Solving Problems Related to Performance Testing

[glen1941]

[Moderator's note: In a prior thread in the PERFORMANCE forum the author was attempting to perform boat and engine speed tests on his MONTAUK 17, but a number of problems were encountered. He later wrote about those problems and how he corrected some of them. That post has been moved to THE GAM for further discussion.]

[In my earlier report on boat performance] everything seemed to be going wrong:

• [seawater] was coming into the [MONTAUK 17] boat [when] the cockpit sump plug [was] out;
• the steering was really difficult when accelerating;
• there appeared to be something wrong with the tachometer accuracy; and
• the depth gauge was useless.

Here are some thoughts about those problems and how I solved them:

Water coming into the boat

• I thought "the foam is full of water";
• I weighed the boat; its weight was very much within parameters;
• I drilled four inch holes [perhaps means he drilled four 1-inch holes] through floor [cockpit deck] down to hull, [and found the foam was] completely dry;
• I found no water when installing new drain tubes.

After reading many [unspecified] threads on continousWave and other [unspecified] websites, I found out that to have water deep in the stern [sump area] with the sump drain plug out was completely normal. To have had this said earlier would have been nice. Next, I moved the 22-gallon Moeller on-deck fuel tank to be forward of console. Now the freeboard at the stern when the fuel tank holds 15-gallons of gasoline win 0.5 to 0.75-inches higher [than it was before with the fuel tank somewhere else].

Steering
What I thought was a big problem has turned out to be totally normal. To have been told this would have been nice. I have installed hydraulic steering by UFlex and it is really nice. I am very glad that I spent the money for hydraulic steering by UFlex.

Tachometer inaccuracy
The [BRP] OEM tachometer had the pulse setting slightly off [with the result that at full-throttle the engine speed was indicating] an RPM greater than the rev-limited. I installed a new Sierra Lido tachometer. The Sierra Lodo tachometer quality is much better [the prior tachometer]; the Sierra Lido tachometer reads directly from the engine but still has a manual pulse setting. At the same time I installed a NMEA-2000 network and added a Capn NMEA KISS (Keep it Simple Scanner). The engine speed indication on the Capn NMEA KISS and on the Sierra Lido tachometer are almost exactly the same. I now know I have an accurate tachometer.

Depth finder problems
The Lowrance Eagle 7's depth reading was either obviously wrong or maybe correct or no reading was given, and it sequenced through all three. I removed the Lowrance depth transducer. I installed a new Faria depth finder and transducer. The Faria's readings bounce around but are always there. The readings are generally correct, particularly a boat speed below 20-MPH, and [agree with the soundings on a] C-map electronic chart in water less than 50-feet deep.

[Moderator's note: For more information on the $120 Capn MNEA product see:

https://goldenchannels.com/product/capn-nmea/ ]

[jimh]

Regarding your solution to determining the engine speed more accurately:

The Sierra Lido tachometer is a conventional tachometer that relies on a pulse signal from the engine. The tachometer functions as a crude frequency counter and counts the number of pulses provided by the engine. For any frequency counter a time base signal is necessary to determine the interval of the frequency, which in the case of engine speed is in minutes. The typical analog tachometer implements the time base with a simple RC-time constant. A frequency counter would be more likely to use a crystal controlled oscillator for the time base.

The Sierra Lido tachometer is a conventional, traditional, analog type, and universal type, meaning that there is a calibration control that permits the adjustment of the tachometer to suit engines whose tachometer signals are various ratios of pulses per engine revolution. This sort of "calibration" is subject to error.

Fig. 1. The rear panel of the Sierra-brand LIDO tachometer, showing its calibration and settings controls.

tachometerRearPanel.jpg (54.08 KiB) Viewed 236 times

As seen in Figure 1, above, the particular LIDO tachometer mentioned as a solution to inaccurate tachometer readings is quite unusual in that it provides both a general settings control to match the type of signal being provided by the engine for the number of pulses per revolution or the number of cylinders, and a calibration control to further adjust the tachometer reading. Exactly how the device is calibrated in the field by a typical user is not known, but one can assume that it could be adjusted to match the readings of another tachometer if that other tachometer was considered a reliable instrument.

Further, the Sierra Lido tachometer displays the engine speed on a dial pointer gauge. The graduations on the dial face are in increments of 200-RPM.

The E-TEC engine sends its engine speed as part of the standard NMEA-2000 engine datagram, with an accuracy of ± 1-RPM. However, most displays of this data will perform a rounding function and show the engine speed to a more course value, usually ± 50-RPM.

