CONTINUOUSWAVE

A 60-HP two-stroke outboard will burn about 6-GPH at full throttle. If the boat goes 36-MPH then the fuel economy would be 6-MPG.

Generally with a classic carburetor two-stroke the BEST fuel economy will be at about 80-percent of full throttle.

By far the WORST fuel economy will be at idle and slow underway speeds.

Describe the measuring method you use to deduce fuel consumption in miles-per-gallon.

Thank you, Jim.

I simply divided miles traveled by gallons consumed. It was very approximate, especially since the use was mixed: some WOT, some idling, and some in between. I do think I'm being generous at 3.5 MPG though. I'll collect more precise data this weekend, now that Dorian has passed us by.

The engine is currently mounted three-holes-up. The AV plate is dead even with the bottom of the hull. I have read it should be higher.

I think you may not have that right.

When we refer to "holes up", this is referencing how many empty holes are above the top bolt.

Top set of bolts:
0 <------ bolt here is all the way down
0 <------ 1 hole up
0 <------ 2 holes up
0 <------ 3 holes up.

When 2 holes up, the anti-ventilation plate will be ~1 1/2 - 2" above the keel. This is the recommended position to start with and make adjustments based on prop selection, load and typical sea conditions.

Phil, [the engine mount plate has] five bolt holes. The bolt is right where your graphic denotes: three holes up. There is one higher mounting hole left.

Speaking of which: although the AV plate is level with the keel, it is still an inch or so below the waterline when planed off. Should I use that last hole?

The acceleration from a standing start onto plane is satisfactory—I guess—and top speed today was 37 MPH with me and the wife and 12 gallons of fuel. We ran both directions and averaged the two top sustained speeds (36 and 38). I was happy with that number.

It does seem like I'm trimmed 90% of the way down, 90% of the time. Should that be telling me something?

What happens when you are trimmed out? Does the bow settle down and speed increase?

It is appropriate to "trim out" every time you are above planing speed. The amount of trim depends on speed and load distribution.

Phil T wrote:What happens when you are trimmed out? Does the bow settle down and speed increase?

Yes, it does. In fact, at WOT and near-glassy conditions, the prop will ventilate before the boat porpoises. I'm just surprised by how very little trim is required.

And I was wrong about the anti ventilation plate being an inch under water. It's actually closer to THREE inches under. So even if I raised the motor to the highest hole, the plate will be nowhere near the surface.

Can you take a photo from the side showing the engine mounting and a straight edge (use a rake handle or other straight object) on the keel extending past the engine?

It is reading as if you have a extra long shaft motor (25") when a long (20") is standard.

sailor dude wrote:I simply divided miles traveled by gallons consumed.

Yes, I am sure you did that math, but I asked for the method of measurement, so to be more clear:

—how did you MEASURE the distance traveled?

—how did you MEASURE the fuel consumed?

Ah! Sorry.

I got the miles from Navionics. I got the gallons from the display on the gas pump, when I finished refilling the tank. I used a tape measure to bring the fuel back up to the same level.

Snapped this pic Sunday. The visible plate is 4" above the AV plate, so that gives an idea how deep the AV plate is. I raised the motor to the top hole today, and hope to give it a run this weekend.

We ran 68 miles on Sunday. Flat and calm the whole time. One-half to three-quarter-throttle at 95/100ths of the way, maybe ten minutes WOT and about 100-yards idling. MUCH MUCH better fuel mileage. I still can't believe it, but it came out to almost exactly 7-MPG this time. Top speed with two people and 17 gallons of fuel was 37-MPH. Eager to see what raising the motor will do.


Fig. 1. View of engine gear case underway.

I do not think they made a 60hp 2stroke, especially with the small gearcase that is 25" in length.

biggiefl wrote:I do not think they made a 60hp 2stroke, especially with the small gearcase that is 25" in length.

Hey Biggie, I was wondering if you might chime in! I've read a lot of your posts in my many "Dauntless 15" searches. Thank you!

But yeah, there's a 1995 60-HP two-stroke Mercury bolted to the back of my boat. It's 20-inch though, not 25. I was under the impression a lot of old Whalers came with these motors. True?


Fig. 2. 1995 Mercury 60-HP engine mounted four-holes up on transom of DAUNTLESS 15.

That Mercury engine looks like new. Like many Mercury engines, the engine mount has five sets of holes for adjustment of the engine mounting height.

The engine mounting height as seen in Figure 2 (above) is four-holes-up. This mounting height puts the engine 3-inches higher than the lowest position. This is a very high engine mounting height.

On a small boat, the boat trim will be sensitive to the position of crew weight. If a crew goes to the very stern of the boat and leans over the transom to take an image of the position of the engine anti-ventilation plate relative to the waterline, the movement of the crew weight to the extreme aft end of the boat may affect the position of the plate relative to the waterline.

sailor dude wrote:I got the miles from Navionics.

Did the device called "Navionics" have a trip log function that accumulated the distance the boat travelled based on the deduced position of the boat from a position finder like a GPS receiver?

Or did you perform some sort of visual estimation based on an electronic chart from Navionics?

sailor dude wrote:I got the gallons from the display on the gas pump, when I finished refilling the tank. I used a tape measure to bring the fuel back up to the same level.

Using a tape measure to measure the height of fuel in the fuel tank is quite a good method to establish a reset level for the fuel in order to deduce the fuel consumption. Your deduced fuel consumed figure should have good accuracy, assuming the fuel retailer dispensing pump flow meter was accurate.

That is a 20", they did not make them in 25". I had the same engine on an old blue hull 16. Good motor but not the strongest 60 as far as power goes. I think due to the smaller gear case. I am kinda old school when it comes to engines and I base my assumptions on what I am familiar with. I have owned 15 sports with OMC 70, Mercury 70, Yamaha 70 and the OMC was by far the most powerful, the Merc being the weakest(1983 3cyl). I have owned MANY 16/17's and the OMC 90 V4 and the tower of power merc were the best. The Yamaha 90 is more like 80hp. I know I am off subject but I am not being biased about your engine, great engine, just a little weak top end wise which again I blame on the small lower unit and lack of props available. I think the largest Merc makes for them is 17" pitch. Then again, most who know me here know I am biased about Mercs but that has changed over the years as they have improved greatly along with everything else.

You're not off subject at all Biggie, I appreciate the info. I'm not surprised there are stronger 60's out there. I really wish the boat had come with a 75 HP, but what can ya do. My plan is to get this 60 dialed in the best I can, then enjoy it for as long as I can.

We're gonna launch in Crystal River tomorrow and do a little sea trial with the motor at four holes up. At this point I'm happy with everything except I'd like 300-500 more RPM at WOT. Max range for the motor is 5000-5500, I'm barely at 5000. Maybe raising the motor will give me some of that.

jimh wrote:Did the device called "Navionics" have a trip log function that accumulated the distance the boat travelled based on the deduced position of the boat from a position finder like a GPS receiver?

Yep, exactly.

Are you using a tablet as a chart plotter and using an App from the Navionics company?

How far out are you trimming the engine? In the pic it does not look trimmed at all or barely. You need to trim it all the way out until it breaks loose and then blip it down until it catches(at WOT). At cruise you want a nice flat wake, no tall skinny wake and no spray from the sides.