Does your narrowboat pull to the right ?

Question

Hi Boaties,

Mine does, and no-one has a decent solution

OK, ignore engine / prop torque, that is for ski-boats

Rudder misalighnment - no, it it is fine

What on earth causes the fine beast to veer off if the tiller is left alone for a moment to grab of beer.

It always heads for the right side of things, in an alarming manner

I have got used to it, but >

Any notions ?

Bob the Boat

Answer 1

I had a Davison Brothers Cutwater NB built 1988 and even with her keel she used to pull to the right but only slightly,,in reverse it was like trying to manoeuvre a tank sideways,,but as for the pull right you and I experienced I always assumed it was the prop,however like you I soon got used to it,,

Answer 2

no comments

Answer 3

It is prop torque.  Happens on every motor.  There is a small adjustment near the prop to help correct this or you can adjust the tension on the motor.

Answer 4

we have heard various possible reasons,engine alignment, too short a rudder,but what if the rudder wasn't sitting central when you let go?.also what if the boat was badly balanced,lopsided,surely this would also cause it.

Answer 5

what boat engine/ combo do you have make and model

Answer 6

Hi Bob,

Mine does the same. I kill the throttle, even knock the prop into neutral yet still it veers to the right.

Takes about 6 trips below deck to make a drink, hence the narrow boat owners dependancy on cans of beers rather than tea.

Answer 7

Mine bends to the left

Answer 8

your motor must not be centered

Answer 9

It is a phenomenon called (believe it or not) 'paddle-wheel effect'. This is distinct from propellor torque - small, high-speed propellors have so much power delivered to them so quickly by the engine that it (the engine) tends to push (lean) the vessel over in the opposite direction from the propellor, causing it to list to that side but not 'veer' to that side. It is only a problem on small, high-speed single-engined craft. On twin-s***w vessels the effect is eliminated by counter-rotating propellors which cancel each other out. It is reduced on small vessels by placing the helm on the 'high' side, so the weight of the person at the controls helps offset it.

Paddle-wheel effect is different. It is typically associated with much larger, slower moving propellors such as those found on narrowboats. Rather than push the vessel over to one side, as with propellor torque, it pushes its stern to port or starboard (around, not over. Affecting steering, not stability). It is much more noticeable when going astern, as opposed to forward.

Paddle-wheel effect is a result of the fact that pressure increases significantly with depth (technically 'head' - the amount of 'head' of fluid above the point in question). In this case the point, or points, in question are the propellor blades. Blades at the bottom of their rotation are subjected to greater pressure from the water than blades at the top, therefore enabling them to produce more force than those at the top.

The net result is that the stern has a tendency to slew around, just as if it had a paddle-wheel driving it across at 90 degrees to the keel of the vessel, even though the 'paddle-wheel' in this case is totally submerged, not mostly above the waterline, as on 'stern' and 'side-wheelers'. In addition to pressure alone, propellor blades are never 100% efficient, producing ONLY forward or ONLY backward force - some of their effort actually is expended in 'paddling'.

In fact, on some single s***w cargo ships - particularly oil tankers - when they are empty, the propellor is very much exposed above the waterline and they experience extreme paddle-wheel effect. For most journeys in big tankers not actually loaded with cargo, sea water is loaded in its place, to submerge the propellor again and  reduce the effect.

Unfortunately the only things that helmsmen and women can do is learn to live with it and to use it, along with other factors like wind and current, to their advantage - that is, be mindful that while turns in one direction will be assisted by the propellor, turns in the opposite direction will be hindered. This knowledge can be incorporated into how the helm plans each manoeuvre, and the effect can be thus-used to advantage. Bow-thrusters can give additional help, and can even be used in conjunction with the effect, to make the vessel travel slowly sideways, in light airs!

It can be a real problem on a large (eg. 50ft to70ft) narrowboat on a windy day. If the cross-wind is not in your favour, progress can sometimes require that a crewmember walks along the towpath with either a rope, or pole to the foredeck (depending on which side the towpath is on vis-a-vis the wind direction). Of course, if the cross-wind is in your favour, (and against the effect) you will have better-than-normal steering.

Good luck and happy cruising.

Answer 10

Little boats are worse!  Especially when going slowly.

I had no problems with a 65' steel boat when I did my Helmsman's, but my 30' aluminium alloy nb is always seeking to sit on the RH bank.  And like Happy Murcia's nb, she reverses like a reclaimed house brick!

The Brainy Lass has hit the nail on the head with the paddle wheel effect.

Answer 11

The sail area of your hull is imbalanced.  The center of lateral restriction (underwater) should be in line with the center of effort of sail area (above water).  Adjust weight distribution (trim) to regain balance.

Answer 12

Sounds like your rudder is too short, the prop is washing up the left hand side of the rudder but cutting underneath on the right as you look at it from the rear, unless your prop is running counterclockwise then obviously  it'll be opposite.

Basically the water that is spiraling off from the prop is running up one side of your rudder and running down and escaping prematurely off the bottom of the other side as the rudder is too short.

You can't even peg the rudder like you can if the hull is distorted as the effect increases with the amount of throttle you use so if you clamp it in place to go straight ahead at 2mph it will pull left at 1mph and right at 4mph.

A deeper rudder is your best bet.

Failing that if the prop is too low to allow you to to extend the rudder you can either offset the rudder or fit an L shaped baffle at the bottom of the rudder to balance it out.