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Performance numbers for Outrage 25' Cuddy with Suzuki 250
|Author||Topic: Performance numbers for Outrage 25' Cuddy with Suzuki 250|
posted 07-23-2004 09:41 PM ET (US)
I just hit the 10 hour break-in mark today, and decided to see how the boat performs with the new Suzuki 250hp Four Stroke. The motor is supposed to run WOT between 5500 and 6100 rpm. Today, I had 750+lbs of fuel, 300 lbs. water in the livewell and water storage tank, 1 adult, and two kids aboard, plus fishing equipment. I also had a bimini top up during the sea trial. Sea conditions were calm. The boat is a standard notched transom, and has the super console, and bait prep/rigging station/leaning post. Here are the numbers:
3800 RPM 25.4 mph
The prop is a SS 16" diam. x 20" pitch. The engine is mounted in the 2nd to the lowest hole.
In order to get closer to 6000-6100 RPM at WOT, I'm wondering if I need to move the motor up one hole and/or drop the pitch to a 19"? Or am I getting exactly what I should be getting considering that I had a nearly full fuel and livewell tank, a speed-robbing bimini top, and the seas were calm? Any suggestions? The motor doesn't seem like it's creating a bunch of excess spray, but if I look at the anti-ventilation plate while running, it seems as if it submerged deeper in the water than the last motor (1991 Yamaha 250). I also have to trim that motor waaaaaaaaay out to see 5750 RPM. With moderate trim, the motor only hits 5500 RPM and 38.5 mph.
I plan on running tomorrow with the top down to see the difference. As I run the fuel down some, I'll see how the numbers change without the bimini and with less weight.
Overall, I'm pretty darn happy with the motor. I can hold a cell phone conversation in normal talking voice at 30 mph cruising speed. Acceleration to plane is nearly instantaneous. I haven't checked fuel economy yet, but from the tank gauge, I'm estimating that I used about 20 gallons to travel 60 miles today. When I fuel up, I'll post the fuel economy numbers here, too.
posted 07-23-2004 10:51 PM ET (US)
Seems like you are doing great with the set up. I am not familiar with the boat, but that Suzuki seems to be doing the job it was designed for. The 2.3:1 or so gear reduction with that big prop looks like it is really paying off for you on a boat that size. Amazing you are planing that quickly with a single 250 on a boat that size with a 20" pitch prop. What size prop were you running with the 250 Yamaha?
I considered that motor when I was shopping for my repower on a 1997 21' Outrage. If there was a dealer closer and I was more familiar with their reputation that motor would have been my choice. I would have spent the extra money if a local dealer who I had confidence in sold them.
For every one inch of pitch you will typically gain around 200 rpms. By raising the motor you may lose prop "bite" and ability to plane easily, in addition to ventilation problems in certain seas. If you can try the lower pitch prop before raising the motor I would recommend that based on my own experience regarding engine height and prop selection.
I have a Mercury 250 EFI and a 19 pitch gives me 5400 rpm with a moderate load on my boat. The 17 pitch puts me at 5800. My 16 pitch 4 blade runs around 5750.
I can only imagine what kind of numbers I would get with that motor on my boat with a larger pitch prop. Good luck with it.
posted 07-23-2004 10:56 PM ET (US)
That WOT number looks very good when compared to the predicted performance with 300 HP on the transom as found in the table at continuouswave.com/whaler/reference/performancePrediction.html .
For an estimate of fuel consumption at various engine speeds and fuel economy at various boat speeds, you might use the fuel consumption data from the peformance reports published at Suzuki's web site as a surrogate for a fuel flow meter. At 4000 RPM, the DF 250 will burn about 10 GPH and about 15 GPH at 5000 RPM so it looks like you are getting about 2.5 MPG in the cruising range. Seems pretty good.
I would hold off changing anything until you see how it runs lightly loaded.
posted 07-23-2004 11:04 PM ET (US)
I was running a 15" diam. x 17" pitch with the Yamaha 250hp...and was hitting 5600rpm on the nose, with a top speed about 38 mph.
The old motor needed about 4700-4800 RPM to see 30 mph. The suzuki does it at 4300 RPM, which is 70% of the max engine speed of 6100 RPM. The Yamaha needed 80-85% of the max engine speed to see 30 mph. I expect fuel economy to at least double when cruising 25-27 mph.
The reason I was thinking about having the dealer raise the engine at the 20 hour service rather than change the prop, is because I could always change the prop myself later on if it needed it. Currently, the motor doesn't even come close to cavitating in rough seas or sharp turns. I doubt raising it 1 bolt hole would cause cavitation problems.
posted 07-23-2004 11:10 PM ET (US)
I think that the 1 inch of pitch yields 200 RPM is a good general rule for the conventional V6 running 2:1 and under gear ratios. However, with the significantly higher ratios run on the 4-cycles, I believe that there will be greater changes in engine speed for every inch of pitch, perhaps on the order of 250 per inch. So a 2 inch jump might yield a 500 RPM change.
