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Author Topic:   Montauk 17 with 90-HP Mercury

jamscarey posted 06-24-2007 08:36 PM ET (US)
I need suggestions regarding poor performance of a 1987 Montauk 17' with 2002 90HP Mercury. The Mercury is spinning a 14 x 13-inch pitch propeller at about 5,700-RPM. The Mercury is mounted in the third hole, anti-cavitation plate about 1.5-inch above hull. However the best top speed is approx 30-MPH measured with GPS. Mercury Prop Selector recommends Black Max 12.75 x 21P or LaserII SS 13.25 x 21P. Any advice would be appreciated.
Dick E posted 06-24-2007 09:31 PM ET (US)
The LaserII has a 20-inch pitch not 21-inch. They are both good props . The stainless will give you more top speed and better handling. I ran both on my 90-HP Mercury. Your speed should be in the low 40-MPH range with either propeller and a light load. The cavation plate 1.5-inch above the hull is good
By the way, the 14 x 13 propeller is wrong propeller. Take off and get one that the Mercury selector picked.
jamscarey posted 06-24-2007 10:44 PM ET (US)
Thanks guys. I just purchased the engine used and didn't realise the propeller size until sea trials. The performance [I] achieved indicated a problem. Now [I] need help selecting the best option.
Tom W Clark posted 06-25-2007 12:33 AM ET (US)
WHOA, Whoa, whoa, 5,700-RPM at WOT? Only 30 MPH? That is not possible with 90 HP on a Montauk. Either the motor is running on only two of its cylinders, the thottle is not moving all the way forward or you are reporting the wrong data.
Dick is correct. The Laser II for a Merc 90 is 13-1/4" x 20" (the smallest Laser II made) and should push a Montauk to the low 40s.
jamscarey posted 06-25-2007 07:08 AM ET (US)
Should [I] expect a top speed higher than 30=MPH with a 14 x 13 propeller? If a cylinder is out will [I] still get max RPM out of the engine?
jamscarey posted 06-25-2007 07:29 AM ET (US)
Looking at the prop calculator on this site it appears theoretically impossible for a 13P prop spinning at the shaft speed of 2360 rpm to achieve greater than 30 mph
L H G posted 06-25-2007 09:33 AM ET (US)
Data posted above on 4-1/4-inch tube Mercery Laser II props (75 to 115-HP engines) is wrong. They are made in 19-, 20-, 21-, 22-, 24-, and 26-inch versions.
Tom W Clark posted 06-25-2007 09:40 AM ET (US)
Sorry Larry, my 232 page Mercury Propeller guide does not include any small tube Laser IIs in the 19" or 21" pitches. There is a 26" pitch. Odd size pitches are for large tube Laser IIs only (V-6 motors).
This is not to say that at one time there was such a thing as a 19" small tube Laser II but I have [not] seen or heard of one.
nanzpac posted 06-25-2007 02:03 PM ET (US)
Just to throw in my experience: My 1980 Montauk with a 1991 100-HP Merc had a 13-inch pitch aluminum on it and the boat at WOT over-revved to 6,200-RPM and was only going 30=MPH. Only did it for a few seconds. Evidently no rev limiters on these motors. I reproped to a old 17 pitch Mercury alum and RPM dropped to 5,300 and 40-MPH WOT. This 17 pitch I scrounged is old and has a chip in it. I think if I had a new SS 17 pitch I could get low 40's.
Your 13 pitch hurting you by 10 MPH. I am suprised though your motor was still under 6000 RPM's at WOT with a 13 pitch.
SS17 posted 06-25-2007 04:06 PM ET (US)
I had this very same post some months ago about my Montauk/Mercury 90. The same debate over the existance of odd Laser II pitches occurred, and it was probably LHG that mentioned that they were introduced with the advent of the 4 strokes.
I have no idea if they actually exist or not, but they are listed on the Merc web site.
P/N 899004A46, and 899006A046 are shown as being 13 1/4 X 19 and 21 respectively.
