Arne wrote:

I guess Paul S has made the forward batten pockets a bit longer than those on Boudicca, to let him further increase the mast balance.

By the way, love the junk sailing: being able to post here, while navigating in these tight waters

Paul S wrote:

Just measured:

Camber: 9.6% (47 cm at 490 cm chord length), measured at position of max camber

Balance: 23,3% (114 cm at 490 cm chord length)

Arne, I guess my camber is a bit higher then your estimation because I slackened the batten tension quite a bit (you proposed 2-4cm. Probably I overdid it a bit and went for 4-6cm). However, I'm quite happy with that increased amount of camber.

Good  -  and you of course remembered to subtract the thickness of the battens? 
Those 23.3% mast balance, is that before or after you latest adjustment?

As for tacking angle in light winds, there are two possible reasons for that:

• Tacking angle on the chart will always be worse in light winds than in strong winds, since the headwind (boat speed) component is relatively stronger than in stronger winds. We don't sail twice as fast in 12kts winds as in 6kts.
• Some fin-keels may lose grip in lighter winds. My former boat, Johanna was not so good in that respect.

Arne

Arne, another reason for the (rather little) deviation of your and Ketils camber to mine could be, that we used different curves: as I read it, you used a bending wooden spline, whereas I used CAD. In principle the same, however in practice some deviation would be expectable.

It might be interesting to compare those curves. Do you have any foto from above of your curve? We could easily put my drawing on top and compare (though it would admitedly be rather academic).

Cheers,

Paul

Graham wrote:Hey Paul, that is a beautifully-setting sail.  I'd be interested to know what your camber is.  I am interested in the relationship between camber and displacement, and what people like Arne, Paul Thompson etc, think is the ideal ratio.  I'm envious, looking at all these beautiful junk sails.  I'm looking for a cheap, suitable, fibreglass boat between 26-28' (8-9m), with moderate displacement, as I do not think my current boat is right for the project.

Camber and sail area versus displacement.

Graham, I cannot say that I have found that ideal general ratio between camber and displacement. I used to say that heavy displacement boats should have more camber than the others, but these days I am not so sure. Maybe on auxiliary rigs mainly meant for reaching and running...

For my own boats I have settled on 8% (real, measured) camber, as this has proven to both be close-winded and easy to keep in that groove between luffing and stalling. In addition, this modest camber (compared to genoas with 12-15%) works well as the wind picks up. Remember, the camber in a junksail cannot be adjusted under way. What can be easily adjusted is the sail area, so I generally rig generously. This extra sail area gives a nice long luff (including the 60-70° head) for improved upwind performance, but also spreads out a big nice area for running before.
Then, while the Bermudan sailors flatten their sails in rising winds, I drop a panel (..or three...).

Paul S. has demonstrated this beyond any doubt with his generously rigged Maxi. That sail was originally meant for a much heavier boat.

Soo, if I after all dare present a rig size and camber strategy, it may look about like this:

·         Decide how tall and heavy mast(s) the boat can carry in the conditions it is likely to meet. The answer depends on what material the mast is to be made of. This again depends on what is available at a tolerable cost. I try to keep the mast below 3% of the boat’s weight.

·         Then, rig as big a sail as possible.

·         As said, I stick with the 8% camber in the lower panels, as this is easy to make with the barrel cut method (plus Amateur Method B). The top panels are made progressively flatter, but never completely flat (..the top panel on Paul’s Maxi has a 44mm Round at both the yard and top batten...).

I hope this makes some sense...

Cheers,
Arne