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Is anyone out there running an Optimax 90 on their 17 Montauk? If so, what prop did you settle on, and what specs can you give me? I'm about to put a 2008 optimax on the boat, and it will arrive propless, so I will need to get the right prop the first time. Let me know what works! Not finding much specific in previous threads.

Please give me details like:
Brand/Diameter/Pitch/WOT RPM/Max Speed/Load, plus any other details.

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My son in law has a 17 Montauk with a 90 merc 2-stroke. A few years ago I gave him a stainless 13.5x17 prop that came new on a 1985ish 115 Yam 2-stroke. He is very happy with it.

I have a Yam. 90 2-stroke with a Yam painted stainless 17K and it is great.

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All Merc 90's after 1986 (last year of the in-line-6 90) use a 2.33 gear ratio.

If you want stainless, your fastest accelerating and top speed will be the new 4 bladed Spitfire X7 in 19" pitch, or maybe 21" pitch.

https://www.mercurymarine.com/en/us/p...itfire-x7/

Another option is the 20" Laser II.

If you want aluminum, the Spitfire 4 blade aluminum is your best choice, 19" or 21" pitch. The 3 bladed Black Max 21" pitch is also a decent prop, probably the best aluminum 3 blade you can buy.

In all cases, mount the engine in the third (middle) set of bolt holes.

Except for the Spitfire X7, the other three props are also available under Mercury's Quicksilver branding, at slightly less cost and widely available on the web from discounters.

What I would recommend in order to determine correct pitch is buy the bottom line 3 blade alum Black max in 21" pitch (about $100) and see what RPM you get. Then you can accurately spend up for a stainless model, keeping the alum for a spare.

jacosmarine.com is your best pricing for any Mercury SS prop. When using SS, be sure to use the Flo-torq III hub kit to eliminate clutch rattle at low RPM.

The Montauk should run 42-45 MPH with Opti 90.

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Thanks mtown and Finnegan.

mtown, With the 17 I was thinking he would max out his RPM, but maybe his 90 runs a lower gear ratio... If it's like 2.0, a 17 would probably be just right. Mine is a 2.33 ratio.

Finnegan, thanks for all the details, exactly what I was looking for. I'm thinking that if I can actually push one of those 21's at 5750 and 10% slip, I could hit 44. That would be awesome if I can do it, but even if I can turn a 20 that fast I should get 42ish. The boat currently has a 40 and will push it to 27 or 28 on a good day with a 13 pitch on it. Which is like 16% slip, but I think the motor is just way too small, so it's going to slip more.

I will probably go aluminum only because I do tend to do some rivers and explore unknown places, and beach the boat pretty often, so I'm probably more likely to hit bottom than most folks. If I'm more interested in efficient cruise and top end than hole shot, do you think the Opti would turn the 3 blade or 4 blade better, and if I went all the way to 21, would the 3 or 4 blade put me near the top of the RPM range better? I could see how a 4 might get you out of the hole faster but might be harder to turn, but really don't know enough to know better either way.

Also, when you say mount in the 3rd or middle set of holes, I think mine may be old enough that it might not be the same hole number on the top and bottom set of holes. Do I want to be 2 holes up from having the mount flush to the transom, or 1 hole off the transom? I think the way my holes are drilled, I can't really mount it flush, but the current motor is pretty close to where 1 hole up (maybe 3/4" off the transom) should have been.

Sounds like I should just go for the 21" black max as my best first shot, but if you think the 4 blade aluminum might be a better first choice, maybe I should try that. Any advantages of one over the other?

Thanks again!

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I think SIL's motor is a 1999 , but not sure. It is 1.5 hours from me and 2 hours from him so that won't help. Look at my recent post about mounting height. Joe has posted the link to mounting height terminology.

I think you should mount 3 holes up according to that link. That may not be true if using an aluminum prop though.
I would seriously consider stainless. I used alum for years, just because that is what the first boat came with. After I bought a new Yamaha in 1985 [ in those days they came with SS props] I have never had anything else and I have never even had to get a prop touched up.

This is despite running aground in the one boat almost every use to get in and out of the creek. I am not hitting rocks of course, but the old issue of ruining gears is apparently solved by the hubs employed nowdays.

