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Do single versus dual outboards rule of thumb still apply??

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View Poll Results: Single Yamaha F300 or dual Yamaha 150's?
Yamaha F300
42.06%
Dual Yamaha 150's
57.94%
Voters: 126. You may not vote on this poll

Do single versus dual outboards rule of thumb still apply??

Old 10-20-2012, 09:44 AM
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Default Do single versus dual outboards rule of thumb still apply??

I have always accepted the statement that if you were offshore fishing, lets say average 25 miles, that it is better to have two smaller outboards than a single larger one. Obviously if the boat is over a certain size then the is a moot point because the boat is going to require multiple engines.

With that being said, I have decided to go with the single Yamaha F300 over dual Yamaha 150s for my new Sea Fox 256. I have concluded that the motors are reliable to a point that having a single with better mpg and maintenance costs outweigh the added benefit of two engines.

What's your take?
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Old 10-20-2012, 09:48 AM
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Murphy's law still applies.
25 could encourage you to go 40.
Use twins for offshore unless you have a sat phone and sea tow.
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Old 10-20-2012, 09:52 AM
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Originally Posted by deltarome View Post
Murphy's law still applies.
25 could encourage you to go 40.
Use twins for offshore unless you have a sat phone and sea tow.
I agree with Murphy's Law. I am in the fighter aviation community and have a two engine background. I am now flying a new aircraft with a single engine. The selling point for the single engine was that it was so reliable etc etc. As a pilot I would rather have two, but as a weekend boat operator I think the added risk is offset with sea tow etc.
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Old 10-20-2012, 09:54 AM
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My take it that it is more about tolerance to risk than motor reliability.

Some won't get in a boat at all.
Some won't get in a boat in saltwater.
Some one go offshore (whatever that means) with less than two or more motors.

What is your tolerance for risk?

Some won't fly in airplanes. Then there are the Felix Baumgartner's of the world.
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Old 10-20-2012, 10:01 AM
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Originally Posted by adamg41 View Post
I agree with Murphy's Law. I am in the fighter aviation community and have a two engine background. I am now flying a new aircraft with a single engine. The selling point for the single engine was that it was so reliable etc etc. As a pilot I would rather have two, but as a weekend boat operator I think the added risk is offset with sea tow etc.
Are you flying F16's or maybe the new F35?

You are probably not old enough to remember when airplanes "needed" four (or more) motors. Then they went to three. Now they are down to two, crossing the Pacific and the Atlantic oceans.

From a reliability standpoint, a single engine fighter is more reliable than a twin engine fighter. However, there is a big difference if and when the one motor fails. And then there is the issue of flying a single over land versus over water, far out of gliding to land range.
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Old 10-20-2012, 10:03 AM
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I chose 2 engines, and 2 of everything else ( radios, gps, depth finders, fuel tanks) and 2 EPIRBs. If I go to the canyon 70 miles out) I want to be able to get help in a hurry or have redundancy in my systems to help myself. I subscribe to the theory that 1 is none and 2 is 1.
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Old 10-20-2012, 10:10 AM
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Originally Posted by jethro1 View Post
Are you flying F16's or maybe the new F35?

You are probably not old enough to remember when airplanes "needed" four (or more) motors. Then they went to three. Now they are down to two, crossing the Pacific and the Atlantic oceans.

From a reliability standpoint, a single engine fighter is more reliable than a twin engine fighter. However, there is a big difference if and when the one motor fails. And then there is the issue of flying a single over land versus over water, far out of gliding to land range.
F18 to F35. Funny that with two engines my experience is that pilots invariably add risk by knowing they have redundancy, which ultimately puts them in a more precarious position. Look at mishap rates f16 versus f18 over the years. In addition multi engine fighters are more complex in the emergency procedure matrix, which induces more pilot error versus single engine...."if this occurs, do this, now" type of decision matrix. That's just one man's $.02.

Ok, back to boating.....
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Old 10-20-2012, 10:12 AM
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Originally Posted by marty grady 272 View Post
I chose 2 engines, and 2 of everything else ( radios, gps, depth finders, fuel tanks) and 2 EPIRBs. If I go to the canyon 70 miles out) I want to be able to get help in a hurry or have redundancy in my systems to help myself. I subscribe to the theory that 1 is none and 2 is 1.
True, but there is a cost versus risk equation involved. So would you still choose two of everything if the average run offshore was about 20 miles and use also included family boating in the bay?
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Old 10-20-2012, 10:19 AM
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I'd go with the single if it had better mpg. Sea Tow + proper safety equipment/practices was good enough for me. I had a single F225 and would go 40+ without thinking about it.
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Old 10-20-2012, 10:25 AM
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Let's start with your initial assumption on better mpg. I used to think the same, but pull up any boat tests on the same hull with singles vs twins, and you'll see the twins actually do a little better on average. There is added lower unit drag of course, but also a gain in propulsive efficiency (pushing 2 columns of water vs. one), no torque steer that requires both a torque tab and trim tab to correct (else run with boat leaning, and either way suffer the drag penalty), and you get stern lift from the counter-rotation.

