johnson 6hp prop, with pics

[slate1234]

Hi all just got a rev counter for my 6hp johnson and it wont go over 4500/4600 is this correct, I use it on a 3meter sib with
22lt fuel tank and some fishing tackel and it seems slow I was woundering if a prop change might help View attachment 172940 this is the one at present

 

[Texasmark]

Re: johnson 6hp prop, with pics

I can't make head or tails out of your picture. Usually a low WOT rpm reading is the result of too much pitch in the prop for the load it has to push. That is if everything else is functioning properly.

Mark

 

[slate1234]

Re: johnson 6hp prop, with pics

View attachment 172942View attachment 172943 sorry about the last pic ,here are two more but there are no markings on it anywhere

 

[Texasmark]

Re: johnson 6hp prop, with pics

Sorry. My comment had to do with what may have been the hull of the boat. The prop was clear enough and it looks like a standard alum prop. Can't tell pitch from the end and can't tell from a picture anyway.

If that is the hull and it is a displacement hull then surely you don't want much pitch on an engine of that power level. If that is a standard prop that came with the engine the pitch is probably around 8" so at 200 rpm per inch you might do better with the shallowest pitch they have, like a 5-6".

Mark

 

[slate1234]

Re: johnson 6hp prop, with pics

Thanks for that Mark

 

[steelespike]

Re: johnson 6hp prop, with pics

I notice a whale tail on the motor.While it may help planing if its in the water at speed its probably knocking the speed down.
SIB? Is that an inflatable? Some inflatables are slower than others also tend to be slower than a ridged hull.
Do you have the speed by a gps at 4600?
Have you looked carefully at the underside and top of the hub? A clean up might produce a number.
My info indicate the hp is developed at 4500 rpm.So your right on the nose.
On a light reasonably fast boat it should produce speeds around 12 to 14 mph.

 

[slate1234]

Re: johnson 6hp prop, with pics

yes steelesspike here is a pic View attachment 173035 it also has a infltable keel the seat has gone as I moved the 22lt fuel tank to the front I just have the standerd bench seat now , I will try it with the whale fin off, it was already on when I got the engine, also clean up the prop and try it with a gps, I will report back when I have my findings

 

[steelespike]

Re: johnson 6hp prop, with pics

With those giant trim tabs you shouldn't need a Whale tail. Also if the tabs are set too aggressive they will reduce speed.
The boat itself could be hurting your speed, the seat may have helped the boat to maintain its shape.
Be sure inflation is at the max.
Many times the motor is too low on an inflatable;raising the motor to a point just before venting becomes a problem can help speed.
You should make one change at a time and test.

 

[slate1234]

Re: johnson 6hp prop, with pics

Thanks steelespike, I took the tabs off when I got the 6hp with the whale fins now I am going to remove the whale fin and try that, someone said to raise the engine 1/4" at a time so next time I go out I will take a few shims and try that

 

[Texasmark]

Re: johnson 6hp prop, with pics

I don't know what you are expecting out of this rig but 6 hp is just not all that much hp. It will plane out a light john boat with a couple of folks in it....barely, remembering the early years when I saw a 6 hp Martin planing out a 14' river john with a couple of folks....but alum. johns are probably the easiest boat to plane. I have had: 5 1/2 John, 7 1/2 Merc, 9.9 McCullough, and on up. The 5 wouldn't plane a wood boat with just me in it, the 7 planed my 12' Lowe Lake John pretty good, the 9.9 and up had no problems pushing the associated boats.

I know nothing about an inflatable other than they may not have all that much of a planing surface and the air pressure surely has an impact on the drag coefficient of the hull.

HTH,
Mark

 

[steelespike]

Re: johnson 6hp prop, with pics

The motor is capable of 12-14 mph.Unfortunately that inflatable isn't the boat to do that with.
The idea is to try to get the most possible.
As far as the typical 12 or 14ft boat a 6 would likely need a tiller extension to plane.
Our 5 hp.12 ft flat bottom steel boat planed easily with a tiller extension and a 180 lb driver.
Slate,its possible you may be better off with the tabs if it struggles without the whale tail.
But apply them gently just enough to get on plane.

 

[cbjfan75]

Re: johnson 6hp prop, with pics

Ok, new in the thread. Help me out, what are you calling a tiller extension? I have a 14' aluminum v-hull and I'm looking for something better than my non pushing 3HP but under the 9.9 for the under 10 lakes. Would love something that could possibly get it to plane. Thanks!

 

[steelespike]

Re: johnson 6hp prop, with pics

A tiller extension is just that its a handle you can make or buy to go on your motor tiller so you can sit in the middle
seat.Its much easier to plane.
There is a video on you tube of a 2 hp planing on a light jon with a light driver.
Its possible your 3 might plane with a tiller extension.I think a 3 is rated for about 8 mph.
Our 5hp on the steel boat planed instantly, within 50 ft.
Your 14 ft has the advantage of a relatively large foot print that should help it get up on the water.
If your not too heavy it may plane with a 5 by placing the tank and other weight forward
with no need for a tiller extension. Check youtube for videos of smaller motors under way.
Evinrude and Johnson made wonderful 3,5.5,6,7.5 and 10 hp motors from the 50s into the 70s. Routine parts are still readily available some right here at iboats.

 

[cbjfan75]

Re: johnson 6hp prop, with pics

Thanks! Not sure an extension would work with this Lightwin being a sliding throttle(wouldn't reach to shut it down). Best I've GPS'd it at is 4.1MPH. You've at least got me concidering something in the 5.5, 6, 7.5, or 8 range now. Would like to at least be pushing along around 12MPH.
This 3 has the same high end as the idle speed of my 18.... lol

 

[steelespike]

Re: johnson 6hp prop, with pics

You could rig a throttle with a throttle cable like you might find on a lawn mower.
You could probably find a choke or throttle cable at NAPA or a auto parts store.
If you disconnect the lever and add a return spring to the carb you could probably rig a pull string out of some heavy fishing line.

 

[Texasmark]

Re: johnson 6hp prop, with pics

My grand dad had a 16' planked skiff that he pushed with a late '40's 10 hp Johnson. It had the slide left to right throttle. He had a stick rigged up vertically that had some sort of connection to the engine for steering....was not an extension of the tiller handle. He fished the flats several miles from the boat basin. Once in open water he would put her wide open and sit in the middle seat and steer being able to get the heavy boat to plane out in 1 - 2' waves. Once near the harbor he would return to the rear seat and work his way through the harbor. I was just a tyke so I don't remember particulars on the rigging.

Mark

 

[steelespike]

Re: johnson 6hp prop, with pics

As a kid I had a number of little under powered boats.
had a 1.5 Evinrude on a 10ft flat bottom wood boat it would go a smidge faster with me in the middle seat.
I was only 6 or 7.
had a 2 hp 14' round bottom steel boat the steering was stiff enough I could sit in the middle seat and lean left or right to steer.
It weighed a ton but was long and slim slipped through the water really easy.
When I was 6 you didn't run into a lot of boats and many of them were probably running less than 20 or 25 mph.
A lot more space to maneuver.