Overpowering OUTRAGE 17

Optimizing the performance of Boston Whaler boats
paramedicjoe
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Overpowering OUTRAGE 17

Postby paramedicjoe » Fri Dec 30, 2016 10:22 am

People over-power boats all the time. [Would buying a new engine for a 1991 OUTRAGE 17 that exceeded the Boston Whaler specification for maximum power] be a bad idea[?]

I drive slowly. I am probably only going to cruise at 40-MPH--no need to go faster. [Would it be] nice to only be at one-half to three-quarter-throttle doing [40-MPH] instead of wide open throttle?

Thank you for your opinion.

BACKSTORY: I have a 1991 OUTRAGE 17. On the original Yamaha V4 115-HP outboard engine, I just found one cylinder is bad. Evinrude is offering a 10-year-warranty on any new motor. I am having a hard time deciding what motor to get. Many forums state there is a concern with the weight of the [outboard engine] but there are no specifications [for a 1991 Boston Whaler OUTRAGE 17] on weight-- only maximum power. When the kids were on the bow [of the 1991 Boston Whaler OUTRAGE 17], I never [thought] the stern felt low enough, and the bow was hugging the water.

jimh
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Re: Overpowering OUTRAGE 17

Postby jimh » Fri Dec 30, 2016 2:13 pm

[Would buying a new engine for a 1991 OUTRAGE 17 that exceeded the Boston Whaler specification for maximum power] be a bad idea[?]


Your question regarding fitting a Boston Whaler boat with an engine that exceeds the power rating for the hull is a frequently asked question. The FAQ section of the website has an answer. Please see

Q6: Can I exceed the rated Horsepower?
http://continuouswave.com/whaler/reference/FAQ/#Q6

As for the goodness or badness of having an engine with power ratings that exceed the hull, such an evaluation is mostly a personal decision. The FAQ tends to stick with the legalities. On all the Boston Whaler boats I have owned, I always had an engine that was less than the maximum rated power for the hull. I do not recall ever being in any circumstances where I felt it would have been an improvement to have more engine power available.

jimh
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Re: Overpowering OUTRAGE 17

Postby jimh » Fri Dec 30, 2016 2:28 pm

[Would it be] nice to only be at one-half to three-quarter-throttle doing [40-MPH] instead of wide open throttle?


Your expectation that 40-MPH ought to be your cruise speed is quite outside my experience in operating small boats.I don't think it is reasonable to expect that a 17-foot boat will be able to sustain 40-MPH as its cruising speed, unless you intend to operate the boat only when the sea conditions are dead calm. If you need a boat that can cruise all the time at 40-MPH, I think you ought to move up a bit, to something like a 32-foot to 42-foot deep-vee offshore boat. You just cannot run 17-foot boats at that speed unless the sea state is exceptionally calm.

As for where the engine throttle ought to be at cruise: the notion of a cruise speed contains the notion that the throttle is not at maximum, but is reduced by some amount. Also in the notion of a cruise speed is the attainment of best fuel economy while still on plane and making good speed. Again, this will almost always be found with the engine throttle not at wide open. So ignoring the notion that your cruise speed should be 40-MPH, I think you will find that almost any boat, and certainly an OUTRAGE 17, will probably produce the best fuel economy when on plane with the engine speed about 60 to 75-percent of maximum engine speed.

A further influence on the cruising speed is the boat's ride and the comfort of the occupants. Although my boat can reach about 44-MPH in optimum conditions, I find that I prefer to run the boat about 25-MPH to 27-MPH as the usual cruising or running speed. The ride is better at that speed and the fuel economy is better.

Discussing the throttle opening is not a particularly good way to describe the engine's setting, as there is seldom any way to know exactly where the actual throttle butterfly is set. It is better to talk about engine power in terms of percentage of maximum engine speed. For example, if an engine is able to accelerate to 5,700-RPM at full-throttle, then what would be considered an optimum engine speed for best fuel economy will likely be around 4,000-RPM. This suggests that the "throttle" is then 4000/5700 = 70-percent. However, I think that you will find that the actual position of the throttle is much lower, probably about 40-percent open. (I actually know this for a fact because my engine reports the throttle position in its electronic instrumentation.) When discussing "throttle," it is probably better to use engine speed figures and not a somewhat hard-to-define position of the throttle plate. Note that the position of the remote control throttle handle can be completely different from the actual throttle. The actuation of the actual throttle by remote handle on the controls is implemented with a cam that imparts a non-linear response. Also with mechanical controls there is often some dead band and slop in the linkage, which further obscures where the throttle plate is with respect to the control handle.

jimh
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Re: Overpowering OUTRAGE 17

Postby jimh » Fri Dec 30, 2016 4:35 pm

When the kids were on the bow [of the 1991 Boston Whaler OUTRAGE 17], I never [thought] the stern felt low enough, and the bow was hugging the water.


Re the trim on the boat when two or more people sit in the bow of an OUTRAGE 17: small boats are very sensitive to weight distribution. If two or more people sit in the very front of a 17-foot boat, the result will be the trim on the boat will be down by the bow. There is really no way to overcome this because the movable weight of the people aboard is a significant fraction of the total boat weight. The best remedy to change the trim of the boat is to move those aboard to different locations.

