I have just finished a thorough read of the very excellent book 'High Performance Sailing' by Frank Bethwaite. I recommend this to all sailors interested in going faster.

The book raises the question in my mind as to why catamarans don't have the prebent, tapered, bendy masts that we see on the 49er and 18'Skiffs. (see attachment) The Taipan rules for example proclude them as does the development class the A-class.(as I understand it)

Why aren't they used?
Is the option to use them on the F16HP worth considering?

Rob.

There could a difference between the designs due to the fact that Cats have rotating wingmasts. Most skiffs have fixed masts of an almost round section.



I will read up on the topic in my edition of HP sailing.



WOuter

Berthos,

The skiffs have the bottom 2/3 of their rigs locked in place by shroud tension, and the top 1/3 is a springy composite tip that automatically bends in the gusts and opens the leech of the main. They need this rapid gust response because they are so tippy. The stability and inertia of a cat to capsize means they dont need such fast response so that the square top mains on Tiapans and many other new cats give adequate dumping of power in gusts.

Whan frank considered wing masts on skiffs, they were way too heavy for such tippy boats even if there were aerodynamic benefits to be found. They also required more adjustment to maximise lift and minimise drag, again something he did not feel could be done in a race with shifting winds.

The higher aspect of say a A class or Tiapan rig is more efficient upwind thean a skiffs rig so if one put a skif rig on a cat it would have to be a similar aspect ratio. Also I think achieving enough rig tension would be almost imposible due to the mast being placed on a beam rather than a hull. ( the skiffs use hugh tension to lock the bottom section of their rig, Mast compression on a 49er is about 1 tonne and on a 18ft skiff it is up to 3 tonnes.

Threre is however a kind of cat, the Laser Vortex (www.laservortex.org) tunnel hull that uses a skiff style rig to good effect. Unfortunatly no one has put a prebent wingmast on the same hulls so no comparisons can be made.



Regard



Simon

Thanks Simon,



That seems like a very logical explanation.



Berthos.

A few low powered skiffs use a wing mast to good effect.. i.e. Mg14 & NS14 (100 sq ft sail area) which have the same hull dimentions as the Javelin (150 sq ft ) & I14 respectively 200+ sq ft.. Also Alex Vallings used a wing mas in his R class title win. The R is a 12 foot skiff with a far reduced sail area ( I believe it a number 3 or 4 rig).. In all cases that a modern skiff class uses wing masts they are seeking power in the low to medium range.. A 12 number one rig may be 400 sq ft with a 1000 sq foot kite.. At 5 knots the 12s are fully powered up and dumping power downhill..



As for prebending of the wing.. Most skiff rules do not allow for prebending masts any apparent "prebend" is induced by the rig tension..



Saying this there appeares to be little real advantage between a wing and a flexitip rig on skiffs.. Outside the underpowered condition.. From an outsiders view the MG14 now seems to have both wing and tip rigs in the top few boats.. Alex didnt clear out when he won the R title.. But admittedly his wing was twice the weight of his standard rigs..



Julian is of the opinion that the flexitip is far accurate and reliable than the cats squartop. (A composite tip will fatigue a lot slower than any cloth/batten combination).. His shop was beside Cairns sail loft when Cairns was devloping the square top mains.. So the two rig designs were developed literaly side by side as it were.. As pointed out cats are far more stable and thus dont need the gust response of a skiff..

However as pointed out to me by Julian the more powered the cat the flexier the rig.. So put an 18 sq meter rig on an HP and you will need a rig close to the skiff rig..