Outboard mounting height 1985 Johnson 115 v4

[scottcab]

Re: Outboard mounting height 1985 Johnson 115 v4

Motor runs strong, and looks great for an '85. Congrats on the baby, I can see why you dont want to funnel money into the motor

Thanks Pete,
I appreciate ur time and willingness. I will get to tinkerring with the motor and answer everyone question to get additional help as soon as I get a little time.

 

[bob johnson]

Re: Outboard mounting height 1985 Johnson 115 v4

scott if you look at a motor, the shape of the motor below the Cavitation plate is VERY streamlines...thin and sharp. All to reduce frontal impact with the water and reduce drag...now look at the 5" of motor above the cavitation plate . you can almost be getting into the lower motor mounts housings!!! much thicker and more frontal area...thats isnt supposed to be plowing into the water!!!!!!!!!!!

thus your water splash and spray!!!

if and or when you get the motor raised you wont have that spray any more

bob

 

[scottcab]

Re: Outboard mounting height 1985 Johnson 115 v4

I just checked the current prop. It's a aluminum omc prop 13 3/8 X 17. The other prop that I have at home is a Stiletto Advantage I 13 1/4 X17 Stainless prop. I will probably have better luck with the stainless prop right? Of course I understand that the changing from my one prop to the other isnt going to fix the above listed problems, but I just want confirmation that the stainless would be a better choice.
Thanks
Scott

 

[SparkieBoat]

Re: Outboard mounting height 1985 Johnson 115 v4

I like SS props

 

[emdsapmgr]

Re: Outboard mounting height 1985 Johnson 115 v4

Most stainless props have more cup on the blades. As such, you can mount the engine slightly higher on the transom and not loose any prop bite. Less engine in the water=less drag=more speed. The extra cupping tends to add a pitch or so to the prop, so it may run slightly different rpm's than a basic aluminum prop of same pitch. Usually they have slightly more speed potential.

 

[scottcab]

Re: Outboard mounting height 1985 Johnson 115 v4

Tachometer is installed, I will be taking her to the lake tomorrow to get those rpm/speed numbers for ya. Maybe then we can get a little more figured out. I will be running the test runs with the Stilletto Advantage I 13 1/4" X 17 Prop.

For my tests at the lake tomorrow, the things I want to look for are:
1) that the water line is right at or just below the anti-cav plate
2) at WoT, trim the motor up a little at a time (5 second increments) and record RPMs and MPH
3) time to plane off
4) quality of handling

Is there anything else that I should be looking for?

thanks
scott

 

[AlTn]

Re: Outboard mounting height 1985 Johnson 115 v4

overheat

 

[scottcab]

Re: Outboard mounting height 1985 Johnson 115 v4

overheat

Are you mentioning to make sure that the motor doesn't overheat?

And if so, I have a buzzer alarm in my controls. I can use this alarm to make sure that I am not overheating?

I will monitor the discharge stream from the motor to make sure it remains relatively cool as well.

Any other suggestions?

 

[Haffiman]

Re: Outboard mounting height 1985 Johnson 115 v4

Whatever prop you put on, it will not have much effect as long as your gear case is that low. SS props keeps the shape better under load, opportunity for cupping which increases the grip when engine is lifted, you may rake them to get better boat trim without having to trim the engine to far out etc. However all these advantaged requires that the engine is installed at correct height. Remember that if you hit anything when running a SST prop, the risk for severe damage on the gear case is rather big. With your prop at the moment in 'second basement' that risk is rather high.

 

[bob johnson]

Re: Outboard mounting height 1985 Johnson 115 v4

5 seconds might be a little long. I think you can trim a long way in 5 seconds..id do no more than 3 and let it settle for 15-30 and monitor. its best if the water is calm for these tests.
you should bring a second prop( if you have one to try after you run what you have now)

bob

 

[scottcab]

Re: Outboard mounting height 1985 Johnson 115 v4

Okay all, I ran the boat at the lake today with the new tach installed and was surprised/disappointed with the results. I was able to adjust my idle to the proper speed now which is good.

I do understand that my motor is still about 2 1/2" to low. The shaft was 5" too long, but I mounted the motor up on the bottom holes. This has the motor bracket about 2 1/2" higher than the 20" shaft was. At full trim in, there is way too much motor in the water. The water line is just above the top plate (the plate above the anti-cavitation plate and below the motor mounts) and thus dragging the bull nosed looking part of the lower unit through the water (lots of resistance). Once on plane, I trimmed up in two second increments and found that my max RPM and speed combo was after eight seconds of trimming up. This is when the water line is just over the anti-cav plate. At this trim level, the RPM are 4200 and the speed was 33.7mph peak.
The prop I currently have on it is the Stilletto 13 1/4 X 17 pitch SST Prop. It seems a little slower than the alum 13 3/8 X 17 that I had on it.

