I would be very grateful for any advice on the repair of a port side split plank. 
We are assuming the damage has been caused by the road trailer as it sits directly above the port side support, the split is around 250mm long running from bow to stern and is 10mm above the plank joint.  
Any help or advice would be appreciated.
Thanks, Chris.

Hmm, 
The options rather depend on how much you wish to spend, the condition of the hull (in general) and your aesthetics!

The "simplest" low cost solution is to spring the crack slightly, fill with epoxy (with filler) then clamp (or weight) the plank to close the crack.
I'd then suggest using a fine glass mat with epoxy over the inside surface (you'll need to remove the varnish first). The expoy will turn the mat transparent, so you shouldn't see a major difference.
You may need to do the same on the outside of the hull.

A professional cure may be similar, or replace the plank - depends a lot on the condition of the rest of the hull.

Colin

Drill a small 4mm neat hole through each end of the split, using a wooden block on the other side to drill through into, preventing breakout. This should stop it spreading. Carefully cut along the split in several goes with a sharp stanley knife, maybe from both sides to create a gap for adhesive, not too wide. Clean the area with thinners and fill with epoxy mixed with fibre filler or balloons for strength and pack as much into the slot as possible. Clean off excess with a sharp blade. When fully set, rub down and refinish.

Many thanks all.
The hull is in a very good condition with the exception of this plank. Is there a preference on the best epoxy for the job?

west or sp

Both suggestions are easy enough to do for a d.i.y repair,but whats the trailer like? If its the old 3 position type ,keel,one either side arrangement ,chances are it will happen again. 
    Boats should be supported properly with acradle, especially that old, it would be well worth doing and much kinder to the old girls hull!

We have the original Snipe trailer which we have modified into a combi. It has 2 keel points of contact and 4 hull point. We understand this has been the cause and that we have to act to prevent any further damage. We will manufacture a complete cradle as per modern units over the winter. We  expanded the surface area by increasing the footprint to around 600mm from the original point rollers some 10 years ago, obviously not enough. Problem is we drag her home into dry storage after every race weekend to stop the decks weathering.