2000 Montauk 17 Performance - Need More Help

[Alibertucci]

I have taken my 2000 MONTAUK 17 to a dealer to have the engine checked over, and asked them to raise the engine mounting height from the current lowest-possible position to the two-holes-up position. Both mechanic and dealer expressed concern about the propeller ventilating with the engine mounted two holes up. They suggested that they raise it to one-hole-up to start.

I am inclined to move the motor up one hole and see how that works out. I was determined to raise the motor as previously recommended to two-holes-up, but now I am not so sure.

Give me input on the engine mounting height that should be first tried.

BACKSTORY:
In Spring 2021 I purchased a 2000 Montauk 17 with a Mercury 90-HP two-stroke-power-cycle engine.

I have read the article here on engine mounting height, on the position of the motor, and on where the A-V plate should be at optimal height.

The boat's top speed is about 35-MPH in smooth water and calm wind, with two persons in the boat. That is significantly below the 43 to 45-MPH estimate that many have suggested I should be getting.

Suggestions already made to improve performance are:

• mount the engine two-holes-up, and retest
• verify actual engine speed with another tachometer
• reduce propeller pitch to 19 from the present 22-pitch

The boat is now at a Mercury certified service center that has a good reputation. They are going to check the engine and raise the engine mounting height to two-holes-up. However, the mechanic and the owner of the shop both questioned that. The mechanic trimmed the motor to see where the A-V plate was in relation to the bottom of the keel. It appeared to be maybe an inch above that mark or maybe close to even, it was hard to tell.

The engine was mounted in the lowest position. All four holes are through-bolted to the transom, with the holes appearing to be drilled at where one would expect a template would require them.

[Moderator's note: it is not necessary to show a picture of the engine mounting height if you have correctly described it in your narrative. Similarly, it is not necessary to show a picture of a propeller marked 22P when you have already noted the propeller was 22-pitch.]

[Phil T]

All pre 2000 designed models, except the 13 Sport, should have the engine mounted two-holes -up, top bolt in the third hole down from the top. Lower engine bolts are in the bracket slots and not the blind holes. The engine should have a stainless steel prop, no aluminum.

There are hundreds of posts on this forum explaining the "why" of this in the archives. One-hole-up is only recommended if you frequently encounter large ocean swells or steep three-footers.

As has been said to many owners doing the same thing, tell the shop. "Please mount the engine as I ask. I know what I am doing".

FYI - You can change the engine height as a DIY while the boat is on the trailer with some basic tools and blocks so visiting the shop is not necessary.

As for performance testing.

A new Montauk 17 with a new two stroke 90hp engine, dry hull, no bottom paint or significant gear will reach 46-MPH on very calm water with no tide or wind. A 22 year old hull with an old engine of unknown age and tune will not.

Here is my rational, reasoning:

New boat speed @ 5500 = 46-MPH
--subtract for motor age (less compression, tuning) - 2 mph
--subtract for rough bottom paint - 2mph
--subtract for low engine mounting height - 4 mph
--subtract for incorrect engine trim, boat weight, gear, water current - 2 mph.

Predicted boat speed - 36 mph.

Given the age of the boat and the engine, I think an appropriate target speed for your boat is 40-MPH. Having owned a 1987 Montauk, that is pretty fast.

Recommend you raise the engine 2 holes and retest with the same load, conditions as before. Trim engine out till boat speed and rpms, (speed observed via GPS) starts to fall, then trim in just a bit.

Once you have completed the change and tested it, you can move to the next steps based on the results.

[Alibertucci]

Thank you Phil, your advice is consistent with what you provided to me previously as has others.

The engine is original, 2000 ELPTO 90, verified through Mercury records. It was sold to the first owner with the boat. The propeller is stainless steel 22-pitch.

When I did the tests, I did trim the motor to optimal using boat speed (as measured by a GNSS receiver). I always have done that with prior boats.

The hull does have bottom paint, which for the time being I don't plan to remove. I should have mentioned that in my post. Great point.

I am not able to do the engine work myself. There are four through-the-transom bolts through top and bottom holes (no slots on the motor bracket) and I don't have the gear to safely raise or lower the motor. I am also older which is a factor, unfortunately.

I will have them raise the motor two holes and retest, as you suggested. They are currently checking the compression, assuring the motor is in best shape as can be expected.

