3 blade to 4 blade pitch conversion

[braindeadjones]

I am looking for information regarding converting from a 3 blade to a 4 blade SS prop. My goal is to maintain On Plane in between 15-20mph for wake boarding, skiing, and tubing. We currently fall off plane at around 21mph, (2100rpm).

Here?s what I am currently running:
1989 Glastron Futura 225, 7.4L Bravo One, with a Quicksilver 48-13702A40 SS 14 ? inch 3 blade 21p, WOT at 4200 ? 4600. When unladed and prop was new (mild damage) we could hit 4500 trimmed out and an speedo indicated 60+mph. Now with all the gear, toys, and damage it?s about 4000rpm.

So here are my questions:
Will a 4 blade prop help me maintain Plane at a lower speed?
Should I go to a 19p prop since I am adding a blade or even lower?

I am aware of other options, Dou-Fin, Fat Sack, Bennett Trim Tabs, buy a ski boat, etc. I just wanted to get my 3 blade reconditioned and thought this might be a good time to get a new 4 blade prop for play time and use the 3 blade as a spare. Top speed is no longer a priority...

Thanks for any help or suggestions,
Brian J.

 

[Silvertip]

Re: 3 blade to 4 blade pitch conversion

For less than the cost of a stainless four blade you can add Nauticus Smart tabs that will do far more for staying on plane that the prop change. And you would probably have money left to have the three blade repaired.

 

[braindeadjones]

Re: 3 blade to 4 blade pitch conversion

Thanks for the info on Nauticus. I am thinking of getting tabs next year and have investigated Bennett and Lenco but have not looked into Nauticus yet.

So you don't think a four blade prop will provide just enough torque to keep me on plane at 20 mph?

 

[steelespike]

Re: 3 blade to 4 blade pitch conversion

Thanks for the info on Nauticus. I am thinking of getting tabs next year and have investigated Bennett and Lenco but have not looked into Nauticus yet.

So you don't think a four blade prop will provide just enough torque to keep me on plane at 20 mph?

The 4 blade may help low end performance not sure about staying on plane.
Smart tabs are much less cost, boat will plane quicker,stay on plane at lower speed,ride and handle better and tabs will help control no wake speed wander.

 

[trswenson]

Re: 3 blade to 4 blade pitch conversion

If the shape of the wake is important to you TABS may not be the right answer. I run a 23' Reinell open bow & use the bost in a similiar manner to you. I have to keep my TABS lifted all the way up or my wake takes on undesriable characteristics. Have to keep the outdrive trimmed all the way down too.
I'm in the market for a 4 blade SS also and it sounds like 1 or 2 inches in pitch reduction gives similiar performance to the three blade. Supposedly better hole shot and lower plaining speeds due to stern lift also.
Good luck !!

 

[braindeadjones]

Re: 3 blade to 4 blade pitch conversion

Thanks guys for your responses.

I am concerned about the wake effect of tabs, which is why I originally investigated fully retractable tabs.

iBoats has a 4 blade SS Solas prop that is now in their exchange program. I will investigate the Tab scenarios and let y'all know.

Hope you have a great Memorial Day.

 

[braindeadjones]

Re: 3 blade to 4 blade pitch conversion

Well I went for the Solas Prop Exchange program and ordered a 4 blade SS 14.125 x 19 pitch prop. I won't be exchanging it.

We still hit 4400rpm WOT trimmed up, right in the meat of WOT recommendation. With a full tanks of gas and a standard load (jackets, tools, spares, some toys, wife, and myself) we topped out at 55mph pitot speedo indicated, compared with 65mph using a 3 blade 14.75 x 21 pitch, but there was a lighter load in the boat.

We were not able to fully test with skier, wakeboarder, or tube as it was very windy and considerable chop.

But I did notice a quicker to plane time, (remember my 3 blade was damaged) and an easier to plane when throttle was applied slowly. I also believe that we were able to stay on plane at ~20mph much easier. With the wind and waves pushing us back we stayed on plane, and it seemed there was more stern lift as well. My wife noticed that she could see over the bow easier just off plane.

So the only question remains is how will it react to a toy tugging behind the boat.

I wished for better results than this, but I am not dissatisfied by any means. Since the exchange program only gives you a week to return the prop, I am stuck with my choice.

I will try to post more results as I get more spin time to help anyone else out. We are heading to Lake of the Ozarks at the end of June, I should have a entire hold of information when I return.

 

[rndn]

Re: 3 blade to 4 blade pitch conversion

I had very positve results putting a 4 blade SS prop on my Baja Force 216. With a 21" 3 blade prop I could not plane if someone was sitting in the back seat. It was terrible to have to ask people to climb to the mid to front area of the boat for me to get the thing to plane. It also dropped off plane way to easily. A 4 blade Stiletto prop solved all of my problems. The boat would actually jump out of the water to plane and also plane at a much lower speed. I'm sure tabs would have also helped, but I really didn't want something else attached as I didn't have much room and already had a transducer and a speed temperature sending unit attached for my fishfinder.

