D12 675 fuel consumption question ....

[KajLehtinen]

Hi!

Cant search for D12 so dont know if its been written to death already so please bear with me. I've recently purchased a Sealine T52 with D12 675 engines. The T52 that I purchased was advertised as having 1000 NM range. Its equiped with two extra tanks in the lazarette instead of crewcabin. They hold approx 300 liters (measured outside of tanks) each which gives me a total fuel capacity of 2600 liters. The 1000 NM range doesnt state at what speed. I know it isnt cruising speed but the question is what is reasonable to think it should be in non planning speed? The boat has twin Volvo Penta D12 675 HP engines. Is it

idle/Tickover (6 knots)
750 rpm (7.6 knots)
800 rpms (8.2 knots)
1000 rom (10 ish knots)

If I go backwards it means that the 2600 liters onboard, if it takes me 1000 nm would mean 2.6 liters/nm totally - which means 1.3 liters per engine. At what rpm does the D12 consume that little?

Looking at the datasheet from VP it simply states that 1000 rpm will consume 18 liters/h per engine. From my short testing 1000 rpms means 10 ish knots which translates to 1.8 liters per engine, so my mind says it got to be less than 1000 rpms ... which is where VPs datasheet starts from the low revs.

Also - the 1000 nm that the boat was sold as, doesnt state 1000 nm bone dry tanks or 1000 nm with industry standard 20% reserve. Can my fuelcapacity estimate be slightly off? I mean if they from factory fitted extra tanks perhaps they also fitted larger main tanks?

One way would ofcourse be to run her dry and fill up to see exact size of all the tanks ... But perhaps we can calculate a bit first what would be reasonable?

/Kaj

 

[QBhoy]

This should give you an idea....pretty accurate in my case.

http://www.boat-fuel-economy.com/volvo-penta-diesel-d4-260-300-fuel-consumption-liters

 

[QBhoy]

Obviously scroll on until you get to a d12 or d13 similar.

 

[Portofino]

We have similiar engines 12.8L -700 hp 6,s
Fortunately with quite a bit of data readily available ,so I may be able to assist ?
18L/hr (per side) is just under 800rpm for us just over 8 knots --maybe same as you 8.2 ish .

I D speed @ 825-850 rpm 9.2 knots just over 9 -consuption rises to 20- 22 ish making total 40-44 ish
Load is from memory 50 somthing % EGT,s way down 400 degrees .Ideally to burn off all the crud -soot etc- aiding longevity it needs to be 500 degrees or more .

9 point something is a nice Number man maths as I think it's 10 mph .
10 knots I think we are pushing a bow wave ,ie over optimal D speed and consuption starts to rise 60-70 /L -total ,load and EGT go up .

This is where it's gets tricky as load /EGT are related to fuel in g/h burned .

Any how figure on 40-45 l/h @9 . Something knots or 10mph
Dived between your 2600 is as you suspect about 1/2 of 1000miles --- I think .500-600 mikes in all

My tick over is 7.2 knots 600 rpm .
After a period @ D I tend to finish on the plane anyhow to raise the EGT ,s to burn off /flush out any soot ,so the last 15-30 mins we are doing 170-180 l/h ,so using up to 1/2 that say 70-90 L to add on .

We only do D -not for fuel consuption issues Basicslly to not arrive too soon ,or turned around to spend more time motoring .
Plotter tells me time to target and eta ,distance to run so with that data and the fuel data from the MMDS I can play about a bit .
Tbh I,ve recently in a similar mind figured out a slow Eco planing speed -think about 1550 rpm 24/25 knots between 60/70 L/h per side .
16-17 00 rpm gives 27/28 knots -get about 80 L/h , 80 % load -this where we spend most of the time -in that zone .

1850 is about 30 knots and normally under 90 % load . 90 l/h so 180 total .-that's my fast cruise .
Don,t like going over 90 % load or near 600 degrees EGT,s. for long ,but occasionally if the "red mist " comes down I will ease up to 2000 rpm 34 knots + but L/h goes over 100 per side .
I have seen 120l/h at WOT with a light fuel load etc high thirties ,knots or 40 mph --just with 2400 L tankage that's easy maths 240 L/h 10x40 = 400 miles engine load is 98% or even 100 and EGT,s 625 ish ?

A dirty prop knocks all those numbers down except L/h which goes up by x _%
The max I do with a dirty prop is 95 % load anyhow -depends

So @D 825/850 rpm 9 .x knots or 10mph with a 12.7 L engine x2
2400 L @40 L/h -= 60 hrs x10 miles = 600 miles
Summary
2400 L ---D range 600 miles @ 10mph
WOT --range 400 miles. @40 mph

So can,t see you getting 1000 miles out of 2600L

I can't Remenber tick over figure s cos in the marina ,I,am busy trying not to hit anything ,what i do know is at idle they are 3/4 L/h in N @ the dock ,but soon as you click in gear ,put some load on it goes up 12 ? So combined 24 l/h @ 7 . X ? Knots ,buy its madness to go around @ 600rpm .

So for me conveniently 24 into 2400 gives 100 x say 7.3 = 730 miles or your 2600 a bit more 24 into 2600 -108 xyour 6 knots --about 800 miles until they suck air and stop .
Remember no reserve calc ,s these .

But you would not want to do 108 hrs @ tick over ? -you are gonna have to get the EGT,s up in the interest of engine longevity -from memory they drop way down 200 and something ,that's waaaay off optimum 500- 550 degrees for proper fuel burn .
In fact the MAN manual states avoid tickover for more than 5 mins -"turn off the engines " if longer .

So yup you are correct to challange to 1000 mike range from 2600 L

So for me we just sit @ 1650/1750 ish rpm 27/28 knots all day --it's a planing boat ,so too is yours .