Boat in build pics (Squadron 78)

Hurricane said:
Mike
What are you saying?
I've only really noticed the massive drop in fuel consumption from planing to displacement.
I didn’t think there was a huge difference once you get below or into displacement speed.

Sorry jfm - thread drift - don’t want to increase the size of this thread unnecessarily!!:)
Click to expand...

For sure there will be a big difference in fuel consumption at low d speeds compared to high d speeds. Take your 67 footer which I'm guessing has a waterline length of about 55ft; the theoretical max hull speed is given by 1.34 x sq rt of waterline length which is about 9.9kts. Obviously with a planing or semi-d boat, the boat transitions into planing mode above this speed but, at, say 9.5kts, you'll still be in d mode and pushing a massive bow wave. You would save a lot of fuel by slowing down further; in fact the optimum speed would be the minimum in gear idle speed at I guess around 6-7kts in your case. You could possibly save even more fuel by running on one engine but then there might be an issue with overloading the gearbox on the other engine due to freewheeling the other prop.
I know its not a similar boat but I was looking at a test of Nordhavn 57 the other day which achieved 2.5mpg @ 6kts and only 1.2mpg @ 9kts so the effect of slowing down, even in d mode, is significant
 
Deleted User said:
For sure there will be a big difference in fuel consumption at low d speeds compared to high d speeds. Take your 67 footer which I'm guessing has a waterline length of about 55ft; the theoretical max hull speed is given by 1.34 x sq rt of waterline length which is about 9.9kts. Obviously with a planing or semi-d boat, the boat transitions into planing mode above this speed but, at, say 9.5kts, you'll still be in d mode and pushing a massive bow wave. You would save a lot of fuel by slowing down further; in fact the optimum speed would be the minimum in gear idle speed at I guess around 6-7kts in your case. You could possibly save even more fuel by running on one engine but then there might be an issue with overloading the gearbox on the other engine due to freewheeling the other prop.
I know its not a similar boat but I was looking at a test of Nordhavn 57 the other day which achieved 2.5mpg @ 6kts and only 1.2mpg @ 9kts so the effect of slowing down, even in d mode, is significant
Click to expand...

Interesting, I thought that the point about displacement speed is that you dont "push" a bow wave. I supose (thinking about it) you must and its lifting the bow onto it which affects the consumption big time.
Even then, I didnt appreciate that there would be significantly more to run at just below max d speed that at (say) half d speed.
I have, however, noticed that the electronic displays show a good reduction in consumption at lower d speeds.
IIRC at tick over (about 5 knots) each of my engines burns 7 or 8 litres per hour whereas at 9.5 knots it is aboyt 25 litres per hour (again only theoretical figures from the engine management system). So thats about a third of the consumption to go half as far - definately not the massive saving that you get between d speed and p speed.
Your comments interesting though.
 
Deleted User said:
For sure there will be a big difference in fuel consumption at low d speeds compared to high d speeds. Take your 67 footer which I'm guessing has a waterline length of about 55ft; the theoretical max hull speed is given by 1.34 x sq rt of waterline length which is about 9.9kts. Obviously with a planing or semi-d boat, the boat transitions into planing mode above this speed but, at, say 9.5kts, you'll still be in d mode and pushing a massive bow wave. You would save a lot of fuel by slowing down further; in fact the optimum speed would be the minimum in gear idle speed at I guess around 6-7kts in your case. You could possibly save even more fuel by running on one engine but then there might be an issue with overloading the gearbox on the other engine due to freewheeling the other prop.
I know its not a similar boat but I was looking at a test of Nordhavn 57 the other day which achieved 2.5mpg @ 6kts and only 1.2mpg @ 9kts so the effect of slowing down, even in d mode, is significant
Click to expand...

That seems to make good sense Deleted User

Psychologically though, I find myself wanting to consider my d range to be whatever it is at near hull speed, say 9kts, rather than 5 or 6 knots which might double my mpg. 9-10kts is pretty slow but somehow quite nice (on occasions, not all the time), whereas 6 kts is blooody awful slow and not nice, and i can't see myself ever planning a cruise say France Corsica 100nm at 6kts = 17hours. Indeed, I'd prob spend those 17 hours wondering if the depreciation hit of selling the boat with 1200hrs rather than 700 (say) will cost me more than the fuel saved :-). Just imho, but I think Hurricane has found the same: he speaks of nice slow crusing/pootling, but I think he means 9-10kts not drive-you-mad 5-6kts
 
Hurricane said:
again only theoretical figures from the engine management system
Click to expand...

