1995 Dauntless 17 - High Propeller Slip

[RobertB3]

I have a 1995 Dauntless 17 with a 1995 Johnson 115 OceanRunner model J115SLEOC. [The gear ratio is 2.00:1] [The engine is mounted two-holes-up.]

I need help with what seems like high propeller slip.

DATA for PROP 3 (see below)
RPM = 5500
RATIO = 2
PITCH = 17
MPH = 32
SLIP = 27

Fig. 1. Gear case.

IMG_1365 (1).JPG (140.78 KiB) Viewed 26950 times

BACK STORY

I have attempted to work through this myself but would like the opinion of others with experience on this topic. This is a new to me troubleshooting process and I am learning from scratch about outboard engine setup and propeller.

Propellers:
Original Propeller - SOLAS four-blade in rough condition - Model Unknown - 13-1/2 x 17 pitch. I don’t have performance data for this propeller. I removed it shortly after purchasing the boatdue to condition and moderate vibration. I was also working on engine problems during this time. But I don't remember a sensation of achieving 40 MPH.

Propeller 1- Selected using SOLAS selection app: Model 2413 128 17 - 12-3/4 x 17 pitch four-bladed. I did not understand how to calculate slip at this time.

Propeller 2 - Selected using SOLAS selection app: Model 2413 125 19 - 12-1/2 x 19-pitch four-bladed. I choose got the 19-pitch because I didn't understand that I already had high slip and assumed the 19-pitch would bring down engine RPM and increase boat speed.

Propeller 3- Selected using forum research as a good starting point and currently Installed: Michigan Wheel - Model SSO-517-II-C - 13 1/4 x 17-pitch three-blade. [The data above is from this propeller.]

The engine is mounted [please only describe engine mounting height in number of hole sets raised above lowest possible, and your situation sounds like the mounting height is “two-holes up.” ]

There is a [anti-ventilation plate foil extension] on the lower unit. The boat came with this. I made one test run without the foil extension when I replaced the lower unit. Without the foil extension the engie trim did not have much control over boat fore-aft trim, and the bow wanted to rise and remain elevated at speed.

Propellers 1, 2, and 3 have similar performance characteristics. Testing was with only me in the boat, and a full tank of fresh gasoline. The propeller feels it loses traction around a boat speed of 28-MPH. Top speed is around 32 MPH at 5,500-RPM.

The engine does not feel like it is under full load or gripping well at around 4,800 to 5,500 RPM. There is little feeling of acceleration from 28 to 32-MPH within that RPM range. The engine easily accelerates to 5,500 RPM to 5,700 RPM before I back off the throttle. The manual shows 5,500 RPM maximum engine speed.

The three blade 17-pitch [describes propeller by pitch and number of blades leaving readers to deduce which of the three numbered propellers is being referred to—please just indicate the propeller by your own propeller numbering scheme] does feel that it accelerates the quickest, but I have not recorded times for the acceleration performance.

I have also recently tested the four-blade 17-pitch and 19-pirch with 700-lbs of people and dog. The top speed is still around 31 to 32-MPH with a slower time to accelerate.

The history of this boat is largely unknown and the boat had been sitting for years when I purchased it in 2024. All I knew at the time of purchase is the hull had no visible damage, the Johnson 115-HP engine had even peak cylinder pressure of 127 to 130 PSI, spark on all cylinders, and needed carburetor work. I slowly revived the boat through 2024 and had reliable service through 2025. I have now resolved all known engine problems The Johnson 115-HP engine is performing as I would expect. It has newly rebuilt carburetors, new ignition system components, new spark plugs, new thermostats, and a new 2024 SEI 2.0:1 lower unit after the original developed a knock and "glitter" in the lower unit from what I assume was an abrupt seal failure.

-Robert

[jimh]

To calculate propeller performance parameters use the Propeller Calculated provided by the website at

https://continuouswave.com/calculators/propCalc.php

[jimh]

Figure 1 shows what may be a 25-inch shaft engine on a 20-inch transom. Give the entire model designation of the engine, which will contain the code for shaft length of the engine.

About all I can infer from the one data set is to agree that the Propeller 3 as tested shows excessive SLIP. This could be due to excessive outward trim.

When the engine is of the proper shaft length for the boat transom height and is mounted one-hole-up or higher, when the engine trim is set so the anti-ventilation plate is parallel to the water, and when the upper surface of the anti-ventilation plate is just at or just above the water that flows past the gear case, then the engine mounting height and engine trim-out are in the proper positions.

Study photographs at

Anti-Ventilation Plate Pictures
https://continuouswave.com/ubb/Forum4/HTML/006491.html

[RobertB3]

I get 27.7% value for calculated prop slip when I populate my information in the provided link for the 13 1/4" x 17P 3 Blade SS propeller. I see propeller slip ranges for the Dauntless 17 should be around 12% if setup correctly.

