170 Montauk 90 hp FourStroke propeller slip difference

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  170 Montauk 90 hp FourStroke propeller slip difference

search | FAQ | profile | register | author help

Author Topic:   170 Montauk 90 hp FourStroke propeller slip difference

WT posted 01-26-2010 02:56 AM ET (US)
2006 Boston Whaler 170 Montauk specs
http://img.photobucket.com/albums/v665/warrent/Montauk170/ 2007170Montaukperformance.jpg
6100 rpm
46.6 mph
20 prop pitch
2.33 gear ratio
Yields prop slip of 6.02 http://continuouswave.com/cgi-bin/propcalc.pl
2008 Boston Whaler 170 Montauk specs
http://img.photobucket.com/albums/v665/warrent/Montauk170/ 2009170Montaukperformance.jpg
5900 rpm
42.8 mph
20 prop pitch
2.33 gear ratio
Yields prop slip of 10.76
Why such a difference in propeller slippage?
Warren

Peter posted 01-26-2010 07:16 AM ET (US)
Running with current versus running against current would change the speed over ground by the difference in the current and that would change slip because it is simply a calculated number.
jimh posted 01-26-2010 09:49 AM ET (US)
One boat goes faster than the other. As boat speed increases, the calculated propeller SLIP tends to decrease.
Why there was such a difference in boat speed would be a more interesting answer to seek.
number9 posted 01-26-2010 10:38 AM ET (US)
The earlier test was done in 2005. Yamaha power head on Mercury running gear. The 2007 test using the new heavier motor.
Tom W Clark posted 01-26-2010 11:02 AM ET (US)
Yes, that is a good point.
The Yamaha produced Mercury 90 is faster than the current Veradito 90 by quite a bit.
As a general rule, propeller slip increases as boat speed increases, at least at speeds well beyond the transition to plane.
The difference in slip may be because different propellers were used, or the same props were used but different vent plugs were used.
If the motor mounting heights were not identical, then the slip will be different.
Also, the boat operator will influence slip quite a bit by varying the trim of the motor at WOT.
The weather and water condition will also affect a boats performance. It is not uncommon to see different test results from one day to the next, let alone two different boats tested two years apart by two different people.
WT posted 01-26-2010 11:18 AM ET (US)
Both tested used the same outboards, L4NA or 90 hp FourStroke.
I'm guessing the most recent Boston Whaler test indicating WOT top speed of 42.8 mph is flawed or "toned down" because:
1) my bloated 170 Montauk with same prop, outboard and hull tops out at 44-45 mph.
2) my calculated prop slip is around 6.7%.
3) other 170 Montauks with 90 hp FourStrokes have reported 45 mph top speeds.
My outboard is mounted down 3 holes from the top and I have around 80 pounds extra hanging on my transom. (6hp kicker, bracket, swim platform and stainless steel hydrofoil.)
I suppose my point is that the 90 hp FourStroke is more powerful than the most recent performance test indicates.
Warren
Tom W Clark posted 01-26-2010 11:50 AM ET (US)
Warren -- Are you sure the earlier test was with a Veradito? The test was done in 2005.
At any rate the boat weights/loads were nearly identical as was the weather.
Another thing that is hugely different is the earlier test shows much better fuel economy, 8.12 MPG vs. 6.97 MPG, a 16 percent difference!
number9 posted 01-26-2010 12:09 PM ET (US)
2005, dry weight 1790.
2007, dry weight 1924.
Don't think the Veradito was available in 02-05.
WT posted 01-26-2010 12:50 PM ET (US)
I am positive the earlier test was with the Veridito. I had the 90 Yamaha/Mercury on my 2004 170 Montauk and was shocked when Boston Whaler published the top end of the 170 Montauks with the new 90 hp FourStroke (Veridito).
My bloated 170 Montauk with the old Yamaha/Mercury had a top end around 39-40 mph. I upgraded my outboard to the newer 90 hp FourStroke (Veradito).
