Cruising speeds

8.5 knots, 1350rpm, 24tons, 48' LWL/55' LOA= 6 GPH


Sergio "Alemao" Sztancsa
Sent from my iPhone, using Trawler Forum

Cruising Speed

My 2007 Helmsman 38 has a Cummins QSB 5.9 (380 HP) and weighs 35,000 lbs with full 400 gal of fuel and 140 gal water. It cruises very well at 7.5 Kts with fuel consumption of 2.5 to 3.0 GPH @ 1500 RPM.

When delivered this engine was programmed for 230 HP. For some reason the previous owner decided to have Cummins reprogram it to 380 HP, and put trim tabs on it. I guess he thought he could get it to plane. IMHO someone sold him a bill of goods.

The only time I use the extra power is when bucking headwinds and heavy seas. Then I only use enough power to maintain my 7.5 Kt hull speed. Last time I did that we had 35Kt head winds and 5-6 Ft seas. My fuel consumption went up to 6 GPH at 2100 RPM.

Fwiw we are a full displacement hull,128k pounds with all tanks empty at last haul-out on a little more than 50' of waterline. Speed for us varies all over the place, much more than the amount fuel we decide to feed the engines. Wind, waves, currents, fuel load and bottom growth all have significant effects on our travel speed. Strictly by the numbers the last time I checked; 24.4 k gallons over 4.8k hrs and 33k miles came out to 6 7/8 knots and apparently equal to .95 *sqrt of our waterline. Engine loads at this speed is about 30 to 35 percent. Can't seem to access the polling from the mobile app.


Spell check via iPhone.

I've sent a link from this thread to ' the perpetual motion prize fund'...

...I'm am certain several boats on here will scoop the big $million prize. Lol.

PS: just to make all your claims more credible divide the tonnage of your boat by 5 [5hp/ton @displ. cruise Speed]

This gives you the HP required.....then divide this by 20 [ 20hp/gal for diesels ]

Which , horror.....your fuel consumption has doubled!