Gooseneck on wing mast

We built a wing mast for our catamaran - it will rotate on a spherical roller thrust bearing mounted on a stub
I was planning to attach the boom gooseneck to the base of the mast, mainly because the bottom of the

mainsail would line up with the cars above when the mast rotated
Now having second thoughts because I want to avoid boom thrusting into the mast and countering the rotation
Maybe the boom gooseneck would be OK if it were attached to the cabin top below the mast base
Any thoughts?
Thanks

 

The boom should be used to help the mast rotate. I am not sure what you mean by the "boom thrusting into the mast". If it is a horizontal force applied to the mast, that is dependent on the sheeting angle and can be solved by the placement of the mainsheet blocks.

 

Keep in mind that if the pivot point of the gooseneck is aft of the mast,the sail will gain fullness as the boom goes out.It might be a good thing but how do you propose to control the rotation of the mast? I've only once sailed with a rotating mast that wasn't locked to the boom and it was so long ago I can't remember anything about it.Even though its on a much smaller scale have you looked at how a Tasar rig work?

 

The boom loads induce rotation, which is often a good thing (as Gonzo said). It looks like you have serious tillers for the rotation control.

 

The Rudy Choy 60' racing cat Aikane X-5 had the boom attached to the deck just aft of the wing mast. This had the advantage of automatically increasing the draft of the sail as the boom was eased.

 

Thanks for your thoughts and the picture gentlemen

Like the tiller on that racing cat with the winch mounted on it. Solves a few nasty halyard problems.

The thrust of the boom into the mast is caused by the outhaul on the clew. But I had not thought it through...the clew tensions the foot of the sail and that force opposes the thrust. No net force.

Conclusion: the gooseneck vertical axis will be welded to mast base plate approx under the car track.

Next problem: Because the boom is only a foot above cabin top can't fit a vang

Instead I was thinking of an arc traveler across cabin top and a sliding rigid connection up to mid boom.

This eliminates main sheet. Still need two lines to adjust traveler position.

Camber control would be by the clew outhaul and twist control by an aft "Cunningham" through a block on the clew.

These two lines (vectors) would provide more precise control of sail shape and the mainsail would be self tacking.

This week we are going to build the mould/mold for the boom. It's a wide U shape with chines. The plan is to vacuum bag about eight layers of carbon and epoxy into this trough.

Looking forward to your comments

Michael

 

Using a vang as a mainsheet is going to need massive leverage as is a “Cunningham” as mainsheet. The gearing ratios are going to be orders of magnitude above the “conventional” arrangements.
Why ?

 

All Open 60 boats use a separate gooseneck fixed to the cabin top in front of the mast. It is a safety measure allowing the boom to be swiveled up and used as a jury mast. It usually consists of a piece of U channel with added knees, google for pictures, it's a simple affair and would not interfere with mast rotation.
Have you tought about a rigid vang?

 

A gooseneck in front of the mast on cabin top - that's very interesting - will check images on google
To clarify the idea of the travelling strut to replace mainsheet here is a sketch - this is just the concept

 

You could instead have a half wishbone with a ring set up the mast a metre or so and with a curved boom ... so as to not distort the main as a straight boom does. Then you can dump the curved vang and all the junk. Alternatively go to a conventional double wishbone. Here is Frog with a D shaped cross section mast. The D allows a simple straight boom inside the double mains.

 

Wishbone boom: Possibly. Fortunately I built in a strong bush all the way through the mast one meter up.

But what about when you drop this mother of a main. There needs to be either boom bag or wide boom to catch it.

 

You don't need a vang on a catamaran with a full beam traveller. The downwards force on the sheet is enough.

 

Pretty much the same as conventional setup except you need a different set of lazy jacks going to clew area.

 

Do Open 60's have rotating masts ?

 

Depends on the generation, but yes they do. Usually, if you see deck spreaders it has a rotating wingmast. There were also boats with wingmast and conventional mast spreaders.