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Where is your motor mounted?
All the way down
13%
[1 Vote]
1 hole up
0%
[0 Votes]
2 holes up
25%
[2 Votes]
3 holes up
50%
[4 Votes]
4 holes up
13%
[1 Vote]
Total Votes : 8
Engine Mounting Height for 16/17 Whalers without measuring
Many people lately have been asking what the proper height to mount their particular motor is.
Well, the best way these days is to go by the mounting holes of the motor and which hole you have the bolt in. http://www.whalercentral.com/articles...cle_id=106
We can tell you which hole it should be mounted in without measuring.
Old school technology told us to mount the motor 1 inch to 1 1/2 inches above the bottom of the keel as a starting point for proper engine mounting height. I found this to be difficult if not impossible with regular tools (see below).
So for a reference and to begin with, I wanted to measure the height of my Evinrude 70hp motor on my 1977 Montauk 17'.
Basically I found that I could not measure the level of the Anti-Cavitation plate for several reasons.
1. The keel was resting on a 12 inch keel roller so there was no way of putting a level or piece of wood etc. under the bottom of the boat.
2. Very difficult to launch the boat in the water and try to measure it that way unless you had a face mask and some measuring tools you didn't care to get wet. And you could hold your breath long enough.
How would you go about measuring?
I was able to use a level on the bottom of the hull by adjusting the trailer jack.
Now the bottom of the hull was level.
Then I put the level on the bottom of the anti-ventilation plate and tilted the motor so the plate was level.
The level on the plate hit the hull almost perfectly inline with the bottom making this motor basically even with the bottom of the hull and making it mounted too low.
At this point my motor is mounted in the top bolt hole which makes it mounted all the way down. Again, Too Low.
For most all motors except Mercury, there are only 4 bolt holes. So, this only gives us 3 other choices.
*All the way down = even with bottom of hull
1. 1 hole up = 3/4" above bottom of hull
2. 2 holes up = 1 1/2" above bottom of hull
3. 3 holes up = 2 1/4" above bottom of hull
Through many members here, we do know that the E-Tec mounted on the Classic 16/17 hull is best mounted all the way up.
So #3 above would be 2 1/4" above bottom of hull. Mounted 3 holes up for this motor.
Other motors and prop combination may be better mounted using 2 holes up at 1 1/2" above bottom of hull.
No need to measure anymore that I can see on these old Classic Whalers. There have been enough motors mounted on these boats that give us all the mounting position we need to know just by using the bolt holes.
Sometime in the near future I plan on raising my motor up using the 2 hole up mounting position but I need to drill new 'Green' holes in this diagram. http://www.whalercentral.com/articles...icle_id=82
If anyone has any other info on mounting height using the bolt holes, please let us know what you have or find.
Please no guessing or eyeballing the height if you are going to try and measure.
I realize some of you may have laser measuring tools or water bubble measuring tools etc. Not all of us have those tools so let us know what you might be using.
For now the recommended mounting height looks like these below and No Need to measure anymore.
3 holes up = E-Tec
2 holes up = All other motors except Mercury
Maybe some of you with Mercury can tell us what hole your motor is mounted in for future reference.
One very simple water level is take a length of clear tubing and put water in it. Hold one end at whatever height you want and raise the other end above that height. Now slowly lower the high end and when water starts to flow out you are at or below the original height.
I have seen this used with lengths of 100+ feet of tubing.
My motors are now both 3 holes up and I am very happy I finally did it.
1964 16' with 70hp yam 2-stroke
1966 16' with 90 hp yam 2-stroke
I am amazed how fast the 90 is compared to the 70.
Joe, on my 15 I found it trivially easy to measure. I taped a thin stick to the keel (the keep roller has a notch which the stick went through fine) then another stick to the AV plate on the motor. I adjusted the trim so the two were parallel, then measured the distance between them. I don't remember the result.
I'm two holes up with my F70 (one more hole to go up if needed). I'd be interested to know if anyone else is running a 15 / F70 all the way up.
I might confuse the topic here but on modern Boston Whalers the 3 digit ones like 170, 150, 210, etc. shouldn't we expect Boston Whaler to know where to mount these Outboards. I'm talking about the Mercuries as that is the 'standard' power that they put on.
Bottom line should I check where my Merc sits in comparison to the keel or should I assume the engineers at Boston Whaler and Mercury know what they are doing and leave it as it came from the factory?
Joe - I think your article is excellent, and a good reference article for most. There are two assumptions that I assume you are using, and which could be complicating factors if those assumptions are incorrect in a given situation.
1. The top bolts are drilled at the BIA standard and recommended 1-7/8" Centerline down from the top of the transom. Although this should be case for maximum transom stress safety, it is not always the case. I have seen top holes drilled higher, and even have that situation on one of my boats. Often an installer will do this because of a need to raise the bottom bolts slightly. So everyone should check that situation.
