On a LLM with uncut windsurfing sail, what is the reason why an under sail boom is preferred over using the standard windsurfing boom?
Have a read of this thread.... It may give you an answer to your question.www.seabreeze.com.au/forums/Land-Yacht-Sailing/Sail-making/Mini-sail-design-recycling-windsurf-sails-ideas-logIf you want further follow up on your original question just let me know and I will go into more detail for you.
I understand why a land yacht should in theory have a variable draft sail.
I'm using an uncut WS sail (correctly rigged as for WS) because I saw others on this forum have success with them.
I currently have a below sail boom ( because I liked the look) - I see creases in my sail that I don't have with the WS boom. The outhaul is not pulling at the right angle to the mast. And the sail hits the boom. Hence my question is there a reason for not using a WS boom?
Having success using uncut windsurfer sails needs to be defined. Not knowing any better and miles away from any serious land yacht competition we have a ball out here with uncut sails, just happy to hoot around. (well maybe not, we always want to go faster). After 7 years we still have not cracked 70 kph and not through lack of trying. Having straight runs of only 250m or so before launching into the saltbush limits your ability to wind up gradually after the initial burst of acceleration. In our case above about 50 kph most of our sails start to play up and hit a wall with creases appearing and fluttering starting as we sheet in to match the apparent wind. The creasing is most noticeable on our mylar windsurfer wishbone rigged sails (which also hold our highest speed record to date).
The extra down force on the end of the wishbone changes the bend of the mast about the middle of the sail where the wishbone is attached, drastically altering the sails shape which looked good when rigged initially and up to medium speeds. Landyacht sheeting is unlike anything that happens on a windsurfer where you lean back hard pulling outwards from the centre of the wishbone.
Photos of uncut sail setups with below sail (or slightly overlapping) booms tend to show sails with a flatter foot than the wishbone rigged ones. Their shape is closer to a purpose cut landyacht one. Sheeting an under sail boom in starts the mast bend at the bottom of the sail giving a more even curve. The lower the end of the boom the more side force and less down force when sheeting in so the sail shape stays constant over a greater range of conditions. One day I will muster up the courage to properly cut a sail to suit.
Thankyou - that is helpful.
On my trial run my sail was really misbehaving - I see now it was probably because the sheeting is a lot downwards rather than sideways.
I think I need a different sail, and rig the boom differently. The current sail is an old snap cam - it can be rigged with or without cambers. In my trial run I had no cambers so the sail was flat, but it was a real handful. Only the one crash though.... the seatbelt and foot straps saved me.