"Best cruise speed/rpm"?

tonyjh63

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Got a question. When reading new boat tests, they tend to give top speed, time to plane, 0-30 mph, and "best cruise speed" (apparently indicating most fuel efficient speed/rpm). My question is: how is this "best cruise speed" determined? I mean, some figures are very specific. For instance, one review showed the best cruise speed/rpm of 27.8 mph@5,500 rpm. I do understand that these reviewers have some pretty snazzy equipment, but how can your average boat owner determine his "best cruise speed"? Thanks for any insight!
 

RGrew176

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I use the test results as a guide. With any boat I own I will cruise at various settings on the first few trips always starting out with full tank(s) and refilling upon my return. The data is written down and I compare the data from my various cruising settings to achieve my optimum cruising settings. It does take time using this method but it has worked well for me for 50 years of boating.
 

Scott Danforth

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if youre refering to boattest.com and their published data. they are reading fuel burn rate by measuring fuel flow. they install a fuel flow meter on the test boats.

my searay was 3000 RPM, my Cruisers was 3300 RPM. It varies by boat hull, propulsion, load, etc.
 

southkogs

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I've found that my boats tend to be the most efficient at a speed that's just got them on a good plane. As a rule, I'll climb up on plane and once established back the throttle down until I can feel the hull "mushing" off plane. Somewhere just over that point is where I've generally found the most efficient running for my boats.

I'm still figuring my new boat out, but it looks to be somewhere in the low 30s MPH, between 3,200 and 3,400 RPM.
 

dasboata

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my 254 albermarle cruses at 3000 -3200 28-30 MPH I had a 20 Ft out board that need 4000 RPM to stay on plane I got rid of that you want a boat that stays on plan at about 3000 rpm
 

gm280

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Answer to the OP question, there is no set "best cruise" speed for every situation. It honestly all depends on so many variables that it simply can't be specified but for that instance. The number of occupancies, the weight of the gear you carry, the wind, temps, fuel, so many variables that even from day to day that best speed will change.

The only way to absolutely obtain the best cruising speed is with some fuel flow meters verses GPS MPH readings and a few computer program lookup tables to get that for every outing. The manufacturer can list such cruising speeds, but just for that boat, engine, weight, and everything else for that test. You will figure out your best performance verses fuel consumption after a while of boating. But is that the absolute best? Who really knows. JMHO
 

SkiDad

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This is my theory. Back your rpm approx 1500 lower than full throttle and that will be close.
 

roffey

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My best cruising speed is measured my the smile on my face. Fuel consumption is not really a factor but I do not have a cruiser boat
 

WIMUSKY

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Answer to the OP question, there is no set "best cruise" speed for every situation. It honestly all depends on so many variables that it simply can't be specified but for that instance. The number of occupancies, the weight of the gear you carry, the wind, temps, fuel, so many variables that even from day to day that best speed will change.

The only way to absolutely obtain the best cruising speed is with some fuel flow meters verses GPS MPH readings and a few computer program lookup tables to get that for every outing. The manufacturer can list such cruising speeds, but just for that boat, engine, weight, and everything else for that test. You will figure out your best performance verses fuel consumption after a while of boating. But is that the absolute best? Who really knows. JMHO

Yep. Type of boat, size of engine, how it's propped.....etc....... I too am in the category of getting it on plane and backing off the throttle enough to just stay on plane..............
 
