My daughter proudly owns Merlin Rocket Sail No. 713, built 1 May 1953.

The boat suffers from weather helm in strong winds and I can't help but think it has the wrong rudder which looks more like one off a GP14. Can anyone please provide Details / Dims. / Image of a rudder from this era? e-mail [email protected]

The mast has been replaced with aluminium which may be the problem. Any advice about severe weather helm appreciated.

Alan, if you have the original rudder they do look completly different than a modern Merlin rudder. You will find the boat almost uncontrolable when heeling. All you need is a deeper rudder blade. I had exactly this problem on my vintage boat until I bought a new rudder and that solved the problem. The best person to talk to is either Winder Boats or Phil Milanes. I have attached a link to one of the merlins on the list for sale which has a new Milanes rudder on it.

Hope that helps

Jeremy

Alan - if no-one else is able to provide a photo, give Mervyn Allen a call and see if he can describe one to you!

As per the advice in the past - sail flat and fast and the weather helm will diminish.  Gannet (252 built 1951) is like this too with a swept back fixed rudder but once you get her flat then she is OK. Also - don't forget the vintage events and the CVRDA website

Weather helm is caused when the centre of effort of the sails comes aft of the centre of resistance (essentially the pivot point) of the boat. All manner of things can cause this:
1. The rig - You need to move the centre of effort forward so......Is the mast stepped too far back (not really a problem specific to the strong winds you mention)? Are the sails blown out (they become unstable and the point of greatest fullness, and therefore the centre of effort, moves aft as the breeze increases)? Is there enough cunningham (increasing this has the effect of bringing the point of greatest fullness forward)? Is the outhaul tight enough to reduce the fullness of the sail in strong winds (a sail that is over-full will become unstable and the centre of effort will move aft). Is the mainsail being over-sheeted (the surest way to generate massive weather helm, and a poor kicker can often lead to a tendency to over-sheet to compensate)?
2. The boat - You need to move the centre of resistance aft so....Is the boat being sailed flat in strong winds (heeling to windward generstes weather helm)? Is the centreboard raked back (this will move the "pivot point" aft as well as reducing the heeling moment in strong winds)? 
Obviously the rudder contributes to the centre of resistance of the boat but many previous posts on this forum have attested to the fact that rudder blade shape is not as critical as often thought (you can do a search amongst the "old stuff" on the forum). Admittedly "older style " swept back spoon shaped rudders can make the helm feel heavy at speed (if you try to steer with them!)but they also have good feel and control at slow speed.
I apologise if you knew all this or if this is not the kind of "weather helm comments" you were looking for but there is a lot to try before you NEED to replace your rudder - and most of it is free (well perhaps not a new suit of sails!)

Sorry - just re-read my last post. It should have read "heeling to LEEWARD produces weather helm."

I just want to add to the above, that many Merlins, especially river Merlins, have the ability to have the c/board tip raked forward by 5 or 10 degrees, i.e. fully down is in fact forward. Having the board raked forward creates weather helm for the physics reasons as discussed above.

It is important to know where 'verical' is on your board, and if necessary mark the handle so you can set it accurately.

On modern boats, with raking rigs, we rake the board back (i.e. up a bit) to balance out the weather helm as the wind strength growns and we rake the rig.

You should try the same, as discussed above, as the wind strength grows, the centre of effort move back in the sails, even without raking the rig. As discussed, you can use the cunningham to move the c/e forward, but that won't help if the tip of your c/board is forward of vertical.

I forgot, regarding the rudder, don't spend money of the rudder, you should be able the balance the rig of a merlin such that you can sail all day without a rudder, tack gybe etc, the rudder is fine tuning and emergency steering and thus unlike to be the contributor to a major weather (or lee ) helm issue.

I SHOULD HAVE GIVEN THE BOATS BUID DATE AS MAY 1957 NOT 1953

1953 or 1957 - still a genteel older lady and welcome at both Vintage Merlin and CVRDA events round the country.