Hurricane, are the flow rates theoretical only? Are there not sensors measuring flow rate and return-to-tank rate, and subtracting to give a true measured burn rate? Did you learn details of this at MTU training centre?
 
jfm said:
Hurricane, are the flow rates theoretical only? Are there not sensors measuring flow rate and return-to-tank rate, and subtracting to give a true measured burn rate? Did you learn details of this at MTU training centre?
Click to expand...

There was so much on the course that I cant remember.
I believe the engine management system has some logic incorporated so that it can calculate how much load the engine is under. I think they then map this data to a theoretical fuel burn rate which is then shown on the dash displays as litres per hour. When we took delivery of the boat, I wasn't sure how accurate they would be so I ran some tests and have continued to monitor them since - the burn rate is remarkably accurate.
 
Deleted User said:
Trac stabilizers have been fitted to relatively small displacement boats for years so I guess the transition to smaller planing boats would not be a major step for them. Do you know if the fins and the actuating mechanism are beefed up for planing boat applications as I guess the potential forces on a stabiliser fin are many times higher at 30kts than at 6kts?
Whats the performance issue with the Seakeeper system? Is it the start up time?
Click to expand...

Yup that's right, could even see these on 38ft dayboats in the near future. AFAIK the TRAC actuator assemblies are the same for D or P boats, certainly never seen any info to the contrary. There are however different size fins available for each actuator size. The size fin chosen will depend on your hull, displacement etc and whether STAR (STabilisation At Rest)has been selected.

Yes the start up time is not ideal with the gyro system, nor is the counter dynamic forces on the boat when turning, I call it "bottom wobble" and experienced it in a Manhattan 70 last year. The Gyro is fitted in the crew cabin. Bit like the sensation you get when moving a hand held spinning top through 90 degrees back and forth. The space issue is also a disadvantage, these systems take up a large amount of room, a bigger problem for smaller boats, and on larger boats you may need two which makes it worse actually.
 
jfm said:
That seems to make good sense Deleted User

Psychologically though, I find myself wanting to consider my d range to be whatever it is at near hull speed, say 9kts, rather than 5 or 6 knots which might double my mpg. 9-10kts is pretty slow but somehow quite nice (on occasions, not all the time), whereas 6 kts is blooody awful slow and not nice, and i can't see myself ever planning a cruise say France Corsica 100nm at 6kts = 17hours. Indeed, I'd prob spend those 17 hours wondering if the depreciation hit of selling the boat with 1200hrs rather than 700 (say) will cost me more than the fuel saved :-). Just imho, but I think Hurricane has found the same: he speaks of nice slow crusing/pootling, but I think he means 9-10kts not drive-you-mad 5-6kts
Click to expand...

One more consideration to take into account: while I'm not sure if this is relevant with your engines, but AFAIK running for prolonged periods at just tick over is not healthy for the engines as the exhaust gases tend to linger around the turbos, etc. clogging things up. Revving slightly higher blows the exhaust gases out properly. Apparently modern diesel engines are not very happy being run at idle.

I'm stealing the opportunity to congratulate you on 'Match'. Se is absolutely fantastic!!! And many thanks for this infinitely interesting thread. The effort you've put into sharing this marvelous experience with the like-minded 'boatmad' people of this forum is appreciated beyond words.
 
Last edited:
Deleted User said:
Out of interest why cant the boat be sold to US buyers in US waters?
Click to expand...

It's an import tax thing in the US. Quite common to see non tax paid boats in US waters advertised in this way. A yacht built outside the US can be in US waters without paying the tax, but offering such a yacht for sale to US residents, while in US waters, triggers liability ofr the import tax. So, US residents can purchase a non-US-registered yacht, keep it outside the US, and not be liable for duty on it, but the yacht must also be offered to them entirely outside the US
 
Hurricane said:
I believe the engine management system has some logic incorporated so that it can calculate how much load the engine is under. I think they then map this data to a theoretical fuel burn rate which is then shown on the dash displays as litres per hour.
Click to expand...
I might be totally wrong on this, because I never investigated this matter in detail.
But just on a common sense basis, I always thought that with modern electronically controlled engines, showing the real time consumption is just a matter of using the ECU outputs and do the math.
I mean, since the ECU decides how much fuel to throw into the cylinders at any given moment (based on the inputs from throttle and various sensors, but that's not relevant in this context), there should be no need to use any other sensors for fuel flow/return: whatever the ECU decides is what the engine burns, period. Unless there's any fault somewhere, of course - e.g. a defective injector, a clogged fuel line, etc.
Therefore, it should be just a matter of writing a software which converts some bits - whose main purpose is to drive the injectors - into other bits whose purpose is to show some numbers in a display.
Happy to stand corrected if anyone knows better!
 
