# Setting motor height on transom



## timsmcm (Aug 18, 2016)

Is there leeway in setting height of motor on the transom? My cav plate is about 1 to 1 1/2 inches below the bottom of my boat. I have an 85 Evenrude 15hp on a 94 lowe omc 1440m. Boat runs great, planes easy and fast, top speed seems good. I have a 9.25 x 10 omc prop. The motor sits right down on the very top of the transom and the mount screws are right under the top lip of the transom. Would you guys raise it up or just leave it? I have a couple of picts if need be.


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## timsmcm (Aug 19, 2016)




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## DaleH (Aug 19, 2016)

You want to read this ... https://www.veradoclub.com/index.php?topic=137.0 It is arguably the BEST tutorial, with pictures, ever written on correctly setting the height of your OB motor.

What counts, in a nutshell, is to get the vent plate riding the surface of the water while trimmed out and up on plane.


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## wmk0002 (Aug 19, 2016)

Since it appears you have your motor chained to the boat in addition to the locks on the clamps, I would at least give it a try raising it up some. See how much you need to raise it to get your clamps all the way up over the lip and rip a spacer out of some scrap wood. Then just set it on the spacer and re-tighten your clamps. Your cable/chain will give you some peace of mind that it won't sink to the bottom nor fall off while trailering. Theoretically, it should reduce some drag but its hard to tell if it will help performance-wise. But it will definitely help you get that much shallower which to me would be a big deal.


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## Steve A W (Aug 19, 2016)

Here's another explanation ;


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## timsmcm (Aug 19, 2016)

Steve A W said:


> Here's another explanation ;



What are you trying to point out? That is almost exactly how my motor is setup.


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## Charger25 (Aug 26, 2016)

I'm running pretty much the same set up, timsmcm. I'd leave it as is . just MHO. 

Would like to know where you got that lock thing on the motor though and that sure a nice looking motor. New paint ?


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## timsmcm (Aug 27, 2016)

Charger25 said:


> I'm running pretty much the same set up, timsmcm. I'd leave it as is . just MHO.
> 
> Would like to know where you got that lock thing on the motor though and that sure a nice looking motor. New paint ?



https://www.motorlocusa.com/ it is a great little piece that is easy to use and looks great. The man that imports them is really great to deal with.
As for the motor it is original paint accept for the mid section housing. I had to pull the power head to replace the water line gromets and it looked like someone keyed the paint so I sanded the scratch and sprayed a few coats of the closest color I could find. The rest of the motor looks new. I love my little 15hp omc. Can you tell. She gets taken care of like a baby after every use. That's the problems you run into with ocd.


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## scoobeb (Aug 27, 2016)

I have a 1648 alumacraft jon boat with a 20hp 2 stroke mercury on it and I run the same as you,maybe a hair deeper even, like 13/4 -2" below the bottom of the boat and while it may not be optimum height my boat screams with over 1000lbs of weight in it, 28-30mph. I'm sure there is some drag there because I know my anti ventilation plate is buried for sure. I just don't think moving my motor up will run any faster but maybe run a bit easier which would raise fuel economy a ton I bet. I'm going to fiddle around with mine and raise it as far as I can go also without feeling nervous it may pop off,I'm going to experiment with it to see how much the performance goes up because I'm a big guy at 300lbs so I know the back of my boat is really buried when running so I can probably move mine up a ton and still be under the water. I'm curious to see if u do raise it how it performs. Someone told me to leave it alone if it performs well as it does but if I can gain a hair bit performance and save on gas,why not. I may make like a transom extender out of aluminum so at least the clamps have something to bite to then when I find that perfect running height, bolt her down permanently. That is something you could do to your boat,just extend the transom up a few inches and problem solved once u find optimal height,or just leave it be if it runs great,the worst case is you have some extra drag like me which won't hurt anything from what I been told. I can't complain getting 30mph,any faster in a tiller boat is scary anyways,lol.


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## scoobeb (Aug 27, 2016)

I'm definitely going to follow your thread though to see how it all works out for u,it may peak my interest and get me to do it for sure if you have great results. At least we never have to worry about our prop blowing out or lacking sufficient water because we're buried in water ,lol.


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## timsmcm (Aug 29, 2016)

I am going to get her on plane and look at the cav plate to see how low it is, then will run at 3/4 speed and look at it to see what it is doing. I am like you I just don't see how I can get any more out of a 15hp. Close to 27 mph at wot and it pops up on plane in a boat length with not a lot of throttle. My little boat ain't pretty, does not have new paint but it is very sea worthy and as mechanically sound as any new boat out there.


