Heavy tiller steering

[Seawater]

Is there anyone out there who has a good working knowledge of rudder-performance and related issues, please?

I have a 23' Seamaster sailer with a balanced transom-hung rudder, and a 13.5 hp Beta engine with a 3-bladed prop. Under engine, with no sails set, the tiller is extremely heavy and pulls to port constantly, even when steering in a straight line, to the point that I need to lash the tiller to help take off some of the pressure. This applies at all motoring speeds.

Can anyone explain to me (in layman's language) the advantages of a balanced rudder, versus an unbalanced rudder, and would altering the rudder in some way improve the handling?

Thanks for any help.

 

[pmagowan]

Balanced rudder means the pivot point is roughly in the centre of the rudder whereas unbalanced is towards the front. An unbalanced rudder will always try to move back to the centre due to the force of the watter over it. In a balanced some of the water will try to deflect the rudder (the water hitting the front) and some will try and force it back to centre (water hitting behind the pivot). You need to find out which part of the rudder is exerting too much force and then rebalance. It may also be due to the prop and the force being off centre (depending on angle of blades).
Don't know if that makes sence as really need to sketch it to explain better. My rudder is only slightly balanced and if I have the engine up full then it becomes heavy and tries to stay central. The boat will still go off course due to prop walk.

 

[pmagowan]

Looking at your picture and re-reading I think your prop is sending its stream of water at an angle to port. This is hitting the bit of your rudder towards the front which will force the tiller to port. In order to fix you need to take some off the front of your rudder, add some on the rear or both. Alternatively you might need to look at the prop. When you have your sails well balanced does the tiller pull at you?
It would help you if you move the tiller with the boat out of the water and imagine a stream of water coming from your prop. You should be able to see where the force will hit and what effect it will have.

 

[Burnham Bob]

not sure about the kick to port but i was amazed by the heavy tiller on my Trapper 500 with the same engine when manouvering hard with lots of revs - just got used to it and when going in straight line its still heavy but acceptable

silly question but might the boat have a tendency to pull to port anyway which is exacerbated with heavy flow of water from the prop? the experts always tell me you can steer a boat with the sails and if under sail you are trimming out a weather or lee helm problem (okay so maybe it would move about depending on which tack you were on)

not sure how you would test for that.......

 

[Stu Jackson]

and if under sail you are trimming out a weather or lee helm problem

Not really. A well balanced boat should always have some weather helm.

While your issue may be the rudder, and maybe the proximity of the prop to the rudder, you should be glad you have a balanced rudder.

All boat with inboard engines and standard props have prop walk that moves the boat to the left ALL THE TIME.

Do a search on this or ANY OTHER sailing FORUM on "prop walk" and you'll be reading for YEARS.

 

[LittleSister]

From your photo it looks like the rudder has only a very small amount of balance - it's not really what I'd call a balanced rudder -but that's not the whole issue, I feel.

In my opinion a 13.5hp engine is a bit too big for a 23 footer (I say that as someone with a Beta 13.5hp powered 23 footer) - you can't really use any more than 10hp, and the excess just means a bigger prop -not a serious problem but might be a contributory factor.

You will always get a bit of a shove to one side from a single prop, and it can only be more or less noticeable. The extent to the push to one side or other will depend, I imagine, on how big the prop; how close the prop is to the rudder; and the extent to which each of these are working in the disruption of the flow from the keel, p-bracket or, as in your case, a projection from the hull holding the drive shaft/prop.

I'm wondering if you don't have a 'problem' as such, as much as an unappealing characteristic, but from the very fact you're writing on here about it it must be rather pronounced. Our long-keeled boat tends to steer to port under engine (but not sail), and having to push the tiller a little to the right to go straight under engine could be thought of as mildly tedious but is to me just 'characteristic'.

You want to consider
- checking the propellor is a suitable size/pitch for the engine and hull;
- remodelling the section of the rudder blade to make a better hydrofoil;
- remodelling the profile of the rudder to give more balance, and/or adjusting the distance of the leading edge from the prop.
Another, simpler, thought is your tiller long enough? If you've got room for a longer one then you will reduce the apparent load by increasing the leverage. I notice that a drawing I have of the Seamaster Sailer 23 (is that what you have?) has a curiously short tiller. I also notice that the accomanying review (PBO) mentions it not being as light on the helm as more modern boats, and this might not be just about rig balnce/hull form, perhaps.