Our engine is much older (2005) but the fuel figures showing on our Garmins comes through the canbus / N2k network from the engine and is calculated from sensors relating to throttle position.

i have no idea how accurate this is yet as havent tested but i dont expect it to be that accurate to be honest as surley the amount of fuel used will depend on the context of what conditions the boat is running in. ie. punching tide at displacement the boat will use more fuel at a given throttle level than running with the tide at same level..
 
jfm said:
OK, let's convene an OB committee meeting in SofF in say May 2011? Tell me a weekend when you're down there and I'll stick it in the boat's diary; we'll ask EME and Gareth along for a Lumishore board meeting or something at the same time :-)
Click to expand...

Make it a date then in May. Can't weight to see Match in the flesh in Antibes, agreed OB committee can convene including LED sub committee. I can't test your passerelle thoroughly now though as I have dropped 4 stones plus since last visit to BH3 ;-)

Enjoy the boat show, I don't think I can get to see her there as I am snowed with new venture warming up, will tell you when I see you. Cheers Wakeup.
 
MapisM said:
Didn't you mean registered rather than built?
Click to expand...

I don't know for sure. There are two US taxes relevant here and to which that yachtbroker statement can affect: import duty (about 12% iirc) and a Use tax (6% iirc). "Built" is relevant to the import duty, whereas "registered" is relevant to the Use tax. I don't know the detail beyond that, could find out if anyone needs to know, and I'm happy to be corrected if anyone knows better (though, tbh, my interest in the topic stops at this level!)
 
wakeup said:
dropped 4 stones plus since last visit to BH3 ;-)
Click to expand...


Blimey! Congratulations on that, and if there's a magic diet publish it on here please. OK, good luck with the venture, and I'll email some suggested SofF dates shortly when I put my diary/year planner head on. Best wishes to K
 
MapisM said:
I might be totally wrong on this, because I never investigated this matter in detail.
But just on a common sense basis, I always thought that with modern electronically controlled engines, showing the real time consumption is just a matter of using the ECU outputs and do the math.
I mean, since the ECU decides how much fuel to throw into the cylinders at any given moment (based on the inputs from throttle and various sensors, but that's not relevant in this context), there should be no need to use any other sensors for fuel flow/return: whatever the ECU decides is what the engine burns, period. Unless there's any fault somewhere, of course - e.g. a defective injector, a clogged fuel line, etc.
Therefore, it should be just a matter of writing a software which converts some bits - whose main purpose is to drive the injectors - into other bits whose purpose is to show some numbers in a display.
Happy to stand corrected if anyone knows better!
Click to expand...

Yes that makes total sense Mapis. In fact it is likely to give a much more accurate result than flow sensors installed in a pipe, becuase those are difficult to make accurate anyhow (due to different fluid velocity at each point across a pipe's diameter)
 
MapisM said:
I might be totally wrong on this, because I never investigated this matter in detail.
But just on a common sense basis, I always thought that with modern electronically controlled engines, showing the real time consumption is just a matter of using the ECU outputs and do the math.
I mean, since the ECU decides how much fuel to throw into the cylinders at any given moment (based on the inputs from throttle and various sensors, but that's not relevant in this context), there should be no need to use any other sensors for fuel flow/return: whatever the ECU decides is what the engine burns, period. Unless there's any fault somewhere, of course - e.g. a defective injector, a clogged fuel line, etc.
Therefore, it should be just a matter of writing a software which converts some bits - whose main purpose is to drive the injectors - into other bits whose purpose is to show some numbers in a display.
Happy to stand corrected if anyone knows better!
Click to expand...

I hadnt thought of it like that.
Your comment makes sense.

We were just told that it was a theoritical calc and I suppose it IS theoritical but when you think about it, the electronics control the injectors accurately so they must know how much fuel is being used and I'm sure that the actual calc is far more complicated. Anyway, as I say, it seems very accurate.
 
jfm said:
I don't know for sure. There are two US taxes relevant here and to which that yachtbroker statement can affect: import duty (about 12% iirc) and a Use tax (6% iirc). "Built" is relevant to the import duty, whereas "registered" is relevant to the Use tax. I don't know the detail beyond that, could find out if anyone needs to know, and I'm happy to be corrected if anyone knows better (though, tbh, my interest in the topic stops at this level!)
Click to expand...

Not much I can ad to that ... other than 'Use Tax' varies by State (6% in Florida) and there are surcharges in some specific counties (I believe), there is also a cap in (for example) Florida of somewhere around $17,500. No need to know either, just picked it up in general tittle-tattle last week so probably wrong.
 
You must log in or register to reply here.

Share this page

Top