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I'm planning to repower a 1986 Montauk 17. The existing 90hp Yamaha 2-stroke works great and pulls like hell up to a top speed of around 43mph, but I'd like a modern 4-stroke. I have two main questions:

1) Where's the best place to sell the old 90hp Yamaha? Facebook marketplace? Craigslist? The new outboard dealer? An enthusiast forum like Whaler Central or Continuous Wave?

2) What's a reasonable price for a working 90hp Yamaha 2-stroke? The boat is in storage, so I don't have the engine manufacturing date handy, but I'm pretty sure it's mid 1980s or 1990s.

https://photos.app.goo.gl/DUbXdTPQ3Ls4bHdx5

Thanks in advance for your advice.

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If the engine is clean, paint is good and includes a prop - $2500-3,000.

There are many classic Whaler owners who would like this engine.

It's all about finding the right buyer.

In addition to listing it here, Facebook Marketplace is recommended.

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Thanks Phil, for your Facebook marketplace suggestion and estimate on the price.

Since the title of the post is repowering, can you also please recommend a stainless prop?

I ordered a Mercury 90-HP Command Thrust from a local dealer. I saw on another post (http://www.whalercentral.com/forum/vi...ost_167591) a recommendation of a 21P Enertia for a 115-HP Pro XS Command Thrust, and I know they have the same gear ratio/case.

The Mercury online calculator recommended the Enertia Eco in the 20-22P range, assuming I choose acceleration or overall good performance as a goal. I had already been leaning towards an Enertia or Enertia Eco anyway, so I'm hoping between the Mercury calculator and your earlier recommendation for the 115-HP Command Thrust, that the Enertia Eco in 21P would also be a good choice for the 90-HP Command Thrust.

Thanks!

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The owner tested props I have for the Montauk 17 with a Mercury 90 Fourstroke CT, (gear ratio 2.38) include:

13.15 x 19" Mercury Vengance
13.50 x 20" Mercury Laser II
13.25 x 19" Stiletto Advantage I

Notes:
- Size applies to the specific mfg and model listed and is not transferable.
- Engine mounted 2 holes-up, top bolt in 3rd hole counting down from the top.

The Enertia and Enertia Eco are great props, especially for the larger gear cases BUT are very pricey ($800+) versus $400 for the suggested ones.

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Hey Phil,

Your estimate of value was very helpful, so thank you. The dealer offered me $200 for the scrap value after saying, "no one wants a motor that old." Without your estimate, I might've believed him. I even said, "it seems like a lot of Whaler guys would be interested."

Instead, I listed the motor on Facebook and Craigslist for $2000 since I was in a hurry to get rid of it. Within a few days I think I had 15 people interested, and after paying the shop for a compression test to satisfy all the questions (125, 122, and 123), I got at least six or seven offers of $1500. I eventually settled on $2,200 with a local guy through craigslist after turning down an out-of-state offer for $2600 because I didn't want the hassle of shipping and PayPal.

Long story short, $2500-3000 seems pretty realistic assuming good condition. Good work, and thanks!

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Glad it worked out.

What is the status of the repower?

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Still waiting on them to finish.

I decided I wanted modern gauges using a Mercury SC1000 tach and speedo instead of the four working original Yamaha gauges. That meant two empty holes in the existing dash panels, so I ordered new ones from Sue. Although they were pretty expensive, I'm also happy that the switches are now lighted rocker switches instead of the mismatched chrome plated pulls.

The shop also discovered that the Mercury ignition panel was smaller than the Yamaha, so the hole cut into the console fiberglass was partially showing behind the panel. So that meant a rushed trip to the woodworking supply store for a 1/2" thick mahogany board to serve as a mounting plate. The shop said they would cut it to size and use a router to somewhat match the other wood panels on the console.

They're also planning to sea trial the boat because I specified a stainless prop. Of course, thanks to this forum, I was adamant that the motor should be mounted two holes up.

So long story short, they're still working on it.

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Keep us apprised.

Will want to see photos and performance information.

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Hey Phil,

Got the boat back today. Despite multiple conversations, and diagrams and print outs from Whaler Central with highlighted sections on mounting height, they mounted the motor... one hole up.

Here is the real world testing data I got back from the rigger with the new Mercury FourStroke 90 with 2.38 Command Thrust gearbox and aluminum props:

14.25" x 21P 5600 rpm 44 mph
(unknown diameter) x 17P 6150 rpm 32 mph

With data entered for acceleration, 21P, 5600rpm, and 44mph, the Mercury Prop Selector gives the calculated pitch at 19.60, rpm at 6000, and speed at 46.79mph. It recommends an Enertia Eco 19P, or the regular Enertia in 20P or 21P. However, the Mercury Prop Selector doesn't seem to include the Enertia Eco 20P in its programming, because the recommendation skips directly from 19P to 21P depending on how you tweak the inputs. In fact, I don't think it includes any even numbered pitches for the Eco.