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dingbat

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I run a flow scan system but truthfully, it buys me nothing but confirmation of my gut feeling

At the proper cruise speed, the motor just hums. It doesn't sound like it's being lugged or overworked. Usually right around 4200 RPM, 27-28 knots. I then tweak the rpm to adjust the running angle so the hull's entry point directly under my feet. You can feel (vibration) and hear (rhythmic groan) when the hull is at the proper running angle. I then trim the drive until the prop torque disappears. At that point, I'm usually running pretty darn close to peak efficiency relative to fuel flow.
 

bruceb58

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I have a flow meter on my boat that connects to my GPS so it converts the fuel flow into MPG. On the Wellcraft in my signature, the best MPG is 3500 RPM. Before I bought the flow meter, I always thought it was just above planing speed but I was proven otherwise. So many differences in hulls, power plants and props that you pretty much have to have a flow meter to figure out where your boat is most efficient.
 

tonyjh63

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What is this "fuel flow meter" y'all speak of? Are they expensive, and what other uses for it are there, other than described above? I tried looking for it here on iboats, but no luck...
 

H20Rat

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What is this "fuel flow meter" y'all speak of? Are they expensive, and what other uses for it are there, other than described above? I tried looking for it here on iboats, but no luck...

Find one that integrates to GPS so it gives you actual efficiency/range. This little circular one looks interesting. (you need the guage + NMEA network fuel flow + NMEA network GPS. )

http://www.iboats.com/Multi-Function...view_id.886072


http://www.amazon.com/Garmin-GFS-10-.../dp/B0011MP82G

http://www.amazon.com/Garmin-Next-Ge...EA1JMTY0EBG27P
 
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Mischief Managed

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To answer the OP, they just use the speed above idle that gives the best MPG. The tests are usually done with a light load and not much chop. As conditions change your mileage may vary.

In my experience, a well-powered boat has the best cruising speed (with a typical load) roughly coincide with the engine's torque peak RPM. If you need to go way above the torque peak to hit best cruise, or even plane, the boat is under-powered. Most gasoline I/O engines have torque peaks in the 3000 to 3500 RPM range, outboards peak a bit higher

I have a fuel flow meter with speed sensor that displays MPG in real time. My boat likes 3000 to 3600 RPM for decent mileage and peaks around 3200 RPM with a typical load. It does not feel like it's straining to get on plane and has plenty of power/speed in reserve at cruise. I've been in I/O boats that won't plane below 4000 RPM and they feel badly under-powered. I have no experience with outboards that are under-powered.
 

dingbat

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Find one that integrates to GPS so it gives you actual efficiency/range. This little circular one looks interesting. (you need the guage + NMEA network fuel flow + NMEA network GPS. )

http://www.iboats.com/Multi-Function...view_id.886072


http://www.amazon.com/Garmin-GFS-10-.../dp/B0011MP82G

http://www.amazon.com/Garmin-Next-Ge...EA1JMTY0EBG27P

The LMS would require the purchase and installation of a NMEA 2000 backbone as well. Might be cheaper to buy a cheap combo and install a flow meter on it.
 
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H20Rat

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The LMS would require the purchase and installation of a NMEA 2000 backbone as well. Might be cheaper to buy a cheap combo and install a flow meter on it.

Yeah left that out, although that is the cheapest part. It will give you all kinds of other useful information, and depending on what the OP (or anyone else reading) has already in the boat, they might have pieces of it that they don't realize. (a depthfinder/plotter that talks NMEA and has a GPS on it already)
 

drrpm

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Best MPG will be at idle speed. Best cruise is the most efficient speed once on plane. Its usually a couple miles an hour above minimum planing speed. The differences in efficiency at the speeds slightly above planing speed are small enough not to really worry about.
 

batman99

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my boat's best cruising speed is when its RPM is between 3,500 and 4,000. This RPM range varies due to rear and front bow weight loading. More weight in the front, lower its engine RPMs. For tubing, it likes between 3,800 to 4,500 RPM the best. If wondering, max engine RPM is 5,300ish.
 

bruceb58

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Best MPG will be at idle speed. Best cruise is the most efficient speed once on plane. Its usually a couple miles an hour above minimum planing speed. The differences in efficiency at the speeds slightly above planing speed are small enough not to really worry about.
Did you verify this with a fuel flow meter?
 

tonyjh63

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Can I safely assume that these flow meters work even on carb engines?
 
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