Johnson 115 SPL

[bob johnson]

Re: Johnson 115 SPL

sorry i was way off with the prop. its a 13x19. when i replaced the plugs they looked well worn but overall clean. i looked in the clyinder through the plug holes as best i could and the cylinder walls look smooth. nothing out of the ordinary. i debated on pulling the head but decided against it. with how its running now i am just going to stick with it until something happens or i can afford to repower. i have often wondered about the engine height. the cav plate is even with the back of the hull. but when its up on a plane that plate is still plowing through the water. how does this look?

these pics were taken at wot running with 2 guys and about 5 gal of fuel. so pretty light actually. the boat normally holds 60gal. how is moving the motor up going to affect the boats sensitivity to trim changes? its not bad now. i put the wedges on to get better negative trim which helps with planing. the wedges also allow me to really push the nose down in a chop and plow through. i dont want to loose any of that ability with moving the motor up.

just from the first picture...I would think you could go up one set of holes for sure!!!!

bob

 

[ezeke]

Re: Johnson 115 SPL

sorry i was way off with the prop. its a 13x19. when i replaced the plugs they looked well worn but overall clean. i looked in the clyinder through the plug holes as best i could and the cylinder walls look smooth. nothing out of the ordinary. i debated on pulling the head but decided against it. with how its running now i am just going to stick with it until something happens or i can afford to repower. i have often wondered about the engine height. the cav plate is even with the back of the hull. but when its up on a plane that plate is still plowing through the water. how does this look?

these pics were taken at wot running with 2 guys and about 5 gal of fuel. so pretty light actually. the boat normally holds 60gal. how is moving the motor up going to affect the boats sensitivity to trim changes? its not bad now. i put the wedges on to get better negative trim which helps with planing. the wedges also allow me to really push the nose down in a chop and plow through. i dont want to loose any of that ability with moving the motor up.

The A/V plate should be at least even with, or preferably, slightly higher than the bottom of the boat so that the plate is just above and parallel with the surface of the water when the boat is on plane.

 

[tohg2]

Re: Johnson 115 SPL

i guess it wont hurt to move up a hole and try it. so its really how the plate looks when on a plane that makes a difference. being perfectly even with the bottom is not always correct? i say "supposedly rebuilt" because the p/o was kinda flaky. he claims it was rebuilt in '06 but aside from pulling the heads i dont know how to tell. paint is missing from some of the head bolts and it looks as if the motor has been taken apart but that is to be expected with a 12y/o motor. when i got the boat it was very neglected. but i got such a deal i couldnt turn it down.

edit: the a/v plate is the lower one correct? and its anti ventilation plate? not cavitation plate?

 

[tmt]

Re: Johnson 115 SPL

If you bring the motor up to high the prop will loose its bite in the water do to cavitation when you take off or as your trimming up at higher speed. You will know this by the motors rpm going up fast with out filling the power. The higher you can set your motor with out having this happen will give best mph.

 

[tohg2]

Re: Johnson 115 SPL

i understand that much. how is moving the motor up going to affect the bite off the line. is it going to make the boat more sensitive to trim changes? top speed is not a huge concern. its more about hole-shot and efficiency. with an underpowered motor and relatively heavy boat it seems to be all about fine tuning.

 

[tmt]

Re: Johnson 115 SPL

Put on a set Hydrofoils. They help a lot with hole shot.

 

[tmt]

Re: Johnson 115 SPL

Put on a set of Hydrofoils. They help a lot with hole shot.

 

[ezeke]

Re: Johnson 115 SPL

i understand that much. how is moving the motor up going to affect the bite off the line. is it going to make the boat more sensitive to trim changes? top speed is not a huge concern. its more about hole-shot and efficiency. with an underpowered motor and relatively heavy boat it seems to be all about fine tuning.

A big part of the equation is drag, and the more of the motor that is exposed to the water the more drag you will have.

If you put a hydrofoil on a A/V plate that is underwater, you will just create more drag, so that cannot possibly help unless you first raise the motor.

It is difficult to judge from your photograph, but click the thumbnail to see where it appears that you are now.

