OldDan1943
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If I shut down my main engine on my AT34, the mileage would greatly improve as I coasted to stop. SMIRK
GPH efficiency?
- Thread starter toocoys
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The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
If I shut down my main engine on my AT34, the mileage would greatly improve as I coasted to stop. SMIRK
Simi 60
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Wow, light boat
We are 10 ft longer and weigh more than double.
Interesting our sort of sister ship Santa Barbara has a 6lxb in her.
They reckon 7.5 knots @ 12lph
Throttle must be pushed down a bit further to get there and would love to know what, if any they have left in reserve.
When ours was repowered during the rebuild alongside Santa Barbara , the owner must have considered the Gardner as we have all the numbers on board in some of the paperwork.
Chose the 325 HP Cummins instead and we use approx 100 of those horses for our speed and similar burn but with plenty in reserve at a greatly increased thirst, of course.
https://yachthub.com/list/boats-for-sale/used/power-boats/custom-60-foot-luxury-motor-cruiser/206741
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Arafura II
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The Gardner displaces 10.45 litres and develops 100 HP at 1500 RPM but has bucket loads of torque right through the rev range it will do 10 knots at 1400 RPM but the extra fuel burn is not worth it, when cruising at 8 knots it’s not even breaking a sweat I’ve seen similar boats with much bigger props that cruise at 8 knots at 850-900 RPM if anything I think I’m a bit under proped as you know a lot of fishing trawlers had the 6LX and worked under huge loads for years and 100000 hours before overhaul wasn’t uncommon.
markpierce
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With our fat 14-ton, full displacement boat and 80 HP JD4045 NA diesel engine:
Flank speed (WOT-2400 RPM) of 7.4 knots: 4 GPH
Full speed (2200 RPM) of 7.3 knots: 2.9 GPH
Cruise speed (1800 RPM) of 6.3 knots: 1.7 GPH
Slow speed (1400 RPM) of 5.7 knots: 1.2 GPH
Idle speed (800 RPM) of 3.2 knots: 0.4 GPH
Flank speed (WOT-2400 RPM) of 7.4 knots: 4 GPH
Full speed (2200 RPM) of 7.3 knots: 2.9 GPH
Cruise speed (1800 RPM) of 6.3 knots: 1.7 GPH
Slow speed (1400 RPM) of 5.7 knots: 1.2 GPH
Idle speed (800 RPM) of 3.2 knots: 0.4 GPH
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Nomad Willy
Guru
Those that stew about fuel burn should get a smaller boat.
IMO most all the gph numbers on TF are very optimistic. Arrived at by using the hour meter and the number of gallons put in the tanks. Way different than reality.
IMO most all the gph numbers on TF are very optimistic. Arrived at by using the hour meter and the number of gallons put in the tanks. Way different than reality.
dhays
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How so Eric? On my sailboat it was pretty easy. I filled up about once a year and looked at how many hours I had on the engine. I didn't factor in the fuel used by my furnace. Seems to me that gives a pretty good estimate of gph.
On my current boat I have two methods. The electronic engine tells me exactly how many gph I am burning at any given time. I also am able to divide my gallons purchased at fuel fill against the hours on the clock. I don't see how either of those are terribly optimistic.
menzies
Guru
Interesting comment.
I never go by hours. I go by KM traveled vs. gallons used. I don't worry about current or wind as I just assume that, unless I am very unlucky, it will all even out
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tiltrider1
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I don’t think the gallons per hour are optimistic. I think the speed being claimed is optimistic.
When conditions were perfect I could get 6 kts out of my 34’ sailboat and burn only .5 gallons per hour. In theory this was 12 nmpg. In reality I never saw that, a little wind or chop and the speed would drop. Reality was 9 nmpg.
Some of the boats here are optimized for LRC so claims of 8 nmpg don’t surprise me. Claims of greater than that become suspicious. Yet, a long skinny light boat going slow with a single engine could easily produce some impressive numbers so I’m not calling BS on anyone.
When conditions were perfect I could get 6 kts out of my 34’ sailboat and burn only .5 gallons per hour. In theory this was 12 nmpg. In reality I never saw that, a little wind or chop and the speed would drop. Reality was 9 nmpg.
Some of the boats here are optimized for LRC so claims of 8 nmpg don’t surprise me. Claims of greater than that become suspicious. Yet, a long skinny light boat going slow with a single engine could easily produce some impressive numbers so I’m not calling BS on anyone.
Agreed!
MurrayM
Guru
From the fuel burned and hours on the engine over the first year we had our boat it came to 1.3 gallons per hour. I round that up to 1.5 for estimates and haven’t crunched the numbers since.
Maybe I should take a look at lasts years numbers to see if it’s changed...
Maybe I should take a look at lasts years numbers to see if it’s changed...
AusCan
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The numbers I quoted are optimistic, as they are what I get in calm water. In real world conditions, the water is rarely calm. On an ugly day I sometimes burn double the fuel to achieve half the speed.
Benthic2
Guru
So.....this may be a little off topic.....but.....
