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Old 07-30-2015, 04:17 PM   #1
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What is 'cruising speed'

When looking at ads for trawlers, I see many list 'cruising speed' and 'maximum speed'. What 'cruising speed' mean?

For example, I'm looking at 42'-43' twin engine modified hulls, not 'true' trawlers, that show 'cruising speed' of 11-13 kts. I'll spend virtually all of my time around hull speed of 8ish, so what is 'cruising'?
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Old 07-30-2015, 04:50 PM   #2
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Usually a speed w minimal vibration and acceptable noise.

But it should have more to do w boat design. All boats are designed to be operated within a range of speeds. FD boat always have a very narrow speed range of about 1/2 to one knot depending on mostly length. All others have a design speed range established by the designer w his specified power. One can go faster depending on the maximum power that the specified engine can continously produce. Or go slower depending on the ability for the engine to operate at cooler temperatures that specified cruise speeds.

Planing hulls of course need enough power to gracefully plane and attain that speed.
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Old 07-30-2015, 05:30 PM   #3
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11-13 on a 42' is not cruising speed it is a lie. That is too slow to be on plane and too fast for any reasonable fuel use.


Typically cruising speed on planning hulls is about 15% lower RPM than WOT and well on plane.
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Old 07-30-2015, 05:31 PM   #4
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On a planing boat, it is the optimum fuel efficiency speed when on plane. Most boats and boat reviews will have a graph or chart illustrating this.
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Old 07-30-2015, 06:54 PM   #5
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Its the difference between ungodly amount of fuel use at WOT to mearly incredible fuel use.
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Old 07-30-2015, 07:11 PM   #6
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Example... My 44 is a planing hull. WOT is 2550 RPM suggested cruising is 2250 RPM. At this RPM my speed is about 21knts (depending on load on board). It is supposed to consume 32 GPH total at this speed
When I run on plane I normally run about 2000 RPM which produces about 19 knts. This consumes about 29-30 GPH.
The boat needs 1600 RPM to stay on plane and the speed drops to 14 knts.
It's not happy but will function. I don't spend time there unless required.
Then of course there's hull speed at 3-4 GPH and 8 knts
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Old 07-30-2015, 07:31 PM   #7
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thanks for the replies

I going to go with most fuel efficient/minimum planing speed when applying the term to modified trawler hulls...that work?
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Old 07-30-2015, 07:54 PM   #8
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Quote:
Originally Posted by KalaKai View Post
I going to go with most fuel efficient/minimum planing speed when applying the term to modified trawler hulls...that work?
If it works for you, yes.

For me, cruising speed is that speed at which I'm comfortable going long distances. Mine is a semi-displacement hull so my cruising speed is as much above hull speed as I dare to go before my wallet starts complaining, or about 7 to 7.5 knots. It'll ride nice at 10 knots, but I'm throwing a huge wake and throwing away a lot of money in fuel. I could go 5-6 knots and save a little more fuel, but I tend to get impatient.

On my last boat, a light 29' planing hull, I had two cruising speeds; one just a few knots above a stable plane and another just above hull speed, when conditions required it. Both got a reliable 1.4NMPG.
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Old 07-30-2015, 08:16 PM   #9
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For us cruising speed is the speed the boat goes when we run the engines in their optimum rpm band, which is 1500 to 1800. We run at 1650 which gives us about 8 knots, so thats our cruising speed. Max rated rpm of these engines is 2500.
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Old 07-30-2015, 08:24 PM   #10
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If it works for you, yes.
Cruising speed for me is hull speed, 8 or so. I'm moving from sail to power.

I was trying to understand what the 'specs' on cruising speed meant.

12-20 kts is too fast for me on the water.....if I want to go that fast, I'll travel by car
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Old 07-30-2015, 08:48 PM   #11
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Fuel efficiency has nothing to do with what cruising speed should be.

If your boat burns so much fuel you can't afford it cruising at the recommended speeds you have the wrong boat. You need a different boat.
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Old 07-30-2015, 09:04 PM   #12
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I think cruising speed is whatever speed an owner wants to cruise at. The boats not going to care. The motors might depending on the criteria the owner uses to determine the speed but the boat won't.
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Old 07-30-2015, 09:09 PM   #13
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Quote:
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11-13 on a 42' is not cruising speed it is a lie. That is too slow to be on plane and too fast for any reasonable fuel use.


