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What is 'cruise speed' ?
You often see the 'cruise speed' mentioned in boat descriptions and brochures.
But what is this speed and how is it determined? |
ZanderU wrote:
You often see the 'cruise speed' mentioned in boat descriptions and brochures. But what is this speed and how is it determined? My recollection is that BOATING magazine's "cruise speed" for planing boats is the throttle setting that produces the best fuel economy while the boat is on plane. Typically, it is somewhere around 70-75% of the engine's top RPM on a boat with a gas engine. -- We today have a president of the United States who looks like he is the son of Howdy Doody or Alfred E. Newman, who isn't smarter than either of them, who is arrogant about his ignorance, who is reckless and incompetent, and whose backers are turning the United States into a pariah. What, me worry? |
My recollection is that BOATING magazine's "cruise speed" for planing
boats is the throttle setting that produces the best fuel economy while the boat is on plane. Typically, it is somewhere around 70-75% of the engine's top RPM on a boat with a gas engine. Actually that would not be correct. The greatest fuel economy with a planing hull boat (eliminating the "dead idle" option) is achieved just after the boat reaches plane. Cruise speed is more RPM related. A speed where you do not stress the engine as much as running WOT, but still achieve a reasonable speed. I like to say it's the maximum speed that can be sustained for long periods without unduly stressing the machinery. It's also a speed where engine temp remains under control. Some if it is personal preference and there is no "official" cruise speed for most planing hull boats- but I agree with Harry that many boaters will "cruise" at 70 -80 % of WOT. |
Gould 0738 wrote:
My recollection is that BOATING magazine's "cruise speed" for planing boats is the throttle setting that produces the best fuel economy while the boat is on plane. Typically, it is somewhere around 70-75% of the engine's top RPM on a boat with a gas engine. Actually that would not be correct. The greatest fuel economy with a planing hull boat (eliminating the "dead idle" option) is achieved just after the boat reaches plane. Cruise speed is more RPM related. A speed where you do not stress the engine as much as running WOT, but still achieve a reasonable speed. I like to say it's the maximum speed that can be sustained for long periods without unduly stressing the machinery. It's also a speed where engine temp remains under control. Some if it is personal preference and there is no "official" cruise speed for most planing hull boats- but I agree with Harry that many boaters will "cruise" at 70 -80 % of WOT. Hmmmmm. My fuel flow gauge can beat up yours! Seriously, my experience more closely matches BOATING mag's. -- We today have a president of the United States who looks like he is the son of Howdy Doody or Alfred E. Newman, who isn't smarter than either of them, who is arrogant about his ignorance, who is reckless and incompetent, and whose backers are turning the United States into a pariah. What, me worry? |
Gould 0738 wrote:
Seriously, my experience more closely matches BOATING mag's. It will vary from hull to hull, but if you're just breaking plane at 70-75% throttle, you need to lighten ship. :-) The Parker planes in the 16-17 mph range, but if the conditions warrant, I typically "cruise" the boat at 25-30 mph. The engine seems to have a wide "cruise groove" range between 4000 and 4500 rpm, but will redline at 6000 rpm. Actually, I watch the flow gauge more closely..I try to cruise at no more than 10.1 gph, which corresponds to 4000-4500 rpm. WOT produces 39.9999999999999999999999999999999 mph. The same boat with a 250 hp Yamaha produces about 42 mph, and with a 300 hp, 44-45 mph. But to run at those speeds, you need to be an oil sheik. If I am "driving" from the cockpit, I might run a tad faster, but up forward (way forward) in the cabin, the ride is bumpier over the chop. -- We today have a president of the United States who looks like he is the son of Howdy Doody or Alfred E. Newman, who isn't smarter than either of them, who is arrogant about his ignorance, who is reckless and incompetent, and whose backers are turning the United States into a pariah. What, me worry? |