I don't expect maximum cited boat speed. I just want to get the boat speed to where it should be for a boat this age. Cruising at an engine speed of 3,800 to 4,000 RPM is the norm for us. Optimizing the boat and motor--given their age--is the goal.

Thank you again for your expert advice, as always.

[Phil T]

In 2000, all Boston Whalers were sold to the dealers without an engine or electronics or trailer. It was the local dealer that rigged the engine. The mounting of your engine using the blind holes is typical for the old thinking. All boats post 2002, all boats came from the factory rigged one hole up. Still conservative.

The advice is to remove the engine. Fill the lower holes using wood plugs (never dowels) and epoxy. Shave the last dowel flush and cover with Locktite Marine Epoxy in white. A close color match to desert tan. Re-drill the lower holes using the recommended spacing of the BIA template. This repair should only cost $500. While it is pricey, it would be worth it.

The recommendation to get the boat/engine configured to run WOT at the top of the manufacturer's range is so that the engine operates efficiently at all speeds.

[Alibertucci]

Thanks again for your advice Phil. Yesterday, the mechanic called me to report on the motor and his tests. Compression was good in all cylinders, there was a small oil leak he repaired and then he tested the boat on the Potomac River. He said motor ran well but steering is locking up when he was turning either direction about half way. I never noticed this but have noticed it was hard to maneuver the boat to some extent in tight areas at no-wake speed. He will replace the steering cable (which requires the motor be removed) and make sure everything is in good shape. When he re-installs the motor it will be two-holes up as I instructed him to do.

My boat and motor were both sold at the same time in August 2000, according to Whaler and Mercury records. As you suggest, the motor was probably installed by the dealer in Long Island. There are no blind holes in my transom. The motor is mounted by four through the transom bolts,washers and nuts. See the photo enclosed here showing the four bolts. One Whaler Central member suggested that the bolts should be reversed so that the threaded nuts and washers are on the inside of the transom in the splash well, with the bolt heads on the outside. I will ask the mechanic about that before he re-installs the motor.

Once I have the boat in the water and test again, I will report back here with that information. Thanks again for your insights and experience.

Fig. 1. One of the bottom engine mounting bolts can be seen just behind all the cables and hoses.

IMG_1718.jpg (152.53 KiB) Viewed 6121 times

[Phil T]

Install a steersman nut on the steering tube so that you can perform the seasonal maintence on the steering. This includes adding grease so the steering cable does not corrode and lock up. You use the same marine grease you already use for the engine mounts and cover latch.

http://www.steersman.com

[goldstem]

Another advantage of having the motor higher up is that you can then clear the well edges for replacing the steering cable. You should be able replace the cable by loosening the mounting bolts for the engine and forcing the motor to lean forward to get the extra clearance you need.

[jimh]

Tell the dealer to raise the engine mounting height to two-holes-up if you want the engine at that height. Tell the dealer if you don't like the performance at that height you will pay him to lower it to one-hole-up. Or, as Phil mentions, you can lower it yourself.

If you are really planning on trying to optimize engine mounting height, the only way to know when you have reached optimum engine mounting height is when you have RAISED THE ENGINE TOO FAR. But before you become obsessed with engine mounting height, ANY height other than lowest-possible-mounting-height is going to be an improvement in 999 of of 1000 cases.

When asking for advice about boat performance, you need to give more information.

Give the GEAR RATIO of the engine. Without that data there is really no way to assess the propeller performance. Give the RECOMMENDED FULL-THROTTE ENGINE SPEED RANGE. Those two parameters are most important for assessing performance.

It is also useful to know the number of cylinders and their orientation, and engine displacement, as this can help prevent confusion when there is more than one engine from the manufacturer rated at the particular power. Also the ENGINE WEIGHT is useful.

Clearly and explicitly indicate the UNIT OF MEASUREMENT OF BOAT SPEED, either Statute MPH (preferred) or Nautical-Miles-per-hour (not preferred).

If the tachometer is not an OEM tachometer with a FIXED calibration for the specific engine it is being used with, there could be an error in the tachometer readings. Most older outboard engines used a permanent magnet alternator (PMA), and the tachometer signal produced by the engine is developed from the PMA. A tachometer is really a frequency meter; it reads the frequency of the pulses from the engine. With a PMA, the number of pulses produced by one rotation of the crankshaft depends on the design of the PMA, that is, on the number of pole windings in the PMA stator coil and the number of magnets in the rotor. Many aftermarket tachometers are designed to be universal and have a calibration control that allows the tachometer to be calibrated to different engines. If the tachometer in use is a universal-type, you should CHECK THE CALIBRATION.

