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Shorten the Boom Why do this? You probably think I am nuts to mess with a Herreshoff design, and I may be a little nuts, but on a CCA designed boat like the Bristol, or other boats of the 1960's that make maximum rating (early Albergs, Pearsons, Cape Dorys, Tartans and others) use of massively long booms , inboard keel-attached rudders, long overhangs and relatively short rigs, the result will be a lot of weather helm. A little weather helm is beneficial to help improve the boat's pointing ability; a little is also a good safety factor - if you release the helm the boat will round up into the wind (useful when you fall overboard). When I added the bowsprit in 1988 all my calculations showed that the boat would be faster and weather helm reduced. It was all theoretical at that point, much as shortening the foot of the main is now. I called Halsey Herreshoff and explained my calculations and what I was trying to accomplish. Halsey argued vehemently that I simply didn't know how to sail the boat, that I was keeping the leech too tight and not allowing enough twist in the main. He also assured me that if I moved the headstay forward I would ruin the boat. Well, it turned out I was right and Halsey was wrong, which I think only proves how rig designs are constrained by rating systems. Weather helm was indeed reduced, the boat was faster and stood up more to the wind so reefing was delayed. In addition, the bowsprit gave me a great platform to hold two anchors, and a great perch to watch the bow wave and take photos. Shortening the boom is another way of reducing weather helm. The B29 boom is gigantic, over 13 feet long. The main has a foot measurement (E measurement) of 12.9 ft. I am reducing that measurement to 10.3 ft. With added roach over what the sail maker recommended, that brings the sail area from 201 sf to 181 sf. Keep in mind that that lost area is at the leech, not in the area of power in the chord. That rear area of the sail accounts more for leverage since it moves the CE further aft which is expressed as weather helm. The long boom of the B29 (and other CCA rated designs), when sailing on a broad reach also adds to the lever arm effect, providing more force to leeward and less forward thrust. A shorter boom for any given rig height provides a higher-aspect sail ratio. and gives greater windward power. The shorter boom moves the center of Effort inboard, offering a more aerodynamic shape to the sail, even when the wind is abaft the beam, and keeps the sail powering and not stalling. Since the lever arm is shorter, the sail produces more lift and less drag. Shortening the boom benefits the boat in other ways. It moves the main sheet to the center of the cabin, out of the cockpit and terminated to the middle of the boom instead of the end. Without the sheet at boom's end, a bimini can be more simply and easily erected and used while sailing. Since the mainsheet is terminated midboom, the boom vang is eliminated, and sheet control is close at hand to the companionway (and under the dodger), instead of at the rear of the cockpit. There are a number of factors involved in this small project. One simple act of shortening the boom will effectively commit me to a number of subprojects, all related:
I stripped all the hardware off the boom after
trimming it to its new length (137 inches). The boom looked like Swiss
cheese when I finished--holes all over it from various experiments with
fittings and leads.
At the same time I decided to build a mounting
base
Since I am planning to lead the main
outhaul back to the cabin top for adjustments, it because obvious to me that
I had to lock down the boom from rotating at the gooseneck. As it
stands, the boom will rotate as the main sheet lead "pulls" it, slanting the
boom the more it is let out. The outhaul will run forward from a turning
block to the gooseneck to another turning block, down the the base of the
mast to another turning block and aft to the cabin winch. But this rotation
of the boom will not give me a fair lead for the outhaul at the gooseneck
turning block. So, to make a long explanation a short solution, I poured it
full of epoxy, it it won't turn any more.
Installing Hardware on the Boom Having finished painting the boom with System Three Orcas White LPU, I installed the hardware. Here are some pictures of the "new" 40 year old boom, versus what it looked like before I began this refit.
The padeye at the bottom of the
outboard end of the boom is strickly for a downwind jibe preventer. Here's a
better shot:
Shown here is
The
The old outhaul arrangement
The reefing lines
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Boom Modifications:
New
Garhauer traveler and bridge of 316 stainless. They build these to your
custom measurements so they are an exact fit. Also very inexpensive. |
Copyright © 2005 - 2014 by David Browne, all rights reserved, hosted in USA
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