 

[rob2]

Actually, the definitions of balance so far have been over simplified. A rudder is a hydrofoil and has a centre of effor lifting it into the water flow. On a NACA foil this CoE is typically 23% of the chord from the leading edge. If the rudder pivots at that 23% point, then it is balanced and will require the minimum possible effort to turn it. Most boats have partially balanced rudders (pivotting forward of the CoE), to increase feel on the tiller and to maintain some control should the foil stall. An overbalanced rudder, where the pivot is behind the CoE will always be trying to turn and is almost impossible to control. If you trace animaginary line through the pintles, you will see that very little of your rudder is in front of the pivot.

Is the drive on the centreline? Quite a few boats have the engine offset to accomodate interior furniture and this will always give a pull to one side. It is easiest to manage the pull by standing with the tiller between your legs and steer by swaying sideways. Your legs are much stronger than your arms.

The discussion about weather helm is irrelevant to the motoring issue as it is caused by sail balance and the assymetry of the waterline shape when heeled.

Rob.

 

[Seawater]

Heavy Tiller Steering

Thanks to all of you who have offered suggestions and opinions; these have been very helpful and given me food for thought.

(Incidentally, the tiller already has been extended and it can't be lengthened anymore as the mainsheet traveller bisects the cockpit, and I am used to weatherhelm but this is extreme.)

 

[Bobc]

It's to do with the distance between the prop and the front edge of the rudder.

There's not a lot you do about it other than fit a saildrive or make the boat longer.

 

[CAPTAIN FANTASTIC]

To overcome the problem you need to increase the distance between rudder and prop, which is not easy. The best viable solution is to cut away a bit of the "balance" section of the rudder or at least round it off so that the prop wash will have no way of catching the rudder and throwing it to one direction.

This problem was common on old wooden boats with hang rudders when later owners decided to install big engines with big props; when these boat were never designed for that.

 

[reeac]

Our previous boat [a Centaur] pulled to starboard under power. I found it quite a handy feature as I could sit with the tiller pressed against my leg leaving both hands free most of the time and steering with slight movements of the leg. Depends whether your tiller is at the appropriate height though.

 

[oldharry]

and if under sail you are trimming out a weather or lee helm problem

Not really. A well balanced boat should always have some weather helm.

While your issue may be the rudder, and maybe the proximity of the prop to the rudder, you should be glad you have a balanced rudder.

All boat with inboard engines and standard props have prop walk that moves the boat to the left ALL THE TIME.

Do a search on this or ANY OTHER sailing FORUM on "prop walk" and you'll be reading for YEARS.

ON a well balanced boat it should be possible to trim out the weather helm but at the cost of a bit of speed. I certainly can on mine. Useful when short/single handed as the boat then sails itself jogging gently along at reduced speed while I do other things.

Prop walk depends on the direction of rotation of the propellor. Facing forward, if the prop rotates clockwise you will get prop walk to the right. Anti clockwise, prop walk is to the left.

You can reduce prop walk by using a larger 'flatter' pitched propellor - sometimes! So if you are using say a 16x 14, try swinging an 18 x 12 if space permits. You may lose efficiency marginally, but just may improve the propwalk characteristic. Or not...

The difficulty is that it is a complex combination of charcteristics that causes it.

Looking at the photo, the rudder has very little forward of the pivot to bsalance it. Designing and making a new rudder is not so difficult with a transom hung rudder, and giving it a degree of aerofoil section - even just tapering the blade back over about 60% of the trailing area can make a big difference in effectiveness. You should aim to get around 10% of the area forward of the pivot. Might be worth experimenting with something made out of cheap softwood to start with to see what effect it has.

 

[dtripp]

It looks to me in your pic that all of the blade is behind the line from upper to lower pintle (??). If that's correct you need some in front of that line to act as a servo. If your blade pivots, try making the bottom swing forward so that the line cuts it at the centre of the bottom or less. Will make it lighter, but won't help wayward tendencies.