Marina Maneuvers

[Octaman]

Hi guys,

PROP WALK needs to be taken into account ONLY with fixed shaft engines/props (that would be with inboard engines that most fixed keel sailing boats have).

With an outboad the propeler shaft moves with the steering resulting in immediate cancelation of prop walk if steered appropriately.

PROP WALK is NOT an issue when backing with an outboard that turns in any direction required.

Hope this helps.

Happy Power Sailing.

Octaman

[parrothead]

PROP WALK is NOT an issue when backing with an outboard that turns in any direction required.

TRUE -- UNLESS you disconnect and lock your quick-connect rudder linkage in place when trailering, and you are launching at a shallow ramp where you can't drop your rudders, and you forget to re-connect the motor to the steering. Then no matter how you turn your wheel, you back to the side.

Been there.

[MacTommy]

I thought prop walk was a part of the explanation why outboard boats turn better to one side than the other.

But then again, I might have been wrong.

[Russ]

Hi guys,

PROP WALK needs to be taken into account ONLY with fixed shaft engines/props (that would be with inboard engines that most fixed keel sailing boats have).

With an outboad the propeler shaft moves with the steering resulting in immediate cancelation of prop walk if steered appropriately.

PROP WALK is NOT an issue when backing with an outboard that turns in any direction required.

Hope this helps.

Happy Power Sailing.

Octaman

I'm not sure I would agree with this 100%. It is correct that the ability to direct thrust helps, but it does not cancel prop walk. The blade pressure still exists and if used properly can be used for extra advantage. Try it. See which way your boat backs easier.
Another note: I've found my rudders/motor turns further on way than the other. I definitely can turn to starboard further.

[Russ]

I thought prop walk was a part of the explanation why outboard boats turn better to one side than the other.

But then again, I might have been wrong.

Yup.
That's why mine came with a torque trim tab. It adjusts rear prop wash to compensate for sideways blade pressure pulling the wheel to one side.

[seahouse]

(Not wanting to get into a long technical explanation of the sources of prop walk). While prop walk certainly is most dominant and evident in a downward facing fixed shaft of an inboard, those same forces are still in action on the prop of an outboard engine. Engine trim/tilt, lower unit configuration details, and steering etc can be combined to minimze its effect, with the result that it could be quite easy to be totally unaware of it.

There are books and technical papers that explain the effect in detail for anyone wanting to know more.

- Brian.

[bscott]

The Power Thruster on my 9 x 14 prop definately helps with slow speed maneuvering and little evidence of prop walking.

Bob

[Octaman]

Russ MT
Thank you for your comments.

Maybe I should define 'cancels' :
I do not mean that the effect of the turning propeller ceases to exist. Prop walk effect is still there but is neutralized by having the ability to alter the direction of thrust appropriately and setting it at an angle relative to the desired direction of movement. Even if you are backing on the non-favoured side a little more angle and maybe accompanied by a burst of revs will do the trick and allow you to turn equally well in both directions. It is a matter of experimenting and getting to know your boat.

As for the trim tab:
This is of absolutely no significance at low speeds (maneuvering speeds). Additionally the tab is not designed to function when going astern. It is designed to function when cruising forward at high speeds. The shape of the tab and the size of the fin (very small) tell you that. The reason it exists is to put less strain in the steering when you turn your wheel in the direction opposing the torque of the revolving prop (at high revs) when the boat is moving forward at high speeds.

I echo Seahorse/Brian’s posting. I will add that once you understand the principles of physics involved and the effect of the resulting forces, you will find it very amusing to make them work to your benefit.

Naturally, this comes with lots of time on the water and accumulation of experience.

Happy Power Sailing and successful maneuvering.

Octaman

[Russ]

I agree with all of your explanation.

The trim tab only works going forward at higher speeds. My old runabout was missing this tab and it was hard to hold the wheel at high speeds because of the sideways blade pressure. My Mac's trim tab works great to keep the wheel neutral at high RPMs.

And the ability to turn the prop angle is vastly superior to any rudder controls and a huge benefit of our boats.

