maybe a switch to 4 blade....

krisnowicki

Lieutenant Junior Grade
Joined
Jul 11, 2007
Messages
1,172
I have a 19p Stianless I get 4600 rpms and a 21p around 4300. Both are 3 blades, and with 2 grown men on the boat and light gear. I want to switch to a 4 blade to get more hole shot and a quicker plaining speed. My boat is rated for WOT between 4200-4600 what would be the best sized 4 blade to go with and what will i lose in the switch. I will keep the other two so I have spares...
 

180shabah

Rear Admiral
Joined
Mar 26, 2005
Messages
4,995
Re: maybe a switch to 4 blade....

everything else being equal, drop down an inch to 18.
 

krisnowicki

Lieutenant Junior Grade
Joined
Jul 11, 2007
Messages
1,172
Re: maybe a switch to 4 blade....

will i lose top end? and if so how much? fropm what I understand I will lose some top end but get better cruising because of less slip. I currently get about 25-28 at 3000-3200 which figures ot be close to 30% slip
 

Tail_Gunner

Admiral
Joined
Jan 13, 2006
Messages
6,237
Re: maybe a switch to 4 blade....

It looks like you have been doing quite a bit of work on the boat. Have you made a run since all of the work you have done?
 

krisnowicki

Lieutenant Junior Grade
Joined
Jul 11, 2007
Messages
1,172
Re: maybe a switch to 4 blade....

Oh yeah... I bought the boat last year from a dealer.... And well they were definitly were not honest.
The gimbal ring had some repair done to it and it was not done right basically it was jb welded together so at the end of last season when I pulled it out the port side was cracked. The repair was done and painted over so it was very hard to see....This is where it began.

Bascially this is what was needed:
New U joints
Gimbals ring
gimbal bearing
pivot shaft
exhaust, shift and cable bellows
water pump
Belts
Carb rebuild
and while was tearing in to the back half of the boat i cut the hose that transfers the lube from the outdrive to the resivior so i replaced that whole system.
I know what your saying why did he buy it. Well they had it inspected by the local Merc guy ( who turns out works for him and gave me a copy of the inpsection when I bought it.
But, I took it out all week and have put a total of about 16 hours on it since I got ( i put an hours clock on it too)

And now am trying to get the props right to make sure I am taking proper care of the engine.
The results from this weekend we great I had (1300lbs) 6 guys in the boat and one behind it all weekend and it planed fine with the 19p and would reach about 4200 wot with the load. But, with just me and another we got 4600. The tach is right on with my shop tach when I am at the house so i believe it.

So now, I want to get a 4 blade so i can plane quicker with two or three people towing behind us...
 

lrdchaos

Petty Officer 1st Class
Joined
Feb 11, 2008
Messages
265
Re: maybe a switch to 4 blade....

like stated above, if all things are equal drop to an 18p....but If you can find a prop dealer that will let you swap props out, I would go with a 17 pitch. Just to be on the safe side.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: maybe a switch to 4 blade....

Keep in mind that there are 4 blade props made specifically for running deeper and running higher toward the surface. A I/O typically benifits from one made to run deeper.
 

180shabah

Rear Admiral
Joined
Mar 26, 2005
Messages
4,995
Re: maybe a switch to 4 blade....

You could search for a prop exchange dealer. They let you "test drive" different props until you find just the right one.
 

krisnowicki

Lieutenant Junior Grade
Joined
Jul 11, 2007
Messages
1,172
Re: maybe a switch to 4 blade....

Keep in mind that there are 4 blade props made specifically for running deeper and running higher toward the surface. A I/O typically benifits from one made to run deeper.

are certian diameters made for each? how can I tell?
 

180shabah

Rear Admiral
Joined
Mar 26, 2005
Messages
4,995
Re: maybe a switch to 4 blade....

Diameter is a function of design, not the other way around.

As for what application is a prop designed for, the manufacturer will usually say in the product description.......for runabout I/O, for high performance I/O, for high performance OB.
 

krisnowicki

Lieutenant Junior Grade
Joined
Jul 11, 2007
Messages
1,172
Re: maybe a switch to 4 blade....

so I have a 220 hp v8 am I in the middle or am i high porformance or normal io?
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: maybe a switch to 4 blade....

It's not necessairly related to engine power but rather where the prop is located in relation to the hull. Most recreational I/Os have the AV plate (plate right above the prop) about even with the bottom of the running surface. That means the prop will be running relatively deep. You'll be looking for something like the Stiletto Bay Pro II or the Turbo 2+2 TH four blades.

To take advantage of the Bay Pro III or the Ultima 4 the prop should be running a bit higher up toward the surface to take advantage of the technology in the prop.
 
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