New Idea

[Stephen Hutchins]

I just came up with this one while sketching a small single handed racing boat. Extend the foward post of the dagger board case up to just below the main boom. At the top, mount a block on a swivel. Run a line from somewhere aft on the mast, through pulley, down through daggerboard case to weighted daggerboard. Now, when the sailor sheets out, the board will lift, reducing wetted surface when running off the wind, and when he sheets in, it will drop. This setup would also serve as a boom vang.

[Todd Bradshaw]

If you're talking about a "boom goes out, line pulls board up/boom comes in, line allows board to drop back down" type of thing, I think you'll find that it doesn't work well out there in the real world. Mainsheet tension on a deep reach or run is often drastically less than it is on a beat - enough so that the weight of the line itself is a hindrance. Having a weighted board hanging on the same line is just going to make the situation worse. The vang is a similar situation. A boom vang is a very valuable sail control gizmo if you know how to use one and fine-tune it. Trying to automate it's function and tie it into mainsheet and daggerboard control will lkely turn a fairly simple, effective and easy to operate sail-tuning tool into a pretty useless and ineffective one. Then what happens in those situations when you actually want to induce sail twist? You would likely need to unstring the system.

If this is a serious racing boat you would be better off with a simple vang, a cunningham and a loop of shock cord which is made fast, in front of the daggerboard. It gets looped over the board's top (or attached to it) and pulls the board against the front of the trunk. You can then grab the board at any time with one hand, move it up or down, let go and the shock cord will keep it at that height.

[Stephen Hutchins]

Thanks for the feedback, Todd. I think also this idea would have VERY limited aplications however, I post them anyway because you never know where they might lead to.

[Stephen Hutchins]

How about some sort of clutch mechanism to take the weight off the boom when on a run? It would have to be very simple to disengage to make the idea worthwhile.

[Stephen Hutchins]

What is a cunningham?

[Carl Simmons]

Cunningham tightens the luff of the sail by pulling it down toward the boom.

[outofthenorm]

Cunningham - A very crafty pig.

[ 05-04-2005, 11:29 AM: Message edited by: outofthenorm ]

[Todd Bradshaw]

The green line which passes through the ring in this sail a bit above the tack ring/gooseneck area is a cunningham.
http://www.imagestation.com/picture/sraid28/pc146694cd88712b151fe44373be10e45/fd6829f7.jpg

When you tighten the cunningham it pulls down on the fabric just behind the mast and along the luff edge. This edge is the area of the sail where extra fabric has been added to form the sail's luff curve (rather than just being cut straight along the luff, parallel to the mast). The pull of the cunningham essentially "gathers" some of this excess, right behind the mast (sometimes even to the point of forming a vertical wrinkle in the sail there). The end result of this tends to move the sail's draft forward and flatten the sail somewhat, which is generally better for upwind work.

Since the cunningham and vang on most dinghies are often not both in-use at once, it's also sometimes possible to build a small, self-contained tackle with a couple blocks, one equipped with a jamb cleat. You attach the tackle to the back of the mast down low around the partners and fit it with a hook on it's top end. This can then be switched from hanging from the cunningham ring on the sail when sailing upwind, to being hooked on a boom bail off the wind to form a vang.

In general though (and in reference to the clutch as well) I think you'll find that all of these controls (vang, cunningham, daggerboard adjustment system) are so easy to rig and adjust individually for fine tuning the rig that it doesn't make a lot of sense to try to interconnect them and automate the process. Especially if doing so means losing most of the ability to individually apply and adjust them as needed.

The old AMF "Force 5" dinghy (kind of a Laser clone) was a good example. It had a V-shaped cockpit coaming on deck, in front of the footwell/cockpit area. Three clamcleats were mounted on each side of the coaming (port and starboard). These cleats were for the cunningham, vang and outhaul (loose-footed sail, so the outhaul tension actually made a difference in sailshape) and the control lines had a tail on each side so that they could be reached and adjusted on either tack.

http://bosunsupplies.com/images/Force5-5.jpg

A simple system, yet it provided lots of quick and easy adjustment in use. A neat little boat and a lot of fun to sail (looks like somebody is building them again). If you look at the photo, you have the cunningham, boom vang, outhaul, traveler and mainsheet right there at your fingertips while sailing, as well as the daggerboard and tiller extension. A well thought-out layout. By the way, you can also dump this boat, ease the mainsheet, step over the hull onto the board and as it comes back up, step right back in without ever getting wet and sail away - which is really fun to practice and gets lots of raised eyebrows from the folks on shore.

[ 05-04-2005, 12:34 PM: Message edited by: Todd Bradshaw ]