What's your cruising speed.

[Nomad Willy]

Hills,
I take 15 minutes min to warm up enough to go to cruise rpm.
And I’m sure there are parts of the engine not heat soaked even then And perhaps that would take 30 minutes to an hour running at cruise.
My 15 min are done with several steps from 1400rpm to 2300 and 6.15 knots. And 2300 is 700 down from the rated rpm of 3000.

Is your Hat what they call a “flush deck” yacht?

 

[Woodland Hills]

It’s a standard 58’ motor yacht with a factory 5’ cockpit. The factory designation is 63’ Cockpit Motor Yacht, I think of it as a cross between a houseboat and a yacht fisher. In the mid-80’s Hatteras switched from the famous 15’10” beam hull to a new 18’6” hull with same layout, but much more room and that’s the hull we have.

I warm up mine by idling in gear as we leave the dock and head out the inlet.

 

[FF]

"I take 15 minutes min to warm up enough to go to cruise rpm."

This is best done underway ,under light load , not at idle dockside.

We Use 800 to warm up while the hyd windlass pulls the anchor , 1000 under way for 5 min or so then pick up the RPM to cruise.

Diesels are efficient so do not warm much with out a load.

 

[Ski in NC]

Yep, I don't like powering up engines until fully warm. And pretty pointless to warm up at the dock. My engine will take a half hour at no load near idle to get to 180.

I just crank and throw lines, get going and I run at hull speed/950rpm til it gets to 180. Takes about 2nm, and about 15min. Then gradually add power to 1200, then 1600 (on plane) then to 1900 or whatever for cruise. Temp gauge rises about 5deg with power up, but does not spike.

A bud with a bigger Sporty with Daewoo/MAN clone V8 cranks his motors and leaves the dock. 500yds to ICW, makes the turn and powers right up. Engines still cold. I often ride with him and watched the temp gauges. They climb fast, go about 20F over normal, then drop about 20F below normal, then level out. Not liking the thermal stresses that go with that. I advised him to warm them up easy, but he is a knucklehead and does what he wants. Still a good dude, but hard on machinery!!!

 

[jovial_cynic]

I'm looking at 2000 Navigator 5800 with twin Volvo TAMD 122 EDC engines, and the listing says it has a cruising speed of 17 knots at 2100 rpms... but at 22 gallons of fuel per hour!

That's quite a bit more than my old Tollycraft, which gets around 4 gallons of hour, hovering around 8 knots.

So... if you slowed down to... 8 knots, like a normal slow trawler, do we regain that fuel efficiency? Or do these engines not enjoy going slow?

 

[Giggitoni]

You’ll probably regain most of the fuel efficiency. It’ll work as long as your engines are comfy; about 180 *F.

 

[OldDan1943]

So... if you slowed down to... 8 knots, like a normal slow trawler, do we regain that fuel efficiency? Or do these engines not enjoy going slow?

I'm sure someone will again post the theoretical formula for determine the hull speed for your boat. Remember, it is theoretical.... That formula makes no allowance for the weigh of all the stuff we put onboard.

 

[BandB]

I'm looking at 2000 Navigator 5800 with twin Volvo TAMD 122 EDC engines, and the listing says it has a cruising speed of 17 knots at 2100 rpms... but at 22 gallons of fuel per hour!

That's quite a bit more than my old Tollycraft, which gets around 4 gallons of hour, hovering around 8 knots.

So... if you slowed down to... 8 knots, like a normal slow trawler, do we regain that fuel efficiency? Or do these engines not enjoy going slow?

You'll probably use no more than 8 gph and maybe less.

 

[Simi 60]

You'll probably use no more than 8 gph and maybe less.

Ouch.
That's still near twice as much as we use at 8 knots

 

[Fletcher500]

Most often its 6 Knots; total fuel flow about 1.5 GPH which includes the Gen powering the Seakeeper. Enjoying the ride, taking it slow.

