What's your cruising speed.

jovial_cynic said:

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.

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The 12-14 kn figures are kinda believable, although maybe miles per hour rather than knots, and fuel use rounded down. So YMMV.

But at higher speeds, 'everybody's actuals' will be pretty close. Its just the way it is. Speed and weight cost money. Spending it is optional.

Perhaps if they seem unbelievable you should consider them so.

The PO was most likely right.

Most of the fuel burn numbers show 3/4 to 1/2 of reality.

Mostly due to guys posting numbers derived from "fuel going into tank v/s hours on the Hobbs meter" They conveniently seem to forget the boat only runs at cruising speed 65 to 75% of the time. They think it's such a small amount it's close enough. And then others post lower numbers yet so he rounds out low. Soon rediculously low numbers appear .......

jovial_cynic said:

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.

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Don't be sad... Pleasure boating nearly always costs twice what you thought [i.e. wish] it would!!

With Cummins 6BTA's, my best on-plane economy cruise is 16gph (1.1nmpg) at 17-18kts. The boat handles better (tabs retracted and better running angle) at 20-21kts and around 21gph (1.0nmpg), while on the pins at 28-29kts I see somewhere around 31gph (.9 nmpg). This is fully loaded, but with a clean bottom and fresh props. Not too bad really for a 19,000+ sporty. I'm very satisfied with these numbers.

The engines are set up with 160° stats and 195° alarms for running on plane in warm Gulf of Mexico waters. At displacement speeds where there the boost is low, the engines remain pretty cool, and I'm not sure this is ideal. If I ever do get the chance to do some leisurely cruising, I'd up the stats back to 180° for that kind of operation.

When I didn't retire as I had planned, I sold my 30' Fales trawler "Boomarang" (my retirement do-the-loop boat) so I could expand my cruising range with the limited time I now have for boating.

Somewhere I heard "The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails."

I guess I just "adjusted the sails", so to speak, by buying a faster boat for now. Hmmm . . . maybe I should finally learn to fish . . .

Life's good, it really is good

Art said:

Don't be sad... Pleasure boating nearly always costs twice what you thought [i.e. wish] it would!!

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Wifey B: Just be a little more questioning. You can't always trust information from the one selling to you and you don't yet have the knowledge or experience to know what part of it to believe. And I read where someone here recently said about their broker "they seem very honest so I trust them." Well, to someone not expert, the least honest can seem very honest, more so than the honest sometimes. Have you ever seen computer salesmen selling to beginners? Horrifying.

It's like the paragraph about Navigators. I remember asking my hubby which boat brand sold the most when I first started boating. He said, "they all do." I'm not a math expert but I didn't think they all could be. However, they were. Brand A sold the most fiberglass under 30'. Brand B sold the most since the beginning of time. Brand C sold the most I/O's. Brand D sold the most I/O's 24' and above. Brand E sold the most of all including thousands of small aluminum jon and fishing boats. That's like the magic hull design that is 30% more efficient. More efficient than what? Oh our previous design we dropped 20 years ago? Not our competitors designs today.

"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. "

FAT boats do great as displacement boats at a K or two under "hull speed".

A beach ball would be deal, but impractical.

Fat is poor at "semi displacement" as never climbing all the way up , they drag massive water and create massive waves , requiring lots of power.

A boat with a wide stern and enough power does fine IF it has the power to get all the way up.

The hull will be supported on a narrower , wider but shorter surface , a better aspect ratio, same as an aircraft, its more efficient.

Weight counts too,light is expensive to build.

Not many cruisers seem willing to attempt over 30 or 40K for cruise , except the Euros with "company" owned cruisers.

Older 1920's boats with round bottoms and skinny hulls did run well, but at the cost of massive power to overcome the weight of that eras hulls and power plants.

Their trade off was low wave making from the skinny hull , but high surface area from the skinny hull.

Insequent said:

The 12-14 kn figures are kinda believable, although maybe miles per hour rather than knots, and fuel use rounded down. So YMMV.

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Nope...I'm not even giving you that. A boat that big pushing that much water would likely be above 20gph at those speeds....probably more...I'm just guessing. I don't think you're getting a gallon a mile in this boat unless you are below hull speed. ANd like I said in relation to the original post....17kts@44gph is actually pretty damn good for a boat this size and weight. I know Jovial is probably horrified by that statement.

Jovial, sorry man. I didn't mean to get so into this aspect of this post. I just boat with a lot of (larger) planing powerboats. And we are always discussing fuel burn. Your numbers just didn't add up. Physics always wins!! If you love the boat, get it. If the fuel burn bothers you, it isn't the right boat. There are a lot of beautiful boats in that price range that burn less fuel...obviously unable to plane. If you really want to go slow with the related fuel burn, then buy a boat that was designed to do that. Good luck and really meditate on that statement...."if the fuel burn bothers you...it isn't the right boat". If ANY part of the expense of a boat bothers you, it isn't the right boat. We do this for fun...not worry! Have fun!!!