Obviously my RPMs are way off. Assuming that I can't change the motor, what would be better for speed/rpm increase: to install a jack plate, or to change the pitch of the prop down to a 15??

Any thoughts or input would be greatly appreciated.
Thanks
Scott

 

[SparkieBoat]

Re: Outboard mounting height 1985 Johnson 115 v4

jack plate..just do it.

 

[scottcab]

Re: Outboard mounting height 1985 Johnson 115 v4

jack plate..just do it.

I like the quote sparkie. Thats what I was thinking too. Do Yall think with the motor up 3 more inches on a jack plate, the 17 pitch prop will be right, or will I need a prop change too?

I know the rpm is about 1300-1400 low. Could this be fixed by lifitng the motor?
Thanks
Scott

 

[bob johnson]

Re: Outboard mounting height 1985 Johnson 115 v4

the absolute EASIEST solution for you right now, which iis also one of the cheapest( meaning keeping the motor you have now) is to buy a manual jack plate for about $200.... it will allow you to set the motor at the perfect height....and even allow for future adjustments.

if you would go that route.... then id do that FIRST...

then you can see what the final rpms are when you have a more ideal motor trim-boat relationship.
and if needed you can purchase the correct prop for your needs


it could be the waters drag on the lower unit...but you should be running about low 5000's with that pitch and such a small boat?

how heavy is the boat? is it possible it is ladened with excess water in the flotation?

in any case... moving down to a 15 pitch is a possibility......and id say do it...if you are NOT GOING to buy the jack plate

your rpms should be between 4500-5500, so you are not far off.... if you got the rpms up to 5500, and got rid of the drag on the lower unit..i bet youd be running 41 mph or more.

its your call...but for the health of your motor, id get the rpms up past 5,000!

if you do that...and dont do anything else...the worst thing is you are burning more gas than needed, and you are not going as fast as you could.

here at IBOATS...they say ONLY ONE LEFT!!

better hurry ha ha ha

http://www.iboats.com/T-H-Marine-Hi...55729940--session_id.407629075--view_id.40132

bob

 

[BonairII]

Re: Outboard mounting height 1985 Johnson 115 v4

if you do that...and dont do anything else...the worst thing is you are burning more gas than needed

With the cost of gas these days, the jack plate will probably pay for itself in one season.

 

[scottcab]

Re: Outboard mounting height 1985 Johnson 115 v4

Thanks guys,
I am going to get the Jack Plate, I can get the one that bob had mentioned or $145 locally. I appreciate all of the input. Do yall think that after the jack plate I will have the right prop?
Thanks
Scott

 

[BonairII]

Re: Outboard mounting height 1985 Johnson 115 v4

Probably won't be able to tell how the prop will perform until you run the motor at the correct height.

 

[bob johnson]

Re: Outboard mounting height 1985 Johnson 115 v4

Thanks guys,
I am going to get the Jack Plate, I can get the one that bob had mentioned or $145 locally. I appreciate all of the input. Do yall think that after the jack plate I will have the right prop?
Thanks
Scott

the prop you have now will put you in the RANGE of rpm specified by the manufacturer of the outboard!!

its hard to believe that you will gain 1300 rpm......running and lightly loaded boat at 5500 gives you plenty of room to add passengers and picnic coolers and fishing gear and not drop rpms at WOT below 4500!!!!

so you are either looking at the 17 pitch prop you have, or a 15 pitch....a SS prop should give you more rpms and speed....as long as it is designed close to any aluminum prop you might want to try in the same pitch


bob

 

[Haffiman]

Re: Outboard mounting height 1985 Johnson 115 v4

Just be aware that when installing a Jack-Plate, the more set-back it has the higher the engine must be. Moving the engine 5" off, might lead to increase the cavitation plate height above bottom from 0-1" to 1-2".

 

[SparkieBoat]

Re: Outboard mounting height 1985 Johnson 115 v4

mount the jack plate as high as possible, if there is a choice in holes, then run it up as high as it will go and mount motor as high as it will go, you may have to drop it an inch or so if you ventilate in the turns, but probably not.