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Skipper
Posts: 7
Registered: ‎04-15-2020

250 G2 Propeller selection

G'day all,

 

I've got and interesting issue, I've got to find the best prop for a Cruisecraft 685 with a 250 G2, the customer isn't interested in top speed, it is all about cruising and fuel economy, he had a G1 250HO that has 700 hours but mere seconds above 5000rpm, the usual 30% below 1000rpm. (For sale in Sydney BTW)

 

That could get to 5900rpm with a 19"x15?" Rebel. Top speed 83kph @120 liters per hour. (He didn't ask me before deciding otherwise i would have got him to pay the little more for the HO and everything would be perfect.)

 

So we first tried the 17" Rebel, it was way too small, 30% throttle 5000rpm, 70% @ 5800rpm, so i didn't even want to see how easily it would hit the limiter.

 

Although a Evinrude mechanic suggested this was right to be able to use the full range and hit the 6200rpm limiter, so this was the right prop, i can't remember the speed but i doubt it would get over 80kph.....but maybe the customer would get his all important better cruise fuel economy??? I will test it again with the 17" to be sure but i doubt it.

 

Tried a 20'"x15" RX4 but it could only get to 5100rpm with ITrim at 41% (82kph?), 5350rpm at 82% trim @85/kph, 5450rpm with 100% trim, but that was just finding it easier to throw water (and -1kph), so the best was 82% @ 85kph. BUT THAT WAS @80 LITERS PER HOUR NOW, AMAZING.

 

I think 4 miles per gallon was best cruise speed at around 3000rpm, 2.5 at about 5000rpm (from memory), need to do more tests but that was full of fuel (300kg) and 2 people (230kg). So obviously this would get a lttle higher the lighter it got.

 

He doesn't often go out with any more weight then that but does sometimes....so that still needs to be considered.

 

Tried a 19" Viper, noticable vibration and excess noise on acceleration and it dropped off the plane way too easily compared to the RX4 which is amazing, it got to 5700rpm with top speed of 83kph, but three blade propellers will not be an option,

 

I wonder if any G2 boat suits a 3 blade? this one loves the RX4. 

 

So I will next have to try the Cyclone 20"x 14" , i am hoping the 1" smaller diameter difference will allow it to get into the minimal 5400rpm operating range a bit better but the reason for my question is, what if the Cyclone 20" can't match the fuel efficiency numbers of the RX4 20"?

 

Or what if the engine would run easily into the 5700+rpm with a RX4 18"x15"?, would that be faster and be able to get better fuel figures? 

 

What is the benefit of being able to rev the engine more if it worked out the figures were all practically identical? Which i think they will be. 

 

With an engine that tests itself hundreds of times a second, can it be "lugging" anymore? I thought that was only an issue when fuel came through venturi's and the spark was mechanically advanced?

 

Can an engine be lugging when it has knock sensors? And this engine capable of producing 300hp if the computer was programmed to make it, so ..... won't this same computer not lug itself to death only producing 250hp?

 

If this engine can run better fuel numbers with the RX4 20" compared to the Cyclone 20" or RX4 18" regardless of load.....why not run it?

 

And what is the guesstimation on the Cyclone 20" and RX4 18" before trying it?

 

I am hoping for 5500/5600rpm with the 82% trim....but will that be at 83 or 87kph? And which will be the better for miles per gallon?

 

So the question is, RX4 18" or Cyclone 20" next? Because we need to know, i will buy either and then take back which ever one he doesn't want.....so i will have a cheap practically brand new four blade for sale soon.   

 

Thanks.

Highlighted
Admiral
Posts: 9,519
Registered: ‎07-14-2011

Re: 250 G2 Propeller selection

 

 

5500-5600 is an ideal top rpm when trimmed out for best speed. Do not worry about the trim reading as long as the motor is not over-trimmed. Each hull and prop design is different.

 

The RX 4 is much more efficient prop than a Cyclone model.

 

If the new motor is mounted at the same transom height as the old one, it is too low. The built in off-set and the low water pickups with the improved gearcase design allow for a higher mounting and less drag. On many boats a G2 can be mounted 2 holes higher than an equivalent G1. Remember it is trial and error.

 

 

 


"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.


Highlighted
Skipper
Posts: 7
Registered: ‎04-15-2020

Re: 250 G2 Propeller selection

Yeah thanks Bill, it is up on the third hole, would probably still work on the fourth but would look too high on the transom and be stressing it that bit more, G1 was on the top, the water looks good just under the cavitation plate, absolutley amazing in corners at full speed, full tilt, full traction, i can't believe how good the RX4 20" goes, wouldn't want to lose that going one hole higher.

 

The 82% trim seems best, amazed it just keeps lifting, even at the 100% it is only slightly over trimmed, loosing the 1kph and only getting the extra revs from throwing water.

 

So you would suggest the RX4 18"? I wonder if that efficiency is from the bigger diameter or blade shape? I am worried it will gain too much and be able to rev higher but for no benefit, making the 20" RX4 @5400rpm ideal.....unless it would hurt something, that would not be ideal, but what would it hurt and how?

 

But I think that it would suit for when he does want to take out many people, it is going to be interesting though to see if it can better the 20" figures.

 

Strangley the RX4 has the vent holes which BRP says the G2 doesn't need, we tested it with them shut and the holeshot couldn't be faulted so won't bother even seeing what they would do opened.

 

 

Highlighted
Mate
Posts: 3
Registered: ‎09-05-2018

Re: 250 G2 Propeller selection

I have a Robalo R222 CC , appx 3800 lbs dry,  and a G2 250 HO. I Mostly offshore 15-20 miles or so and cruise

I Ran 2 props both  RX 4 and wanted to share my results:

 

1.  RX4 15 X18" W.O,T  48 MPH, 5400 RPM

2.  RX4 15X20" W.O.T.  50 MPH, 5100 RPM

 

Boat had 70 - 80% fuel, myself 190 and 100 lbs gear etc. Trimmed motor up to get highest speed.

 

These are nice props the 18" has a real nice holeshot and low end torque, you can feel the difference from the 20" They plane nicely on pretty low  rpm forgot at what rpm maybe 2700 or so. The 20 had a little less bite and holeshot but top end was faster 2-3 mph. I have been running the 18" over the 20" but give up a little top end. Fuel economy seemed very similiar but I didnt really take notes.

 

The 20" came with boat and I would like to try a 3 blade prop, considering Rebel or Viper props if anyone has advice appreciate it.

 

 

 

 

 

Highlighted
Admiral
Posts: 9,519
Registered: ‎07-14-2011

Re: 250 G2 Propeller selection

The Viper series are not suited well for an offshore G2 powered rig as they are designed more for light faster boats with a G1 or older motors. The Rebel is a decent prop for offshore rigs but was designed before the G2 became available.

The RX4 is a very good prop for the G2 but you may want to try an RX3 which is also designed for the G2

 

 

 


"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.


Highlighted
Mate
Posts: 3
Registered: ‎09-05-2018

Re: 250 G2 Propeller selection

If your getting 5400 out of your RX4 20" that sounds like a very efficient number with that prop and your moving along nicely.The 18" will also work well but you will lose about 2MPH on top end and add 200 rpm or so, both are in range though.

 

The 18 will give you the lower end bite, hole shot and fairly low rpm planing, Might also handle extra weight better. I ran both blades on a 22' CC with a 250 HO, I'm currently running the 18". As for fuel efficiency I didn't measure but seemed pretty much the same. 

 

On 18" I got 48 mph 5400 rpm

 

On 20" I got 50 mph 5200 rpm