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Engine mounting instructions
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| Suamicotom |
Posted on 09/07/10 - 6:15 PM
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I have a 1967 Nauset and I want to mount a 100 hp 1990 Mercury motor. How do you get bolts into the lower holes of the engine bracket. There is no access hole in the transom below the splashwell where the lower bolts need to be drilled. The splashwell is not deep enough to drill and have them in the well. It had an older motor on it and the lower holes were drilled upwards at a real angle. Not a good mounting. This motor has much lower mounting holes. Tom
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| Joe Kriz |
Posted on 09/07/10 - 6:20 PM
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Suamicotom wrote:
This motor has much lower mounting holes. Tom
Much lower mounting holes than what?
All the engines should be have the same BIA mounting holes system with the exception that some have 5 mounting positions and some have 4.
Take a look in the article section under "Outboard Motors and Rigging".
There you will find the Standard BIA Mounting hole pattern plus a little more info.
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| Suamicotom |
Posted on 09/07/10 - 7:26 PM
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This newer motor has the standard mounting holes, but he transom on the whaler does not give access to the inside of the boat at the lower mounting holes because the motorwell is enclosed down that far. I was reading in another area that someone said they used lag bolts on the lower mounts that screwed into heavier wood that is imbedded in the transom for that purpose. Does that sound correct? Thanks for your help
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| Davidk |
Posted on 09/07/10 - 8:05 PM
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I had lots of discussion about this years ago. Although some will argue with me, I will say you can't mount that Merc without modification. Your hull has the holes in it from the older style engines. They will not match the newer engines. Here are some choices: (1) Buy a jack plate and re-drill the jack plate where it bolts to the hull. Then bolt the Merc right on the jack plate. (2)Use lag bolts and bolt the engine into the transom and ignore the existing lower holes in the boat (bad idea to use lag bolts - but some will argue that). (3)...and this is Boston Whalers idea... use the lower bolt holes on the engine. Drill new holes in the transom. Cut an access plate into the hull below the splash well. Remove the foam and bolt onto the new mounting holes you just made. I don't like this idea either. (4) Lastly, buy a Yamaha or Suzuki. Both of these engines retained the old "blind holes" in the engine mount. These two lower holes are threaded and designed to have the bolt run from the inside of the hull/transom out to the engine bracket. These blind holes were kept in their engine bracket over the years. They line up with the old style engine brackets and your transom holes. As far as I know only the Yamaha and Suzuki have these mounting holes.
I bought the Yamaha just for this reason. It was a direct bolt on to my old transom (1962). If you want to keep from damaging the hull and assuming you don't want to buy a new engine, I suggest considering very strongly the use of a jack plate (do a google search if you're not familiar with them). I have a ton of experience trying to solve this problem. Feel free to contact me direct for any help.
Edited by Davidk on 09/07/10 - 8:09 PM |
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| Tom W Clark |
Posted on 09/07/10 - 9:21 PM
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This is an FAQ, a very FAQ.
The answer is to mount the motor "two holes up" on the transom (1-1/2" between the top of the transom and the underside of the "hooks" on the motor.)
When you do this, you also use the motor's highest set of lower bolt holes and the mounting bolts will then clear the transom splashwell with ease.
If you only want the motor "one hole up" (3/4") then you will have to angel the lower bolts upwards a bit. The angle is merely a cosmetic issue; it will be more than strong enough.
The old lower bolt holes can be easily filled.
There is no good reason to mount any modern outboard all the way down on the transom of any 16'-7" Whaler.
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| Joe Kriz |
Posted on 09/07/10 - 9:34 PM
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As Tom W Clark mentions, you want to drill the "Green" colored holes in the article I showed above if you want the engine mounted 2 holes up.
If you do this, you can't go down without drilling other holes.
Drill the "Yellow" colored holes using the angle Tom mentions if you want the engine mounted 1 hole up to start with. This way you could raise the engine if necessary without drilling anymore holes.
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| Finnegan |
Posted on 09/07/10 - 10:12 PM
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As the owner of a couple of 70's Whalers with shallower splashwells, I agree with what Tom and Joe have said. Clarifying a little. here is how I have done it. But anyway you look at it, the engine is going to be mounted higher, but not so high as to not function. You may have to spend a little more for a good SS surfacing prop however. With the mid-range Mercs, 75-125 HP, you are in luck, as for some reason Mercury designed these 20" shaft engines to be longer than 20". So they can take quite a bit of extra height.
