Eureka,
Does #1122 have a single backstay to the center of the transom, or a split backstay to the aft corners? That would determine how you would set it up.

Eureka,
Won't you have to replace the spectra rope every couple of years due to UV exposure? Maybe you should use wire for the two legs? I would ask a professional rigger about this change. There are a LOT of loads involved with the backstay.

The previous owner of our boat gave me a double pulley system for our split back stay for a tensioner. He had purchased this to be used to tension the backstay as the way it works is it brings the split backstay closer together as it is pulled down with such as a vang that is needed yet.

I have where the backstay attaches at the stern a clevis at each point it attaches at the stern. The clevis pin is taking the place of the pin that is normally used to attach the backstay to the tab at the back of the boat.

Then what I presume would happen is a 4 to 1 vang is attached to the double pulley and at the clevis and as you pull down on the vang, it moves the pulley system down towards the stern thus pulling the mast back. I have not put the double pulley on or bought a vang yet for it. It is a very simple system actually.

This brings up a question I have been pondering also. I added 2 Norseman 5/16 backstay insulators last spring. It says the breakage limit is 13555 lb. Does anyone know what the load is on the backstay it self? I know it is not 13555 lbs but I would feel a lot better knowing what the load is. Also has anyone ever heard of any of the backstay insulators failing?

Randy

Randy
You posed an interesting question concerning how to analyze the backstay forces. Looking at it from the simple machines Physics view, you have the 4:1 vang attached to one side of the split backstay through a block to the other side of the split backstay. The block adds a 2:1 mechanical advantage to give the backstay vang a mechical advantage of 8:1. The split backstay can actually be analyzed as an incline plan simple machine. The split length of the backstay on our Mk I C36, hull # 1339 is 15 ft. The are attached to the stern 4 ft apart. If you analyze half of the spit backstay as a simple ramp, the idea mechanical advantage 7.5, 15 ft ramp with a height of 2 ft (15/2 = 7.5). Since the separation is 4 ft, the mechanical of two incline planes is 15/4 = 3.75. The total ideal mechanical advantage would then be (3.75) x (8) = 30. Ideally a force 50 lbs on the vang would produce an additional force of 1500 lbs on the backstay. The actually mechanical advantage would be reduced by the efficiency of our simple machine but block and tackle arrangements can have an efficiency of 90%. The next question is what is a safe working load for the Norseman backstay insulations? If you analyze them like the backstay, the load should probably be less than 20% of the breaking strength but this is a question to raise with Norseman. Hopefully this simple analysis helps.

John I--
s/v Pooka
1994 C36 TR #1339

Our C34 technical editor wrote a backstay analysis article a few years ago, published in [I]Mainsheet[/I], I'll see if I can find it. But it really isn't rocket science, and Tom's right, any rigger will help you out. If you have a split, consider raising the height of the split if it hits your head while you're at it. Here's what we did, with a Garhauer split sheave and a Garhauer vang with simple StaySet for the line. The drawing has a different way of dealing with the split than we installed. There are many ways to do it. We installed oversized D rings at the transom chainplates to handle the vang on starboard and the line to port. Hydraulics on our boats, I believe, is overkill & unnecessary.