 

[Art]

1. No big rush: Displacement speed 6.5 to 7 knts = 3 +/- gph / 2+ nmpg.

2. Get there quick: Planing cruise 16 to 17 knots = 16 to 17 gph / 1 nmpg

3. Go slow: Run one screw; 4.5 to 5 knots = 1.5 +/- gph / 3 +/- nmpg

#1 - 85% of the time
#2 - 10%
#1 - 5%

 

[markpierce]

six point three knots works for me. occasionally increase to a maximum of 7.3 when needed. in my often-crowded waters, such speeds allow one to communicate by phone or radio in most situations. don't know how that works when one goes a lot faster.

 

[Baker]

I'm looking at 2000 Navigator 5800 with twin Volvo TAMD 122 EDC engines, and the listing says it has a cruising speed of 17 knots at 2100 rpms... but at 22 gallons of fuel per hour!

That's quite a bit more than my old Tollycraft, which gets around 4 gallons of hour, hovering around 8 knots.

So... if you slowed down to... 8 knots, like a normal slow trawler, do we regain that fuel efficiency? Or do these engines not enjoy going slow?

I am having a very hard time believing that you get 17kts@22gph in a 58 foot boat!!!! Are you sure that is not per engine. If that is the case, I say keep the hammer down and enjoy the efficiency!!! That is a 64000lb boat with 1300hp. You are burning at least 40gph to get that thing on plane. That or Navigator has a miracle hull design. It is very likely that is 22gph PER ENGINE!!!! And even then that is not bad fuel economy for a boat that big. I know many in my group that do a lot worse and they are not that big.

I would say you can get it down to a gallon per mile at 8kts in a boat that big with engines that big.

My boat...Carver 35 twin Cummins 330....18kts@16gph....24000lbs
Friend's boat....Hatteras 47...8v92(715hp).....20kts@60gph....60000lbs
Friend's boat....Sea Ray 47...Cummins QSC600....20kts@45gph....40000lbs

So 17kts@44gph isn't terrible!!! Yes alarming to someone that is not used to burning fuel at that rate. But not bad for a boat that big on plane.

 

[Insequent]

I am having a very hard time believing that you get 17kts@22gph in a 58 foot boat!!!! Are you sure that is not per engine. If that is the case, I say keep the hammer down and enjoy the efficiency!!! That is a 64000lb boat with 1300hp. You are burning at least 40gph to get that thing on plane. That or Navigator has a miracle hull design. It is very likely that is 22gph PER ENGINE!!!! And even then that is not bad fuel economy for a boat that big. I know many in my group that do a lot worse and they are not that big.

I would say you can get it down to a gallon per mile at 8kts in a boat that big with engines that big.

My boat...Carver 35 twin Cummins....18kts@16gph....24000lbs
Friend's boat....Hatteras 47...8v92.....20kts@60gph....60000lbs
Friend's boat....Sea Ray 47...Cummins QSC600....20kts@45gph....40000lbs

I agree. For me it was about 55,000 lbs, Cummins, 34 gph total for 16kn.

 

[Simi 60]

I agree. For me it was about 55,000 lbs, Cummins, 34 gph total for 16kn.

128 litres??????
And at 8 knots, 1/2 that speed?

 

[Insequent]

128 litres??????
And at 8 knots, 1/2 that?

No. At 8kn, now with John Deere, 25 lph total.

Half the speed, 20% of the fuel. You can probably guess why I installed less horsepower when I re-powered.

At 16kn it was bow-up, even with trim tabs, and ploughing rather than (semi) planing

The Cummins (3000 rpm WOT) were fuel efficient at mod-high rpm, not so much at lower rpm (1650) which gives 8kn.

 

[Group9]

1. No big rush: Displacement speed 6.5 to 7 knts = 3 +/- gph / 2+ nmpg.

2. Get there quick: Planing cruise 16 to 17 knots = 16 to 17 gph / 1 nmpg

3. Go slow: Run one screw; 4.5 to 5 knots = 1.5 +/- gph / 3 +/- nmpg

#1 - 85% of the time
#2 - 10%
#1 - 5%

That’s pretty close to our numbers as well. Although, we’ve never run ours anywhere on one engine, so I’m not sure about that and, our planing cruise speed is a couple of knots slower.

