Moving astern - dealing with the left motion of the stern

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cmedsailor

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Hello.
When reversing (astern) on a sailing boat the anti clock wise movement of the (clock wise) propeller will first move the stern to the left until the rudder begins to respond to the movement.
If you try reversing with more power (higher rpm) will the stern move again the same distance to the left but quicker until the rudder begins to respond? I have tried myself reversing both with slow and high speed and I got the feeling that the boat moves the same distance until start responding. Any ideas? Or any idea how to reverse straight?
Thanks

PS: I hope my question is clear because I am not very familiar with the terminology in English.
 
Most single screw boats will do this under power because of the inefficiency of the prop shape in reverse. The time it takes (and therefore the distance the boat travels through the water) before the rudder begins to bite will depend on the size and speed of the prop, and the hull shape. A long fixed keel will resist the sideways thrust better than a modern 'dagger' shaped keel. Also rudderr size and shape makes a difference. But basically you are stuck with it.

Possibly a folding prop might improve things by being more efficient in reverse?
 
The phenomenon you describe is known as prop walk and can be both blessing and curse. There are occasions when it is advantageous to have the stern kick around sharply, but it can also cause problems. If I really don't want the boat to "go over to port" when going astern, I get crew to walk me down the pontoon, with the prop turning gently in reverse. As soon as there is sufficient way on for the rudder to work, the crew member jumps aboard and we're off.

There is a suggestion that if you run the engine astern againt your warps you will develop enough energy to drive her straight back once you cast off, but I've never tried it in anger.
 
Although it seems wrong - it might be better to gently steer in the direction of the propwalk and gently tease it back to centre. What this does is get the flow across the rudder more quickly rather than just stalling it.
 
Give it a burst of power in reverse, then ease off and wait until the rudder "bites" before giving it normal revs.

You could of course buy an Autoprop propeller which on my boats has improved the situation dramatically; on my current boat before changing the prop I always had to exit the berth in astern and then turn where I had more room, now with the Autoprop I can turn the boat inside the 'canal'.

Alan.
 
Initially, point the BOW of the boat at an angle towards the direction the prop walk will take it.
If prop walk turns to port in astern, point the bow to the left.

Then prop walk will allow boat to straighten up in the direction you actually want it to go.

By this time, you will find that your rudder will correct direction, allowing you to control the reverse.

Prop walk will also be of great help when performing a 3 point turn in a confined space.
In this situation, your initial turn would be the opposite to above & away from the direction of prop walk, allowing the prop walk when in reverse to move your stern away in the other direction, pivoting on your centre. Don't bother adjusting rudder when reversing, keep in over in the position you would like the bow eventually to go, letting your prop perform the turn. When your reverse has stopped, into forward & bow should go where you want it.
 
The Osp has twin aerofoil keels and a full skegged rudder. Hopeless at going astern ! I just live with the fact and try to moor where if I have to go astern I can take full advantage of the kick to port !
 
aha, so there is one advantage to having an outboard rather than an inboard. Just point the outboard in the direction you want to go... theres just the rubbish 1" gear lever, the pull start, cavitation in a swell, noise..... oh well...

On other peoples bigger boats I would spring off if prop walk was sucking me onto the pontoon. Once the stern is hanging right out the prop walk pulls you back to midway by which point you should have gained steerage. The best is a drive leg and a big rudder. Bursts of power forward and reverse are very effective.
 
The best technique, I think, is to give short bursts in ahead to kick the stern back onto course. So, as you back up the stern moves off to one side, give a quick burst in ahead, the stern moves back in line, continue in reverse, the stern moves off line, burst ahead, stern moves back in line, and so on.
I achieved some success with this technique; I started practicing it after I watched a skipper back a long keel boat all the way down a long channel in this manner to applause from watching boats.
 
There are two immediate solutions to the problem of prop walk. But first, check how much the stern moves before rearward movement allows you to steer. Do this in open water. Typically, to start from static, the boat may twist 30 degrees with moderate power, 20 degrees with little power.

