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Old 11-19-2015, 09:50 AM   #1
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Trawler Fuel Economy

Is the fuel economy of a trawler based primarily on its lack of speed? If you took say a Hatteras and only cruised around 8 knots would you get the same fuel economy? I do understand that a Trawler will generally have greater range due to size of fuel tank. Thanks
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Old 11-19-2015, 10:16 AM   #2
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There are way more variables that go into this....... Horsepower, hull design, aerodynamic drag of the superstructure, prop specs, gear reduction ratios, corriolis force...

Lots of people will have a myriad of opinions on this endless discussion, some better founded than others. All I can tell you is that fuel burn vs speed is not a linear curve. To get on plane and double your speed can triple your consumption. (Actual numbers subject to all the parameters, and more, mentioned above.)

Conversely if you throttle back and get 10% this side of hull speed you will be at or close to your optimum fuel burn/mile.

The following is my opinion..... I do not have MIT tank testing to back this up:

If your hypothetical trawler and hypothetical Hatt do not have highly unusual underwatership design, and if they are of the same displacement and waterline length, and if they have similar running gear and if they are operated at similar percentages of hull speed they will probably be pretty close.

See, too many "if"'s.
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Old 11-19-2015, 10:18 AM   #3
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There are two primary factors that influence hp (which is related to fuel useage) required to push a boat: speed and displacement. Less important, but significant is hull form, ie displacement/semi displacement/planing hull forms. And maybe less important, engine size, but still measurable. Water line length is also important if you are talking about speeds near 8 kts for most boats.


So the "true trawler" is a full displacement, single small engine driven boat that goes slow. One typically burns 1-3 gph. The Hatteras (excluding the LRC hull) has big engines, a planning hull form and goes fast.


But lets compare a Nordhavn 40 of about 50,000 lbs displacement with a big Hatteras of the same displacement and waterline length both going the same speed. The Nordhavn will burn 2-3 gph at 7 kts. The Hatteras will burn about double that due to its planning hull form and its big engines. The planning hull form is not very efficient at low speeds so it takes more hp to go the same speed as the Nordhavn, but can go fast with enough hp. The big 1,000 hp engines are less efficient than small engines at light load so burn more fuel for equivalent hp produced.


Both factors mean that the Hatteras will burn about double the fuel at the same speed as the Nordhavn.


But if you can afford a nice Nordhavn or Hatteras, is fuel economy a real consideration?


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Old 11-19-2015, 10:19 AM   #4
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Greetings,
Mr. Gc. Welcome aboard. I wouldn't necessarily say "trawlers" have a "lack of speed", just a much more genteel pace.
From what I have read over the years on TF the answer is yes. The Hatt' will probably achieve similar fuel economy to a "trawler" when operated close to or below hull speed.
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Old 11-19-2015, 12:18 PM   #5
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When we look at the number of engine hours on the boats for sale on Yacht World that are ten years old, ranging from a low of around 500 to 1,000, maybe 1,500 to 2,000 hours for a typical trawler or most other designs, we see fuel cost is not a critical factor for any of these boats. Insurance, dockage, maintenance are the real costs except for constant travelers. If you are making the loop fuel will be a big deal, if you are weekend cruiser the difference between a boat that uses 4 gallons and hour and one that uses 40 gallons an hour may not have be a factor in your yearly cost,
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Old 11-19-2015, 12:27 PM   #6
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Thankyou so much for your thoughtful responses. If nothing else I have a much better understanding of just how many factors go into what I thought was a simple question....Interestingly enough I just reconnected with a very good old friend who went to Webb Institute many years ago, this might end up being a nice conversation over a couple of beers. Even thought he became a Rocket Scientist his roots are in Naval Architecture...
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Old 11-19-2015, 12:49 PM   #7
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"The Nature of Boats" by Dave Gerr and "Voyaging Under Power" by Robert Beebe, revised by Jim Leishman of Nordhavn, are excellent references for this type of question. Hull form has a bunch (but not all) to do with it and the all too loosely used term "trawler" includes boats with a wide variety of hull forms some of which are just like that of a non-LRC Hatteras. A Hatteras LRC having a displacement rather than planing hull. Read the books, they are pretty much designed for the layman.
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Old 11-19-2015, 12:52 PM   #8
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What prompted me to ask this question has everything to do with boat selection for me. I think everyone would agree that even if you had a generous budget, there is no need to waste money. We are in the early stages of research, not even really sure at this point what our use will look like. Watching some Nordhavn videos of regular people circumnavigation the world looks great. Others enjoy trailerable trawlers that give them the abilty to transport and drop them in the water wherever they want, that looks great. Ideally I am sure everyone would like great fuel economy with speed, does this exist, probably not, although the Aspen power cat has an intersting hull design and caught my eye. I will keep reading and absorbing all the great knowledge that is here and elsewhere. In time, what will be correct for us will begin to come into focus, at least that is how it has always worked for me, thanks again, G
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Old 11-19-2015, 01:22 PM   #9
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Greetings,
Mr. Gc. Re-read post #5. Mr. Tucker hit the nail on the head. We've found, in 30+ years of boating that fuel is WAY down the list of expenses. That being said, the majority of our boating has been shorter weekend/week long adventures.
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Old 11-19-2015, 02:39 PM   #10
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Quote:
Originally Posted by Genecop View Post
What prompted me to ask this question has everything to do with boat selection for me. I think everyone would agree that even if you had a generous budget, there is no need to waste money. We are in the early stages of research, not even really sure at this point what our use will look like. Watching some Nordhavn videos of regular people circumnavigation the world looks great. Others enjoy trailerable trawlers that give them the abilty to transport and drop them in the water wherever they want, that looks great. Ideally I am sure everyone would like great fuel economy with speed, does this exist, probably not, although the Aspen power cat has an intersting hull design and caught my eye. I will keep reading and absorbing all the great knowledge that is here and elsewhere. In time, what will be correct for us will begin to come into focus, at least that is how it has always worked for me, thanks again, G
I think a catamaran is going to be the answer for speed AND fuel economy. Shannon made a pretty cool boat...it was 38 feet I believe. The one in the link below looks nice AND even comes with a new boat warranty!!!....as it is the personal boat of designer/owner of Shanno Yachts, Walt Schultz.

