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Author Topic:   Montauk: Mercury 115 and 18-inch pitch

ward1 posted 09-25-2003 11:41 AM ET (US)
Recently purchased "pre-smirk" montauk like (has console and rps in bare hull with side rails) Boston Whaler with 1998 Mariner 115 inline 4. With light load (2 adults approx 200 lbs each and 6 gals gas), the boat will run 5200 (I believe the WOT range is 5200 - 5500) rpm and 40 mph (Garmin 76 GPS WAAS enabled). The boat had bad (old) gas so I will run it with fresh tonight. The engine is properly mounted (av plate 2" above "keel"). The prop is a stock aluminum which I think is at 18" pitch. I am firmly convinced the boat should run mid to upper 40's. Other than fresh gas, any insight to increased performance would be appreciated.
Thanks,
Ward
Bigshot posted 09-25-2003 11:46 AM ET (US)
Do a compression test on it. Make sure all cyls are within 10% of each other. Run fresh gas and a Techron in it which should clean up your carbs and pistons. Do NOT mess with timing, it rarely ever goes out. Should be running a bigger prop(21"), you sure the tach is accurate?
ward1 posted 09-25-2003 12:30 PM ET (US)
Will run compression test...forgot to mention Carbs rebuilt and there are 130 total hours on engine. Where can one purchase Techron? Is it available separately or only as an additive in Chevron gasoline? What other products are available which would offer similar results to separately? I live in south FL so there are marine stores all over the place.
Thanks,
Ward
ward1 posted 09-25-2003 12:31 PM ET (US)
Will run compression test...forgot to mention Carbs rebuilt and there are 130 total hours on engine. Where can one purchase Techron? Is it available separately or only as an additive in Chevron gasoline? What other products are available which would offer similar results to Techron? I live in south FL so there are marine stores all over the place.
Thanks,
Ward
Bigshot posted 09-25-2003 01:28 PM ET (US)
Ward where the heck is Hax....where do you live?
techron is available at ANY autoparts store for about $6 a can which I would use the whole can in a 6 gal tank. I know many here run 21's on their 90 mercs but I forgot you have a different engine so gear ratio may not be the same. With a 115 you should run 43+ but do not expect high 40's with the 4cyl.....you may hit it though.
Is the hull dry? Bottom smooth and clean? Sure the tach is right?
ward1 posted 09-25-2003 02:14 PM ET (US)
Bigshot:
Hypoluxo is between Lantana and Boynton Beach, I'm about a mile from the Boynton Beach Inlet. I have not weighed the hull but based on observation she looks to be floating right, not much deeper than my fathers katama with a 75 Merc. The bottom is clean (freshly painted) but is not terribly smooth (several coats of old bottom paint). So based on what you said (43+) my 40 +- isn't too far off the mark? Can I expect another couple mpg with a ss prop (say 13.25 X 17 or 13.25 X 19)?
Bigshot posted 09-25-2003 02:53 PM ET (US)
find out what you are swinging first. Do you have a prop shop by you that can tell you? Even though it may say 17" people have modified props before so it could be a 19", etc. You need to know what you are running before you buy anything. Can you borrow one from someone?
Bigshot posted 09-25-2003 02:54 PM ET (US)
Borrow your Dad's prop and see wht she does.
ward1 posted 09-25-2003 03:00 PM ET (US)
Dad's boat is in Westhampton, NY...sigh :-( I will take a closer look at existing prop tonight to see if I can establish what it is.
Ward
JayR posted 09-25-2003 07:48 PM ET (US)
I have a 1967 Montauk. Powered with an Evinrude 1988, 88 Special. I can do 41 (GPS) with it. I would hope a 115 would push better than low 40's.
jimh posted 09-25-2003 09:40 PM ET (US)
Check your owner's manual for the recommended RPM range. The current Mercury Outboard Engine catalogue lists the 4-cylinder in-line engines (115/125) at 5,250 Maximum.
You are right at maximum crankcase speed now, so watch out for over-revving.
jimh posted 09-25-2003 09:50 PM ET (US)
I just ran your numbers through the Propeller Calculator, a handy little device available here on the website (see Hyperlink below).
The results:
RPM=5200
Ratio=2.07 (from catalogue)
Pitch=18
Speed=40 MPH
Slip=6.6-percent (calculated)
I'd say you are perfectly set up.
You can't really run the engine faster. If you want more speed
try a higher pitch propeller. If you could turn a 19-inch pitch propeller at 5200, you would have....about 42 MPH.
