markpierce
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oops duplicate post
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Cruising speed...
- Thread starter NewbieFromNJ
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The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
markpierce
Master and Commander
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My peak torque is at 1400 RPM on a naturally-aspirated 80-HP JD4045. (WOT is at 2400, but maximum speed obtained at 2200.) It's (1400) my warm-up speed as well as minimum cruising speed (5-plus knots) while maintaining satisfactory engine temperature..
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AusCan
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Eric;
Here's the torque curve for my engine, and I would expect yours is the same or very similar.
Yes - it is very flat, (which I like). Maximum torque is 1800rpm which happens to be my normal cruise speed under power. The speed works out to anywhere from 4 to 7 knots depending on sea state, wind, current, sail use, bottom cleanliness etc.
It averages about 5.8 knots.
Attachments
Nomad Willy
Guru
AusCan,
Yes the same.
Mitsubishi S4L2 engine.
My cruise is 6.15 at 2300rpm. WOT 2950. Wish it was 3050.
I'm using a little more power I think probably due to weight. Willy is 8 tons.
Yes the same.
Mitsubishi S4L2 engine.
My cruise is 6.15 at 2300rpm. WOT 2950. Wish it was 3050.
I'm using a little more power I think probably due to weight. Willy is 8 tons.
eyschulman
Guru
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Cruising speed is a little better than Recreational Trawler as a word to define something. Somewhere along the curve of what a boat can travel at, the owner picks a point and may say that is my cruising speed and it can slide up and down at best it is a statement of preference. In the advertising and sales world it may be a value based on an alterative reality. My boat idles with both engines at 4K and tops out at 20K and I consider my cruising speed any where from 7K to 20K depending on my mood or need to cover distance. Obviously a full displacement boat has a narrower scale but still a scale allowing for choice. If maximum economy is the target the choice is quite narrow as would be the case if maximum speed is the target. When others use words out of full context, like Trawler and cruising speed, I need more information before I can fully understand what is involved.
Nomad Willy
Guru
Eye,
7 to 20 knots?
I'd call it closer to 10 to 14.
If you're going 7 or 20 knots you've got the wrong boat.
Just because a boat can do something dos'nt mean you should do it. Especially over long periods of time.
Many of us have the wrong boat but it's expensive to change.
7 to 20 knots?
I'd call it closer to 10 to 14.
If you're going 7 or 20 knots you've got the wrong boat.
Just because a boat can do something dos'nt mean you should do it. Especially over long periods of time.
Many of us have the wrong boat but it's expensive to change.
Wifey B: Well, I'm going out tomorrow. WOT 42 knots. Cruising speed 35-37 knots. Slow cruise 30 knots. Real slow cruise 17 knots. Idle 11 knots. Ok not really that's 1000 RPM. And just the right boat.
markpierce
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Band, what's your strategy to avoid skin cancer? How's your berthing and cooking accommodations?
Nomad Willy
Guru
That's correct for FD boats.
SD is a bit higher. 1/2 to several knots depending on weight and hull design.
SD is a bit higher. 1/2 to several knots depending on weight and hull design.
Britannia
Wannabe
Your fuel economy is not at a max. It continues to improve as your speed drops. At least mine does down to 4.8 kt at 1000RPM (the lowest I've measured).
Richard
Wifey B: Top up so covering us, helm seat is in middle so no truck driver arm tan, lots of suntan lotion. Berth is one berth in the forward V (actually id toes have a single bed mid boat that they call a crew cabin, but no one ever sleeps in). Cooking, a small galley, microwave, burner, but we don't cook on it. It's for day or just overnight, not a cruising boat. It's my play boat. My Baby.
Mine too (Most economical is about 4 knots at 1000 rpm)
Nomad Willy
Guru
Oh no Aus ....
Let me guess ... you got a Kansacki gear box.
I practically eliminated the rattle but it was quite a job and almost a boat buck.
Let me guess ... you got a Kansacki gear box.
