Is driving a planing boat at displacement speed a false economy?

[jfm]

Are you chaps measuring consumption with a fuel flow meter?

These days it mosly comes from the engine's ecu by interogating the j1939 bus and bridging that data to the n2k netwrok. This tells you the fuel the ecu wants the engine to get rather than what it gets, the differences being imperfections in the injectors, but that gives you 99% + accuracy. The plotter then does the simple arithmetic of dividing by speed (STW or SOG, you choose) to give mpg

 

[Vitesse]

Thanks, JFM. That's an education! There's a whole world I know nothing about.

My experience with car diesels is that the engine electronics are not robust. I imagine the situation is better with boats, given the different environment and usage patterns.

 

[dj43]

From personal experience , I find it impossible to stop myself nudging the throttles forward ,I tend to start with the
intension of traveling at displacement speed for a leg of a long run, but always seem to have a reason to leave the slow leg for later ,be it tides, weather or that look from swmbo,then impatient's kick's in,so any savings made at displacement speed is lost getting to cruising speed,so this year going to try and do all short trips at displacement and long trips at cruising speed ,got to admit had not thought about the extra engine hrs .

 

[rafiki_]

Thanks, JFM. That's an education! There's a whole world I know nothing about.

My experience with car diesels is that the engine electronics are not robust. I imagine the situation is better with boats, given the different environment and usage patterns.

Modern light and heavy duty diesel electronics are very robust, they have to be to ensure the OBD works and is reliable. Clearly your experience is different.

 

[benjenbav]

Mebbe, in answer to the original conundrum you could run at slow displacement speed on one engine. Alternating the engines would cut the extra hours in half and still give you most of the fuel saving.

 

[gravygraham]

Interesting thread Mike. I would like to say that your buyer B, the closet eco-warrior, is seriously in denial if he's buying a mobo!

 

[MapisM]

The longest trip we did at 7kts lasted about 8hrs and I found that pretty tedious.

This is the key point, which rules out the rest.
If you think along these lines, obviously you have not seen the light (not yet, anyway), so why bother with economics?
Just do the math again with both A and B cruising the same number of hours rather than the same number of miles, and see what happens.

See, what you (and most other posters) are actually saying is that you measure your fun in terms of distance cruised and/or number of places seen for any given timeframe.
Mind, there's nothing wrong with that. I've also done the same for many years, btw.
Actually, you might find that a Pershing with Arnesons is the best type of boat, in this respect.

It's only if and when you will change your mindset, and measure your fun based on the time spent cruising, enjoying the trip, the company, the sea, the comfort and silence, all regardless of the destination, that displacement cruising will be worth considering. And the savings will be just incidental.

But it does take a different approach to the boating thing.
I'd dare saying to the whole way of living, in a sense...

 

[wakeup]

This is the key point, which rules out the rest.
If you think along these lines, obviously you have not seen the light (not yet, anyway), so why bother with economics?
Just do the math again with both A and B cruising the same number of hours rather than the same number of miles, and see what happens.

See, what you (and most other posters) are actually saying is that you measure your fun in terms of distance cruised and/or number of places seen for any given timeframe.
Mind, there's nothing wrong with that. I've also done the same for many years, btw.
Actually, you might find that a Pershing with Arnesons is the best type of boat, in this respect.

It's only if and when you will change your mindset, and measure your fun based on the time spent cruising, enjoying the trip, the company, the sea, the comfort and silence, all regardless of the destination, that displacement cruising will be worth considering. And the savings will be just incidental.

But it does take a different approach to the boating thing.
I'd dare saying to the whole way of living, in a sense...

Do you sit in the lotus position at your helm

 

[vas]

Do you sit in the lotus position at your helm

helm position?

you probably don't even need a seat there!
afaik you only use it during mooring and if things turn nasty (and in either case you don't really seat down, do you?)



that's the whole point (IMHO) a/p on and look at the scenery, read, chat, work

V.

 

[henryf]

And pick up lobster pots because you weren't paying attention

 

[desperatelyseeking]

Yeah but there are plenty of owners like me who still want the option of either going fast or slow when the mood or the necessity take them and therefore a planing boat makes sense in terms of boat choice. At this stage in my boating life I neither want a D boat that is incapable of breaking 10kts and nor do I want a SD boat which uses even more fuel than a P boat at speed

Sounds like the soon to arrive Greenline Ocean Class 57 might be the perfect boat for you. I'm looking forward to seeing how the superdisplacement hull manifests itself in economy. Top end 20knots but efficient at 8-10knots - could be the perfect mix.

 

[Deleted User YDKXO]

Are you chaps measuring consumption with a fuel flow meter?

I'm taking my figures from the Cat engine instrumentation on my boat which gives lph figures. How accurate they are I don't know but the fuel consumptions I have calculated from the indicated lph figures seem to accord with actual fuel usage

 

[Deleted User YDKXO]

If you think along these lines, obviously you have not seen the light (not yet, anyway), so why bother with economics?