Based on the calculated pitch of 19.60, I've got a line on a used Enertia Eco 20P, but I'm worried that maybe a 19P would be better? I was also hoping the 20P could work if I played around with the performance venting to help it spin up a bit faster.

Thoughts? Thanks for your advice.

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Not to sound too harsh but why did you accept the boat with the engine rigging not as you specified?

The prop recommendations I listed came from Montauk 17 owners who repowered with the Mercury 90 Fourstroke CT engine. I would not dismiss them and go with a generic prop calculator.

The Enertia Eco is the most expensive prop Mercury sells at $850-$900.

The Vengence is $500 and the Stiletto is $300.

Raise the engine.

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No worries - not too harsh. I just plain missed it, and found it when I got to the launch.

The mechanic that did the rigging said they would try to mount it as low as possible for the most mounting options, and then would raise it if necessary based on testing. In his words, "you can always go up." He also said they'd raise it if I tried it at one hole up and wasn't happy.

To be honest, talking to boat mechanics made me feel like what I imagine a woman feels like walking into a typical auto mechanic. I even called the guy I use for annual maintenance and winterizing to ask what it would cost to raise it one hole when I drop it off in October. He said, "why would you wanna do that?" I said, "for less drag, easier steering, more speed, and because a consensus of Whaler people on the internet said so." His next reply was "everybody on the internet thinks they're an expert." Then I tried to explain that it was Whaler Central, that Phil is an admin and studies this stuff ad nauseum... Then he explained that he's been doing this stuff since the 70s and went to Evinrude and [something] school, and "what you want is the anti-cavitation plate even with the bottom of the hull." I basically just gave up arguing, since I felt like a kid in the principal's office.

I plan to call the dealer to have them raise it, but convincing my wife to help me take the boat back out for a 3/4" change in the motor height is like trying to explain astrophysics to an alligator with a toothache.

P.S. The Enertia Eco 20P I'm looking at is $600 shipped, and it's been balanced and polished. So it seemed like a pretty good deal instead of the $850-900 you mentioned.

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John -

You have 3 choices:

Learn the phrase: "I am paying you to do it the way I want. So do it.

Find a mechanic who actually provides customer service for the hundreds, if not thousands, of dollars you give them.

Learn to do these things yourself (with our help).

Word of warning about props. There is a reason I compile prop recommendations from owners who did testing.

Prop selection is really hard and one model is not the same as another. A Solas 13x19 does not behave the same way as a Eco 13x19.

Props are not returnable unless there are special allowances. I only know of 1 vendor (www.propgods.com) who takes back a prop. He charges a small restock fee.

Sent you an email

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I recommend you go to the Boston Whaler website, look up the performance report on the $50,000+ new 170 Montauk with a Mercury 90, and see what prop line has been selected for the factory package. Whaler does extensive testing of their boat/engine combinations in conjunction with Mercury, so you can assume they use the best suited prop.

I think the regular Enertia line is what you want, although maybe higher pitch of 20, 21 or 22 inches. I can't image that the huge Eco prop would be correct for a lightweight boat like a Montauk. They are for heavy multi-engine boats with high HP, and as a more economical alternative to the Revolution 4, also for the same applications.

Edited note to PHil: The three props you mentioned above are for a standard mid-sized gear case on a Mercury 90.
The Command Thrust gearcase uses the large size props of the higher HP engines. As an example, the large hub Vengeance props are 14" x 19". Laser II props in the large size gearcase were never made in 20" pitch, only 19, 21, 23 and 25, and they are now discontinued. The 20" Laser II props are for a mid-sized gear case.

Ever since the Montauk was introduced, BW recommended the engine be mounted up one hole. With an Enertia prop you can go up one more hole, using the middle (3rd) hole of the five, so that recommendation is correct. This whole situation should give you top speed in the range of 45-46 mph, if you are actually getting 44 with the 21 Aluminum. One of Mercury's old tricks of the last 50 years is to design the engines with a slightly shorter mid section than the OMC or Yamaha competitors, for the obvious reason of an automatic slight rise in running height. This is one of the reasons Mercs have always been faster then the same HP competitors engine, and only need to be up in the 3rd holes.

Finally, with an Enertia prop, be sure you are given the new "Flo-Torq SSR" quiet shift hub kit.

https://www.mercurymarine.com/en/us/d...the-clunk/

This is good advice - don't ignore it.