Others on here will hopefully chime in about that.

On another note, I just paid $75 for a 17K Yamaha SS last weekend on Craigslist. I am considering a new project boat and motor and figured the price of a prop that I might need was too good to pass up.

Maybe you can find something used for your first try and then buy new and keep it as a spare if correct.

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I don't think you can get the 4 bladed aluminum Spitfire (or Quicksilver Nemesis) in 21" pitch for a mid size gearcase. But if you can, that is what I would buy. Otherwise the 21" Black Max (Quicksilver Black Diamond) would be the one to buy.

https://www.mercurymarine.com/en/us/p.../spitfire/

See the video links for more info.

Walmart on-line has the 21" pitch Black Diamond for $79.50 shipped!

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The prop selector here:
https://www.mercurymarine.com/en/us/propellers/selector/#/step-one
Shows a 23 pitch and 47 MPH! But if I really load up the boat with gear, more like a 22 or 21 pitch and lower speed. Anyone think the 23 is a little too steep, or tried on on a Montauk? I generally have 2 people on board, about 410lbs people and gear

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The original engine on my boat was a 1989 3 cylinder Mercury 90 HP. Not sure of the gear ratio it had at this point (I replaced it in 2012) but the Mercury aluminum prop it came with was 21 pitch. That was fine for light loads, however I ended up going to a 19 pitch in later years. It would do 40 -41 on my hand held GPS with the 21 pitch.

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If you ever suffer a propeller strike with an aluminum propeller you will probably upgrade to stainless steel. A stainless steel propeller will almost always out perform an aluminum propeller.

Buy a stainless steel propeller and avoid all the limitations of aluminum.

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Your gear ratio was 2.3 and the engine was rated 5000 to 5500. Do you remember what RPM you were turning with the 21 pitch?

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I can't remember the exact RPM, I'm thinking right around 5,000-5,100 with the engine trimmed out. The original engine was also installed all the way down which did not help performance. The 19 gave much better all around performance with more than just a person or two in the boat. Both of these were aluminum propellers, the 21 was an older Quicksilver that was on the boat when I bought it, the 19 was a Solas.

I'm currently running a 90 Etec with a Stiletto Advantage II stainless steel 15 pitch and 2 holes up. (It could go up another hole, I just haven't taken the time to do it.) I remember when doing the research it being stated on here that the Stiletto props acted like they were a couple of inches more than the stated pitch. If you can find a 19 pitch Stiletto. it might be a good choice (it will act similar to a 21 pitch). They'll run well with the engine up as high as you can mount it. Beyond that, I'll defer to those that have run the Optimax. Other than the gear ratio, I'd think the Optimax would be a completely different and much improved engine over what I had. The 21 inch pitch stainless steel recommendations above are likely a good match to it. Good luck!

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Went with a 21 and Torq Flo III hub... Will report back with details once I get it in the water (probably at least 2 weeks away, it's 23°F here now). Will look for a stainless prop once I establish correct pitch.

Thanks for all the great info everyone, hope to add to it soon!

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Bingo. 21 pitch is fine. I went out alone with my new (to me) Optimax 90 and I love it. Really nice machine. I hit about 42-43 at 5500 RPM, and got one reading as high as 45, with a full tank, but just me on board. It seems to have two modes with the trim that I'm not used to, I think I can trim it up and start making it chop the water (top blades probably not hitting) and I can get to 43+ that way but it will be turning 5600-5700 RPM. Then I can lower the nose a bit and it will bite a little harder and I can lower the RPM quite a bit and still maintain 40, so I think that's probably better mileage. I can run 42 pretty easily though with almost any reasonable trim. The two modes I'm describing also have an influence on torque steer too that I never noticed before. If I'm running along and trim up, I can adjust torque steer with it. Too much trim, pulls left, too little, pulls right. This might have something to do with the countersteer plate, not sure. It is aimed to steer left a little, but maybe I'm changing how the water is hitting it. I'll have to wait until my wife drives it so I can see what's happening.

Beautiful day here, 75°, nice to be back on the water! Yay!