2004 Shannon SRD Power Boat For Sale - www.yachtworld.com
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Old 11-19-2015, 02:58 PM   #11
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You can run a planing hull at displacement speed and get great economy. We did that one summer in a Riviera 36 with a shaft coupling/alignment issue. At 8 kn we used 1/4 of the fuel we would normally have used to go the same distance at 20 kn. We cruised about 600 miles during our summer holiday.
The limitation is the size of the rudders, they just don't work so well at slow speed - especially in a following sea.
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Old 11-19-2015, 03:28 PM   #12
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Back to your question. The biggest difference between a trawler and other yachts is a single engine.
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Old 11-19-2015, 04:23 PM   #13
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I think a catamaran is going to be the answer for speed AND fuel economy. Shannon made a pretty cool boat...it was 38 feet I believe. The one in the link below looks nice AND even comes with a new boat warranty!!!....as it is the personal boat of designer/owner of Shanno Yachts, Walt Schultz.

2004 Shannon SRD Power Boat For Sale - www.yachtworld.com
That's a nice boat, I have seen some other Shannon stuff, beautiful lines, just not enough living space, but something like that might be a good start for us..
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Old 11-19-2015, 05:34 PM   #14
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Back to your question. The biggest difference between a trawler and other yachts is a single engine.
So a Grand Banks is not a trawler?
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Old 11-19-2015, 05:43 PM   #15
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Old 11-19-2015, 05:46 PM   #16
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So a Grand Banks is not a trawler?
Not according to some...and they will prove it through references to Grand Banks sales brochures and no doubt expert experts.
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Old 11-19-2015, 05:49 PM   #17
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So a Grand Banks is not a trawler?
Let's not debate the definition of the word "trawler" again. There are plenty of previous threads that have beat that one to death.

Let's keep it to a discussion of high powered boats versus slow, low powered boats, a topic that has also been beat to death here .

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Old 11-19-2015, 07:10 PM   #18
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Fuel economy at speeds up to about 1.3-1.4 times "hull speed" (hull speed in knots = 1.34 x square root of waterline length in feet) depends mostly on displacement and waterline length followed by Length to beam ratio, hull form parameters, etc. Things like transmission gear ratio don't matter since prop sizing takes that into account.

Displacement is by far the most important factor with LWL secondary.

Note I am only using hull speed to set a speed range not as some sort of magic number.
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Old 11-19-2015, 10:50 PM   #19
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Another way to think about it is how is the cost from a cruising lifestyle budget.

If you were spending time in a cruising lifestyle, seeing the sights, harbor or anchorage hopping...

And wanted to move between ports say once a week at an average of 100 miles per move then...

A boat that gets 1.5NMPG (like my semi displacement hull with twin 330 hp diesels) would burn 66 gallons a move or 265 gallons of diesel a month. at$3.50 a gallon that is a $930 a month bill.

Take the same path in a single engine trawler like the N46 at lets say for discussion sake 3.0 NMPG and the monthly fuel cost drops to $465 a huge difference!

As was said above fuel burn might not make up much of a recreational boating budget for weekenders, but cruise as a retirement lifestyle and it is a much bigger deal.
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Old 11-20-2015, 03:02 AM   #20
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I thought I learned here that the difference between a trawler and other boats was the nets!
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