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ContinuousWave: Whaler Performance
Outrage 25 Suzuki 300 Performance
|Author||Topic: Outrage 25 Suzuki 300 Performance|
posted 06-06-2010 12:42 AM ET (US)
Here are [data about the performance of a Boston Whaler OUTRAGE 25 powered by a 300-HP Suzuki four-cycle outboard] that I meant to provide last summer. Life has been hectic, and I'm sorry they are so late.
[Data about the performance of a Boston Whaler OUTRAGE 25 powered by a 300-HP Suzuki four-cycle outboard] were recorded yesterday in Martha's Vineyard Sound. It was fairly calm out, and I ran in what seemed to be an almost slack tide. I did not record these [data] in both directions, because I had a limited window to get to the fishing grounds. I was by myself and did the best I could to record accurate numbers. My boat is a 1985 Outrage 25 re-powered last summer with a Suzuki 300. This year I switched the prop to a 16" x 18-1/2" Suzuki stainless steel three-blade propeller (from a 16 x 20), and raised the motor up to the third hole (from the second hole). I had about 50-gallons of fuel, and a light load. The boat is bottom painted, and I do not have a T-Top.
RPM MPG MPH
posted 06-06-2010 10:22 AM ET (US)
Thanks for the data about the performance of your OUTRAGE 25 with a Suzuki 300-HP engine. I love the fuel economy of the Suzuki engine when running between 25 and 30-MPH. Getting 3.6-MPG with a big boat like a Boston Whaler OUTRAGE 25 is wonderful performance.
What instrument provided the fuel flow rate? I am guessing the answer is the engine itself.
|Tom W Clark||
posted 06-06-2010 12:51 PM ET (US)
Wow! Those fuel economy figures are so good, I am suspicious. If they are valid, I want a DF300 for my 25 foot Whaler.
posted 06-06-2010 08:41 PM ET (US)
Well I have A 300DF on my 22'Outrage with a Whaler drive ... you numbers don't sound to out of line with what I've seen, but I reading off the digital portion of the Suzuki gagues, which are hard to see, especially when running the boat and wearing sunglasses.And never seem to fine the time to top off tank to check the fuel numbers ... just use less fuel than the old 225 Evinrude (major difference).
My 300 came with a 3 blade 16 X 21.5 prop and I've never been able to get more than 5700 RPM ... but my GPS indicates 50+ MPH, depending on the conditions,
I've noticed that I have to trim all the way down on the hole shot or I get prop slip.... all of which implies I really need to change the prop to less pitch ... which I hate to do, since I think it will affect fuel usage. Did you see any change in fuel usage or over rev'ing with the smaller prop?
Believe the motor is mounted in the second hole.
Did you improvements going to the third hole?
I just installed a 30 Bait tank over the one in the floor and installed a transom mounted pump for the tank. Even with the tank empty, I have more prop slip went starting out.. and even worse went the tank is full.
posted 06-06-2010 10:46 PM ET (US)
Let's look at the data more closely. First, we will assume the engine is making 300-HP at maximum throttle. At that point the boat was going 50.5-MPH and getting 2.1-MPG. This means the engine fuel flow was
50.5-miles/1-hour x 1-gallon/2.1-miles = 24-GPH
Now we can figure the brake specific fuel consumption (BSFC) of the engine:
24-gallons/1-hour x 6.25-lbs/1-gallon x 1/300-HP = 0.5-lbs/HP-hour
This is a reasonable figure for the engine, and, actually, is a bit higher than I expected.
Now let's look at the cruising speed data. At 25-MPH we are getting 3.64-MPG, which means 6.9-GPH. We'll need to estimate the horsepower. We can figure the horsepower from the boat speed ratio to maximum. We know speed increases with the square-root of the power increase:
S1/S2 = (P1/P2)^0.5
4 = 300/P2
P2 = 300/4 = 75-HP
Now we again find the brake specific fuel consumption:
6.9-gallons/1-hour x 6.25-lbs/1-gallon x 1/75-HP = 0.58-lbs/HP-hour
A BSFC of 0.58-lbs/HP-hour is very reasonable, and actually is a bit higher than I expected.
|Tom W Clark||
posted 06-06-2010 11:52 PM ET (US)
That's a very good and interesting analysis, Jim.
However, I do not believe that 75 HP will propel a 25 foot Outrage at 25 MPH.
