Rotating Mast Conversion for Com Pac 16

[Pacman]

As I mentioned in another thread, I have designed and built a rotating mast conversion for my Com Pac 16.

My design goals were as follows:

1. Move the center of effort forward on the main sail to reduce weather helm.  This reduces the amount of tiller drag because the tiller does not have to create as much turbulence to hold the boat on course.

2. Increase the effective sail area of the main sail by making the leading edge of the mast part of the airfoil.

3. Eliminating, or at least greatly reducing, the drag created by eddys in the air flow just behind the mast on the standard set-up by creating an unbroken airfoil surface to maintain continuous laminar flow from the mast and onto the sail.

So far, it seems to be quite a success and I am still tuning the rig for the best result.

I'll try to post pictures so you can see how the new mast base works and how the whole thing works to improve sail shape.

When the development work is complete, I may explore the idea of producing kits but there is a lot of work to be done before that could be feasible. 

[Salty19]

Can't wait to see your pics and hear of further testing results.   Sounds like a great idea!  Nice job!

[skip1930]

Too much thought, too much work, too little gain.
It's the same hull, plowing throught the same water
with the same effort.
Old norm. '15 pounds at the sail gives you 1 pound at the keel.'
The Cutty Sark clipper ship with all rags out pulled with several
million pounds in the rigging on a record run.

But turn your mast? Go ahead.

skip.

[Pacman]

The GPS will tell the story.

Testing will begin next week.

[Salty19]

Skip, same hull but probably about 8 more sq foot of forward sailing area adding the foil.  The CP16 could use this change, IMO.  It's under canvassed and has weather helm.  Contrast to your CP19 that is canvassed well and does not have much weather helm (with a foiled rudder).   They are two different boats.

[skip1930]

And two different boat designers. Would this idea be void if the mast was round-and not an airfoil?

Well I'm just thinking like an aeroplane guy. The wing is the same yet the angle of the dangle may allude to a more efficient airflow, but is that more power or less drag?
I have no idea.

More power get's you more speed. Less drag get's you more speed. But how do you tell?
I do know that power gets you altitude while speed comes from the vertical and horizontal stabs on the tail.

Back on the sail. I fly those tell-tails on the leech and luff edges of the sail and can plaster all tell tails to both sails if conditions are right and I'm a wake.

So what I think your trying to do is to make the luff work better, luff less and pull a bit more? Might work.

skip.

[Pacman]

Tried out my new rotating mast set up today on Sarasota Bay.  Wind was between 4 and 12 knots.

The mast now rotates between 15 and 30 degrees off center when I tack depending on point of sail and boom position.

That is, about 30 degrees off center on a beam reach with 10 knots of breeze and closer to 15 degrees off center on a beat to windward. 

The mast base was moved forward 1" from stock when I installed the rotating mast mount.  That, and the fact that the mast is now part of the airfoil, have had two dramatic effects:

1. The boat now points higher than before. It is difficult to accurately determine how many degrees higher but the effect is a significant improvement over stock.  I was not all that happy with the way my boat pointed in stock form but now it is much more satisfying when sailing close to the wind.

2.  There is far less weather helm than there was in the stock configuration.  That definitely makes it so that there is less tiller pressure required to stay on course so it probably sails a bit faster than before (if there is anything to the theory that tiller pressure  = rudder drag).

I don't know how to post photos but next time I go out I plan to take some pictures.  If another member would be willing, I could e-mail them for posting.

This is turning out to be a very interesting and successful experiment so far.








.

[Bob23]

Pac:
   This is a very interesting modification. It would have been nice, however if only the rotating mast was tested without moving the entire rig 1" forward. That in and of itself, would improve the handling of the boat. So we really don't know how much, if any, the rotating mast contributed to the improved handling. Theoretically, the mast rotating should help but it's nice to see results. Any time the center of effort moves forward, less weather helm should be the result. Both moving the mast forward and rotating the mast should've helped individually.
   Don't get me wrong. This is definitely cool and thank you for sharing it with us.
   If you email some photos, I'll do my best to post  them.
Thanks,
Bob23

[Pacman]

Bob23,

I agree that it would have been better to have done the modification in two steps so that we would know how much effect was gained by moving the mast base and how much to attribute to the rotating mast.

The reason I did both at once is that when I set out to construct the base for the rotating mast I had not considered moving it.

It was only during construction that I saw that there was room to move the mast base forward and I thought it would look nice too so I just went ahead.

I couldn't resist that opportunity because the weather helm on my stock C16 was serious enough that I had considered selling the boat.  Now it is definitely a "keeper".

Thanks for your offer to post some pictures.  What e-mail address should I use to send them to you?

[Bob23]

Click on my name on any post which will bring you to my profile. My address is there. Maybe put "rotating mast" as a subject so I don't deleteit. Looking forward to seeing the pics.
Bob23
(ps: I had a lot of help, coaching and a good bit of needling while on my way to learning to post photos. I'll see if I can pass that top secret info to you in an easy to understand manner. Although, I think that it's already been done.)

[Salty19]

Pacman...nice work.    Now you need a foiled rudder.  You won't believe how high she'll point.