I referenced the SEI lower unit order bill of materials it included a 20" length drive shaft. The 20" SEI shaft is what is currently installed and operational. The boat is in local storage but from memory the motor name plate sticker is weathered and the first half of the sticker "J115SLEOC" is more resiliant than the following information with how OMC printed the sticker characters.

I studied the linked anti-ventilation plate position discussion. I will have an opportunity next weekend to bring a passenger with me to take a picture of the anti-ventilation plate position in the water at a cruising speed.


I used the wrong original phrasing but can confirm the motor is mounted two-holes-up.

Fig. 2. Detail of engine height nmounting position.

IMG_1376.JPG (78.23 KiB) Viewed 26901 times

[jimh]

Check the tachometer calibration. If the tachometer reading is not accurate, then the engine speed could be slower than indicated. Using an incorrect value for engine speed will cause the value for SLIP that is calculated to be incorrect.

[RobertB3]

Thank you for recommending tachometer calibration. I had an opportunity to get on the water today and confirmed that my tachometer is the problem.

When the tachometer showed 5,500 RPM, the multimeter measured the stator pulse at 475-Hz. If the 6 pulses per revolution conversion chart is correct for my engine, the actual engine speed is 4,750 RPM while the tachometer was showing 5,500 RPM. The tachometer is reading about 14-percent higher than the measured stator Hz converted to RPM.

I briefly attempted to reach top speed using the multimeter and watching for 550 Hz (5,500 RPM). I got close to 540 Hz and reached 36 MPH with my normal load (wife, dog, full gas tank). The corrected propeller SLIP is then 16.3-percent.

It was windy and water conditions were rough today. My trim was not optimized for the top speed run.

Fig. 3. The position of the AV-plate at 30-MPH: completely buried.

IMG_1402.JPG (106.03 KiB) Viewed 26815 times

Q1: Would you recommend I raise the motor up one more hole, to three-holes-up?

Tachometer Calibration Test Method

Fig. 4. A meter being held by a hand near a dashboard.

IMG_3152.jpeg (36.12 KiB) Viewed 26746 times

Connected multimeter alligator clip leads to the "PUL" and "GND" studs on the gauge. The multimeter set to measure stator pulse in Hz. I found a 6 pulse per engine revolution to RPM conversion chart. I ran the engine at different RPM speeds on the tachometer and recorded the multimeter Hz values. If the tachometer was properly calibrated or functioning correctly, the multimeter should measure 300 Hz at 3000 RPM for my 6 pulse per engine revolution motor.

RPM = (Hz x 60)/PPR = (Hz x 60)/6 = Hz x 10

(239.8 Hz x 60) /6 = 2,398 RPM is what my multimeter measured. My tachometer showed 3000 RPM. That is how I confirmed that my tachometer is reading improperly. I will now look at the selector switch on the back of my tachometer to confirm it is set at 6P and not at one of the other settings such as (5P, 4P, 3P, or 2P,). If my tachometer selector switch was improperly set to 5P, it would match the deviation from the multimeter measurement. I will confirm when I return to the boat in storage. If the tachometer selector switch is set to 6P, I will replace the tachometer.

I would recommend using a chart that matches your outboard PPR at various RPM ranges to minimize mistakes and make life easier.

[jimh]

My advice:

• remove the foil appendage from the AV Plate;
• raise the engine at least one hole higher;
• explain to readers what is being illustrated in Figure 4.

[RobertB3]

Thank you again, jimh.

I will attempt to raise the motor to three-holes-up, which will be highest position possible with the current engine and transom setup. I will remove the foil appendage from the AV plate and retest to see how the boat handles.

I do not expect that the engine raised to three-holes-up will be high enough for optimal AV plate position in the water.

I am curious how others with my model 1995 Dauntless 17 have setup their engine.

Visually to me, the upper engine mounting holes on the transom look like they are lower [than the recommended layout].

I found descriptions that the 1995-1996 Dauntless 17 had a 20 inch transom and in 1997 Dauntless 17 had a 25 inch transom.

[jimh]

Visually to me, the upper engine mounting holes on the transom look like they are lower [than the recommended layout].

The centerline of the upper set of engine mounting holes on the boat transom according to the BIA standard recommendation should be 1-7/8-inch below the top of the transom.

More details are given in

FAQ: Q9: What is the standard transom hole layout?
https://continuouswave.com/whaler/reference/FAQ/#Q9

Also there is a useful diagram showing BIA standard hole layout at

Transom Engine Mounting Hole Layout
https://continuouswave.com/forum/viewto ... f=7&t=5808

If the engine mounting hole positions on your boat were drilled lower than recommended, the next option may be to use a short jack plate to raise the engine higher.

I also wonder if the SEI aftermarket gear case might be somewhat longer than the OEM gear case, also contributing to your lower-than-optimum overall engine mounting height.