This is going to take some explaining, it follows on from the last post on rig.
The sail is essentially the oceanic lateen – there are upsides and downsides to it. The up are that it spills wind better than any other before human hand can get to it. She looks nice and has enormous drive off the wind through that vortex. She loses that advantage dead downwind.
This is Gary Dierking’s version in NZ:
There are two massive downsides:
1. With two bamboo poles or two squarish yards, she is not efficient upwind. Her range is between about 50 degrees from the wind to about 160 degrees.
2. She does not reef and as someone pointed out – it’s all very well having brails to kill the sail in a wind but the canvas is still up there, innit?
There are ways around this though.
Make the sail asymmetrical, scalloped on the unsupported ‘north-east’ edge, forcing the CE downwards somewhat. While losing vortex effect along the yards, a second move buys you efficiency.
This is the class I used to race, called A Class catamaran – far more sophisticated nowadays, modern materials etc. but the principle’s the same. Difficult for you to see the teardrop section mast in the photo but it rotates to face the wind and the sail then ‘trails’ behind it in a foil shape [with camber]. This is how most racing boats do it.
The wing is modest, maybe 8 inches deep by maybe 4 inches thick and I was thinking that that’s not too hard to build. I’ve already mentioned that to make the yard anyway, I need a three piece ‘sandwich’ – central strip with the sail edge wrapped around and tacked down, then the two outer strips – well if I’m going to have to do that anyway, then why not with the leading yard in the shape of a wing? I know the weight – about 40lbs.
There are immediate criticisms but bear with me. One is that a boat does not go to sea with a rotating mast because the stays must all lead forward of the masthead, one goes to sea with a rigid mast, held in place with stays to the gunwhales.
All right, look back at the Dierking photo again, at the three wooden components – a solid mast, the leading yard and then, on the far lower side of the sail – the other yard or boom. Make the mast two-thirds of the length of the leading yard and brace it as standing rigging.
A halyard then attaches to the leading edge of the shaped yard, the yard’s foot attached near the base of the mast.
The boom can pretty much be as one wishes in section. The sheeting, by the way, is continuous in a triangle – boom to port, then starboard, then back to boom, 8:1.
The teardrop yard has an enormous effect on wind flow, especially as it falls to leeward of the mast, unobstructed. No longer rising just as a vortex, the wind is now slipping over the leading edge of the yard which is hanging at an angle facing the wind direction, as in the A Class above. The wind flows across the yard almost all the way up.
This gives an efficiency of around 1.3 and lets the boat sail upwind, but it also allows less sail area to be carried overall.
There’s one other component using the rotating yard and that’s called a
mast yard rotation lever, bolted either side of the base of the yard, leading back to a line cleating above the boom. It allows the boom to rise and spill wind, which kills the angle of attack as well, which protects the boat. When the boom settles back down, the mast lever rotates to leeward by default.
That rotation is critical, it’s a major factor for me – far less stress on spars and on the boat itself, not to mention on the sail, not to mention the advantage in heeling moment. it’s also the second component in wind spillage.
When reefing time does come, one of the yard/sail/booms comes to deck via halyard, is rolled and covered, the boat sails on two sails. Then one sail if necessary. Then they are all replaced by low area stormsails [65 sq ft each]. They’re also dropped one by one.
The default position is all sails in their racks on deck and tied down, the stubby masts still up. In a storm, two masts come down, one stays up with the storm sail.
The stubby mast is 17 feet by 4 inches, the long yard is 23 feet by six inches by three inches [hollow], the boom is 16 feet [solid], the angle is 45 degrees. The cost is still vastly less than a sailmaker-made suit of sails. if the cloth rips, there’s more below deck – unscrew yard/boom ‘sandwiches’ next day and put a new sail in.
If at sea, she sails on two sails while this is being done.
Cost and ease of replacement is one factor, also the ability to use less area. It involves no sewing but plywood corner ‘sandwiches’ bolted or rivetted [I prefer the rivets].
There is another minus- they are used extensively in Pacific swells, not so much in Atlantic chop and vertical waves. I’m thinking though that that’s a good reason to have the V pointing down, largely avoiding the wash over the deck.
In the end, it’s in the seamanship. Also, did I mention the boat looks pretty with those sails? Did I mention the full keel?