Best GPH on Force 120 / Trophy

[Excalibur222]

Greetings all. I'm new here. Have a question concerning GPH / MPG on a Force 120.<br /> What I was hoping to find out was the best RPM for fuel economy ( in the 3,000 - 5,000 ) RMP range for this engine / boat combo without buying a $500 Fuel Flow Meter. Seems like my Boat drinks a lot more fuel than it should. I hunted for an answer on the normal search engines but couldn't find it.<br /> Boat is a 22' Trophy 2002 WA - 1999 year<br /> Engine is a 1998 Force 120 w/ 13 1/4 x 19 prop<br /> Normally have about 700 lbs of gear and 3 people on board.<br /><br /> WOT = 4950 RPM as loaded above with a speed of <br /> approx 36 MPH.<br /><br />With this load, it seems like until you're around 3500 - 3800 rpm it's next to impossible to plain the boat out.<br /><br /> Any advice on getting the best mileage out of this engine with the above set up would be greatly appreciated as it seems lately that I have to run around out there all day trying to find anything to catch. I'd like to take the boat out further into the gulf ( so far 30 miles out has been about the limit both due to the storms here as well as not knowing the GPH or trusting the fuel gauge)<br />Thanks in advance,<br />Tom

 

[ricksonntag]

Re: Best GPH on Force 120 / Trophy

I'm new here, too. But I'll share a few things I've learned over the years.<br /><br />My father once gave me a rule of thumb for 2-cycle outboards. At full throttle, they'll burn a gallon per hour for each 10 horsepower. By this rule, my 50 would burn 5 gal./hour at full throttle. I think my Force 50 does a little better than that, but I'm not sure - I rarely run full throttle because my 15' Trophy is too light and pounds like crazy at full throttle unless the water is like glass. By this rule, you'd burn 12 gal/hour at full throttle with your 120. That's probably a little high too, but if you're interested in traveling out further, you want a conservative estimate.<br /><br />I'm a chemical engineer with PhD in fluid mechanics. I can tell you that the most economical speed for any boat is the slowest throttle setting that keeps your boat on a plane. If you're not on a plane, you're pushing water out of the way, which consumes a lot of energy. Once you're on a plane, going any faster is done by brute force of the engine, also uneconomical. For top economy, you want to be just up on a plane. The best way to tell you're on a plane is just after your bow lowers - that means your stern has risen on top of the water. (I'm sure you know this already.)<br /><br />One phenomenon you've probably noticed, but may not have thought much about, is hysteresis. After your boat gets on a plane, you can actually REDUCE your throttle a bit and still stay on the plane. This gets you your absolute best economy! But when your boat falls off the plane, you can't get back on it at that throttle setting - you need to give it more gas first to get back on the plane, then you can ease off it again. This phenomenon of having two speeds at the same throttle setting - depending on whether you're approaching it from above (on a plane) or below (pulling out of the water) is known as hysteresis.<br /><br />As you can probably tell, my outboard does not have a tach - I rely on slight and sound to optimize my throttle setting.<br /><br />I hope this helped more than it confuses...<br /><br />-- Rick

 

[22trophy]

Re: Best GPH on Force 120 / Trophy

Outstanding Info!!<br />Thanx