2008 PHANTOM 50 FUEL BURN?

[SC35]

The point still stands ... if running at lower rpms at the same speed, this means that the engine with the higher output will be running closer to an overload condition throughout the rev range.
See the definition of being "over propped" and what ultimately happens if you were take this to the extreme.

But as I said, the components inside the engines will have been specced and tested to have a reasonable lifetime with the uprated output.
As to running at slightly lower rpm, that's most likely not much of a benefit: as above, leisure marine engines rarely "wear out".

 

[jrudge]

No idea how engine life comes into consumption. Anyway.

To the op I have d12/715 in my squadron 58. In flat water if the boat is clean I am 7/8 l per nm. If dirty then up to 10/11 l per nm. The 58 is bigger so yours should be better than that.

I have real time consumption display so can see it degrade when the hull is dirty. Also whilst it may of may not be obvious the consumption rises significantly in rougher seas.

Personally I would make a trip of it and spend a few days in mallorca and Ibiza but time may not allow

 

[SC35]

Remember guys the longer lasting lower rated commercial engines of the same block run at LOWER rpms .

Indeed.
The commercial versions turn down the wick and prevent operation at the upper end of the scale both in terms of RPMs and power output.

 

[Portofino]

The point still stands ... if running at lower rpms at the same speed, this means that the engine with the higher output will be running closer to an overload condition throughout the rev range.
See the definition of being "over propped" and what ultimately happens if you were take this to the extreme.

But as I said, the components inside the engines will have been specced and tested to have a reasonable lifetime with the uprated output.
As to running at slightly lower rpm, that's most likely not much of a benefit: as above, leisure marine engines rarely "wear out".

The engine with the higher output surely has a greater denominator the lower number just to be clear , because it’s greater bang ( to remap etc ) so you have it the wrong way round , it will be further away from its 100 % or potential overload compared with the lower .

Eg 95 L over 100 = 95 % load
95/ 110 = 86% load

95 L being the same number to make the same Hp move the same hull at the same knots .
110 being the new max wot fuel burn of the updated same block motor To get that additional Hp it needs to create a bigger bang , the remap has squirted more fuel added an extra event in the multiple injector behaviour, ie gone up from 5 to 7 events / opening s , net result it makes a few more ponies . But it is not taking its full Hp never see s 110

But in reality if you factor in the diff prop which you did quite rightly initially the higher Hp might get the same speed at lower rpms with that a lower load fwiw , and obviously obviously lower wear .

As said the commercial guys aim to lower the rpms for longevity.

load is an algorithm I am not disputing that , what JFM posted , just dropping in lower rpms ( with in spec ie not chronic under loading as per Mapishs unhelpful tick over at the dock )

If you can somehow as boats age bear in mind lowering the load it helps as the yrs go by with longevity.
The links I posted support that .

@ JRudge I know you are late but we arrived at the fuel burn early no one’s disputing the range given for the Op.

What we did not see at at the start , sea trial info relating to wether it reached rate rpm .
We got its speed fwiw ? But the really interesting number is wether it reached rated rpm and that’s why I said “ speed is irrelevant “ which sparked all this off .
So really in factoring in the cruise speed I would want to know wether it reached its rated rpm .
Fuel burn is related to wether it’s overloaded ie the load .



Technically we don’t know because we never got confirmation it reached rated rpm @ WOT .So in some ways bringing in load and potential overload is relevant .

 

[MapisM]

not chronic under loading as per Mapishs unhelpful tick over at the dock

Guilty as charged for having (willingly) made an unhelpful comment, in the hope to be at least funny.
As opposed to your reiterated reasoning, which pretty sure isn't - and neither useful, for that matter.

 

[Portofino]

Guilty as charged for having (willingly) made an unhelpful comment, in the hope to be at least funny.
As opposed to your reiterated reasoning, which pretty sure isn't - and neither useful, for that matter.

It’s very useful to know if the boat reached rpm at wot .See my post #4 .
Also see post #11 bt SC35 , the graph .

SC 35 failed to mention it only applies if the boat reaches rated rpm at wot , which is what I said .

If it doesn’t then this graphs pretty meaningless .He’s gonna be up at the higher end or over of the ranges suggested .

 

[SC35]

The graph quite clearly says "at calculated propellor load".
If the boat was failing to reach rated rpm at wot then the propellor load and the curve would be different.
The graph is only indicative anyway, as it doesn't take into account "hump speeds" of actual hulls for example.

 

[Portofino]

The graph quite clearly says "at calculated propellor load".
If the boat was failing to reach rated rpm at wot then the propellor load and the curve would be different.
The graph is only indicative anyway, as it doesn't take into account "hump speeds" of actual hulls for example.

That’s the point we don’t know the Op s boat it’s reaching rated rpm .That’s was my point waaay back @ post #4 .

Fast Fwds 10 - 20 yrs and there’s a risk said OP s or anyones now can’t.So invalidates using manufacturers graphs .
Those graphs assume rated rpm is achieved.If it can’t reach rated rpm the fuel burn gonna be higher across the rev range .Worth knowing imho before doing the range maths



.Before anyone bites my head off of course I only have pics / info of the infamous Itama , why would I not ?

Show me your rated rpms at wot guys !

This is what you need to see first to validate your engine manufacturers graph .
WOT for me btw 2200 . 20 yr old tub with 20 y old in excess of 1000 hrs engines .Taken last Sep , boat into the water early June .No pre sterngear / hull cleaning , just taken out “as is “.