Other important data to include in any performance report:

• date
• location
• air temperature
• humidity
• water salinity
• water temperature
• elevation of the body of water
• wind speed and wind direction during the test relative to boat course
• any current in the water, its speed and direction relative to boat course
• engine mounting height in term of number of holes up from lowest possible mounting
• full information about the propeller under test:
  • make
  • model
  • material
  • NUMBER OF BLADES
  • pitch
  • blade rake
  • blade cup
• engine trim settings used
• abnormal behavior such as the bow oscillating up and down, the propeller ventilating, the boat listing to one side, and so on

Develop a table of data showing engine speed in increments of 1000-RPM up to about 4,000-RPM, and then in 500-RPM increments until maximum engine speed is reached.

Don't be dissatisfied with your boat performance because some guy reported his similar boat could go 10-MPH faster. There are many influences. Maybe the guy with the faster boat was testing in very cold saltwater with a current assisting him, going down wind and down sea, on a cold day with very low humidity, running on 98-octane fuel, had 5-gallons of fuel aboard, no one else with him, and he picked the highest number he saw flash on his GNSS receiver that has a horizontal dilution of position metric (HDOP) of 4.0 and had only a low-precision position fix, and then wrote it down wrong.

[jimh]

Regarding the rigging seen in Figure 1:

I would pull the extra engine electrical harness cable forward in the rigging tunnel and store the extra cable under the console. This will improve the rigging in the following respects:

• the transom will be much neater
• the extra cable won't be exposed to seawater and sunlight
• the drag on the engine when turning will be less without all the extra cable weight to pull around
• there should be enough room under the console to neatly coil the excess.

You should verify the engine mounting holes in the transom at at the BIA template locations. See the article in the FAQ on engine mounting hole locations in the transom.

Q9: What is the Standard Transom Hole Layout?
https://continuouswave.com/whaler/reference/FAQ/#Q9

I don't see the fuel hose primer bulb in Figure 1. The primer bulb should be inserted in the fuel supply line near the engine so the primer bulb is oriented vertically and the arrow on the bulb points skyward. See the article

A PRIMER ON PRIMERS
https://continuouswave.com/whaler/reference/primer.html

In Figure 1 I see a fuel filter mounted exposed to the air and water with corrosion. If you have to keep the fuel filter exposed to the elements, get a fuel fitting manifold that has a a white weather resistant finished or is chrome plated.

ASIDE ON PROPELLER PITCH
I suspect that a 19-pitch propeller may be more suitable for your boat. But without knowing the engine gear ratio, there is no way to assess the relationship between engine speed and propeller shaft speed, and pitch and boat speed. That said, if I assume the gear ratio is 2:1, and if the engine can accelerate at full-throttle to 5,600-RPM, and if the SLIP is about 8-percent, then the boat speed would be 45.8-MPH.

I have created a propeller calculator to work out the mathematics. See

https://continuouswave.com/calculators/propCalc.php

[Alibertucci]

Whew--lots of information to digest.

The mechanic called and told me the work is completed. The new steering cable is installed, and the motor raised to two-holes-up.

The engine under discussion in an in-line three-cylinder 1.385-liter displacement Mercury 90-HP outboard with a gear ratio of 2.3:1. The full-throttle engine speed range is 5,000 to 5,500-RPM

The propeller calculator shows a 22-pitch propeller will produce more speed than a 19-pitch propeller at a given RPM of say 5,200 RPM.

I found the information I recorded from my test in Fall 20221. However, I will wait until I test further to post any data. With the motor serviced and minor repairs performed. and the engine mounting height raised, more test runs are appropriate before further evaluation can be done. I will post information on future testing when I have a chance to do that.

The corrosion of the water filter mounting bracket and manifold and need for its replacement has been mentioned to me before. I plan to replace the mounting bracket; the filter is new.

I have been given advice that a fuel-water separating filter is not needed in this application; I plan to keep the filter. I tend to use gasoline without ethanol. I do not feel there is harm in having the filter. At some point I may have to purchase gas with ethanol.

Fig. 2. Location of fuel tank under reversible pilot seat. Note fuel primer bulb.

IMG_1727.jpg (46.93 KiB) Viewed 6054 times

The in-line fuel primer bulb is near the Moeller Tank under-RPS. I have been given advice to move the primer bulb to be near the engine, and also advice to leave it where it is located now. I had decided to just leave it, but after reading the information provided by jimh, I will probably relocate the bulb and install it so it is vertical.