If I have a typo I'm sure someone will jump on it, but you get the idea of why a poster may ask about the (small hub) 21" pitch Laser...it is because Merc lists them on the prop selector page.
BTW, I bought a new 13 1/4 X 21 Powertech for my Montauk it it performed very well. Gps around 42 mph at +- 5400 rpm.
SS17 posted 06-25-2007 04:22 PM ET (US)
Here is the old post where this was discussed previously. Hope it helps.
[The other posting has been appended below. It was a nice discussion but was in the MARKETPLACE area and would not have been archived--jimh.]
Nauti Tauk posted 06-25-2007 06:09 PM ET (US)
Something has got to be wrong here. I just came back from the lake to test my 170 and 90 Mercury four-stroke to see how it ran with a new 20 gallon livewell full of water. It turned 5,800-RPM at 41.9-MPH by GPS. The prop is the standard issue 2003 SS Vengence 19P that I've had some cup added to. Also the engine cavitation plate is 3-inches above the bottom of the boat. A 13P should be way way to little pitch I'd think. Listen to Tom Clark. The man knows.
Dick E posted 06-25-2007 07:58 PM ET (US)
He is using a 13" pitch. He should be using about 19-21" pitch. 13 is about 2/3 of 20. So he's going about 2/3 of what he should be going, which is in the low 40's mph.
Tom W Clark posted 10-18-2006 09:33 AM ET (US)
Intermediate gearcase Laser IIs come in even size pitches. You would want a 20" Laser II.
I have a 20" Laser II you can have for $300.
tom@tomwclark.com
SS17 posted 10-18-2006 11:18 AM ET (US)
Tom,
I thought the Laser IIs were only even as well, but the Merc prop selector shows 48-899006A46 as a 21 pitch.
I was thinking of a 12.75 x 21 when I posted as well.
What has been your experience with the prop you have? Has it been run on a Montauk, and what were the results?
Though up front I'll admit that $300 is more than I currently intend to pay for a used prop for this rig.
an86carrera posted 10-18-2006 11:41 AM ET (US)
48- 16990A46 Rotation - Right Diameter - 13 1/4 Pitch -20
48- 16992A46 Rotation - Right Diameter - 13 1/2 Pitch -22
48- 16994A46 Rotation - Right Diameter - 13 1/2 Pitch -24
48- 16996A46 Rotation - Right Diameter - 13 1/2 Pitch -26
These are the Laser II props that will fit your engine
Len
Eddy G posted 10-18-2006 12:28 PM ET (US)
My Montauk had a 90 Merc with a 13-1/4" x 22" Laser II when I bought it. I repitched it to 20" and it seemed perfect for that set up. Since then, I have repowered with a Yamaha F90. I tried the Laser at 20" but a little too tall. Can't repitch any lower so it's not being used. It has a new Yamaha hub in it at this time. $225.00 if anyone is interested. I am in Baton Rouge, Louisiana.
egallegos@vaughanroofing.com
SS17 posted 10-18-2006 01:01 PM ET (US)
So the midrange Yamaha hub is different than the 3&4 cylinder mercs and you had to re-hub it as well? I'd be interested if it fit. I know the flo torq hub kit is different, so this makes sense.
48-89006A46 is a 13.25x21 LaserII (2)with flo torq, but I'll take a 13.5x20 LII.
Eddy G posted 10-19-2006 09:34 AM ET (US)
I used the Laser II with the Mercury hub in it for a while, but it didn't slide onto the shaft as far as it should. When I had it repitched to 20", I had the prop shop install the Yamaha hub which used the nut and cotter pin as it should be on that motor. The Mercury hub did work though.
Eddy G.
Tom W Clark posted 10-19-2006 10:18 AM ET (US)
Mercury and Yamaha props are interchangable, intermediate gearcase or large gearcase. The thrust washers are not interchangable between motors. So use a Yamaha prop on your Mercury but use the Mercury thrust washer you have now.
There is nothing wrong with using the Mercury tab washers in lieu of a cotter pin when using a Mercury prop on a Yamaha outboard.
