DelftShip Sample
Doug Halsey

Doug Halsey: DelftShip Sample

Doug Halsey, Jun 12, 2018
    • RumnCoke
      Hello Doug,
      Nice to hear from you. Yes, you are correct, I will need to find a shop that can CNC a two piece aluminum mold for me. It will not be cheap. I am sure I can make some money with Keels anyway. Its all doable. I only need to make some wise choices regarding a naca foil to use and How much chord thickness to start with at the top and How much taper I can live with at the bottom. I am thinking .200 at the top and .170 at the bottom. The top being the Keel line. I will need to extend that another 3 inches for a trunk into the boat. More than likely to be cut down some. Now I understand why the IOM keel makers simply do a rectangular fin. Very much easier to process. They simply cut to length, cut an attachment purchase and sell it out the door. My keel will definitely be a complex shape. I don't plan on any great production, but true US1M keels are not being made by anyone. I only have to make a decent one.

      Now, regarding the DelftShip sample. There do appear to be similarities, but they are only in casual perception. I don't know who's Marblehead design that is. The Keel rocker is definitely similar, but has more curve in the forward sections and much flatter in the aft sections. My boat has more rocker aft. You are looking at a 50 inch boat vs 39 inch on mine. Also, the actual power lines at station do appear similar, but they are of a U shape design, a constant, uniform curve. My Station curves are parabolic for the most part, accept at the stern, but the body plan view gives the impression of alike curves because of the stearn. Now you can look at the plan view and see a very large difference. Max beam on this boat starts a lot sooner from the bow, about 40% back. There is not a lot of flotation in the forward sections of the hull, but there doesn't have to be since its a 50 inch Marblehead, they can get a fine entry and still have enough floatation to support the downwind leverage pressure. The lines from max beam to the stearn are almost straight. Basically a missile, like so many other designs today. They simply rely on the Length of Waterline Rule.
      The dynamics in my boat are much more imaginative, even at 39 inches. Max Beam on my boat is about 60 percent back from the bow, the lines on my boat open up very quickly and serve to provide more surface area forward and provide a flatter profile curve tricking the boat into thinking its a longer waterlline. I know its not tricking anyone, but it provides a kind of scow like waterline, a more flat, longer curve. At max beam the boat profile closes quickly, but not so much underneath. You can see how full it is down there. The lines there originally were to provide lift for the boat to plane but the boat was a bit too short, too heavy, and not enough sail area to get the speed necessary to lift and plane. It came close and many skippers swore it was planning at times, but I don't think so. It was very fast off the wind. So now with the remake, those lines in the aft 30% of the boat are smoothed and tapered to the end just to provide less drag now (no more planning lift). The guy in New Zealand, who did the computer work for me is a farmer. He comes from a family of boat builders and has all the math and computer skills required for the job. He claims over an 8% improvement, less drag, than the original, in flow tests. So maybe now I understand why that gentleman Tansl on these boards keep saying he saw my boat somewhere. Not a discerning eye, that one. A lot of todays models tend to look the same but, it takes a study to see the differences. My boat profile looks more like a .308 bullet, than a missile.
      I would let you have a look at my work. All I ask is that you do not share it with anyone. We could then have some discussion.
      Regards,
      Dave
    • SailDesign
      @RumnCoke - I'm curious as to why you would want the max width so far aft in a model - most of the faster ones appear to have it at less than 50% as the hulls are so skinny that rig-induced bow-burying becomes common, and volume is therefore moved forward.

      No criticism, since you've obviously looked carefully at these things, just curious...
    • RumnCoke
      @SailDesign If you look closely you will see that the my lines open very quickly from the bow. There is no "fine" progression from the bow to max beam, as in most racer designs. My design provides good flotation against burying the bow as you said. It also works to straighten out the waterline curve in the same way as a scow might with the broad front and a shallow curve, essentially spoofing the hydrostatic flow into thinking the boat has a much longer waterline. Check out the scow designs and you will see the max draft back in the 60% region on the racers. The only thing missing on my boat is the wide stern. It closes more like a canoe profile. My hull design is not so much a displacement design as it is a planning design, although this new iteration has lost the power curves in the aft section of the boat, meant to get it up on plane, in favor of a more faired line continuation. Max draft on my hull is 1.5 in. The result is significantly less dynamic drag. Most displacement skinny's may move the beam forward, but it really does not solve the problem of floatation against downwind sail leverage. With the fine lines to the bow they incorporate, there just isn't enough floatation at the keel line. So they compensate by adding more rocker up front. And what is the result? Perhaps a slight improvement, but still the end result is a buried bow. Having more rocker in the aft section will help to raise the bow much the same way as an airplane will raise the nose by adding downforce at the tail. Not only do I have more hull surface up front, I have the added lift from the aft section. I have a longer (spoofed) waterline curve. One last point. Most all designers have been content to use the continuous uniform curve "U" at their stations in boat design. Its not so bad. Many good designs have been done this way. I am of the mind that the Parabolic curve can provide more well defined dynamics in overall shape and performance. My boat has the "U" shape at the "0" station, but going forward you will find the Parabola at the heart of things.
      I have been away from boats, and sailing for a decades. I had not really read into these forums much. Today, I spent a little time reading down in the Design section. Many members are having the same discussions. The design dynamics on my hull are being explored in several racing boat classes. The point I am trying to make is that my ideas are not novel or unique. The idea is to build a faster boat and then of course compete. I am guessing the quest for the ultimate hull designs will stretch on far into the future.
      Beautiful work on that Piccola. Like your rudder profile as well.
    • SailDesign
      @RumnCoke - thanks! Always nice to hear the rationale behind the opinion. :)
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    Doug Halsey
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    Jun 12, 2018
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