Dropping down to a 19 in the case of Raydent's rig would yield nearly 6100 RPM at WOT under a nearly fully loaded condition. In a lightly loaded situation, I believe he would be well over the 6100 redline.
posted 07-23-2004 11:11 PM ET (US)
Thanks for the info. The prop calculator puts slip at almost 15% the way it's currently setup. That's the reason I thought about repropping or moving the motor up a notch. Can the extra heavy load also skew the prop slip calculation ? If so, then you're right...I should wait to see how it runs with a lighter load.
The fuel burn numbers you predict are good news. Dropping the pitch would probably hurt fuel economy while trying to squeeze out that extra 300 RPM. Probably not worth it.
Nevertheless, the boat doesn't seem to be as responsive to engine trim (less ability to raise the bow) as the last motor. I figured that it had to do with the engine height. Is that possible?
posted 07-23-2004 11:13 PM ET (US)
Dropping from a 20" pitch to 19" is a 1 inch change, isn't it? Wouldn't that change WOT 200-250RPM rather than 500 RPM?
posted 07-23-2004 11:53 PM ET (US)
Peter--That is a very interesting observation you made above. To restate: the change in engine RPM resulting from change in propeller pitch will be affected by the lower unit gear ratio.
|John from Madison CT||
posted 07-24-2004 06:26 AM ET (US)
Wow, what a nice engine. Super choice.
posted 07-24-2004 08:06 AM ET (US)
In Raydent's case, plugging in his current data in the prop calculator, it calculates slip at nearly 14.5 percent. For a 19 inch propeller, the prop calculator predicts nearly 6100 RPM with the assumptions that the 19 inch propeller will also experience 14.5 percent slip and the top speed will remain 40.5 MPH. Slip might actually go down with the lower pitch prop and if so then the WOT RPM will go down for the same 40.5 MPH top end.
The relationship between engine RPM and propeller RPM has to be affected by the gear ratio. Thus, a change in pitch is also affected by the gear ratio applied to the propeller.
My experience has been that when the boat is fully loaded slip increases. Slip is much affected by engine height, propeller design and whether the manufacturer has done a good job at denominating the actual pitch. Also, the more slip you have, the less effective the engine trim will be because the propeller isn't giving you as much leverage to get the bow up.
Your fuel economy may not go down simply because you reduce pitch. I think this is a common misconception which causes folks to run propellers that have too much pitch to keep the revs down (thinking they are saving fuel). The engine still needs to produce the same amount of work to push the boat the same speed regardless of what pitch the propeller is. The only savings that will come will be from the propeller that best enables the engine system to convert the fuel into usuable thrust.
The only way you are going to know what is the best propeller for your situation is by trying different ones out. To the extent that you do experiment with different propellers, I highly recommend that you get a fuel flow meter such as the Navman 3100 or Flowscan that has the economy computer built in. It will help you quickly determine which propeller is doing the best job. I also think it will pay for itself by allowing you to dial in the most efficient speed for the conditions.
posted 07-24-2004 09:49 AM ET (US)
Great info! Thanks. So from what you are saying, dropping to the 19" prop should lower prop slip. If it also raises the engine RPM, I should end up with a higher speed at WOT. Also, like I said before, the boat doesn't seem to be as responsive to engine trim as it used to be. I assume that it's like you said--it's due to the prop slip. (The old prop on the old motor was a 15"x17").
Here are the actual numbers I am seeing using real-world data plus the prop calculator:
posted 07-24-2004 10:04 AM ET (US)
In my case regarding engine height, when the motor was mounted on the middle or third hole, there was very little response from the boat when I trimmed the motor out.
Dropping the motor down one hole greatly improved the boats reaction to the trimming of the motor.
If you have an easy way to adjust the motor up and down it certainly cannot hurt to try different engine heights and propeller combinations to see how the boat reacts to the changes. Around here it is difficult during the season to get work done quickly. If that is your case, if you bring the motor up and find that you do not like the performance, you may be stuck with it at that height for a while.
The fuel flow meter is a great suggestion. I set my Smartcraft to read gallons per hour when I am looking for economical performance. I keep an eye on the gauge to keep the boat running at a certain fuel consumption rate.
posted 07-26-2004 11:13 AM ET (US)
Zukis like to be raised, go up 2 holes. Forget the prop, your main reason for slwer than expected speed is the full tnak of gas. Get down to 1/4 tank and see how she runs, if still sluggish? then reprop.
posted 08-03-2004 12:21 AM ET (US)
I agree with Bigshot.
Raise that puppy up a couple holes & see how she likes it, then if she still can't reach 6100 try the 19p.
