| T O P I C R E V I E W |
| pdecat |
Posted - Jan 10 2012 : 15:47:25
An RO just bought a boat with twin 240 HP diesels, total 440 HP.
He expects to use about 4 GPH at hull speed, maybe 8 KTS.
How much fuel would he use at that same speed if the boat had 440 HP, total 880HP engines? |
| 17 L A T E S T R E P L I E S (Newest First) |
| pdecat |
Posted - Jan 13 2012 : 08:39:19
quote:
a true low hp, single screw, sea kindly design hull, does indeed have a better fuel burn.
The best example being a sailboat hull not a square hull with falt aft sections.
The power needed to push a boat through the water is roughly independent of the number of engines. You chose your new boat for reasons other than the engines. If it had one engine or two bigger engines the fuel use would be very similar.
The original question was about fuel not overhaul costs but if as Bob stated above 10,000 hours between overhauls is expected that is a question for your grand kids. |
| rbmitchell |
Posted - Jan 13 2012 : 04:44:25
A Cummins 300+ hp diesel running at two gph is expected to see 10,000 hours before rebuilding. (Based on 20,000 gallons consumption before major overhaul.)
Turbo charged engines, when run at rated load/speed, are three or four percent more efficient than naturally aspirated versions of the same engine. But not, of course, at hull speed without the turbo recovering exhaust heat energy.
The bigger engine offers some emergency speed and you are never likely to see a rebuild. You'll see a lot more capital investment however. |
| Woodsong |
Posted - Jan 12 2012 : 23:20:46
quote:
Originally posted by Hyperfishing
Best part about tiny, low powered engines, is at rebuild time. Oooooooh yeah! That REALLY changes the ownership economics.
now THAT is an absolute fact!! BIG BIG BIG difference in rebuild costs!!!
There is no way around the fact that cost of ownership for a twin engine, turbo charged, etc. diesel boat is going to be WAY more than a low hp, single screw diesel. |
| Woodsong |
Posted - Jan 12 2012 : 23:19:12
Bruce, for a semi-displacement hull you are correct. The biggest difference in fuel burn between a semi-displacement trawler and a motor yacht will be whether it has twin or single diesels for obvious reasons. Once you switch to a true full displacement hull though obviously the game changes and over a certain hp there is no need to increase hp as it is a complete waste. I think the trawler world has a lot of hype and marketing- fast trawlers, etc. But a true low hp, single screw, sea kindly design hull, does indeed have a better fuel burn. The engines also last, or can, much longer if in continuous duty. A low hp, non turbo diesel with no electric nonsense is nothing more than a simple farm tractor and it will just go and go and go. Trawlers aren't just about fuel burn. We didn't switch to the pilothouse to go faster- it is more about the need for space and more room. We would have been very happy with a defever 49 or marine trader 50 but we didn't limit our search to just trawlers. If it were just my wife and I there is little doubt we would have kept our monk for a very, very long time- perfect boat for a couple.
P.S. ours are 220hp not 240. If you get over 130hp or so you will have a turbo engine- even the 165hp diesels typically have a turbo on them.
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| Hyperfishing |
Posted - Jan 12 2012 : 20:25:17
Best part about tiny, low powered engines, is at rebuild time. Oooooooh yeah! That REALLY changes the ownership economics. <gg>
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| pdecat |
Posted - Jan 12 2012 : 14:09:11
I am primarily referring to used boat choices where buyers avoid more power because they fear more fuel use. Non planning, displacement, boats generally were not sold with an over abundance of power options but many of the "trawlers" are semi planning. If your boat has flat sections aft it is not a displacement only hull. OTOH a slippery keel sail boat hull wont plane, period.
But you make a good point, buying a low powered new boat instead of more powerful engine options also fits. |
| getakey |
Posted - Jan 12 2012 : 14:04:26
I agree with you on semi planning boats, but If it is a non-planing hull, then adding more horsepower than necessary will push the initial cost up.
Secondly, with more HP, you could add throttle (depending on prop choice) to try to make the boat go faster and will consume more fuel at virtually the same speed. |
| pdecat |
Posted - Jan 12 2012 : 13:57:27
83% of BE folks got it right. Bigger engines dont cause more fuel use in the same boat at the same speed. Bigger engines do allow faster speed with more fuel use if the need arises but consume the same fuel at low speeds.
It is for that reason that calling a low powered boat a trawler is misleading. The island trader, monk and even the beautiful grand banks are just low powered semi planning boats.
Many buyers today want economy and think that only with low powered engines do they get better economy when the truth is engine size doesn’t matter much with diesels. Boat weight, slippery hull design and lower air resistance affect fuel consumption much more than maximum engine HP. More powerful engines usually are heavier but at slow speeds that affect is minor.
With so many boat available to choose from limiting choices to low power just for economy sake achieves no benefit and limits cruising options. |
| pdecat |
Posted - Jan 11 2012 : 09:58:14
 |
| Ghost |
Posted - Jan 11 2012 : 09:41:29
Veebyes....is that a manicooler, multi cooler or whatever they called that? OOOOH...watch those O-rings!
Actually I love old Perkins, very hard to kill.
Bruce, yeah I know, but let a man stir the pot if he wants to. BTW, I love it when your get creative in the winter, heh heh heh.
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| ronlord |
Posted - Jan 11 2012 : 09:35:16
quote:
Originally posted by pdecat
Where are all the trawler fans??
We are all out buying guns to shoot ourselves ..except for Tony who decided to buy a faster boat instead. |
| pdecat |
Posted - Jan 11 2012 : 09:20:27
Ghost: You maybe surprised how many lower HP diesels have turbos. |
| Veebyes |
Posted - Jan 11 2012 : 09:16:16
240hp, sounds like it might be a Perkins. My ex workboat had one a Perkins 240hp & burn at hullspeed most of the time was about 2gph. Tough motor. No gee wiz electronics.
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| pdecat |
Posted - Jan 11 2012 : 07:50:26
Where are all the trawler fans?? |
| The Other Gary |
Posted - Jan 10 2012 : 19:06:57
I have twin 330's and burn 4GPH at 1100 rpm for 8 knots or 2.7 gph at 1400 rpm on one engine for the same speed.
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| Ghost |
Posted - Jan 10 2012 : 18:21:03
I'm going to guess that fuel consumed per hp generated is about the same. But it will take him twice as long to get anywhere with the 880HP engines because he's going to be too busy trying to maintain those turbochargers and aftercoolers that he won't have to maintain on the 440HP setup.
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| abalmuth |
Posted - Jan 10 2012 : 16:05:15
8 Knots is a touch above idle for me, about 5GPH-ish
only 1320HP |
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