Masthead mast rake is measured...

[Drinky Crow]

...at level of boom or right on the deck?

[cal40john]

It's measured to where the directions from the sailmaker or boat designer say to. The problem with standards is that there are so many of them.

On smaller boats there are many different ways that they say to measure rake.

[Don C L]

In my case it was measured at the deck. I have the drawings of my boat though from the designer.

[Jim Cate]

Unless we are talking three-deck catamaran (with the boom 12 or more feet above the deck, there won't be a significant difference in the measurements, so I'd be inclined to use the deck as the level.

Jim

[Alan Mighty]

Originally Posted by Drinky Crow

...at level of boom or right on the deck?

Ivar Dedekam (Sail and Rig Tuning, Wiley, 2000) says at the boom.

Dedekam further recommends up to 1 degree for masthead rigs and 2 - 3 degrees (measured from masthead) for fractional rigs. He has a table for converting from distance along the boom (i.e. the 'b' dimension in the diagram) to degrees from the masthead.

[Jim Cate]

If the aim is to set the mast at some specific angle from vertical, then it does not matter where you make the measurement as long as you use the correct P dimension or its on-deck analog.

However this leads me to a more sophisticated query: how do you measure rake in a mast with pre bend? With a curved mast you can't easily define a rake angle, can you?

Perhaps it doesn't matter... adjust rake until the balance is what you want and then just measure the location of the plumb line as a future reference, and don't worry about the "angle".

Jim

[Don C L]

Do curved masts get a rake? I mean aren't they meant to be vertical and then adjusted as needed w/backstay tension?
BTW make sure the boat is on her lines correctly before hanging the plumb bob of course.

[s/v Jedi]

You first set the rake, bend comes later. I recommend the Ivar Dedekam book too. The rigger who took me as apprentice during our rerigging made me buy it and I still use it every year.

[cal40john]

Originally Posted by Don C L

Do curved masts get a rake? I mean aren't they meant to be vertical and then adjusted as needed w/backstay tension?
BTW make sure the boat is on her lines correctly before hanging the plumb bob of course.

Rake is still important with a mast that bends. They have different tasks. Bending the mast mostly reduces draft, de-powering the sail.

[Jim Cate]

I was talking about PRE-bend that is set initially, before any trim bend is invoked. Some catamaran masts, for instance, have quite a bit permanently set before the mast is even stepped on the boat.

Jim

[s/v Jedi]

Originally Posted by Jim Cate

I was talking about PRE-bend that is set initially, before any trim bend is invoked. Some catamaran masts, for instance, have quite a bit permanently set before the mast is even stepped on the boat.

Jim

Oh I did not know that. We have a catamaran rig with pre-bend but that is set by capshroud tension with aft swept spreaders. When the shrouds are without tension, the mast is straight.