2005 12:56:41 -0700, "Camilo" wrote:

~~ snippage ~~

My only reason to have a flow meter on my boat (GPH) is to ultimately -
through a mental calculation- determine the most efficient speed, in
other words, the speed that maximizes MPG.

Nowadays, it becoming more common have the flowmeter GPH input to the
GPS's MPH measurement to give you an MPG reading on your GPS screen.
If I could afford a new unit, I would definitely get that feature -
because again, that's the only reason to measure GPH in the first place.

I mean no offense here. Don't get upset - just follow me through
this.

To do a MPG calculation you basically need to know how many miles you
have traveled. Which means that you either need to know that by
experience or stop to use a chart or take a measurement with a GPS.

Now, you already know how many gallons you are using per hour. So all
you need to do is know how much gas is in your boat and how many hours
you have been traveling.

That seems a hell of a lot easier than doing arithmetical calculations
on the fly.

And just to add a complication, let's say that your GPS is kaput for
some reason. You have no idea how many miles you have traveled, but
you have a good idea of how many gallons you have left and how much
time it takes to return. That's a GPH calculation, yes?

Later,

Tom

On Thu, 12 May 2005 02:44:18 GMT, "Bill McKee"
wrote:

I know when the gas guage stops bouncing, I need to be near a gas station.

ROTFL!!!

Damn straight. :)

Later,

Tom