Yes

The experts say that CF does not suffer from 'fatigue'…

My belief is that all materials will fatigue given enough abuse. The CF test pieces I have are fine as long as there is no separation (anywhere) between the fibres and the resin.

For a solid rod – just watch for any fretting – top, bottom and sides.

For a tube – separation will most likely show first at the external surfaces.

If in doubt, I usually reinforce with Kevlar (an Aramid). I'd have thought that a 6mm o/d will be plenty strong enough. However, if you want the mast to flex – consult the others with sailing experience !

Hello Carl

Just to remind you what Ashley said. I don't think any of us would live long enough for a model yacht mast to fail due to cycle / stress. On your boat you don't need to have a bendy mast. The rigging should keep it in column more or less.

A lot of what is called carbon tubs and rod is not what you might think at all. It is black but the black is in the resin and possibly carbon black used as a pigment. The fibres are glass (ie white), totally unidirectional and very closely packed to give a high glass to resin ratio. I have some tapered glider fuselages that are extremely light, a mixture of carbon and aramid and you can see the tows very easily through the clear resin. The wall thickness is a fraction of the faux carbon rods and tubes but the faux materials are fine for our purpose.
The most likely way of splitting the unidirectional is when attaching fittings with screws (often of the self tapping type). A pilot hole only is drilled and the screws engage with the material in its least resistant plane splitting it. That's why I I try to use adhesives only and if I can't get a large enough gluing area, insert a pin. The pin goes into a close fit hole and therefore acts like a rivet which clamps with very little expanding force.

You are clearly highly qualified engineer but this is probably leading you to over-think everything. Our models are usually hugely over-built with enormous margins of safety compared with what you are used to. Most model I suspect are either damaged by pets (in my case!) dropping or loading into the car.

I am enjoying your posts as you raise interesting questions about which most of us take for granted. Most of all you should finish your model as frankly there are no difficult technical obstacles and the satisfaction you get when it hits the water will bring you a rosy glow.

Tim R

Carl, unless you are planning to sail your model yacht in a hurricane, I really wouldn't worry…

However, if you want to re-assure yourself further, you could always use the "Buckingham Pi" theorem to relate scale speeds /bending moments etc. to full-size wind speeds.

Could be fun on a wet, rainy day I suppose !

Regards,

Dave

There is a school f thought that reckons that higher aspect sails are more efficient, probably true for the real thing. My thought is that since model boats generally sail at the bottom of a hole in the scenery, the top bit gets moving air before the rest of the sail simply because it is less sheltered by the bank.