I'm trying hard to see the light, Mapism. 22yrs of zooming around at 20kts+ is a habit that is hard to kick

Just do the math again with both A and B cruising the same number of hours rather than the same number of miles, and see what happens.

Thats stating the obvious but then you might as well ask why anyone would buy a boat at all to do 100hrs a year at 7kts

See, what you (and most other posters) are actually saying is that you measure your fun in terms of distance cruised and/or number of places seen for any given timeframe.
It's only if and when you will change your mindset, and measure your fun based on the time spent cruising, enjoying the trip, the company, the sea, the comfort and silence, all regardless of the destination, that displacement cruising will be worth considering. And the savings will be just incidental.

Crikey, you're going to tell me to get a sailing boat next

 

[MapisM]

why anyone would buy a boat at all to do 100hrs a year at 7kts
...
Crikey, you're going to tell me to get a sailing boat next

LOL, you're saying that as if it were a sort of crime...
I can think of a couple of forumites, tcm and magnum, who moved from pretty fast and big mobos to sailboats.
And while I'm not sure about the latter, as I understand Matt cruised quite some miles since then.
In fact, let's face it: for serious long distance cruising, sailboats are much better than mobos in many respects, not just because they burn much less fuel.

Anyway, re. your question above, I for one do.
Ok, I actually cruise at 9 rather than 7 knots, and on average I make maybe 150 rather than 100 hours per season, but you see what I mean.
Otoh, I enjoy every minute of those hours as much (if not more) as I would if I were going faster, which is what really matters, innit?
Besides, since a few years, I typically spend most of my time onboard from may/jun to sep/oct, with roughly one third of it anchored in some of the best waters the Med has to offer. Which means that I actually measure my yearly boating hours in thousands rather than hundreds, regardless of what the engine gauges show.
And to me, that's what really justify the hassle of owning a boat - much more so than the distance cruised.
But each to their own, of course.

Oh, and re. other comments...

@wakeup:
nope, actually I very rarely seat at the helm at all, both on the f/b and inside the p/house. Pretty much as Vas said, in fact.
I understand that it might sound weird and/or risky to anyone used to cruise at P speed, but I can assure you that it's perfectly sensible to be in command on a boat cruising at D speed and have a beer while talking with the other friends onboard.
Of course, I only do that while on the flybridge, with an unrestricted view regardless of whether you are at the helm or not.
But in the Med, that's where you spend most of the cruising time anyway.

@henryf:
Lobster pots? Wazzat? You must really follow jfm suggestions I reckon, and move to some proper cruising grounds...

 

[Spi D]

I'd rather have a well used engine with high hours than a low hour, poorly preserved one....

Frequent use and low load usually means better reliability in the long run... so a thousand (or a couple) hours on a decent & well maintained diesel engine over a 5 year period is not excesive... too many engines stand to death these days and once started up, people expect the animal to behave just like their car which they use every day... as in out of the drive and accellerate up, without thinking that this iron lump need more time to heat up, get proper lube around into high load components etc... then they go for a30 min blast and stop engine... leaving it to cool down and stay in a beautifully corrosive environment because shaft seals are dripping.... when they then lift the lid up a couple of months later, they wonder where the rust and seized components fome from ..... and end up blaming it on poor engine....

IMHO ... Give me a well used, and cared for engine any time !!

+1
All moving parts, boats or not, benefit from being used. Part of TLC, IMO.

 

[Hurricane]

We've just completed a nice 300nm meander through the Dalmatian islands in Croatia moving our boat from it's winter base in N Italy to it's summer base near Split. For the first time, I forced myself to do a substantial part of this trip at minimum in gear speed which on my boat happens to be 7.3kts, in order to save fuel. My smugness at having saved several hundred Euros worth of diesel soon evaporated however when I filled in the log book at the end of the trip and found that the trip had put about 30hrs on the engines, which is not far off half my normal annual usage. I then began to wonder whether the few hundred Euros I'd saved was more than wiped out by the extra depreciation I'd incurred by putting those extra hours on the engines.
So I started to think about the numbers on this. Say that 2 people, Buyer A and Buyer B, buy 2 new 45ft flybridge cruisers which they intend to keep for 5yrs. Buyer A doesn't care about fuel consumption and he cruises everywhere at 21kts consuming fuel at a rate of 20 gals/hr. Buyer B is a skinflint and closet ecowarrior and cruises everywhere at 7kts consuming fuel at 2 gals/hr. Lets assume also that diesel costs £5/gal and both Buyer A and Buyer B cruise on average 2100nm per season (equivalent to an average 100hrs at 21kts). Without going into the detailed maths but anyone can work it out, Buyer A will spend £10,000 per year on fuel and Buyer B will spend £3,000 per year which, after 5yrs, will result in a very handy £35,000 saving for Buyer B.
But here is the big but, after 5yrs Buyer A will be selling a boat with 500hrs on it and Buyer B will be selling a boat with a massive 1500hrs on it. Buyer B may have saved £35,000 in fuel costs over 5yrs but I bet that saving will be more than wiped out by the extra depreciation he has incurred on the value of his boat. Now you can argue about the reality of the figures and maybe you can argue that Buyer B is going to do less mileage in a season than Buyer A anyway. Maybe the logical conclusion of this is that if you intend to do displacement cruising, buy a displacement boat and them when you sell it, its not going to have more hours than other boats on the market. Maybe used boat buyers should be educated not just to judge a boat on engine hours but on total mileage covered, like cars. Or maybe the logical conclusion is that all we planing boat owners should blat everywhere at max speed to minimise engine hours
There's been a lot said on this forum and in the mobo mags recently about slowing down to save fuel but maybe we planing boat owners aren't really saving money at all by doing this?