2. Not all engines are designed with the same middle section dimension, either 20" or 25". This can be difficult for a consumer to measure or determine. Engine manufacturers do not generally give this dimension. In other words, the difference between the vertical dimension from the top bolt hole to the anti-ventilation plate can vary, often considerably.
Regarding the E-tec 90 on a Montauk, where I keep reading the engine has to be mounted all the way up in the 4th bolt hole, I find it very hard to believe that the engine is running 2-1/4" high. This is the realm of high performance surface piercing racing and limited purpose speed, with special cooling intakes needed. Not even many props can truly handle this height. My best guess is that the Evinrudes have a longer than 20" mid section length, so that an engine up 2-1/4" may actually only be up 1-1/4", which is considered plenty high for most applications. Regarding the mid-range Mercuries, and Big foot gear cases, Mercury actually indicates that these are longer than normal, and need higher mounting. I can verify this from my own experiences. When I changed the power on my 18 Outrage from the older Mercury "towers", I had to raise the newer 90's up another 1" to acheive the same height, with same prop line. The 90's are at least 1" "taller" than the older engines, and also taller than my Merc V-6's.
On my Montauk, I have the jackplate mounted Merc "tower" running about 1-1/4" high, and even with a Laser II high performance prop, this is all the boat can handle for all around good holding and performance. There is no way an E-tec 90 could be running 2-1/4" high for all around use, without major slippage and ventilation. So I assume the E-tecs have a longer/taller mid section.
About the only way to completely predict mounting height would be to keep track of actual situations, as has been done with the E-tec 90 on Montauks.
I guess my point here is that if you mount an engine in the third set of holes, a good starting point for maximizing performance, don't assume you are up 1-1/2". It may be less if the engine has a longer than standard shaft length.
Yes Larry, we need to assume that they have the Standard BIA mounting top holes anyway.
This discussion does not take into account with folks that have Jack Plates.
This info is for standard operators only. Not racers or others with Special Needs like Jack Plates, etc. Most these owners know what they want and what they are doing anyway.
Yes, this is a good starting point as even if someone could measure very accurately, it would still only be a starting point.
Differences in props, how the boat is loaded, and other variables cannot be factored in to this discussion as again, this is a reference starting point.
Next will be the Outrage 18's with single motors. (2 holes up) (NO Jack Plates)
Again, standard applications and standard mounting procedures.
Anyone has something different will have to adjust to what someone else did to their boat. Or maybe what they did?
One thing I really like about the Mercury is that it has 5 mounting holes.
I wish all the motors had the same feature.
It would make this much easier.
It is going to be tough to compare all the other motors height to the Mercury line due to this.
Already we have one member that has his Mercury mounted 4 holes up, all the way. Don't know what hp or any other info beside what is shown in the Poll.
Joe,
I was the one who voted 4 holes up. You should probably delete my vote as I have a jack plate and estimated the height as 4 holes up if the jack plate wasn't there. 1985 Evinrude 90.
Since this discussion is about classic 16/17' boats, I can say with some experience that if you are mounting or running and older Mercury, such as a 1984-1988 in-line 6 (90 or 115 HP) or 1984-1986 in-line 4 (75 HP), two holes up is the maximum height, and would require a surfacing prop such as a Laser II. Mercurys older than 1984 do not have the BIA bolt pattern, and are difficult to mount very high because of the old thumb screw clamp bracket at the top.
If you are running a 1987 or later Merc 75, 90 or 115, 2-stroke, Optimax or 4-stroke, I would start with three holes up, since these engines have the "taller" mid section. A performance prop is also required. If it is too high for the prop being used, the engines can then be dropped down one hole.
I have also had experience with an older (1979) Evinrude V-4 100 HP engine mounted on a 16' Currituck. The engine was mounted two holes up, because of the shallow transom splashwell, and with a Stiletto prop, this was all the height the boat could accomodate. The boat ran 50 mph with this setup. Evidently, the older V-4's do not have as tall a mid section as the newer E-tec 90's.
One last issue on the smaller 40-60HP Mercs, with either standard gearcase or the BigFoot gear case.
Mercury says that Bigfoots run deeper (meaning more than 20" length) than the conventional gearcase (which is why they are recommended for pontoons), so a regular gearcase engine cannot be mounted as high as the Bigfoot models. With regular gearcase, 2 holes up would be maximum, although I think with such low HP on a 16/17, there is not much to be gained over one hole up. The Big Foot models could be mounted 3 holes up, but once again, not much to be gained over two holes up.
My thought is that with any brand engine under 90 HP, and combinations that run under 40 MPH, there is not much to be gained in performance by any more than one hole up, except for a deeper Big Foot gearcase.
