Prop walk

[cliffordpope]

Is my boat a long-keeler?

I ask because all threads on these forums seem to assume that long-keelers are the worst of all boats for steering astern.
Yet I was experimenting at the weekend, and confirmed that on my boat, prop-walk simply does not exist. If Xenia is stationary in the water, and I engage astern, the stern immediatey follows the direction I point the rudder. It is exactly like driving a car. If I put the rudder hard over she does a tight turn, or midships she goes straight.

Is this unusual? Why?

 

[sarabande]

She has a short-coupled turning axis of about 2 to 3 m, and a relatively large rudder area. It's easy therefore, for the rudder to exert a strong influence on the required direction of turn.

What neat and attractive lines; she looks like a fine little lady.

 

[Poignard]

I reckon that Sarabande is right. My Twister is nowadays regarded by many as a 'long-keeler' but in proportion to your boat it isn't at all. Although it is sometimes possible to coax her in some general direction astern it certainly can't be called 'steering' and I reckon this is mainly caused by the long narrow rudder being masked by a fat keel.

 

[mylo]

Doesn't the prop coming through the centre line make a huge difference to how boats handle astern?

 

[cliffordpope]

Yes, I'm sure having the prop in the centre helps enormously - I can see that with a quarter installation there isn't a hope of getting any useful steerage until the boat has picked up speed. But even centre-prop boats are reported as experiencing prop-walk.
I'm just curious to know what Xenia has that is different.

How do you work out the close-coupled turning axis of 2-3 metres? The keel is virtually straight, and slopes upwards from a draught of about 3 feet at the rudder post to about a foot just behind the stem post. The Centre of Lateral Resistance, by calculation and observation, is about half way along the overall length, or 10 feet back along the waterline length which is about 18 feet (the stem is plumb).

I had assumed that a characteristic of a long keel is that the boat wants to plough on in a straight line. That is certainly the case under sail. Experimenting at the weekend (new mainsail with the aft overhang cut down) she was perfectly balanced, with very little correction needed from the rudder. Close hauled I could let go of the tiller and she maintained her course. Coming about was straightforward once I learned to release the jib instantly, but maintain the main hard in to drive her round.

Under power the handling characteristics are completly different. She will swizzle round in about twice her length, forward or astern, and coasting in neutral will steer any course as long as way remains. The prop aperture is no larger than necessary, and is entirely in the deadwood, with a straight rudder post, which has only a slight rake.

I am learning all this anew, having last sailed her 25 years ago when the mast was much too far forward and the engine had no astern. So I was expecting to find the much-discussed prop-walk, and instead found none!

 

[Simon_and_Tanja]

Interesting

Our Stella has an almost identical profile to the Twister and I find the only surefire way to steer in reverse is by having a piece of rope attached to something ashore. If there is any breeze at all she weather-cocks pretty quickly and there is nothing in the reverse direction that can be done about it.

Immediately obvious differences are you have a plumb stem and we a spoon bow, you have a big broad rudder and we have a tall narrow little thing, your rudder post is near vertical and our transom mounted rudder is at a significant angle...

I suspect it is the last aspect that makes a big difference - might try a few experiments with the kids toys in the bath tonight

Never really noticed any of this much fabled propwalk on my boat ???

 

[Poignard]

Never really noticed any of this much fabled propwalk on my boat ???

Nor I on the Twister. Bow windage dictates what happens.

However, I find that prop walk does become noticeable (and sometimes useful) if the boat is moving slowly ahead and astern gear is engaged. This swings the stern to port(right-handed prop).

I use this when picking up a mooring by approaching so that the buoy is just off the starboard bow (where I can see it) and then by putting the engine astern the bow swings to starboard towards the buoy and, as the boat stops, the Old Guvnor (if she's awake) can just drop a loop of rope over it.

If she makes a bog of it I just leave the engine in astern and the boat pulls clear of the buoy and then (after a bit of swearing) I go ahead and have another go.

 

[bakermargar]

Ethel: You always have some smart a** answer to every question........whats up with that?????

2 years ago
what am i? : you should not be a human being, if your gonna be rude don't answer my questions THANKS! : )