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Author Topic:   E-TEC 90 Prop Replacement for Montauk

Ducktown posted 08-10-2010 10:27 PM ET (US)
I've got the standard issue Stiletto 13.25" X 15" stainless prop on my 1988 Montauk's 90 hp E-TEC. Since purchasing this rig used last fall, I've been puzzled by the RPMs at WOT being @ 4700. I've been pondering dropping to a 13" pitch to see if I can get the WOT RPMs to slightly above 5000.
This weekend the issue was forced as I clanked my prop on a submerged mooring, bending one of the blades.
Knowing I'm likely to repeat this atrocity in the future, I'm now looking for an aluminum prop that will transmit less of the force of future strikes to the lower unit.
The questions:
- Given my RPM issues, is a 13" pitch the right way to go - even though it sounds too low?
- Will a 13.25" X 13" aluminum prop give me roughly the same RPM performance results as a stainless prop of the same dimensions?

Tohsgib posted 08-11-2010 12:03 PM ET (US)
Something wrong....all montauks I have seen are running the 15" beyond 5k.
Ducktown posted 08-11-2010 03:51 PM ET (US)
I suppose it could be a faulty tachometer, but top speed (as measured by GPS) is only @ 36 or 37 mph with 24 gallons of fuel and one 210 lb body.
Nonetheless, does should a similarly configured aluminum prop behave roughly the same as a stainless one?
crabby posted 08-11-2010 07:21 PM ET (US)
How high up is the motor mounted? Don't discount motor height. My similar rig is mounted three holes up (only one more to go) and I pull 5200-5400 rpm's. Once you get the height set correctly you will also need to trim the motor out a bit; you will know if the motor is trimmed a little too much if it loses grip in fairly tight turns (or loses grip due to picking up the stray weed). You may need to check your trim: when my big Lab rides up front I lose a little speed (but gain in bottom clearance).
Search this forum and you will find many threads that more or less echo what I just posted for folks running a similar setup (boat, motor, prop).
--Paul
2004 90hp E-Tec (since September 2004)
1985 Boston Whaler Montauk (since August 1985)
Ducktown posted 08-11-2010 07:49 PM ET (US)
The 90 hp E-TEC is on a jack plate. The anti-ventilation plate is @ 1.5 to 2 inches above the bottom of the transom. Could be I've been operating the boat with the trim too tight to the boat. Could this really explain such low RPMs at WOT?
In any case, I still need to replace the stainless prop due to the damage. Should I just approximate the size and pitch of my current stainless with an aluminum replacement or "pitch down" a bit?
Nauti Tauk posted 08-11-2010 08:14 PM ET (US)
Sounds to me like the engine isn't trimmed up when you're running. I absolutely agree with Nick, there's something wrong. With a jack plate and the vent plate above the boat bottom you should be ripp'in 42-43 at 5250. If your not seeing those numbers after trimming the motor out at WOT I would think a trip to the dealer would be in order. Tom Clark is the prop guru but a good 15" stainless should be your best bet.
meridian posted 08-11-2010 09:27 PM ET (US)
I have the same set-up. I'm running a Stiletto 13.25 x 17 and got 44.4 @ 5,300rpm w/one aboard and about 10 gal fuel. When I had the Stiletto 13.25 x 15, it would run up to 5,700rpm. I have a 6" jackplate and I'm about 2" up.
Ducktown posted 08-11-2010 10:15 PM ET (US)
Ok then. Thanks all. Looks like I'll be taking it in for service.
Tom W Clark posted 08-11-2010 10:18 PM ET (US)
There have now been so many Montauk repowers with the Evinrude E-TEC 90 and the 13-1/4" x 15" Stiletto Advantage that I suspect there may be something wrong if such a motor cannot turn that prop.
Yes, there have been a few rare instances where the 17" Advantage was the better fit, for whatever reason, but none where it should necessitate a drop down to the 13" pitch model.