The Parker planes in the 16-17 mph range, but if the conditions warrant,
I typically "cruise" the boat at 25-30 mph. The engine seems to have a wide "cruise groove" range Your Parker gets better fuel economy at 25-30 mph than on plane at 16-17? Very unusual, indeed. I'll have to see if there are some test results that show others have had a similar experience in the same boat. Could it be that trim or something is unnaturally and seriously *reducing* your Parkers nmpg at the slower velocity? |
Gould 0738 wrote:
The Parker planes in the 16-17 mph range, but if the conditions warrant, I typically "cruise" the boat at 25-30 mph. The engine seems to have a wide "cruise groove" range Your Parker gets better fuel economy at 25-30 mph than on plane at 16-17? Very unusual, indeed. I'll have to see if there are some test results that show others have had a similar experience in the same boat. Could it be that trim or something is unnaturally and seriously *reducing* your Parkers nmpg at the slower velocity? I'll take some notes, but, yes, I'm pretty sure I'm getting more mpgs at the higher rpms. My car has a fuel flow gauge, too. I get better mpgs at 60 than at 50...according to the gauge. -- We today have a president of the United States who looks like he is the son of Howdy Doody or Alfred E. Newman, who isn't smarter than either of them, who is arrogant about his ignorance, who is reckless and incompetent, and whose backers are turning the United States into a pariah. What, me worry? |
Gould,
I thought you got better gas mileage in gallons per hour right after a planning hull gets on plane, but you got better gallons per mile at "cruising speed". I was wrong. I checked out the actually gas consumption used in boat tests and it appears that while the gallons per mile varies from boat to boat some being better at planning speed, some better slightly higher than planning speed, and some are actually higher at 4000 rpm, with Cruising Speed being 3000 rpm. So it would appear that Gould's statement cruising speed is based upon the highest RPM that will not stress the engine is correct, but their are some boats that actually got better MPG at higher than cruising speed. "Gould 0738" wrote in message ... The Parker planes in the 16-17 mph range, but if the conditions warrant, I typically "cruise" the boat at 25-30 mph. The engine seems to have a wide "cruise groove" range Your Parker gets better fuel economy at 25-30 mph than on plane at 16-17? Very unusual, indeed. I'll have to see if there are some test results that show others have had a similar experience in the same boat. Could it be that trim or something is unnaturally and seriously *reducing* your Parkers nmpg at the slower velocity? |
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On Friday 24 September 2004 2:47 pm in rec.boats ZanderU wrote:
You often see the 'cruise speed' mentioned in boat descriptions and brochures. But what is this speed and how is it determined? The number is determined mainly by marketing issues. In general it is the speed at which the boat was designed to operate in a continuous cruise with reasonable comfort and fuel economy. The tank range is usually specified at this speed. The word "reasonable" here is rather subjective and will be interpreted by the brochure writers according to the market they are targeting and/or competitor figures. In some cases, such as CAT engines, the engine manufacturer specifies a maximum continuous power and a higher 30 minute intermittent rating. This may constrain cruising speed on some boats. You can go faster, for example to punch a tide, but the ride will probably get rough and you will use a lot of fuel. -- My real address is crn (at) netunix (dot) com WARNING all messages containing attachments or html will be silently deleted. Send only plain text. |
Chris Newport wrote in message news:3340094.BAxqyOrQ7F@callisto...
