Fuel consumption

We are looking at buying a trawler style yacht it is powered by a 1968 Cat D333 rated at 180 Hp. The boat is 57' by 18'6" and draws 6.5' has a canoe stern. The current owner claims it only burns 4 gals. /hr. at 1700 rpm doing 8kts does this seem possible? It is all aluminum construction built by Palmer Johnson weighing 92000 lbs. I've tried to find some performance charts but have had no luck so far. It has a 4 blade 38" x 22" prop.

 

With 4 Gal/hr the engine can generate 30-45 hp, depending on its condition.
Moving 92000 lbs @ 8 kts under optimal conditions is not impossible but I think the average consumption will be considerably higher.

 

More like 5.5 to 6 gph at 8 knots.

 

Fuel consumption is usually computed by using the hours shown on the hour meter and the # of gallons of fuel put into the tank/s. Most just conveniently overlook the fact that lots of running is done w the hour meter going at it's usual speed and the boat running at much less than cruising speed and even stopped.

 

Counting on my fingers the boat is over 40 tons.

With 2 or 3 hp per ton required to part the waters that's 80 to 120hp for modest , not yet "hull speed".

With a magnificent engine installed properly set up and working to perfection , in theory 80 hp @ 4gph could be gotten from the engine , but probably not at the propeller.

I would think if you can be happy cruising a 8GPH you might perhaps get the 8K cruise.

And 4gph could be done , but the speed might only be 5K or so.

Not bad for 40+ Tons.And if she were slippery that 5K might be 6K , you wont know till you run from a 5 gal jug and measure for real..

FF

 

Poplariv

Thanks for the info, the boat is 92000 lbs taken off a travellift. I'm thinking hull speed is about 9.5 kts and 8kts at 5-6 gal /hr would be nice 8 would be too high. From what I've been able to get off the net so far I should be okay. The boat has a day tank with a fuel meter so when we do the sea trial later this week it should be easy to confirm.

 

I'm guessing this is Weston Farmer's design All Ten B, original design weight was 74,000 pounds and the designer claims she did 10 knots with the 333. That engine will go through 10.5 usg/hr at 2200.......8 knots and 4usg/hr seems unlikely....perhaps imperial gallons?

 

You are correct, All Ten B. Does 5.5 usg/hr. seem reasonable for 8 kts the current owner claims 1700 rpm for 8 kts.

 

"8 knots and 4 usg/hr seems unlikely....perhaps imperial gallons?"


Perhaps statute miles?

FF

 

Unrealistic Fuel Consumsion Claims

Perhaps the vessel is in dead calm waters & always runs around with a 15 K tail wind?

Perhaps the number is based on a 12 hour day with 50% of the time idling around, & that's an average?

Perhaps he is appealing to the ignorant as to real operational conditions in the real ocean?


Put a reasonable average of 15 knots of wind and 3-5 ft head seas into the equation, and you don't move 40+ tons at 8K's on 60-70HP (4 gph and a CAT 333). If the CAT 333 was propped to its rated HP and RPM, ( maybe 190HP at 2000-its lowest factory rating- the engine spec sheet I have does not show a 180HP version) , it would consume not less than 11 GPH at rated per the factory graphs. Back off to 1700 RPM and you are in the 7-8 GPH range with the CAT 333 making about 130 HP. Per CAT, this engine is in the .41-.44 lbs/BHP/HPH range -- lousy by today’s standards and would be considered a fuel hog based on its BSFC. At that time, these numbers were right at the head of the pack for this type of pre-combustion engine design in the 10L size class. Also, I would assume your gear reduction is around 3:1, or deeper ?

Now, add some weather to this equation, and I could easily see at the same RPM, a vessel of this statue slowing down 1-2 K’s and the GPH rising 1-2 GPH.

Sorry, but the numbers that you are being fed are a wet dream by any standard.

Marine Nut

 

Thanks for the info and cat spec sheet, but this is a 180 hp version that is older than the spec sheet you have. The hull is well designed and very smooth, not sure if this makes a difference but in sea trial we used 5 usgals/hr doing 7.5 knots at 1600 rpm. We have since bought the boat and will be doing a longer test soon. Also on a run to Alaska he used 477 gals over 89 hrs and 70 hrs generator so 1gal/hr for gen and 407 gals for 89 hrs leaves 4.5 u.s.gals per hr. This all per his fuel log etc.

 

i did a 2000 nm trip in an old tug, it was 48 ft, weighed 40 metric tons, we constantly monitered fuel because the day tank had scales on the sight glass. it consistently used 14 litres per hour at 7.5 knots. the engine was a 175 hp gardner 6l3. i think your figures sound about right. i don't where some of the huge figures on this thread come from but it is not from experience.