In order for the display of engine speed on the dial pointer tachometer to "exactly match" the display of engine speed on a NMEA-2000 instrument, the operator has to interpolate the dial pointer reading to 50-RPM increments, which means interpolating between the 200-RPM graduations to one-quarter of the width between the marks. Unfortunately the width of the dial pointer is quite large, so precisely judging which one-quarter of the width between the 200-RPM graduations the dial point is exactly in will be quite subjective.

Fig. 2. View of the dial pointer of the LIDO tachometer. The dial pointer is pointing between 600 and 800-RPM, but without the three new tick marks I have added between the 600 and 800 graduations, reading the tachometer to a resolution of 50-RPM would be difficult. Also parallax due to the angle of view will affect the apparent position of the dial pointer. Precision analog dial-pointer meters often include a mirror in the scale so all parallax can be eliminated, and they employ an extremely thin dial pointer end indicator so the location of the dial pointer relative to scale graduation marks is very precise.

tachometerDialFaceWithAddedGraduation.jpeg (3.49 KiB) Viewed 235 times

Fig. 3. A legacy Triplett "Volt-Ohm meter" precision dial with a mirror scale and very thin dial pointer. The mirror appears to be black in the view. Reading on the top black scale, the indicated value is 124.

TriplettMeterScaleWithMirror.jpg (70.34 KiB) Viewed 204 times

More about meter scales with mirrors at
Can you trust your voltmeter?
https://www.nutsvolts.com/magazine/article/can-you-trust-your-voltmeter

The previous tachometer which you referred to as a "BRG OEM" tachometer, which I would infer you meant to mean a BRP OEM tachometer, would typically NOT have a calibration adjustment control. The tachometer would come preset to match the E-TEC engine pulse rate. That your previous tachometer appears to have had a calibration control suggests it may NOT have been a BRP OEM tachometer for an E-TEC but rather a generic model.

The general problem with any analog tachometer that relies on a user-adjustable calibration control to determine its accuracy is there may be some contact resistance built up in the small switch. A good way to restore the calibration switch on an analog tachometer with an adjustable calibration control is to use this procedure:

• observe the original setting of the calibration control and make a note of that position
• using a properly sized screwdriver, insert the screwdriver into the slot of the calibration control;
• rotate the calibration control setting back an forth through its range of settings, repeating this at least five times;
• then reset the calibration control switch to the original setting

This procedure will help remove any oxidation in the switch contacts that could be causing errors in the calibration of the tachometer.

Also, most modern recreational boats will have a chart plotter and SONAR combination device, and it is very typical that the device will support communication via NMEA-2000. When a multi-function chart plotter and SONAR device is on a NMEA-2000 network with an E-TEC engine also on that network (which you apparently have already gone to the trouble to install and connect in order to use the Capn NMEA device) the multifunction display will be able to display a great deal of engine-related data sent by the E-TEC.

Regarding having the ability to see engine speed on a smartphone by using some unspecified application on the smartphone to view data being sent via the Capn NMEA device and using some unspecified wireless connection does not seem to be a particularly handy method to get high-accuracy engine speed. Getting that same data on a multi-function display that perhaps is already in use on the boat would be a more useful and less expensive approach.

[jimh]

Regarding your solution to getting more accurate measurement of water depth:

The LOWRANCE depth sounders are very well known for providing excellent SONAR returns of the bottom echo as well as from targets such as fish. If they were incapable of doing this, LOWRANCE would have failed as a company decades ago.

If in a particular installation problems with maintaining a bottom echo occur, the most likely cause of the problem is a poor installation location of the depth sounder transducer. Also, the typical LOWRANCE depth sounder will offer many options in the set-up of the SONAR configuration, such as SENSITIVITY, RANGE of depth, COLOR shading, FREQUENCY, and AUTO operation. In some instances adjustment of some of these controls may be necessary to get reliable performance for maintaining bottom echo.

If a particular LOWRANCE depth sound and SONAR were incapable of maintaining a bottom echo at its intended depth range, one would expect that there would be many complaints about this fundamental problem in the operation of the SONAR.

Before abandoning the LOWRANCE depth sound, a careful inspection of its transducer should be done. Look for the transducer having moved in its angle adjustment in its bracket. Also look for upstream hull elements like a strake that can disrupt the smooth flow of water into the transducer. And, more fundamental, look at the depth of immersion and angle of the transducer to insure that it is alway submerged into non-aerated and smooth water flow coming off the hull at the transom.