Fuel Ecomomy Better on Go Fast then Trawler?

[bluesun]

The main reason I was attracted to trawlers was the economy of operation. I did not want to be stuck on the dock being unable to pay for the fuel of a day out. But upon getting more serious it seems that a lot of twin diesel boats have really good mileage as long as they are going slow.* Trying my best to compare two similar boats, here are numbers I have been able to find:

MainShip 34 Trawler with twin Yanmar 240hp. (20,000 pounds, 250 gallons fuel)
1500 rpm,* 8mph,* 2.2 miles per gallon, range 500 miles
2500 rpm, 13mph, 1.5 miles per gallon, range 335 miles
3500 rpm, 23mph, 0.9 miles per gallon, range 204 miles

Tiara 3500 Sovran with Volvo IPS 400 (ips being the pod drives) (17,000 pounds, 250 gallons of fuel)
rpm, mph, miles per gallon, range
700,**** 5.2,* 6.8,* 1525
990,**** 7.1,* 4.6,* 1035
3010, 27.6,* 1.3,** 286
3385, 33.5,* 1.3,** 281
3535, 35.4,* 1.2,** 263

Now, the ips is supposed to improve effeciency 25% but it seems the Tiara uses half the fuel at the same speed and has the ability to go much faster if needed. The Tiara was tested with all tanks full and 5 people on board. The Tiara also has a lower draft (33" vs 39" for the mainship), a lower air height (9' vs 15' for the mainship) which are the other two reasons to use a trawler (for great loop at least).

The price for 2011 models (35' model for mainship is 376k) and 399k for the Tiara although I think the tiara has more equipment standard.

Now my first thought is that the Mainship must be better in rough seas or something. But apparently the opposite is true. The tiara numbers were supported by two magazine reviews, but they read the numbers off the drive management system. Mainship seems very hesitant to verify any numbers and the data was supplied by Yanmar.* I was at a boat show and saw some good fuel numbers on "condos on the water" and so I have been investigating.* Please let me know what I am missing.* Thank you.

 

[FF]

Some hulls are cheaper on the plane than others.The 10 mph difference with similar power is common.

The re will be a difference in the "ride" the best in offshore at speed is the deep V , but it always costs more to push it.

An almost flat bottomed scow , that had a good aft section would be faster in flat water , but might have 8G accelerations in rough water.

Slow (displacement slow ) is cheap at about the Sq RT of the LWL in K.

That's how the 5.2 mph (high 4K) gets that 6.8 stat mpg.

 

[jleonard]

If you want*realistic numbers for the Mainship you should join the Mainship owners group.
It is a Yahoo group and free to join (I am a moderator there). Why not subscribe and ask real owners what they get for economy, how they handle, yada, yada.


-- Edited by jleonard on Monday 18th of October 2010 02:52:33 PM

 

[bluesun]

I did join the mainship yahoo group but I still can't figure out yahoo groups. Discussion boards seem to be much easier to use.

 

[jleonard]

Yes they are I agree. Unfortunately the yahoo groups are pretty much an unorganized free for all.
But for you most of the owners are on that group so*perhaps you can put up with it long enough to learn what you need?
Just go in and post your questions. I know you'll get some answers.