rod vs conventional wire rig

[jonasa]

I lost a shroud last week on my 41 ft yacht, the rig is farly old so I am going to get a new standing rig including all shrouds and stays.

Can anyone direct me to information that analyses the sailing performance difference between a rod rig and a conventional wire rig.

The rod is obviously much stiffer, and more expensive, but what about the sailing performance gain?

/Jonas

[gonzo]

Is this a very high performance machine? The stiffness of the rod will only help if the rest of the boat and rig can take the load and is rigid enough. Wire strechtes some and absorbs the load shocks..

[jonasa]

I think it should be considered as a stiff-rigid boat.

It is a Wasa410, a Swedish built cruiser-racer by Leif Ängermark built in 1980.
Key numbers:
41ft long by 11.65 ft wide, draught 7.2ft
lead fin keel with free standing rudder.
keel: 7260 lb, the design weight is 16280lb but our yacht weighs 2200 lb more.
Masthead rig P=47.6ft, E=16,4ft, main sail about 463 sqft
It has a ORC Club rating of 622 s. (would be about the same in IMS)

Some info about this probably not so well known yacht in the US can be found at
http://www.wasayachts.com/wasacl/wasa410.html

/Jonas

[Tom Lathrop]

At the ripe age of 23 years, I betcha it is not as stiff as when it was new and it was probably not stiff enough then to gain much benefit from solid rigging. The one and only job of masts and rigging is to hold up the sails. Sometimes we forget that and waste too much time and resources on trivia.

[jonasa]

The benefits of Rod rigging are as I understand it:
1. Stiffness. The mast bend is reduced and hence sail shape is easier to control

2. Smaller diameter for given strength, gives reduced airodynamic drag.

3. Lighter weight for given strength, gives reduced weight of rig.

My question is if anyone has an idea of the performance gain. If anyone has done a performance study to see the effect on performance due to the three effects above. You might both be right, but since rod rigging is getting evermore popular you wonder wether it is just a hype, or if it gives a real performance increase.

My yacht has a 1980 straight untapered Selden aluminum mast with wire halyards, and I think the performance gain due to decreased weight using rod is small allthough I do not know this for a fact.

/Jonas

[gonzo]

Smaller diameter does not translate to less drag. The smaller radius starts producing turbulence (flow separation) at a lower windspeed. Also, smaller diameter rigging vibrates more, which in turn increases turbulence too.

[Tom Lathrop]

That is often true Gonzo. Another thing is that stranded wire may benifit from the turbulence generating effect of the strands which can retard separation of airflow. This is what the dimples in a golfball are for and the little tabs often seen on the upper surface of aircraft wings. The main culprit in drag of cylindrical shape like stays is the generation of vortices which flow alternately from one side of the wire and then the other. This is what causes the vibration or singing of the wire.

It also causes the centerboards and rudders of fast sailboats to sing. Many think that it is non-symetry or imperfection of the foil that causes the vibration but I think it is most likely just the opposite.