Passenger ferrie consumption

[JMestre]

I'm studying the diesel consumption of a passenger ferry (47 meters) that is propelled with water jets and is used to cross a river in a distance of about 8.2 km.

Do you have suggestions of how do I calculate the most efficient velocity for that ferry?

Is it possible that this particular vessel consume more fuel (per distance) travelling at 22 knots than at 28-29 knots?

Thanks
J Mestre

[marshmat]

Without knowing anything about the boat, it's hard to say.... I presume it's a displacement catamaran? And I presume it's for a school project of sorts?
My only suggestion at present is that, if you have the hull design, then Michlet could be used to estimate the power requirements over a range of potential speeds. Then you would combine the Michlet output of power required in a spreadsheet with the fuel consumption curve of the engines you're considering, to get the boat's estimated fuel burn per hour at each speed in question. That data is easily converted to fuel burn per mile.

[JMestre]

Thanks Matt,
Yes, I'm refering to a catamaran.
But can you tell me if it's normal for a catamaran of this sort to have bigger fuel consumptions per mile at 22 knots than at 29 knots?

Thanks again
J Mestre

[marshmat]

Many boats, in particular those that plane, often show a decrease in fuel useage per mile as they speed up. Without knowing anything about yours, other than it is a 47 m cat (which tells me nothing at all about its hull shape, operating regime, displacement, power source, etc), I can't say what to expect from it.

[JMestre]

I’ve looked in this forum for measures to improve energy efficiency in passenger ferries but I only found out measures for smaller boats. And I’m trying to find out measures that could be paid in the short-medium run for monohull and catamaran ferries with a capacity of around 500 passengers. For example, finding the optimal speed or reducing the weight. Can anyone help me in this subject with general measures or with references to previous studies?

I’m also trying to find companies that operate in similar river crosses (2 km and 8.2 km) (1.24 and 5.1 miles) and with similar vessels to possibly start a benchmark process. I would be very happy if anyone could give me this information.

If you need I can give more details about the boats.

Thanks,
JMestre

[marshmat]

Well, this isn't exactly my field, but I'll suggest a few avenues of exploration.
- A large part of the drag on a fast cat is due to skin friction. Cleaning weed and barnacles off the hull more often, or using better antifouling paint, might save a fair bit of fuel.
- If you have enough information about the hull to build a computer model of it, there are a number of CFD routes that could help you find the boat's best operating speeds. Some, like Michlet, are fairly easy and will give you drag/speed or power/speed curves, from which you can calculate fuel consumption if you have good data on the engine as well. If you have the resources, then a more advanced CFD analysis could give more information about what factors are contributing most to the drag on the hull. You'd probably need a good CFD technician to get very far this way, though.

[Toot]

At all costs, passengers should be dissuaded from consuming faeries. While they taste delicious when barbecued and seasoned with cinnamon and sugar, and though their wings are quite the delicacy, it can nevertheless be a cause of bad luck.

However, the more I think about it, I suppose it's not quite as bad as eating an albatross.


Hope this helps!


Ben

[JMestre]

Not really Ben…

I’m working on that Matt, today I’ll see if I can get someone to do that.

But what about measures to reduce the boat’s consumption? And studies about this subject?

Here’s a list of possible measures:
- Proper hull and propeller maintenance
- Better antifouling paint
- Optimal speed
- Better routing
- Optimal trim
- Minimum ballast
- Optimal rudder
- Teaching economical navigation

Thanks.
JMestre

[CORMERAN]

To JMestre,

you will not find a lot of studies and FREE information on the
fuel consumption of Catamarans or ferries.

- As difinitive data on fast ferry fuel consumption is worth millions of dollars.
- And represents decades of research by hard working designers.
- Why do you expect us, to give you this information for free ?!

I will give you a few hints - that are well known - and you could find
out yourself. With some DILIGENT research.

First: the fuel consuption is logicaly HIGHER.
- However - the increase in speed might mean more PASSENGER MILES
per shift. Before the operator of the ferry has to start paying overtime.

- Therefore: an increase in fuel costs will be accepted if:
- REVENUE is increased over a given time period.
This has nothing to do with hydrodynamics.
Ferry design is all about PASSENGER MILES.

There are a number of other howevers - that ARE hydrodynamic.

i.e.
- Many hull shapes will show a brief " bump" in fuel consuption
at lower speeds. ( As much as double the fuel rate - as seen at cruise.)
- To confuse you further - the HULL it's self might be more efficient
at 22 knots.......
- However.....the ferry operator wants the boat to operate at 28 knots
98 % of the time. So they instruct the designer to spec. out jets
that are most efficient at said speed.
( Because that will give the operator the most PASSENGER MILES and
the best return on investment.)
- It is well understood, by people in the business, that jet drives - within
a specific speed range can exceed props in fuel economy.
However......!!
- When the jet falls off the ideal envelope - and the vessel SLOWS
down - fuel cost can go UP !
( As this is only for 2 % of the time - the ferry operator will live with it.)

We have not gone into wether the hulls are displacement,
semi - displacement or so called " planing " hulls.

In other words you WILL NOT get a simple answer to you homework
assignment - by spending a few mins. on the the net.