Na - Mike
You've got it all wrong
7 knots is only just tickover for most of us
That's NOT what POOTLING is about.
Most of our passages these days are about 100 ish miles - I think yours could be much the same.
If you do it at 7 knots you are not much better that a sailing boat and wouldn't do these passages inside daylight hours.
IMO, it's what awaits you at the other end of the passage that matters.
Our POOTLING is done at 10 knots (just enough to start pushing the bow wave
Work it out the difference between 7 and 10 knots can be significant when you are considering planning a passage.
For example, if you are heading for an anchorage overnight, you need to get there before is gets dark.
At the beginning of the passage, you might not be able to get everyone up early enough in order to get to your anchorage on time.

The point here is 10 knots - 100 mile - 10 hours
Less a little bit of time because you want to look after the engines and give them a little exercise during the passage.

Then there's the enjoyment of a gentle cruise in your own boat on flat seas - why waste it buy running at planing speeds all the time.

IMO, the economics of low speed running come into their own at a proper displacement speed vs the cost of running at a full planing cruise.
The other argument I make is that (by pootling for about 75% of our longer passages) I can spend three weeks in the Balearics without needing to go into a marina to fill up until we get home to mainland Spain - and that includes heavy generator usage.

My numbers are
10 knots(ish) - 22litres per hour per engine
24 knots(ish) - 175litres per hour per engine
I don't even have any confirmed figures for 6/7 knots - we just don't do it - the electronics suggest that it would be about 10 litres per hour per engine.
Anyway - the big picture - the difference in fuel consumption is significant when you get on the plane.

As far as depreciation is concerned, all of us take huge hits in depreciation that an extra argument of engine hours makes very little difference to the "Big Picture"

 

[davids0865]

@henryf:
Lobster pots? Wazzat? You must really follow jfm suggestions I reckon, and move to some proper cruising grounds... [/QUOTE]

ROFLMHO

So thousands of hours aboard for only a couple of thousand litres of go-juice, bliss

 

[Deleted User YDKXO]

Our POOTLING is done at 10 knots (just enough to start pushing the bow wave
Work it out the difference between 7 and 10 knots can be significant when you are considering planning a passage.

I dont know about your boat, Mike, but there's a huge difference in fuel consumption between 7kts and 10kts with my boat. At 10kts, my boat is consuming nearly 3 times as much fuel as at 7kts. Don't forget that for a 53 footer such as mine, 10kts is pushing way beyond theoretical hull speed and is beginning to plane. My attitude is that if you're going to pootle, you might as well do it properly and save as much fuel as you can

The other argument I make is that (by pootling for about 75% of our longer passages) I can spend three weeks in the Balearics without needing to go into a marina to fill up until we get home to mainland Spain - and that includes heavy generator usage.

Is that because fuel costs less in S Carles?

My numbers are
10 knots(ish) - 22litres per hour per engine
24 knots(ish) - 175litres per hour per engine

My combined figures for both engines are according to the Cat engine instrumentation
7.3kts 11 lph 3.0mpg
10kts 30 lph 1.5mpg
24kts 166 lph 0.66mpg
So you can see why I stick to 7.3kts when pootling

As far as depreciation is concerned, all of us take huge hits in depreciation that an extra argument of engine hours makes very little difference to the "Big Picture"

I'm glad you're so relaxed about it. I'm looking at used 68/72 footers at present and the difference in asking price between high hours and low hours boats is as much as €400k although of course I dont know actual transaction prices. Either way high engine hours definitely costs a lot of money

 

[MapisM]

So thousands of hours aboard for only a couple of thousand litres of go-juice, bliss

Well, tbh it's a bit more than a couple of thousands.
The old lady is not thirsty, but it still takes some power to move around all the 35 tons of her, even at D speed.
Anyway, 20/22 LPH in total (both engines, including also the odd genset usage), hence 3k litres or so per season, is something I can live with.
And even more so when compared with the MONTHS of boating rather than to the engine HOURS, of course!

 

[MapisM]

IMO, it's what awaits you at the other end of the passage that matters.

Well, if/when what really matters is moving from A to B (and I fully accept that it is, in many cases), most other means of transport are much better than even the faster pleasure boat to get the job done...