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Post by naughtyfox on Oct 20, 2019 13:24:07 GMT
In July 2018 we filled the diesel tank at Great Haywood, and again, in October 2018, at Overwater Marina near Audlem. We could roughly count the hours we'd driven and came out with an answer of 0.5 litre/hour for our little engine. We filled up at Reading this August, and again last Wednesday in Newbury, having taken the boat Reading -> Devizes -> Newbury. Pearson's guide has this distance at 56 hours, and we took 31 litres - which comes out as 0.55 litres/hour. If one takes a bit off for idling before driving, and general hanging-around, then probably 0.5 litres/hour is more like it for straight driving. So.... now we know. I've changed the engine oil 6 times in this distance, and at about 0.8 litres/change that comes to 4.8 litres of engine oil, which is less than the fuel consumed (roughly 1 litre of oil to every 6 litres of diesel).  |
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Post by Mr Stabby on Oct 20, 2019 13:28:17 GMT
What's that red thing where the engine should be?  |
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Post by Deleted on Oct 20, 2019 14:06:48 GMT
So if we take as a rule of thumb 175 grams per horsepower per hour and diesel specific gravity being around 0.85 (850) this seems to indicate the average power required to shift your boat is 425/175 which is 2.4hp.
That is pretty impressive I reckon.
Of course I suppose a lot of that is idling in locks assuming you leave it running so it would be a bit higher maybe 4hp actually pushing the boat.
Difficult to work it out properly
Disclaimer: all the above may be nonsense. Despite being a math genius at school most of my answers were wrong. Good marks for the "working out" part !
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Post by TonyDunkley on Oct 20, 2019 14:39:47 GMT
In July 2018 we filled the diesel tank at Great Haywood, and again, in October 2018, at Overwater Marina near Audlem. We could roughly count the hours we'd driven and came out with an answer of 0.5 litre/hour for our little engine. We filled up at Reading this August, and again last Wednesday in Newbury, having taken the boat Reading -> Devizes -> Newbury. Pearson's guide has this distance at 56 hours, and we took 31 litres - which comes out as 0.55 litres/hour. If one takes a bit off for idling before driving, and general hanging-around, then probably 0.5 litres/hour is more like it for straight driving. So.... now we know. I've changed the engine oil 6 times in this distance, and at about 0.8 litres/change that comes to 4.8 litres of engine oil, which is less than the fuel consumed (roughly 1 litre of oil to every 6 litres of diesel). A fairly reliable 'rule of thumb' is that a diesel engine will burn 1 x gallon of fuel per hour for every 20 bhp it's producing, . . so if those figures for fuel consumption and hours run are accurate then your engine's average power output underway in a canal is only 2.5 horsepower, and if your speed in the pounds is comparable with other boats then your engine/propeller/hull matching has to be remarkably good, . . certainly far better than most modern canalboats. |
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Post by Clinton Cool on Oct 20, 2019 16:43:16 GMT
I have a little Vetus 2 pot think it's 11hp. I've never measured consumption while cruising but did a test for consumption when running the engine to charge the batteries, it worked out around 3 hours per litre.
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Post by naughtyfox on Oct 20, 2019 17:41:00 GMT
In July 2018 we filled the diesel tank at Great Haywood, and again, in October 2018, at Overwater Marina near Audlem. We could roughly count the hours we'd driven and came out with an answer of 0.5 litre/hour for our little engine. We filled up at Reading this August, and again last Wednesday in Newbury, having taken the boat Reading -> Devizes -> Newbury. Pearson's guide has this distance at 56 hours, and we took 31 litres - which comes out as 0.55 litres/hour. If one takes a bit off for idling before driving, and general hanging-around, then probably 0.5 litres/hour is more like it for straight driving. So.... now we know. I've changed the engine oil 6 times in this distance, and at about 0.8 litres/change that comes to 4.8 litres of engine oil, which is less than the fuel consumed (roughly 1 litre of oil to every 6 litres of diesel). A fairly reliable 'rule of thumb' is that a diesel engine will burn 1 x gallon of fuel per hour for every 20 bhp it's producing, . . so if those figures for fuel consumption and hours run are accurate then your engine's average power output underway in a canal is only 2.5 horsepower, and if your speed in the pounds is comparable with other boats then your engine/propeller/hull matching has to be remarkably good, . . certainly far better than most modern canalboats. 10hp engine. At top speed we can do 4mph / 6kmh. That would mean half a gallon in our case, which is 2.27 litres (if it's 1 gallon per 20bhp) (1 gallon = 4.54 litres). But we are driving at 0.5 litre per hour, so it would appear. Sometimes I open up to top speed to listen for a 'whistle' (air going into the air filter? sounds like a turbo on its way out on a Leyland bus) which tells me there's nothing round the prop, but we generally pull the stick back and go at something like 60% as there's no point wrecking an engine with overheating and thrashing it, and it's better to 'glide' through the water rather than push a big wave up in front of you and battle against it. Now that we have a figure of 0.5 litre per hour, and we are filled up, next time we fill up we can check the figure again. We can run to Pearson's times in his guides, but that is pushing things a bit, so if his book says 3 hours I think that'll be 4 for us. |