Just the top line from your tachometer or better still if sea trialing an engineer with a strobe in the ER checking tacho calibration .I realise not everyone’s got screens or an engineer like VP tucked away with a strobe in the ER .
But I will accept a tachometer pic only .


From the Ops maths roughly 2000 L full tanks he thinks he will burn 14/1500 L leaving an acceptable 500 L , 1/4 left .
This is working on 8-9 L NM , of which there’s no disagreement .
But if it’s effectively overloaded by a figure yet to be worked out because we haven’t got the rated rpm , …..and he sets cruise at 25 knots he might eat up a large quantity of those 500 L a dangerous quantity.We just don’t know .

Esp if 1900 rpm is giving 23 knots and there’s big ( ish realise to boat size ) waves on the nose , a strong wind on the nose , poor new boat to him trimming etc etc To get to 25 knot it’s gonna need 2000 to 2100 rpm + with full tanks .

 

[John100156]

Thanks for all the posts and informative comments and arguements; we completed a well planned and executed trip from Portals Nous Marina to Marina de Las Salinas commencing at 07:00 on 24th July, I will do a write up in the next day or so, bumpy as predicted for the last 50nm.

Now with respect to fuel burn etc, this is how the boat actually perfromed on the trip:

a) Full fuel and water loads, two crew
b) Actual trip length 262nm
c) 75% relatively flat sea, 0.1m to 0.5m swells and calm wind state
d) 25% rough and lumpy having to throttle back
e) Cruised perfectly at 25-6 knots and 2000rpm
f) Throttled back to 16 knots (less economical I know) to minimise slamming and meet the frequency of the waves on the nose
g) Actual trip duration: 10 hours
h) Total tank(s) capacity: 1980L
i) Approximate amount of fuel burn: 1612L

The following data prepared for the owner (and former berth holder at Sant Carles de La Rapita) shows useful data on this size of boat and engine layout:



I hope to post a report with images of the trip in the next few days.

Thanks again to all those that commented - I hope you find the above of interest...!

 

[MapisM]

b) Actual trip length 262nm
g) Actual trip duration: 10 hours
i) Approximate amount of fuel burn: 1612L

That means an overall average speed of 26kts, with just a tad more than 6 litres/Nm fuel burn.
A very good result indeed!

 

[Sticky Fingers]

That means an overall average speed of 26kts, with just a tad more than 6 litres/Nm fuel burn.
A very good result indeed!

Seems surprisingly reasonable. Very good, I’d be happy with that.

 

[John100156]

Yes I must say I was quite surprised of actual compared to theoretical, the boat was well trimmed and did perform really well, much to the delight of the new owner. It seems this match of engines/boat works really well, mind you it had only just been antifouled and engines fully serviced...!

These were the sort of conditions (As predicted by Windy) running around the top of Ibiza, fierce I know, it was hard work but someone had to do it ;-)

 

[Sticky Fingers]

How do these figures compare with your P45 @John100156, I would assume a little higher.

 

[John100156]

That means an overall average speed of 26kts, with just a tad more than 6 litres/Nm fuel burn.
A very good result indeed!

Yes, the chart is accurate but checking there must be something wrong I think with the total mileage 'logged' figures scribbled down, it was bumpy. It seems far too long for the journey, creating a false actual fuel burn figure. I will plot the actual route taken from the hourly Lat/Long recordings taken on route, tomorrow. I estimated the trip length around 200-220nm max., we cannot possibly have done 262nm.

@Sticky Fingers
With regard to my P45, I have not done a similar exercise on as long a trip as this, from full-full yet, so I usually estimate burning about 5 litres/nm with a mixture of cruising and some pootling.

 

[Sticky Fingers]

That seems about right. Be interesting to see how the P50 figures come out after re plotting the mileage.

 

[John100156]

OK there was an incorrect entry in the passage log, I blame the crew...! I just called out the numbers (need one of Hurricanes talking loggers)

Corrected figures as follows:

a) Full fuel and water loads, two crew
b) Actual trip length 212.9nm
c) 75% relatively flat sea, 0.1m to 0.5m swells and calm wind state
d) 25% rough and lumpy having to throttle back
e) Cruised perfectly at 25-6 knots and 2000rpm
f) Throttled back to 16 knots (less economical I know) to minimise slamming and meet the frequency of the waves on the nose
g) Actual trip duration: 10 hours
h) Total tank(s) capacity: 1980L
i) Approximate amount of fuel burn: 1612L

Final fuel burn for this trip: 1612/212.9 = 7.57 litres/nm

I originally estimated (#1) 175 litres/hour, based on an 8 hour run, but due to weather conditions we actually achieved 161 litres/hour on a 10 hour run likely due to throttling back.

Actual route taken:



Plus a few shots taken on the way:

First is Portals Nous marina - Last is proud new owner in Puerto de Las Salinas:

 

[roa312]

Thank you for sharing the data and images. It's interesting to see, because the D12 715hp engine was used in many different boats spanning quite a range in sizes.

 

[Portofino]

Great thread thx .You ought to see if reaches rated WOT , rpm s while Its fresh / clean .
Tis the only date missing .

 

[jfm]

Thanks John. Nice data- nice trip.

 

[Sticky Fingers]

Thanks for the update. Makes the average speed look more plausible too, of course. Great to see the pictures too