The RS100 Owners Thread

I think its a suprisingly complicated subject...
Unless a rudder blade is completely balanced with the pivot point exactly over the centre of lateral resistance then it will be tugging on the tiller if its taking up any sideload. If its not taking up any sideload then you are dragging a big foil through the water without it doing anything until you change direction, which seems a waste of wetted surface area...

I've never understood how anyone can realistically judge what angle the tiller is at to the centreline from sitting out of the side of the boat - I'm sure *I* can't judge it accurately - but it seems to me that the optimum position for the tiller must depend on:

• the lowest drag angle of attack for the rudder compared to the centreboard: they are different sections so perhaps they shouldn't be parallel


• the angle of the centreboard to the boat if you have a gybing board


• the angle of leeway the hull is making


• how flat the boat is


• and probably lots more I haven't thought of!

Originally posted by JimC I think its a suprisingly complicated subject... Unless a rudder blade is completely balanced with the pivot point exactly over the centre of lateral resistance then it will be tugging on the tiller if its taking up any sideload. If its not taking up any sideload then you are dragging a big foil through the water without it doing anything until you change direction, which seems a waste of wetted surface area... I've never understood how anyone can realistically judge what angle the tiller is at to the centreline from sitting out of the side of the boat - I'm sure *I* can't judge it accurately - but it seems to me that the optimum position for the tiller must depend on: the lowest drag angle of attack for the rudder compared to the centreboard: they are different sections so perhaps they shouldn't be parallel the angle of the centreboard to the boat if you have a gybing board the angle of leeway the hull is making how flat the boat is and probably lots more I haven't thought of!

Jim,

Interesting subject. What's the difference then (if there is one) between a tug on the tiller due to the centre of effort being behind the centre of lateral resistance (centreboard pivot point?) and that caused by, say, the rudder blade not being fully down (which I presume is not 'proper' weather helm at all)?

this is why we train with the rudder up an inch as it forces you to sail upright
and enables you to get the 'feel' of upright. I remember at first we always
wanted to sit in as it felt like the boat is falling on top of us

Originally posted by Jamesd this is why we train with the rudder up an inch as it forces you to sail upright and enables you to get the 'feel' of upright. I remember at first we always wanted to sit in as it felt like the boat is falling on top of us

Now I like that idea! We always try to sail with what feels
like 5 degrees of windward heel which invariably is flat,
but then your mind drifts and your heeling again. At least
the pull on the rudder would wake me up again!

Originally posted by Steve411 What's the difference then (if there is one) between a tug on the tiller due to the centre of effort being behind the centre of lateral resistance (centreboard pivot point?) and that caused by, say, the rudder blade not being fully down (which I presume is not 'proper' weather helm at all)?

Well, if the rudder blade isn't fully down then the force required to counteract sideload is naturally greater because of leverage... That's why Lasers feel quite heavy - they have a raked back rudder blade which was conventional at the time. But also a raked back tiller has an increased self centering effect which makes steering feel heavier...

Weather helm is, I think, a distinct phenomenum. That's where the boat wants to steer round a corner and you have pull the rudder to windward to hold it straight. Surely that has to be slow in all circumstances, but in dinghies, in my experience since I've started thinking about this sort of thing, its almost entirely heel related.
This (and it could be *****) is why I don't think weather helm is a big issue on dinghies... AIUI, and simplistically, to get weather helm the centre of effort of the sails has to be aft of the centre of lateral resistance of the foils. But the centre of lateral resistance is somewhere between rudder and centreboard. So in this pic green is a fairly normal mast position, and the side load is probably 3/4 cb, 1/4 rudder. In the red position you have lee helm, because even with 100% load on board and nothing on the rudder the sail centre is still in front of the foil. By contrast as the rig rakes back there's more and more load on the rudder and less and less on the cb, but you won't get weather helm until the rig is raked right back to the blue position so the centre of effort is aft of the rudder (or if the side load on the rudder gets so great the blade just stalls out).



In the days of yachts with no separate rudder then the centre of lateral resistance was effectively fixed, and so weather or lee helm was much more likely, and I suspect even with modern yachts the rudders are so small in proportion that the clr doesn't move very far...

But this is lunchbreak theorising - certainly very over simplistic and possibly even nonsense!