davids0865
Well-Known Member
Fantastic, looks like the boat I will buy s/h in 20 years time.............no, can that I'll be too flipping old!
The costs of pulling the throttles back
- Thread starter dylanwinter
- Start date
Fantastic, looks like the boat I will buy s/h in 20 years time.............no, can that I'll be too flipping old!
MapisM
Well-Known Member
Precisely.
Of course, hours will still be a good enough indicator for those boats that can't actually be used at anything else than their "typical" speed, like pure displacement trawlers. But as P boats, possibly with stabs, are increasingly used also at slow speed, the difference can be relevant.
Though in fairness, I don't think anyone would change the boating habits for resale considerations alone - and rightly so!
Nick_H
Well-Known Member
How many boats have fuel monitoring anyway, is it now fairly standard on mainstream marine engines?
BartW
Well-Known Member
J,
When you're doing this capture,
could you make at the same time a simple table:
speed, RPM, consumption,
at different (constant) cruising speeds, 5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,2324,25, ..30 kn
and then calculate cons/hr and cons/nm
would be interesting to see the curve,
especially in the semi displacement area, (which speed to avoid...)
and the full planing area (has 19kn the same consumption as 22kn per mile ? boat has less drag...etc)
your hull and engines are different, but there must be some similarity's with my boat,
and I can't read the data as you know
rustybarge
Well-Known Member
Keen_Ed
Well-Known Member
It's not that you're only making six knots. It's the fact that you're sailing. For me, a day on the water only really starts when the engine gets switched off, the magic of c
lift and drag takes over.
D
Deleted User YDKXO
Guest
Well that can only be related to operating hours. If I was a buyer looking at your boat and the engine hour meters said 200hrs, I'd say s**t he's run it flat out everywhere and run a mile. If on the other hand, the hour meters said 1000hrs, I'd think s**t he's never worked the engines and also run a mile. If the hour meters said 600hrs, I'd probably say that's a fair mix of fast and slow cruising and buy the boat
But my point remains; until total fuel burn is a widely available and accepted figure, operating hours is going to be the major indicator of engine condition to boat buyers and, all things being equal, a high hours boat is worth less than a low hours one.Incidentally, in the construction equipment industry, operating hours is still a major determinant of value, despite fuel burn data being routinely recorded and analysed
Tender_aft
Well-Known Member
Well that can only be related to operating hours. If I was a buyer looking at your boat and the engine hour meters said 200hrs, I'd say s**t he's run it flat out everywhere and run a mile. If on the other hand, the hour meters said 1000hrs, I'd think s**t he's never worked the engines and also run a mile. If the hour meters said 600hrs, I'd probably say that's a fair mix of fast and slow cruising and buy the boat
Incidentally, in the construction equipment industry, operating hours is still a major determinant of value, despite fuel burn data being routinely recorded and analysed
But none of that takes account of the bad drivers that go straight to WOT and back to tickover, which is a killer for engines. I guess that is why oil analysis and cameras in cylinders is the next step.
With modern engines even this data can be collected of course....it's just whether they choose to.
rbcoomer
Well-Known Member
I misinterpreted that at first and was thinking along the lines of underwater cameras: Thought "that's an interesting concept - going to need a pretty fast shutter speed to capture any detail and keeping the lens clean could be fun..."
Then brain caught up with what you meant. 
D
Deleted User YDKXO
Guest
I know this is not relevant to your boat but I did this for my existing boat about 3 yrs ago using the lph data from the Cat engine instrumentation and noting the GPS speed. I chose a flat calm day with the boat having about 50% fuel/water and blackwater tank loads and 3 people on board to represent an average load. The hull was clean and at every speed, I optimised the boat speed using the trim tabs. The nmpg v speed curve looks like this
3 things surprised me. First, at D speeds, the fuel consumption climbs significantly from minimum in gear speed of about 7.7kts to a fast D speed at about 10kts at which the fuel consumption is more than doubled. Second, at least on my boat, there doesn't seem to be an inefficient hump speed at which going faster uses less fuel. Third, there is little difference in fuel consumption between 15kts and 25kts and between 20 and 25kts, the fuel consumption in nmpg terms is constant. I suppose this makes sense in that a planing boat design like mine must be optimised to cruise in the 15-25kt range.
