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I have been reading several threads on installing a new motor on a Classic Montauk 17 and I'm a little confused. Please bare with me, as I'm a first time boat / Whaler owner as of about two weeks ago and have no experience in this area.

I have heard several posts suggesting that the motor should be mounted two or three holes up and I have come to learn that this is in regards to holes in the motor bracket itself (I originally thought this was referring to holes in the boats transom). If you guys could help to clarify a few things for me, it would be greatly appreciated.

My boat is a 1979 Montauk 17 and had a 1979 Johnson 70 on it. My boat is currently at the shop where they will be installing a brand new Yamaha F70 on it. My biggest concern is that they will be drilling the transom (if needed) in the correct area. I was under the impression that they would be able to use the top two holes from where the Johnson is located and have to drill two lower holes using a template which is provided with the motor? They would then fill the lower holes where the Johnson was mounted before. Do I need to be worried about if they will be drilling in the incorrect area? Is there certain preset holes that should be drilled for a new motor? I've read about the issues with a shallow splashwell, but I'm not sure if that applies to my boat.

With regards to which holes to mount the motor on, I have seen suggestions on two or three holes up and that the anti cavitation plate should be 1 to 1.5 inches above the bottom of the boat. What are the advantages and disadvantages of mounting the motor higher? It seems the disadvantages of mounting the motor two low are porpoising, tougher steering, slower to jump on plane, nose two high when running. The advantages of mounting it higher are the exact opposite of what I just mentioned. Could the disadvantages be stress on the transom and making the boat more top heavy and prone to turtling? I'm in southern California and will be boating in the rough pacific. I'm wondering if mounting the motor higher, could become an issue in a following sea? I will have two batteries in the console and a 30 gallon bait tank directly behind the RPS.

My other question is on an aluminum vs stainless steel prop. I was planning on going with the OEM Yamaha Aluminum 13 1/2 Diameter, 15 pitch, 3 blade prop. The shop recommended aluminum over stainless steel for a few reasons. They said stainless steel props can end up causing more gear case damage overtime due to their weight. It takes more to start rotating them and stop rotating them. There is also the argument about hitting something with a stainless vs aluminum prop, which appears to be a huge debate. They said if I was constantly running long distances off shore at fast speeds and wanted peak performance, then stainless would be the way to go. But since I will be fishing inshore, making short runs a few miles here and there in rougher seas, where I can't run do fast. I might as well get aluminum as it could save me from having to do gearcase work in the long run. Does this seem logical to you?

If so, should I still mount the motor two or three holes up if I'm considering the above aluminum prop?

Please help me out as I want to make sure they are doing things correctly. Sorry for such a long post, I just want to make sure I had everything covered and I only have about one day to make sure everything gets done right.

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I can tell you my experience, I have a 1988 17' Montauk, I mounted a brand new 70 yamaha 4 stroke. At first the boat store mounted it one hole up, that means the second hole from the top. I ran it about 6 hours in two trips and it seamed fine. But then I was told by Tom Clark on this sight I should mount it three holes up in other words mount top bolt in the fourth hole from the top. WoW what a difference. Easier stearing get's up on plane faster. I'm sure a few mph faster, don't have speedo.

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Morgan -

As a new owner there is alot of information to learn about your boat. The good news is you are asking all the right questions.

Engine Mounting:


In the old days engine bracket bolt patterns were not standard. Most engines were mounted "all the way down" and resting on the top of the transom. This left the anti-cavitation plate under water. The result is more drag and slower top speed.

For Boston Whaler's it has been determined, through trial and error, you want the anti-cavitation plate at or just above the surface ofthe water when planing. One way to describe this engine height is 2 holes up.

As I said above, older engines did not have standard bolt layouts. There has been a standard that all manufacturers now follow. With a motor using the old pattern most installers used lag bolts in the "blind holes at the bottom and not the slots.

Here is a reference article about engine mounting that is worth a good read. Follow the link to the discussion thread.

http://www.whalercentral.com/articles...icle_id=82

Propeller Choice:

Your dealer is wrong. Stainless is stronger and will take more abuse without being damaged. Don't fall for their bs. Go with the Yamaha painted stainless steel prop.

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One more thing. For any old holes they have to fill, tell them to use wood plugs and not a dowel. Dowel grain runs the wrong way.

