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post #1 of 19 Old 06-07-2016 Thread Starter
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docking with different engine setups

This may belong some place other than where im posting.

Looking for input on How different engine setups affect reversing, for instance, into your slip.

Im familiar with inboard engine reversing and "prop wash" however what about those with outboard motors, how do they tend to reverse? do outboard motors have the same prop wash, or is it less severe?

how do outboards mounted on brackets behave on larger boats? what about outboards mounted on brackets that are off-center?

on my siren 17, quite a small boat, i had a 2.5hp that could rotate 360* so it was no issue to get it to behave in any way needed, not to mention it was well under 2000 lbs
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post #2 of 19 Old 06-07-2016
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Re: docking with different engine setups

I've found outboards tend to have much less "prop walk" (I'm thinking that's what you mean by "prop wash", ie the side force of the prop?) than inboard propellors, maybe because outboards are up in "thinner" water pressure. Also outboards can (usually) rotate, so the steering ability trumps any prop-walk.

Off-center doesn't seem to matter that much, I don't know why.
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post #3 of 19 Old 06-07-2016
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Re: docking with different engine setups

IMO, the main reason why you don't get nearly as much prop walk effect with an outboard engine as you do with an inboard is because the prop on an outboard engine usually doesn't interact with the rudder. With an inboard engine, the prop is usually situated forward of the rudder. When the prop turns, it pushes or pulls a flow of water over the rudder's surface, and, when the rudder is turned, that flow creates pressure on one side of the rudder, tending to push the stern in the opposite direction. Consequently, you have the combined effect of prop walk and prop wash.

The prop on an outboard engine is usually situated aft of the rudder, and often to one side or the other of it, and prop wash doesn't interact with the rudder.

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post #4 of 19 Old 06-07-2016
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Re: docking with different engine setups

I was taught any engine, out board, in board, what ever that rotates on the truly horizontal axis will have minimal or no prop walk. Motor boats with two counter rotating props with have none.

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post #5 of 19 Old 06-07-2016
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Re: docking with different engine setups

I don't think you get a lot of prop walk with outboards, mainly because many outboards in reverse are working in a mass of exhaust bubbles and don't get a good enough 'bite' to really 'walk'.

The steer-ability of outboards is useful if you can easily reach it and still see where you're going, which isn't always the case. Docking often doesn't end well when the helmsperson is butt-high and looking at the transom on approach I've seen some clever rudder and outboard linkages so you can turn both with the tiller.

I don't think an off center outboard significantly affects how the boat behaves..

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post #6 of 19 Old 06-07-2016
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Re: docking with different engine setups

All good answers as the Boats are usually designed around either one or the other. Its when you try to get by with an outboard when the inboard gives up that you get in trouble. I've seen it tried on some awfully heavy Boats.
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post #7 of 19 Old 06-07-2016
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Re: docking with different engine setups

Hey,

I think it's hard to generalize.

My first boat was a Catalina 22 with a small OB. Controlling the boat under power was challenging. Reaching back to adjust the throttle, shift into gear, steer with tiller or OB was not easy. I also wasn't that experienced, so docking was stressful.

Next boats were inboard diesel with shaft and fixed blade props fun keel and balanced rudder. Lots of prop walk, backing up took practice. I liked the prop walk for docking - I tried to use it like a stern thruster.

My current boat has a saildrive and folding prop, deep keel and balanced rudder. This boat goes straight forward and straight backwards. No prop walk, very easy to control.

My buddy has a heavy cruiser with inboard diesel, prop in an aperature, full keel. That boat goes straight like crazy but is almost impossible to back up. It goes a certain way in reverse, and you are just along for the ride.


Good luck,
Barry

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post #8 of 19 Old 06-07-2016
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Re: docking with different engine setups

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Originally Posted by outbound View Post
I was taught any engine, out board, in board, what ever that rotates on the truly horizontal axis will have minimal or no prop walk. Motor boats with two counter rotating props with have none.
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I don't think you get a lot of prop walk with outboards, mainly because many outboards in reverse are working in a mass of exhaust bubbles and don't get a good enough 'bite' to really 'walk'.

The steer-ability of outboards is useful if you can easily reach it and still see where you're going, which isn't always the case. Docking often doesn't end well when the helmsperson is butt-high and looking at the transom on approach I've seen some clever rudder and outboard linkages so you can turn both with the tiller.

I don't think an off center outboard significantly affects how the boat behaves..
Prop walk is caused by the angle of the prop to horizontal, as well as the fact that the lower half of the prop is what produces the most thrust, because of water flow near the hull, versus further from he hull (hence a saildrive being better, and outboards as well)

My knotmeter started working the other day. Turns out I'm faster when it's not working.
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post #9 of 19 Old 06-08-2016
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Re: docking with different engine setups

Angle of the prop from horizontal is only part of the equation. With an inboard, the prop is usually under the hull, and the hull interferes with flow around the prop. That also contributes to prop walk. With an outboard on the transom, usually the motor is horizontal and the prop is not under the hull, so neither of these factors apply and there is no prop walk. If the outboard is in a well the prop is under the hull so there may be a little walk.
With an inboard with the prop forward of the rudder (on my Columbia 36 the prop is aft of and above the rudder so none of this applies), in forward gear the slightest touch on the rudder counteracts any prop walk so you don't even notice it. In reverse the rudder has no effect on the prop at all so prop walk can take over control completely. With outboards this is less pronounced but still can sometimes be felt to some extent. There's really too many variables to make any generalizations. You just have to practice and learn how your particular geometry behaves.
One trick that I found very helpful on my first boat that had the outboard mounted along side the outboard rudder was to put a linkage between the motor and rudder so the motor turned with the rudder. That was the best handling sailboat under power I've ever owned but it was also the smallest which helped. You don't want the two connected when sailing though as the weight of the motor will effect the steering when heeled over.
My current boat with the prop sticking out aft of the rudder is a real b**ch to handle under power. I'm a professional mariner, I handle big boats for a living, and that sailboat has embarrassed the hell out of me on a few occasions. Except for the stopping part that boat would be easier to dock under sail. I love a challenge.
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post #10 of 19 Old 06-08-2016
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Re: docking with different engine setups

Outboards are very hard to take in slow. They stall and so you have to guesstimate how much you'll slow down. sometimes this works sometimes you com in too fast. An alternative if you have the money is a Torqeedo. With this you can come in very very slowly, and it will never stall.
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