Position of rotation on a 45ft carbon mast built in France 1989

[JIAFox]

Hello I would like to raise a discussion and pick all your brains from a few year ago

Its about an aft positioned Ball/cup on a rotating mast from thelate 80’s

I wanted to explore the pros and cons

Made in France by J.P Marechal in 1989 out of Carbon and reasonably lightweight with a wall thickness of 5mm but obviously strong enough to put winches on

so could support a built on carbon gooseneck and spanner like the photos I have included.
They must of been a good reason why it was designed like this in the first place any ideas?



Also i ask in relation to the gooseneck position which will effect mast rotation
Mast or deck mounted ?

Before the Gooseneck had been a deck mounted affair and would like to consider various options on a new boat as old boat does not exist anymore
I did hear the mast tended to self center in light winds hence exploring new gooseneck and spanner design options here



Many thanks for looking and fair winds to all

 

[kruiter]

I'm interested in this discussion, but not immediately understanding the photos or the questions.

 

[Rasputin22]

The best explanation I have for the aft end of the chord placement for the mast rotation ball is that when the mast rotates the aft end of the mast doesn't move to leeward and choke the slot with the jib. Better for the forward CL of the mast to move to windward. But it also does have an effect on self rotation but that is what the mast tiller is for. Also needing to be considered is where the mast hound attachments are, usually on the thickest part of the mast chord where there is usually a structural web or perhaps not. Using a Jesus shackle for both capshrouds and the forestay on the very front CL of the mast is a whole other story though.

 

[JIAFox]

interested in this discussion, but not immediately understanding the photos or the questions

Thanks for your interest
trying find out where and what type of gooseneck to use on this early well built carbon mast and also the design reason behind it
ie why it didn’t take off?

 

[JIAFox]

The best explanation I have for the aft end of the chord placement for the mast rotation ball is that when the mast rotates the aft end of the mast doesn't move to leeward and choke the slot with the jib. Better for the forward CL of the mast to move to windward. But it also does have an effect on self rotation but that is what the mast tiller is for. Also needing to be considered is where the mast hound attachments are, usually on the thickest part of the mast chord where there is usually a structural web or perhaps not. Using a Jesus shackle for both capshrouds and the forestay on the very front CL of the mast is a whole other story though.

Many thanks for your input

The tang is on the forward part of the mast for cap shrouds and Jesus shackle so rotates smoothly

As I said before the deck mounted gooseneck made the mast elf center and de powered the sail in light winds when you want the deepest sail shape

What style gooseneck would you recommend?
Here is another idea to control the mast rotation

 

[longy]

Taking the gooseneck off the mast removes a large high stress point - but now the axis of boom movement is not aligned with the sail track, so sail shape changes with rotation & boom angle. gooseneck on deck also removes a large compression force on the mast ball. Having the mast rotation point as far aft as possible reduces sail shape changes as mast rotates. To mount gooseneck on mast will require a large saddle wrapping around mast to spread load out. I do not have any feel for how much load this will add to the spar & ball.

 

[JIAFox]

Any links to another mast with a similar point of rotation?
Should I keep it or possibly add 15 ft the the 45ft mast by finding another mast broken with a gooseneck already on so I can use the sets of sails fully as they were originally designed for a 57ft -60ft mast

Thanks for your ideas so far