The odd size Laser IIs are only for large outboards (V-6). A 21" Laser II will not fit a Mercury 90, but I do have three 21" Mercury laser IIs I would sell if anybody else is interested.
Try Ebay for a good deal on props but the Laser IIs do not sell for much less than $250 there and you have to be very careful about what you are getting. One bent blade and a visit to the prop shop and you will spend more than a brand new prop from your local dealer would cost.
CAKGT posted 10-19-2006 10:45 AM ET (US)
I have a New 21" Rapture XHS Prop For Sale. Brand new in box, used 5 min. for testing. Flo-Torq II hub not included. Model number 993106. 13.25" diameter X 21" pitch. $ 150 plus shipping.
Landlocked posted 10-19-2006 11:14 AM ET (US)
I have a 21" aluminum prop on my 2stroke Mercury 90/Montauk rig. WOT is at about 5,250 rpm.
While the aluminum prop and the stainless aren't directly comparable, My gut says moving down to 20" is probably what you want to do.
Ll
SS17 posted 10-20-2006 09:45 AM ET (US)
Not sure about the prop trivia, but the Merc part # above is for a 13.25x21, for midrange 3&4 cylinders, as shown on the merc prop selector. The V-6 props are 13.75 diameter. Evidently an error by merc (?) or new prop that no one here has run yet.
LHG posted 10-20-2006 05:36 PM ET (US)
Because of the new Merc EFI Verado block 75-115 4-strokes, 19" and 21" models have been added to the small bore Laser II line. Doubt if you'll find any used.
SS17 posted 10-20-2006 10:13 PM ET (US)
Thanks for the info. That makes sense. Used not a requirement, but it won't be long before they are on the used market. Used Enertias are already for sale.
New LII 20s are available for under 300, so I may just order one of those.
jimh posted 06-26-2007 08:16 AM ET (US)
If your three-cylinder engine is actually only running on two cylinders, it will not be able to produce the same wide-open throttle engine speed under load as when the engine is running on all three cylinders.

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Author	Topic: Montauk 17 with 90-HP Mercury
jamscarey	posted 06-24-2007 08:36 PM ET (US) I need suggestions regarding poor performance of a 1987 Montauk 17' with 2002 90HP Mercury. The Mercury is spinning a 14 x 13-inch pitch propeller at about 5,700-RPM. The Mercury is mounted in the third hole, anti-cavitation plate about 1.5-inch above hull. However the best top speed is approx 30-MPH measured with GPS. Mercury Prop Selector recommends Black Max 12.75 x 21P or LaserII SS 13.25 x 21P. Any advice would be appreciated.
Dick E	posted 06-24-2007 09:31 PM ET (US) The LaserII has a 20-inch pitch not 21-inch. They are both good props . The stainless will give you more top speed and better handling. I ran both on my 90-HP Mercury. Your speed should be in the low 40-MPH range with either propeller and a light load. The cavation plate 1.5-inch above the hull is good By the way, the 14 x 13 propeller is wrong propeller. Take off and get one that the Mercury selector picked.
jamscarey	posted 06-24-2007 10:44 PM ET (US) Thanks guys. I just purchased the engine used and didn't realise the propeller size until sea trials. The performance [I] achieved indicated a problem. Now [I] need help selecting the best option.
Tom W Clark	posted 06-25-2007 12:33 AM ET (US) WHOA, Whoa, whoa, 5,700-RPM at WOT? Only 30 MPH? That is not possible with 90 HP on a Montauk. Either the motor is running on only two of its cylinders, the thottle is not moving all the way forward or you are reporting the wrong data. Dick is correct. The Laser II for a Merc 90 is 13-1/4" x 20" (the smallest Laser II made) and should push a Montauk to the low 40s.
jamscarey	posted 06-25-2007 07:08 AM ET (US) Should [I] expect a top speed higher than 30=MPH with a 14 x 13 propeller? If a cylinder is out will [I] still get max RPM out of the engine?
jamscarey	posted 06-25-2007 07:29 AM ET (US) Looking at the prop calculator on this site it appears theoretically impossible for a 13P prop spinning at the shaft speed of 2360 rpm to achieve greater than 30 mph
L H G	posted 06-25-2007 09:33 AM ET (US) Data posted above on 4-1/4-inch tube Mercery Laser II props (75 to 115-HP engines) is wrong. They are made in 19-, 20-, 21-, 22-, 24-, and 26-inch versions.