[seahouse]

Yup to the trim tab for higher speeds.

Also note that for more sensitive steering setups, the tab can really only be in the “ideal” position within a certain given (higher) speed range, and at other (higher) speed ranges it will be less effective. It’s a matter of personal preference which speed range you want to have it set to be most effective in. (Usually at the speed you travel most frequently at).

If there is excessive friction in the steering mechanism, or the friction adjustment is set high, this difference will be less noticeable (such as when you release the steering wheel).

Years ago I was told to “adjust the trim tab in a direction opposite to what you think it should be adjusted to”.

I will rephrase that to more accurately say “adjust the tab in a direction opposite to what you think it should be adjusted to if you don’t study it too closely”.

Play with the tab if you haven't already and you’ll know what that means. Adjust it so that it pushes the back part of the motor in the direction you want it to steer. Intuitive for some people, not so for others.

Got your meaning, Octaman ; agreed -not that it doesn’t exist, but that just being able to compensate with the wheel makes prop walk not a problem.

[Octaman]

All good. Thanks guys.

Whipsyjac, we’re not stealing your thread here. All is relevant to Marina Maneuvers.
Hope you benefit from this; and remember, practice makes perfect.

Go out there on your own so that you can concentrate and not listen to other people's well-intentioned remarks that most of the time are wrong (smile) and just do it over and over again.
Learn to get it right where you have plenty of space to make up for your mistakes without banging the boat into something.

I have to tell you, I always drop the keel half way when going into a harbor or confined space – standard procedure for me – yet, . . . . on occasion, I do forget. With experience and by getting to know your boat you will immediately feel the wide turn the boat goes into and you suddenly realize you forgot the keel up. It takes 3 seconds to lower it and then you are back on track and you have saved the maneuver!

The tough part is getting in on the trailer with a bit of a side wind where keel has to be up all the way. Where I am from, sometimes we need to launch the boat form a primitive ramp on the beach where there is no dock to tie up against in the process. So we cannot take lines and guide the boat onto its trailer which is ideal. In this case, your approach and departure are under power and straight on, straight off.
(That is a bummer because then you need a second person to drive the car and trailer off the ramp to free it for the next guy in queue.) Anyway . . .

There are some good threads on the topic of launching and retrieving that you may want to look up in our great website, the MacGregor Sailor. I remember one suggesting tying two lines, one on each side of the trailer from the ‘goal-posts’ to the front where the ladder is. This helps lead your bow into the ‘groove’. Simple and smart. For me this is now standard procedure too.

Happy maneuvering trials!

Octaman

[mastreb]

Crabbing in reverse is quite normal for Macs, both X and M. I reverse out of the slip routinely, and just ignore the fact that the boat is 30 degrees or so from the direction I'm actually traveling. The boat goes with the wind and current, but the motor goes where I tell it to, and we just agree to disagree until I'm in the channel and moving ahead.

[Catigale]

so is trying to get the boat on the trailer with the engine.

...called 'power loading ' here in the Northeast. Be advised it is usually a frowned upon, if not banned, practice at most ramps in this corner of North America...one reason linked below...


http://www.dnr.state.mn.us/water_access ... ading.html

[RobertB]

so is trying to get the boat on the trailer with the engine.

...called 'power loading ' here in the Northeast. Be advised it is usually a frowned upon, if not banned, practice at most ramps in this corner of North America...one reason linked below...


http://www.dnr.state.mn.us/water_access ... ading.html

I think there may be a difference between driving the boat onto the trailer (as shown in the Macgregor promo material) as opposed to gunning the engine from a stop to force the boat up onto the trailer (this is what I consider power loading). Reason is the effect on the lake/river bed below. Approaching the trailer directly instead of using the dock has no effect below. Revving the engine from a stop causes alot of turbulence that digs up the bottom (now I am thinking about a trailer mod to go from two axles and wheels to tracks ).

[Catigale]

Idling up to the trailer under motor power is fine, correct. Pushing up the bunks or rollers with engine power is the bad practice....