Propeller Calculator at:
http://continuouswave.com/cgi-bin/propcalc.pl
Clark Roberts posted 09-26-2003 07:21 AM ET (US)
Ward, Jim's advice is right on the mark! You should NOT run that engine over 5250 rpm! If you want more speed a 3 cyl Merc 90. with a 20" pitch prop (I used to run a 1995 Merc 90 with a 20" Hi-Five prop)
will get you mid to very high 40's top speed... Happy Whalin'.. Clark
ward1 posted 09-26-2003 09:40 AM ET (US)
New observation on whaler/mariner 115...at 5250 rpm there is still some throttle to go. When I push the throttle forward from there the engine starts (for lack of a better term) "surging". At a lower rpm I would suspect fuel starvation but, the surging dosen't decrease rpm's, just dosen't allow them to increase. Does anyone know if this engine (1998 mariner inline 4 115 hp) could possibly have a "hard" limit (like a governer) on it? If so, I would like to try a higher pitch to see if it will run to 5250 without the surging. Does this make any sense?
Ward
Bigshot posted 09-26-2003 02:28 PM ET (US)
Makes sense and since she aint EFI, I doubt on a rev limiter. If she is hiting a limiter then your tach is off because rev limiters are usually 300-600rpm ABOVE redline. My friends 300 promax beeps when you hit the rev limiter. My Suzuki will sputter like a "stutter box" on a dragster. Reason I know is she has one in neutral above 2500 rpms or so.
Bigshot posted 09-26-2003 02:29 PM ET (US)
I take that back....I think my 225 carbed Johnson has a rev limiter even though I have never hit it. It is tied into the "SLOW" feature.
ward1 posted 09-27-2003 11:32 AM ET (US)
New information, upon further investigation, I am running a stock alum. prop which is 13.25 x 17. Plugging these values and my top speed of 42.00 mph. (GPS) into the prop. calculator shows I'm turning almost 5700 rpms. My guess I should run a 13 x 19 or 20 in a stainless steel prop. Is this about correct? Any reccomendations here?
Thanks (again!)
Ward
ward1 posted 09-27-2003 11:33 AM ET (US)
Forgot to mention, I also confirmed 5250 as max WOT for this engine.
Ward
lhg posted 09-30-2003 05:28 PM ET (US)
A strong 4 cylinder Mercury 115 (yours may not be!) should be running a 22" prop on a 16' Whaler, for a top speed around 48 mph. As Clark says, the Merc 90, properly set up, will also do this. Don't ask me why.
An older in-line 6 115 would push that boat up to about 51 mph, running a 2.00:1 gear ratio and 21" prop.
ward1 posted 10-09-2003 07:42 PM ET (US)
Update: Replaced original alum. prop (13.75 x 17) with new ss rapture 13.25 x 21. Now we're doing 46 mph at 5100 +/-, big improvement! Now for the question part...I'm currently running with the vent holes open...do they affect top end or only holeshot? In other words, will putting the plugs in give me any additional top end or should I just leave well enough alone?
Perry posted 10-09-2003 10:06 PM ET (US)
Vent holes only effect hole shot by letting air in and allowing the prop to spin a little quicker. Once the boat is up on plane they are in effect sealed by water moving past them.
Clark Roberts posted 10-10-2003 07:32 AM ET (US)
War, check that the carbs are truly 100% wide open when throttle lever is full forward. Since there are four of these puppies there is a good chance that one or more are not wide open... look down carb throat to verify and very, very easy to bring into position via the carb linkage rod! The above not to just get all the speed available but also to make for better set-up and running/economy at all speeds... check it out .. clark... Spruce Creek Navy
PS> also replace that little in-line fuel filter between the fuel pump and carbs! Replace it even if it seems to be free and open! Good advice on all above posts!
KDW posted 10-18-2003 09:41 PM ET (US)
WARD1,
I just read your thread completely and it sounds like I may be seeing the same "surging" as you. I have a '98 Merc. 100HP 2s and run a LaserII 20 Prop. However, I can't seem to get close to the 5250 RPM max for the motor. I can't understand right now if my surging is caused by fuel starvation or if there is some device built into the engine to prevent excessive RPMs. I have been told by others that there is no rev. limiter on this motor.
It is very well possible my tach is off and I'm already above 5250 RPMs. I did read under the section for Maximum Timing adjustment in the Merc. Service Manual "(Due to the advance characteristics of iginition system, this cranking speed adjustment will automatically be reduced to 23 BTDC at engine speed of 5000 RPM).
Anyhow, just curious to know any similarities that might help.