The influence of weight at the bow has particularly high sensitivity because the cross section of the hull at the bow is usually V-shaped; in order to obtain the necessary displacement of a weight of water to create buoyant force, the hull has to be immersed more into water at the bow than it would at the stern, where the area of hull immersion is usually the full beam or width of the boat, and the immersed portion is much less V-shaped.

flymo
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Re: Overpowering OUTRAGE 17

Postby flymo » Sat Dec 31, 2016 6:46 am

Joe, I think your question is whether it would make sense to overpower your Outrage 17 such that you can run at 40 MPH at 1/2 to 3/4 throttle. The answer is no, it would not make sense. It is hard to say what horsepower you'd need to achieve that, but it is certainly higher than 200 horsepower - maybe much higher. The weight of such a motor would make the boat unmanageable, and you'd burn a ton of gas compared to a properly-sized motor.

"Cruise speed" is generally considered to be the planing speed at which you get the best mileage. On almost all boats in the 15 to 25 foot range that ends up being between 3500 and 4000 RPM and between 23 and 28 MPH. 40 MPH is well above that range - it's not a very comfortable speed in a 17 foot boat. I certainly don't think I'd want to run around at 40 all day.

Regarding the bow down attitude with people up front, have you tried trimming the motor out? I assume your motor has power trim, but maybe it does not. Your new motor will have it, and it should make a difference. If you want still more bow lift, you can change your prop - some designs tend to lift the bow more than others.

All things considered, you may want to look at the E-TEC 115 H.O. That keeps you nominally within your boat's recommended power range in case that is an concern--either for you or someone you want to sell the boat to down the road--while still giving you about 130 real horsepower to work with. That's what I would do in your situation. I am not sure, but I think you may be able to keep your existing controls, which will save you some money.

On the other hand, if you really want to cruise around at 40 all day and put people on the bow with no change in the boat's attitude, I'll quote a certain movie sheriff: "You're gonna need a bigger boat."

Flymo
Last edited by flymo on Sun Jan 01, 2017 3:38 am, edited 3 times in total.

jimh
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Re: Overpowering OUTRAGE 17

Postby jimh » Sat Dec 31, 2016 7:36 am

To assess the horsepower needed to reach 40-MPH at half-throttle, we have to know two elements:

--the power necessary to accelerate the boat speed to 40-MPH

--the amount of power the engine produces at "half throttle" compared to full throttle.

For an OUTRAGE 17 we can make a rough approximation of the horsepower needed by referencing the specification for minimum power recommended by Boston Whaler. This is the minimum power needed to get the boat onto plane. We figure the weight to be about two-times the bare hull weight. Now we go get some data from Boston Whaler:

For OUTRAGE 17 from 1994 catalogue:

Dry hull weight = 1,020-lbs
Minimum HP = 50
Maximum HP = 100

Now we use Crouch's method to calculate a typical boat speed for a boat with the following values:

POWER = 50
WEIGHT = 2040 (double the bare hull weight)
HULL FACTOR = 180 (typical for Boston Whaler moderate V-hull)
Speed Estimate = 28-MPH

That's a good outcome. We know the boat will certainly be on plane at 28-MPH. I suspect our weight figure is a bit too low. But let's go ahead with these values. Now we look for the boat speed at maximum horsepower

POWER = 100
WEIGHT = 2040 (double the bare hull weight)
HULL FACTOR = 180 (typical for Boston Whaler moderate V-hull)
Speed Estimate = 40-MPH

That is an interesting outcome. It looks like an OUTRAGE 17 will only hit about 40-MPH with the rated 100-HP maximum power. Now we turn to the question of the engine power needed to his this speed at "half-throttle."

If we want to be able to reach 40-MPH at "half-throttle" we now need to estimate how much power the engine will have at full-throttle. This is a bit harder to know with real precision. If we just use a linear approximation, then "half-throttle" means half-power; we'd need a 200-HP engine to be able to "cruise" at 40-MPH and half-throttle.

But I don't think that is how it would work. Half-throttle is probably less than half the maximum power. Using some calculations from my experience with engine power, cruising speed, and maximum speed, it looks to me like the ratio of engine power at cruise speed to engine power at maximum speed is not 0.5 as used above, but more like 0.38 to 0.40. Using that proportionality, we'd need an engine with 250 to 263-HP to be able to "cruise" at 40-MPH.

Either estimation, 200 or 263-HP, is very far beyond the maximum power rating for the hull. These power levels are so far above the ratings that I think it WOULD be "bad" to rig the boat with an engine of those horsepowers.

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Phil T
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Re: Overpowering OUTRAGE 17

Postby Phil T » Sun Jan 01, 2017 11:50 am

As a former owner of a 1991 model year and a new owner of a 1992, here is some additional information.

The Outrage 17 I built from 1990-1995 is has a maximum horsepower rating of 120hp. This comes from the actual capacity plate on the boat.

A 115 hp motor with a light load will produce a wide open throttle (WOT) speed of 45mph. Even on calm seas, higher speeds are risky. Where can one cruise at 40 mph for long periods of time?

This model has some unique characteristics that include being sensitive to stern engine weight. I personally don't recommend anything higher than 400 lbs.

This model is also sensitive to bow weight. 2 adults in the bow result in a observable bow down attitude while at headway speeds. On plane is not a problem provided proper engine trim is selected. Below is a photo with myself and my friend Matt (CatBoatSailor) during the Piscatisqua River gathering.

Note there is just the two of us, 50 lbs gear, full tank of fuel.
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