MONTAUK with 90-HP Yamaha - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  MONTAUK with 90-HP Yamaha

search | FAQ | profile | register | author help

Author Topic:   MONTAUK with 90-HP Yamaha

Appleton68 posted 05-25-2009 11:25 AM ET (US)
I have a 1981 Boston Whaler Montauk 17 re-powered with a Yamaha 90-HP two-cycle and a propeller marked 13 1/4 X 17-K. There is nothing extra in the boat; just the usual battery, tool box, extra oil, life jackets, etc. With just the driver, it seems to max out at 4,900-RPM and 23 MPH. From reading this board it seems it should be getting more engine speed and boat speed. Any comments? TY
jimh posted 05-25-2009 11:54 AM ET (US)
An article in REFERENCE
http://continuouswave.com/whaler/reference/16-17/repower.html
gives some target speeds calculated for various combinations of engine with the MONTAUK. For your set-up the target is 45-MPH. The performance you are reporting is woefully below that target. It is so bad that I suspect there is something significantly wrong. As speed is primarily a function of horsepower, I would say your Yamaha 90-HP motor needs attention and possibly repair.
Phil T posted 05-25-2009 12:33 PM ET (US)
WOT RPM's for that motor should be 5500.
In addition to having the engine looked at by a certified Yamaha mechanic, additional information is needed.
Please specify weight of fuel, gear, persons. Does the boat have bottom paint and if so, what condition is it in?
What was the sea state, wind speed, water current? How was the weight distributed.
Was the engine trimmed out?
What mounting position is the motor in?
Is the engine bracket sitting on the top of the transom or is it raised up? If raised, how many empty holes are there above the top sets of engine bolts? Can you clarify "seems to max out"
Was speed measured by engine gauge, external pitot tube or GPS.
My 1987 Yamaha 90 with a Yamaha 13.5x17K would push my 1987 Montauk , mounted on the transom, with bottom paint, light gear, single person and 10 gallons of gas to 40-41 mph.
Tohsgib posted 05-26-2009 11:56 AM ET (US)
My same setup would do just like above, 40-42 at best and 5500rpm with same prop and bottom paint. 45mph as Jim suggested is not going to happen.
Moby Dick posted 05-26-2009 01:29 PM ET (US)
My 1978 Montauk with a 1979 Johnson 100HP(rated at the crank) will hit 41 mph with 2 people at 5,100 rpm.
jimh posted 05-26-2009 02:51 PM ET (US)
The speed prediction page I mentioned uses a consistent approach to estimate the speed potential based on weight and horsepower, and, as noted, it might be too optimistic. But at least it gives a target, and here the outcome is so far off the target that we have to assume there is something significantly awry. The boat ought to be going faster with half as much horsepower.
Tohsgib posted 05-27-2009 10:22 AM ET (US)
It is a great target as Jim suggested...carry on.
Joninnj posted 05-27-2009 06:28 PM ET (US)
Appleton,
Something is wrong with the engine or set up... I run a 17 with a Yamie 90 Stroke. With the 17 I hit 5700 RPM, with a 19 I get 5200... a big drop but also see 42MPH on a GPS... I have not tested the 17 with a GPS but I suspect it will very close.
Jon
kazankota posted 05-29-2009 10:03 PM ET (US)
I would weigh your boat first. The problem could be that easy...water.
Chris posted 06-08-2009 10:23 PM ET (US)
I have a 1989 Montauk with a 2002 90 Yammie couldn't get above 3800 rpm.. I found lower carb float was plugged...Simple fix and am up to 5400-5500 RPM
Tohsgib posted 06-10-2009 09:50 AM ET (US)
Do a compression test. Running with a lean carb can do serious damage.

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: MONTAUK with 90-HP Yamaha
Appleton68	posted 05-25-2009 11:25 AM ET (US) I have a 1981 Boston Whaler Montauk 17 re-powered with a Yamaha 90-HP two-cycle and a propeller marked 13 1/4 X 17-K. There is nothing extra in the boat; just the usual battery, tool box, extra oil, life jackets, etc. With just the driver, it seems to max out at 4,900-RPM and 23 MPH. From reading this board it seems it should be getting more engine speed and boat speed. Any comments? TY
jimh	posted 05-25-2009 11:54 AM ET (US) An article in REFERENCE http://continuouswave.com/whaler/reference/16-17/repower.html gives some target speeds calculated for various combinations of engine with the MONTAUK. For your set-up the target is 45-MPH. The performance you are reporting is woefully below that target. It is so bad that I suspect there is something significantly wrong. As speed is primarily a function of horsepower, I would say your Yamaha 90-HP motor needs attention and possibly repair.
Phil T	posted 05-25-2009 12:33 PM ET (US) WOT RPM's for that motor should be 5500. In addition to having the engine looked at by a certified Yamaha mechanic, additional information is needed. Please specify weight of fuel, gear, persons. Does the boat have bottom paint and if so, what condition is it in? What was the sea state, wind speed, water current? How was the weight distributed. Was the engine trimmed out? What mounting position is the motor in? Is the engine bracket sitting on the top of the transom or is it raised up? If raised, how many empty holes are there above the top sets of engine bolts? Can you clarify "seems to max out" Was speed measured by engine gauge, external pitot tube or GPS. My 1987 Yamaha 90 with a Yamaha 13.5x17K would push my 1987 Montauk , mounted on the transom, with bottom paint, light gear, single person and 10 gallons of gas to 40-41 mph.
Tohsgib	posted 05-26-2009 11:56 AM ET (US) My same setup would do just like above, 40-42 at best and 5500rpm with same prop and bottom paint. 45mph as Jim suggested is not going to happen.
Moby Dick	posted 05-26-2009 01:29 PM ET (US) My 1978 Montauk with a 1979 Johnson 100HP(rated at the crank) will hit 41 mph with 2 people at 5,100 rpm.
jimh	posted 05-26-2009 02:51 PM ET (US) The speed prediction page I mentioned uses a consistent approach to estimate the speed potential based on weight and horsepower, and, as noted, it might be too optimistic. But at least it gives a target, and here the outcome is so far off the target that we have to assume there is something significantly awry. The boat ought to be going faster with half as much horsepower.
Tohsgib	posted 05-27-2009 10:22 AM ET (US) It is a great target as Jim suggested...carry on.
Joninnj	posted 05-27-2009 06:28 PM ET (US) Appleton, Something is wrong with the engine or set up... I run a 17 with a Yamie 90 Stroke. With the 17 I hit 5700 RPM, with a 19 I get 5200... a big drop but also see 42MPH on a GPS... I have not tested the 17 with a GPS but I suspect it will very close. Jon
kazankota	posted 05-29-2009 10:03 PM ET (US) I would weigh your boat first. The problem could be that easy...water.
Chris	posted 06-08-2009 10:23 PM ET (US) I have a 1989 Montauk with a 2002 90 Yammie couldn't get above 3800 rpm.. I found lower carb float was plugged...Simple fix and am up to 5400-5500 RPM
Tohsgib	posted 06-10-2009 09:50 AM ET (US) Do a compression test. Running with a lean carb can do serious damage.