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Author Topic:   170 Montauk with 90-HP Two-cycle
BYABOATBJAHNS posted 03-10-2004 01:26 PM ET (US)   Profile for BYABOATBJAHNS   Send Email to BYABOATBJAHNS  
What stainless propeller (4-blade) can I put on a 170 Montauk with 90-HP 2-stroke for higher speed?
jimh posted 03-10-2004 03:10 PM ET (US)     Profile for jimh  Send Email to jimh     
Test data from Boston Whaler factory testing is available in the Reference Section. See:

At these boat speeds and horsepower an aluminum propeller often shows good performance.

LHG posted 03-10-2004 03:30 PM ET (US)     Profile for LHG    
This rig appears to be right on a dividing line between possible Mercury props. That is probaly why so many indicate a 19" aluminum came with the engine. An aluminum will, however, give the lowest level of performance. I wouldn't use one any boat that will do over 30.

Looking at Mercury's prop charts, and 18" SS Vengeance is a bit low on pitch, and a 20" Laser II a touch high. If you lift the engine up to the 3rd set of mounting holes (mandatory to run one of these), a 20" Laser should give the absolute best performance, bow lift, best ride, and top speed. With a light load, you should get near max RPM, maybe to 5300 or so. These are great props, and I run them on both of my Whalers. On a 90, the 20" model has a top speed potential of 45 mph.

Another alternative would be to try an aftermarket performance prop like the Mich Wheel Rapture, or Stilleto. in 19" pitch. These are your best brands, I believe. Cabela's also sells the Rapture under their "house" brand.

Forget a 4-bladed Mercury Trophy for this rig. See comments in Marketplace re: one that is for sale.

BYABOATBJAHNS posted 03-10-2004 04:37 PM ET (US)     Profile for BYABOATBJAHNS  Send Email to BYABOATBJAHNS     
Thanks for the information. I think the 20-inch is the way I'll go. The boat comes from the factory with a 21-inch Black Max aluminum propeller. I would like this boat to go 45-MPH with a light load.
Thanks for the advice!
LHG posted 03-10-2004 06:54 PM ET (US)     Profile for LHG    
Good luck and keep us posted. You should be able to find a new Laser II for $360-$400. No need to pay more than that.
There are several places in FL that will ship to you in this range, and without sales tax.
jimh posted 03-11-2004 10:53 PM ET (US)     Profile for jimh  Send Email to jimh     
It would be a good idea to take some careful observations of boat speed versus engine speed (using a GPS with high accuracy) before and after the propeller change. Often people are happy with the results with a new propeller (especially a $350 propeller) even if the data is not exactly overwhelmingly convincing.

[Nota Bene: I edited all your articles to lower case. All upper case text is very strongly discouraged.]

John O posted 03-12-2004 09:45 PM ET (US)     Profile for John O    
How much more performance and or speed will result from switching from the factory installed Aluminum to a stainless steel?

Is it worth the risk of destroying the the lower unit if the SS hits a soilid object vs the give on the alum.?

fitn217 posted 03-13-2004 11:53 PM ET (US)     Profile for fitn217  Send Email to fitn217     
LHG a few quetions for you. I own a 2 stroke 90 salt water series motor on a 2003 170 Montauk.

I just bought the laser II 20" pitch for my 170 Montauk. But have yet to install it.

1- Do I HAVE to raise the engine up to the third set of mounting holes?
2- What are the plusses and minuses of leaving the motor in the same set of mounting holes it originally came in with the Laser II prop?
3- I use my boat for fishing and am unconcerned with top speed. What I'm looking for is best rough water holding performance (as I often fish the ocean), best cruising speed & gas mileage characteristics. And last but not least better planing at slower speeds. Wouldn't mounting the engine higher decrease the prop's holding power in wavestrewn aerated water? I assumed ( I know make an ass out of you and me) that raising the engine was better for top speed and calm conditions.

Thanks for your insights.

AQUANUT posted 03-14-2004 12:49 AM ET (US)     Profile for AQUANUT  Send Email to AQUANUT     
heres my two cents and where i got it from...

after sitting thru a three hour "mercury e-skill VHS tape on the proper propping of mercury engines..."......and also viewing a similar "vhs" from yamaha...{I rig at a boston whaler dealership that is mercury/yamaha/honda all under the same roof.....}

these are the basics...

performance ..hmmm...performance on the hull chosen sometimes is not the same definition when referencing a vessel with 800hp mercruiser I/ where the average whaler is average operating average water conditions....the holes used by the factory techs/riggers are usually correct for the hull specified..

different props attain different results.....
mercury states in its training videos...depending on hull design....anti cav plate/or ventilation plate can be as low as 1" below keel...and up to 5 inches above the keel in the case of step hulls...used on bass boats

you ask what prop will hold in the turn under wot....hmm.....that better addressed by the builder with the use of strakes or chines/keel.
obviously more blades better bite{traction} long as you have the hp to turn the wheel.

this doesn't have to be rocket science...
do you want a hole shot or do you want top end?
do ya wanna go cheapest route..or do you wanna spend some dough...ya usually get what ya pay..thats why we own boston key west/carolina skiffs....right?