I practically eliminated the rattle but it was quite a job and almost a boat buck.
Bay Pelican
Moderator Emeritus
Frequent debate, time vs money. Bay Pelican gets 4mpg at 6.5 kts and 2.5mpg at 7.5 kts.
We pay Caribbean prices for diesel, perhaps $5 US per US gallon.
On an 80 mile run, the time difference is an hour and a half while the cost difference is $60 US.
We pay Caribbean prices for diesel, perhaps $5 US per US gallon.
On an 80 mile run, the time difference is an hour and a half while the cost difference is $60 US.
What rpm for 4mpg at 6.5 kts and 2.5mpg at 7.5 kts.?
Or should that be 2.5mpg @6.5kts and -----------
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Bay Pelican
Moderator Emeritus
Bay Pelican is full displacement and has a Lehman 135 hp engine. Generally, at 1600 rpm we cruise at 6.5kts. At 1800-1850 we cruise at 7.5kts.
Of course this is subject to sea conditions.
Of course this is subject to sea conditions.
ranger58sb
Guru
Wrong is maybe in the eye of some beholders.
Just cause a boat can only do one thing doesn't mean it'd be right for everyone.
We can run comfortably from 6-24 Kts. We usually translate that to about 8 kts or about 19-20 kts. Depends on our mood, destination, time available, sea states, etc... so probably about half and half...
It's a right boat for us.
-Chris
Nomad Willy
Guru
ranger42c wrote;
"Wrong is in the eye of some beholders"
Good one Chris.
However your mood has nothing to do w what the designer intended for the boat. You could go 6 knots w a guided missile cruiser to take it to a greater extreme. Of course you can run 6 knots and call it one of your cruising speeds but no knowledgeable person will say the boat was designed for that speed to go from point A to point B. Moving about in a harbor yes, point ATo point B no. A to B is cruising.
However you would have dificulty finding a boat that was designed for 6-24 knots. How much time you spend at 6 knots is an element here. If you spend 75% of your time at 6 knots I'd say you do'nt need a 24 knot cruising speed. I'm not saying not to do it .. just that the boat was'nt designed for that. Not at all.
"Wrong is in the eye of some beholders"
Good one Chris.
However your mood has nothing to do w what the designer intended for the boat. You could go 6 knots w a guided missile cruiser to take it to a greater extreme. Of course you can run 6 knots and call it one of your cruising speeds but no knowledgeable person will say the boat was designed for that speed to go from point A to point B. Moving about in a harbor yes, point ATo point B no. A to B is cruising.
However you would have dificulty finding a boat that was designed for 6-24 knots. How much time you spend at 6 knots is an element here. If you spend 75% of your time at 6 knots I'd say you do'nt need a 24 knot cruising speed. I'm not saying not to do it .. just that the boat was'nt designed for that. Not at all.
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ranger58sb
Guru
Yep, but when there's a difference between what designer intended and what user wants... who wins that discussion? The user. Often without complete regard for designer's intentions.
-Chris
Designers design boats to run at variable speeds every day. Just because you don't need a 24 knot cruising speed, don't try imposing your need as universal. It is quite common for a boat to be designed to cruise very efficiently at hull speed or slightly less but to be able to cruise much faster when needed. One of the most common purchasers of boats today is the purchaser who wants to save money most of the time but be able to get somewhere quickly when desired. Let's just start with the largest selling boat line, Sea Ray. All the Sundancers are designed for that dual purpose.
The statement that if you spend 75% of your time at 6 knots you don't need 24, is just wrong as many do and to say the boat wasn't designed for that is false. Boats are designed for that. Most boats are not designed to be run the same speed all the time.
eyschulman
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One of the main requirements of the Moon River design was a sliding scale of speed to include 7 to 16K cruise ability. It is not 7 or 20K . It is a continuous scale of 7 to 20K. Most of my travel time is between 9 and 10K with a hull speed based on 46+ foot WL, hull speed of about 9.2K. I can select the speed based on comfort fuel burn or need to get some place or current and weather conditions. I am willing to pay for the luxury of the sliding scale which I perceive as a clear benefit over the FD boats I have owned in the past. Tony Flemming the man behind Flemming Yachts has a very similar take on cruising speed and has incorporated it into his SD boats. Yes this philosophy is not for the weak of wallet, On the other hand it is not overtly wasteful.