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On approximately 1986 models and below, Tom W Clark states to drill the "Green" holes in this diagram.
http://www.whalercentral.com/articles...icle_id=82

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I just installed an engine on a 1979 Montauk, and the information Joe indicated above is correct. The vertical spacing between the top and bottom sets of holes has to be 6-1/2" (green) because the Whaler's splashwell is shallow.

I also removed a 1979 OMC engine that was blind hole mounted, as yours probably is. Depending where they are located, the existing top holes MAY work, or they MAY NOT!
In my case I had to gelcoat over all four original holes and
start over.

The controlling factor for installing a modern engine on these boats is to have the top hole of the BOTTOM SET of holes go into the splashwell where a washer and nut can be installed on the bolt. This will determine AUTOMATICALLY how high the engine will be on the transom, as the engine can't go any LOWER. Once the two bottom holes are determined, the installer can determine which of the TOP SET of holes should be used, based on how close to the top of the transom he wants them to be.

Or as an alternative, to utilize the existing top holes, simple measure down 6-1/2" for the bottom holes and see if the bolts will enter the splashwell with enough clearance for a washer and nut. If so, the existing top holes can be used.

In either case, the engine will be up around 1-1/2" at least, and I would recommend a transom stiffener across the top bolts as shown here on my Montauk:

http://smg.photobucket.com/albums/v42...ic0013.jpg

Bottom bolts go in from the outside, top bolts from the inside.
Because the boat design forces the engine up, you are most likely going to NEED a perfromance oriented SS prop.

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Finnegan,

I love how clean your boat is - it's my inspiration as I clean up my wiring/rigging this winter. Not to hijack the original thread, but where did you get that "transom stiffener" brakcet to go between the top engine bolts? I'd like to install one on my Montauk.

Thanks

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Thank you, TarHeel.

The transom stiffener I used is by T & H Marine, purchased at Bass Pro Shops. This brand, and others like it, are widely available on line.

If I can be of additional Montauk information, I would be glad to help.

Larry

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Perfect, thanks Larry!

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Thanks for everyone for their replies and tips.

hilyert...I really appreaciate you sharing your first hand experience. It's nice to hear from something who has been where I am.

Phil...I will definitely tell them to us plugs and not a dowel to patch any transom holes.

Joe...That diagram is very helpful, I have printed it out and will be giving it to my mechanic for the install. They said they will mount the motor up and I can go over the install with them.

Finnegan...I was still very confused about everything until I read your above explanation. You explanined it very clearly and now I know exactly what to tell them. Thank you so much, I thin that everybody who installing a new outboard on a Montauk should read what you read. I will look into the transom stiffener and see if my dealer has one.

I still have a couple questions. I have heard people mention that the motor should be mounted 3 holes up instead of 2. Is this ideal for the rough conditions in the pacific? Could this result in prop could blow out(ventilate) in swells? Also, when raising the motor us and mounting it higher. Why does it become necessary to have a stainless steel prop?

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The prop choice will determine how many holes up the engine will tolerate. I don't have experience with 17' whalers but my Stilletto tolerates 1 hole up more than my OMC sst prop. I would imagine the same would hold true for most aluminum props as well so 2 holes up for aluminum props would be what i gather from reading these forums, 3 holes up for the stilleto. The new Yamaha SS prop are also the same as the Stilletto props.

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I have no experience with the Yamaha 70, but considering your heavily loaded use on big water, and the relatively low HP of the engine in 4-stroke form, I would install the engine as low as the '79 transom configuration allows. Even then as described above this will be up 1-1/2". I think that is plenty, and about all an aluminum prop will tolerate, since your objective is not all out top end speed. I see no reason to run a highly jacked up outboard in your case.

Even with mine running a 115HP Merc, that is where I have mine set. It gives me 52 MPH top end, and that is plenty.

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Captain Morgan, think of is as a modern, stainless steel prop having better grip - it can thus can be mounted higher without blowing out.

As others have mentioned, your mechanic is just plain wrong about stainless props causing gearcase damage. If I were mounting a new motor, I wouldn't even consider aluminum -in fact I didn't, when I put my F70 on my 15. You can get a stainless Stiletto and hubkit from Dan's Discount Props or other places for probably just about the same price as your dealer will sell you an aluminum for. I believe a 13.25x13 Stiletto Advantage 1 will work perfectly on your Montauk.

