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Author Topic:   MONTAUK Engine Mounting Height

RobertRibley posted 05-12-2006 10:02 PM ET (US)
I find this talk of propellers and motor heights very interesting. I have ordered a new prop for my Johnson V-4 90 hp. The prop I ordered is a four blade 13.25 x 15 Stilletto. Now I am looking at motor height. I believe my motor is set down as low as is can be, and I do not know if this is correct. I would appreciate any comments on correct motor heigth for the 1982 Montauk. Again, we use this boat for skiing and fishing.
Thanks for any thoughts,
Robert
sosmerc posted 05-12-2006 10:30 PM ET (US)
Why the 15 Pitch? I would think a 19 would be needed to keep that engine in the 5000-5500 RPM recommended range.
As for engine height...with a good stainless performance prop you should be able to raise the engine several holes and experience better handling, and better top end.
RobertRibley posted 05-12-2006 11:34 PM ET (US)
With the present height of the motor, the WOT was 5500 with the aluminum 15. Going to a 4 blade stainless steel was trying to achieve more hole shot for water skiing. The plate just above the prop appears to be the same level or 1/2 " above the keel. With the motor raised to proper height, which I am not certain it should be, does that have an effect on the pitch of the prop that you use?
Thanks for any help.
Robert
Tom W Clark posted 05-13-2006 01:33 AM ET (US)
The reason Robert needs a lower pitch prop is because (I suspect) he operates his boat at elevations of 1000-2000 feet of altitude and he waterskis.
If a stock 15" three blade prop is not too much pitch the four blade Stiletto will be worse. Stilettos seem to be comparable to stock props with two more inches of pitch. A 15" Stiletto will perform like a 17" stock prop.
Also, when switching to a four blade from a three blade you need to reduce one inch of pitch to compensate for the extra blade area. I suspect the 15" four blade Stiletto to perform like an 18" three blade stock prop. I do not think this is what Robert wants but we will see.
Robert,
I wish you had told me you wanted that Stiletto. I could have gotten you that four blade for $275 delivered to your door.
Tom W Clark posted 05-13-2006 01:39 AM ET (US)
Robert,
I'm sorry, I completely ignored your question. I think you would be better off with the motor raised at least one bolt hole, but I suspect you will have to deal with the blind holes in the motor mounting bracket being used for the lower motor mounting bolts.
You would need to remove the motor from the hull, fill the lower mounting bolt holes in the transom and then drill two new holes that clear the splashwell and enter the very top of the lower bolt slots. You would then use the second set of bolt holes for the upper bolts.
jimh posted 05-13-2006 10:36 AM ET (US)
Manufacturers and dealers tend to be conservative when installing outboard engines, and you will often find they mount an engine as low as possible on the transom. In general, higher mounting will improve performance because it will reduce the drag by reducing the amount of the engine immersed. Increased mounting height will also reduce the propeller immersion and may result in the propeller sucking air or venting--often called "blow out." Radically increased mounting height may also reduce the effectiveness of the water pick-up on the engine gear case and reduce the water pressure in the cooling system.
It is fairly common on Boston Whaler boats to mount the engine "one hole up", i.e., using the second from the top mounting hole. I do not see why this could not be done with a MONTAUK.
Blackduck posted 05-13-2006 01:05 PM ET (US)
One Hole Up-
goinboatn posted 05-13-2006 02:14 PM ET (US)
I have a 84 montauk with a v-4 rude and man get a bob's jackplate! Use it all the time, no more adjustment or mounting complications. Oh it's getting shallow vvrrrrr 6 inches outta do it! Or man these waves are getting bigger need more bite vvrrrr - prepare for take off.
Teak Oil posted 05-14-2006 11:03 AM ET (US)
As Tom said you cant simply raise your motor one hole up because it is bolted through the "blind holes", not the slots at the bottom of the bracket that allow for sliding the motor up and down.
