1994 OUTRAGE 24 250-HP

Optimizing the performance of Boston Whaler boats
cwdave
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1994 OUTRAGE 24 250-HP

Postby cwdave » Sun Apr 19, 2020 10:01 pm

I have a 1994 Outrage 24 that has been re-powered with a 2005 Yamaha F250 engine. I run the OUTRAGE 24 in southern California, and it is set up for fishing. The original 195-gallon fuel tank was changed to a 131-gallon plastic tank. There is a small tower on this OUTRAGE 24 that is, essentially, an overbuilt T-top with a hoop up top so we can look for birds. There is no upper control station, but the small tower definitely adds weight compared to an OEM T-top.

With the 2005 Yamaha F250 engine I am generally getting over 2-MPG fuel economy. When the OUTRAGE 24 is loaded for fishing with three guys, full 50-gallon bait tank, full 131-gallong fuel tank, ice, and so on, [the boat speed] gets slower. The OUTRAGE 24 will still cruise along at greater than 20-nautical-miles per hour [greater than 23-MPH]. Some round trips will be greater than 150-[nautical] miles, and insufficient fuel capacity has never been a concern. As [the total weight of the OUTRAGE 24] lightens up, the boat speed increases some.

Often, I am running much lighter and with not a full 131-gallons of fuel. When running really light, I calculed 3-MPG. All in all, great efficiency.

I would like to pick up some boat speed.

TEST PROCEDURE
I recently ran the OUTRAGE 24 and marked specific speeds. I also made runs at full-throttle in calm water to make sure I was getting [the 2005 Yamaha F250 engine] to accelerate to full rated speed. Below is what I found. All speeds were [speed over ground] from a GPS and fuel flow rates were from the Yamaha instrumentation. The intervals of engine speed are close because when I found a section that the RPM and nautical-miles-per-hour boat speed stabilized, I wrote down the data, hence 4500 and 4600 RPM. I also trimmed up the engine, and the trim tabs were all the way up.

ENGINE MOUNTING HEIGHT: The engine is mounted as high as it can go.

TEST CONDITIONS
The fuel volume was greater than 25-gallons; the bait tank was empty; only I was aboard. I consider this condition to be a light load. The data was taken was in the Pacific Ocean on a sunny 75-degree-F day with waves one-foot.

PROPELLER UNDER TEST: The propeller is Yamaha SWS II 17M. I don't know know the diameter, but it may be 15-1/4-inch.

PERFORMANCE
RPM          GPH   NMPH     MPH     MPG
4200 8.5 23.6 27.1 3.2
4500 9.6 25.6 29.4 3.1
4600 9.8 26.7 30.7 3.1
6100(WOT) 37 42.6


GOALS
I don't care about boat speed at full-throttle. I only tested at full-throttle to see what maximum engine speed would be with the Yamaha SWS II 17M propeller under test. I would like to pick up speed in the mid-range so I can cover more distance a little quicker.

Q1: Is the Yamaha SWS II 17M propeller correct for this application?

Q2: Is the performance (given above) all I can expect with this boat-engine combination?

Please impart your collective wisdom as I would welcome hearing some some thoughts on propeller options.

Thanks in advance.
Dave

jimh
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Re: 1994 OUTRAGE 24 250-HP

Postby jimh » Mon Apr 20, 2020 9:16 am

What is the gear ratio of the Yamaha F250 engine?

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Phil T
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Re: 1994 OUTRAGE 24 250-HP

Postby Phil T » Mon Apr 20, 2020 9:27 am

The 1994 OUTRAGE 24 l weighs 3100-lbs dry (which means without an engine or fluids). The minimum and maximum power ratings are 200 to 400-HP.

I am not sure sure I understand your question. [Your are] pleased with MPG, [and your are] interested in mid-range boat speed.

Is [the MPG or boat speed when the boat is] loaded or light?

The MPG is good so why not just increase engine RPM?

Also with fuel prices at a 15-year-low, the payback period [for a new propeller] will be quite long.

I think your performance is actually quite good given weight, T-top. and mid-range horsepower. I don't think changing a propeller will give you significant improvement at mid-speed.
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jimh
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Re: 1994 OUTRAGE 24 250-HP

Postby jimh » Mon Apr 20, 2020 9:28 am

I am very impressed with your report of fuel economy greater than 3-MPG (statute miles) for a 24-foot moderate V-hull boat with 250-HP engine. For me that seems like excellent fuel economy at moderate planing speeds. I really am surprised at that data. I would not have expected the fuel economy to be above 3-MPG.

On that basis, I think your present propeller is working well.

On my 24-foot boat with 225-HP engine, I have tested many propellers. The best propeller for overall use, including best speed and best fuel economy at cruise, was a three-bladed large diameter low-rake propeller. I presume that is likely a good description of the propeller you have now.

In order to get more boat speed at "mid-range" you just need to increase the engine throttle setting.

jimh
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Re: 1994 OUTRAGE 24 250-HP

Postby jimh » Mon Apr 20, 2020 9:44 am

From your data:

GPH = 8.5
NMPH =23.6
NMPG= 2.77
GAL = 131

I can calculate range as 363-NAUTICAL-MILES. As your round trip is only 150-NAUTICAL MILES, you have excellent fuel reserve.

cwdave
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Re: 1994 OUTRAGE 24 250-HP

Postby cwdave » Mon Apr 20, 2020 11:29 am

Thanks all for the replies. Here is some additional information

Based on my research, I believe that engine has a 2:1 gear ratio.

The engine is mounted as high as it can go and doesn’t have any blowout. Nor does it appear to be mounted too low.