After filling in old holes, including those terrible blind hole mounts that OMC used (and Yamaha copied), What I do is measure how far down the bottom holes can go in the splashwell, and still enter the splashwell on a perpendicular
basis. Using a 1/2" standard washer, hold it on the inside of the splashwell where it will lay flush, and trace the hole onto the transom. The centerline of that hole is your controlling dimension for the top hole of the bottom set of holes on the engine. You can then transfer that dimension to the outside of the transom. Normally, per Merc's recomendations, this centerline would be 9-7/8" below the top of transom. Your measurement will likely come out something near 8-1/2", which means your engine will be up 1-3/8", and can't go any lower than that. This is good, and works very well for the longer shaft 90 Merc. Even 1/4" higher will work also, as I mentioned.
Now that you have the bottom holes positioned height-wise, you have to determine where to drill the top holes. EVen though the engine manufacturers recommend 1-7/8" below the transom top, you can go higher, to about 1-1/4" if necessary. Here I would use one of thse transom stiffener bars. Obviously, the BIA vertical spacing of 8" won't work, but the next hole down on the engine, 7-1/4" may, and the next one down, 6-1/2" above the bottom holes, will definitely. So you can decide which to do if you are mounting directly to the transom.
If you want to use a jackplate, I recommend an anodized aluminum Detwiler, since they come factory pre-drilled with two sets of holes, 1" apart vertically. This allows you to use a 7" vertical spacing, which works well on these older splashwells. Here is photo of mine, using the Detwiler 7" vertical spacing:
http://smg.photobucket.com/albums/v42...G_0356.jpg
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| Davidk |
Posted on 09/08/10 - 6:30 PM
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Tom W Clark wrote:
This is an FAQ, a very FAQ.
The answer is to mount the motor "two holes up" on the transom (1-1/2" between the top of the transom and the underside of the "hooks" on the motor.)
When you do this, you also use the motor's highest set of lower bolt holes and the mounting bolts will then clear the transom splashwell with ease.
If you only want the motor "one hole up" (3/4"  then you will have to angel the lower bolts upwards a bit. The angle is merely a cosmetic issue; it will be more than strong enough.
The old lower bolt holes can be easily filled.
There is no good reason to mount any modern outboard all the way down on the transom of any 16'-7" Whaler.
Sorry Tom....I have to disagree. You say that there is no good reason to mount a modern outboard all the way down. Tell me....what's the down side? I have a modern 4 stroke Yamaha 100HP. Its mounted all the way down and rests on the transom. I used all the original holes that were in the transom and did not have to drill any new holes in my restored 62 Nauset. This was really important to me. I can plane in about two and a half seconds and I reach top speed of 46.3 MPH on GPS. I find no problems with using those awefull blind bolt holes (as somebody called them). I can't imagine any reason they shouldn't be used. That's what they're there for.......And for those that respond saying I cant raise my engine up any higher......Why would I want to with the performance I'm getting. Further, the other solutions people suggest will not allow moving the engine either. (The only solution to raising/lowering the engine is with a jack plate).
So to original poster... I stand by my solution (Yamaha or Suzuki). I completely understand that you may have just bought the Merc and want to find a way to make it work. That being the case, I still recommend the jack plate.
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| Tom W Clark |
Posted on 09/08/10 - 6:53 PM
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...what's the down side?
- Slower acceleration.
- Slower top speed.
- Reduced fuel economy.
- Greater tendency to porpoise.
- Greater tendency to list to port.
- Heavier handling with added steering torque.
- Potential for undesirable spray form the lower unit.
- Harder to clean the transom directly below the outboard.
- Increased draft with greater potential for hitting bottom.
But other than those items, not much.
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| Joe Kriz |
Posted on 09/08/10 - 7:04 PM
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I've never seen a 16/17' model that was setup properly with the engine all the way down.
The engine was always too low in that installation.
Adding a Jack Plate may help to install the engine but may open up a larger can of worms. Some setups could suffer from more porpoising and less performance.
Example:
If you knew that your fuel mileage and top speed would double by raising your engine up one hole, would you do it?
Unfortunately a person won't know unless they try...
I owned a Montauk with the engine all the way down. The engine needed to be raised up one hole for sure. Maybe two.
There was entirely too much spray coming from the cavitation plate which shouldn't be considered normal.