The easiest way to accomplish raising the motor is with an adjustable jackplate. With a jackplate no drilling or filling of the hull is necessary. Otherwise you need to brush up on your fiberglass skills.
My jackplate:
http://smg.photobucket.com/albums/v735/MontaukBob/Jack%20Plate%20Install/
RobertRibley posted 05-14-2006 11:11 AM ET (US)
Stiletto also makes a 3 blade S.S 13.25x15 maybe better all thought they claim 4 blade has quicker acceleration I will raize motor height 1 hole or 1 to 1.5 from keel then retest Thanks for help Robert
Teak Oil posted 05-14-2006 11:21 AM ET (US)
Sorry
http://smg.photobucket.com/albums/v735/MontaukBob/ Jack%20Plate%20Install/
Landlocked posted 05-15-2006 05:30 PM ET (US)
I have a 21" stock Mercury aluminum prop on my Mercury 90 2-stroke. The plate is set 1.5" above the keel. I'm turning 5,250 RPM at WOT.
RobertRibley posted 05-16-2006 01:57 AM ET (US)
One more ? would raising engine give more Hole shot for sking.Got a day off and skied all day 2000 foot elv.lake can pull the woman up with ease seems like I drag 3 X longer WOT with 13.3/4x15 5000. All agree The Montauk is one of the Best boats to ski behind. The wake is perfect Whalers can do it All. Robert
Tom W Clark posted 05-16-2006 09:36 AM ET (US)
Robert,
Raising the motor one more hole *might* help, but if it does, it will not be a huge difference.
The three blade 13-1/4" x 15" Stiletto Advantage I will perform like a 17" OMC prop. If you have a 15" OMC prop and want better acceleration, the Stiletto is probably not the prop you really want, but you never know until you try. If you want one of those props, here is a very good deal on one:
http://continuouswave.com/ubb/Forum2/HTML/011413.html
One thing about all the Stiletto props that will help you is the fact they have vent holes in them which should contribute to a better hole shot.
RobertRibley posted 06-02-2006 12:18 AM ET (US)
I received the 13 25 x 15 four blade Stiletto and was able to test it today. I tested it at a flat reservoir, glassy water. Two people in the boat, 9 gallons of gas and maybe 100 lbs of extra gear. There was very little wind, if any. The hole shot seemed to be strong but I did not ski as we only had two people. I also moved the motor up two holes. It was at the lowest setting and now it is on the third hole. On plane and WOT the cavitation plate was just above the water. AT WOT, the RPM was 4700 and the speed, trimmed out, was 36 mph. I believe Tom mentioned that he thought the four blade 15 would act like an 18 and I think that is exactly what happened. My question is, do they make a 13 four blade Stiletto? Or would a three blade 15 ss have the same RPM as a 15 aluminum? Any help or suggestions are appreciated.
Thanks,
Robert
Tom W Clark posted 06-02-2006 12:23 PM ET (US)
I do not think the 15" pitch Stiletto Advantage I will work for you because it will perform much like a 17" pitch prop from anybody else.
Unfortunately, Stiletto does not make anything that will fit your motor with less than their nominal 15" pitch.
I'm trying to think of what would work for you. The 13-3/4" x 15" you already have puts your motor at 5500 RPM which is right where you want it. The next prop to try might be the stainless steel version of that prop, the BRP SST #177034.
You could also drop down to their #175013, 13-3/4" x 13" which is a triple cupped prop designed for pontoon boats, i.e. designed for pushing a heavy load, like water skiing.
Ultimately, the problem you face is operating your boat at 2000+ feet of altitude which simply reduces the available power of your motor.
RobertRibley posted 06-07-2006 01:31 AM ET (US)
Tom I think the testing I have done is not accurate. I made the mistake of not checking my throttle linkage. I think the butterfly cartridges are opening 3/4 of the way or less.
I will try to correct this but I am not sure of how to do this. After I solve this problem I will retest with the Stilleto ss 15 3 blade.
