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  #11  
Old 08-11-2021, 08:26 PM
Northwoodswalleye Northwoodswalleye is offline
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Originally Posted by plnwtf View Post
Why would you want more RPM and the same speed? Lower RPM is easier on the motor and the pocket book.
I like to prop for maximum rpm with an empty boat. Usually gets out of the hole much better with a load. I have a few props I play with and by playing with the jackplate I get identical fuel mileage with a 21p rev 4 or a 24p bravo FS
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  #12  
Old 08-11-2021, 09:08 PM
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plnwtf plnwtf is offline
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Quote:
Originally Posted by Northwoodswalleye View Post
I like to prop for maximum rpm with an empty boat. Usually gets out of the hole much better with a load. I have a few props I play with and by playing with the jackplate I get identical fuel mileage with a 21p rev 4 or a 24p bravo FS

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  #13  
Old 08-12-2021, 08:25 AM
SLE SLE is offline
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I've ran all of the props that you are looking at and will offer the following. The Rev 4 will turn the hardest and will be down 100-200 rpms compared to the same pitch tempest, the tempest runs true for the RPM and the Bravo's spins a little easier than the Tempest normally running about 100 rpm higher than the same pitch Tempest. You are on the low end of the recommended rpm range and you will likely gain a far amount of performance by getting the top rpm up to around the 6200 max rating for that engine.

As you sit currently with a 19P Tempest turning 5,700 rpm and 56 mph I would estimate the following performance from my knowledge of these props.

An 18P Tempest should add 200 rpm (5,900). It'll be slightly quicker acceleration and similar top speed. You may pick up a mph with the engine more in it's ideal rpm band where they make power. A 17P is likely going to run you up to 6100 and possibly even a touch more. this is going to get you very close to the max RPM and will likely yield the best overall performance that you can get out of a Tempest.

For a Rev 4, you will likely lose some top speed as they are a big wheel and turn hard for there respective pitch. A 17P Rev 4 will likely net you close to 6,000 rpm. It will likely be the best handling prop you'll find. It's like AWD for your boat. They lift the entire boat. As far as a prop goes, it'll provide the ultimate in bow control.

On to the Bravo, particularly the FS. It's a big a wheel but turns easy. It's a good stern lifting prop and will run similar speed to the Tempest with plenty of bow lift. Being a large diameter prop, they can be ran higher in the water and therefor you have less drag from your lower unit. An 18P will likely run around 6000 rpm and 17 around 6,200 rpm. To me this is a great prop that balances the speed of the Tempest and the handling of the Rev 4. It won't handle quite as good as the Rev but will be faster, and might be down just tick off of the top speed of a tempest but will handle quite a bit better.

Now these are all general rules of theumb and a specific prop might run a little worse or better depending on how good the manufacturing tolerances are on that particular prop. If you want the best of the best, you'll find the prop that most suites your needs and send it off for a balance, blueprinting and some customization. but that's another topic.

Good Luck

Food for thought.
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  #14  
Old 08-12-2021, 08:34 AM
SLE SLE is offline
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Originally Posted by plnwtf View Post
Why would you want more RPM and the same speed? Lower RPM is easier on the motor and the pocket book.
This is completely wrong. You prop a boat for the max rated rpm of the engine. This allows the engine to operate at it's fullest potential both at low speed an high speed. It places the engine in the operating range that it was intended to run. normally you prop for max rpm with the lightest load you would run, and therefor still have the proper prop to work within the recommend operating range when the boat is loaded with a medium or heavy load. Lugging a marine engine is not good for the engine or for boat performance and will accelerate wear and fuel usage as the engine is working harder to pull the same load. Think of it as gearing in your pickup. Too tall of gearing make for poor performance, lugging the engine, lots of downshifting, and excess heat. fortunately for your truck, you can shift into a lower gear unlike your boat.
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  #15  
Old 08-12-2021, 11:37 AM
3M TA3 3M TA3 is offline
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I believe you're already obtaining optimum performance. Actually, finding it hard to believe you're getting 56 MPH with that engine on an 18.5. Amazing.
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  #16  
Old 08-13-2021, 05:38 AM
Real1 Real1 is offline
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Quote:
Originally Posted by SLE View Post
I've ran all of the props that you are looking at and will offer the following. The Rev 4 will turn the hardest and will be down 100-200 rpms compared to the same pitch tempest, the tempest runs true for the RPM and the Bravo's spins a little easier than the Tempest normally running about 100 rpm higher than the same pitch Tempest. You are on the low end of the recommended rpm range and you will likely gain a far amount of performance by getting the top rpm up to around the 6200 max rating for that engine.

As you sit currently with a 19P Tempest turning 5,700 rpm and 56 mph I would estimate the following performance from my knowledge of these props.

An 18P Tempest should add 200 rpm (5,900). It'll be slightly quicker acceleration and similar top speed. You may pick up a mph with the engine more in it's ideal rpm band where they make power. A 17P is likely going to run you up to 6100 and possibly even a touch more. this is going to get you very close to the max RPM and will likely yield the best overall performance that you can get out of a Tempest.

For a Rev 4, you will likely lose some top speed as they are a big wheel and turn hard for there respective pitch. A 17P Rev 4 will likely net you close to 6,000 rpm. It will likely be the best handling prop you'll find. It's like AWD for your boat. They lift the entire boat. As far as a prop goes, it'll provide the ultimate in bow control.

On to the Bravo, particularly the FS. It's a big a wheel but turns easy. It's a good stern lifting prop and will run similar speed to the Tempest with plenty of bow lift. Being a large diameter prop, they can be ran higher in the water and therefor you have less drag from your lower unit. An 18P will likely run around 6000 rpm and 17 around 6,200 rpm. To me this is a great prop that balances the speed of the Tempest and the handling of the Rev 4. It won't handle quite as good as the Rev but will be faster, and might be down just tick off of the top speed of a tempest but will handle quite a bit better.

Now these are all general rules of theumb and a specific prop might run a little worse or better depending on how good the manufacturing tolerances are on that particular prop. If you want the best of the best, you'll find the prop that most suites your needs and send it off for a balance, blueprinting and some customization. but that's another topic.

Good Luck

Food for thought.


Thanks SLE
This is the kind of answer I was looking for.
It's difficult to make a choice right now. The props are difficult to find here in Canada. Some are not offered in lower pitch and I know the improvements will not be major.
The speed recorded was GPS and not on one occasion
The RPM was off Vessel View Mobile.
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  #17  
Old 08-13-2021, 11:08 AM
SLE SLE is offline
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Quote:
Originally Posted by Real1 View Post
.............
The speed recorded was GPS and not on one occasion
The RPM was off Vessel View Mobile.
That's as good as you can get and solid info to use. I'm not sure you'll gain speed out of a change or not but I wouldn't expect you will lose any. You will gain overall boat performance throughout the entire rpm range buy getting that motor more into the mid to upper part of the rpm band. By doing that you help "unload" the engine and your also likely making a little more HP with more rpm (hard to know without a Dyno graph). Sometimes this is enough to pull a few more rpm than expected for a certain prop which can translate into a mph or two more. For the naysayer's, I had a 18.5 ft glass boat powered by a 200 Optimax that would tick just shy of 60 mph loaded with 2 guys, gear, and full fuel. The factory seen over 62 mph on the boat unloaded so it can be done if that's what your after!

Good luck
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