Once you get the motor initially mounted properly, you'll be able to move it up and down fairly easily. If you go with the Stiletto, in your situation I'd start with 2 holes up and see how you go, and maybe try three holes up (up all the way) as an experiment at some point.

With all respect to the previous poster, you don't want the motor slammed all the way down - unless you like hard steering, a boat that porpoises, and wasting gas.

I do have a like-new 13.25 Stiletto with the hubkit for the F70 - if you want to pay the shipping, you are welcome to borrow it for a trial.

Tim

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Have your motor mounted as high as it can go, three holes up. There is no reason not to. The bolt hole spacing in the transom will not be the BIA standard but the horizontal spacing will match the BIA spacing but the lower holes in the transom will be only 6-1/2 inches below the top holes instead of 8 inches.

Yes, it is possible to mount a motor only one hole up on a 1979 Montauk with 7-1/4 inch vertical bolt spacing but you have to angle the lower bolts upwards to reach the splashwell. This is a terrible detail and since there is NO REASON ON EARTH why anybody would want an outboard mounted only one hole up on the transom of a classic 16'-7" Whaler, there is no reason to do so.

Your dealer is wrong about the use of stainless steel propellers; it will cause no harm at all to your new motor in the short or the long run. There is exactly one reason aluminum propellers still exist: that are a lot cheaper to buy initially. Beyond that, they offer exactly zero advantages over a stainless steel prop and because they are so much more durable, even the cost advantage goes away over time.

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Very informaticve post!

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Installing/running an engine mounted in the third hole down from the top generally means the engine anti-ventilation plate is 2-1/4" above the water flow under the hull. That kind of height generally requires a high performance surface piercing prop. One also has to be sure the upper water intake slots are not sucking in air.

On my Montauk, with 115 L-6 Merc and Laser II surfacing propeller, I can't run the engine that high without excessive slip and blowout. I am surprised the little Yamaha 70 can run that high with conventional aluminum props. My Mercury sure can't.

Here is the engine running at 2 holes up on a jackplate. You can tell by the prop wash that it is up high.

http://smg.photobucket.com/albums/v42...G_0447.mp4

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No, that is completely false in the case of the classic 16'-7" Whaler hull and a Yamaha F70, as evidenced by the several Whaler owners who have executed this repower and mounted their motors as high as they can go. No need for special high-performance propellers; a basic modern stainless steel prop will suffice. Even some modern aluminum props will tolerate the highest mounting height.

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Well if that is the case with Yamaha F70, either the boat transom or the engine is out of the 20" convention.

1st hole means the engine is all the way down. Theoretically, the AV plate would be flush with the water flow.

2nd hole means up 3/4". Same for AV plate over flow.

3rd hole means up 1-1/2". Same for AV plate over flow.

4th hole means up 2-1/4". Same for AV plate over water flow. This is what Tom is recommending.

So either the Whaler transom is less than 20" design convention, or the Yamaha 20" leg is longer than convention.
I do know that Mercury's 75-125 HP engines since 1987 have a 1" longer than conventional leg according to the operating manual. And sure enough. On the same hull, I have found that my 2-stroke late model 20" 90's can run 1" higher than the classic 2-stroke 20" Towers.

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Ah. We've found the source of your misunderstanding. A 20" motor mounted all the way down on the 20" transom of a Whaler will have its AV plate very well buried in the water flow, perhaps an inch or inch and a half. Having the motor raised to the fourth set of holes (three holes up) will result in the AV plate being 3/4 inch to 1-1/4 inch above the water flow at high speed, which is where you want it to be with a modern propeller.

Let me take moment to digress on the subject of "shaft length" and "transom height" because there continues to be confusion around these terms even after years of repeated explanation.

Shaft length of an outboard motor simply means the approximate height of the transom it is designed to fit on. Shaft length is NOT the distance between the motor mounting bracket "hooks" (or apex of its clamps) to the AV plate. That distance is typically a little more, though in some instances it is actually a little less.