On Friday 24 September 2004 2:47 pm in rec.boats ZanderU wrote: You often see the 'cruise speed' mentioned in boat descriptions and brochures. But what is this speed and how is it determined? The number is determined mainly by marketing issues. In general it is the speed at which the boat was designed to operate in a continuous cruise with reasonable comfort and fuel economy. The tank range is usually specified at this speed. The word "reasonable" here is rather subjective and will be interpreted by the brochure writers according to the market they are targeting and/or competitor figures. ... This sounds right since (for displacement hulls) I consistently see cruise speed as just under hull speed. I would be much more interested in the speed that would maximize range. That would be quite a bit lower than cruise speed then! |
Harry Krause wrote:
My recollection is that BOATING magazine's "cruise speed" for planing boats is the throttle setting that produces the best fuel economy while the boat is on plane. Typically, it is somewhere around 70-75% of the engine's top RPM on a boat with a gas engine. and Gould 0738 commented: Actually that would not be correct. The greatest fuel economy with a planing hull boat (eliminating the "dead idle" option) is achieved just after the boat reaches plane. I think you are both correct but some tweaking of Gould's comment is required. Engine load and fuel flow rate won't be minimized simply by getting the boat on plane. Once on plane, proper trim of the boat via load distribution or engine, outdrive or tab trim will often result in an increase in RPM and speed for a given throttle setting. Properly trimmed and on plane, the ideal cruise speed (with best fuel economy) may be several knots or mph higher than the boats natural planing speed. Diesel engines are easy. The manufacturer's recommended cruising RPM on my boat is 200 below maximum RPM. Simple. Eisboch |
Properly
trimmed and on plane, the ideal cruise speed (with best fuel economy) may be several knots or mph higher than the boats natural planing speed. Doesn't that contradict the law of physics? "On plane" can be a question of degree, but once the drag from the surface has reached its minimally attainable amount, adding additional speed, especially through a single speed transmission, will burn fuel *less* efficiently. I'll go along with "the ideal cruise speed" may be several knots faster than the speed at which a vessel achieves plane, but I can't buy into a theory that states fuel economy improves with increased engine rpm (after the vessel is on plane, properly trimmed). |
On Saturday 25 September 2004 9:56 am in rec.boats ZanderU wrote:
The number is determined mainly by marketing issues. In general it is the speed at which the boat was designed to operate in a continuous cruise with reasonable comfort and fuel economy. The tank range is usually specified at this speed. The word "reasonable" here is rather subjective and will be interpreted by the brochure writers according to the market they are targeting and/or competitor figures. ... This sounds right since (for displacement hulls) I consistently see cruise speed as just under hull speed. I would be much more interested in the speed that would maximize range. That would be quite a bit lower than cruise speed then! This is where you have to do some simple sea trials. Assume that you always want to arrive with 20% fuel in reserve for contingencies. If you want a more conservative contingency adjust the numbers below. Take the maximum design load (which you will usually need when leaving on a long crossing), with the weight of full fuel tanks. Fuel up to 20% and add ballast to get to the weight at which you would arrive (max - 80%fuel). Now do trials at various speeds and plot the fuel consumption. Repeat with 60% and 100% fuel, to get halfway and departure consumptions. With any luck you now have 3 lines on the graph which will give you the optimum consumption speed at 3 loads. These should be about the same but slightly worse at full load. If you have things like aircon and stabilisers you need to make sure that you include these in the test, this may mean adding in the generator consumption if your generator needs to be running. Keep these graphs and compare them with actual daily fuel usage - this will tell you when something is going wrong such as fouling or wear. In practice you will find that heavy seas and weather will also have an effect. -- My real address is crn (at) netunix (dot) com WARNING all messages containing attachments or html will be silently deleted. Send only plain text. |
Eisboch wrote:
Gould 0738 wrote: Properly trimmed and on plane, the ideal cruise speed (with best fuel economy) may be several knots or mph higher than the boats natural planing speed. Doesn't that contradict the law of physics? "On plane" can be a question of degree, but once the drag from the surface has reached its minimally attainable amount, adding additional speed, especially through a single speed transmission, will burn fuel *less* efficiently. I'll go along with "the ideal cruise speed" may be several knots faster than the speed at which a vessel achieves plane, but I can't buy into a theory that states fuel economy improves with increased engine rpm (after the vessel is on plane, properly trimmed). I think my original statement included "for a given throttle position". The increase in RPM and speed at a given throttle position is a result of further reduction of drag and load on the engine due to proper trimming. No increase in throttle is required. Eisboch BOATING magazine's tests show that for most real planing boats, the most economical cruise speed while the boat is on plane is quite a bit higher than "several" knots faster than the speed on which a boat achieves plane. -- We today have a president of the United States who looks like he is the son of Howdy Doody or Alfred E. Newman, who isn't smarter than either of them, who is arrogant about his ignorance, who is reckless and incompetent, and whose backers are turning the United States into a pariah. What, me worry? |