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Post by TonyDunkley on Oct 20, 2019 18:27:07 GMT
A fairly reliable 'rule of thumb' is that a diesel engine will burn 1 x gallon of fuel per hour for every 20 bhp it's producing, . . so if those figures for fuel consumption and hours run are accurate then your engine's average power output underway in a canal is only 2.5 horsepower, and if your speed in the pounds is comparable with other boats then your engine/propeller/hull matching has to be remarkably good, . . certainly far better than most modern canalboats. 10hp engine. At top speed we can do 4mph / 6kmh. That would mean half a gallon in our case, which is 2.27 litres (if it's 1 gallon per 20bhp) (1 gallon = 4.54 litres). But we are driving at 0.5 litre per hour, so it would appear. Sometimes I open up to top speed to listen for a 'whistle' (air going into the air filter? sounds like a turbo on its way out on a Leyland bus) which tells me there's nothing round the prop, but we generally pull the stick back and go at something like 60% as there's no point wrecking an engine with overheating and thrashing it, and it's better to 'glide' through the water rather than push a big wave up in front of you and battle against it. Now that we have a figure of 0.5 litre per hour, and we are filled up, next time we fill up we can check the figure again. We can run to Pearson's times in his guides, but that is pushing things a bit, so if his book says 3 hours I think that'll be 4 for us. Apparent discrepancies in speed/horsepower/fuel consumption calculations come about because the horsepower a propeller absorbs at any given rpm doesn't increase as a lineal function, . . it goes up along what's known as the Propeller Law Curve - a curve which steepens as the rpm's increase, which is the opposite of what engine bhp curves do. They generally go up less steeply as rpm's increase, and the trick to the ideal matching of the propeller to the engine is to get the two curves to meet and cross each other at or just slightly below the engine's maximum rated rpm. |
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Post by Deleted on Oct 20, 2019 20:40:54 GMT
Out of idle curiosity TonyDunkley or anyone else who knows, how much effect will the size of prop have, rather than the engine revs or size of engine? Our boat at 55' has a Beta 43 with a 21" prop whilst my mate has a 60' boat with an Izuzu 42 with only a 16" prop. His tick over speed is unbelievably slow ... I have to drop out of gear if behind him, yet we're doing the same rpm. Rog |
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Post by peterboat on Oct 20, 2019 20:48:30 GMT
My big boat only uses 4 hp to push it along at 3 MPH thats 3k watts as its electric, the problem is the increase in power to do every extra mph is way more than 1k watts to get to 6 MPH it uses 23K watts over 30 hp just shows you how much spped costs doesnt it?
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Post by TonyDunkley on Oct 20, 2019 21:18:07 GMT
Out of idle curiosity TonyDunkley or anyone else who knows, how much effect will the size of prop have, rather than the engine revs or size of engine? Our boat at 55' has a Beta 43 with a 21" prop whilst my mate has a 60' boat with an Izuzu 42 with only a 16" prop. His tick over speed is unbelievably slow ... I have to drop out of gear if behind him, yet we're doing the same rpm. Rog The short answer to the question about propeller size is that it has a massive effect on any boat's performance because it's the one and only thing that's turning the engine's power output into the propulsive effort that pushes the boat through the water. If considered along with propeller diameter and pitch, comparison figures and spec's giving both idling and rated engine rpm's and gearbox reduction ratios for your boat and your friend's boat would reveal the reasons for the differences in performance, but consideration of the propeller diameter in isolation from all the other influencing factors will never give a full answer to your question. |
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Post by Deleted on Oct 21, 2019 5:48:09 GMT
My big boat only uses 4 hp to push it along at 3 MPH thats 3k watts as its electric, the problem is the increase in power to do every extra mph is way more than 1k watts to get to 6 MPH it uses 23K watts over 30 hp just shows you how much spped costs doesnt it? Have you done tests for all different speeds say in 0.5mph bands? That would be a nice bit of data to see on a graph. |
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Post by peterboat on Oct 21, 2019 7:32:27 GMT
My big boat only uses 4 hp to push it along at 3 MPH thats 3k watts as its electric, the problem is the increase in power to do every extra mph is way more than 1k watts to get to 6 MPH it uses 23K watts over 30 hp just shows you how much spped costs doesnt it? Have you done tests for all different speeds say in 0.5mph bands? That would be a nice bit of data to see on a graph. I will be, I am fitting an automatic variable pitch propeller to the boat and I will be doing graphs and speed trials before and after with power used ar each rpm, should be interesting |
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