Transom height is the vertical distance from keel to top of transom. It is approximate too, though in the case of the classic 16'-7" Whaler (and all the other small classic Whalers that take Long shaft motors) it will measure almost exactly 20". Remember now that I said vertical distance, not the distance along the face of the transom. If you hook a tape measure on the top of the transom and measure down to the keel of your Montauk you will find the measurement is about 21 inches. But because the transom of almost all small boats, and Whalers especially, are angled backwards, you are actually measuring along the hypotenuse of a right triangle and not its altitude. A right triangle with a 20 inch altitude and a hypotenuse sloping backwards at 15 to 17 degrees (the angle of the transom of a Whaler) will have a hypotenuse length of about 21 inches.

The classic 13 footers have even steeper angles to their transoms, as much as 20 degrees. How many times have we had threads where somebody is perplexed when they measure the transom of their Desert Tan 13 footer and find it measures 21-1/2 inches long (or the length of their blue 13 footer's transom and finds it is 16-1/2 inches long)? Well, that's because a right triangle with a hypotenuse at a 20 degree angle and an altitude of 20 or 15 inches (the transom height) will have a hypotenuse length of 21-1/2 or 16-1/2 inches. In fact the transom height is 20 inches and 15 inches respectively.

The other aspect of motor mounting height that many folks do not understand well is that though we measure the height from the keel and project a line back from the keel to the outboard motor when trying to gauge where the AV plate should be, this does NOT represent where the surface of the water will be when the boat is running. From the perspective of the boat, the water coming out from under the transom when the boat is on plane will rise up as it moves further away from the boat. Because the gearcase of an outboard is not at the face of transom but rather spaced away from it as much as a foot even when the motor is bolted directly to it, the surface of the water will be above the keel by the time it gets to the gearcase and the propeller. The amount of rise of the water's surface is dependent upon the boat speed.

The faster the boat goes, the less rise there will be. A Whaler that is barely on plane will see the water's surface rise up steeply to meet the outboard motor and the propeller will be very well buried regardless of how the motor is mounted. As a boat accelerates to higher and high speeds, the more of the outboard will be exposed above the water's surface. But also as speed increases so does the ability of a cupped propeller to resist ventilation from operating in a mixture of air and water. This is what allows a motor to be trimmed out to very extreme heights during wide open throttle (WOT) runs even though only half of the propeller may be in the water

Outboards are manufactured with different shaft lengths to fit different transom heights. The correct terms for shaft length are as follows:

Short Shaft = 15"
Long Shaft = 20"
Extra Long Shaft = 25"
Extra Extra Long Shaft = 30"

Again, this does NOT mean you will measure and find the distance to the AV plate matches these nominal numbers. Many small outboards with a Long Shaft will measure about 22-1/2" to the AV plate, though I once measured an old Mercury with a Long Shaft and found to only measure 19-1/2" to the AV plate. All manufacturers, and even models within a given manufacturer's line up, will have different actual distances to their AV plates.

Likewise, boats from different manufacturers may have different actual transom heights even if the nominal transom height is the specified as the same, though classic Whalers almost all have actual transom heights that correspond very closely to their nominal transom heights.

Deciding how high to mount an outboard motor on the transom of a boat depends on the boat and motor but also on how fast the boat is expected to go, what condition the boat is likely to operated in, what the performance goals of the boat owner are and what propeller is being used. In the case of a classic Whaler, we do not need to consider the special conditions that high performance boats operate in. There are no Whalers that go 80 MPH or operate in boat races. With very few exceptions, Boston Whalers, new or old, large or small, all have top speeds in the 25 and 50 MPH range. None of them require specialized high performance propellers, though all of them will benefit from propellers with modern designs.

Lastly, given all the variables described above, it is understood by manufacturers that there will be the need to vary the mounting height of an outboard on a boat. That is why all manufacturers provide multiple sets of mounting holes on their motor mounts, typically four different sets of holes and, in some cases, five sets of holes.

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Here is another data point:

A friend of mine repowered his 2002 classic Montauk this fall with a Yamaha F70. On my advice, he had the motor mounted at its highest mounting position, three holes up.

After trying the 13-1/4" x 16" Yamaha Performance Series three blade, it was determined that was too much pitch. A 13-1/4" x 14" Yamaha Performance Series three blade was substituted and it turned out to be perfect, 38 MPH at 6200 RPM with a two people and a normal load.

It should be noted that the 13-1/4" x 14" Yamaha Performance Series three blade is essentially the same propeller as a 13-1/4" x 13" Stiletto Advantage 4.25, both are made by Precision Propeller Industries, Inc. as is the 13-1/4" x 13" Turbo 1.