4700 RPM does not seem right. How heavy is that boat?
cinegamma posted 08-14-2010 12:03 AM ET (US)
Ducktown,
Here's a link to a thread where I had a similar issue:
http://continuouswave.com/ubb/Forum4/HTML/007227.html
I will say that depending on conditions, my WOT can vary between 4,800 and 5,000. 1984 Montauk, 2007 90hp E-TEC, 13.25 x 17 SST prop, mounted 2 holes up.
cinegamma posted 08-14-2010 12:05 AM ET (US)
Ducktown,
Here's a link to a thread where I had a similar issue:
http://continuouswave.com/ubb/Forum4/HTML/007227.html
I will say that depending on conditions, my WOT can vary between 4,800 and 5,000. 1984 Montauk, 2007 90hp E-TEC, 13.25 x 17 SST prop, mounted 2 holes up.
Ducktown posted 08-16-2010 01:22 PM ET (US)
Once again, the CW Team comes through!
This weekend I played around a bit with the trim at WOT and got 5000+ RPM out of it. I clearly had it too tight to the hull at higher speeds. I'm still only getting about 38 MPH as measured by my GPS unit. This can most likely be attributed to a heavier than normal hull. I'm quite sure I've got water in there as, not unlike myself, my boat is a bit "left-leaning" relative to the waterline.
Tohsgib posted 08-16-2010 02:06 PM ET (US)
Try new plugs, might perk her up a bit.
ratherwhalering posted 08-18-2010 03:24 PM ET (US)
Check that your GPS is set to MPH and not KNT.
Tom W Clark posted 08-19-2010 08:43 AM ET (US)
The list to port has nothing to do with water weight gain; it is a result of propeller torque and is often aggravated by a misadjusted trim tab on the outboard.
Ducktown posted 08-19-2010 08:27 PM ET (US)
The list is always there. Whether moving or sitting still on the mooring.
wstr75 posted 08-28-2010 09:31 AM ET (US)
My newly re-powered 1987 Montauk (90 hp E-Tec, 15" Stiletto propeller, half-full 24 gal new Moeller fuel tank, 195 pound man) was straight-line run in opposing directions yesterday afternoon on an open lake with little wind and a smooth surface. The speed both directions at 5050 - 5100 RPMs was 42.3 mph. Air temperature was about 90 degrees F. The propeller provides great all-around performance (speed, turns and acceleration). Thanks to all the previous folks on CW who posted their propeller/engine performance results!
Bill in NC

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Author	Topic: E-TEC 90 Prop Replacement for Montauk
Ducktown	posted 08-10-2010 10:27 PM ET (US) I've got the standard issue Stiletto 13.25" X 15" stainless prop on my 1988 Montauk's 90 hp E-TEC. Since purchasing this rig used last fall, I've been puzzled by the RPMs at WOT being @ 4700. I've been pondering dropping to a 13" pitch to see if I can get the WOT RPMs to slightly above 5000. This weekend the issue was forced as I clanked my prop on a submerged mooring, bending one of the blades. Knowing I'm likely to repeat this atrocity in the future, I'm now looking for an aluminum prop that will transmit less of the force of future strikes to the lower unit. The questions: - Given my RPM issues, is a 13" pitch the right way to go - even though it sounds too low? - Will a 13.25" X 13" aluminum prop give me roughly the same RPM performance results as a stainless prop of the same dimensions?
Tohsgib	posted 08-11-2010 12:03 PM ET (US) Something wrong....all montauks I have seen are running the 15" beyond 5k.
Ducktown	posted 08-11-2010 03:51 PM ET (US) I suppose it could be a faulty tachometer, but top speed (as measured by GPS) is only @ 36 or 37 mph with 24 gallons of fuel and one 210 lb body. Nonetheless, does should a similarly configured aluminum prop behave roughly the same as a stainless one?
crabby	posted 08-11-2010 07:21 PM ET (US) How high up is the motor mounted? Don't discount motor height. My similar rig is mounted three holes up (only one more to go) and I pull 5200-5400 rpm's. Once you get the height set correctly you will also need to trim the motor out a bit; you will know if the motor is trimmed a little too much if it loses grip in fairly tight turns (or loses grip due to picking up the stray weed). You may need to check your trim: when my big Lab rides up front I lose a little speed (but gain in bottom clearance). Search this forum and you will find many threads that more or less echo what I just posted for folks running a similar setup (boat, motor, prop). --Paul 2004 90hp E-Tec (since September 2004) 1985 Boston Whaler Montauk (since August 1985)
Ducktown	posted 08-11-2010 07:49 PM ET (US) The 90 hp E-TEC is on a jack plate. The anti-ventilation plate is @ 1.5 to 2 inches above the bottom of the transom. Could be I've been operating the boat with the trim too tight to the boat. Could this really explain such low RPMs at WOT? In any case, I still need to replace the stainless prop due to the damage. Should I just approximate the size and pitch of my current stainless with an aluminum replacement or "pitch down" a bit?
