The evolving riddle of Duet’s mast rake… Part 1

June 15, 2014 at 2:39 pm
Weather Helm
  1. a tendency in a sailing ship to head into the wind if the tiller is released.

So, Duet has awful weather helm. Her steering is really heavy as she wants to point into the wind all the time and you have to counter-act that with the tiller and rudder, which in turn causes unnecessary drag and slows her down and causes unnecessary fatigue on the helmswoman.

In fairness, a little bit of weather helm is desirable so that in gusts her automatic response is to luff up (or turn into the wind) and de-power, rather than turn away (from the wind) that could cause the boat to become over-pressed and difficult to steer and control (dangerous!).

Now, Hurley 22s do have a tendency towards weather helm, due predominantly to the rudder being a little small.  Later examples (like Duet) have a different rudder design though are supposed to be improved.  Another simple way of improving them is to put a reef in the main so that more of the power is coming from the genoa in front.

However, I had noticed that someone (a previous owner?) had actually cut a notch in the tiller stock, presumably to give it more purchase and to help with her really heavy steering. However, the effect of this is that the tiller then hangs really low in the cockpit and it’s uncomfortable to steer anyway! Clearly not good, and clearly to be improved.  I want to play with sheet to tiller steering this summer and the boat needs to be as balanced as possible for that.

I had also become aware that Duet has an uncomfortable looking mast rake (the angle at which the mast bends backwards) so after polling a few other owners in the yard I took a picture and posted it to the Hurley Owners Yahoo Group.  The verdict was that it didn’t look right, and the mast on a Hurley 22 should be pretty much upright. Someone also suggested that it might cause weather helm, and a little lightbulb went on in my head…

Hurley 22 Mast Rake Weather Helm

(Left) Duet’s bent back mast (Centre and Right) The notch cut in the tiller – I put the screw in last season as the tiller hangs too low in the cockpit!

The reason that mast rake (and reefing the mainsail) impact weather helm is all to do with the balance between the centre of resistance of the hull, and the centre of pressure (of the sails).  If the centre of pressure is astern of the centre of resistance to the hull then there will be weather helm (the boat will want to turn into the wind) and if it is in front of the centre of resistance then there will be lee helm (the boat will want to bear away from the wind)

So on Duet, the mast rake is effectively moving the centre of pressure backwards, and putting it behind the centre of lateral resistance.  Similarly, putting a reef in the main makes the sail behind the centre of resistance smaller and moves the centre of pressure forward again counter-acting the weather helm.

There is other stuff that impacts the centre of resistance of the hull like the size of the rudder, and also the amount of heel on the boat (and her underwater profile) but let’s not complicate stuff any more at the moment:  Its pretty clear to me that we need to pull the mast upright again.

However, it wasn’t to be that easy… The rake of a mast is controlled by the rigging, in particular the forestay (the front wire).  Unfortunately Duet’s forestay is as tight as it will go, but luckily (and a bit bizarrely) the split backstay is loose.

Standing Rigging Hurley 22

(Left) Forestay as tight as it can go (Right) One of the split backstays, looks adjusted but is actually quite loose

This can only mean one thing: the mast has to come down and I need to take off the roller reefing and have the forestay shortened.  Which is quite complicated.#sadface

Also, there is clearly something going on with her rigging…