Perhaps I am getting all I can out of the boat-engine-propeller combination. The efficiency is great. Assuming my fuel flow meter is accurate, I can get 3-MPG--which is good.

I have thought about upgrading to the F300 engine but not sure how much of a performance gain I would get.

Has a four-blade prop been used [on 1994 OUTRAGE 24]?

With the current 250-HP would [a four-bladed propeller] give 1994 OUTRAGE 24 with 250-HP any benefit?

Has a Yamaha F300 or F350 been rigged on a 1994 OUTRAGE 24?

I am familiar with the flywheel failures on the F350, but as a result, you can find them cheap.

What performance would occur with an F350?

Thanks again. Dave

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Re: 1994 OUTRAGE 24 250-HP

Postby jimh » Mon Apr 20, 2020 2:16 pm

DAVE--I have no knowledge about what engines have been rigged on a 1994 OUTRAGE 24. Since it is rated for 400-HP, I am sure that some OUTRAGE 24 boats are rigged with more than 250-HP.

Regarding the effect of increased horsepower on boat speed: all boat speed is in proportion to power-to-weight ratio to the 0.5 exponent. If engine power is increased to 350-HP from 250-HP, and if the weight remained the same, then the power-to-weight ratio change would be proportional to 350/250=1.4. The speed increase would be 1.40.5 or 1.18-times.

For your reported top speed of 42.6-MPH, the expected increased speed would be 42.6 x 1.18 = 50.4-MPH.

FIguring speed increase with 300-HP is left for an exercise for the reader.

Of course, you MUST factor in weight. Usually engines with more power are heavier. The added weight reduces the speed increase.

Also, I have no knowledge of what possible four-blade propellers may have been used on a 1994 OUTRAGE 24. Many people believe there is a magic quality to a four-blade propeller, and I have no doubt that someone who has a 1994 OUTRAGE 24 must have tried one. As I mentioned earlier, I have always found the best performance from three-blade propellers.

You seem to be determined to make a change. If you want to buy a new engine or a new propeller, you should buy them. It may not be entirely rational, but what the heck, boating itself is not entirely rational.

conch
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Re: 1994 OUTRAGE 24 250-HP

Postby conch » Tue Apr 21, 2020 9:56 am

The Yamaha SWS II 17-pitch propeller diameter is 15.5-inches, and the suffix is T, not M. I am not clear what propeller you have.

The boat seems to be running well now.

Try a magical four-blade--but I doubt performance will improve much or the engine will be able to accelerate to 6100-RPM.

A Yamaha F300 has a gear ratio of 1.75:1; the F250 has a gear ratio of 2.00:1.

Picking a propeller is half math and half magic.

I think it will be hard to improve the performance from what you have already. The engine is only 250-HP. The Yamaha F350 would be interesting re-power, but yhr F350 would need different rigging.

I prefer a [power-to-weight] ratio of 10-HP (or more] to every 100-lbs of bare hull weight.

Chuck

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Re: 1994 OUTRAGE 24 250-HP

Postby biggiefl » Tue Apr 21, 2020 11:48 am

What is max rpm of the F250?
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

jimh
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Re: 1994 OUTRAGE 24 250-HP

Postby jimh » Wed Apr 22, 2020 12:04 pm

conch wrote:I prefer a [power-to-weight] ratio of 10-HP (or more] to every 100-lbs of bare hull weight.


That is an interesting metric for setting a baseline for engine power for a hull. Let me test that with a few other models:

MODEL / DRY WT ---> power at 10-HP per 100-lbs
MONTAUK 17 900-lbs ---> 90-HP (rated 100-HP maximum)
OUTRAGE 18 1,250-lbs ---> 125-HP (rated 150-HP maximum)
OUTRAGE 22 2,050-lbs ---> 205-HP (rated 240-HP maximum)
OUTRAGE 25 3,300-lbs ---> 330-HP (300-HP maximum)

and for the boat under discussion

OUTRAGE 24 3,100-lbs ---> 310-HP (rated for 400-HP)

cwdave
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Re: 1994 OUTRAGE 24 250-HP

Postby cwdave » Thu Apr 23, 2020 3:27 pm

A metric of 10-HP for every 100-lbs of dry hull weight is interesting. Perhaps I just need to add more power.

Again, [the performance of the 1994 OUTRAGE 24 with 250-HP is not] bad.

Since we are in quarantine and I'm spending way too much time on-line researching such things, I am [still looking for data] for a 24 Outrage (1994 to 1998) with a single outboard of 300-HP or more.

JSK55
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Re: 1994 OUTRAGE 24 250-HP

Postby JSK55 » Wed Jun 10, 2020 11:46 pm

A late reply: I run a Yamaha 250 Ox66 two-stroke-power-cycle engine on my 1994 24 Outrage. I run two different propeller: a three-bladed Yamaha SWS stainless steel 19-pitch, and a three-bladed Mercury MIRAGEplus 17-pitch.

With Tom Clark’s help we ran several tests at different engine heights. We found the engine mounted three-holes-up was the optimum height. At this height there was no discernible improvement between either propeller. Maximum engine speed was attained with either choice. And performance at all engine speed ranges was so close it’s hardly worth a mention. I hope this helps.

Also, I can assure you the fuel economy of my 1994 24 OUTRAGE is nowhere near 3-MPG with my 250-H two-stroke-power-cycle engine set-up--probably no surprise. My boat's fuel economy is closer to 2-MPG or less.

Maybe someday I’ll re-power with new technology and see that 3-MPG figure. I’m jealous.