Evinrude E-NATION, for those dedicated to water, power, fishing and fun
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Captain
Posts: 174
Registered: ‎09-12-2016

Re: 3 Blade Prop Vs 4 Blade


@arzwrote:
18” or better start with 20”?

I would start with an 18".

Skipper
Posts: 5
Registered: ‎03-22-2018

Re: 3 Blade Prop Vs 4 Blade

My dubt is that i have to buy the prop... here in italy is about 800€... 1000$.... 20” is a medium size.. I sow on many forum that lot of people use 20, 22 and also 24”. Goal is 5600rpm wot with normal load?
Captain
Posts: 174
Registered: ‎09-12-2016

Re: 3 Blade Prop Vs 4 Blade

I would shoot for 5600 to 6000, the higher the better. All I can say is if you are overpropped (rpm too low) you risk engine damage and voiding your warranty. If you are underpropped at least there is no damage risk.

 

I would like to see these internet posts where 23 ft 5000 pd boats, are propped properly with 24 or 22 inch rx4s. If these are the same guys recommending a Raker, I would disregard.

Skipper
Posts: 5
Registered: ‎03-22-2018

Re: 3 Blade Prop Vs 4 Blade

evinrude spec says the right range is 5400/6000 rpm... I just spoke with a guy who have an G2 250 on his saver 750 wa (like mine..). His prop is rx4 15" 20". Result is 43 knot at 5700 rpm with 2 people and 150 liters of fuel. How does it worth 50 hp more?  

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Captain
Posts: 174
Registered: ‎09-12-2016

Re: 3 Blade Prop Vs 4 Blade


@arz wrote:

evinrude spec says the right range is 5400/6000 rpm... I just spoke with a guy who have an G2 250 on his saver 750 wa (like mine..). His prop is rx4 15" 20". Result is 43 knot at 5700 rpm with 2 people and 150 liters of fuel. How does it worth 50 hp more?  


 

 

Hi,

 

The best way to prop a boat is to gather information about similar boats as you have done.

 

The weight of the motor, fuel and people is about 1200 lbs, you stated 1800 lbs. If you added another 600 lbs to that boat you would drop the rpms considerable, probably 53-5400 rpms.

 

I recommended you try for 5600- 6000 rpm because targeting the low end is not a good idea, it's a cushion in case you take on extra load temporarily. My boat is propped to 5800, my boat before was 6000. 

 

50 HP might give you 3-4 knts, marine propulsion is tough because of the drag, you might get 300 rpms.

 

The last thing is I don't believe the 5700 rpm quoted on that boat. A lot of people hit full throttle and trim there engine to 100% and note the rpms. This is not correct. You have to note the rpms at the trim position when the prop begins to ventilate, this will be the point at which trimming any further produces no gains in speed.I believe the WOT rpms is much less than 5700.  Here's why. I have a 3300 lbs boat ( with engine, gear, people, fuel), it's a 225HO which is about 250HP motor, same as that boat. With my 20 inch RX4, at 5800 rpm my speed is 58knts, almost 40% faster than that boat. I'm at about 60% trim at that speed. This means that your guys boat is undergoing EXTREME slippage, way more than that hull would produce, the only explanation I can think if is the motor was trimmed up way too far and is ventilating. It likely means that boat is overpropped, or not setup properly engine mounted too high perhaps.

 

You might get away with a 20, but I don't see the value in trying to hit the low end of the rpm range personally.

Captain
Posts: 36
Registered: ‎04-03-2018

Re: 3 Blade Prop Vs 4 Blade

[ Edited ]

Hello,

I´m currently running a Raker h.o on a Brig eagle 580 RIb with a evinrude 150 H.O G2. Topspeed is 52knots WOT at 6000 rpm. Size 14.15 x 22"

The problem is that i want the boat to go in much rougher sea and more handling in turns and hit waves better. What prop should i go for? Even tough the boat is handling really good i would like to know what i can go for. 4 blade? Weight is with people on board and fuel is approx 900-1000 kg`s

 

 

Answers are highly appriciated!

 

Best regards, Osbar

Admiral
Posts: 7,114
Registered: ‎07-14-2011

Re: 3 Blade Prop Vs 4 Blade

 

 

Finding the best all around propeller takes trial and error. First you want to be sure that the motor is not mounted too low on the transom. The Evinrude E-TEC G2 can run higher than other engines due to its setback and gearcase design.  You want the anti-ventilation plate to be on top of the water while running on plane.

 

The RX4 prop would probably work the best as it holds well in tight turns and rough water. Start with a 22" pitch as the G2 engine's flat hp and torque curve allow it run more efficiently in the mid rpm range or a bit lower 5600-5800 is a good range to shoot for. See if you can work with a dealer to try a couple of props, or find someone who would loan you one. My guess is that it will either be a 22" or 20" depending on the top rpm with a normal load onboard.

 

 

 


"There is never just one thing wrong with a boat";
                    -- Travis McGee, main character in a book series by John D. McDonald 


 



***************

The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.

The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.


Captain
Posts: 36
Registered: ‎04-03-2018

Re: 3 Blade Prop Vs 4 Blade

Thx,

what do you say about the bravo 1 prop? i know there is hub kit for them but the props are good?

Captain
Posts: 36
Registered: ‎04-03-2018

Re: 3 Blade Prop Vs 4 Blade

[ Edited ]

how does the rx4 perform in waves for fun? compare to the raker. Sometimes it can smash when i go into a wave, i do not think it is the hulll becuase the hull is a really good deep V 22 degree. Will that make a diffrence? Like waves from big boats to just run over smoothly instead of have to turn down the speed. Explain that please!

Admiral
Posts: 7,114
Registered: ‎07-14-2011

Re: 3 Blade Prop Vs 4 Blade

Sorry but we cannot assist with non-Evinrude products

 

 

 


"There is never just one thing wrong with a boat";
                    -- Travis McGee, main character in a book series by John D. McDonald 


 



***************

The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.

The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.