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## wmk0002 (Aug 29, 2016)

timsmcm said:


> I am going to get her on plane and look at the cav plate to see how low it is, then will run at 3/4 speed and look at it to see what it is doing. I am like you I just don't see how I can get any more out of a 15hp. Close to 27 mph at wot and it pops up on plane in a boat length with not a lot of throttle. My little boat ain't pretty, does not have new paint but it is very sea worthy and as mechanically sound as any new boat out there.



Do you happen to know your rpms? I just used a prop calculator tool and assuming no prop slip, which is impossible, and 27 mph you would be turning 6970 rpms. Assuming 5% slip, which is still incredibly low, you would be turning 7263 rpms. Your model motor either has a WOT range of 5500-6500 rpms or 5500-7000 rpms. I would lean to it being 6500 rpms but someone may confirm.

I say this because as your motor sits now, you could stand to go up in prop pitch. If you went up to an 11" pitch 4 blade prop you would see your rpms drop by a couple hundred or more which would get you closer to your WOT range. If you did raise up your motor, you would reduce drag and probably gain a few rpms back. Typically with a larger pitch prop, you will see a small speed increase even with the lower rpms. You may not want to go any faster, but if you paired a larger pitched prop with dialing in your motor height, you may significantly increase your fuel economy.


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## scoobeb (Aug 30, 2016)

There is a guy on you tube who has a 1236 alumacraft and runs a 15hp johnson and he runs 25.8mph so 27mph can,be possible depending on weight,etc.... Alot of people don't think my 20hp 2 stroke mercury can push over 1000lbs near 29mph but I will show anyone my gps gladly and the other 5 I've used. I know science says things are impossible but some things are unexplainable to. I think it's very possible to run 27mph even know it seems impossible. My 20hp 4 stroke Suzuki ran near 27mph with me (315lbs) friend (200lbs) in my 1436,there was near 900lbs of weight total it was pushing and it ran fast with a 11 pitch prop. Some things are just unexplainable as I said. That was also with many different gps's as I couldn't believe the speed either. Go to you tube and there are tons of people going 25-27mph in a small boat and using 15hp 2 strokes and 4 strokes. I mean tons of them. I don't know how to explain it but all these people gps can't be wrong.


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## wmk0002 (Aug 30, 2016)

scoobeb said:


> There is a guy on you tube who has a 1236 alumacraft and runs a 15hp johnson and he runs 25.8mph so 27mph can,be possible depending on weight,etc.... Alot of people don't think my 20hp 2 stroke mercury can push over 1000lbs near 29mph but I will show anyone my gps gladly and the other 5 I've used. I know science says things are impossible but some things are unexplainable to. I think it's very possible to run 27mph even know it seems impossible. My 20hp 4 stroke Suzuki ran near 27mph with me (315lbs) friend (200lbs) in my 1436,there was near 900lbs of weight total it was pushing and it ran fast with a 11 pitch prop. Some things are just unexplainable as I said. That was also with many different gps's as I couldn't believe the speed either. Go to you tube and there are tons of people going 25-27mph in a small boat and using 15hp 2 strokes and 4 strokes. I mean tons of them. I don't know how to explain it but all these people gps can't be wrong.



Oh, I know it is possible. I wasn't questioning his speed report but rather letting him know that he is likely exceeding the motors recommended WOT range (which isn't a concern to some people).


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## scoobeb (Aug 30, 2016)

I didn't mean what I said in a direspectful way at all,I was just saying how strange things are and how crazy things are possible even know science says it isn't. For instance I just sold a 2002 25hp 2 stroke mercury that was a sweet running motor but get this,my 1993 20hp 2 stroke mercury can hang with it at wot which makes no sense to me,I'm talking as close to identical wot speed as you can get and one has 5hp more,now on the torque the 25hp has more get up out of the hole,but not much. I have been,reading that people claim some of these older outboards ,say 80s to early 90s outboards were so much faster then say like the late 90s to early 2000s of the same outboards which I find so strange how that's possible. I read and even heard of some merc guys saying some of the early 20/25hp mercs put out near 30+hp at the prop,how real that is I don't know but I know my merc pushes my 1648 like no other 20hp 2 stroke I've ever used. Maybe his evinrude is like this,anything is possible I guess.


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