Unfortunately I never got around to raising it before I sold it.
I have however experimented with my Outrage 18' and there is a huge difference in how the boat performs when the engine is set at the correct height.
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| Davidk |
Posted on 09/08/10 - 7:28 PM
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Tom...I not sure you read my post in its entirety.
Slow acceleration? ... No. It planes in about two and a half seconds.
Slower top speed? ... No. It runs 46.3 MPH
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Reduced fule economy? ... No, but what is reduced? I can run all day at 32 MPH
and burn about 3.5 gallons. Not enough to worry about.
Greater tendency to porpoise? ... It never has at any speed.
Greater tendency to list? ... Never has.
Heavier handling? ... It turns nicer than my BMW.
Undersirable spray? ....Never has. Remember its not the Merc that's shaft is a
little longer.
Harder to clean? .... Never had a problem, but I don't think this should be
considered a major issue even if it was.
Increased draft? .... What, by an inch? I don't run it over sand bars anyway.
Joe..... I agree with your statements about a jack plate. I think it may open a can of worms. There is certainly an increased chance of misalignment and porpoising. The bass boats that use them seem to swear by them. I think for me, I considered it a last resort.
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| Tom W Clark |
Posted on 09/08/10 - 7:37 PM
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David -- I think it is your reading comprehension that needs work.
I never said your boat was slow, indeed you have very good performance numbers to report. But you could be doing better by raising the motor. By not doing so you are giving up the potential performance gains.
If you are happy with it, that is great. It is not my place to tell you you need to do better. I merely answered your question about what the down side is.
I am also pointing out to others who are reading along with this thread that there is no good reason to have a motor all the way down on the transom of a classic 16'-7" Whaler. Being afraid to fill two little 1/2" holes in the transom is not a very good reason.
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| Davidk |
Posted on 09/08/10 - 8:14 PM
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And I think my performance indicates your assertion is incorrect. There is a good reason to have your engine all the way down (at least a 100HP 20" Yamaha). My performance is at the top of the scale. It is unlikely I get much more performance out of these huills. If I lift the engine up, could it be better? Well, there is no reason to try. It just doesn't get much better. Is it theoretically possible? Perhaps. And I believe that is your point.
I don't think it is a foregone conclusion that an engine should always be lifted up some. At this point I will sit back and try to stay out of this. I said my peace and I have too much respect for you (Tom) to want to spiral this down. We may just have to agree to disagree.
Edited by Davidk on 09/08/10 - 8:16 PM |
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| Tom W Clark |
Posted on 09/08/10 - 9:18 PM
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My performance is at the top of the scale.
What scale?
My assertion is a simple one: If you raise your motor, your boat will go faster, accelerate quicker, draw less water, get better fuel mileage and have lighter steering effort. This does not mean you can double you boat speed by raising the motor one set of bolt holes; the improvements will be (literally) marginal, but it takes exactly the same effort to bolt an outboard one or two holes up as it does to bolt it a set of holes too low. So the question becomes: Why wouldn't you want a little more speed, a little faster acceleration, some more miles per gallon of gasoline for exactly the same installation effort?
For the Whaler owner is repowering his classic 16'-7" hull and who has to decide where to mount the motor, as Suamicotom, the originator of this thread does, my advice is to NOT mount it all the way down on the transom. If you want to disagree with that advice, that is fine but please show us where the advantage of mounting the motor all the way down is. You haven't presented any and I know of none apart from the aforementioned avoidance of filling the old lower bolt holes, a trivial task.
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| Gamalot |
Posted on 09/09/10 - 5:41 AM
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Coming to WC every day is like going to school! I hope I can learn what i need to know with out hijacking the thread.
I have a 1974 Montauk 17 and I think it is the 16' 7" Hull. It has a 1984 Evinrude 90 V4 mounted on it and the engine is mounted all the way down with the mounting bracket sitting on top of the transom ledge. The top holes are thru bolted with nuts while the bottom holes are what I think you call blind bolted. These bottom bolts appear to go in to threaded holes in the mounting bracket and have no nuts.
I have never had this boat/motor on the water and have no idea if this is the correct mounting or not.
If I am reading this thread correctly, I think my engine should be raised a hole or 2 and I do plan to remove it soon for over winter maintenance. When I re mount the motor and if I decide to raise it by virtue of the wisdom here, I will have holes to fill and new holes to drill.
