Up until recently I had 3mm perspex sheeting on the back to cover the transdom flaps on my NSM IV. Unfortunately the ingress of a rather large wave proved too much and snapped the perspex clean through as the water hit the back of the boat. 

My question is what material works best for the flaps, I would prefer something transparent, but settle for opaque just as long as its flexible enough not to snap again the first time its hit more than a dribble. As I beach launch and haven't quite got this mastered yet my transom flaps get a lot of work!

Try this.

Or this.

On the subject of 1mm transom flaps, I have fitted these to my boat, havent sailed it yet. They are pretty bendy, cant help thinking they wont work very well at keeping water out unless I stiffen them up a bit (perhaps by laminating another strip of 1mm stuff over the top). One good gust and they blow open. Would any one like to comment?

I've got the thin perspex sheet style - that is - shaped in 1 piece, and held to the transom by the pintle & gudgeon fittings.

It does also need a piece of elastic bungee (hole in the centre of the transom cut-out) and a little - only a little - tension on the bungee.

The flap seals quite well because the overlap around the cut-out (on the transom) is flat, any water trying to get in pushes the flap against the transom enhancing the seal.

My Solo has the thick plastic flaps - there'e a right pain! When I do the next re-furb on it I'll go for the same thin perspex (see the P&B website).

HTH

COlin (3387)

These work well

Thanks all, looks like 1 piece of thin 1mm perspex may be the way to go so am going to try this and secure it to the mid transom. Hopefully it should flex enough from there should i get swamped again and remain in one piece.

Perspex .. is absolutely NOT what you want.  Perspex is the trade name for acrylic sheet, it has a variety of useful properties, but toughness and flexibility are NOT among them. Its brittle and (as you found out) will snap and shatter.

What you want is polycarbonate sheet. The most common trade name is "Lexan" but there are others. Its the stuff they make police riot shields and visors from. I have taken a small 300mm piece of 6mm thick Lexan, put it across wooden bearers and smacked it HARD with a lump hammer, many times. It does nto break .. it barely even gets marked. Its UV resistant and almost indestructable. It is used as a replacement for glass in security applications.

If you look on Ebay, you can find offcuts of Lexan in 1, 1.5 2mm etc for very reasonable prices.

I just made some new flaps from acrylic / perspex. Must be about 5mm thick. Fixed them using a bit of webbing as a hinge. 
Difficult to cut neatly without a workshop, and it is brittle, so you need to take care. Nonetheless, they work brilliantly - My rudder snapped last week, and whilst faffing around at the back of the boat, the water level way half way up the flaps and they barely leaked at all. Got a good sized offcut of the perspex from a motorbike repair workshop for a tenner.

Anyone got a spare rudder blade (hinged) that they want to sell?
Brand new ones from P&B look lovely, but cost almost as much as I paid for the boat!

Otherwise, will have to try repair or making a new one.

are you just after the blade - or do you need a stock too?

you should be able to glue it with epoxy ... be as strong as it ever was, assuming it split down the grain

I just mounted some new transom flaps out of 2mm lexan, copied a system I had seen on a Boon Boats National Solo ... no hinges! ... just two holes drilled on the top edge through the flap and the transom .. a piece of shock cord knotted behind the transom . fed through  hole, and back through the other hole and knotted again .. works perfectly and no hinge! :)  The shock coard not only locates the flap in the right place but serves as a self closing hinge too ...

There you go ... shock cord hinge and 2mm lexan flap

Thanks for the advice.

Epoxy seems to have done the job, with an epoxy 'bandage' for good measure...just need to tidy it up, as it's an unsightly repair at the moment.

No grain - its a bizarre composite constyruction, fairly hollow with glass fibre 'rods' inside and some kind of plastic / foam. Loads of body filler too - it's obviously broken in the same location before. Intend to get some timber and make a better one some day.

I'm just on with a similar job replacing the transom flaps on MR2794. Robin Szemeti how did you cut the lean so neatly?

I'm just on with a similar job replacing the transom flaps on MR2794. Robin Szemeti how did you cut the lean so neatly?