sounds like a very much more detailed project than my current one - although we are both doing similar things. I have a block of wood on bottom of hull lined up with the keel. It has 5 different (partial - not through) holes slightly larger than the mast diameter. At deck level, I have the same layout using a very thin aluminum plate but holes go completely through the aluminum. This flat plate can be moved fore/aft and is held in place by several “Bull-Dog” paper clips during trials.
Basically the rig mast goes through the aluminum plate, and the mast base rests inside the wood holes on bottom of hull. The plate shifts fore/aft to provide mast rake - and I can move the entier rig fore/aft by using different holes. Sounds complicated, but it is for finding the optimum mast location. Once located, a carbon or brass tube (sealed at bottom) is fixed permanently and through the deck. Once deck is attached, the mast location is fixed (not great idea but works “ok”) and sheet is attached to “fixed boom” to adjust angle of attack. Keep in mind, bearings, sliding surfaces, etc. are disregarded - this is for mast location only and the items are temporary.
Reading your explanation, perhaps a premanent track on deck and in hull would allow mast relocation at any time… assuring the open holes are sealed to provide water entry.
I have to disagree about the comments that a Swing Rig is not more prone to diving than a conventional rig… In a conventional rig, the jib tends to lift the bow when going downwind… With a swing rig, once the boat is trimmed bow down (in a gust) the entire sailplan is now pushing the boat deeper… Regardless of how it occurs, the next step is even more important… Once a boat with a swing rig dives, there is a good chance that the jib yard will hit the water… This results in the jib filling with water, reversing due to the forward motion of the boat, and quickly pulling the boat over to “windward” (ie the jib side)… In an extreme case (which I have seen many times) the boat ends up laying flat in the water, with the mast sticking out on one side and the keel on the other… and it stays that way until there is no longer enough wind in the main to keep the boat moving forward… No winch is powerful enough to sheet in against the jib full of water…
Not only does this usually put you a long way behind in the race… It can result in catastrophic damage to your boat and the following yachts… They are suddenly faced with a stationary obstruction in their path as wide as the height of a rigged yacht from bottom of keel to top of masthead… I have seen (and been involved in) some horrible collisions resulting in everything from broken masts to severed keels to yachts sunk… Not a pretty sight… It is to help avoid these problems that my Viper+ Marblehead was fitted with a swing rig (actually a "STING rig - for STerne swING rig) as the top suit only… The yacht used conventional rigs for the “B” and “C” rigs and that was a part of its success… Swing rigs have their place… and one that is properly tuned and sailed is a very effective weapon in light conditions… providing you take it off before diving becomes a problem…
I’ll make one other comment about the jib/main ratio… My STING rig uses a 30/70 ratio in order to improve the windward performance… I was able to do that by using a highly bent mast to move the CE of the mainsail back further behind the axis of rotation of the mast… That allowed a larger jib to be used and yet still have the total CE of the rig behind the mast… The mast on the Viper+ was bent back about 8" at the top so that the LEACH of the main was vertical and there was about 2.5" of luff round in the mainsail… The mast bend was achieved (and adjusted) by using a very long mast crane and a “backstay” attached to the end of the yard… The profile of the mainsail approached an elliptical shape intended to emulate the “Schumann” planform used by high-performance Sailplanes… Here is a link to a photo of the Viper+ with STING rig…
It is good to see you weighing in on swing rigs. That we disagree on a lot of points is good for the debate.
The jib lifting the bow is a bunch of hoo-ha. Even on conventional “B” rigs the line between the hoist and the pivot point is too vertical to do much to keep the bow from going down. In “C” rigs you may see a bit of that but at “C” rig level winds the jib’s shape is hard to control so how much lifting action it contributes is debatable. I am not alone in choosing swing rigs over conventional ones, Roger Stollery uses swing rigs for his quiver of rigs and I would say that the UK sees some pretty strong winds and he wins a lot of races.
The Viper was a great boat, and I’m sure if you brought out an RG65 based on the Viper or your Venom 36/600 it would be right up there with the top designs. With your reputation it would be a boost to the class.
I only sailed against a Viper with your Sting rig a few times, they never really made a presence on the East coast. I thought the boat was elegantly executed but I didn’t like the rig much. The mast, in order to impart that much curve seemed too flexible at the top. I guess you used a lighter section tapered carbon blank than Elmaleh’s Pinter masts (which I used for my swing rig kits). I’ve seen the Sting mast vibrate or pump and deflect to leeward more than I’d like, I assume as a result of the light mast section and the large amount of area the mainsail carried in the upper third to fill in the 2.5" of luff next to the mast. The larger area jib was an interesting idea too but because of the extreme mast bend the jib was not a full 80% hoist tall but a lower aspect ratio which in turn required a longer foot and longer yards forward. Longer yards to bury the jib on the windward side in a dive situation dead downwind.
I think that another element that relates to a larger jib on a swing rig, especially one with a lower aspect ratio and a long foot, is an issue of leverage. The weathercocking effect of the large main of the swing rig is present to prevent having the rig reverse itself. If any of you have sailed a swing rig then you’ve probably experienced the rig reversing. It happens in shifty conditions or when there is a lot of wind shear on the pond. When the wind suddenly comes from a different direction the rig can fill backwards or in reverse which stops the boat in its tracks and can result in a stall that is hard to get out of. Experience sailing a swing rig can reduce the times that you are caught aback to almost nil. But it is not just the sail ratio, or even how far aft the rig’s CE is, but the lead of the rig (that area before the mast) that exerts leverage that must be controlled by weathercocking. The longer the lead the more unstable the rig is in shifty conditions. Bear in mind that the jib is not tethered to the deck and is only held in check by the larger area of the main. The jib usually is the sail that sees the new wind first and can react to that wind before the main fills. The longer the foot of the jib, and the farther it extends in front of the mast the more leverage it can exert when it fills first. A large lead is more difficult to tack with in light conditions as well. On my rigs I use the length of the foot of my mainsail to determine the lead from the mast to the leading edge of the jib.
When I started to develop swing rigs I based my ratios on the Stollery rigs. I too went with a bent mast under tension for the same reasons that Bob did, I just didn’t take it to the same extreme. Both main boom and the forward jib extension are angled up from the horizontal, 10 degrees for the mainboom and 12 degrees for the jib extension to keep the spars from catching in the water on extreme angles of heel. I also try to broad reach rather than run straight downwind when the conditions are dicey. Then the only time my boat is vulnerable to a death roll is when it comes time to jibe onto the other tack. Swing rigs are much easier to swap in and out so that you are more likely to choose the right rig for the conditions.
Obviously there are a lot of opinions out there. I hope that for folks like Kurt who are just starting out in swing rigs that all this isn’t confusing the issue but that they would be able to glean some insight from all the talking points. It is the different approaches that make it a horse race and keep it interesting.
based on the thread hijack, I don’t know if it matters, but the current ratio is 24.5/75.5, and it sails beautifully. Now that I’ve received the help I needed, Hijack away, it’s a good debate.