does the 1/4 going to make a difference

[salmonite]

I have a 14 * 21 prop right now. My dealer wants to put a 14 1/4 * 21 on there. Is this a big difference? Also i have a 1998 johnson 115 hp fast strike, do i need a 15 or 13 tooth spine?

 

[bob johnson]

Re: does the 1/4 going to make a difference

I have a 14 * 21 prop right now. My dealer wants to put a 14 1/4 * 21 on there. Is this a big difference? Also i have a 1998 johnson 115 hp fast strike, do i need a 15 or 13 tooth spine?

i would guess you have the 13 spline small gearcase lower unit...I have the ocean runner 115 ...all the ocean runners ocean pros faststrike and Intruder 115s had the same gear case.

that is a lot of pitch...do you have a real light boat????

I have an aluminum 21 footer seemingly light at about 1100 lbs...

and I am propped at 15-17 pitch

I have never seen a prop for the small gear case 60 degree looper V4s larger than 14"...but i measured mine gear case and I think a 15.5" would actually still clear!!!

I found a thread that mentioned they may have made some 115s with the large gear case...so you might want to measure the hub dia

about 4" even or slightly smaller is the small gear case housing.

well over 4". maybe 4-5/8th or so... and it is a larger gear case

small takes the 13 spl;ine..large takes the 15 spline

they 15 spline has many props over 14" in dia!!!!



good luck

bob

 

[salmonite]

Re: does the 1/4 going to make a difference

bob,
my boat is a tank. weighs a lot!

also thanks for info

 

[Silvertip]

Re: does the 1/4 going to make a difference

The issue is "WHY" does the dealer want to change props -- especially with the same pitch. The 1/4 inch diameter difference is part of prop "design". In other words, a 14 x 21 prop from Manufacturer "A" may not and usually does not perform the same as a 14 x 21 from manufacturer "B". Prop design includes more than just diameter and pitch. It includes, blade shape, cupping, rake, finish, material (aluminum/steel/composite) and hub design. So what's the issue with your boat? The 1/4 inch probably won't mean a thing in this particular case.

 

[salmonite]

Re: does the 1/4 going to make a difference

well the there is no issue. I just said i need a new prop and they said what size? I said 14 * 21 and they said i have a 14 1/4 * 21. and i said oh ok

never had to buy a prop... I just figured to buy the exact same as what i had on there before

 

[salmonite]

Re: does the 1/4 going to make a difference

i would guess you have the 13 spline small gearcase lower unit...I have the ocean runner 115 ...all the ocean runners ocean pros faststrike and Intruder 115s had the same gear case.

that is a lot of pitch...do you have a real light boat????

I have an aluminum 21 footer seemingly light at about 1100 lbs...

and I am propped at 15-17 pitch

I have never seen a prop for the small gear case 60 degree looper V4s larger than 14"...but i measured mine gear case and I think a 15.5" would actually still clear!!!

I found a thread that mentioned they may have made some 115s with the large gear case...so you might want to measure the hub dia

about 4" even or slightly smaller is the small gear case housing.

well over 4". maybe 4-5/8th or so... and it is a larger gear case

small takes the 13 spl;ine..large takes the 15 spline

they 15 spline has many props over 14" in dia!!!!



good luck

bob

its 4 inch in diameter and the boat probably weights 3000 pounds with engine. 2500 dry weight on my safety coast guard panel.



reccomendations????????????????

 

[usskydvr]

Re: does the 1/4 going to make a difference

I agree forget about the 14 vs 14 1/4 issue. I agree that a 21 seems a bit much. What is your current wide open throttle (WOT) RPM with your normal load? that will give you a starting point.

 

[salmonite]

Re: does the 1/4 going to make a difference

i just did the prop wizard online and it reccommended 13-1/4 x 17 for speed and performance 13 3/4 x 15 for heavy loads and towing.

sound right?

 

[usskydvr]

Re: does the 1/4 going to make a difference

More what I would expect, but before spending $$ find out your current WOT RPM. That will really let you be able to know which prop to get.

 

[salmonite]

Re: does the 1/4 going to make a difference

More what I would expect, but before spending $$ find out your current WOT RPM. That will really let you be able to know which prop to get.

wide open she runs about 5500 to 5700 rpms with current load and prop. not sure what i am supposed to run at though

 

[bob johnson]

Re: does the 1/4 going to make a difference

wide open she runs about 5500 to 5700 rpms with current load and prop. not sure what i am supposed to run at though

wow...that is perfect...it amazes me that you can get that with the load and pitch you have....i wouldnt change a thing......5700 is perfect....I think the fast strike may have a rpm range of 5500-6000 rpms..

but yours is a fitch..so i dont know for sure...i thought it was a carbed motor at first..

all other aspects of the prop being equal ...1/4 " in diameter difference..means nothing....

the prop recomender you mentioned recomends the props I have for my boat.. and whcih give m,e 5400-5800...rpms

my motor is an eagle 60 degree looper 115 carbed motor....


based on the 4" dia...sounds like you have the small gear case... and will need a 13 spline

what did the dealer pick out????

bob

 

[steelespike]

Re: does the 1/4 going to make a difference

Based on your boat I would want to varify your tach is accurate.
I'm betting the speed doesen't match the rpm based on a 2:1 ratio.

 

[salmonite]

Re: does the 1/4 going to make a difference

i only top out at 30 mph on the gps

 

[bob johnson]

Re: does the 1/4 going to make a difference

i only top out at 30 mph on the gps

thats a red flag....turning 5500 witha 21 pitch prop....dont see how you are only going 30 mph...

I wonder if you tach is set right....

a boat turning 5500 with a 21 pitch prop should be doing like 45 plus mph..is my guess...maybe even faster...

I run 38 with a 17 pitch aluminum prop at 5400 on my 115 hp

I actually got 39 mph with a 15 pitch SS prop at 6200 rpms!!

today i actually ran 5800 rpms with that 17 pitch prop..maybe because i really trimmed out and my GF was up front....

I was amazed at the rpms...the gps battery dies so i dont know my speed....but I could almost keep with a boat with 2, 200 yamahas

course i was in his flat wash!! ha ha


bob

 

[salmonite]

Re: does the 1/4 going to make a difference

i always thought it was due to my boat was so dam heavy that the 115 couldn't push her.