Always used a rule to keep the main sheeted tight, centered,
when flying the spin on my Nacra F-18. I've also kept the
rotation tight.
My buddy with a Tornado, is telling me that he rotates his, mast, and allows for some main in 15-20 knot (balancing the
pull from the spin).


I think he's crazy, One of us is wrong
Your Thoughts

Thanks

Let the rotator out so it will be close to the front beam (just let the control all the way off).

Thanks David,

But with the mast rotated, how are the diamond wires going to keep the mast from bending.
Maybe I've been sailing my spin wrong.

Appreciate your advice

Steve

Steve

I really don't know the reason except it creates better flow on the back of the main. This is for the Infusion so all the settings won't be the same for your boat
http://www.katamaranspecialisten.se/manuals/f18_infusion.pdf

I allow full rotation, and travel out 6 to 12 inches, in the interest of maintaining flow on the lee side of the main(on both the Stealth and the Javelin HT). I agree that them mast would seem stronger with less rotation, but maybe it's strong enough in this configuration.

Dave

Ok...


The SPI loads up the mast above the hounds and diamond, so if the mast is going to break it will be the unsupported section just above the hounds. so we can rule out the diamonds as being a factor in supporting the mast.

the SPI is loading up the mast in a forward and leeward direction. you would hope more forward if the boat is going fast. The main support for the forward force is the main sheet, a tight main sheet will act as a back stay preventing the mast from failing from the forward forces.

The leeward force is being supported by the major axis of the mast, particularly in a wing mast as it is very strong across its major axis (the fore and aft one). if you don't have the mast rotated you will be presenting the minor axis of the mast to the leeward forces and make it more susceptible to failure.

as far as performance goes, the mast should be rotated downhill to 90 degrees anyway.

On inquiring some time at AHPC concerning this subject, I received the following reply:
"The mast rotation should be at about 80deg on the downwind leg. The tuning guide is not accurate in this description as 80 deg would have the mast spanner pointing slightly forward of the sidestay.
In practice if the mast is completely free to rotate downwind at times it will rotate past 90 deg. The only problem with this is that the boat is not quite as fast. If the mast is rotated a lot less, say 50 deg, then the mast bends too much sideways which can be bad for the mast. Also the air flow around the mast is not as good and the boat is slower."

I always let it not go to full 90 deg as i feel this a lot extra dragg, usally go to about 70-80 deg so that the mast is working better as a aerofoil forward through the air

Thanks one and all.

Another lesson learned,

Appreciate your posts

Regards

Steve

when they do break don't they normally break between the spreaders and the hounds? That where I have have seen them go (not my own mast)

in my I14 days we used to have a telescopic type mast setup, such that light days = big rig, heavy days = small rig. you would reef the mainsil from the bottom. i.e. roll and zip up the bottom 700mm and you would have two sets of tack/clew points. one of our guys thought it would be easier to leave mast at full height and just run the main up the mast so the head was about 700mm from the top. end result was ( in this order and about same timing as you are reading)
1, round top mark
2, kite goes up to mast head
3, sheet comes on
4, top of mast comes off
it was plain and simple to see that it is the leach / sheet tension of the mainsail that holds the mast up under spin
p.s. and we were all using diamonds to the mast head, swept back at about 45 degrees.

Certainly good advice when buoy racing.For distance racing if you have a stout mast (not a wing mast) then you can rotate in to depower when reaching - this bends off the top of the mast. Looks horrible - but lets you carry the spin higher than not doing it - which can be the difference between dropping the kite and dropping back - or keeping it up and staying out front. Not advisable on a wing mast...

We saw Flumpy doing this on his Tiger during the T500. He was pulling away from us on the Infusion on the unbelievably tight spin reaches. We rotated in to try it out, it's faster, BUT it makes the wing mast contort in directions that it was never meant to go. We watched it for about 30 seconds, and decided that blowing the rig out was not going to be fast....

Anybody ever think of changing from a wing mast to a 'standard' mast for the distance stuff for this reason alone?

Yes. Of course you also need a sail cut for that standard mast to be competitive.

I would imagine a Tybee 500 puts enough hours on your main to warrant a new sail every year anyways (average of 8 hours for 5 days, 40 hours just in one Tybee, add on training and a full season and I'm sure you are pushing the 150 hour mark in one season).

Just a thought, more of an academic thought. Wonder what you would change for a 'standard' mast on the sail, I woudl suspect the draft would change a lot, specifically in the luff area.

Java just kicking in, I find this interesting to think of having a 'distance racing' rig and main sail.

The sail would be bigger for a start as the sail area is main sail + mast area. Picking up a mast with less circumference will allow for more sail area somewhere else.