[MHml] mast rake

[Dan Frenette]

Great explanation.

If you want to reduce drag start from the bottom and work up.

1) Reduce boat weight any way reasonable.
2) Get the boards in balance with the boat.
3) Look at the board shape. some shapes are a bit better than others. I 
like the NACA 2d profiles. The rake, swept back in the shape to do 
things like control... They all mater if they don't break step 2 or if 
done with the rig change to get back to step 2.
4) Get the bottom smooth and clean. That means before each race or long 
trip clean it. If you think your boat is slower than it should be then 
clean the bottom. This maybe more important the the previous but it 
needs to be done often.
5) Look at the sail shape. If it's bagger than designed get new sails.

I bring this up because a rotating vs a fix rig is further down the "list".

I have a furniture boat that I changed from a fixed rig to a rotating 
rig. The weight of the boat will dampen the effect of this change. I 
took me years to understand weight is drag and drag is lack of speed. 
It's so suttle that you don't even notice it until you race and see the 
net effect. It's that little extra scoot on every puff, a bit of extra 
surf action on every wave you don't kick off on and someone else does...

What did I think it bought me?

Well my actual performance is about 20 seconds a mile faster. Same boat, 
crew, methods, and prep methods.

Where do I think the speed came from?

1) The mast is about 2.5' taller. The sail area in the jib is reduced by 
the amount of going from a genoa to a jib. So by design the sail area of 
the genoa lost is moved into the main. So net/net the same sail area but 
a small amount taller. I haven't calc'ed the change in the center of 
effort. So more efficient sail plan.

2) The mast area is generally not rated sail area. This amounts to about 
38 ft^2.

3) Removing the stall zone seems to let me point a few degrees higher to 
weather without a lose in boat speed.

4) Off the wind I added 2' to the luft of my spin. This lets me sail a 
bit deeper without a loss in speed.

If you aren't racing it isn't something you can measure.

What did I loose?

1) The fixed mast was lighter. It took 2 tries to get the weight out of 
the top of the mast to get pitching under control. If the top of the 
mast isn't lighter or at least the same then it's like adding weight to 
the hull.


John Andrew Metza wrote:
> As you know, your rotating mast (if properly set in rotation) will greatly
> increase the efficency of your rig.  Less drag means more speed.  With this
> increase in speed a pressure wave will build on the leading edge of the
> mast.  The rake in your mast will allow this wave to travel up to the tip
> and into wake vorticies that will be shed behind your boat.  Thus you will
> pass though the sound barrier more easily than with a straight mast.  Make
> sure you are far off shore when this happens so beach front homes are not
> dammaged.
snip..

To put this in perspective. The Macgregor 36 isn't a light boat by most 
standards. Changing the rig is going to help it but the fact that you 
will need new sails or at least rework your sails will have most of the 
effect.

You need to look at the condition of your rigging, sails, and lines. If 
it's time to replace things then the cost isn't going to be that much 
different. If the mast has a bit of rot etc then go for it.

In my case going with line vs cable and being able to make most of the 
stuff myself the rotating mast was thousands cheaper.

JMHO

Dan Frenette