Biggest thing that keeps us going slow (besides fuel costs) is diesel exhaust noise. Conversation is easy at 6.5 to 7 and impossible at planing speed rpm’s.

 

[Art]

That’s pretty close to our numbers as well. Although, we’ve never run ours anywhere on one engine, so I’m not sure about that and, our planing cruise speed is a couple of knots slower.

Biggest thing that keeps us going slow (besides fuel costs) is diesel exhaust noise. Conversation is easy at 6.5 to 7 and impossible at planing speed rpm’s.

Among other items of note... here is something good to say about gasoline engines:

They are quiet! Conversation is easy inside salon at 16 to 17 knots cruising plane. On bridge it's simply a whisper coming from engines.

At 6.5 to 7 knots [just below calced hull speed of 7.58 knots] the engines purr quietly. A pleasure to be sure. I love on bridge to faintly hear their synchronized song to one another. At that speed, if I take a hard turn, the sync alters its beat. Then, once straightened out the sync regains its composure. To me... that sounds like a couple o' twins singing songs to one another!

Above 17 knots the four barrels open up. Then not so quiet... and 1 mpg drops dramatically.

Nice to have em perform wide open once n' a while, for a very short duration [couple minutes]. On bridge is fun at 22 to 23 knots! Wish our Tolly would do that tall speed at 1 mpg or better! at WOT I can only guess .5 mpg = 44 to 46 gph . And - lots of stress on gas engines if kept at that speed for too long. Much better to run easy on gassers!

Happy Boat-Speed Daze! - Art

 

[Codger2]

I am having a very hard time believing that you get 17kts@22gph in a 58 foot boat!!!! Are you sure that is not per engine. If that is the case, I say keep the hammer down and enjoy the efficiency!!! That is a 64000lb boat with 1300hp. You are burning at least 40gph to get that thing on plane. That or Navigator has a miracle hull design. It is very likely that is 22gph PER ENGINE!!!! And even then that is not bad fuel economy for a boat that big. I know many in my group that do a lot worse and they are not that big.
.

I tend to agree! My boat is a 42' & 33,000 lbs and although I don't happen to have photos of comparable rpm and gph settings, here is a photo I took at 15 kts & .5 gpm. The engines are Yanmar 440s. (Sorry, the tach is not completely visible in that photo but it appears to be around 2600 rpm.)

IMHO, many of the fuel flows posted on this forum are not accurate.

 

[Art]

I tend to agree! My boat is a 42' & 33,000 lbs and although I don't happen to have photos of comparable rpm and gph settings, here is a photo I took at 15 kts & .5 gpm. The engines are Yanmar 440s. (Sorry, the tach is not completely visible in that photo but it appears to be around 2600 rpm.)

IMHO, many of the fuel flows posted on this forum are not accurate.

What do you get at just a bit under hull speed for fuel usage stats? That is of course if you ever actually cruise at that slow a speed!

 

[jovial_cynic]

I am having a very hard time believing that you get 17kts@22gph in a 58 foot boat!!!! Are you sure that is not per engine. If that is the case, I say keep the hammer down and enjoy the efficiency!!! That is a 64000lb boat with 1300hp. You are burning at least 40gph to get that thing on plane. That or Navigator has a miracle hull design. It is very likely that is 22gph PER ENGINE!!!! And even then that is not bad fuel economy for a boat that big. I know many in my group that do a lot worse and they are not that big.

I would say you can get it down to a gallon per mile at 8kts in a boat that big with engines that big.

My boat...Carver 35 twin Cummins 330....18kts@16gph....24000lbs
Friend's boat....Hatteras 47...8v92(715hp).....20kts@60gph....60000lbs
Friend's boat....Sea Ray 47...Cummins QSC600....20kts@45gph....40000lbs

So 17kts@44gph isn't terrible!!! Yes alarming to someone that is not used to burning fuel at that rate. But not bad for a boat that big on plane.