If you were repowering a boat with a hull speed of...say 9 knots.....and it took ( random guess here) 100 horsepower to do that speed....would the ideal be to pick an engine a little greater than 100 hp to compensate for headwind...current....bottom growth and so on ? I just have such a hard time fathoming ( did you see what I did there ? ) big boats with small engines. I had a 16 foot, 500 pound boat that had a 25 horse engine....I have a 17 foot boat that has a 140 hp engine.....and some of you guys have serious boats with less hp than my little bowrider.....Its hard to wrap my head around this concept. I know displacement boats are a different animal than planing boats....but .....not to single anyone out...but scrolling back I see Mark has a 14 ton boat with an 80hp engine. it blows my mind....sorry for the off topic rant.
If you were repowering a boat with a hull speed of...say 9 knots.....and it took ( random guess here) 100 horsepower to do that speed....would the ideal be to pick an engine a little greater than 100 hp to compensate for headwind...current....bottom growth and so on ? I just have such a hard time fathoming ( did you see what I did there ? ) big boats with small engines. I had a 16 foot, 500 pound boat that had a 25 horse engine....I have a 17 foot boat that has a 140 hp engine.....and some of you guys have serious boats with less hp than my little bowrider.....Its hard to wrap my head around this concept. I know displacement boats are a different animal than planing boats....but .....not to single anyone out...but scrolling back I see Mark has a 14 ton boat with an 80hp engine. it blows my mind....sorry for the off topic rant.
I get a big kick out of us all [well pretty much all - lol] with boats we either love or at very least that well suites our agendas/objectives/desires/needs.
Therefore... unless any of us are doing poorly financially and need relief from our boat's fuel expense... the cost of fuel is usually a minor piece of "boat dollars" annually spent.
Therefore x 2... Use your boat's power as economically as you want to or feel need to... while you enjoy life aboard - Your Boat!!! How lucky we all are!
BTW, Bottom and Prop degree of cleanliness is very much a nmpg altering item I've not seen mentioned [among the oh so many items that were mentioned]. This cleanliness factor also alters in intensity week to week or month to month or via bottom cleaner's proficiency. Its state of affairs can skew the numbers gotten by observation. Just sayen!
Therefore... unless any of us are doing poorly financially and need relief from our boat's fuel expense... the cost of fuel is usually a minor piece of "boat dollars" annually spent.
Therefore x 2... Use your boat's power as economically as you want to or feel need to... while you enjoy life aboard - Your Boat!!! How lucky we all are!
BTW, Bottom and Prop degree of cleanliness is very much a nmpg altering item I've not seen mentioned [among the oh so many items that were mentioned]. This cleanliness factor also alters in intensity week to week or month to month or via bottom cleaner's proficiency. Its state of affairs can skew the numbers gotten by observation. Just sayen!
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You might get hooked on the 9 knots... 10.357 mph / Instead of 7.9 knots...9.09 mph. - Just kiden. :lol:
7.58 knots is calculated speed for hull WLL of our Tolly. We often cruise somewhat under that at 6.5 to 7 knots for fuel efficiency. At that speed we get just under 2 nmpg using both engines. If we shut one engine down, leave other prop freewheeling [BW Velvet Drive trany is OK with that] and cruise at 4.5 to 5 knots our Tolly approaches 3 nmpg. When we want to cover some distance on plane we push throttles up and cruise at 16 to 17 knots doing right around 1 nmpg. WOT is 21 to 22 knots and OMG fraction of nmpg. I only ever use WOT when absolutely necessary or required... such as at first sea trial, when testing an engine repair and very seldom for a minute or so if things get too hairy on the water due to some sort of confusion that needs to be put behind us or that we need to immediately veer away from.
BTW - Arthur is a good name!
Attachments
Arthurc
Guru
Agreed on the name! I actually was thinking that I’m really getting use to running at 2000rpm but the big difference for me is that at 1475 it’s right before the turbo kicks in, so much quieter in addition to the saved fuel 
MurrayM
Guru
Agreed on the name! I actually was thinking that I’m really getting use to running at 2000rpm but the big difference for me is that at 1475 it’s right before the turbo kicks in, so much quieter in addition to the saved fuel
Have you checked the operators manual for running it below where the turbo kicks in for extended periods? I don't remember the specific details, but Yanmar suggests running our engine at a specific high rpm for a set number of minutes after running at low rpm every couple hours or so.
A fellow down the dock thought he might run his boat below where the turbos kicked in to save fuel and seized them up on both his engines...
Ski in NC
Technical Guru
Displacement hulls certainly are different animals than a planing bowrider. Completely appropriate to spec a low hp engine for those.
A typical 40' trawler will use like 40-50hp to run hull speed of 7-8kts. But you don't want to spec a 50hp engine as it is not good for it (nor quiet!) to run an engine at max power. So typical practice is to spec one so it runs at around 50% of its rated power at like 2/3 rated rpm. For most engines this is a "happy spot". So you shop for a 100hp engine...