Here is the only performance test I ever found for the Yamaha/Mercury 90 Four-Stroke that came with a 18 pitch Vengeance prop.
http://myweb.cableone.net/barney9014/images/performance.jpg
Warren
Tom W Clark posted 01-26-2010 12:51 PM ET (US)
2005, Test weight 2209.
2007, Test weight 2291.
number9 posted 01-26-2010 01:05 PM ET (US)
Tom,
Saw the test weights too, but found the difference in dry weights interesting. What's going to make the 134 lb. difference on the rigged boat?
WT posted 01-26-2010 01:06 PM ET (US)
Here's a prop slippage chart for the old 90 hp Yamaha/Mercury Four-Stroke by, CW member Moe.
http://myweb.cableone.net/barney9014/images/performance2.jpg
http://continuouswave.com/ubb/Forum8/HTML/001115.html
Slippage drops as rpms increase. Looks like slppage at WOT should be around 6-7% with a stainless steel prop on a 170 Montauk spinning around 5800-6000 rpm.
Warren
WT posted 01-26-2010 01:17 PM ET (US)
Using Jim's prop calculator.
http://continuouswave.com/cgi-bin/propcalc.pl
All 170 Montauks with Yamaha/Mercury outboards came with the 18 pitch Vengeance prop. All newer 170 Montauks with FourStroke come with 20 pitch Laser II prop.
Old 170 Montauk
6000 rpm
2.33 gear ratio
18 pitch prop
6.5% slip
Estimated speed is 41.04 mph
New 170 Montauk
6,0000 rpm
2.33 gear ratio
20 pitch prop
6.5% slip
Estimated speed is 45.6 mph.
The newer Mercury 90 is a stronger motor able to spin a larger pitch prop at 6,000 rpm.
Warren
Tom W Clark posted 01-26-2010 01:20 PM ET (US)
number9 -- More fuel and heavier occupants.
number9 posted 01-26-2010 01:40 PM ET (US)
Tom,
Fuel and people are added to empty weight.
Bill
Tom W Clark posted 01-26-2010 02:13 PM ET (US)
That is correct.
Are you wondering why the two listed dry weights vary? Good question.
The 170 Montauk is specified as weighing 1400 pounds in 2005 and 2007. I do not believe there is any weight gain in this time frame.
The difference between the Montauk's weight and the dry weight is the weight of the motor. That difference is:
2005: 1790 - 1400 = 390 pounds
2007: 1924 - 1400 = 524 pounds
Perry posted 01-26-2010 10:48 PM ET (US)
The 2005 Mercaha 90 weighs around 390 lbs and a Verado based 90 sold in 2008 weighs about 524 lbs.
Does this mean that the Montauk 170 in the performance report from 2006 has a Mercaha 90 ?
L H G posted 01-27-2010 01:35 AM ET (US)
The difference in weight between the two 4-stroke 90's is 13#. (386 vs 399)
I would not agree with Tom that the Mercaha is faster than the Verado engine, introduced 2007 model year boats.
SC Joe posted 01-27-2010 09:57 AM ET (US)
The test results are interesting, and different than what I witness on my boat.
My 2008 Montauk has a 21" prop, not a 20.
It will also go faster (regularly 44 MPH via GPS) than what is listed. I have seen 45.8 mph once when it was brand new (<30 hours) via GPS, but I think there was a wind at my back as I have not been able to duplicate that speed.
Also, my Smartcraft enabled Northstar GPS reads 6000-6100 rpm before it starts to cut out (presumably due to an electronic rev limiter, but it could be blowing up I guess).
SC Joe posted 01-27-2010 10:04 AM ET (US)
Adding to the weight argument above--also remember that the console is taller by 4" starting in 2008. I don't how much, if any weight that adds.
My 2008 170 boat on the trailer with a spare tire and wheel, two batteries in the boat and one full tank of gas (6.6 gallons) weighs 2660# according to a truck scale.
Perry posted 01-27-2010 12:11 PM ET (US)
Larry, those are dry weights you listed. The motors hanging on the test boats had motor oil, gear oil and props on them.