Okay, here's the deal. Sit down and let's put the end cap on this, IMO
Two identical boats.... one half loaded with fuel and water .... same weather and water conditions, same RPMs, clean bottom. The other boat, a full time cruiser or live aboard. Which one will get the best mileage?
Next take the same identical boats, move the load from boat B to boat A. One might expect the mileage to be identical but, on just the reverse boat.
I maintain, it wont happen. It may be close but not, identical. WHY? Daymned if I know why but, it just wont be.
Comparing a displacement hull to a semi-displacement boat.... the old apple and oranges comparison.
Watch your fuel usage meter/gauge ..... what is best for you, is best for you.
IF you are burning 2gph at a given speed. We know it will take X time to get to our destination. Compare that to a semi-displacement hull that burns Y+ gph a speed+, sure you get to your destination but, at what fuel cost.

If you are racing the weather and or tide through the cut, you lose interest in fuel economy, that too is a given.

Basically, the only way you can increase your own fuel economy is to start throwing the stuff overboard. That's not really economical because you will need to replace it. LOL

You bought the boat, you were given the headaches along with the boat. There is very little you can physically do to improve fuel economy other than determine your very own "sweet spot" as determined by that magical gph read out.

Those are my thoughts on the fuel economy.

Baker said:

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.

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Nope... That is totally accurate. The Navigator hull design (full planing hull BTW) is an incredibly efficient and well designed hull. It's why, for the same class boat, you will always see engines in other boats have far more horsepower than Navigators. So at our cruising speed of 19mph (sorry... I don't do knots yet) with our TAM63 motors (318hp each), we get in the low 20's COMBINED in fuel burn. But that is up on plane and really scootin' it. That said, at 8 or 9 mph, we get 8gph combined.

And for the record... all Navigators are like that. Regardless of size. Jules was THAT good.

Tom.B said:

Nope... That is totally accurate. The Navigator hull design (full planing hull BTW) is an incredibly efficient and well designed hull. It's why, for the same class boat, you will always see engines in other boats have far more horsepower than Navigators. So at our cruising speed of 19mph (sorry... I don't do knots yet) with our TAM63 motors (318hp each), we get in the low 20's COMBINED in fuel burn. But that is up on plane and really scootin' it. That said, at 8 or 9 mph, we get 8gph combined.

And for the record... all Navigators are like that. Regardless of size. Jules was THAT good.

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First off, you confirmed me "gallon a mile" prediction with your figures. And you really didn't help the argument by saying YOUR boat does 17kts@22gph combined. YOUR boat is 37000lbs(figure taken from YW) and the boat in question is 68000lbs(YW figure...another said 64000). YOUR boat at 636hp total. The boat in question has 1300hp. So what we are seeing here is a boat that is basically twice as heavy with twice as much horsepower. You do the math. Of course I am assuming a linear relationship. Someone could counsel me on why that would not be the case.

Tom.B said:

Nope... That is totally accurate. The Navigator hull design (full planing hull BTW) is an incredibly efficient and well designed hull. It's why, for the same class boat, you will always see engines in other boats have far more horsepower than Navigators. So at our cruising speed of 19mph (sorry... I don't do knots yet) with our TAM63 motors (318hp each), we get in the low 20's COMBINED in fuel burn. But that is up on plane and really scootin' it. That said, at 8 or 9 mph, we get 8gph combined.

And for the record... all Navigators are like that. Regardless of size. Jules was THAT good.

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Can we see different angle photos of bottom on the hard? Any MA or ME drawings-plans you could print copy of?? I'm very interested to learn Jules' Navigator super efficient design factors compared to other boats' hulls.

Oh wait....I was using 48 foot specs. YOUR boat 30000 pounds(straight from the Navigator promotion pamphlet).... Do you not think other manufacturers would have adopted this hullform if it was so extremely brilliantly efficient? I will buy a Navigator 58 tomorrow if it burns 22gph at 17 knots. That is insanely efficient. 44gph at 17 knots is not bad at all....If I were Mr. Jules and that is a real figure, I'd be pretty damn proud of that figure. But I will stand by my "suspicions". And the only way to convince me would be real life....not he said/she said....especially someone that is trying to sell something.

Also see what my boat weighs and burns at cruising speed as I posted earlier and then scale it up to yours....right in the ballpark!!! No unicorm magical hull going on here!!! I even have the same HP engines as you do and just a slightly lighter boat.

In these big fast boats weight has more to
do w efficiency than hull form generally speaking.

But like FF says fat boats don't do well.

