Phantom 46 speed vs fuel consumption

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crazy4557

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As the Fairline Phantom 46 is a known quantity having been launched some 9 years ago does anyone have the fuel consumption vs speed graph.
Mine runs the TAMD 74p's with 500 hours and recently serviced and a clean bum. I generally cruise around the 20 - 22 knots running about 2000 - 2100 rpm.

Can anyone suggest from experience of this boat/engine size if this is the best speed range to give the most cost effective fuel consumption or whether to increase the speed to give less load but higher rpm and possibly better mpg?
What with fuel at 80ppl+ any easy tips of reducing the usage would be gratefully accepted....
 
Hi Andy, thought you had asked me before about this.

My friends p 46 the one I look after does average 0.7 mpg thats around 2200rpm giving approx 22 knots on an average tide direction, you wont get a deal better than that.
 
I have 74P's, albeit in an S48. At 2000/2050 RPM, giving 21kts through the water, the fuel flow meters show each engine using 2.4 litres per mile when going WITH a 2 knot tide, rising to around 2.8/2.9 litres per mile when punching INTO the same tide.

Presumably, these (Volvo) meters are reasonably accurate Paul??
 
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nicho said:
I have 74P's, albeit in an S48. At 2000/2050 RPM, giving 21kts through the water, the fuel flow meters show each engine using 2.4 litres per mile when going WITH a 2 knot tide, rising to around 2.8/2.9 litres per mile when punching INTO the same tide.
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That's just nuts. It doesn't make any sense at all. That just cannot be happenening, at least not with any repeatability, unless your boat is haunted or something, because a boat engine cannot sense tidal flow. Surely you are mistaken? Did you mean SOG?
 
jfm said:
That's just nuts. It doesn't make any sense at all. That just cannot be happenening, at least not with any repeatability, unless your boat is haunted or something, because a boat engine cannot sense tidal flow. Surely you are mistaken? Did you mean SOG?
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He has to mean SOG otherwise it doesn't make sense. Even so it seems a hell of a difference, 20% more fuel for, in effect, 4 kts difference
 
Hi guys. They read litres used per mile when on the move when boat SOG is fed into the unit from the gps (litres per hour when stood still). If you have two kts of tide working against you, it takes longer to cover that mile, hence more fuel is used to cover that mile.

We are currently in Dartmouth. Halfway across Lyme Bay, the tide turned and the llpm gradually reduced from around 2.6 lpm each to 2.4. The bigger the tide against you, the more fuel you use to cover a mile if the boat speed remains constant.

Anyway, that's how I understand it from the manual, but I am happy to be corrected by a higher authority!
 
volvopaul said:
Hi Andy, thought you had asked me before about this.

My friends p 46 the one I look after does average 0.7 mpg thats around 2200rpm giving approx 22 knots on an average tide direction, you wont get a deal better than that.
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Pual,

If I can achieve .75mpg by travelling at say 21 knots at 2100rpm then that's a worthwile saving of 7%. Multiply that over a season means a few extra freebie gallons! It's bit hyperthetical but in reality having as close an optimum rpm has to the best balance for saving fuel.
 
Deleted User said:
He has to mean SOG otherwise it doesn't make sense. Even so it seems a hell of a difference, 20% more fuel for, in effect, 4 kts difference
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Hi Mike,

I think that's about right isn't it? At 20 knots speed through the water, two knots of tide with you, as opposed to two knots against you = 4 knots or 20%. I don't think we always realise just how much a fuel penalty there is by punching the tide. In these tough economic times, perhaps we should pay more attention to tides. Coming to Dartmouth last week, we had spring tides against us all the way, except for the last 90 minutes. I reckon it added half an hour to our journey (and around an extra 50 litres of fuel)
 
The magazines these days use engine manaufacturers power curves as they cant be arsed to set up the fuel monitoring equipment. this does not give the interface between the actual drag of the hull at different speeds and what thrust the powertrain develops and then the actual litres per mile through the water.

Ihave older 63p's without fuel burn metres and I want to do the same for my boat a semidisplacement. I looked at an american Floscan system which is quite expensive and teh range interface with strong tides is pretty useless so I was looking for How much am i burning at various speeds and where the sweet spot is for economical cruising.

Easiest option is if Fairline will let you have the data for a Phantom 46 , they may not let you have it for commercial reasons, but you can ask.

Option 2 is to find someone with the same boat and same engines but with the Volvo Penta fuel burn software and ask them niceley to run their boat and let you have the LPM at certain RPM's say every 200 from 1200 rpm to flat out and draw a graph.

I would have thought your sweet spot for reasonable progress at a near cruising speed is about 18 knots otherwise off the plane at 12 to 13.

Tim Bartlett has views on this, first i would ask Fairline.

A very important factor is the cleanliness of your hull, MBM did an exercise where they measured the fuel burn on a Princess 435 at certain rpm's at 12 months since a pressure wash and antifoul and then following a wash and antifoul. I reworked the figures to give Litres per mile and if like most folk you run at a set cruising RPM the difference before and after was 29.5% more fuel per nm through the water. If you do a lot of hours it is worth considering a wash partway through the season I do and the speed and fuel burn after is markedly less.
 
A very important factor is the cleanliness of your hull, MBM did an exercise where they measured the fuel burn on a Princess 435 at certain rpm's at 12 months since a pressure wash and antifoul and then following a wash and antifoul. I reworked the figures to give Litres per mile and if like most folk you run at a set cruising RPM the difference before and after was 29.5% more fuel per nm through the water. If you do a lot of hours it is worth considering a wash partway through the season I do and the speed and fuel burn after is markedly less.[/QUOTE]



I only went back in the water in March so will be a reasonably clean bum but not good enough to give ideal performance. I'm going for a lift and blast before my summer cruise to the West Country then Guernsey.......will need the best economy possible for that little journey!

I will try the fairline factory request, if not maybe someone on here has a 46 with the fuel burn data equipment, would be pleased to here from anyone with this.
 
nicho said:
Hi guys. They read litres used per mile when on the move when boat SOG is fed into the unit from the gps (litres per hour when stood still). If you have two kts of tide working against you, it takes longer to cover that mile, hence more fuel is used to cover that mile.

We are currently in Dartmouth. Halfway across Lyme Bay, the tide turned and the llpm gradually reduced from around 2.6 lpm each to 2.4. The bigger the tide against you, the more fuel you use to cover a mile if the boat speed remains constant.

Anyway, that's how I understand it from the manual, but I am happy to be corrected by a higher authority!
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Thats right but, in your first post, you said "through the water" which is why we queried it
 
jimg said:
Hope you are enjoying the rain and wind today.

Where abouts are you?
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B28, Darthaven Marina. We've been here a week now, and the weather has been just right for us generally - reasonable temperatures, sun and cloud and a couple of less good days. We are here until Friday, then we are going to Weymouth.

We've been caning our bus passes all week, Salcombe, Totnes, Brixham etc. Never used them before, but they are great!!

We have friends here too on their Broom 425. Are you in the vicinity?
 
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