Adding or Improving Adjustable Shrouds on a Non-Waterat Boat
Older 505s which origionally were rigged with magic boxes or non adjustable shrouds do not have the shroud tubes through the tanks which are necessary to rig the Waterat system (I guess also first known as the Lindsay system). The Waterat system has a turning block on the rail which a shroud extension runs through, then down through the shroud tube, and to a 6:1 purchase with wire located at the base of the mast.
As an alternative the 6:1 can be moved up to the rail with no loss of mechanical advantage and only a slight penalty in windage. On 4565 the magic boxes, shroud extensions, and rail mounted turning blocks were removed completely (you can see the outline where they were taken off). For the 6:1 I used the small high load Ronstan blocks (I believe called Series 19). On the rail, a Series 19 treble block with a becket replaces the old turning block. On the end of the shroud is a plain treble block. The Series 19 blocks seem to have the best combination of strength, weight, and size, and are quite capable of handling the loads on a 505 shroud.
For the 6:1 I used 1/8" Technora cased line. 1/8" Spectron 12 has a slightly higher breaking strength, but the strength of the blocks falls well within the load capabilities of the line and I felt the case might make the line less subject to wear. I did however use the Spectron 12 as a preventer tied between the blocks in case of equipment failure somewhere in the system.
From each rail the line must be led to the center of the boat. On magic box boats this was accomplished with a small turning block mounted inboard of the box. On 4565 I have moved this block further outboard to straighten the lead somewhat. . In doing so I've moved the line from in front of the opening, and the block is also now able to be mounted over the same backing plate which previously backed the magic box. This is a stronger part of the bulkhead and the block is less likely to pull out and cause damage.
In the center of the boat the lines are led aft by blocks attached to the bulkhead. I used the same blocks which the magic box used. Before strengthening the bulkhead, it used to flex aft over 1" under medium rig tension (on the dolly). Flexing the bulkhead dissapated a lot of energy from the rig in puffs, and also seemed unhealthy for the boat. On 4565 I laid up about eight layers of fiberglass, alternating cloth and mat, in an area aproximately 10" by 16" centered where the blocks attach to the bulkhead (on the back side ie. toward the bow). There is probably a better and lighter way to strengthen this area, but this has seemed to do the trick and was very easy to do.
Once the lines are led aft at the bulkhead they attach to a 4:1 purchase with a thicker line which cleats where the skipper can reach it. In the photo, this is the light green line with blue flecs which cleats at the aft end of the centerboard trunk. The cleat arrangement on my boat still needs work, so do not use it as a good example. The place where the thwart attaches to the centerboard trunk is probably a pretty good strong place at which to attach the fixed end of the purchase.
I havn't used this system in really heavy air yet, but it is a major improvement over the magic boxes in every way. Total cost was around $80. The blocks were $18 and change each (four blocks, two treble and two treble with a becket), and 40' of 1/8" Technora was $7 and change (this left me with a lot of extra line, but it's not worth getting it too short with prices this cheap). This price does not include the hardware or line for the 4:1 as that was recycled from the old system.
According to a reliable source, this system is similar to that on the World Champion K. Bergstrom's boat.
Andrew Cole
LaserAndy@aol.com
As an alternative the 6:1 can be moved up to the rail with no loss of mechanical advantage and only a slight penalty in windage. On 4565 the magic boxes, shroud extensions, and rail mounted turning blocks were removed completely (you can see the outline where they were taken off). For the 6:1 I used the small high load Ronstan blocks (I believe called Series 19). On the rail, a Series 19 treble block with a becket replaces the old turning block. On the end of the shroud is a plain treble block. The Series 19 blocks seem to have the best combination of strength, weight, and size, and are quite capable of handling the loads on a 505 shroud.