I personally set my 2004 montauk 170 up 1 hole when i repowered it the day I got it in my bay...canned the 2 stroke 90....replaced it with a 115hp EFI 4 stroker...
6 props later I am running a vengeance 14p three blade
however i chine walked into a 50 mph wind @ Wide Open Throttle WOT 6000rpm. condidering going down a hole to middle one on brackett...juries still out on that...

good luck on your the guys I work with are great about handing out loaner props to our valued customers to try out...the elevations here range from sea level to 5500 proping varies to where you intend to operate the vessel...more so on two strokes and non-EFI fourstroke engines....if the customer doesn't trash the prop we trade...its a fair deal when offered to all.

BYABOATBJAHNS posted 03-17-2004 12:23 PM ET (US)     Profile for BYABOATBJAHNS  Send Email to BYABOATBJAHNS     
LHG posted 03-24-2004 03:40 PM ET (US)     Profile for LHG    
Fitn217 - From what I understand, Merc Laser II props should be run surface piercing, about 1 1/2" high, which generally means the 3rd (center) set of mounting holes. Obviously, boat transom design can affect this.

Mercury states that running a Laser II fully submerged can increase effective pitch by 2", which will reduce max PRM. Some of it's performance enhancing properties may also be lost.

fitn217 posted 03-25-2004 02:18 PM ET (US)     Profile for fitn217  Send Email to fitn217     
Thanks for the reply LHG. I guess I'm going to leave the motor as is, with the motor in the same mounted position that it came in. If however I see that I'm not reaching max RPM or getting the performance I should be getting than I may experiment with the mounting position.
trueblue posted 02-22-2015 11:07 AM ET (US)     Profile for trueblue  Send Email to trueblue     
Not sure if a thread this old can be resurrected, but here goes:

I bought a 170 2 years ago that came with a 90 HP 2-stroke and an aluminum prop. I'm planning to upgrade to a Laser II (SS, 3-blade, 13.25" 20 pitch). This is my first power boat and I'm trying to feel my way along. Can anyone share some experience? Opinions are great, but I'd really love to hear from someone who has tried this prop on this boat.

Are you happy with yours? Did it have a noticable effect on performance (hole shot, top end)? One last question, did you end up changing the transom mounting hole?



tedious posted 02-23-2015 10:03 AM ET (US)     Profile for tedious  Send Email to tedious     
Chuck, can you share more information on your current prop - make, model, diameter and pitch, and what RPM and speed you now achieve?

Being somewhat familiar with the 170, and just going on previous posts in this thread, it sounds like the Laser II is a full-on speed prop, designed for maximum speed. Is that your goal? Or if not, what aspect(s) of performance are you looking to improve?


trueblue posted 02-26-2015 07:59 AM ET (US)     Profile for trueblue  Send Email to trueblue     

The current prop came with the boat and is a 12.5" x 21 pitch 3-blade Quicksilver prop. With the current prop, WOT is about 5400, but I don't often run her that hard because I don't want to stress the engine too much and ride is more important to my wife. I my Whaler mostly to motor around the river and bay here and occasionally to take the kids tubing. I'd say my most common speed is 25 - 30 kts.

I've read what I can find in the forum and there's a fair amount of conflicting info, but a lot of folks seem to have liked the Laser II. I picked one up on eBay that's 13.25" x 20 pitch.

My goal is to get on plane faster, fuel economy, and good top end (although that's not as important). I'm finding it difficult to gage what will give me the best mix



tedious posted 02-26-2015 09:47 AM ET (US)     Profile for tedious  Send Email to tedious     
Chuck, I have no familiarity with the Laser II - my concern was simply that the previous posters described it as a flat out speed prop which needed to be run with the motor very high, in surface-piercing mode. From that, I inferred that the Laser II might be a high-strung thoroughbred, great for top speed runs, but not so good for general use. But since you already have it, give it a try. Or maybe someone else will chime in and discuss the Laser II in more detail, relative to your usage model.

I have had very good luck with the Stiletto Advantage series of props, so I would recommend them.