Thanks for all the help.
Robert

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Author	Topic: MONTAUK Engine Mounting Height
RobertRibley	posted 05-12-2006 10:02 PM ET (US) I find this talk of propellers and motor heights very interesting. I have ordered a new prop for my Johnson V-4 90 hp. The prop I ordered is a four blade 13.25 x 15 Stilletto. Now I am looking at motor height. I believe my motor is set down as low as is can be, and I do not know if this is correct. I would appreciate any comments on correct motor heigth for the 1982 Montauk. Again, we use this boat for skiing and fishing. Thanks for any thoughts, Robert
sosmerc	posted 05-12-2006 10:30 PM ET (US) Why the 15 Pitch? I would think a 19 would be needed to keep that engine in the 5000-5500 RPM recommended range. As for engine height...with a good stainless performance prop you should be able to raise the engine several holes and experience better handling, and better top end.
RobertRibley	posted 05-12-2006 11:34 PM ET (US) With the present height of the motor, the WOT was 5500 with the aluminum 15. Going to a 4 blade stainless steel was trying to achieve more hole shot for water skiing. The plate just above the prop appears to be the same level or 1/2 " above the keel. With the motor raised to proper height, which I am not certain it should be, does that have an effect on the pitch of the prop that you use? Thanks for any help. Robert
Tom W Clark	posted 05-13-2006 01:33 AM ET (US) The reason Robert needs a lower pitch prop is because (I suspect) he operates his boat at elevations of 1000-2000 feet of altitude and he waterskis. If a stock 15" three blade prop is not too much pitch the four blade Stiletto will be worse. Stilettos seem to be comparable to stock props with two more inches of pitch. A 15" Stiletto will perform like a 17" stock prop. Also, when switching to a four blade from a three blade you need to reduce one inch of pitch to compensate for the extra blade area. I suspect the 15" four blade Stiletto to perform like an 18" three blade stock prop. I do not think this is what Robert wants but we will see. Robert, I wish you had told me you wanted that Stiletto. I could have gotten you that four blade for $275 delivered to your door.
Tom W Clark	posted 05-13-2006 01:39 AM ET (US) Robert, I'm sorry, I completely ignored your question. I think you would be better off with the motor raised at least one bolt hole, but I suspect you will have to deal with the blind holes in the motor mounting bracket being used for the lower motor mounting bolts. You would need to remove the motor from the hull, fill the lower mounting bolt holes in the transom and then drill two new holes that clear the splashwell and enter the very top of the lower bolt slots. You would then use the second set of bolt holes for the upper bolts.
jimh	posted 05-13-2006 10:36 AM ET (US) Manufacturers and dealers tend to be conservative when installing outboard engines, and you will often find they mount an engine as low as possible on the transom. In general, higher mounting will improve performance because it will reduce the drag by reducing the amount of the engine immersed. Increased mounting height will also reduce the propeller immersion and may result in the propeller sucking air or venting--often called "blow out." Radically increased mounting height may also reduce the effectiveness of the water pick-up on the engine gear case and reduce the water pressure in the cooling system. It is fairly common on Boston Whaler boats to mount the engine "one hole up", i.e., using the second from the top mounting hole. I do not see why this could not be done with a MONTAUK.
Blackduck	posted 05-13-2006 01:05 PM ET (US) One Hole Up-
goinboatn	posted 05-13-2006 02:14 PM ET (US) I have a 84 montauk with a v-4 rude and man get a bob's jackplate! Use it all the time, no more adjustment or mounting complications. Oh it's getting shallow vvrrrrr 6 inches outta do it! Or man these waves are getting bigger need more bite vvrrrr - prepare for take off.
