Paul Schnabel wrote:
1. Aerodynamics tell that at about 33-35% is the position of the neutral point of an airfoil, and as such the maximum of mast balance.
2. If I remember correctly, Paul Thompson did already built sails with a mast balance higher than 30%. Correct me if I'm wrong.
Slieve did a fine job using the almost maximum possible mast balance, close to the neutral point. I see no reason, from a fluiddynamic perspective, why the non-split rig shouldn't be capable of the same. (That discussion is maybe something for its own thread...)
Cheers
Paul
32 % mast balance - could that be possible?
I apologise to Thomas for coming up with yet another rig design.
However, Paul’s recent suggestion that an un-split JR could be stable with up to 33-35% mast balance, had me try this one, with 32% balance.
I have followed my Johanna style concept with seven panels of equal area and yard and battens of equal length - so this could be called a Johanna 50 JR!
For the sail to be acceptable, it has to tick these boxes:
- 1. With a slack sheet, the sail must feather from top to bottom, both in light and strong winds.
- 2. The yard and battens must not have to be made overs-strong and heavy to stay straight (i.e. not bend at the mast).
- 3. The rig must not be noticeably slower overall to windward than present cambered junkrigs, with mast balance between 15 and 27%.
- 4. The ‘groove’ where the telltales fly at the leech must be reasonably wide on both tacks (as on present sails).
- 5. The speed and helm balance must be quite equal on both tacks.
If it turns out that such a Johanna 50 sail ticks the boxes above, and both behaves and performs (I am sceptical), then all of a sudden some very interesting possibilities open up:
- · Such a sail will be simple to design and make, using barrel-shaped panels and assembled using the ‘Amateur Method B’.
- · One gets the geometrical CE closer to the CL (here 1.13m), giving easier steering downwind (as with SJR).
- · Sheeting forces will be light (as with SJR).
- · The 50° yard angle ensures a moderate halyard angle, and room for adjusting the sail’s position, to optimise helm balance.
- · This HM-style top end makes better use of the mast length, so a bigger sail can be set on an available mast. Big is beautiful
Summed up, this means that one can increase sail areas to 50-80sqm before one needs to consider a ketch or schooner rig. Such a big sail must still be hoisted, but there are after all winches around, even electric.
Anyway - dreams are cheap...
Arne
(full size diagram in Arne's sketches, section 9)