From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

[feles99]

I need to change my 3 aluminum blade prop 13.5x17 to a 4 blade prop. This prop used to be 15x17 but I cut it myself for WOT tests. The reasons for changing to 4 blade: Engine setup is 3 1/2 inches higher than where it should be. Cavitation plate is 6 1/2 " higher than keel. However, engine platform has a setback of 36" which allows to set engine 3" higher.
Concluding, I need more grip. I only used the boat to idle in canals and to cruise, not top speed.

Johnson 130HP V-4 operates between 5 and 6K rpm. Currently WOT is 5600. Still 400 rpm to go up.

Currently at WOT 5600rpm 32mph. Cruise at 4000 rpm 22mph, 4500rpm 26mph. Large and heavy Boat: Renken 20', V-hull cuddy cabin, 2840 lbs.

Any suggestions in what size prop should I use?
Should I go higher in diameter to get even more grip and reduce pitch?

I was thinking 14x16 but think rpms go lower.
How about 14x15? I saw Amita 4 in 13x15. How about Michigan Vortex? Budget goes for a used SS.

 

[feles99]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

I also accept suggestion to go with a 3 blade SS. I do not see any 4 blade matching what I need, exept for a 15x15.
In 3 blade there are plenty.

Looking at 3 blade I will need a prop with a lot of grip. Any suggestions?
Going up in diameter will increase acceleration, idle speed and grip?
Is there any problem using a lower diameter than what manufactureer suggest?
This engine is design to use 15x17, 15 1/4x15 and 14 1/2 x19. I cut the 15x17 to 13 1/2 x17 and rpm went up from 4600 to 5600 rpm at WOT.

 

[Billfo]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

I cut the 15x17 to 13 1/2 x17 and rpm went up from 4600 to 5600 rpm at WOT.

What happened to your top speed when you increased 1000 rpms ?

 

[feles99]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

What happened to your top speed when you increased 1000 rpms ?

Cannot answer. By that time there was no GPS. I jut remmember the engine rev to 4600

 

[Billfo]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

Did you feel a very noticable increase in speed ?

 

[feles99]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

Did you feel a very noticable increase in speed ?

Do not remmember, but if use the calculator with a 20% as it is currently, top speed at 4600 rpm will be 26 mph. If you reduce slip to 15, top speed could be 29mph. Still, this is not really related to my current situation.

 

[junior1113]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

u opened another post on this rig? really think 15x15 4 blade will suit you well. i run a turbo 4 and love it throw the 3 blade away

 

[dingbat]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

Going up in diameter is going to put a hurtin on your hole shot.

You have something else going on. In comparison, I'm running a 14 x 17 Evinrude offshore 4 blade on a 200HP Ocean Pro. Turning it at 5500 RPM getting 40 miles per hour on a boat a lot bigger than heavier boat than yours

 

[feles99]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

Going up in diameter is going to put a hurtin on your hole shot.

You have something else going on. In comparison, I'm running a 14 x 17 Evinrude offshore 4 blade on a 200HP Ocean Pro. Turning it at 5500 RPM getting 40 miles per hour on a boat a lot bigger than heavier boat than yours

Thanks for diameter flag. You are correct.
Boat weigths 2840. WOT test at 5600 rpm had 2 batteries, 3 people, 12 gal water and 16 gal of gas.
Yesterday, I talked to PowerTech factory. They recomended 14x14 for $618, which is not in the budget.
I got a cheap used Vortex alum 15x16. I am taking it to a technician, make it to 14x15 and test it. If rpm got lower than 5600 I will need to reduce diameter from 14 to 13 1/2 or reduce pitch from 15 to 14. WHAT IS BETTER?

Currently 13 1/2 3 balde. Do you think increasing the diameter from 13 1/2 to 14 will help a lot or not. For instance: 1) Does larger diameter help on grip considering high engine? 2) Does larger diameter help on cruising at lower speeds? By increasing diameter I need to reduce picth a lot, which I do not like.

 

[feles99]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

u opened another post on this rig? really think 15x15 4 blade will suit you well. i run a turbo 4 and love it throw the 3 blade away

I had to. Nobody is giving opinions in the 3 to 4 blade change.

 

[dingbat]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

I had to. Nobody is giving opinions in the 3 to 4 blade change.

The reason why your not getting to many responses is becouse your working outside normal installation parameters.

The change from a 3 blade to a 4 blade, at least in my boat, is very noticeable. I do a lot of running offshore and it cut down on the blow out when running in slop. My boat is setup properly so I?m not sure you can relate my boat?s performance to a boat that is not setup properly.

As far as the diameter is concerned, your light on HP for a boat of that weight. Increasing the diameter is only going to exasperate the problem.

 

[feles99]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

Digbat. Thanks. Would please let me know what size prop you use with 3 and then with 4 blade. Examples like that are the ones I am looking for.
I concluded that my test will be 14x15. If not more than 5600 rpm. I will reduce to 13 1/2. Technician told me they will add some rake and cup. I will inform results in about 2 weeks.

 

[junior1113]

Re: From 3 to 4 blade Johnson 130, heavy cruiser. Sizing..

was running a omc ss 3x14.5x19p @5650 44mph to a turbo ultima4 ss 4x14.25x17p @5900 47mph. had to raise motor 2.5" to get the 4 in its sweet spot. just an example for you.