CindyNeedshelp
New Member
We’re selling our Catalina 42, and wanting to buy a 41 American Tug (with a Volvo D9-500 engine). On the mechanical survey we were burning 24 gallons of fuel at 10 knots. That seems high. Thoughts??
Newbie, I hope you’re a nice crowd
- Thread starter CindyNeedshelp
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BruceK
Well-Known Member
Specs ( https://www.navaboats.com/pdf/D9-500 Inboard.pdf ) say max 25 US gal per hour. However pushing a 41 Tug to 10 knts shouldn't take 500 hp imo but as a displacement boat probably wont exceed 10 knts no matter how much power you push it with.
Farmer Piles
Well-Known Member
Welcome!
Seems very high to me. Could it be that you are trying to push it beyond its natural hull speed? A very different hull, but my mate had twin Cummins 500s in a semi D hull. Working hard at cruising speed they burned around 14 gals per hour each - imperial gallons. At full chat 22 gph each that is.
He has since moved to a 55ft trawler hull with twin 600hp. He found that by cutting his cruising speed from 10kts to 8kts his fuel consumption halved. Just that drop of 2kts moved his boat from bulldozing water to its natural hull speed.
Hope this helps or provides food for thought.
Seems very high to me. Could it be that you are trying to push it beyond its natural hull speed? A very different hull, but my mate had twin Cummins 500s in a semi D hull. Working hard at cruising speed they burned around 14 gals per hour each - imperial gallons. At full chat 22 gph each that is.
He has since moved to a 55ft trawler hull with twin 600hp. He found that by cutting his cruising speed from 10kts to 8kts his fuel consumption halved. Just that drop of 2kts moved his boat from bulldozing water to its natural hull speed.
Hope this helps or provides food for thought.
CindyNeedshelp
New Member
This is semi-displacement and can go to 17 kts, and then we would expect it to burn 24 g/hr. At slower speeds it shouldn’t burn that much…
Bajansailor
Well-Known Member
Welcome to the Forum Cindy.
Here is a link to an American Tug 41 for sale (actually, the sale is 'pending') -
2007 American Tug 41 Tug for sale - YachtWorld
The '41' appears to have been superceded by the 435, which now has a 550 hp Cummins main engine.
American Tug 435 — American Tugs
In this test report they note a maximum speed of 20 mph - but they do not mention the fuel consumption.
American Tug 41
In this report they mention some fuel consumption figures -
American Tug 41 – Boating World
And here is a quote :
"As we moved out of the marina into the open water we found that 100 rpm gave a GPS reading of just a hair more than 6.5 knots, while getting 2.85 nautical miles per gallon of fuel burned. Range at that speed is about 1,650 miles, with a 10 percent reserve in the 640-gallon tank. At 1800 rpm speed increased to 9.95 knots and fuel consumption was 1.05 nautical miles per gallon. At 2600 rpm the boat planes comfortably at about 17 knots and gives a range of about 415 nautical miles, with a 10 percent reserve â “ more than adequate for coastal cruising."
So why does this test boat get 1 mile per gallon at 10 knots, while Cindy's sistership gets only a quarter of this, ie 0.24 miles per gallon?
Here is a link to an American Tug 41 for sale (actually, the sale is 'pending') -
2007 American Tug 41 Tug for sale - YachtWorld
The '41' appears to have been superceded by the 435, which now has a 550 hp Cummins main engine.
American Tug 435 — American Tugs
In this test report they note a maximum speed of 20 mph - but they do not mention the fuel consumption.
American Tug 41
In this report they mention some fuel consumption figures -
American Tug 41 – Boating World
And here is a quote :
"As we moved out of the marina into the open water we found that 100 rpm gave a GPS reading of just a hair more than 6.5 knots, while getting 2.85 nautical miles per gallon of fuel burned. Range at that speed is about 1,650 miles, with a 10 percent reserve in the 640-gallon tank. At 1800 rpm speed increased to 9.95 knots and fuel consumption was 1.05 nautical miles per gallon. At 2600 rpm the boat planes comfortably at about 17 knots and gives a range of about 415 nautical miles, with a 10 percent reserve â “ more than adequate for coastal cruising."
So why does this test boat get 1 mile per gallon at 10 knots, while Cindy's sistership gets only a quarter of this, ie 0.24 miles per gallon?
BruceK
Well-Known Member
Was this boat making rated top revs? If not it could be as simple as excessive fouling preventing her from getting to speed. Was she overly heavy? i.e. with such a large passage making tank can she actually plane with the tank full? 500 hp in such a large and heavy boat sounds a bit marginal for 17knt SD planing speeds to me.
Farmer Piles
Well-Known Member
If you are relying on a fuel flow readout, could the fault be there - an inaccurate reading? The only way to be sure I suppose is to fill up, do a trip and refill and measure what's used.
CindyNeedshelp
New Member
CindyNeedshelp
New Member
Yes indeed, that IS the question!
Irish Rover
Well-Known Member
Are you sure your 0.25 MPG is correct? Also it would be interesting to know at what revs the OP was making 10 MPH?
rotrax
Well-Known Member
You might find some expert help from owners on the excellent Trawlers Forum, a predominately American site.
Bajansailor
Well-Known Member
Apologies, mental maths was never my strong point.
Re the 24 gallons (I presume per hour) at 10 knots mentioned by Cindy, this works out to 0.42 mpg, not 0.25 mpg.
Even so, this is still considerably worse than the 1.05 mpg quoted in the test by Boating World.
Greg2
Well-Known Member
First of all can I say what a lovely boat the American Tug 41 is - shame they aren’t available in the U.K. We wanted to buy a Nordic Tug, which were imported to the U.K. for a short time, but we missed it and ended up with our Hardy Commodore 36, which is far from being a consolation prize. 
We are smaller and have twin 265hp engines, so a total of 530hp. That gives us a maximum of 18 knots and whilst I haven’t got a handle on fuel consumption the previous owner said that it was eye watering at WOT but we cruise at 10 - 12 knots and it doesn’t seem to be too bad. The American Tug is longer, so hull speed will be higher than ours, but has a notably wider beam and is 50% heavier than us so 18 knots sounds optimistic and I am thinking that the engine will be working very hard at anything above hull speed. Having said all that 24gph does seem high at 10 knots.
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We are smaller and have twin 265hp engines, so a total of 530hp. That gives us a maximum of 18 knots and whilst I haven’t got a handle on fuel consumption the previous owner said that it was eye watering at WOT but we cruise at 10 - 12 knots and it doesn’t seem to be too bad. The American Tug is longer, so hull speed will be higher than ours, but has a notably wider beam and is 50% heavier than us so 18 knots sounds optimistic and I am thinking that the engine will be working very hard at anything above hull speed. Having said all that 24gph does seem high at 10 knots.
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