The minimum horsepower required to plane this hull satisfactorily is 115 HP and the minimum planing speed is only 20-22 MPH.
posted 06-07-2010 12:31 AM ET (US)
An alternative method to analyze the horsepower needed at various engine speeds is to use the propeller power curve analysis method. We could make an estimate using a propeller power curve and say that at 5,900-RPM we hit 300-HP. Now we estimate propeller power for a lower engine speed based on the relationship
HP = C x RPM^2.7
We don't know C but we let our data define it:
300 = C x 5900^2.7
Solving for C we get
C = 300 / 5900^2.7
C = 0.000000019761542
Now we solve for HP at 3500
HP = 0.000000019761542 x 3500^2.7
HP = 73.3
I tend to agree with Tom's opinion: you'd think at 25-MPH a Boston Whaler OUTRAGE 25 would need more than 73 to 75-HP to stay on plane. However, we keep getting those figures from our usual methods of analysis.
posted 06-07-2010 12:35 AM ET (US)
For more on the propeller power curve relationship, see
Propeller Power Curve
posted 06-07-2010 07:09 AM ET (US)
Below is a table of data reproduced from Suzuki's test report for the Suzuki DF 300 on a Dusky 233 Open:
RPM MPH GPH MPG
Same 16 x 18.5 propeller is being used. As compared to the Dusky, the Outrage 25 appears to plane at a lower speed. The Dusky has its motor mounted on a bracket.
posted 06-07-2010 08:25 AM ET (US)
The Suzuki DF300 four-cycle engine reported above appears to use more fuel than crow's engine. One explanation for this is that in crow's data we have imputed fuel flow from his data on fuel mileage. His data on fuel mileage may be influenced by the effect of favorable winds, seas, and currents on the speed of the boat.
posted 06-07-2010 09:54 AM ET (US)
Crow, if you come back to this thread, it would be helpful if you would confirm that your speeds are by GPS and in statute MPH, and the fuel flow numbers are from the engine's fuel flow meter.
Thanks for taking the trouble to post your info.
posted 06-07-2010 11:19 AM ET (US)
75 hp may not get the Outrage on plane, but it may be enough power to keep it on plane once the bow wave has been climbed. The 115 hp minimum may be the requirement to climb the bow wave and get the hull planing. Once planing, that 115 hp may be throttled back to 75 hp or so and still keep the boat on plane.
Also consider that just a moderately favorable current can make a difference in these numbers. Even with that, the 300 hp Suzuki seems like an impressive and efficient power plant.
posted 06-07-2010 11:23 AM ET (US)
Whats interesting about these mileage numbers is I don't think this DF300 has the new lean burn changes that Suzuki just announced in Feb that could yield another 15% mpg at cruise: http://www.suzukimarinepress.com/release/000022/EN/
They first introduced the lean burn system in the new DF70/80/90 last year, with the DF90 getting 8-9mpg!
The DF90 is definitely on the top of my list for repowering my classic Montauk.
posted 06-08-2010 03:07 AM ET (US)
Good point about the amount of power required to keep on plane. Using Crouch's Speed Calculator certainly supports the Outrage 25 staying on plane on 73.3hp.
Another thing to keep in mind, the 115hp is the minimum recommended for general use of the boat, not the minimum to plane. My mid-eighties moderately loaded Outrage 18 powered by a 50hp is a good example. Granted it might not get on plane if another 500-700lbs. is added bringing it to maximum capacity. I have no doubt that the minimum 75hp for the boat could easily plane the maximum weight and run 25-30mph.
|L H G||
posted 06-08-2010 11:56 AM ET (US)
[Changed topic of discussion.]
posted 06-08-2010 12:35 PM ET (US)
[Responded to L H G's bait.]
posted 06-08-2010 09:11 PM ET (US)
Fellas--Our discussion is performance. We are not discussing geo-politics, economics, or the social order. Please stay on topic.
If anyone has other reliable data on the performance of the SUZUKI DF300 or any comments about the performance data given above, you are welcome to join the discussion. Please do not enter the discussion only to change the topic
posted 06-08-2010 11:02 PM ET (US)
GTL, I switched to the 16"X18 1/2" prop last August because the engine was only reaching 5500 rpm at WOT with the 16"x20" prop. This prop allowed the engine to reach 5700-5750 rpm. This April I raised the motor up one hole (to the third one up), and I am now reaching 5900 rpm at WOT. I have not experimneted with other props, but I am happy with my current set-up. I don't believe that I am experiencing too much prop slipage.
Jim, I took the GPH #s from the Suzuki gauge then converted them to MPG
Boatdryver, the speed #'s were recored off of my Garmin 545s.
I ran the boat today and recorded these two readings. I was by myself, had a a light load, and had appx. 125 gallons of gas. I was going with a 10mph wind and with the current. (I don't know how fast it was moving.)
5900 2.12 51.62
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