Per my broker, who piloted it from Olympia to Seattle, when I asked the actual fuel economy he experienced:

"That [fuel economy] is for both as when we speak about fuel it is the total for both. When we ran it to Seattle we avg 12 to 14 knts and the owner said we would use 12 to 14 gal per hr or 1 gal per mi which is very good for a vessel of this size and displacement."

Now, they didn't take it to 17, so clearly they know a thing or two about the exponentially-increasing cost over speed. But I guess that's what we're looking at.

Thoughts?

 

[jovial_cynic]

Also, from the navigator website:

"Navigator Yachts hull shape was designed with one thing in mind: make the best use of a minimum amount of fuel and horsepower, and retain the maximum amount of boat speed and efficiency. In doing so, Navigator created a wide hull shape that is stable at rest and at displacement speed, while achieving 30% less wetted running surface when on a plane. The result is a hull with much less drag, a significantly smoother ride, and far better fuel economy."

: shrug :

 

[South of Heaven]

18 knots is a good all day cruise speed for my boat. I'm also gonna do some testing at hull speed.

 

[BandB]

Per my broker, who piloted it from Olympia to Seattle, when I asked the actual fuel economy he experienced:

"That [fuel economy] is for both as when we speak about fuel it is the total for both. When we ran it to Seattle we avg 12 to 14 knts and the owner said we would use 12 to 14 gal per hr or 1 gal per mi which is very good for a vessel of this size and displacement."

Now, they didn't take it to 17, so clearly they know a thing or two about the exponentially-increasing cost over speed. But I guess that's what we're looking at.

Thoughts?

Wifey B: A broker's BS. That's my thoughts.

 

[BandB]

Also, from the navigator website:

"Navigator Yachts hull shape was designed with one thing in mind: make the best use of a minimum amount of fuel and horsepower, and retain the maximum amount of boat speed and efficiency. In doing so, Navigator created a wide hull shape that is stable at rest and at displacement speed, while achieving 30% less wetted running surface when on a plane. The result is a hull with much less drag, a significantly smoother ride, and far better fuel economy."

: shrug :

Wifey B: Like the literature of every boat ever built. I could go to ten websites right now and post 10 different builders version of that same statement. Naivety is cute, but dangerous. If everyone improving efficiency had been successful we'd all be running boats today on no fuel at all.

 

[BandB]

Wifey B: At 17 knots on my Baby Riva, 44', I do only use 24 gph. On and on our Contender with triple Yamaha 300's we use only 16 gph.

But then both of those weigh far less than the boat discussed.

 

[Nomad Willy]

Why are you so obsessed over fuel consumption.
This thread was declared about speed but .......

 

[Baker]

Per my broker, who piloted it from Olympia to Seattle, when I asked the actual fuel economy he experienced:

"That [fuel economy] is for both as when we speak about fuel it is the total for both. When we ran it to Seattle we avg 12 to 14 knts and the owner said we would use 12 to 14 gal per hr or 1 gal per mi which is very good for a vessel of this size and displacement."

Now, they didn't take it to 17, so clearly they know a thing or two about the exponentially-increasing cost over speed. But I guess that's what we're looking at.

Thoughts?

I can tell you right now...if this is true, then you have found my retirement boat for me....Volvos be damned. But.....I would be willing to bet 17 knots in this boat would yield at least 40gph!!!...and I would truly be willing to bet!!! A wide hullform as stated in your post below this one is an inefficient hullform....you may have heard of "beam to length ratio"..??? Fat boats don't do well. Anyway, there ain't no free lunch. A 58 foot 64000lb boat is NOT going to burn only SLIGHTLY more fuel than my 24000 boat at the same speed. But I may be wrong....

 

[Arun52]

33,000Kg boat cruising at 16.5kn I'm using 160L per hour.
At 11kn burning 73L per hour but the engine don't like being run so slow.
2 x Cat D343 460Hp
I find some of the figures on here unbelievable also.

 

[jovial_cynic]

As everybody's *actual* figures on a large boat seem to be double the estimate given by the owner of this boat, I'm really thinking that they were mistaken, and that the figures were just for one of the two engines.

That's disheartening.