Tom W Clark	posted 06-25-2007 09:40 AM ET (US) Sorry Larry, my 232 page Mercury Propeller guide does not include any small tube Laser IIs in the 19" or 21" pitches. There is a 26" pitch. Odd size pitches are for large tube Laser IIs only (V-6 motors). This is not to say that at one time there was such a thing as a 19" small tube Laser II but I have [not] seen or heard of one.
nanzpac	posted 06-25-2007 02:03 PM ET (US) Just to throw in my experience: My 1980 Montauk with a 1991 100-HP Merc had a 13-inch pitch aluminum on it and the boat at WOT over-revved to 6,200-RPM and was only going 30=MPH. Only did it for a few seconds. Evidently no rev limiters on these motors. I reproped to a old 17 pitch Mercury alum and RPM dropped to 5,300 and 40-MPH WOT. This 17 pitch I scrounged is old and has a chip in it. I think if I had a new SS 17 pitch I could get low 40's. Your 13 pitch hurting you by 10 MPH. I am suprised though your motor was still under 6000 RPM's at WOT with a 13 pitch.
SS17	posted 06-25-2007 04:06 PM ET (US) I had this very same post some months ago about my Montauk/Mercury 90. The same debate over the existance of odd Laser II pitches occurred, and it was probably LHG that mentioned that they were introduced with the advent of the 4 strokes. I have no idea if they actually exist or not, but they are listed on the Merc web site. P/N 899004A46, and 899006A046 are shown as being 13 1/4 X 19 and 21 respectively. If I have a typo I'm sure someone will jump on it, but you get the idea of why a poster may ask about the (small hub) 21" pitch Laser...it is because Merc lists them on the prop selector page. BTW, I bought a new 13 1/4 X 21 Powertech for my Montauk it it performed very well. Gps around 42 mph at +- 5400 rpm.
SS17	posted 06-25-2007 04:22 PM ET (US) Here is the old post where this was discussed previously. Hope it helps. [The other posting has been appended below. It was a nice discussion but was in the MARKETPLACE area and would not have been archived--jimh.]
Nauti Tauk	posted 06-25-2007 06:09 PM ET (US) Something has got to be wrong here. I just came back from the lake to test my 170 and 90 Mercury four-stroke to see how it ran with a new 20 gallon livewell full of water. It turned 5,800-RPM at 41.9-MPH by GPS. The prop is the standard issue 2003 SS Vengence 19P that I've had some cup added to. Also the engine cavitation plate is 3-inches above the bottom of the boat. A 13P should be way way to little pitch I'd think. Listen to Tom Clark. The man knows.
Dick E	posted 06-25-2007 07:58 PM ET (US) He is using a 13" pitch. He should be using about 19-21" pitch. 13 is about 2/3 of 20. So he's going about 2/3 of what he should be going, which is in the low 40's mph.
Tom W Clark	posted 10-18-2006 09:33 AM ET (US) Intermediate gearcase Laser IIs come in even size pitches. You would want a 20" Laser II. I have a 20" Laser II you can have for $300. tom@tomwclark.com
SS17	posted 10-18-2006 11:18 AM ET (US) Tom, I thought the Laser IIs were only even as well, but the Merc prop selector shows 48-899006A46 as a 21 pitch. I was thinking of a 12.75 x 21 when I posted as well. What has been your experience with the prop you have? Has it been run on a Montauk, and what were the results? Though up front I'll admit that $300 is more than I currently intend to pay for a used prop for this rig.
