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?

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).

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.

On 24 Sep 2004 06:47:00 -0700, (ZanderU) wrote:

You often see the 'cruise speed' mentioned in boat descriptions and brochures.
But what is this speed and how is it determined?

Depends on if you are running a displacement hull or a planing hull.
Also depends on engine horsepower, engine type (diesel,gas, two/four
stroke, etc.), dry/wet weights, wind/wave conditions, etc.

There really isn't a blanket answer, but the easiest way to describe
cruise speed is the fastest speed at which the engine is at it's most
efficient. On some boats, it can be WOT. On some, 2/3 throttle. On
my Ranger, it's about 4000 RPM (5600 max) @ 30 mph @ 4.3 Gph. On the
Contender, it's 4800 RPM (5800 max) @ 44 mph @ 5.7 Gph per engine.

Take care.

Tom

"The beatings will stop when morale improves."
E. Teach, 1717

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.

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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!