How to find the pitch of the prop. What is better a 3 blade or 4 blade stainless prop

[boatingtattman]

I need to find the pitch of the prop on my 1990 90hp johnson vro v4. It has a stainless steel 3 blade on there now. I checked the inside of the prop hub and on the outside of the prop and there are no numbers.
Also what is the best stainless steel prop to get? Will a 4 blade make the boat faster and give it a better hole shot? What is the most reasonable place to purchase it that still sells a good product? I didnt pay to much for the boat and dont want to sink alot of money into it. I just want to be able to have fun this summer with the kids sking and tubing..thanks

 

[RogersJetboat454]

Re: How to find the pitch of the prop. What is better a 3 blade or 4 blade stainless

I need to find the pitch of the prop on my 1990 90hp johnson vro v4. It has a stainless steel 3 blade on there now. I checked the inside of the prop hub and on the outside of the prop and there are no numbers.
Also what is the best stainless steel prop to get? Will a 4 blade make the boat faster and give it a better hole shot? What is the most reasonable place to purchase it that still sells a good product? I didnt pay to much for the boat and dont want to sink alot of money into it. I just want to be able to have fun this summer with the kids sking and tubing..thanks

May need to pull the prop off and take a good look all over it for #'s. Even if you don't find the diameter and pitch, you may be able to find a part # that can be looked up to determine what you have.

A 4 blade prop will give you a better hole shot than a 3 blade, but it will loose a few MPH in the top end. Take a look at the props here on IBoats, they are reasonably priced, and will give you an idea whats available.

 

[Art Bernard]

Re: How to find the pitch of the prop. What is better a 3 blade or 4 blade stainless

Look on the rear of the prop, should be stamped there, if not there look at the thrust washer under the prop nut, might be there. Here is a copy of a previous post I did, might help you with prop choices.

Art




Is 56mph @4800rpm at wot (wide open throttle)? Your engine has an operating rpm range, you want to stay within that range. I dunno what you know about prop pitch and you haven't posted your current prop size so here is an explanation I hope will help you. A prop's size is measured by diameter (first number) and pitch (second number) so a 15 x 15 prop will be 15" in diameter with a 15 deg pitch. with reguards to pitch, the higher the pitch number the more agressive the angle of the blades and the less rpm you will turn but you will get more "power" but less speed. The lower the ptich number the less agressive the angle of the blades and the higher the rpm you will turn. This will give you more top end speed, but sacrifice power and hole shot. Each degree of pitch is worth approx 400-500rpm so lets say your engine has a rpm range of 5000-6500rpm and the prop you have on it now (lets say a 15 x 15) is turning 5500rpm @ wot. If you drop a degree of pitch making your prop a 15 x 14 you should turn around 5000rpm. If you raised your pitch making it a 15 x 17, you should turn aroun 6000rpm. Cup is another way to gain a bit of pitch. Cupping your prop is worth about 250rpm and can be done to fine tune the prop. Lets say you are turning 6000 rpm with a 15 x 17 prop. Adding cup would put you around 6250 rpm. Bear in mind to that your boats hull, the weight of your boat, and how the weight is distributed around the boat will effect rpm. I recomend a stainless prop, you will get better performance out of them and I strongly recomend that you do not exceed the rpm range for your motor, if fact you should leave a bit of cushion. Hope this helps you and good luck.

Art

 

[Robbabob]

Re: How to find the pitch of the prop. What is better a 3 blade or 4 blade stainless

Input information was in the wrong spot...

 

[cp]

Re: How to find the pitch of the prop. What is better a 3 blade or 4 blade stainless

with reguards to pitch, the higher the pitch number the more agressive the angle of the blades and the less rpm you will turn but you will get more "power" but less speed. The lower the ptich number the less agressive the angle of the blades and the higher the rpm you will turn.

the prop you have on it now (lets say a 15 x 15) is turning 5500rpm @ wot. If you drop a degree of pitch making your prop a 15 x 14 you should turn around 5000rpm. If you raised your pitch making it a 15 x 17, you should turn aroun 6000rpm.

Art

Aren't these two excerpts from the quote contradictory? The first says lowering pitch will raise rpm yet the second gives an example of lowering from a 15p to 14p resulting in a drop in rpm, 5500 to 5000. Likewise, the first says raising the pitch will lower the rpm but the second gives an example of raising the pitch from a 15p to a 17p and increasing rpm from 5500 to 6000. Everything I've ever read and experienced agrees with the first quoted paragraph above, so the second paragraph seems in error. Just saying, in the interest of accuracy...

 

[Dhadley]

Re: How to find the pitch of the prop. What is better a 3 blade or 4 blade stainless

A 4 blade prop will give you a better hole shot than a 3 blade, but it will loose a few MPH in the top end. QUOTE]

Not necessairly. Many times we find the correct 4 blade not only gives a great holeshot and mid range but it can be the fastest too.

 

[Dhadley]

Re: How to find the pitch of the prop. What is better a 3 blade or 4 blade stainless

Look on the rear of the prop, should be stamped there, if not there look at the thrust washer under the prop nut, might be there. Here is a copy of a previous post I did, might help you with prop choices.

Art




Is 56mph @4800rpm at wot (wide open throttle)? Your engine has an operating rpm range, you want to stay within that range. I dunno what you know about prop pitch and you haven't posted your current prop size so here is an explanation I hope will help you. A prop's size is measured by diameter (first number) and pitch (second number) so a 15 x 15 prop will be 15" in diameter with a 15 deg pitch. with reguards to pitch, the higher the pitch number the more agressive the angle of the blades and the less rpm you will turn but you will get more "power" but less speed. The lower the ptich number the less agressive the angle of the blades and the higher the rpm you will turn. This will give you more top end speed, but sacrifice power and hole shot. Each degree of pitch is worth approx 400-500rpm so lets say your engine has a rpm range of 5000-6500rpm and the prop you have on it now (lets say a 15 x 15) is turning 5500rpm @ wot. If you drop a degree of pitch making your prop a 15 x 14 you should turn around 5000rpm. If you raised your pitch making it a 15 x 17, you should turn aroun 6000rpm. Cup is another way to gain a bit of pitch. Cupping your prop is worth about 250rpm and can be done to fine tune the prop. Lets say you are turning 6000 rpm with a 15 x 17 prop. Adding cup would put you around 6250 rpm. Bear in mind to that your boats hull, the weight of your boat, and how the weight is distributed around the boat will effect rpm. I recomend a stainless prop, you will get better performance out of them and I strongly recomend that you do not exceed the rpm range for your motor, if fact you should leave a bit of cushion. Hope this helps you and good luck.

Art

Just so we're not confused - pitch is measured in inches, not degrees. Rake is measured in degrees. A higher advertised pitch will not automatically result in a worse holeshot. It may but blade and hub design plays more of a role in that. Each inch of pitch will not necessairly result in a give number of rpm. Again we have to consider design. And not all manufacturers measure pitch in the same way. Especially progressive pitch. And cup does not mean more pitch. Cup is simply water flow control over the blade area.

 

[Bamaman1]

Re: How to find the pitch of the prop. What is better a 3 blade or 4 blade stainless

If you're having problems choosing a prop, I would suggest you find a good propeller reconditioner--prop shop. That's often their only business, and their experience and knowledge allow them to tell you right off the top of their head what'd be the best prop for your use.

They're no more expensive than a marine dealership for props, and often have used props available for testing and purchase.

I have a dealership 35 miles away that stocks all of Mercury's exotic propellers. They're also big into pleasure boat racing and outboard drag racing. A high performance dealership like this would be great if you're running a 250 hp bassboat or other high performance boat.