Perry posted 01-27-2010 12:15 PM ET (US)
Clicked enter too fast. I meant to say that even with fluids and props, there has to be something else to explain the weight difference between the 2 test boats.
WT posted 01-27-2010 12:31 PM ET (US)
Both performance tests were with the same Verado based Mercury 90 hp FourStroke.
The latest test indicates a slip of over 10% which I believe is an error.
My prop slip at WOT is around 6.7%. Do you guys know your prop slip factor?
Warren
tbyrne posted 01-27-2010 04:11 PM ET (US)
I think the prop calculator is of tenuous value - you get different prop slip calculations because the model incorrectly assumes that the stated pitches are accurate and a constant. Unless you are using identical models of props, the pitches are not a constant and the slip numbers are simply the product of nominal pitch numbers.
On my 18' Rothbilt with a 80 hp Yamaha four stroke, the OEM 13.25 x 17" pitch Yamaha ran all the way to 6,000 rpms. A SS Stiletto that was nominally a 15" pitch only ran to 5,600 rpms but had a slightly higher top speed. I replaced it with a 15" Stiletto that then ran to 5,750. After it was re-pitched at the factory to 14", I got about 5,850-5,900.
If you assumed the pitch numbers were accurate, your slip numbers would have been all over the place.
Tom W Clark posted 01-28-2010 10:31 AM ET (US)

quote:
I think the prop calculator is of tenuous value...
Boy, I have to completely disagree with that. The Propeller Calculator is a very useful tool, I use it every day, but you have to understand what it does. It simply does some tedious arithmetic, no more.
The Propeller Calculator simply crunches numbers. It cannot take into account different models of propellers. It allows one to estimate any one of five different variables given the other four.
Propellers are not generic pieces of hardware like a wood screw from the hardware store. Different designs of propellers will perform differently for a hundred different reasons.
In the course of repeated testing we have come to know what to expect form many different models of propellers. The Propeller Calculator has shown me what to expect by demonstrating the performance differences between many different models.
It is precisely because of the Propeller Calculator that I have come to understand how to gauge a Stiletto brand propeller vis-a-vis other brands. That is not something I could have done without it.
Your experience with the Stiletto propellers on your own boat are exactly what I would have expected and I have the Propeller Calculator to thank for that education.
Tom W Clark posted 01-28-2010 10:39 AM ET (US)
Getting back to the subject of slip, there is a great misconception out there that somehow less slip is better. This is a completely false idea.
There is also a misconception that propeller slip is the same thing a efficiency. This is also completely wrong.
If a boat is faster (or more fuel efficient, or accelerates better, or handles better) with a prop that has a high calculated slip, then so be it. It is the better propeller for the application.
The one and ONLY place where less slip is better and indicates greater efficiency, is when the the SAME propeller is test on the SAME boat with different adjustments to the rigging are made and this is only true everything else is constant.
Slip calculations are used as a relative point of comparison, it is not a goal in, and of, itself.
SC Joe posted 01-28-2010 09:46 PM ET (US)

quote:
The 2005 Mercaha 90 weighs around 390 lbs and a Verado based 90 sold in 2008 weighs about 524 lbs.
Does this mean that the Montauk 170 in the performance report from 2006 has a Mercaha 90 ?
I missed this earlier. I'm not sure how anyone figured the newer Mercury FourStroke to weigh 524 pounds.
It weighs 390 pounds. In fact Montauk 170's come from Boston Whaler with a large red sticker that expressly states to NOT mount an engine that weighs more than 410 pounds.
Perry posted 01-28-2010 10:42 PM ET (US)
It was a typo. It was meant to read 424, which would be close to the weight of the motor after you add oil and a stainless prop.
Peter posted 01-29-2010 07:22 AM ET (US)
The Veradito 90 weighs 399 lbs, dry. Add about 10 lbs of oil to the crankcase and gearcase and a propeller and I bet the total weight isn't far from Perry's estimation.
