Fuel Consumption

[Hockham Admiral]

Very interesting, Warp. The top red/green lines match our speeds exactly and go to prove what I originally started this topic about!

[Guest]

Attached is a chart of hull speeds mapped to mph.

 

If you locate your waterline length on the bottom and scan up then green lines should roughly correspond to low wash and red ones to high wash.

 

Hull speed is not an absolute limit as canoes surfboards dinghies etc regularly prove. It just means that you are moving into a planning mode (loads of boats can exceed their hull speed even sailing boats).

 

Taking the x axis as the waterline length in feet, and the y axis as the speed in mph, then the top red trace does appear to correspond to the 1.4 multiplier in the formula, ie hull speed when the bow wave trough reaches the stern.

 

I don't understand the significance of the several other red and green traces below, as the graph has no legend.

 

Yes, many hulls are semi-planing, even sailing dinghies that can get nicely up on the plane with a really good blow.

 

The point about the "maximum" theoretical hull speed is the enormous losses in power/efficiency at that point, coupled with the huge wash from the hull sitting up against it's own bow wave, before it can hydro-dynamically lift itself up onto it, if it has enough power to weight, and a lifting underwater design.

 

It's an unfortunate  no-compromise decision, maximum displacement hull design efficiency does not try to lift at all, but cut through the water as cleanly as possible, with minimal power and wash. 

 

Whereas all planing or semi-planing hulls are less efficient at displacement speeds, because the hull form underwater is always trying to lift as well as push through the water.

 

Something like a Thames slipper launch is a good example, hardly a ripple at "hull" speed, but even if you put a very powerful engine in it, it would go no faster.

[donnygeoff]

Just got back from a 4 day short break..

 

60 quid fuel deposit, engine only went over 1000 revs when I was on barton broad otherwise it sat at 8-900....

 

Just got £28 and some pence back....... 4 days cruising for about £8 per day...

 

[SPEEDTRIPLE]

Just got back from a 4 day short break..

 

60 quid fuel deposit, engine only went over 1000 revs when I was on barton broad otherwise it sat at 8-900....

 

Just got £28 and some pence back....... 4 days cruising for about £8 per day...

 

 

 

CHEAPSKATE.

[10B]

Just got back from a 4 day short break..

 

60 quid fuel deposit, engine only went over 1000 revs when I was on barton broad otherwise it sat at 8-900....

 

Just got £28 and some pence back....... 4 days cruising for about £8 per day...

 

 

 

Might as well had one of those Rag & Stick things.  

 

Or a house boat.

[SPEEDTRIPLE]

We seem to have gone round in a circle with this thread.

 

The pertinent points remain.

 

The BA has to have a workable method to be able to prosecute blatant speeders or there will be an increase in boats going faster and  faster and getting away without being able to be prosecuted.

 

The only practical way to maximise BA Ranger's time in monitoring speed appears to be by the use of static radar guns.

 

Since toll payers are paying their wages, it's in all our interests for the task to be carried out as efficiently and effectively as possible.

 

If anyone can suggest a practical alternative method to radar guns for proving excessive speed that will stand up in court, I'm sure the BA would be very grateful to hear it.

 

 

i`l make this my last comment on the subject as it`s well off topic.

 

This goes back to my comment about watching you wash. If you can go at say 7mph over the water, which might be 5 mph over land, the amount of extra wash you`ll produce could cause problems to moored boats. When the speed was measured over moving water, you would be doing the 5mph, with little wash which would be 3mph over land, and more considerate to moored boats.  Now, all they`ve done is to legalise irresponsible use of a LEGAL speed limit, which if caused an accident would get the reply "i was within the speed limit, so i`m not responsible" or something like it. I`l always think it`s best to measure speed over water, and nothing anybody can say will make me change my mind. If you need to make up time by going faster than 5 mph over the water, go with the tide and not against it.

 

I`m not going to comment anymore, as i`ve gone off topic for too long.

[SPEEDTRIPLE]

Might as well had one of those Rag & Stick things.  

 

Or a house boat.

 

 

Geoffers,

 

you`ll NEVER have a yacht on the broads :Sailing

[Guest]

.... I`l always think it`s best to measure speed over water, and nothing anybody can say will make me change my mind. .....

 

I quite agree with that as regards maintaining acceptable wash and steerage way Neil.

 

The problem is how can the BA monitor the speed of another boat moving through the water, sufficiently accurately as to be able to win a prosecution ?

 

The only way I can think of is by the BA launch following it, with the same current flow, measuring it's own speed with a very accurate speed log.

 

Whereas a single Ranger, moored up with a radar gun, can monitor hundreds of boats per day.

 

Over most of the popular and busier areas of the Broads, the tidal effect is no more than one mph on average.

[ExUserGone]

I though speed limits were there for safety and reduction of wash damage, not just for ease of prosecution, in most cases a quick shouting at would probably do the job.

Back on the gt.ouse I can understand the use of mph limits as the main navigable bits are non tidal and normal flows barely make 1/2 a knot.

I'll shut up on this one now, I'm with Speedtriple on this.

[Guest]

I though speed limits were there for safety and reduction of wash damage, not just for ease of prosecution, in most cases a quick shouting at would probably do the job.

Back on the gt.ouse I can understand the use of mph limits as the main navigable bits are non tidal and normal flows barely make 1/2 a knot.

