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Johnson 1988 15hp help with pitch and speed

A

astra-taranis

New member
Dears,

My name is Henrique, I'm from Brazil (south america), please, sorry about my poor English.


I have a johnson 15hp 1988 (I think that have only 50 hours os less) original Long Shaft, but I make Short Shaft.


My Boat is calaca flash bass (http://www.calaca.com.br/flashbass/) with 5 meters or 16.40 feet. And weight about 90kilograms.


In original (long shaft) with 9 1/2 x 10 propeller my speed is: 20 km/h (12.4 mph) with 2 people (pilot and friend) .


In short shaft with same propeller my speed is: 22km/h (13.67mph) with same 2 people .


So I put a new propeller 9x11 pitch and my speed now are:


Alone : 38.2kmh (23.61 mph)


With 2 people: 22 kmh (13.67mph)


With 2 people , but the other person in first chair: 26kmh (16.15 mph).


So the questions are:


1- Put I make a mistake with pitch?


2- What the pitch I have to put now (9 or 10 pitch)?


3- If I buy a 9 pitch I will broke my outboard ?


4- What speed I can dream with a 9 and 10 pitch with me and other person?

5- Putting pitch 9, I'll imagine that I will get speed loaded? Today I'm 13.75mph can imagine something near 18-19mph ?? Or will not be as great progress as well?6- They said these johnsons 15hp 88 has in reality no more than 13hp, so go unless other engines like yamaha 15, you confirm that?


or I need to put this motor is garbage and buy a tohatsu 18 ?


Best regards! From Brazil!
 
Dears,

My boat have only 90kg .. Thats correct, the boat are made for 15 to 25hp.

Here in Brazil it is common boats that measure weighing just that.
I'm currently using propeller 9x11

thanks for help !
 
What is the maximum rpms for that engine4500-5500? That would be the rpms your engine needs to reach if propped correctly, you will need a tachometer to measure engines rpms, auto parts store will have one.
 
Yes, get a tach you want to prop for about 6500 rpm for that motor. You went the wrong way on the prop. A 9" would probably suit your needs better. Also you are at about 50% of the rated HP so propping will be critical. That motor is a full 15 hp.
 
johnnygjr said:
What is the maximum rpms for that engine4500-5500? That would be the rpms your engine needs to reach if propped correctly, you will need a tachometer to measure engines rpms, auto parts store will have one.
Click to expand...

Johnny, I dont know the maximum rpms for that motor, I dont have the manual, can you known?

In my searchs I found 5500 , but sometimes I found 6500 too... So I dont known.
 
flyingscott said:
Yes, get a tach you want to prop for about 6500 rpm for that motor. You went the wrong way on the prop. A 9" would probably suit your needs better. Also you are at about 50% of the rated HP so propping will be critical. That motor is a full 15 hp.
Click to expand...

Scott, Yes, the tach will talks the correctly rpm, but here in Brazil this isnt available, here the tachs that I founded is made in China and dont have accuracy .

My doubt is about the speed that will have if I buy a 9pitch, cause now, with 2 people my speed is very slow, is I put a 9 pitch how speed i'll can go? 1, 2 ow 5-6 mph better?

thanks for all...
 
I have seen 7000 rpm max, maybe from leeroys site. I am getting 7435 rpm with a 4 blade 10p prop on a 1232 jon boat. I have researched and worked on it for 2 years on my 15omc to get there. I don't run wot for more than 10 seconds. I have run an 8p when the motor was stock and works better loaded.

Point is just get the max size motor for the hull. I try to go with the most displacement per unit weight, not max hp. The '93 and up are more displacement by about 2cubic inch. Nothing beats cubic inches.
 
Sunkinmess said:
I have seen 7000 rpm max, maybe from leeroys site. I am getting 7435 rpm with a 4 blade 10p prop on a 1232 jon boat. I have researched and worked on it for 2 years on my 15omc to get there. I don't run wot for more than 10 seconds. I have run an 8p when the motor was stock and works better loaded.

Point is just get the max size motor for the hull. I try to go with the most displacement per unit weight, not max hp. The '93 and up are more displacement by about 2cubic inch. Nothing beats cubic inches.
Click to expand...

Dears Sunkinmess,

I put a 7435rpm on a johnson 15? What mod you made? have a site to learn?

I read all in leeroys site, but leeroys same 4500-5500 and 6500 too.

Why you dont run more than 10 secs? Here in Brazil we run full time in 100% throttle.

I wanna a original motor, just put another pitch proppeler (here is brazil man, we dont have facilities to other modifications)
 
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