Your report is very good.
posted 08-03-2004 07:51 AM ET (US)
posted 08-03-2004 08:00 AM ET (US)
Do you think the very high prop slippage (almost 15% at WOT) will decrease by raising the motor? Or do you think that the heavy weight of all that fuel was responsiblefor the high prop slip calculation?
I was able to get the motor to hit 5900-6000 rpm the other day, but I had to trim it waaaaaay out to the point where the prop was almost breaking loose. Top speed didn't change however...which means that prop slip went up even higher. I'm down to a little under 3/4 tank of gas (probably still have 100 gallons).
posted 08-03-2004 10:54 AM ET (US)
My suzuki loves to be trimmed to the point I am shooting a tail when going for WOT run. Mine redlines at 5800 and I pull 5600 or so with light load. Without extreme trimming she will only pull 5300-5400 and is 2mph slower.
posted 08-03-2004 02:29 PM ET (US)
Ray, I'm not all that familiar with Suzuki props.
My thinking is, you have the wrong style prop if she's slipping at 15%.
No I don't think raising the engine will cure the slipage.
posted 08-03-2004 07:01 PM ET (US)
So do you think that dropping to a 16x19" prop instead of the 16x20" that's on there now would both a) decrease slip, and b) allow the engine to reach the higher RPM?
Based on the high prop slip that I've calculated at WOT, do you still recommend raising the motor? Or do you now recommend decreasing the pitch?
In an ideal world, I would try one change, and then I'd try the other and see which is best. But I have to get the dealer to pull the boat to raise the engine or swap the prop, etc. I'm at my 20 hour service point, so I really only have this one shot to get it right...or I have to pay some $$$ to try something else. If you were in my shoes, would you swap props or move the motor up?
posted 08-03-2004 09:21 PM ET (US)
Ray, I wish I could give you the exact prop size & style, & the correct number of holes to raise the engine.
But I'm afraid you may just have to take the boat out of the water more than once.
First I'd raise the engine 1 set of holes & you should gain 100 rpms or so but if the slipage is still there or worse, I'd leave it that high & try a different style prop.
Merc has the best selection & makes the best props of all the engine makers so I'd lean towards a Merc 4 blade & that should cut the slipage.
You will have to contact Whaler & ask them which Merc prop they suggest as they only run Mercs on their boats.
posted 08-04-2004 03:10 PM ET (US)
Suzuki's literature on this 3.6 liter block indicates that they had to design special large 16" diameter props for it, to maximize performance. This might be one instance where the smaller diameter Mercury Revolution 4 or Mirage props, used on the Verados, may not be the best option.
posted 08-04-2004 08:30 PM ET (US)
Suzuki must have an especially large aperture on their lower units for the propeller. A 16-inch diameter propeller is a very close fit on most outboards! In the Mercury line, propellers of that diameter are usually in much smaller pitches, like 15-inches.
posted 08-04-2004 08:59 PM ET (US)
The gearcase on the Suzuki must be a little bit larger than the other manufacturers'. I don't believe that any other outboard brands can accept a 16 inch diameter propeller.
I do not believe that a 25 Outrage Cuddy requires a propeller with a 16 inch diameter so I suggest that you give a Mercury Mirage 15 1/4 x 19P a try. With the final gearing that the Suzuki has, you may even give the Mirage 21P a try as well.
The problem with getting overly concerned with the calculated slip is that you don't know how accurate Suzuki is with its pitch size designation. If they round a 18.5P actual to a 19P nominal, that will throw the calculation off adversely. That is why I believe a fuel flow meter and preferrably a fuel economy computer is essential for determining what is the most efficient propeller and mounting setup for a given rig. I have one and have tried several different propeller styles and the fuel economy computer really helped confirm my observations on what was going on back at the transom. I believe that it will pay for itself over the course of a 75 to 100 hour season.
posted 08-21-2004 08:23 PM ET (US)
OK. I had the dealer raise the motor 2 holes, and it had virtually no effect on engine speed or boat speed. I gained approximately 1/2 mph at each recorded engine speed increment, but I attribute that to the fact that I had burned nearly 300 lbs of fuel since I last recorded the numbers.
I probably need to get the dealer to reprop with the 19" pitch to get me to the 5900-6100 maximum WOT engine speed. Of course, without a fuel flow meter, I don't know how dropping the pitch from 20 to 19 will affect the fuel economy at the midrange cruising speeds. If the lower pitch prop drops the prop slippage, it's possible that fuel economy will remain the same or improve. Otherwise, I'm guessing that a lower pitch will reduce the fuel economy.
Since changing a prop is pretty easy, I'm going to try it just to see what happens. Overall, however, the boat is performing satisfactorily enough as it is.
I expect optimum cruising speed to deliver close to 3 mpg.
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