CONTINUOUSWAVE

I bought [a 1998 Dauntless 13 ] last winter and took it out for a shakedown cruise yesterday. It has a Yamaha 40-HP two-stroke-power-cycle engine. I've got a few concerns to sort out.

The Yamaha 40-HP outboard engine is mounted all the way down and the A-V plate is buried. I assume I want [the A-V plate] just out of the water when on plane.

Unless the trim was set all the way in, when on plane the boat will porpoise [bow oscillates up and down].

There is a problem with the throttle linkage. The throttle cannot be advanced to full throttle on the slides. This required my 100-lbs wife to move to the bow to get the DAUNTLESS 13 to plane.

Once on plane, the DAUNTLESS 13 ran 28-MPH [speed over ground from GPS receiver]. Currently, the propeller is 13-pitch and stainless steel.

Am I correct about raising the engine to get the AV plate out of the water?

Do readers have any propeller recommendations for this boat?

I can't find any top speed data. In looking at the SUPER SPORT 13, it looks like it hits 32-MPH with a 40-HP four-stroke-power-cycle engine. I know these boats are similar but not identical.

Any other info, suggestions, and ideas would be greatly appreciated

The Sport 13 is a skiff bottom boat. I believe the Dauntless has a modified V-hull shape and weighs more than the Sport thus requires more horsepower to equal the performance of the Sport.

I would raise the engine mounting until the A-V plate is just above the hull bottom or even another hole up and see how that works out. You can always come down a hole if needed.

I can't help with a propeller recommendation but 28 MPH with a limited throttle setting and the engine semi-buried seems pretty decent to me. Raise the engine and get the throttle working then post the results.

For advice on the position of the A-V Plate relative to the flow of water around the gear case, see

A-V Plate Pictures
http://continuouswave.com/ubb/Forum4/HTML/006491.html

Engine mounting height at the lowest position is generally never the optimum mounting height. Usually at least one-hole-up is the starting point, and in some instances higher engine mounting improves top speed, although there are other elements of the boat's handling to consider, such as the ability of the propeller to not ventilate in rough seas, that might limit mounting height.

At the 40-HP power level I am surprised the boat has a stainless steel propeller. Aluminum propellers work well at lower power levels and are less expensive--but not as durable as a steel propeller.

Any evaluation of a propeller requires measurement of engine speed. You will need a tachometer to assess propeller choice. You also need to discover the manufacturer's recommended full-throttle engine speed range. And you need to adjust the throttle cable linkage so you can achieve wide-open throttle setting. When all that is done, then post data about about the engine speed (RPM) and boat speed (MPH) at various throttle settings. Give us the gear case ratio of the engine, too.

When you have the following data:

--engine speed in RPM
--engine gear ratio (example: 2.33:1)
--propeller pitch (in inches)
--boat speed (in MPH taken at slack current, no wind, no waves)

then you can use a propeller calculator to find SLIP. A value of SLIP of less than 10 indicates the propeller is generally working efficiently.

A good propeller choice is one that allows the engine to accelerate to the upper one-third of the recommended full-throttle engine speed range when the boat is operated with its normal load.

I had a 1997 Dauntless 13 with a Honda 40 that I sold about three years ago. I had it for about 10 years and thought it was an amazing 13-foot boat.

It came with a 11 x 13 aluminum propeller and the engine mounted in the lowest position. The boat would hit 31 MPH (SOG) at 5800 RPM with one person and no gear. With three people, fishing gear, and eight gallons of fuel, it dropped to 25 MPH at 5300 RPM. It was sluggish to get on plane and I felt that it just didn't handle well: too much bow rise, pounding and porpoising.

I ended up with a 12 x 11 Stiletto Star SS propeller, a SE Sport 200 hydrofoil, and the engine mounted two-holes-up. This changed the boat completely. The bow rise, pounding and porpoising was gone. The DAUNTLESS 13 got on plane in half the time, held plane at a lower engine RPM, and gained about 4 to 5-MPH at WOT.

Keep in mind that this is a four-stroke-power-cycle engine with a 2.08:1 gear ratio and four possible mounting positions. Your Yamaha may need something different. I hope this helps.

There is a problem with the throttle linkage. The throttle cannot be advanced to full throttle on the slides.

Fix this first and re test the performance.

Rigging a motor takes incremental steps. Make a change, test. Make another change, test.

Well, I'm getting closer. Thanks to all the suggestions. After messing around with the throttle cable, I realized that it's unlikely to have stretched as it pushes the throttle rather than pulling it. I noticed that the roller on the throttle shaft wasn't contacting the throttle cam. I tried to loosen the screw that would allow me to rotate the cam. Wondering why it wouldn't come loose and thinking 'there's no way you should need an impact on a carb screw" I had a brain flash.

The screws are LEFT HAND THREADS. Yikes. I got it adjusted though now I've got a slight hi rpm idle concern. I brought the engine up one hole. Both of these made a huge difference. I bought an inductive tach which was a complete waste of 30 bucks. Idle speed seems right but wot reads 3800 rpm. The A/V plate is still a little low but I hit 36 mph on the GPS and time to plane was about 5 seconds. I'll have to get a real tach but it sounds like I'm pretty close to spec. Up one more hole and sort out the idle and I think I'm good.

Thanks everyone and if you want a peek, take a look here: https://www.youtube.com/watch?v=SeAg_ePM1vo

The tachometer for the typical older two-stroke-power-cycle outboard engine is really a frequency counter that counts the pulsed DC current in the 12-Volt alternator using a half-wave tap into the rectifier. The calibration of the tachometer is adjusted to match the number of poles in the stator winding of the alternator. The more poles, the more pulses per one revolution of the crankshaft and flywheel.

Yamaha used to make some fancier tachometers that had a digital read out of the engine speed instead of a dial-pointer gauge. There are some universal outboard engine tachometers with adjustable calibration controls. They all generally wire directly to a dedicated conductor called the tachometer signal, which comes out of the alternator circuit. The signal typically has a pulse rate whose frequency varies directly with engine speed of rotation. It is typical to have four, five, or six pulses per rotation, depending on the brand of engine and the horsepower. (Larger horsepower engines usually have more poles in the alternator stator winding.)

I watched your recording. It looks like you were having fun and the boat is running quite well. Be careful boating alone on a lake in early Spring. There won't be any other boats around to rescue you if you get into trouble.

jimh wrote:I watched your recording. It looks like you were having fun and the boat is running quite well. Be careful boating alone on a lake in early Spring. There won't be any other boats around to rescue you if you get into trouble.

Thanks for the explanation about the tach. I'll try some different settings as there is no way it's only running at 3800 rpm. As for safety, I hear you. I had my life jacket on and the lanyard which is something I don't often do if I'm completely candid. That's the St Croix river btw about 1 mile up from the confluence of the Mississippi. Great boating if you ever get the chance.