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One reason we turned away from a potential Fleming purchase was even with his cruising speed, it still wasn't fast enough for our desires. However, Fleming is an excellent example to support your point. It is designed to have the capability to run at many different speeds.
psneeld
Guru
All boats can run at many speeds...it's not like they sink if you don't.
Some are more flexible, and some more efficient at certain speeds, but like cars, some get driven 100,000 miles below 50 and others 100,000 miles over 65.
It's like saying as humans we should all go through life at a certain speed or two.....
Ludicrous.....
Some are more flexible, and some more efficient at certain speeds, but like cars, some get driven 100,000 miles below 50 and others 100,000 miles over 65.
It's like saying as humans we should all go through life at a certain speed or two.....
Ludicrous.....
Nomad Willy
Guru
Everybody wants everything.
And at times anybody can get a big chunck of everything. But if one is regularly running a boat under or above the designers intent the question of "do I have the right boat" should emerge.
I do'nt for example but it's an economic issue for me. I could have a boat that burned twice as much fuel but was capable of capable of running 8 to 10 knots at times (or even continiously) but I made the personal decision have the better economy and way better seaworthyness. I like to go 10 or 12 knots so my boat is'nt designed for that (ca'nt either) so I run 6.
But hey these are toys, the're ours and we are feee to do whatever we want.
And at times anybody can get a big chunck of everything. But if one is regularly running a boat under or above the designers intent the question of "do I have the right boat" should emerge.
I do'nt for example but it's an economic issue for me. I could have a boat that burned twice as much fuel but was capable of capable of running 8 to 10 knots at times (or even continiously) but I made the personal decision have the better economy and way better seaworthyness. I like to go 10 or 12 knots so my boat is'nt designed for that (ca'nt either) so I run 6.
But hey these are toys, the're ours and we are feee to do whatever we want.
Al
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Similar formula here. WOT (Over propped) is 2100 RPM,(2800 Factory WOT) cruise RPM is 1450-1500 RPM. Both Nomad and myself of reflects a 600 RPM cushion between cruise and WOT.
Hull speed formula for our boat is 6.75 knots. Our cruise average is 6.5-7.2 tide and sea condition knots.
Fuel burn works out to 1.5 GPH
AMJ-Ketchikan
Lucky Chucky
Senior Member
On my 43' trawler with a 305 Cummins single screw, there's a rated cruising speed but that's based on certain factory tested conditions with a certain base weight.
However, I like to listen to my engine, feel the propeller shaft vibrations, watch the PSI and engine temp. 1800 rpms is a good place to start, but depending on wind, current, etc., I tend to come up or down to find the sweet spot. Sometimes it's 1910 rpms @ 8 kts with 6 gph, and sometimes it's all the way down to 1320 rpms with 1.8 gph. Yesterday it was 1740 rpms @ 8.2 kts with 4.3 gph.
Hope this helps.
~Lucky Chucky
However, I like to listen to my engine, feel the propeller shaft vibrations, watch the PSI and engine temp. 1800 rpms is a good place to start, but depending on wind, current, etc., I tend to come up or down to find the sweet spot. Sometimes it's 1910 rpms @ 8 kts with 6 gph, and sometimes it's all the way down to 1320 rpms with 1.8 gph. Yesterday it was 1740 rpms @ 8.2 kts with 4.3 gph.
Hope this helps.
~Lucky Chucky
Wifey B: Oh my.
You're missing the point with all this designer's intent stuff. The designer's intent is that you run it at any speed your little heart desires. The designer doesn't care if it's 8 knots or 20 knots. They designed it to do all. 
