Liveliner
Well-known member
How to Choose a Propeller for your mid sized boat.
This is simplified and I know that most of you guys know this info already. However, there may be a few folks on the forum that may get help with this post.
If you have anything to add, please do so.
My opinion from experience. The difference with 3 and 4 blade props is; A 3 blade gives you a little more on top end and good range of power throughout. A 4 blade bites better at take-off and in tight turns and can push a heaver load. You will loose a little speed at top end.
The way that you choose a prop is by running it to test it. A boat will generally run better in slightly choppy water. Therefore if you test several props at different times, make sure you have the same conditions on the water.
* Know your engines maximum RPM range and DO NOT exceed it.
* Load your boat as you would normally use it alone. Batteries, fuel, rods, tackle and only you in the boat.
* Trim the engine all the way in. Accelerate hard and keep the throttle full forward. The boat will gain speed and RPMs and will stable out at a point. At that point start trimming the engine out slowly. You will start to see a gain in speed and RPMs. While the engine is still trimmed in you can feel that there is more drag on the steering on one side more that the other when you slightly turn left and right. Your speed will start to level out and stop gaining as you are trimming your engine out at full throttle. DO NOT ALLOW YOUR RPMs TO GO ABOVE THE LIMIT When you see your speed level out, stop trimming your engine and feel the balance of the pull on the steering wheel. If it is even on left and right, you are there. If not, watch your RPMs and slowly trim out some more to the balance in the steering is even. By over trimming your engine your boat will slow down and over-rev your engine. If this starts to occur, trim back a little to the balanced steering point.
NOW based on what you saw in that test it will tell you what you need.
1. If the maximum speed that you acquired was reached at a point less than your maximum RPM and you could not reach your maximum RPM, Your prop has too much pitch.
2. If you max'ed out your RPMs before your boat was trimmed to the point of balanced steering, You need more pitch.
3. At near perfect pitch for your boat. It should come out of the hole while trimmed in. It will gain speed and RPMs while you are SLOWLY trimming the engine out at full throttle. At the point where you are nearing your maximum RPMs you should feel the steering balance. At that point you should also have just reached your maximum speed. At that point where your trim and throttle is set, and without moving them, you may get an increase in speed without gaining RPMs. The reason for this is that the faster you go the less drag you have on the hull. Therefore at top speed you may lose some drag which will in turn let you gain speed.
With the factors that I pointed out to test a prop, The speed you reached is what that prop will do. The speed is what you get from that setup and that is it.
All props that you test from three blade to five blade should be tested the exact same way. You will see that they will have differences in their performance.
On my Proline Bay boat, I run two different propellers for the results that I want.(one at a time). With my three blade in fresh water. Alone in my boat it runs 51MPH at 5600RPMs, with two persons its 48MPH and so on to Four persons at 44MPH at 5200 RPMs. With the Four blade prop, I get 48MPH at 5600 RPMS loaded or not. I use my four blade in salt water and for playing in freshwater. I use it to pull water toys, It gets out of the hole and turns on a dime. The Four blade has much more mid range bite and control in tight turns and very good in keeping the bite in very rough water. It will also perform better with a heaver load.
Now on top of all that. If you want to gain more performance out of your prop, you can start adjusting the cup, rake and shape of the blades.
Another thing to know is that on props that exhaust through the hub there may be holes in front of the blades. Those holes are there to allow air to pass in front of the blade at take off to help get the RPMs up quick for a hole shot. Some props have plastic inserts that can be changed to change the hole size. The larger the holes, the more air you get in front of the blades. The holes have no effect at high speeds.
This is simplified and I know that most of you guys know this info already. However, there may be a few folks on the forum that may get help with this post.
If you have anything to add, please do so.
My opinion from experience. The difference with 3 and 4 blade props is; A 3 blade gives you a little more on top end and good range of power throughout. A 4 blade bites better at take-off and in tight turns and can push a heaver load. You will loose a little speed at top end.
The way that you choose a prop is by running it to test it. A boat will generally run better in slightly choppy water. Therefore if you test several props at different times, make sure you have the same conditions on the water.
* Know your engines maximum RPM range and DO NOT exceed it.
* Load your boat as you would normally use it alone. Batteries, fuel, rods, tackle and only you in the boat.
* Trim the engine all the way in. Accelerate hard and keep the throttle full forward. The boat will gain speed and RPMs and will stable out at a point. At that point start trimming the engine out slowly. You will start to see a gain in speed and RPMs. While the engine is still trimmed in you can feel that there is more drag on the steering on one side more that the other when you slightly turn left and right. Your speed will start to level out and stop gaining as you are trimming your engine out at full throttle. DO NOT ALLOW YOUR RPMs TO GO ABOVE THE LIMIT When you see your speed level out, stop trimming your engine and feel the balance of the pull on the steering wheel. If it is even on left and right, you are there. If not, watch your RPMs and slowly trim out some more to the balance in the steering is even. By over trimming your engine your boat will slow down and over-rev your engine. If this starts to occur, trim back a little to the balanced steering point.
NOW based on what you saw in that test it will tell you what you need.
1. If the maximum speed that you acquired was reached at a point less than your maximum RPM and you could not reach your maximum RPM, Your prop has too much pitch.
2. If you max'ed out your RPMs before your boat was trimmed to the point of balanced steering, You need more pitch.
3. At near perfect pitch for your boat. It should come out of the hole while trimmed in. It will gain speed and RPMs while you are SLOWLY trimming the engine out at full throttle. At the point where you are nearing your maximum RPMs you should feel the steering balance. At that point you should also have just reached your maximum speed. At that point where your trim and throttle is set, and without moving them, you may get an increase in speed without gaining RPMs. The reason for this is that the faster you go the less drag you have on the hull. Therefore at top speed you may lose some drag which will in turn let you gain speed.
With the factors that I pointed out to test a prop, The speed you reached is what that prop will do. The speed is what you get from that setup and that is it.
All props that you test from three blade to five blade should be tested the exact same way. You will see that they will have differences in their performance.
On my Proline Bay boat, I run two different propellers for the results that I want.(one at a time). With my three blade in fresh water. Alone in my boat it runs 51MPH at 5600RPMs, with two persons its 48MPH and so on to Four persons at 44MPH at 5200 RPMs. With the Four blade prop, I get 48MPH at 5600 RPMS loaded or not. I use my four blade in salt water and for playing in freshwater. I use it to pull water toys, It gets out of the hole and turns on a dime. The Four blade has much more mid range bite and control in tight turns and very good in keeping the bite in very rough water. It will also perform better with a heaver load.
Now on top of all that. If you want to gain more performance out of your prop, you can start adjusting the cup, rake and shape of the blades.
Another thing to know is that on props that exhaust through the hub there may be holes in front of the blades. Those holes are there to allow air to pass in front of the blade at take off to help get the RPMs up quick for a hole shot. Some props have plastic inserts that can be changed to change the hole size. The larger the holes, the more air you get in front of the blades. The holes have no effect at high speeds.
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