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Author Topic:   Montauk 90 Four-stroke Propeller
cape_rover posted 06-02-2006 08:58 AM ET (US)   Profile for cape_rover   Send Email to cape_rover  
Why and when did Boston Whaler change to an 18-inch pitch for the 90-HP [four-stroke combustion cycle outboard motor] from a 16-inch pitch? Does the new 90-HP EFI [four-stroke combustion cycle outboard motor] generate that much more power that they can turn a 18-inch pitch propeller?

My 2004 boat specs

Current whaler site:

DoTheMath posted 06-02-2006 10:40 AM ET (US)     Profile for DoTheMath  Send Email to DoTheMath     
I've got an 2006 170 with the new EFI [four-stroke combustion cycle outboard motor] on it and it swings the 18-inch just fine, right up to 5,900 rpm. So, not sure if it is the motor or what but it has a good hole shot and pulls nice all the way to the top, which was 42-MPH with two adults, 20 gallons of fuel, flat fresh water and the bimini up (but closed). All-in-all I am very happy with this boat.
Barney posted 06-02-2006 12:09 PM ET (US)     Profile for Barney  Send Email to Barney     
A good many of the carburetor four-stroke 90's had 18-inch pitch props:
Tom W Clark posted 06-02-2006 12:32 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
The gear ratios are different. The 2004 Mercury 90 four-stroke had a gear ratio of 2.07:1 while the current 2006 model has a more typical Mercury gear ratio of 2.33:1.

It is interesting to note that the early configuration produced a significantly higher top speed in factory performance tests.

cape_rover posted 06-02-2006 03:27 PM ET (US)     Profile for cape_rover  Send Email to cape_rover     
Thanks, I forgot about the gear ratio.
bigjohn1 posted 06-02-2006 07:35 PM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
Tom, that gear ratio info is news to me. For the past few years, the 115 EFI had the 2:07:1 while the carbed 90 four-stroke motors had 2:33-1. Perhaps that is different now but the 2:33:1 is not new for the Merc 90 four-stroke.

Cape - when was Whaler ever supplying 16P props with the Merc 90 four-stroke motors? The 18 Vengeance has been the propellersupplied at least for the past three model years.

Barney posted 06-02-2006 10:19 PM ET (US)     Profile for Barney  Send Email to Barney     
Mine has the 2:33. Jim
jimh posted 06-03-2006 10:31 AM ET (US)     Profile for jimh  Send Email to jimh     
If the new motor generated more power they would probably re-rate it and market it as a 100-HP. These days the rated horsepower is closer to the actual horsepower than was often the case in the past. This is due to the influence of emission standards based on horsepower.
Tom W Clark posted 06-03-2006 12:09 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Barney and Bigjohn,

Again, I refer you to the Reference article about the 170 Montauk linked to above.

Barney posted 06-03-2006 03:08 PM ET (US)     Profile for Barney  Send Email to Barney     
Tom/ caper_rover, I had to go back and find out how I knew the gear ratio.

I'm gonna refer to the "Service Manual 75/90 FourStroke" page 1A-9:

Gear Housing (2.33:1) 75/90 (4-Stroke) 2003 and Newer S/N-OT599000

Gear Housing (2.07:1) 75/90 (4-Stroke) 2002 and Prior S/N-OT598999


bigjohn1 posted 06-04-2006 08:49 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     

Sorry, I re-read that linked article and now see where the prop and gear ratio info comes from. Is this is Whaler and/or Merc factory info or a third party's interpretation of them? It contradicts the gear ratio info stated in the official Merc factory manual for these engines and the stated prop pitch contradicts factory literature as well. Several 2003-2006 model year 170 Montauk buyers on CW have stated the 18 Vengenance prop came on their engine. Not trying to stir the pot or make something out of nothing but in the interest of keeping things straight and not confusing people:

- Through model year 2005 at least, the Merc 90 4-stroke comes with a 2:33-1 gear ratio.

- Whaler/Merc was supplying the 18 Vengeance prop to buyers ordering the 90 4-stroke option. Even if they supplied the 16 Vengeance, it is likely that prop would allow a Merc 90 4-stroke to over-rev in some cases.

Barney posted 06-04-2006 09:01 AM ET (US)     Profile for Barney  Send Email to Barney     
I believe the reference article is for an early production 170 Montauk, 2002 model. I can understand the confusion. Jim
jimh posted 06-04-2006 01:42 PM ET (US)     Profile for jimh  Send Email to jimh     
At the time that article was written, the specifications were believed to be accurate. As far as I can recall, no one has ever written to me to inform me of any error or variance in the article, nor has anyone ever written to advise me that it contained out of date information.

You should note that the article includes the statement:

"This article first appeared February 21, 2002."

The information in the article regarding the gear ratio of the motor most likely taken from information available in Mercury literature at the time the article was written. The article has been available for four years.

The beautiful part of on-line information is the ability to update it and re-publish it. However, it is impossible to undertake revision of every article and every specification presented on the website when a manufacturer changes something.

Direct email communication which mentions the URI of the article and offers a citation of information which may be invariance with the contents of any article which is believed to be in error will be appreciated.

Barney posted 06-04-2006 02:17 PM ET (US)     Profile for Barney  Send Email to Barney     
Moe pointed the change out 2 1/2 years ago. I just forgot about it:


bigjohn1 posted 06-05-2006 12:09 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
O.K, I think I have this figured out now after reading Moe's linked thread - Merc changed the 90 4-stroke gear ratio after 2002. I am not trying to cast anything negative about your excellent article Jim. Matter of fact, it contributed to my decision to purchase the 170 Montauk.
WT posted 06-05-2006 12:53 AM ET (US)     Profile for WT  Send Email to WT     
My 2004 Montauk 170 90 horsepower 4 stroke outboard came with an 18 inch pitch Vengeance propeller. My top speed is around 38-39 mph at 6000 rpm.


imko posted 06-05-2006 10:41 AM ET (US)     Profile for imko  Send Email to imko     
I have tried 3 props. (Montauk 170 with 90 merc. 4 stroke 2003)

Vengeance 18P, Trophy plus 19P(4 blade) and the Laser II 20P.
The Laser prop is the best prop for your boat/engine combo.

DoTheMath posted 06-05-2006 12:18 PM ET (US)     Profile for DoTheMath  Send Email to DoTheMath     
imko~ What gear ratio do you have on your lower (2.33?) and what hole(s) are you using in the mounting plate of your engine? I'm turning 5,900 right now W.O. w/ the 18" Vengeance and I have mine in the stock mounting hole(s) (2nd one down from the top) but I'm thinking about moving it up one to the middle set of holes. However, am I looking at a prop change if I do so? I have read both yes and no once the x-dimension is changed with this configuration, just looking for one more opinion.
Tom W Clark posted 06-05-2006 02:31 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

Thanks for pin pointing the changeover. It would seem Jim's Reference article is correct and accurate.

I still think it is remarkable that the earlier configuration was faster.

If anybody needs a 20" Laser II, I have one for sale. $250.

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