Since you're new to this game, I'll pass on some general thoughts and opinions, stuff I've gleaned from reading this and other forums and experimenting on my 15:

- almost any newer stainless prop will be better than an older aluminum model, in terms of durability, economy, and performance.
- there is an old wives' tale that a stainless prop will cause motor damage when striking an object, and aluminum will make it OK. This is BS, but you hear it all the time from dealers and others.
- outboards are spec'ed to have a maximum RPM range. For best overall performance (hole shot, economy, top speed) you want your WOT RPM to be right at the top of that range (which is likely the same as the motor's redline) when lightly loaded.
- running at high RPMs is not stressful to 2-stroke outboards. It's far more stressful to run at mid-RPMs, heavily loaded - that's like bogging down your standard transmission car by shifting up too early.
- modern, cupped stainless props allow you to mount the motor higher, so if you're coming from an aluminum prop, you should move the motor up. This will improve performance and economy, and reduces any chance of porpoising.
- to find the right motor height, start with the AV plate about an inch above the keel line. Move up until you have problems, then drop it down one hole from there.
- propping is not an exact science - there's no substitute for experimentation!

Hope some of that helps...


64nauset posted 03-03-2015 03:44 PM ET (US)     Profile for 64nauset  Send Email to 64nauset     
More to think about: a few years back I posed the same question about my particular boat, a 1963 Nauset with a 1996 Evinrude 88-HP two-cycle engine. This rig would not be too different from yours when considering a propeller. I got replies back from a fellow who had my exact setup and here's what I bought: a Stiletto Advantage 13.25 x 15, purchased from Tom Clark for $250 delivered. This is a three-blade stainless steel propeleller.

I had to press in the rubber adapter and clutch. No problem. The new propeller ran off and left the factory aluminum prop in the dust. Performance improved greatly. Top speed 42-MPH, no cavitation in tight turns, [engine speed] maxed out at 5200-RPM, and a hole shot to write Mom about. Better fuel economy too. The [outboard engine] was already mounted one-hole-up so I didn't have to fiddle with that. The company that makes the propeller said that speed would increase slightly if the motor was mounted two-holes-up, but cavitation would start sneaking in. Fine, the boat runs better than it ever has and 42-MPH is fast enough for that hull. I don't feel the need for two-holes-up.

Will this propeller work as well for you? It might. Note: I allow no one near the back of the boat. That Stiletto is razor sharp, and I haven't the heart to sand it dull.

jimh posted 03-05-2015 06:33 AM ET (US)     Profile for jimh  Send Email to jimh     
I don't believe there is any sort of a clutch in the propeller hub insert. The insert is a typically a plastic coupling that always transmits the propeller shaft rotation to the propeller, until the coupling fails due to too much force. If it is to be called a clutch, it must be clear that it only works once. I don't think clutch is a good term for the propeller hub coupling, and I don't recall it being referred to as a clutch. Also, I don't believe the hub adaptor is rubber. Usually these newer propeller are designed to use a more or less universal plastic insert. The older propeller hub design using a rubber insert seems to have gone almost completely out of fashion. In any case, the rubber inserts are not field replaceable. They need considerable force to press them into the hub. The propeller mentioned above is probably the America Boat Propeller product called the Stilleto "D" Series SS part number D-811315. According to the application chart, it uses a hub kit model DE-503 for Evinrude engines.
64nauset posted 03-09-2015 01:17 PM ET (US)     Profile for 64nauset  Send Email to 64nauset     
You're right Jim. I should have left out the word "clutch" in the post.
Tom W Clark posted 03-15-2015 03:04 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
I have never heard of propeller made by "American Boat Propeller"

The propeller used by 64nauset is a Stiletto Advantage 4.25. It uses a field-replacable hub kit. Such hub kits are designed to provide shock protection and can be made of either plastic or rubber.

jimh posted 03-18-2015 07:37 AM ET (US)     Profile for jimh  Send Email to jimh     
American Boat Propellers is a dealer, not a manufacturer. They have a decent website with a listing of many propeller products, including ones called Stiletto. Unfortunately their website has a rather misleading page on which they write in the first person as if they were the manufacturers. See

It might be helpful to have hyperlinks to the actual manufacturer's website for the Stiletto propeller under discussion, and to the unusual field-replaceable rubber hub kit product. Is there a manufacturer's website for "a Stiletto Advantage 4.25"?

I think Stiletto-branded propeller are made by Precision Propeller Industries in Indiana, and they are a wholly-owned subsidiary of Yamaha.


But I'll be darned if I can find a listing of propellers called "Stiletto" on that website.

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