Solution one is to anticipate this twist. Point the stern 20 dgress to the left of where you want to go, then by the time you're steering, you're pointing correctly so steering is easier.

Solution two can be seen on Sunsail boats in the Ionian! That is, start moving astern a very long way from your destination where the twist doesn't matter, then once you're under way, go gently rearwards all the way into your harbour - and berth.

If you try the latter, remember how your right of way rules work when you're going backwards . . .
 
You either position the boat at an angle so that the initial prop walk straightens it up by the time the rudder starts to bite, or you give a burst ahead on full opposite lock to get the stern swinging, then go slow astern.

The thing not to do is to put the rudder hard over and just give more revs in reverse out of desperation. This invariably simply increases the prop walk, and the cavitation makes both the rudder and the power ineffective.
Boats have different characteristics, but once learned the phenomenon should be seen as an aid to manoeuvring not a hindrance.
 
Having a heavy long keeled boat has meant that going astern was never simple but I was taught that with the boat moving in reverse and at a reasonable speed, turn the rudder in the direction of the prop walk. Then use forward throttle for a short sharp burst. This should not stop the boat but the thrust of water against the rudder will spin the boat back on course.
Works well but needs a little practice.
The same procedure can be used to turn the boat in a very tight space and negate the use of a bow thruster.
 
I'd add that steering backwards gives better visibility in the direction you are moving, and usually (wind permitting) allows for a more precise positioning of the hull in narrow berths (better view, and you enter the wider part of the boat first).
 
[ QUOTE ]
If you try the latter, remember how your right of way rules work when you're going backwards . . .

[/ QUOTE ]

Would you like to remind us? I can't find that bit in the colregs.

Alan
 
It's all part of the whole process of getting to know how your boat responds under power. My normal system is to get the boat going backwards and look nonchalent. She will go where she wants to.
More seriously; prop walk is one factor which you know about and can apply. Short burst in ahead also help.
The other principal factor is wind. Usually the bow blows down wind. You should have a little think before leaving your berth. If it looks dodgy then use a spring to turn th boat or wait till the tide slackens or turns.
There is no earthly reason why you shouldnt proceed out of your berth and the marina in reverse if turning appears difficult. Once the boat is moving hen the prop wash problem largely disappears. The remaining problem is not going too fast in reverse or the tiller may get away from you and bang you on the shins - or worse.
 
Well spotted that man!

There is no reference in colregs to the effect of making stern-way.

However, you should sound three blasts of your horn, or if under 12m and you have chosen not to have a horn on board, you should sound your suitable alternative sound signal.

A prudent mariner may also choose to hoist three shapes in line - ball/diamond/ball (dreamer).

As to whether you should treat your manouevre as converting your stern to 'the front', and port to starboard, the rules are silent . . . but you'll note that most ferries which frequently reverse direction re-define which end is which by swapping their lights around.

So, does 'the stern' become 'the bow', or what?

Well, it was time for a bit of colregs bulls**t, wasn't it!
 
Another factor to consider is the direction of wind and its strength
If the wind is astern, this will aid your reversing as the bow always blows off and will counteract your prop walk somewhat. If prop walk kicks your stern to port, then a crosswind from Starboard will neutralise the effect somewhat, depending on the strength of either, however a strong crosswind from port will make the manoeuvre nigh on impossible.
A strong headwind wil be equally difficult if not impossible, but if reversing with the anchor down Med style then it will be the easiest of the lot, simply let the anchor keep your head to wind by gently paying out as you reverse.

The most important thing is to know how the boat reacts in given situations by practicing the manoevres where no damage can be done. It is important to know for instance if having entered a marina and gone down between the finger pontoons with the wind behind you, whether you boat has a strong enough prop walk to turn around or if it would be better to reverse out if necessary.
If in doubt before you enter take a couple of minutes to get the feel of the boat in the given conditions
 
With some steering systems, reversing can put considerable pressure on the rudder and can cause the rudder to go past it's maximum position, and thus jam. Requires a quick trip below to unlock it.

Philip
 
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