Hi
Dug out a landyacht I was putting together 6 years ago - never tried it.
I remember trying to design it so I could use my good windsurfing gear - just attach the rig and go. I set it up now with an old mast and sail. It looks like it should work but I would like some opinion on whether its a good idea before I hurt myself. The boom has a pin going down into the stub mast, the mast is on a plastic ball and the whole rig rotates easily. I think I reinforced the stub mast?? The boom could be attached to the stub mast with a strap instead of the pin - which is what I would do with my good gear..
I could ditch the setup and just poke the mast (with modifications for the downhaul) into the base socket. Maybe its better to have a mast and sail dedicated to the land yacht.

I think you will have problems where the pin goes into the stub mast. As it is the only connection point apart from the main sheet, most of the force from the good sail / mast combination is concentrated at this single point. The loose bottom of the mast will try to slide sideways if there is any imbalance between the force on the sail above and below the wishbone. Landyacht masts need to be much stronger in the base section than a windsurfer mast because there is no flexible rubber base and no one standing up, holding the boom and transferring lots of force down to the board through their feet as well as acting as a gust shock absorber of sorts. Stiffening up the lower meter or so of a windsurfer mast by either fitting some timber up the centre or preferably gluing a section cut from higher up on another mast that fits neatly inside.
Initially we just shoved a standard mast into the base socket which worked well until we got a bit more confident, the wind came up and we started sheeting hard to go faster. Creak , crack, crunch and we had a sail and mast flat on the ground with a 250mm long shattered fibreglass tube left in the base socket.
Once you work out the tuning, a dedicated landyacht mast in combination with a reasonably matching sail doesn't take long to set up and can take a lot of punishment.

Thankyou for those observations.

The plastic ball joint has a 10mm bolt up the middle of it - loose to allow the mast foot some deviation. I don't think it would break but there may well be some interesting dynamics - I hadn't thought of the fact you do put a lot of force down through the mastfoot when windsurfing. (or why)

Given that I was uncertain whether the arrangement would work, I modified an 600mm aluminium windsurfer extension tube to go down into the land yacht socket (has a plastic ball point on the end) with the downhaul pulleys and cleat just above the top of the socket, with the mast ending up just above that. There is a plastic spacer at the top of the socket to help the mast rotate, and also there is a screw attached to the socket to retain the mast in the socket. That gives about 400mm aluminium inside the mast. Should be enough?

Still using a windsurfer boom.

The plan is to try both setups. With uncut windsurfing sails because that is what I have.

Keen to try making a sail but unsure exactly how to proceed - like how stiff should the mast be (a windsurfer mast?) and what shape to cut. I'm sure the answer is on this great website but have to sort through a lot to find it.

Sorry mulgachook I misunderstood your point regarding the attachment to the top of the stub mast. yes . Although that load will be transferred to the base of the stub mast. And cause the stub mast to break at the base. So I need to reinforce the stub mast much like you do with the conventional method of using a windsurfing mast. I did reinforce the stub mast when I made the yacht but in retrospect it probably it is isn't enough (just a piece of wood inside the stub mast).

Its looking like there's not much point in the stub mast design, unless it goes better .

By all means try different things. just like windsurfing if you can match a mast to a sail curve it will perform. I think I can see a seat belt on yours, absolutely necessary once you get a little speed and start turning hard. Dedicated sails to suit landyachts tend to have a flatter foot so the whole sail can be lower giving less tipping force and still clear the pilots body and head. In the case of your sail in the photo another eyelet 250mm up from the foot and pulling out the botton batten would nearly allow a single boom to be used or allow you to lower the whole sail significantly so that sheeting the windsurfer boom exerts more sideways force than downwards. Just roll up the excess foot of the sail. Realistically only a small area of the sail has been lost to give a more landyacht friendly shape.

Almost finished the new version of this yacht.
A question regarding the mainsheet - what length is typical? like how far out does the sail go in use? Also is there a knot tied in the end or do you leave it free to run in case of wanting to release all power?
Are foot straps to retain feet onboard, in addition to a seatbelt, a good thing?

Finally after all these years . First go , very strong wind. Sail too big and not enough outhaul, but nevertheless was very smooth and exciting sailing. has ski suspension which worked really well.