Most economical speed?

HUMBER P4VWL · 17 February 2012, 18:06

What is the most economical speed per mile to run at?

Is it the speed to maintain planing ability, whatever your boat/engine?

Or is it slightly quicker to have less boat in the water as long as you're not pushing your engine to its limits?

C'mon techies.

wiLlfish · 17 February 2012, 18:16

Quote:

Originally Posted by HUMBER P4VWL

What is the most economical speed per mile to run at?

ow lorng didd yew sitt ther finkin 'wots de darftist kwestiun i cann axe'

ps yorr a still

HUMBER P4VWL · 17 February 2012, 18:27

Quite a while. Sat on a train from Birmingham. Glad to be leaving.

I guess though it's immaterial if I stay attached to a bouy anyway!

willk · 17 February 2012, 18:30

Quote:

Originally Posted by wiLlfish

ps yorr a still

still aye nobbur yew mean? i fownd diss - doo yew fink itts is?

HUMBER P4VWL · 17 February 2012, 18:32

That would be a quality hat for the April Cruise!!

HughN · 17 February 2012, 18:41

I've just made this box (for my non-rib boat!). It is connected to a fuel flow sensor in the fuel line that sends a pulse for every 0.4 ml of fuel that is used. The number of pulses, GPS speed and lat/long get logged to an SD memory card once per second. The SD card also contains a programmable calibration factor to change the 0.4ml to whatever it needs to be to be accurate.

By setting the initial fuel quantity it counts down as fuel is used.

It also generates a little scrolling bar chart of flow rate as it varies with time:

(and shows GPS position, speed, etc.,)

The plan is to use this data to find out exactly how fuel consumption varies with speed (it gets told ho many people are in the boat and the amount of fuel, so total mass is guessable). With enough data, I hope to be able to get a good idea of fuel burn rate vs speed and, if I can log it, r.p.m.

I know wind, tide, etc,., will affect speed over the ground, which is why I will get as much data as I can and weight the data with the number of points at each speed. The aim is to build up a 'map' of " fuel consumption rate" vs "speed" (and also generate KML for each trip that can be viewed in Google Earth).

It might not work in practice, but I'm sure going to give it a try!

The sensor is fuel-proof, air-tight, able to cover a wide range of flow rates and has no metal-to-metal contact. With only 5V going to it, I am confident it won't blow up on me. I just need to get the boat wet now..

Engineers, eh?!

tony t · 17 February 2012, 18:48

[QUOTE="HUMBER P4VWL"]Quite a while. Sat on a train from Birmingham. Glad to be leaving.

And what's wrong with Birmingham yea Cheshire snob

MarkM · 17 February 2012, 18:48

I put it up before, but these are my findings.
The orange line shows the reach with a certain amount of fuel.
At 1000 rpm you get the furthest but it will take ages to get there.
The most economical speed is between 3000 and 4000 rpm though. In my case anyway.

The blue line shows the speed and the pink line the fuel used.

wiLlfish · 17 February 2012, 18:50

Quote:

Originally Posted by willk

doo yew fink itts is?

nar. dis iz iz att

Quote:

Originally Posted by HUMBER P4VWL

That would be a quality hat for the April Cruise!!

wot wiv yew an dat kirny nobbur inn iz ledderhosen wot wil de welch peepuls fink

tony t · 17 February 2012, 19:02

Quote:

Originally Posted by wiLlfish

nar. dis iz iz att

wot wiv yew an dat kirny nobbur inn iz ledderhosen wot wil de welch peepuls fink

You crack me up fishy

Nos4r2 · 17 February 2012, 20:31

Quote:

Originally Posted by HUMBER P4VWL

What is the most economical speed per mile to run at?

Is it the speed to maintain planing ability, whatever your boat/engine?

Or is it slightly quicker to have less boat in the water as long as you're not pushing your engine to its limits?

C'mon techies.

It's the one where it does the most MPG

ppenman · 17 February 2012, 21:05

Usually the most efficient compromise (economy versus speed) is around peak engine torque. However this varies according to prop, leg gearing, weight, hull length etc. 4000-4500 is usually near it. Have a look at the testing done by Ribeye and Yamaha a few years ago which may give you a better idea.

RIB Engines

thomas · 17 February 2012, 21:22

A little bit of trim can give you a couple of gallons an hour.

jambo · 17 February 2012, 22:13

Quote:

Originally Posted by willk

still aye nobbur yew mean? i fownd diss - doo yew fink itts is?

That would be a 'Cardinal' bunnet. Rules & regs state you must wear one if you are stationary for any length of time

tony t · 17 February 2012, 22:38

Quote:

Originally Posted by jambo

That would be a 'Cardinal' bunnet. Rules & regs state you must wear one if you are stationary for any length of time

like 6 months

biffer · 17 February 2012, 22:45

I though shall I post or not but thought I thought. What the hell give it a go. My answer turned out to be. Who cares. You can't put a price on fun and happiness

mister p · 17 February 2012, 23:50

Quote:

Originally Posted by Nos4r2

It's the one where it does the most MPG

Very true.......but your engine will have it's most efficient point at peak torque.
If you then match the prop to maximise it's thrust at this same speed for the particular vessel then you will be at max mpg.
Now on a rib you will have two max mpg's. One for displacement and one for planing. Your prop will be matched for planing efficiency but you could have it matched for displacement and regear your transmission.
So........engine efficiency is fixed.
It is mated to suit your hull by prop pitch and slip for best economy if you so wish.
Economy is often forgone for maximum speed and so props will not generally be fitted to make the most of a particular engine's torque for the hull it is fitted to. Esp. on RIBs.
A tug however will generally have it's prop suited to best engine torque.
Torque is the rate of change of engine speed. When this rate is high, acceleration at this point is high because the engine is at it's most efficient. In water this point can be maintained because of fluid coupling despite variations in load. Gears or torque converters assist in getting engines to this sweet spot and keeping them there. This is why acceleration drops of as you approach peak revs......because the efficiency is tailing off.
Cool?

wiLlfish · 17 February 2012, 23:56

Quote:

Originally Posted by tony t

like 6 months

admirulty rools

arfter sikks munfs hee becums a azard too navigashun an az succh iz lykely too bee blowen upp bi de royul mareens orr uvver nobburs wiv mor ekslposivs thann comon sence (reed royul enjineers, ira, wna, hizbolla an de menia strait oister cachers.

Dhf · 18 February 2012, 01:02

Quote:

Originally Posted by biffer

I though shall I post or not but thought I thought. What the hell give it a go. My answer turned out to be. Who cares. You can't put a price on fun and happiness

Just what I thought,

So hear goes,

Well i've got a 120 L tank under deck and inline fuel flow reader fitted just after the water seperater, Which gives me a digital flow rate, display built into the rev counter, So I can easily see how many litre's per hour, at whatever rpm, so this is what I get,
1000 rpm uses 4lt per hour, averaging 7 knots, on full tank = 210 nm, depending on tide flow
3200rpm uses 20lt per h, averaging 24 knots, on full tank = 144nm
5000rpm uses 50lt per h, averaging 43 knots, oft = 106 nm
So yea you'll travel much further useing lower rpm, But probably won't do the engine much good,

Low Flyer · 18 February 2012, 10:59

Im with Biffer on this one,if you are worried about cost buy a rowing boat,you can go as far as you like then!!And keep the flow meters for how much ale you drink.....