Best way to determine efficiency of various propellers is with a fuel flow computer that can display instant MPG. The propeller that produces the highest MPG is the most efficient irrespective of what the calculated slip number happens to be.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: 170 Montauk 90 hp FourStroke propeller slip difference
WT	posted 01-26-2010 02:56 AM ET (US) 2006 Boston Whaler 170 Montauk specs http://img.photobucket.com/albums/v665/warrent/Montauk170/ 2007170Montaukperformance.jpg 6100 rpm 46.6 mph 20 prop pitch 2.33 gear ratio Yields prop slip of 6.02 http://continuouswave.com/cgi-bin/propcalc.pl 2008 Boston Whaler 170 Montauk specs http://img.photobucket.com/albums/v665/warrent/Montauk170/ 2009170Montaukperformance.jpg 5900 rpm 42.8 mph 20 prop pitch 2.33 gear ratio Yields prop slip of 10.76 Why such a difference in propeller slippage? Warren
Peter	posted 01-26-2010 07:16 AM ET (US) Running with current versus running against current would change the speed over ground by the difference in the current and that would change slip because it is simply a calculated number.
jimh	posted 01-26-2010 09:49 AM ET (US) One boat goes faster than the other. As boat speed increases, the calculated propeller SLIP tends to decrease. Why there was such a difference in boat speed would be a more interesting answer to seek.
number9	posted 01-26-2010 10:38 AM ET (US) The earlier test was done in 2005. Yamaha power head on Mercury running gear. The 2007 test using the new heavier motor.
Tom W Clark	posted 01-26-2010 11:02 AM ET (US) Yes, that is a good point. The Yamaha produced Mercury 90 is faster than the current Veradito 90 by quite a bit. As a general rule, propeller slip increases as boat speed increases, at least at speeds well beyond the transition to plane. The difference in slip may be because different propellers were used, or the same props were used but different vent plugs were used. If the motor mounting heights were not identical, then the slip will be different. Also, the boat operator will influence slip quite a bit by varying the trim of the motor at WOT. The weather and water condition will also affect a boats performance. It is not uncommon to see different test results from one day to the next, let alone two different boats tested two years apart by two different people.
WT	posted 01-26-2010 11:18 AM ET (US) Both tested used the same outboards, L4NA or 90 hp FourStroke. I'm guessing the most recent Boston Whaler test indicating WOT top speed of 42.8 mph is flawed or "toned down" because: 1) my bloated 170 Montauk with same prop, outboard and hull tops out at 44-45 mph. 2) my calculated prop slip is around 6.7%. 3) other 170 Montauks with 90 hp FourStrokes have reported 45 mph top speeds. My outboard is mounted down 3 holes from the top and I have around 80 pounds extra hanging on my transom. (6hp kicker, bracket, swim platform and stainless steel hydrofoil.) I suppose my point is that the 90 hp FourStroke is more powerful than the most recent performance test indicates. Warren
Tom W Clark	posted 01-26-2010 11:50 AM ET (US) Warren -- Are you sure the earlier test was with a Veradito? The test was done in 2005. At any rate the boat weights/loads were nearly identical as was the weather. Another thing that is hugely different is the earlier test shows much better fuel economy, 8.12 MPG vs. 6.97 MPG, a 16 percent difference!
number9	posted 01-26-2010 12:09 PM ET (US) 2005, dry weight 1790. 2007, dry weight 1924. Don't think the Veradito was available in 02-05.
WT	posted 01-26-2010 12:50 PM ET (US) I am positive the earlier test was with the Veridito. I had the 90 Yamaha/Mercury on my 2004 170 Montauk and was shocked when Boston Whaler published the top end of the 170 Montauks with the new 90 hp FourStroke (Veridito). My bloated 170 Montauk with the old Yamaha/Mercury had a top end around 39-40 mph. I upgraded my outboard to the newer 90 hp FourStroke (Veradito). Here is the only performance test I ever found for the Yamaha/Mercury 90 Four-Stroke that came with a 18 pitch Vengeance prop. http://myweb.cableone.net/barney9014/images/performance.jpg Warren
Tom W Clark	posted 01-26-2010 12:51 PM ET (US) 2005, Test weight 2209. 2007, Test weight 2291.
number9	posted 01-26-2010 01:05 PM ET (US) Tom, Saw the test weights too, but found the difference in dry weights interesting. What's going to make the 134 lb. difference on the rigged boat?