There are still negatives to twins, primarily added initial and maintenance costs, and added weight.

Everything else is in favor of twins. Boat also drives better, with no roll when you go airborne, and better maneuvering at the dock.

It's also safer. Another motor does reduce overall reliability (more things to break), but now you can lose an entire motor and still come home on your own (best if you can plane on 1 engine).

The aviation equivalent (as mentioned above) is dropping down to 2 engines for over-water flights, requiring a special cert (ETOPS). Do any but military aircraft fly these routes on a single engine?
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Old 10-20-2012, 10:31 AM
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Wait a second - new information has come to light since my previous post in that you are an F-35 pilot:

If you are flying the non-STOVL version, go with two engines.

If you are flying the STOVL version with a 3-bearing swivel nozzle and a lift fan just behind your seatback driven by a big angry military turbofan at military power, through a clutch, you'll be just fine with the single.
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Old 10-20-2012, 10:34 AM
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I think one reliable of any item is better that two so so quality items. Is the motor well maintained good service.
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Old 10-20-2012, 10:39 AM
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Originally Posted by WaterDamage View Post
Let's start with your initial assumption on better mpg. I used to think the same, but pull up any boat tests on the same hull with singles vs twins, and you'll see the twins actually do a little better on average. There is added lower unit drag of course, but also a gain in propulsive efficiency (pushing 2 columns of water vs. one), no torque steer that requires both a torque tab and trim tab to correct (else run with boat leaning, and either way suffer the drag penalty), and you get stern lift from the counter-rotation.

There are still negatives to twins, primarily added initial and maintenance costs, and added weight.

Everything else is in favor of twins. Boat also drives better, with no roll when you go airborne, and better maneuvering at the dock.

It's also safer. Another motor does reduce overall reliability (more things to break), but now you can lose an entire motor and still come home on your own (best if you can plane on 1 engine).

The aviation equivalent (as mentioned above) is dropping down to 2 engines for over-water flights, requiring a special cert (ETOPS). Do any but military aircraft fly these routes on a single engine?
Thanks for the input.

STOVL so the whole two engine debate is moot. Coming from a traditional wing lift aircraft a lift fan is still nuts to me!
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Old 10-20-2012, 10:39 AM
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Originally Posted by Bugsbunnyboater View Post
I think one reliable of any item is better that two so so quality items. Is the motor well maintained good service.
the f300 will be brand new.
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Old 10-20-2012, 03:43 PM
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What about the single motor for regular running and a mothballed 15hp or so in a bag to get you home eventually if the other one fails?
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Old 10-20-2012, 04:27 PM
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On a 25 foot boat, two props applying 1/2 of the same total HP to the water is better than one applying all of the same total HP.

It's like which is better in the snow, one wheel drive or 4 wheel drive? Twin outboards on a 25 footer is like having 4-wheel drive in the snow. The boat will track better in the rough stuff.
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Old 10-20-2012, 06:02 PM
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Originally Posted by gfretwell View Post
What about the single motor for regular running and a mothballed 15hp or so in a bag to get you home eventually if the other one fails?
Yeah, a kicker would be a good thing for offshore. The Yamaha T9.9 is enough for light conditions. Button up and throw out the sea anchor if things get dicey.

More HP will do better in heavy weather, but selecting the right engine gets tricky. If your transom layout will work with a 20" shaft you have a bunch of options. If you want to stick with Yamaha, then the T25 might be a good choice (~200 lbs dry weight...).

If you don't mind mixing brands, then the Suzuki DF40A, at ~230 lbs, looks really nice. While it's not marketed as high-thrust, it does have a 2.27:1 gear ratio (compared to the typical 2.33:1 of most of the brands/models marketed as high-thrust), so just re-prop it.

Most of the 15-25HP models available with 25" shafts weigh in around ~280lbs.
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Old 10-20-2012, 06:42 PM
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I just like the look of a twin engine wake! As far as the OP's question goes, yes the F-300 is one heck of a machine. Well maintained, it should give you few if any issues.

PS: I voted for twins!

Last edited by dm; 10-20-2012 at 06:55 PM.
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Old 10-20-2012, 10:07 PM
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I was a pilot in a previous life, but I never made a connection between aircraft and boats. Lose all your power in a boat and it's a pain in the ass, but probably not immediately life threatening. Loose all your power in an aircraft and you're an aerodynamic rock, some being less aerodynamic than others ...
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Old 10-20-2012, 11:50 PM
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Why put up a poll?

your mind was made up before you ever posted.....
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