I plan to pull the engine harness cable slack through the tunnel into the console; thanks for that advice. I agree with the recommendation, and I would prefer that the transom looks neater.

[Phil T]

Not sure the steering cable had to be replaced.

Be wary. Shops find it easier to just replace parts then to fix things. Cleaning out the tilt tube and re-greasing the cable is a bit messy.

I am still running the original steering cable on my boat.

[jimh]

As seen in Figure 2 above, the orientation of the primer bulb is vertical, but the direction arrow indicating fuel flow is pointing downward. Orientation of the primer bulb should be with the direction arrow indicator pointing upward. This will cause the check valves in the primer bulb to work much better, and obtaining a stiff primer bulb with a few pumps will become possible.

The propeller calculator shows a 22-pitch propeller will produce more speed than a 19-pitch propeller at a given RPM of say 5,200 RPM.

You don't need a propeller calculator to postulate that at a given speed of rotation of the propeller, the higher the propeller pitch the greater the speed of advance.

But you cannot assume that your 90-HP engine is going to be able to turn the 22-pitch propeller as rapidly as it can turn the 19-pitch propeller.

The greater the propeller pitch, the more power needed to turn the propeller. The 90-HP engine can only supply a certain amount of power. When the engine power output reaches the amount of power needed to turn the propeller at the speed the engine is then producing, the engine stops accelerating. The power needed to turn a propeller as a function of the rotation speed is known as the propeller power curve.

The optimum propeller for a particular engine will be the propeller whose propeller power curve meets the engine power output at the engine's highest rated engine speed for full-throttle. If the propeller has too much pitch, its power curve will stop the engine from accelerating below the maximum rated engine speed.

If you are interested in a greater understanding of the propeller power curve, read my article on that topic:

PROPELLER POWER CURVE
https://continuouswave.com/whaler/reference/propellerPowerCurve.html

Now that the gear ratio of the engine under discussion is known, the Propeller Calculator can be more useful. For example, looking at the claims that a similar boat could accelerate to 46-MPH can be analyzed. If the engine speed were kept to the recommended 5,500-RPM, and here we are assuming the engine was able to accelerate to that speed, and assuming a SLIP of about 8, the necessary propeller pitch to accomplish that is calculated to be 22-inches.

So far the ONLY DATA provided about your boat is the top speed is 35-MPH and the propeller pitch is 22-inches. If that data is entered and the engine speed calculated (assuming a slip of about 15 because the propeller is not working as efficiently at that boat speed) the engine speed should have been around 4,500-RPM.

Another way to estimate the speed is to use a calculator that predicts boat speed as a function of weight and power, with allowance for a certain type of planing hull. For the classic Boston Whaler hulls like a MONTAUK 17 hull, there is a good estimate of the hull coefficient: 190. Using a speed predicting formula based on that hull coefficient and a power of 90-HP, we can calculate the total boat weight that can be allowed to reach 46-MPH. There is another calculator that I have created for this purpose. It is based on well-known principals developed by a naval architect, George Crouch:

Crouch's Calculator
https://continuouswave.com/calculators/crouchCalc.php

With input of hull coefficient 190 and horsepower of 90, to be able to accelerate to a planing speed of 46-MPH suggests the total boat weight must be no greater than 1,535-lbs.

Given the bare hull weight of the c.2000 MONTAUK 17 is 950-lbs, and the engine weight for a Mercury 90 is about 310-lbs, that leaves only 275-lbs for EVERYTHING else on the boat, include the driver, the fuel, and all the rigging and gear. If the boat had 12-gallons of fuel aboard, then that fuel alone adds 75-lbs of fuel, leaving only about 200-lbs for everything else, including the boat driver. Let's say the boat driver is a svelte 175-lbs, so now we are down to 25-lbs for ALL THE OTHER STUFF on the boat. In other words, the claimed speed of 46-MPH must have been accomplished with an extraordinarily light MONTAUK 17.

Even boosting the hull coefficient to 200, to hit 46-MPH with 90-HP still limits boat weight to 1,700-lbs, a rather modest increase of 165-lbs in allowed weight.

I think a better target speed is probably 40-MPH. Going back to the propeller calculator with a 19-pitch propeller with SLIP=8, the engine speed needed is only 5,560-RPM. That sounds much more attainable than 46-MPH.