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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> <HTML> <HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html;CHARSET=iso-8859-1"> <META NAME="GENERATOR" Content="Symantec Visual Page Mac 1.1.1"> <META NAME="Author" Content="Dave Culp SpeedSailing"> <TITLE>MIchael Schacht's Diamond Head</TITLE> </HEAD> <BODY BGCOLOR="#FFFFFF"> <P ALIGN="CENTER"><IMG SRC="DiamondHead.jpg" WIDTH="617" HEIGHT="671" ALIGN="BOTTOM" BORDER="0"></P> <P> <TABLE BORDER="0" WIDTH="100%"> <TR> <TD WIDTH="20%"> </TD> <TD>Hi all, <BR> <BR> I thought that since Dave was airing his dream boat, I thought I might as well, too. This is a rough draft, certainly not a final design. It shows the way I am leaning in proa design as far as rig, rudder, and leeway prevention is concerned, and would appreciate comments, criticisms, and opinions. <BR> <BR> The side profile was done in Corel Draw 8, which is a new program for me. I am familiar with 3D modeling, but am now learning a 2D vector graphics program. Fun with fonts, fills, and transparencies! <BR> <BR> This boat is almost a 1/2 scale model of Dave Culp's big (make that huge) proa, at 58' LOA. For me, it would be an ultimate ocean cruiser/racer. I use the term "cruiser/racer" in the sense that it used to be used with the old Cruising Club of America rule, which to my mind produced some of the most desirable monohull sailing yachts ever. The boats designed to that rule have a continual charm and popularity that has never diminished, no matter what the current fashion happens to be in yachts. If that isn't a true test of good design, I don't know what is! This is my take on what a CCA proa would have looked like if proas were allowed into CCA of the 50's! There is a particularly beautiful old racing yacht moored at the Shilshole Bay Marina in Seattle. She is at least 60, maybe 70 ft. long, with an incredible raking bow and perfect sheer. She is a TRANSPAC winner, I understand, and is maintained in Bristol condition by the current owner. Her name is Diamond Head, and she is the inspiration for this proa that carries her name. <BR> <BR> This boat is meant to be fast, of course. Why build a proa if the goal isn't speed under sail? To that end I would keep the hull very fine lined, with a length:beam ratio of at least 17:1. Almost no wave making drag is the goal, as well as an extremely smooth and well modulated ride over ocean waves. The smooth ride is comfortable for the crew, and increases aerodynamic efficiency with a steady sailplan. It would be light as only a proa can be, yet cary enough gear, stores and accommodations for extended voyaging for a crew of 2-4. This boat will also be comfortable, with standing headroom in the bridgedeck cabin, and two private double cabins, one in each end of the hull. The bridgedeck cabin will be similar to a catamaran's, with a settee, dining table, chart table, and a panoramic view. This cabin is located just to windward of the hull, and the cockpit is to windward of that. Open netting will span the gap between cockpit and ama. <BR> <BR> Diamond Head follows the blueprint of the traditional ocean-going proas of the Pacific Islanders. The canoe hull is long and very narrow, the rig is a modern variation of the traditional oceanic lateen, and the ama, or log, is dense and heavy, containing meaningful weight for ballast. The weight of this ama comes from a combination of heavy stores such as drinking water, fuel and batteries, and is augmented in heavy windward going by water ballast. <BR> <BR> The percentage of overall boat weight carried in the windward ama has been a subject of debate on the AYRS mailing list currently. Some think the ama should be light, to promote early ama flying, and indeed to keep the ama flying at all times. Others think the ama should be about 25% of the overall displacement of the boat. Others say the ama should be most of the boat, with all accommodations, crew and stores located there, and the leeward hull used only for mounting the rig, rudders, and boards on. <BR> <BR> I reject the concept of all accommodations and crew to windward. That is optimizing the boat only for windward work in strong winds, where of course righting moment is what rules. Other courses will be penalized with higher than needed wetted surface and with serious weather helm created by the large and deeply immersed ama. For racing, perhaps that is the correct solution, but hardly for a dual-purpose racer/cruiser. This proa will be required to have a light and balanced helm at all times, and be equally proficient at ghosting through the zephyrs of Puget Sound as well as surfing the ocean swells in the roaring 40's. To that end, it will have an ama whose weight is adjustable through a wide range, to suit varying conditions. <BR> <BR> The rig is a wishbone lateen. Its geometry is similar, though not identical to the Pacific model. It is an attempt to remove the neccessity of hauling the tack of the oceanic lateen from one bow to the other during a shunt. The main change is that it is symmetrical end to end, so that the tack becomes the head, and vice-versa with every shunt. The yard is hung from the mast at its center, and the yard pivots around that point, with a tack line pulling the high end of the yard down to the bow, while the previous tack is allowed to swing up. This sail need never reverse its curvature during a shunt, with dedicated windward and leeward sides. This opens up many possibilities for interesting sail/yard/batten combinations, perhaps taking a cue from ultralight aiplane technology. <BR> <BR> The mast rakes for and aft in order to place the sail forward of the c.g. of the boat, and to make the CoE widely adjustable. The sail is also adjustable up and down. The yard may be positioned nearly vertically for light conditions and to get the sail area up as high as possible. Conversely, the yard can be angled down to a 45 degree angle in heavy going. This keeps the CoE as low as possible, and the rake of the yard converts half of the sail's force to lift, further reducing heeling forces. This adjustable nature of the sail is expected to mitigate the need for reefing in most cases. (Which is a good thing, since reefing and furling are still not very well thought out for this concept.) <BR> <BR> Underwater foils consist of a low-aspect ratio keel, and a kick-up rudder in each bow. The keel is simple, strong, weedless, and resistant to grounding or flotsam. The hull will be assymetrical in shape, with the keel simply beeing an extension to improve windward performance. I have seen a Marshall Islands proa with a nearly identical keel shape. <BR> <BR> Diamond Head will have rudders, and not steering oars. Oars on a boat this size would be unwieldy by a crew of 2, and though the proa can be expected to steer itself on most courses, I still want the directional authority that only a rudder provides. The rudders are located in slots in each bow, the bow being split by the slot. Only one rudder is used at a time. The forward rudder is raised to close the slot in the bow, and to create a modest wave cutter. The aft rudder pivots down to lower, and will harmlessly kick up if hit, which is not too likely since it is protected by the keel. The rudders are located in the extreme ends of the boat, where they have the most leverage to act upon. Unlike many modern proa designs, this boat is not afraid of shoals with delicate "rudder-boards" in vertical cases, and can be sailed with confidence by the skipper in waters with questionable charts. <BR> <BR> I would build Diamond Head out of cedar-strip/epoxy, most likely. <BR> <BR> Many thanks to the members of this list, and to MhML, and the AYRS list for the constant flow of ideas and information that promote this tiny but fascinating area of sailboat design. <BR> <BR> Michael Schacht <BR> <A HREF="http://www.schacht.com">http://www.com-cepts.com/mss/</A></TD> <TD WIDTH="15%"> </TD> </TR> </TABLE> </BODY> </HTML>