 

[MikDee]

Re: 3 blade to 4 blade pitch conversion

I'm sorry I missed tis post, but I would have recommended a 17" pitch 4blade, anywhoo,,, I'd put some synthetic blend, or full synthetic oil in there, to free up the friction in your engine. It should increase rpm a bit, & torque all around.

 

[Barry T]

Re: 3 blade to 4 blade pitch conversion

I have a 26 ft Pacemaker inboard with the 318 cu in engine, I am running a 13X10 RH 3 blade prop that came with the boat. My question - is there any advantage to changing the prop from a 3 blade to a 4 blade ? If there is an advantage what is it, fuel economy, performance etc, etc ? The other question, most boats around my area are running a larger prop 14, 15 in - would there be an advantage to change up the size or pitch ? Please advise - Thanks !

 

[braindeadjones]

Re: 3 blade to 4 blade pitch conversion

Barry T
First let me say I AM NOT AN EXPERT in this field. There are several websites out there that help explain the functions of prop types that can give you more detail.

http://boatpropellers.iboats.com/pr..._prop/?**********=670736175&*******=048331888

One of the big concerns for people is going from 3 blades to 4 blades takes away from the top end of your boat. I personally did see a ~10mph drop, but my loading of stores has increased significantly. My goal was to get more "torque" with a 4 blade prop to keep my 21' Glastron on plane at ~20mph so we could wakeboard/tube easier. It helped, but if I hit a wake or the skier swings out to cut back, it can be enough to slow me down and drop off plane. My hull was just not designed with this speed in mind. So I would have to go with trim tabs.

Unless you know that one of the boats in your area is exactly like yours and carrying the same amount of goods, do not concern yourself with what they are using.

The big thing to remember is keeping your engine in the MFG recommended WOT (Wide Open Throttle) range. So look at it this way, the more "Load" the lower the RPM, the lighter the "Load" the higher the RPM.

Adding a Blade increases load, so the pitch or diameter must decrease to maintain proper WOT.

If your boat is running properly, in the meat of WOT with standard stores, up on plane in less than 30 seconds, good throttle response, I would leave well enough alone. The gains will be minimal in my NON EXPERT opinion, it will be more of a preference, and possibly a better application to suit your needs.

I recommend reading several websites and talking to people with similar boats to see if they have had any experiences. Perhaps there is a dealership that will give you guidance, and have a few loaner test props you can try out. Boaters love to talk boats.

 

[Tail_Gunner]

Re: 3 blade to 4 blade pitch conversion

:redface: oops this is a old thread.. Barry start a new one

 

[steelespike]

Re: 3 blade to 4 blade pitch conversion

A 4 bld. prop will get you on plane easier and stay on plane with less power.
It may lower your top end a little. Usually they drop 1" in pitch assuming
your present prop is right on.
As far as what pitch for your setup it depends on your max rated rpm and your present max rpm. A 1" increase in pitch usually results in "about" 200 rpm decrease
in rpm. and viceversa.You want your motor to be able to operate within its reccomended rpm range. If you run alot with a big load of people and gear you might
go with less pitch and be careful of your rpm when lightly loaded.

 

[torbjorn]

Re: 3 blade to 4 blade pitch conversion

I am looking for information regarding converting from a 3 blade to a 4 blade SS prop. My goal is to maintain On Plane in between 15-20mph for wake boarding, skiing, and tubing. We currently fall off plane at around 21mph, (2100rpm).

Here?s what I am currently running:
1989 Glastron Futura 225, 7.4L Bravo One, with a Quicksilver 48-13702A40 SS 14 ? inch 3 blade 21p, WOT at 4200 ? 4600. When unladed and prop was new (mild damage) we could hit 4500 trimmed out and an speedo indicated 60+mph. Now with all the gear, toys, and damage it?s about 4000rpm.

So here are my questions:
Will a 4 blade prop help me maintain Plane at a lower speed?
Should I go to a 19p prop since I am adding a blade or even lower?

I am aware of other options, Dou-Fin, Fat Sack, Bennett Trim Tabs, buy a ski boat, etc. I just wanted to get my 3 blade reconditioned and thought this might be a good time to get a new 4 blade prop for play time and use the 3 blade as a spare. Top speed is no longer a priority...

Thanks for any help or suggestions,
Brian J.

First, torque is determined by the motor, has nothing to do with the prop. You're probably running a 4 stroke motor, right? Problem. Only thing you can do in any case is go to lower pitch, maybe a bit more diameter.