Ok so we have been noticing that when pulling on the downhaul, and sheeting rather tight up wind the mast gets some weird bends in it above the hounds. Almost looks s like in shape. Nigel had sailed olies boat 2 weeks ago and thought maybe the dimonad wire tension was off, or the spreaders not set right since the mast should bend more back not side to side (i believe that is what he was getting at since this is 2nd hand info). So now we are moving blade 1s spreader rake back and lengthing the spreader more. We are keeping mine the same and gonna try some comparasion next race. The question is will moving the spreaders like this change the prebend any, and will is cause the mast to bend more in the long axis then in the short axis. I am not an engineer so it confuses me. Thanks for the help

Not qualified to speak as an engineer but will take a stab at it.
Imagine a mast with straight spreaders and no diamond wire tension. It is straight.
Start tightening the diamonds. Which way does it bend? Probably pretty random depending on which side is tighter and/or slight bends in the 'straight' spreaders.
So now sweep the spreaders back. The tension from the diamond wires are now definitely pulling the mast in a particular direction. So now when you tighten the downhaul (shortening the distance between the foot and head of the sail) the leverage you are applying is already oriented in this particular direction.
Now to complicate this a bit more. Longer spreaders will give you the same bend with less diamond tension. Less diamond tension will result in a less side to side support (the original purpose of the diamonds). This is when rotation comes into play.
Or so I think.
Clear or mud?

The portion of the mast above the diamonds does not have diamonds to force it to bend on its long axis. Naturally, it will bend on its short axis.

Rotate the mast to allow the sailcloth's tension to bias the bend in one direction (sideways bend) rather than to have the sailcloth's tension pulling straight down without any bias to one side or the other which, results in an "S" shaped bend.

In short, rotate your mast a little bit more and you will see the top section take shape in a "(" shaped curve rather than in an "S" shaped curve.

GARY

Makes more sense than what I said. I missed the idea that we were concerned with only above the hounds.
Thank you Gary.

The alu F16 mast is very flexible side to side, but it works impressively well nevertheless. Don't worry to much about strange curves in the top of the mast unless you are flying a spinnaker and the S-curve is pointing forwards. Don't compare yourself to much to other boats (masts)

The mast can take most of it without a hitch. just trim the mains so it feels fast and smooth.


Adjusting spreader rake doen't induce more stiffness to the mast between spreaders and hounds; that only changes the prebend and the distributation of spreader induced stiffness over the side-to-side and fore-aft-place. Some refer to this as changing the amount of "pumping" the rig will do.

The only way to increase mast stiffness between spreaders and hound it to use thicker (or stiffer) diamond wires and to increase spreader arm length.

To change the bending of the top otherwise then through the mast rotation control you can only move the hound fitting up the mast, there are no other factors to play with here. But of course moving the hounds up is not a simply modification by any stretch. So here you are stuck with the mast rotation as the only control.

Play with the mast rotation with a tight mainsheet and see how the top reacts to that. There are sweet spots to be found there, but they are sensitive to the right rotation setting.

Wouter