GPH efficiency?

[OldDan1943]

Originally Posted by Steve91T

How many people shut a main down while under way? How does it effect mileage and handling?

If I shut down my main engine on my AT34, the mileage would greatly improve as I coasted to stop. SMIRK

[Simi 60]

Originally Posted by Arafura II

50 foot 30 ton I have a Gardner 6LX and at 1050 RPM get 8 knots at 8 liters per hour.

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-...cruiser/206741

[Arafura II]

Originally Posted by Simi 60

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-...cruiser/206741

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]

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

[Nomad Willy]

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.

[Simi 60]

Originally Posted by Nomad Willy

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.

Hour meter and liters/gallons in tank is the very definition of reality.

[dhays]

Originally Posted by Nomad Willy

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.

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]

Originally Posted by Nomad Willy

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.

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

[tiltrider1]

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.

[Art]

Originally Posted by AusCan

If it cost me $500 a month in fuel then I'd be making some changes, as well.

Boating does not have to be expensive.
Boating can be whatever budget you want it to be, as long as you are realistic about it. Just don't buy a mega-cruiser when you have a row boat budget.

Agreed!

[MurrayM]

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...

[AusCan]

Originally Posted by AusCan

I burn 3 litres (0.8 US gallons) per hour @ 1800 rpm averaging 6 knots
That works out to 0.13 gallons per mile in imperial measurements. or 7.5 mpg

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]

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.

[Art]

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!

[Arthurc]

Agreed the Prop makes a big difference. New JD6068 and I will cruise at 7.9 knots at about 2.4gph, but right now I’m breaking her in so running at 9 knots and 6.8gph
AC

[Art]

Originally Posted by Arthurc

Agreed the Prop makes a big difference. New JD6068 and I will cruise at 7.9 knots at about 2.4gph, but right now I’m breaking her in so running at 9 knots and 6.8gph
AC

You might get hooked on the 9 knots... 10.357 mph / Instead of 7.9 knots...9.09 mph. - Just kiden.

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!

[Arthurc]

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

[siestakey]

Originally Posted by Art

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!

Agreed but I would love my fuel expense to be a much higher % of my annual cost

[MurrayM]

Originally Posted by Arthurc

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]

Originally Posted by Benthic2

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.

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!!