Exactly what is weather helm? Weather helm is the tendency for a yacht to round up into the wind.
If the helmsman has to pull the tiller towards him or her to make the boat go in a straight line then the boat is said to carry weather helm. The opposite to weather helm is lee helm
Increasing the size of the rudder is not a total solution to the problem as a larger rudder can in itself be a disadvantage.
A small amount of weather helm is desirable as it gives you a feel for the helm but if weather helm is excessive you have to put the helm hard over, effectively putting the brakes on as the rudder sits at an angle and acts as a flap.
You have a 'balanced boat' when the forces put on the hull by both sails when it turns on its central line of lateral resistance are equal. That is when both the genoa and mainsail are equally balancing the boat out laterally.
My Hurley 24 can often be described as well balanced. The high aspect rig with narrow main and large genoa balance the boat well but give a little weather helm which feels reassuring as the boat would round up into the wind should I fall overboard.
More weather helm is felt during strong winds when the genoa is furled in and the mainsail takes over as the main source of propulsion.
Although the masts are nearly the same height, the Hurley 22 sail plan is very different. The mainsail is comparatively larger. In fact the sail area of the 22 is more despite the displacement being smaller!
- Hurley 22 - disp 1,769 kg - sail srea 24mē
- Hurley 24 - disp 2,285kg - sail area 20mē
Therefore I would conclude that balancing the boat by effective reefing and good quality sails is of paramount importance and a more effective way of reducing weather helm on a narrow beamed yacht than the size of the rudder alone.
Weather helm can be managed by reducing the size of the mainsail or increasing the size of the genoa/jib.
This adjustment in sail area and relocation of the main driving force can be described as moving the centre of effort.
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The hull of a yacht turns on a point called the Centre of Lateral Resistance (CLR).
The CLR is the central area of the underwater profile of the yacht.
The wind force on a sail creates a point called the Centre of Effort (CE).
Both the main and the jib/genoa have their own CE. Both CE points combine and create the boat's CE. If the boat's CE is aligned with the CLR then the boat will be balanced.
On the Hurley 22 the CE is often aft of the CLR. The pressure of the wind turns the stern away and the bow towards the wind creating excessive weather helm.
At this point the main should be reefed.
The hull shape makes a big difference, too. For example, the Hurley 22 has overhangs at the bow and stern so that the wetted area of the hull is kept low when the vessel is upright but the waterline length is increased when the boat is heeled over when sailing.
The Hurley 22 is narrow compared to modern yachts and carries its beam just forward of the CE. This means that when the boat is heeled over the buoyant beamy part of the boat kicks in and tries to float up, pushing the bows around to windward thus creating forces exaggerating the weatherhelm.
The Hurley 22 widens dramatically as you look at the profile above the waterline.
Modern boats carry their beam much further aft making the boats a lot lighter on the helm.
The maximum speed of a hull is around 1.4 times the square root of the waterline length in feet or x 3.28 in metres.
Therefore the hull speed is greater when the hull is heeled over, but conversely the more rudder is needed, putting on the brakes and slowing the boat down.
It used to be considered that a slim boat was a fast boat, as seen on Bloodhound for example. Modern boats are very beamy and blisteringly fast but need to be sailed upright as their waterline length does not increase much when heeled as they have stubby bow stems and flat transoms.
So try trimming and reefing your sails before you buy a bigger rudder!
Nick Vass is a marine surveyor and the technical advisor and vice chairman of the Hurley Owners' Association:
www.hurleyownersassociation.co.uk
and www.omega-yachtservices.co.uk