With all this talk of 14 - 17 - 20 knots, I'm feeling a bit inadequate with my top speed of 11 mph - but at cruising speed of 8 mph I'm burning about 4.3gph in my twin Lehman 135's.

Art said:

That is of course if you ever actually cruise at that slow a speed!

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LOL...Art, you hit the mark with your above quote! Next time out, If I think of it, I'll take a few photos of fuel flow at various speeds and rpm. After reading this thread I'm kinda interested in the info myself!

FoxtrotCharlie said:

With all this talk of 14 - 17 - 20 knots, I'm feeling a bit inadequate with my top speed of 11 mph - but at cruising speed of 8 mph I'm burning about 4.3gph in my twin Lehman 135's.

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Don't feel bad, my top speed is 8.5 knots. But then I cruise at 7 knots at 2 GPH.

Ted

FoxtrotCharlie said:

With all this talk of 14 - 17 - 20 knots, I'm feeling a bit inadequate with my top speed of 11 mph - but at cruising speed of 8 mph I'm burning about 4.3gph in my twin Lehman 135's.

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Hey Charlie,
That sounds about right.

For what it's worth

Tom.B said:

For what it's worth

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Not bad at all Tom!!!!

Come on folks, you look at the window sticker of a car..... no one believes it.
That sticker makes no allowances for the 'style' of the driver, YOU.
Take that factory/builder's 'window sticker' and build your very own, personalized table.

OldDan1943 said:

Come on folks, you look at the window sticker of a car..... no one believes it.
That sticker makes no allowances for the 'style' of the driver, YOU.
Take that factory/builder's 'window sticker' and build your very own, personalized table.

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What are you saying, Dan? Are you calling me a liar and this document false? I am a Navigator owner and have talked to a lot of other owners. We have a Facebook page where we talk about... go ahead and guess... Navigators. Correct. But, for a moment, let’s say I am full of sh1t and this document is fake, how far off do you think it is? 2x? 4x? 100x?

Tom.B said:

For what it's worth

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We cruised many 100+ nmile legs with a 48 Navigator alongside and those numbers look pretty much in line with what he was getting.

That spec sheet is in error. It states a D6-330 pair burns 27gph (total?) at full power, 3500rpm. Volvo spec sheet has a single D6-330 burning about 18gph at full power. I can believe 36gph, but not 27, for a pair.

It is wrong whether for a single engine or for both. You are not going to get 660hp out of 27gph on two little high rev Volvos.

Puts the rest of the data into doubt.

Fine... just drop the whole thing and move on.

Ski in NC said:

That spec sheet is in error. It states a D6-330 pair burns 27gph (total?) at full power, 3500rpm. Volvo spec sheet has a single D6-330 burning about 18gph at full power. I can believe 36gph, but not 27, for a pair.

It is wrong whether for a single engine or for both. You are not going to get 660hp out of 27gph on two little high rev Volvos.

Puts the rest of the data into doubt.

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Don't know about the WOT numbers but the cruise speed and typical nmpg for the 48 Navigator is right on the spot where our friends boat was.
Just not that surprising for that boat though - the other sizes and engines we cannot comment on as we have no experience.

FWIW- our 47 Bayliner would use less fuel then those numbers at fast cruise on long legs of trips.
YMMV

We keep getting testaments on 42's and spec sheets from the builder but none of these have the boat or the engines in question on them. It's like saying on a 44' Riva with 800's, I get this and then apply it to a 63' Riva with 1360's. We're talking a 58 which is at least 80% more boat than the 42. We're talking larger engines. I'm not speaking to what anyone is getting on the 42, but I am stating the numbers initially stated on the 58 are wrong.

Tom.B said:

What are you saying, Dan? Are you calling me a liar and this document false? I am a Navigator owner and have talked to a lot of other owners. We have a Facebook page where we talk about... go ahead and guess... Navigators. Correct. But, for a moment, let’s say I am full of sh1t and this document is fake, how far off do you think it is? 2x? 4x? 100x?

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Tom,
No I am not calling you a liar. I am saying, take the published data with a grain of salt. A lot depends upon the weight of the stuff we put on board, the seas, the currents, wave height and and and.

I have the data sheet on my AT34 (sea trial of my hull #, loaded 1/2 1/2). It maybe close but, I would not bet my last 5 gallons on reaching my destination.

Please, ReRead the caption at the top of your document.

jovial_cynic said:

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?

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I am not familiar with that Navigator or those specific engines but here is a boat test on a 2004 - 56' Navigator that may help out some....
https://www.powerandmotoryacht.com/boats/navigator-56

I have found at times you can also get additional information that is not online by heading to your local library and asking for help with the microfilm and past periodicals - helped me secure some old boating tests that I then copied.

WOT 11 knots

Cruise @ 7-8

Original 34' Mainship with perkins 165hp