WT	posted 01-26-2010 01:06 PM ET (US) Here's a prop slippage chart for the old 90 hp Yamaha/Mercury Four-Stroke by, CW member Moe. http://myweb.cableone.net/barney9014/images/performance2.jpg http://continuouswave.com/ubb/Forum8/HTML/001115.html Slippage drops as rpms increase. Looks like slppage at WOT should be around 6-7% with a stainless steel prop on a 170 Montauk spinning around 5800-6000 rpm. Warren
WT	posted 01-26-2010 01:17 PM ET (US) Using Jim's prop calculator. http://continuouswave.com/cgi-bin/propcalc.pl All 170 Montauks with Yamaha/Mercury outboards came with the 18 pitch Vengeance prop. All newer 170 Montauks with FourStroke come with 20 pitch Laser II prop. Old 170 Montauk 6000 rpm 2.33 gear ratio 18 pitch prop 6.5% slip Estimated speed is 41.04 mph New 170 Montauk 6,0000 rpm 2.33 gear ratio 20 pitch prop 6.5% slip Estimated speed is 45.6 mph. The newer Mercury 90 is a stronger motor able to spin a larger pitch prop at 6,000 rpm. Warren
Tom W Clark	posted 01-26-2010 01:20 PM ET (US) number9 -- More fuel and heavier occupants.
number9	posted 01-26-2010 01:40 PM ET (US) Tom, Fuel and people are added to empty weight. Bill
Tom W Clark	posted 01-26-2010 02:13 PM ET (US) That is correct. Are you wondering why the two listed dry weights vary? Good question. The 170 Montauk is specified as weighing 1400 pounds in 2005 and 2007. I do not believe there is any weight gain in this time frame. The difference between the Montauk's weight and the dry weight is the weight of the motor. That difference is: 2005: 1790 - 1400 = 390 pounds 2007: 1924 - 1400 = 524 pounds
Perry	posted 01-26-2010 10:48 PM ET (US) The 2005 Mercaha 90 weighs around 390 lbs and a Verado based 90 sold in 2008 weighs about 524 lbs. Does this mean that the Montauk 170 in the performance report from 2006 has a Mercaha 90 ?
L H G	posted 01-27-2010 01:35 AM ET (US) The difference in weight between the two 4-stroke 90's is 13#. (386 vs 399) I would not agree with Tom that the Mercaha is faster than the Verado engine, introduced 2007 model year boats.
SC Joe	posted 01-27-2010 09:57 AM ET (US) The test results are interesting, and different than what I witness on my boat. My 2008 Montauk has a 21" prop, not a 20. It will also go faster (regularly 44 MPH via GPS) than what is listed. I have seen 45.8 mph once when it was brand new (<30 hours) via GPS, but I think there was a wind at my back as I have not been able to duplicate that speed. Also, my Smartcraft enabled Northstar GPS reads 6000-6100 rpm before it starts to cut out (presumably due to an electronic rev limiter, but it could be blowing up I guess).
SC Joe	posted 01-27-2010 10:04 AM ET (US) Adding to the weight argument above--also remember that the console is taller by 4" starting in 2008. I don't how much, if any weight that adds. My 2008 170 boat on the trailer with a spare tire and wheel, two batteries in the boat and one full tank of gas (6.6 gallons) weighs 2660# according to a truck scale.
Perry	posted 01-27-2010 12:11 PM ET (US) Larry, those are dry weights you listed. The motors hanging on the test boats had motor oil, gear oil and props on them.