Thanks,
Kenny
jimh posted 10-25-2003 12:47 AM ET (US)
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Author	Topic: Montauk: Mercury 115 and 18-inch pitch
ward1	posted 09-25-2003 11:41 AM ET (US) Recently purchased "pre-smirk" montauk like (has console and rps in bare hull with side rails) Boston Whaler with 1998 Mariner 115 inline 4. With light load (2 adults approx 200 lbs each and 6 gals gas), the boat will run 5200 (I believe the WOT range is 5200 - 5500) rpm and 40 mph (Garmin 76 GPS WAAS enabled). The boat had bad (old) gas so I will run it with fresh tonight. The engine is properly mounted (av plate 2" above "keel"). The prop is a stock aluminum which I think is at 18" pitch. I am firmly convinced the boat should run mid to upper 40's. Other than fresh gas, any insight to increased performance would be appreciated. Thanks, Ward
Bigshot	posted 09-25-2003 11:46 AM ET (US) Do a compression test on it. Make sure all cyls are within 10% of each other. Run fresh gas and a Techron in it which should clean up your carbs and pistons. Do NOT mess with timing, it rarely ever goes out. Should be running a bigger prop(21"), you sure the tach is accurate?
ward1	posted 09-25-2003 12:30 PM ET (US) Will run compression test...forgot to mention Carbs rebuilt and there are 130 total hours on engine. Where can one purchase Techron? Is it available separately or only as an additive in Chevron gasoline? What other products are available which would offer similar results to separately? I live in south FL so there are marine stores all over the place. Thanks, Ward
ward1	posted 09-25-2003 12:31 PM ET (US) Will run compression test...forgot to mention Carbs rebuilt and there are 130 total hours on engine. Where can one purchase Techron? Is it available separately or only as an additive in Chevron gasoline? What other products are available which would offer similar results to Techron? I live in south FL so there are marine stores all over the place. Thanks, Ward
Bigshot	posted 09-25-2003 01:28 PM ET (US) Ward where the heck is Hax....where do you live? techron is available at ANY autoparts store for about $6 a can which I would use the whole can in a 6 gal tank. I know many here run 21's on their 90 mercs but I forgot you have a different engine so gear ratio may not be the same. With a 115 you should run 43+ but do not expect high 40's with the 4cyl.....you may hit it though. Is the hull dry? Bottom smooth and clean? Sure the tach is right?
ward1	posted 09-25-2003 02:14 PM ET (US) Bigshot: Hypoluxo is between Lantana and Boynton Beach, I'm about a mile from the Boynton Beach Inlet. I have not weighed the hull but based on observation she looks to be floating right, not much deeper than my fathers katama with a 75 Merc. The bottom is clean (freshly painted) but is not terribly smooth (several coats of old bottom paint). So based on what you said (43+) my 40 +- isn't too far off the mark? Can I expect another couple mpg with a ss prop (say 13.25 X 17 or 13.25 X 19)?
Bigshot	posted 09-25-2003 02:53 PM ET (US) find out what you are swinging first. Do you have a prop shop by you that can tell you? Even though it may say 17" people have modified props before so it could be a 19", etc. You need to know what you are running before you buy anything. Can you borrow one from someone?
Bigshot	posted 09-25-2003 02:54 PM ET (US) Borrow your Dad's prop and see wht she does.
ward1	posted 09-25-2003 03:00 PM ET (US) Dad's boat is in Westhampton, NY...sigh :-( I will take a closer look at existing prop tonight to see if I can establish what it is. Ward
JayR	posted 09-25-2003 07:48 PM ET (US) I have a 1967 Montauk. Powered with an Evinrude 1988, 88 Special. I can do 41 (GPS) with it. I would hope a 115 would push better than low 40's.
jimh	posted 09-25-2003 09:40 PM ET (US) Check your owner's manual for the recommended RPM range. The current Mercury Outboard Engine catalogue lists the 4-cylinder in-line engines (115/125) at 5,250 Maximum. You are right at maximum crankcase speed now, so watch out for over-revving.
