Masthead vs Fractional

[Paul B]

The above post is mine. For some reason the forum shows it as Guest. Strange, since I was logged in when I wrote it.

[Bradonvashon]

Wow that is very helpful feedback. I don't know the measurements off the top for the old rig--but I can get them. I haven't done a drawing of the new rig,so haven't done the calcualtions.

The twist on this is that this is an existing mast that met the basic dimension and strenght I needed--so I've kinf od back in to this whole thing. But the cost and the availability were too tempting to walk away from this as a replacement t the mast I lost.

This thread has been very helpful to me. One questions I have is about mast bend depowering the sail. If the mast bends it should make the sail fuller not flatter, right? As the wind rises don't you want is flatter to shed lift?

[SailDesign]

If the mast bends, Bradon, then the distance from the leech to the luff increases, which perforce (sorry - big word for the day) flattens the sail. I know it FEELS like it should make it fuller, but it donesn't.
Imagine the sail lying on the ground. If you want to flatten it the most, you have to pull on the luff.....

[Bradonvashon]

Sorry I'm having trouble with the geometry of this

If the mast bends aft, Doesn't the distance from the head to the clew decrease? You are closing the angle.

Using an anology if I stand up straight I have no wrinkles in my shirt (normal luff), if I bend backwards (fore) my shirt is really taught (tight luff), if I bend toward my knees (Aft) my shirt is all loose and poochy (loose luff). A rather odd example, but does't that work?


Will the book Sail Power explain/illustrate this all a little better for me??

Brad

[Paul B]

Yes, the head does get closer to the clew, if the clew doesn't move. Simply pulling on backstay opens the leech. But the boom is not locked at a 90 degree angle from the mast. Pull on a bit of mainsheet as you bend the mast and the distance between the head and clew remains the same, so it doesn't add fullness or twist.

Anytime you make a change to a sail control you will probably need to make other changes to get the result you want.

Bending the mast does increase the distance from the leech of the main to the luff, so this removes camber and flattens the sail.

I often suggest that people should tie their boats to the dock on various points of sail (in light breeze) and pull all the control lines one at a time to watch the effects from all angles. This will teach you a good deal about what strings you want to pull to get the shape you want.