 

[emdsapmgr]

Re: Johnson 115 SPL

Ezeke has pointed out that your engine may be mounted slightly low, causing excess drag and poor fuel economy. The water running under your boat is breaking on top of the antiventilation plate. That indicates the engine is mounted slightly low. Move it up one hole on the transom. You will pick up holeshot and top speed. Try that before you invest in the hydrofoil-most don't work as advertised.

 

[tohg2]

Re: Johnson 115 SPL

thanks for the tips. i had always thought the motor seemed a bit low once on a plane but i just never knew who to ask, or believe for that matter. the guys at my local shop are less than trustworthy. before i put the wedges on i was considering a "permatrim" on the l/u. i have heard good things about the way they work. the 5degree wedges cut my planing time in half. i was very satisfied with the result and for $35 i really couldn't beat it. if the weather cooperates this weekend and i will move the motor up and post back with the results. thanks again for the help.

 

[bob johnson]

Re: Johnson 115 SPL

I have a jack plate on my boat and i have played with the heights and checked speed..here is a picture of the cav plate right at the waters surface it seems, with the jack FULL UP!!!

when the jack is full up I can not do more than 20-22 mph before the prop washes out...and I lose bite

at half height or below i can go full speed...

but at half height i have to watch how fast i make turns or the prop washes out and grabs air.....

all the way down i get about the same speed but i can make any turns i want...

I am wondering about your quest to get the cav plate out of the water...

dont think it is feasable and get all the performance you can from the boat-motor still.

my hole shot is unbelievable, probably because the boat drafts so little and the flotation pods keeps the stern way up...

bob

 

[tohg2]

Re: Johnson 115 SPL

what kind of height range are we talking? the full distance of that slot on your jack plate? 4 or 5 inches? i'm not really looking to pull the cav plate out of the water, maybe just not have it plow so much. the boat has a 7'9" beam and about a 15degree deadrise, so there is alot of hull in the water at the stern. like i said before the motor is definitely underpowered for what the hull needs.

 

[bob johnson]

Re: Johnson 115 SPL

what kind of height range are we talking? the full distance of that slot on your jack plate? 4 or 5 inches? i'm not really looking to pull the cav plate out of the water, maybe just not have it plow so much. the boat has a 7'9" beam and about a 15degree deadrise, so there is alot of hull in the water at the stern. like i said before the motor is definitely underpowered for what the hull needs.

the jack pate has 6" of height range...

when all the way down the cav plate is about even maybe slightly below the bottom of the hull!!!

my hull has a 12 degree dead rise and the beam is 98" the chine width is 72"( which is more relavant)

the jack plate really offers a huge amount of flexibility...

with three sets of holes on the motor...two sets of holes on the jack where it bolts to the transom, and two sets of hole on the jack where the motor mounts....there has to be more than a dozen combinations of mounting heights...then you have the height adjustment of the jack unit!!!

really a worth while piece of equipment, in my book!!

bob

 

[tohg2]

Re: Johnson 115 SPL

from what i understand the setback of a jackplate will help also. is yours manual or hydraulic? do you really adjust it that often or did you just use it to dial everything in? i guess a hydraulic would make sense if you were planing on moving it with the changing sea conditions. but is it really necessary?

 

[bob johnson]

Re: Johnson 115 SPL

I bought mine so I could motor the very shallow areas i get into...the tide drops where I use my boat a lot and being able to raise the motor just so I can turn the prop...gets me moving.....and out of the area before it gets too shallow and I get stuck..

since I am back in these areas most of the time..the hydraulic jack was the way to go...once out in deeper water, I can drive the motor back down... and motor along on plane

I can raise the motor to the point the prop is barely in the water...as long as my water pickup is supplying me with water...I am good...

I wish I could mount my motor higher than it is....so i could motor in water that JUST floats my boat...maybe even drag my skeg in the sand and mud....


I actually looked at my motor today and there are FOUR sets of holes for mounting the motor , on the motor itself!!

I did find a trim issue I will open a new thread about, that id like to clear up..

bob