Hello. I am running a 1977 Montauk 17 with a 1977 Mercury 115-HP [six-cylinder in-line] Tower of Power. The tachometer came up to 6100. The propeller is a 13 -1/4 x 17 Solas aluminum. My GPS speed was 42 to 43 MPH.
Is the tach reading correctly?
I put the [above] data into a calculator and it say about 5500.
I am not sure about prop slippage. if [the engine is] turning 6100 I think that is entirely too high.
I read those 115 Mercury engines were rated at 5,300-RPM. Let me know your thoughts. Thanks.
Just wanted to add the 5,500 I got from the calculator was putting in a 3-percent prop slip. I was just reading it is not out of the ordinary to have a 10-percent or more slip. That puts me at 6000 plus. Just wanted to get some thoughts on it. Thanks.
Tachometer Accuracy
Re: Using estimation of SLIP as a method to calibrate a tachometer.
What is the gear ratio of the engine?
There is really no way to measure SLIP with sufficient accuracy to use that as a basis for assessing the accuracy of a tachometer.
A tachometer whose accuracy is suspect must be tested by connecting a second tachometer of known accuracy to the engine and comparing readings between the two.
There is really no way to measure SLIP with sufficient accuracy to use that as a basis for assessing the accuracy of a tachometer.
A tachometer whose accuracy is suspect must be tested by connecting a second tachometer of known accuracy to the engine and comparing readings between the two.
Re: Tachometer Accuracy
Thanks Jim. I ordered a digital photo infrared tach reader from Amazon. You place a piece of reflective tape on the flywheel and point the infrared beam at it. The reviews claim it will read dead on. Will try it next weekend and report back. For 17.99 we shall see.
Re: Tachometer Accuracy
For this data:
PITCH = 17
RATIO = 2
MPH = 42
SLIP = 7
The calculated engine speed is
RPM = 5611
PITCH = 17
RATIO = 2
MPH = 42
SLIP = 7
The calculated engine speed is
RPM = 5611
Re: Tachometer Accuracy
Whaler672: what did the new tachometer read this past weekend?
EJO
"Clumsy Cleat"look up what it means
50th edition 2008 Montauk 150, w/60HP Mercury Bigfoot
"Clumsy Cleat"look up what it means
50th edition 2008 Montauk 150, w/60HP Mercury Bigfoot
Re: Tachometer Accuracy
Hi Dutchman. I haven’t been on the boat yet. Bad weather and commitments. Will post after we check it. Thanks
Re: Tachometer Accuracy
https://www.amazon.com/HDE-Professional ... op?ie=UTF8
Made it down to the boat. Put a piece of reflective tape on the flywheel and the optical tach reader would not read. If I covered it up with my hand around it shading it, I could get it to read at idle but would not want to put my hand that close to the flywheel at 4 or 5000 RPM's. Might work if tried when it was darker out. Might be better to just buy another tachometer.
Made it down to the boat. Put a piece of reflective tape on the flywheel and the optical tach reader would not read. If I covered it up with my hand around it shading it, I could get it to read at idle but would not want to put my hand that close to the flywheel at 4 or 5000 RPM's. Might work if tried when it was darker out. Might be better to just buy another tachometer.
Re: Tachometer Accuracy
Something is off.
Is this boat new to you? If not, what was past performance that has you questioning this latest run?
Is the hull heavy? Weight?
Do you go out running light or loaded with gear, people?
Is the engine tuned? Carbs clean and synched?
Typically, a 1997 Montauk, lightly loaded with a classic 115 with the appropriate prop, mounted 2 or 3 holes up would be able to attain 49+.
LHG, a respected member who runs many Mercury engines in his fleet reports 50+ running a 22" Laser II prop.
See his comments down a bit in this archived thread:
http://continuouswave.com/ubb/Forum4/HTML/007546.html
Is this boat new to you? If not, what was past performance that has you questioning this latest run?
Is the hull heavy? Weight?
Do you go out running light or loaded with gear, people?
Is the engine tuned? Carbs clean and synched?
Typically, a 1997 Montauk, lightly loaded with a classic 115 with the appropriate prop, mounted 2 or 3 holes up would be able to attain 49+.
LHG, a respected member who runs many Mercury engines in his fleet reports 50+ running a 22" Laser II prop.
See his comments down a bit in this archived thread:
http://continuouswave.com/ubb/Forum4/HTML/007546.html
- Scan_Pic0009.jpg (202.82 KiB) Viewed 12601 times
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003
Re: Tachometer Accuracy
[The MONTAUK 17 boat under discussion in this thread] is a 1977. The [Mercury 115-HP in-line six-cylinder two-stroke-power-cycle] engine is a 1977.
The boat is not new to us. We used to run a 1986 Johnson 110-HP on it. The Mercury is new on the boat. It is mounted two-holes-up. [Boat speed is] 42 to 43 on the GPS receiver, but the tachometer is showing over 6,000-RPM. Once we figure out if that's the true RPM, we can go to a 19-pitch stainless propeller. The boat is usually loaded heavily and has a 28-gallon fuel tank under the seat.
PhilT--what year is that 115? What pitch and propeller are you turning on yours?
The boat is not new to us. We used to run a 1986 Johnson 110-HP on it. The Mercury is new on the boat. It is mounted two-holes-up. [Boat speed is] 42 to 43 on the GPS receiver, but the tachometer is showing over 6,000-RPM. Once we figure out if that's the true RPM, we can go to a 19-pitch stainless propeller. The boat is usually loaded heavily and has a 28-gallon fuel tank under the seat.
PhilT--what year is that 115? What pitch and propeller are you turning on yours?
Re: Tachometer Accuracy
The boat image in Phil's post is not Phil's boat. Based on the Illinois registration and the 25-year-old Cadillac sedan towing it, the boat must be Larry's.
Unless your goal is to get the maximum possible boat speed under the calmest sea state with the lightest possible load, choosing a LASER 22-pitch will probably not be the best all-round propeller. Your intention to try a 19-pitch is probably a good choice.
Unless your goal is to get the maximum possible boat speed under the calmest sea state with the lightest possible load, choosing a LASER 22-pitch will probably not be the best all-round propeller. Your intention to try a 19-pitch is probably a good choice.
Re: Tachometer Accuracy
Thank for the data on the propeller, RPM, boat speed, and slip.
We bought a new tachometer and the engine speed indication came up to 5,600-RPM with a boat speed of 42 to 43 on a GPS receiver using a stainless 13-1/4 x 17 slightly cupped propeller.
The engine ran great all summer until the exhaust manifold started leaking. I found another one on eBay. But I am going to mount a 1986 Johnson 110-HP engine for next spring.
Again, Thanks.
We bought a new tachometer and the engine speed indication came up to 5,600-RPM with a boat speed of 42 to 43 on a GPS receiver using a stainless 13-1/4 x 17 slightly cupped propeller.
The engine ran great all summer until the exhaust manifold started leaking. I found another one on eBay. But I am going to mount a 1986 Johnson 110-HP engine for next spring.
Again, Thanks.