Nauti Tauk	posted 08-11-2010 08:14 PM ET (US) Sounds to me like the engine isn't trimmed up when you're running. I absolutely agree with Nick, there's something wrong. With a jack plate and the vent plate above the boat bottom you should be ripp'in 42-43 at 5250. If your not seeing those numbers after trimming the motor out at WOT I would think a trip to the dealer would be in order. Tom Clark is the prop guru but a good 15" stainless should be your best bet.
meridian	posted 08-11-2010 09:27 PM ET (US) I have the same set-up. I'm running a Stiletto 13.25 x 17 and got 44.4 @ 5,300rpm w/one aboard and about 10 gal fuel. When I had the Stiletto 13.25 x 15, it would run up to 5,700rpm. I have a 6" jackplate and I'm about 2" up.
Ducktown	posted 08-11-2010 10:15 PM ET (US) Ok then. Thanks all. Looks like I'll be taking it in for service.
Tom W Clark	posted 08-11-2010 10:18 PM ET (US) There have now been so many Montauk repowers with the Evinrude E-TEC 90 and the 13-1/4" x 15" Stiletto Advantage that I suspect there may be something wrong if such a motor cannot turn that prop. Yes, there have been a few rare instances where the 17" Advantage was the better fit, for whatever reason, but none where it should necessitate a drop down to the 13" pitch model. 4700 RPM does not seem right. How heavy is that boat?
cinegamma	posted 08-14-2010 12:03 AM ET (US) Ducktown, Here's a link to a thread where I had a similar issue: http://continuouswave.com/ubb/Forum4/HTML/007227.html I will say that depending on conditions, my WOT can vary between 4,800 and 5,000. 1984 Montauk, 2007 90hp E-TEC, 13.25 x 17 SST prop, mounted 2 holes up.
cinegamma	posted 08-14-2010 12:05 AM ET (US) Ducktown, Here's a link to a thread where I had a similar issue: http://continuouswave.com/ubb/Forum4/HTML/007227.html I will say that depending on conditions, my WOT can vary between 4,800 and 5,000. 1984 Montauk, 2007 90hp E-TEC, 13.25 x 17 SST prop, mounted 2 holes up.
Ducktown	posted 08-16-2010 01:22 PM ET (US) Once again, the CW Team comes through! This weekend I played around a bit with the trim at WOT and got 5000+ RPM out of it. I clearly had it too tight to the hull at higher speeds. I'm still only getting about 38 MPH as measured by my GPS unit. This can most likely be attributed to a heavier than normal hull. I'm quite sure I've got water in there as, not unlike myself, my boat is a bit "left-leaning" relative to the waterline.
Tohsgib	posted 08-16-2010 02:06 PM ET (US) Try new plugs, might perk her up a bit.
ratherwhalering	posted 08-18-2010 03:24 PM ET (US) Check that your GPS is set to MPH and not KNT.
Tom W Clark	posted 08-19-2010 08:43 AM ET (US) The list to port has nothing to do with water weight gain; it is a result of propeller torque and is often aggravated by a misadjusted trim tab on the outboard.
Ducktown	posted 08-19-2010 08:27 PM ET (US) The list is always there. Whether moving or sitting still on the mooring.
wstr75	posted 08-28-2010 09:31 AM ET (US) My newly re-powered 1987 Montauk (90 hp E-Tec, 15" Stiletto propeller, half-full 24 gal new Moeller fuel tank, 195 pound man) was straight-line run in opposing directions yesterday afternoon on an open lake with little wind and a smooth surface. The speed both directions at 5050 - 5100 RPMs was 42.3 mph. Air temperature was about 90 degrees F. The propeller provides great all-around performance (speed, turns and acceleration). Thanks to all the previous folks on CW who posted their propeller/engine performance results! Bill in NC