posted 02-08-2007 07:22 PM ET (US)        

  RPM    MPH     GPH
 1000    3.8     0.2
 2000    7.1     1.3
 3000   12.8     2.8
 3500   20.0     3.6
 4000   27.3     5.2
 5000   34.3     8.2
 5700   41.2    11.1 (WOT)

The boat planes at about 3200 RPM 14.6 MPH 3.1 GPH with the help of Lenco 12"X12" trim tabs.

posted 02-09-2007 08:40 AM ET (US)            

In addition to the other suggestions, I would check your throttle cable to make sure that its capable of fully opening the throttle linkage. Also, make sure you have no fuel line restrictions (check with vacuum gauge against Honda specifications for maximum vacuum). Finally, try dropping down to a 17P propeller to see what happens.

posted 02-09-2007 01:47 PM ET (US)            

http://www.honda-marine.com/pdfs/BF150_advantage.pdf

Were prop RPM to be equal the speed would be equal.

Another consideration is the additional weight 50lbs more for the 4 stroke, minus the 25lbs for the oil and tank.

That brings up another warm fuzzy, no oil to buy.

posted 02-09-2007 06:20 PM ET (US)            

You should prop so when you are alone in the boat the engine will just touch the WOT rpm limit. It does not hurt the motor whatsoever to run at the rpm limit. You are not doing the motor any favors by overpropping it and making the WOT rpms lower. You will be doing just the opposite.

The additional weight of the new motor over the old one is insignificant compared to the overall weight of the rig. Therefore with 15 more hp you should be at least as fast as the old motor, if not faster.

Either raising the motor for more rpms or dropping the pitch to 17 or 18 inches is in order.

posted 02-09-2007 10:57 PM ET (US)            

Why don't you want to be propped to be at the top of the RPM range at WOT? 6000 RPM is the max, and it is exactly where you want to be at WOT. You don't have to ever reach 6000 RPM if you don't want to but your motor will have less strain at lower RPM with a heavy load if it's propped that way. Also peak HP is achieved at 6000 RPM so it makes sense to be able to reach peak HP doesn't it?

I don't understand what you mean when you say that your engine was designed for the middle of the range. The BF150 was in fact designed to run between 750 RPM (idle) and 6000 RPM and these Honda's like to be run in the upper end of the WOT range. This same basic motor that's in the Acura TSX produces 205 HP at 7000 RPM.

Peter made a very good observation regarding the low fuel consumption at WOT and pointed out that the throttle is probably not adjusted to achieve full throttle. Its easy to check. Push the throttle lever all the way down and look to see that the throttle arm under the cowl is touching the stopper.

You say that your not sure you'll make the adjustments to give it full throttle because you may end up having to reprop. Well it might not rev over 6000 RPM with that prop even if you do adjust the throttle so it reaches wide open. And if it does go beyond 6000 RPM, just back off the throttle a little.

You paid for 150 HP, and this motor actually produces 160 HP at 6000 RPM so I if I were you I would get my money's worth and adjust the throttle and prop the motor so it reaches 6000 RPM

posted 02-10-2007 08:00 PM ET (US)            

What still bothers me is the 12% prop slip at WOT. That 4 blade Offshore prop should be more eficient than that. If it produced a more normal slip of 5% it would equal a top speed of 50 MPH.

posted 02-11-2007 12:13 AM ET (US)            

quote:

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They are great propellers if your motor can handle it.

---

posted 02-11-2007 12:20 AM ET (US)            

Though the blade area of the Revolution 4 is relatively large, the diameter is modest at 14-5/8'. I think of the Rev 4s as being well suited to the 20 foot and larger class. Your Outrage 17 II is a heavier boat though and may do well with one.

posted 02-11-2007 12:10 PM ET (US)            

5600 RPM @ 44.0 MPH with the OptiMax 135 calculates to 12.6 percent slip.

6200 RPM @ 45.8 MPH with the BF150 calculates to 12.1 percent slip.

posted 02-11-2007 12:25 PM ET (US)            

I would try that 19" Stiletto Advantage that Tom has. They are supposed to have a good bite, are fast props and are relatively inexpensive. A good value.

posted 02-11-2007 01:46 PM ET (US)            

Marv, when I plug in the data for my 4 blade 14.25 X 17 Solas Titan prop, it shows less than 3% slip. That is why I assumed your 4 blade Offshore prop would have had similar results.

posted 02-11-2007 06:35 PM ET (US)            

Stiletto and Turbo brand propellers can actually calculate with negative slip figures which are impossible. The explanation is simple: they under rate the pitches of their propellers. Thus a Honda TURBO propeller (made by Turbo) can seem to have a remarkably low slip when in fact if you make the calculation with 2" of pitch added, you will see a more normal slip percentage.