Perry	posted 01-27-2010 12:15 PM ET (US) Clicked enter too fast. I meant to say that even with fluids and props, there has to be something else to explain the weight difference between the 2 test boats.
WT	posted 01-27-2010 12:31 PM ET (US) Both performance tests were with the same Verado based Mercury 90 hp FourStroke. The latest test indicates a slip of over 10% which I believe is an error. My prop slip at WOT is around 6.7%. Do you guys know your prop slip factor? Warren
tbyrne	posted 01-27-2010 04:11 PM ET (US) I think the prop calculator is of tenuous value - you get different prop slip calculations because the model incorrectly assumes that the stated pitches are accurate and a constant. Unless you are using identical models of props, the pitches are not a constant and the slip numbers are simply the product of nominal pitch numbers. On my 18' Rothbilt with a 80 hp Yamaha four stroke, the OEM 13.25 x 17" pitch Yamaha ran all the way to 6,000 rpms. A SS Stiletto that was nominally a 15" pitch only ran to 5,600 rpms but had a slightly higher top speed. I replaced it with a 15" Stiletto that then ran to 5,750. After it was re-pitched at the factory to 14", I got about 5,850-5,900. If you assumed the pitch numbers were accurate, your slip numbers would have been all over the place.
Tom W Clark	posted 01-28-2010 10:31 AM ET (US) quote: I think the prop calculator is of tenuous value... Boy, I have to completely disagree with that. The Propeller Calculator is a very useful tool, I use it every day, but you have to understand what it does. It simply does some tedious arithmetic, no more. The Propeller Calculator simply crunches numbers. It cannot take into account different models of propellers. It allows one to estimate any one of five different variables given the other four. Propellers are not generic pieces of hardware like a wood screw from the hardware store. Different designs of propellers will perform differently for a hundred different reasons. In the course of repeated testing we have come to know what to expect form many different models of propellers. The Propeller Calculator has shown me what to expect by demonstrating the performance differences between many different models. It is precisely because of the Propeller Calculator that I have come to understand how to gauge a Stiletto brand propeller vis-a-vis other brands. That is not something I could have done without it. Your experience with the Stiletto propellers on your own boat are exactly what I would have expected and I have the Propeller Calculator to thank for that education.
Tom W Clark	posted 01-28-2010 10:39 AM ET (US) Getting back to the subject of slip, there is a great misconception out there that somehow less slip is better. This is a completely false idea. There is also a misconception that propeller slip is the same thing a efficiency. This is also completely wrong. If a boat is faster (or more fuel efficient, or accelerates better, or handles better) with a prop that has a high calculated slip, then so be it. It is the better propeller for the application. The one and ONLY place where less slip is better and indicates greater efficiency, is when the the SAME propeller is test on the SAME boat with different adjustments to the rigging are made and this is only true everything else is constant. Slip calculations are used as a relative point of comparison, it is not a goal in, and of, itself.
SC Joe	posted 01-28-2010 09:46 PM ET (US) quote: The 2005 Mercaha 90 weighs around 390 lbs and a Verado based 90 sold in 2008 weighs about 524 lbs. Does this mean that the Montauk 170 in the performance report from 2006 has a Mercaha 90 ? I missed this earlier. I'm not sure how anyone figured the newer Mercury FourStroke to weigh 524 pounds. It weighs 390 pounds. In fact Montauk 170's come from Boston Whaler with a large red sticker that expressly states to NOT mount an engine that weighs more than 410 pounds.
Perry	posted 01-28-2010 10:42 PM ET (US) It was a typo. It was meant to read 424, which would be close to the weight of the motor after you add oil and a stainless prop.
Peter	posted 01-29-2010 07:22 AM ET (US) The Veradito 90 weighs 399 lbs, dry. Add about 10 lbs of oil to the crankcase and gearcase and a propeller and I bet the total weight isn't far from Perry's estimation. Best way to determine efficiency of various propellers is with a fuel flow computer that can display instant MPG. The propeller that produces the highest MPG is the most efficient irrespective of what the calculated slip number happens to be.