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Author Topic:   MONTAUK: Engine Mounting Height

MikeF1 posted 09-26-2013 11:05 AM ET (US)
I just bought an 1982 Montauk that came with a 1998 Mercury 115-HP 2+2 motor. The boat leans to the left at higher speeds. I've read MANY posts about propeller torque and the trim tab on the lower unit, and I will try tinkering with that. I've also read that placement of the motor on the transom can have a significant impact. How high should it be mounted? The lean is annoying enough (to me) that I will consider trim tabs if I can't correct it with other adjustments.
I spent five years as a marine police officer here in NJ 25 years ago and the Montauk was our primary patrol boat. I always loved the boat but don't recall the torque lean ever being an issue. We ran 115 Johnsons and 90 Evinrudes way back then.
Tom W Clark posted 09-26-2013 11:08 AM ET (US)
Where is the motor mounted now?
What propeller is being used?
jimh posted 09-26-2013 05:33 PM ET (US)
The trim tab on the gear case can help to reduce steering torque. It will not stop the boat from leaning.
Boston Whaler boat hulls tend to lean into the wind. You many be observing that effect, in addition to propeller torque.
Tom W Clark posted 09-26-2013 09:18 PM ET (US)
Well, that not quite right. The trim tab is there to correct for steering torque not boat list, but it can have a profound effect on that list, making it much, much worse usually.
If the trim tab is not set correctly, and the Boston Whaler Owner's Manual offer advice on that point, it can exacerbate the list to port caused by propeller torque.
This seems to be more of a problem on boats that are equipped with no-feedback steering systems where a mis-adjusted trim tab is less evident at the helm. If the trim tab is set with its trailing edge to port, the list can be greatly increased.
Combine that with a motor set too low, too much negative trim of the motor, an propeller with too much pitch and the list can be very significant and irritating.
MikeF1 posted 09-27-2013 09:36 AM ET (US)
The tab is set neutral, the motor is in the second hole from the bottom and I'm not sure about the prop (3 blade aluminum) but the previous owner said that he changed it. It turns a little over 5000 rpm WOT resulting in low to mid-40s MPH with two POB and 22 gallons of fuel. The boat is out of the water for the season. At normal cruise its fine but at about 3500 RPM the lean becomes noticeable and just gets worse at higher speeds. It does have the NFB steering and I don't recall if it was difficult to turn to starboard.

Tom W Clark posted 09-27-2013 10:47 AM ET (US)

quote:
...the motor is in the second hole from the bottom
That is ambiguous. The 1998 Mercury 115 has five sets of motor mounting bolt holes. Your upper bolts are going through this hole?
o
o
o
o <-- Mounting Bolts Through This Hole?
o
If so, and if you have a 20" shaft length model, that is the right height for a good stainless steel propeller. I cannot see how an aluminum prop would grip very well at that height.
Set the trim tab with its trailing edge to starboard, just as both Mercury and Boston Whaler recommend. That will help.
But I suspect there is more to this story...
Tom W Clark posted 09-27-2013 11:11 AM ET (US)

quote:
It turns a little over 5000 rpm WOT resulting in low to mid-40s MPH with two POB and 22 gallons of fuel.
I find this odd too. A properly set up Montauk with a Mercury 115 should be good for close to 48 MPH.
The WOT range for this motor is 4750-5250 RPM so what you are getting now is good, but we don't know what propeller you have. I suspect a Mercury 12-3/4" x 21" , a common prop for this boat/motor combo.

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Author	Topic: MONTAUK: Engine Mounting Height
MikeF1	posted 09-26-2013 11:05 AM ET (US) I just bought an 1982 Montauk that came with a 1998 Mercury 115-HP 2+2 motor. The boat leans to the left at higher speeds. I've read MANY posts about propeller torque and the trim tab on the lower unit, and I will try tinkering with that. I've also read that placement of the motor on the transom can have a significant impact. How high should it be mounted? The lean is annoying enough (to me) that I will consider trim tabs if I can't correct it with other adjustments. I spent five years as a marine police officer here in NJ 25 years ago and the Montauk was our primary patrol boat. I always loved the boat but don't recall the torque lean ever being an issue. We ran 115 Johnsons and 90 Evinrudes way back then.
Tom W Clark	posted 09-26-2013 11:08 AM ET (US) Where is the motor mounted now? What propeller is being used?
jimh	posted 09-26-2013 05:33 PM ET (US) The trim tab on the gear case can help to reduce steering torque. It will not stop the boat from leaning. Boston Whaler boat hulls tend to lean into the wind. You many be observing that effect, in addition to propeller torque.
Tom W Clark	posted 09-26-2013 09:18 PM ET (US) Well, that not quite right. The trim tab is there to correct for steering torque not boat list, but it can have a profound effect on that list, making it much, much worse usually. If the trim tab is not set correctly, and the Boston Whaler Owner's Manual offer advice on that point, it can exacerbate the list to port caused by propeller torque. This seems to be more of a problem on boats that are equipped with no-feedback steering systems where a mis-adjusted trim tab is less evident at the helm. If the trim tab is set with its trailing edge to port, the list can be greatly increased. Combine that with a motor set too low, too much negative trim of the motor, an propeller with too much pitch and the list can be very significant and irritating.
MikeF1	posted 09-27-2013 09:36 AM ET (US) The tab is set neutral, the motor is in the second hole from the bottom and I'm not sure about the prop (3 blade aluminum) but the previous owner said that he changed it. It turns a little over 5000 rpm WOT resulting in low to mid-40s MPH with two POB and 22 gallons of fuel. The boat is out of the water for the season. At normal cruise its fine but at about 3500 RPM the lean becomes noticeable and just gets worse at higher speeds. It does have the NFB steering and I don't recall if it was difficult to turn to starboard.
Tom W Clark	posted 09-27-2013 10:47 AM ET (US) quote: ...the motor is in the second hole from the bottom That is ambiguous. The 1998 Mercury 115 has five sets of motor mounting bolt holes. Your upper bolts are going through this hole? o o o o <-- Mounting Bolts Through This Hole? o If so, and if you have a 20" shaft length model, that is the right height for a good stainless steel propeller. I cannot see how an aluminum prop would grip very well at that height. Set the trim tab with its trailing edge to starboard, just as both Mercury and Boston Whaler recommend. That will help. But I suspect there is more to this story...
Tom W Clark	posted 09-27-2013 11:11 AM ET (US) quote: It turns a little over 5000 rpm WOT resulting in low to mid-40s MPH with two POB and 22 gallons of fuel. I find this odd too. A properly set up Montauk with a Mercury 115 should be good for close to 48 MPH. The WOT range for this motor is 4750-5250 RPM so what you are getting now is good, but we don't know what propeller you have. I suspect a Mercury 12-3/4" x 21" , a common prop for this boat/motor combo.