"Does a high slip percentage equate to poor fuel economy in relation to a prop that produces much less slip?"

posted 02-11-2007 10:56 PM ET (US)            

My prop is the power tech offshore 4 blade 15.25X16.

It revs to 6200 rpms and was the fastest of the 4 blades.
That Honda Turbo 4 blade 14.25X17 was too tall for my boat.
Even very lightly loaded with about 20 gallons of fuel and just me aboard i could only pull 5500rpms max.

The power tech thats on there now is a perfect set up.

I noticed you were talking about negetive slip with the offshore prop.
Maybe this could be a major issue with my vibration at idle as the prop may want to go backwards.
Is that possible? Iam talking about just at idle.

But then there's still that growling issue.

posted 02-12-2007 09:24 PM ET (US)            

Tom, your suggestions are always welcome.

posted 02-21-2007 07:32 PM ET (US)            

I was only able to ahceive 5300 RPM (WOT) with a drop in speed to 41.6 MPH.

Something else I don't really understand is an increase sensitivity to trimming the engine up. There was a significant increase in porpoising as the engine was trimmed up. The porpoising started at an earlier trim angle and it was much more pronounced. Can anyone explain this characteristic. I haven't done a great deal of prop testing, but the same prop in 19" pitch is mush more docile when trimmed out a little too far.

posted 02-21-2007 09:32 PM ET (US)            

I'd continue to try different props like a Stiletto Advantage II or a Powertech OFS. If you want to keep with a 4 blade prop, Stiletto also makes a good one as well as Powertech and the Mercury Reolution 4.

posted 02-22-2007 09:41 AM ET (US)            

I still smell a rat. Are you sure the rim tabs were retracted during this most recent test? Are you sure you are getting true full throttle?

posted 02-22-2007 01:26 PM ET (US)            

I'm no expert on props but the old prop has marked clearly 48-825900A46 19P on the outside and the new one has 48-825902A45 21P. The markings on the new prop aren't as distinct and appear to have faded . Another obvious difference between the two is the new prop does not have the PVS plugs that the old one did.

I haven't given up. I'm continuing my search for the right prop. I want one that provides the same handling as my OFFSHORE 19P but brings the RPM down to 6000. Any increase in speed would just be gravy. After all 46 MPH ain't bad while dragging this T-Top along.

posted 02-22-2007 01:59 PM ET (US)            

The conditions were the same or better. There was a light wind and I was the only one on the lake, because it was misting a light rain. The Temp was in the high sixties as opposed to the low fifties on the previous test. The only difference was in weight, I had not refueled, so the boat was lighter.

The trim tabs were fully retracted. I have not made any adjustments on the throttle since the previous test. I didn't mention it but the fuel consumption during this test was 13.3 GPH. I attributed the drop to operating at the lower RPM. Was I wrong in making that assumption?

posted 02-23-2007 08:59 AM ET (US)            

Regarding Mercury's propeller part numbers, the 825900A46 and 825902 are the essential part numbers of the particular propellers.

The A45 suffix indicates a Flo-Torq hub but no PVS holes. A46 is the next generation of Flo-Torq hubbed propellers and differs only by the addition of the PVS vent holes.

The 19P and 21P are simply the nominal pitch.

posted 02-23-2007 08:12 PM ET (US)            

I decided to do what you suggested. After testing your prop the other day I put my OFFSHORE 19P back on.

I took your 21P prop with me and headed back out to the lake with the intention of retesting it after retesting mine. However, I didn't around to retesting the 21P prop.

To make a long story short I was only able to reach 6000 RPM with my prop. I pulled the cowl to see if the throttle linkage was reaching full throttle, and it was.

I asked my mechanic, (who has been with me during each of the test), why there had been a decrease in power. He attributed the drop in RPM to the increase in temperature.

Today the temp was in the high 70s. I should have known that performance decreased with temperature increase, but didn't think that it would be quite so much. There was roughly a 25 degree difference in temperature between the the original WOT test on this prop and the one today. I will mostly be using the boat in temperatures above what it was today.

I can live happily with the prop I have. Thanks, to everyone for their contribution. Perry, Tom and Peter