FWIW, I then used these figures to construct a range v speed curve for my boat. The figures given for range assume zero safety margin
Just a bit of a caveat here. I don't know how accurate the lph data from the engine instrumentation is, especially at v low speeds. However, based on actual fuel consumption over the 4 seasons I've owned the boat, it does consume fuel at an average rate of around 0.65 - 0.7nmpg so the engine instrumentation data is there or thereabouts
rustybarge
Well-Known Member
Just wondering how accurate the slow speed numbers are. There was an article in MBM a couple of years ago about a 52' privateer twin engined(120hp?)displ. Boat that went across biscay to Majorca, and back again to the Uk, and they averaged about 2-2.5mpg IIRC at 7 kts.
D
Deleted User YDKXO
Guest
A common misconception. People often assume that just because a boat is only designed for displacement speeds, it is, by definition, more economical than a planing boat at displacement speeds. In fact it's usually quite the opposite. A planing boat at 7kts is usually more economical than a displacement boat at 7kts and the reason for that, of course, is that planing boats have to be built much lighter to be able to plane whereas displacement boats have no such weight constraint. My Ferretti 53 may be a similar length to a Privateer 52 but the Privateer weighs about 11 tonnes more and, however good the hull design, it costs fuel to push around a heavier boat
Hurricane
Well-Known Member
Well that can only be related to operating hours. If I was a buyer looking at your boat and the engine hour meters said 200hrs, I'd say s**t he's run it flat out everywhere and run a mile. If on the other hand, the hour meters said 1000hrs, I'd think s**t he's never worked the engines and also run a mile. If the hour meters said 600hrs, I'd probably say that's a fair mix of fast and slow cruising and buy the boat
Incidentally, in the construction equipment industry, operating hours is still a major determinant of value, despite fuel burn data being routinely recorded and analysed
Interesting - our engines are showing a tad over 600 hours!!!
Does that make me a careful owner?
Actually, our engine management system won't let me thrash our engines
When cold, they won't power up to cruising speed without a proper "ramp up"
When hot they still "ramp up" but over a different time frame.
A friend once drove her and was disappointed that the power didn't come up immediately.
There are override buttons that will give full power whatever but they've never been used - I believe that the engine management system records and reports any abuse to the factory when next connected to an engineers computer.
I've always assumed that average use for most boats is about 100 hours per year.
D
Deleted User YDKXO
Guest
Yes and it makes me a careful poster
bozlite
Well-Known Member
This seems to fit with something I read in an article by Andrew (?) Wolstenholme, which pointed out that, although you can calculate the hull speed of a boat by the sq. root x 1.34 formula, there will be a doubling of resistance as you go from 1x sq. root to 1.34 x sq. root. By this reckoning the most efficient displacement speed for your boat would be just over 7 knots.
D
Deleted User YDKXO
Guest
Actually, my boat's most efficient displacement speed is on one engine only at which she is still making 5kts and consuming fuel at a rate of 4.3nmpg. IMHO all this proves is the old adage that speed costs fuel. The slower you can go, the less fuel you will use doing it
oceanfroggie
Well-Known Member
Its an interesting dilemma, measure fuel cost against total time spent on the water, or against distances covered.
The two are not the same thing!
The two are not the same thing!
Firefly625
Well-Known Member
2012 average fuel consumption on our Hardy Mariner (4.5 tonne, 26ft, 230hp Yanmar, SD hull) was exactly 10LPH, we normally cruise at 2700rpm which gives us between 15 & 17knots depending on conditions, sometimes we plod at 7 knots if weather lovely and not in a hurry but more often that is not the case. Each fill up I log consumption / mpg etc and this year we have had as low as 7.5LPH and as high at 12.5LPH so I would imagine average will be about the same as last year... I think that it pretty good.
rustybarge
Well-Known Member
With Ref. to the ultimate engine test MBM last year, an Aquador 23' , 2.4 tons, 220hp volvo uses 18.5 ltr/hr at 18 kts.....
Nearly twice your consumtion.
Firefly625
Well-Known Member
Yup, when ever I get chatting to folk who believe they have a really economic mobo, they always are a little surprised when I tell them of our cumsumption (or lack of it)