regarding mast rake backwards, I understand the need to do this to tune up the position of the CE with the CLR for good balance/steering. However if the mast could be vertical would this be the ideal? Or not? Like is there any aerodynamic advantage in raking the sail back on a landyacht?

Are you referring to RC yachts or human size yachts?

I'm interested in knowing the answer, whether RC or full sized landyachts.
I think the effects will be much more noticeable, if there are any, on a full sized yacht.
On a windsurfer there is something called closing the gap where you rake the rig back so the foot of the sail lies along the board = supposedly faster.

Ok then, lets have a think about things already out there....
Gliders (aircraft) they have very long straight wings with little or no rake...Why? The reason is a 'wing' with little or no rake gives a high lift BUT it is very exacting in the angle of attack of the wing, higher drag, lower speed.

Raking the wing back gives a wider effective angle of attack, thats why the QANTAS / Virgin etc aircraft have raked wings, much better in takeoff and landing and much more forgiving in balancing an aircraft.... BUT its not as higher in performance as a glider. (less lift but slightly speed)

The Australian Army / airforce aircraft the F1-11 has a swing wing that try to get the best of both types of wing, wing straight for high lifting in take off to get the heavy loads into the air then swing the wings back to get additional speed during flight.

Lets think about land yachts then a tall high aspect ratio rig with minimal rake would be good for light winds and slower speeds (small open sites) BUT the yacht will be more tippy.
If your sailing site has strong winds or disturbed air or is large where high speeds can be obtained then raking the mast back might be useful.

Many years ago the Class5 yachts had an overall height restriction on them, by raking the mast back a higher aspect rig (greater lift) could be used and still meet the height restrictions.

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Gizmo said..

Many years ago the Class5 yachts had an overall height restriction on them, by raking the mast back a higher aspect rig (greater lift) could be used and still meet the height restrictions.

I dont recall 5's having a height restriction.
certainly the promo 5 uses that principle. I recall the 5 having a combination of mast length and distance to ground from base of mast =5.5m

[I'll apologize in advance for a overly brief description of sail aerodynamics.
The best single reference I know of is: www.nz.northsails.com/RADUploads/How-Sails-Work.pdf]

High-speed aircraft (ex. jet airliners) use wing sweep to reduce drag as the approach the speed of sound.
At the speeds we operate other effects are more important.

There are significant aerodynamic effects of sweep/rake, but as mentioned above, it is often used for the practical purpose of shifting the center-of-effort fore/aft to trim the boat's handling.
This is also done with aircraft, a notable example being the DC-3. The leading edge of the wing was slightly swept late in the design to shift the lift aft to balance the plane without major structural redesign.

First, the induced drag (i.e. the drag generated simply as a result of creating lift) is inversely proportional to the aspect ratio of a wing/sail (i.e. longer/narrower wings generate less drag than wider/shorter wings of the same area).

Second, the most important effect of sweep at our speeds has to do with the varying angle of attack (AOA) along the leading edge of the sail.
In general, the AOA increases from the base to the tip of a an aft-sweep sail.
This means that the top of a sail is mostly likely stall first.
This effect is independent of any change in wind angle with height above the ground.

Conversely, a the AOA decreases from the base to the tip in a forward-sweep sail.

You may think that a forward sweep isn't important for sailboats, but the sweep is measured at the quarter-chord line (i.e. the point 1/4 from the front of the sail), so for a tapered sail with a vertical leading edge (ex. the mainsail on a typical boat) the sail is actually swept forward (see diagram below).

Finally, the AOA also increases along the leading edge of a tapered sail/wing.

Since we tend to have somewhat aft-swept, tapered sails, the biggest effect to consider is the increase in AOA from the base to the tip of the sail.
This is the reason that the tell-tales at the top of the sail stall first (and why most sails are cut with some twist in them).

Thanks for this info guys.
The link to Northsails is very good.
Now I'm interested in what the practical limits are.