I have looked at the articles section for mounting an engine and I do see the color coded holes but I do have some confusion and hope to get that cleared up.
My engine bracket has 4 bolt holes and my top bolts are through the top holes. The bottom mounting hole is a slot. I see another issue as well. If I raise the engine I will completely cover the splash well drain tube. My engine does not have power tilt and trim although I have purchased this part and plan to ad it over the winter.
Please let me know if I am making sense and if I am on the right track here.
Gary
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| Tom W Clark |
Posted on 09/10/10 - 6:52 AM
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Gary -- OMC motors used a continuous slot instead of individual lower holes. Nonetheless, the length of the slot represents the range of individual holes other motors have, so treat it exactly the same, in other words, the top of the slot is the "top hole" and where your lower mounting bolt will go.
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| Gamalot |
Posted on 09/11/10 - 7:50 AM
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Tom W Clark wrote:
Gary -- OMC motors used a continuous slot instead of individual lower holes. Nonetheless, the length of the slot represents the range of individual holes other motors have, so treat it exactly the same, in other words, the top of the slot is the "top hole" and where your lower mounting bolt will go.
Thank you Tom. I guess my question goes more to what benefit I might get by raising an OMC motor that was originally mounted all the way down. I sure don't like the idea of completely blocking off the splash well drain. Filling the old holes is not an issue nor is drilling new ones in the bottom slots but can you or any one tell me if I will see a noticeable difference in performance and/or handling by doing this move?
As I said, I don't have a clue yet as to how the boat performs with the engine mounted as it is now but I do want to get it right during my refit.
Gary
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| tedious |
Posted on 09/11/10 - 11:37 AM
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Gary, my Supersport 15 arrived at my door with the 1989 Johnson 70 mounted all the way down, and turning a 13x17 SST prop. I bought a decent, newer stainless prop (13.25x17, but with a lot more cup which effectively adds pitch) and raised the motor two holes. The top speed went up, and handling got quite a bit better - less bow lift when taking off from a dead stop (an issue for the 15 / 70 combo, believe me!) and in general, a lighter feel to the steering. I did not measure the mileage to any great accuracy, but it did seem to improve. One additional benefit was an inch and half of extra skeg clearance when moving the boat around on the trailer - it made a lot of things easier!
That said, this was a 15 which didn't have any problem with the splashwell drain holes.
Tim
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| Gamalot |
Posted on 09/12/10 - 8:26 AM
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Thanks Tim but I am not sure if what works on your 15 will work on my 16.
I would love to hear from others who have 1973-1976 Montauk 17s with OMC motors and how theirs is mounted. The best I could ask for is another member who had the motor mounted all the way down and moved it up a hole or 2.
My suspicion leads me to believe the motor is mounted all the way down so it does not block the splash drain. It sure sounds like moving it up a hole or 2 will be the better performance modification but at the cost of loosing the drain.
Considering I have the tool and left over drain tube I suppose I could always move the drain over after I raise the motor.
Gary
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| Tom W Clark |
Posted on 09/12/10 - 9:04 AM
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Gary,
Your motor is mounted all the way down because that is how it was done in the mid 1970s.
It is hard to get folks to understand how much time has passed and how much better outboard propellers have become. In the mid 1970s there were only (for all practical purposes) aluminum propellers for use on small outboard powered boats. The first commercially successful stainless steel propeller had just been introduced by OMC (the SST) and it was an early design that had only very modest cupping.
With these old fashioned aluminum props. the cavitation (AV) plate needed to be fully submerged so the motors were installed as low as they could go.
Many smaller outboards did no have an power trim either so one trim setting was all you got unless you wanted to manually move the tilt pin and even then you only had four or five choices.
By the 1980s the OMC SST had shown the benefits of the stainless steel propeller, but they were expensive so not many folks adopted them. Dealers were set in t heir way and they just continued to mount the motors as low as possible. This continues today with old mechanics who just never figured out how to correctly set up a motor with the right prop.
In your case you have the unique problem of covering your drain tube. You have to have a working drain tube so you will either add a new one, space your motor back from the transom with jack plate, or modify your motor to allow water to drain form the exiting drain tube.
No matter what you do, I recommend you actually use your boat the way it is rigged now so you can better appreciate how much improvement can be had by raising the motor next year and installing an appropriate stainless steel propeller.
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