jimh	posted 09-25-2003 09:50 PM ET (US) I just ran your numbers through the Propeller Calculator, a handy little device available here on the website (see Hyperlink below). The results: RPM=5200 Ratio=2.07 (from catalogue) Pitch=18 Speed=40 MPH Slip=6.6-percent (calculated) I'd say you are perfectly set up. You can't really run the engine faster. If you want more speed try a higher pitch propeller. If you could turn a 19-inch pitch propeller at 5200, you would have....about 42 MPH. Propeller Calculator at: http://continuouswave.com/cgi-bin/propcalc.pl
Clark Roberts	posted 09-26-2003 07:21 AM ET (US) Ward, Jim's advice is right on the mark! You should NOT run that engine over 5250 rpm! If you want more speed a 3 cyl Merc 90. with a 20" pitch prop (I used to run a 1995 Merc 90 with a 20" Hi-Five prop) will get you mid to very high 40's top speed... Happy Whalin'.. Clark
ward1	posted 09-26-2003 09:40 AM ET (US) New observation on whaler/mariner 115...at 5250 rpm there is still some throttle to go. When I push the throttle forward from there the engine starts (for lack of a better term) "surging". At a lower rpm I would suspect fuel starvation but, the surging dosen't decrease rpm's, just dosen't allow them to increase. Does anyone know if this engine (1998 mariner inline 4 115 hp) could possibly have a "hard" limit (like a governer) on it? If so, I would like to try a higher pitch to see if it will run to 5250 without the surging. Does this make any sense? Ward
Bigshot	posted 09-26-2003 02:28 PM ET (US) Makes sense and since she aint EFI, I doubt on a rev limiter. If she is hiting a limiter then your tach is off because rev limiters are usually 300-600rpm ABOVE redline. My friends 300 promax beeps when you hit the rev limiter. My Suzuki will sputter like a "stutter box" on a dragster. Reason I know is she has one in neutral above 2500 rpms or so.
Bigshot	posted 09-26-2003 02:29 PM ET (US) I take that back....I think my 225 carbed Johnson has a rev limiter even though I have never hit it. It is tied into the "SLOW" feature.
ward1	posted 09-27-2003 11:32 AM ET (US) New information, upon further investigation, I am running a stock alum. prop which is 13.25 x 17. Plugging these values and my top speed of 42.00 mph. (GPS) into the prop. calculator shows I'm turning almost 5700 rpms. My guess I should run a 13 x 19 or 20 in a stainless steel prop. Is this about correct? Any reccomendations here? Thanks (again!) Ward
ward1	posted 09-27-2003 11:33 AM ET (US) Forgot to mention, I also confirmed 5250 as max WOT for this engine. Ward
lhg	posted 09-30-2003 05:28 PM ET (US) A strong 4 cylinder Mercury 115 (yours may not be!) should be running a 22" prop on a 16' Whaler, for a top speed around 48 mph. As Clark says, the Merc 90, properly set up, will also do this. Don't ask me why. An older in-line 6 115 would push that boat up to about 51 mph, running a 2.00:1 gear ratio and 21" prop.
ward1	posted 10-09-2003 07:42 PM ET (US) Update: Replaced original alum. prop (13.75 x 17) with new ss rapture 13.25 x 21. Now we're doing 46 mph at 5100 +/-, big improvement! Now for the question part...I'm currently running with the vent holes open...do they affect top end or only holeshot? In other words, will putting the plugs in give me any additional top end or should I just leave well enough alone?
Perry	posted 10-09-2003 10:06 PM ET (US) Vent holes only effect hole shot by letting air in and allowing the prop to spin a little quicker. Once the boat is up on plane they are in effect sealed by water moving past them.
Clark Roberts	posted 10-10-2003 07:32 AM ET (US) War, check that the carbs are truly 100% wide open when throttle lever is full forward. Since there are four of these puppies there is a good chance that one or more are not wide open... look down carb throat to verify and very, very easy to bring into position via the carb linkage rod! The above not to just get all the speed available but also to make for better set-up and running/economy at all speeds... check it out .. clark... Spruce Creek Navy PS> also replace that little in-line fuel filter between the fuel pump and carbs! Replace it even if it seems to be free and open! Good advice on all above posts!
KDW	posted 10-18-2003 09:41 PM ET (US) WARD1, I just read your thread completely and it sounds like I may be seeing the same "surging" as you. I have a '98 Merc. 100HP 2s and run a LaserII 20 Prop. However, I can't seem to get close to the 5250 RPM max for the motor. I can't understand right now if my surging is caused by fuel starvation or if there is some device built into the engine to prevent excessive RPMs. I have been told by others that there is no rev. limiter on this motor. It is very well possible my tach is off and I'm already above 5250 RPMs. I did read under the section for Maximum Timing adjustment in the Merc. Service Manual "(Due to the advance characteristics of iginition system, this cranking speed adjustment will automatically be reduced to 23 BTDC at engine speed of 5000 RPM). Anyhow, just curious to know any similarities that might help. Thanks, Kenny
jimh	posted 10-25-2003 12:47 AM ET (US) [Administrative post]