an86carrera	posted 10-18-2006 11:41 AM ET (US) 48- 16990A46 Rotation - Right Diameter - 13 1/4 Pitch -20 48- 16992A46 Rotation - Right Diameter - 13 1/2 Pitch -22 48- 16994A46 Rotation - Right Diameter - 13 1/2 Pitch -24 48- 16996A46 Rotation - Right Diameter - 13 1/2 Pitch -26 These are the Laser II props that will fit your engine Len
Eddy G	posted 10-18-2006 12:28 PM ET (US) My Montauk had a 90 Merc with a 13-1/4" x 22" Laser II when I bought it. I repitched it to 20" and it seemed perfect for that set up. Since then, I have repowered with a Yamaha F90. I tried the Laser at 20" but a little too tall. Can't repitch any lower so it's not being used. It has a new Yamaha hub in it at this time. $225.00 if anyone is interested. I am in Baton Rouge, Louisiana. egallegos@vaughanroofing.com
SS17	posted 10-18-2006 01:01 PM ET (US) So the midrange Yamaha hub is different than the 3&4 cylinder mercs and you had to re-hub it as well? I'd be interested if it fit. I know the flo torq hub kit is different, so this makes sense. 48-89006A46 is a 13.25x21 LaserII (2)with flo torq, but I'll take a 13.5x20 LII.
Eddy G	posted 10-19-2006 09:34 AM ET (US) I used the Laser II with the Mercury hub in it for a while, but it didn't slide onto the shaft as far as it should. When I had it repitched to 20", I had the prop shop install the Yamaha hub which used the nut and cotter pin as it should be on that motor. The Mercury hub did work though. Eddy G.
Tom W Clark	posted 10-19-2006 10:18 AM ET (US) Mercury and Yamaha props are interchangable, intermediate gearcase or large gearcase. The thrust washers are not interchangable between motors. So use a Yamaha prop on your Mercury but use the Mercury thrust washer you have now. There is nothing wrong with using the Mercury tab washers in lieu of a cotter pin when using a Mercury prop on a Yamaha outboard. The odd size Laser IIs are only for large outboards (V-6). A 21" Laser II will not fit a Mercury 90, but I do have three 21" Mercury laser IIs I would sell if anybody else is interested. Try Ebay for a good deal on props but the Laser IIs do not sell for much less than $250 there and you have to be very careful about what you are getting. One bent blade and a visit to the prop shop and you will spend more than a brand new prop from your local dealer would cost.
CAKGT	posted 10-19-2006 10:45 AM ET (US) I have a New 21" Rapture XHS Prop For Sale. Brand new in box, used 5 min. for testing. Flo-Torq II hub not included. Model number 993106. 13.25" diameter X 21" pitch. $ 150 plus shipping.
Landlocked	posted 10-19-2006 11:14 AM ET (US) I have a 21" aluminum prop on my 2stroke Mercury 90/Montauk rig. WOT is at about 5,250 rpm. While the aluminum prop and the stainless aren't directly comparable, My gut says moving down to 20" is probably what you want to do. Ll
SS17	posted 10-20-2006 09:45 AM ET (US) Not sure about the prop trivia, but the Merc part # above is for a 13.25x21, for midrange 3&4 cylinders, as shown on the merc prop selector. The V-6 props are 13.75 diameter. Evidently an error by merc (?) or new prop that no one here has run yet.
LHG	posted 10-20-2006 05:36 PM ET (US) Because of the new Merc EFI Verado block 75-115 4-strokes, 19" and 21" models have been added to the small bore Laser II line. Doubt if you'll find any used.
SS17	posted 10-20-2006 10:13 PM ET (US) Thanks for the info. That makes sense. Used not a requirement, but it won't be long before they are on the used market. Used Enertias are already for sale. New LII 20s are available for under 300, so I may just order one of those.
jimh	posted 06-26-2007 08:16 AM ET (US) If your three-cylinder engine is actually only running on two cylinders, it will not be able to produce the same wide-open throttle engine speed under load as when the engine is running on all three cylinders.