Teak Oil	posted 05-14-2006 11:03 AM ET (US) As Tom said you cant simply raise your motor one hole up because it is bolted through the "blind holes", not the slots at the bottom of the bracket that allow for sliding the motor up and down. The easiest way to accomplish raising the motor is with an adjustable jackplate. With a jackplate no drilling or filling of the hull is necessary. Otherwise you need to brush up on your fiberglass skills. My jackplate: http://smg.photobucket.com/albums/v735/MontaukBob/Jack%20Plate%20Install/
RobertRibley	posted 05-14-2006 11:11 AM ET (US) Stiletto also makes a 3 blade S.S 13.25x15 maybe better all thought they claim 4 blade has quicker acceleration I will raize motor height 1 hole or 1 to 1.5 from keel then retest Thanks for help Robert
Teak Oil	posted 05-14-2006 11:21 AM ET (US) Sorry http://smg.photobucket.com/albums/v735/MontaukBob/ Jack%20Plate%20Install/
Landlocked	posted 05-15-2006 05:30 PM ET (US) I have a 21" stock Mercury aluminum prop on my Mercury 90 2-stroke. The plate is set 1.5" above the keel. I'm turning 5,250 RPM at WOT.
RobertRibley	posted 05-16-2006 01:57 AM ET (US) One more ? would raising engine give more Hole shot for sking.Got a day off and skied all day 2000 foot elv.lake can pull the woman up with ease seems like I drag 3 X longer WOT with 13.3/4x15 5000. All agree The Montauk is one of the Best boats to ski behind. The wake is perfect Whalers can do it All. Robert
Tom W Clark	posted 05-16-2006 09:36 AM ET (US) Robert, Raising the motor one more hole might help, but if it does, it will not be a huge difference. The three blade 13-1/4" x 15" Stiletto Advantage I will perform like a 17" OMC prop. If you have a 15" OMC prop and want better acceleration, the Stiletto is probably not the prop you really want, but you never know until you try. If you want one of those props, here is a very good deal on one: http://continuouswave.com/ubb/Forum2/HTML/011413.html One thing about all the Stiletto props that will help you is the fact they have vent holes in them which should contribute to a better hole shot.
RobertRibley	posted 06-02-2006 12:18 AM ET (US) I received the 13 25 x 15 four blade Stiletto and was able to test it today. I tested it at a flat reservoir, glassy water. Two people in the boat, 9 gallons of gas and maybe 100 lbs of extra gear. There was very little wind, if any. The hole shot seemed to be strong but I did not ski as we only had two people. I also moved the motor up two holes. It was at the lowest setting and now it is on the third hole. On plane and WOT the cavitation plate was just above the water. AT WOT, the RPM was 4700 and the speed, trimmed out, was 36 mph. I believe Tom mentioned that he thought the four blade 15 would act like an 18 and I think that is exactly what happened. My question is, do they make a 13 four blade Stiletto? Or would a three blade 15 ss have the same RPM as a 15 aluminum? Any help or suggestions are appreciated. Thanks, Robert
Tom W Clark	posted 06-02-2006 12:23 PM ET (US) I do not think the 15" pitch Stiletto Advantage I will work for you because it will perform much like a 17" pitch prop from anybody else. Unfortunately, Stiletto does not make anything that will fit your motor with less than their nominal 15" pitch. I'm trying to think of what would work for you. The 13-3/4" x 15" you already have puts your motor at 5500 RPM which is right where you want it. The next prop to try might be the stainless steel version of that prop, the BRP SST #177034. You could also drop down to their #175013, 13-3/4" x 13" which is a triple cupped prop designed for pontoon boats, i.e. designed for pushing a heavy load, like water skiing. Ultimately, the problem you face is operating your boat at 2000+ feet of altitude which simply reduces the available power of your motor.
RobertRibley	posted 06-07-2006 01:31 AM ET (US) Tom I think the testing I have done is not accurate. I made the mistake of not checking my throttle linkage. I think the butterfly cartridges are opening 3/4 of the way or less. I will try to correct this but I am not sure of how to do this. After I solve this problem I will retest with the Stilleto ss 15 3 blade. Thanks for all the help. Robert