Typically cruising speed on planning hulls is about 15% lower RPM than WOT and well on plane.
On my 44. cruising speed at cats recommended 2200 rpm is 13
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Old 07-30-2015, 09:22 PM   #14
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Last year I cruised the whole summer at 6.5 knots. I had an engine down, and IF I had wanted to go any faster I couldn't, as that was running the single engine at the same temp as I am used to when both are healthy. My fuel burn was the same on that engine as when both are running, but I lost 1.75 knots.
Now that I am using both again, I have returned to my usual 8.2 knot "cruising" speed. I could go faster, but then I would be making a taller stern wave, with its attendant cost, and as I came from sail, I have never felt the need to go any faster.
So yours will be whatever you want.
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Old 07-30-2015, 09:49 PM   #15
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I have a Ranger 27 Tug, semi-displacement hull. Cruising speed is 10 - 12 knots, depending on conditions. On a nice calm day @ 12 knots, 3200 RPMs, 6.5 GPH and 2 NMPG. I can go slower, but the fuel burn is about the same. (2.0 NMPG). I can get her up to 16 knots, but that means 10 GPH and 1.4 NMPG. I consider cruising speed "the sweet spot". It just feels right and I'm not burning excess fuel.
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Old 07-30-2015, 09:56 PM   #16
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It appears it is more of a marketing gimmick than a firm and fast rule that defines Cruising speed versus maximum speed. Everyone wants to know 'how fast' their new boat will run. Then the next question is: how far can I make it on a tank of fuel. So, in reality, these are two completely different (but just as important) sets questions to be concerned with.

All boats have a different speed they go, depending upon how fast, how much fuel and when you want to get there is concerned. Cruising speed and Max speed is typically marketed as: what the sales pitch is trying to sell the boat as. Max speed is the speed that the boat originally came off the ways with almost NO gear onboard, with only one person driving it, and almost no water or fuel on board. Cruising speed is how far you can calculate your distance 'till empty.

If you ask a boat owner what their 'listed' speeds are (if they are honest) they will tell you the actual speed they make, not the brochure speed. I have yet to find a broker who won't quote the original specs as if they are gospel.

As an example, on my little boat I have a Perkins 2800 rpm engine. I have only gone up to 2800 once in a year of owning her. I usually cruise at 1800 to 2000. We get around 1700 rpms for 6 to 6.1 knots. This always burns less than one gallon an hour. However, if I push it to 2000 I get 'all the way up to' 7.1 or 7.3. But the fuel consumption almost doubles to 2 gallons (or so)

There is a mathematical equation for fuel consumption on boats. It reads something like this: Lesser speed is to Greater speed what Lesser fuel used is to Great fuel used (cubed.) Of course this does not apply to planing hulls, but to semi and full displacement vessels. It even applies to yachts! I found figures on my particular brand boat that stated .75 gallon at 6 knots, and 5 gallon at 8.5 knots. So, the fuel conservation ratio holds true to some extent.

Personally, I think cruising speed is where the boat runs smoothly, not pushing a whole lot of a bow wave, and not throwing much wake. The fuel consumption is up for interpretation by your wallet.
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Old 07-30-2015, 10:40 PM   #17
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As far as ads are concerned, I think cruising speed is calculated at the maximum continuous rpm as listed by the engine manufacturer. Max speed would be at WOT. The individual boat owner probably picks a cruising speed (rpm) where the fuel consumption, noise and boat feels about right.

For my boat (planing hull) cruising speed would be about 24 knots at 22gph. Max speed is 27kts at 30gph.

I like to cruise at 18 kts and 14gph. On a relatively calm day, with no arrival time pressure, I cruise at 7.5 kts on 2 gph.
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Old 07-30-2015, 11:04 PM   #18
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My boat isn't a trawler so I'm not sure this info will be of help.


My WOT rpm is 2150. At that rpm I'm doing 31.3 kts and burning 65 gallons per hour. Not a speed I run at EVER.


My planing rpm is ~1750. At that rpm I'm doing about 22kts. I don't know the fuel burn rate at that speed


My hull speed is around 950 rpm's and I'm doing about 10.5 kts. I'm guessing a bit here but I think my fuel burn is about 1 mpg.
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Old 07-31-2015, 03:52 AM   #19
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My FD boat has a plate near the helm, placed by the engine manufacturer (Volvo Penta). It says:-

"Cruising speed 200rpm below obtained top speed"

Whilst I wouldn't dream of contradicting the expertise of the engine manufacturer, obtained top speed will be at max revs - 3600rpm officially, although it's deliberately a bit overpropped for comfort, so a bit less than that. There's no way I could cruise at 3400 rpm!

I generally cruise at around 2000rpm, or 7.1 kn which seems the best speed for noise / vibration / speed / fuel consumption compromise.

I'm told maximum speed is around 8.5 kn with a huge wash, but I haven't been brave enough to try it, there doesn't seem much point in stressing the old girl unnecessarily.
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Old 07-31-2015, 06:16 AM   #20
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All the replys show almost the same answer, it depends on how quickly you wish to empty your wallet.

Slow cruising boats will travel at about the sq rt of the LWL ( In Knots) plus a tiny bit.

Most fast boats seem to top their speed at 1 MPG , as fast boats may not have large enough tanks for a full days running.

Go fast or go far , your choice.

The simplest compromise is a 50 hp outboard on the back of a small dink.
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