Now getting to pick an actual engine gets complicated. There are not infinite choices out there. JD makes a nice 4cyl in the 80-150hp range, but many don't like the low rpm shake of a 4cyl. Their six is very nice, but like Cummins, a little overkill. Ford Lehman 6cyl 120hp is still available, but not from the original packager, which complicates things. Cummins lowest hp six is a turbo at 210, way overkill on hp, but still ends up being a nice trawler engine just with lots of headroom. And then there are little car based engines and low market share vendors that have another set of issues.
Few of us actually get to pick our engine. We get to pick a boat that comes with an engine and hopefully you like both!!
Mo Miles Traveled at Mo Throttle Applied = Mo Money for Fuel $$$$ Expense!
You can raise the %age... if desired!!
Nomad Willy
Guru
Art wrote;
“Therefore... unless any of us are doing poorly financially and need relief from our boat's fuel expense... the cost of fuel is usually a minor piece of "boat dollars" annually spent.”
If it’s so minor why all the obsession about it?
“Therefore... unless any of us are doing poorly financially and need relief from our boat's fuel expense... the cost of fuel is usually a minor piece of "boat dollars" annually spent.”
If it’s so minor why all the obsession about it?
Nomad Willy
Guru
Simi 60 wrote;
“Hour meter and liters/gallons in tank is the very definition of reality.”
Sure but it’s far from derived at 100% cruising speed. I’ll bet most would be shocked to learn how many hours are accumulating on the hour meter that are at running speeds and loads very far from cruising loads and speeds.
dhays wrote;
“The electronic engine tells me exactly how many gph I am burning at any given time.”
If you mean during any period of time that can be taken to the bank if the engine speed/boat speed is never changed during the period.
But most of us don’t have such sophisticated equipment. And of course the “equipment” is subject to error.
“Hour meter and liters/gallons in tank is the very definition of reality.”
Sure but it’s far from derived at 100% cruising speed. I’ll bet most would be shocked to learn how many hours are accumulating on the hour meter that are at running speeds and loads very far from cruising loads and speeds.
dhays wrote;
“The electronic engine tells me exactly how many gph I am burning at any given time.”
If you mean during any period of time that can be taken to the bank if the engine speed/boat speed is never changed during the period.
But most of us don’t have such sophisticated equipment. And of course the “equipment” is subject to error.
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healhustler
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Good post. Case in point, the Kadey Krogen Manatee of which 99 were built from 1984 to 1991. Empty, 12 tons, 34 ft waterline. Original engine for the first dozen or so examples (including Skipper Bob’s) were Perkins 50’s (and they are still around) which would push the boat to it’s hull speed. Add a big alternator, air compressor or maybe a hydraulic accessory of some kind and there was no surplus to draw from. Next came the Volvo TAMD series 90HP and subsequent 100 and 110 HP versions. The 90’s were more than adequate in any situation and still are unless they get tired. I’ve seen the Manatees repowered with as much as a 160 Volvo, but I can tell you that the only thing anything over 100 HP does with a 22 x 13 prop is dig a bigger hole. My boat has also been repowered with a 140 Yanmar. I can’t think of a moment wherethe extra HP was useful or evident, save for perhaps dunking the swim platform. Another friend of mine just repowered his boat with the same Yanmar I have, but his Volvo 90 was really tired and he also added some pneumatic fin stabilizers, requiring a big air compressor. The fins also added a half-knot drag at cruising speed, and his plan includes adding a huge alternator, so it may have been a useful upgrade for his particular application, but otherwise in the great majority of these vessels, more than 90 HP is a waste.
Jeff F
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Me too. I've found that with my typical use and (low) speed that I use a pretty consistent 1 litre per NM including generator use, about 4 mpg. That's sufficient information for me to plan fuel stops and budget. I don't really get the whole gph fixation. I guess if you're just out cruising around for the day it might be meaningful, but for traveling doesn't it boil down to how far you can go on a tank of fuel, or how much fuel a voyage will take?
Ski in NC
Technical Guru
I too go by NM traveled vs gallons gone via dipstick. My Furuno 1650 (??) old bottom machine/backup gps plotter if you toggle through the plotter screens there is one that has an odometer. Very handy when doing burn calcs.
If you use the hourmeter, (which I do log each fuel check and fuel load), it does not take into account the minimal fuel burned (yet hours logged) while idling around an anchorage or dockage or waiting for a bridge. Hourmeter use will skew your gph downward from reality.
But after each trip, I calc the nmpg and gph and it all ends up real consistent, so the numbers are good enough for further trip planning.
If you use the hourmeter, (which I do log each fuel check and fuel load), it does not take into account the minimal fuel burned (yet hours logged) while idling around an anchorage or dockage or waiting for a bridge. Hourmeter use will skew your gph downward from reality.
But after each trip, I calc the nmpg and gph and it all ends up real consistent, so the numbers are good enough for further trip planning.
siestakey
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Mo Miles Traveled at Mo Throttle Applied = Mo Money for Fuel $$$$ Expense!
You can raise the %age... if desired!!
No I do not raise the throttle just need more time cruising
Mrwesson
Senior Member
X2
Obviously someone's never run a 35'+ boat at planing speeds.
45 GPH is not minor.