Gould 0738 wrote:
Properly trimmed and on plane, the ideal cruise speed (with best fuel economy) may be several knots or mph higher than the boats natural planing speed. Doesn't that contradict the law of physics? "On plane" can be a question of degree, but once the drag from the surface has reached its minimally attainable amount, adding additional speed, especially through a single speed transmission, will burn fuel *less* efficiently. I'll go along with "the ideal cruise speed" may be several knots faster than the speed at which a vessel achieves plane, but I can't buy into a theory that states fuel economy improves with increased engine rpm (after the vessel is on plane, properly trimmed). I think my original statement included "for a given throttle position". The increase in RPM and speed at a given throttle position is a result of further reduction of drag and load on the engine due to proper trimming. No increase in throttle is required. Eisboch |
The fuel flow test results shown in boating mags shows that with many boats,
Eisboch is correct. . "Gould 0738" wrote in message ... Properly trimmed and on plane, the ideal cruise speed (with best fuel economy) may be several knots or mph higher than the boats natural planing speed. Doesn't that contradict the law of physics? "On plane" can be a question of degree, but once the drag from the surface has reached its minimally attainable amount, adding additional speed, especially through a single speed transmission, will burn fuel *less* efficiently. I'll go along with "the ideal cruise speed" may be several knots faster than the speed at which a vessel achieves plane, but I can't buy into a theory that states fuel economy improves with increased engine rpm (after the vessel is on plane, properly trimmed). |
Eisboch wrote in message ...
Harry Krause wrote: My recollection is that BOATING magazine's "cruise speed" for planing boats is the throttle setting that produces the best fuel economy while the boat is on plane. Typically, it is somewhere around 70-75% of the engine's top RPM on a boat with a gas engine. and Gould 0738 commented: Actually that would not be correct. The greatest fuel economy with a planing hull boat (eliminating the "dead idle" option) is achieved just after the boat reaches plane. I think you are both correct but some tweaking of Gould's comment is required. Engine load and fuel flow rate won't be minimized simply by getting the boat on plane. Once on plane, proper trim of the boat via load distribution or engine, outdrive or tab trim will often result in an increase in RPM and speed for a given throttle setting. Properly trimmed and on plane, the ideal cruise speed (with best fuel economy) may be several knots or mph higher than the boats natural planing speed. Diesel engines are easy. The manufacturer's recommended cruising RPM on my boat is 200 below maximum RPM. Simple. Eisboch unfortuantely for me testing as many boats as i have has taken the shine from boating. cruising speed is a mix of comfort AND mecahnical load in my mind. as some have touched on it is around 75% of wot. there are a lot of factors involved for planing hulls but a correctly powered correctly propped boat is what we are discussing. i have found that cruising speed rpm for sterndrives is slightly higher, usually around 80% of wot. engine load is definately lowered in a planing boat, if ever im checking for ignition,preignition,detonation problems in a rig i always use the half plane position as here is the most load. remember a prop is designed for maximum efficiency at wot, so at takeoff the engine is working the hardest, there are ways to lessen this of course such as vents behind the prop blades, helping a boat achieve plane much faster. bottom line, cruise for comfort and safety. |
The fuel flow test results shown in boating mags shows that with many boats,
Eisboch is correct. . About what? About a properly trimmed boat getting better fuel economy once on plane and at a given throttle setting? Yes, indeed. About the easy misread of his post implying that boats get progressivley better fuel economy at higher RPM's, once properly trimmed and on plane? I don't think that's what Eisboch meant. There is a period of time when the boat is technically over the bow wave and could be said to be "planing" where there is still more resistance than there will be when the boat achieves optimum plane. In this window, the "giving it more throttle improves the fuel economy" model might apply......but the boat hasn't actually met the condition of being truly on plane during that period. |
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