I'll shut up on this one now, I'm with Speedtriple on this.

 

 

Yes Leo, safety and reduction of wash damage, that's all I can think they're for too.

 

I don't see radar guns so much a case of "ease for prosecution", but more for "ability to prosecute".

 

I think your confidence in the effect of Rangers "shouting at" some of the speeders is a little optimistic !

[donnygeoff]

Geoffers,

 

you`ll NEVER have a yacht on the broads :Sailing

 

too much like hard work for me.

 

And 10B, house boats can't get under wroxham or wayford bridges, and just tie up to trees when they want.

 

or go through Horning during a regatta, (that was fun) 

 

                : 

[littlesprite]

I've largely tried to stay out of this but what the hell, in for a penny in for pound.

 

I see two different arguments here, one about speed and one about engine revs, I've never agreed with the speed over water verses speed over land nonsense.

Speed in miles per hour is a formula for distance travelled in a given time, whether on land or water a mile is a mile and one hour is one hour, therefor measured on land or water travelling 5 miles in one hour is identical.

There is the argument about punching against a tide of 2 miles per hour means you are travelling at 7 miles per hour to achieve 5 miles per hour ARGHHHH, no your not! your travelling at 5 miles per hour but with higher engine revs revs.

Working the logic of speed over water and transferring it onto roads, when going up a hill I need to increase my engine revs in order to maintain 30 mph which would mean I'm really going at 40 mph, no I've simply increased my engine revs and the speed remains constant.

 

Wash created at certain engine revs due to cavitation around the prop is a whole new argument that I won't even start.

 

Back on the original, original, original topic, my boat is really fuel efficient when the engine is switched off.

[kadensa]

I agree with the argument that speed is just a measurement of distance/time, but what people are really talking about is velocity which also involves direction. As far as the enforcement of speed limits go, this isn't a problem  when one is travelling against the current, but is when one is going with it.  For example, supposing the current is travelling at 3mph, then in a 4mph limit  that would mean.that the engine would have to be run at whatever revs produced a velocity of 1 mph. or less.  (I am, of course, assuming that the instrument doing the measuring is stationary).

 

As a matter of interest, what happens in the case of sailing vessels?  I would have thought that a boat with a decent amount of sail, running before the wind on an ebb-tide could easily exceed the limit.

[MauriceMynah]

Sailing boats are exempt from speed limits.

[Matt]

Just got back from a 4 day short break..

60 quid fuel deposit, engine only went over 1000 revs when I was on barton broad otherwise it sat at 8-900....

Just got £28 and some pence back....... 4 days cruising for about £8 per day...

Just back from an 11 day break and spent £102. Brundall-Beccles-Salhouse-Brundall. Amazing what difference filling up at Boulters and Brooms can do!

[10B]

Well said littlesprite, 1 mph = 1 mph, easy.

[SPEEDTRIPLE]

Just back from an 11 day break and spent £102. Brundall-Beccles-Salhouse-Brundall. Amazing what difference filling up at Boulters and Brooms can do!

 

 

I would have thought it best to fill up at Goodchilds on your return leg, as they were reported as being the cheapest on the broads. Then when you get back to Brooms, just fill up a gallon or so.

 

Incidentally Matt, we`re on Lightning for the first time in October (18-25th), will you be aboard then?.

[donnygeoff]

I thought this was about fuel consumption, but here we go on speed......

 

FORGET SPEED, 

 

whether across ground or through water.....

 

IMHO It is the wash that causes the bank erosion.....

 

Keep that to a minimum, and preserve the Broads...

 

If you are doing a certain speed across ground and leaving a big wash, slow down.

 

Simples...

 

 no wash here

 

 lots of wash here

 

Thats only the icons, don't attack me

[JennyMorgan]

I thought this was about fuel consumption, but here we go on speed......

 

FORGET SPEED, 

 

whether across ground or through water.....

 

IMHO It is the wash that causes the bank erosion.....

 

Keep that to a minimum, and preserve the Broads...

 

If you are doing a certain speed across ground and leaving a big wash, slow down.

 

Simples...

 

 no wash here

 

 lots of wash here

 

 

Mine's got two masts, does that mean I make lots of wash?

[donnygeoff]

Thats only the icons, don't attack me

 

 

You missed that bit out of the quote Peter.

They were the only icon things I found with wash and no wash...

 

sail or engine....

 

it's the wash eroding the banks, not speed

 

   

[Guest]

......it's the wash eroding the banks, not speed...... 

 

Why does that remind of when some people say they're afraid of flying, they really mean that they're afraid of crashing into the ground...  

[donnygeoff]

Why does that remind of when some people say they're afraid of flying, they really mean that they're afraid of crashing into the ground...  

is there anywhere else to crash, but into the ground.....

 

sit at the back of a plane, they don't reverse into mountains.....

 

[Guest]

is there anywhere else to crash, but into the ground.....

 

 

.....is there any other way to create excess wash, other than excess speed.....  

[donnygeoff]

.....is there any other way to create excess wash, other than excess speed.....

 

yes.......

 

get my mother in law to jump in.......

 

going to hide now

 

[finny]

Its got a bit diverse has this fuel consumption topic - the weather also plays a very big part in fuel consumption......if its a tad chilly Mrs finny has any warm air like a blast furnace ....and most of the time which surely would put a dint in any fuel deposit

flameonfin