Hello, and thanks for the note. Talking about my boat project is one of my favorite things to do. :-) At 01:55 PM 6/29/98 -0700, Michael Kasten wrote: >I have the following questions... > >Via your S/L numbers, the inference is that you have a 60 foot waterline. >What is actual WL length fully loaded? What is WL length with "average" >load. The stem and the transom are both almost vertical, so I therefore use 60 feet for everything. >Are you using short tons or long tons for your displacement numbers? I used long tons for the purpose of figuring the D/L, but I used short tons for everything else. >Do you have specific fuel consumption data for the engines you will be >using? (probably posted before, but is required with this data too...) Yes, I do; but for the numbers I posted I used a slightly more conservative number. What I used was one gallon per hour per twenty hp. Specific fuel consumption charts can get to be very complicated. I hope to be able to optimize my actual specific fuel consumption by using my variable speed transmission to always operate in the more efficient regions of these charts. >Being a Catamaran, have you considered that both hulls are essentially >separate vessels, each with half the displacement and a much lower D/L or >have you considered the vessel as one? I considered them to be two separate boats in all cases where it made a difference. There is an interesting phenomenon that occurs with catamarans at a particular speed at which each hull "surfs" on the bow wave of the other hull. I have also not taken that into account in any of these numbers. This could significantly reduce fuel consumption, if you could design the boat for this surfing to occur at your desired cruising speed. Many sailboat designers take full advantage of this. I learned about this too late in this project, so I did not take it into account. For the way I plan to use it for commercial fishing, this would be a difficult thing to do anyway. For a passage maker, however; a designer would do well to take full advantage of bow wave surfing. >Using the "two independent hulls" assumption you would then double the >calculated HP requirement, and halve the range derived for each hull to >get the requirement of the vessel as a whole. Yes. >How have you done your calcs re: the above? Pretty much the way you have said. >Ideally, the data we use to enter the Gerr / Beebe / Other algorithm >would include: > >** Waterline Length - Feet AVERAGE >** Waterline Length - Feet FULLY LOADED >** Displacement - Pounds or Long Tons AVERAGE >** Displacement - Pounds or Long Tons FULLY LOADED >** Specific Fuel Consumption of chosen engine Yep, that pretty much sums it up. >Using this "standard" entry data with the various prediction methods, we >can calculate: > >Speed & S/L >GPH at each S/L >Horsepower required at each S/L >Total HP required for target S/L Yep.... >For existing vessels which have good fuel consumption data, in order to >run the calcs backward as a check on the algorithms used, the data would >ideally include: > >** Loaded Waterline Length - Feet >** Loaded Displacement - Pounds or Long Tons >** Fuel Consumed - US Gallons >** Distance Covered - Nautical Miles >** Voyage Duration - Hours > >The first two are necessary, noting the loaded displacement and waterline >length. In lieu of the latter three items, one can instead use US GPH at >each given Vessel Speed in Knots. Yep.... >How has the data been presented for the other "in-use" power cats you >mentioned? That has been the tough part. It has taken me several years to collect this sort of data. First of all, most designers will not talk to me about it, though I have gotten much data from them in round-about ways that I have been able to use. Two designers gave me much help, but neither had ever built a power cat as large as this one. I therefore accepted data on sailing cats in some cases and ran with that. A third designer had built boats very similar to mine, and he would talk for hours about them, but he would clam up when I pressed him to a particular point. One designer had planned at one time to make boats similar to mine, and had done tests with 20-26 foot models. He was very helpful, and even gave me the results of his tests for free. The most useful data has come from the owners, many of whom do not know much about the design parameters of their boats. That also makes it tough. As if to further complicate the task, almost all the boats that I did get data from are located thousands of miles away from me. Length and beam on the water line were fairly easy to get. Many owners really did not know much about their engines at all, so I got fuel consumption data and worked backwards to get power when I could make reasonable assumptions about specific fuel consumption. I found that some of these large cats up to 90 feet in the Pacific are powered by outboards. In those cases, I tried to just get the maximum speed available from whatever engines they used and then make adjustments for the lower propeller efficiency of an outboard propeller. In general, it was the outboards that gave me the most variation. The second largest amount of variation came from sailing multihulls with inboard engines. It would appear as if little thought is given to efficient operation under power by many multihull sailboat designers. Believe it or not, displacement is the most difficult data point to get. Most owners do not have a clue as to what the displacement of their boat is. Some were able to get good numbers for me, but some were not. In those cases, I made my best estimate based upon whatever I had available. In some cases, I compared it to similar boats to estimate displacement. In others, I was able to get enough measurements off the hulls to make a reasonable estimate. I never would have thought that so many people would have no idea as to how much their boats weighed. In all this, it was never my goal to develop my own algorithms. What I wanted to do was to check Dave Gerr's algorithms to see if they were valid for long skinny multihulls. I had some concerns about this, because it appeared to me that he had developed all his algorithms based on monohulls. What I learned is that I can trust his algorithms with my catamaran. I did get a fair amount of variation, but that seemed to be proportionate in most cases to the amount of uncertainty in some of the assumptions I had to make about individual boats. Where I had good data, the numbers compared very well. The numbers for Doulos that I posted to this list were then all based upon Gerr's algorithms. My most interesting calculations are for displacements of 116 tons and greater, which I did not post. They are also the numbers at which I have the most uncertainty, but then fuel consumption would be the least of my concerns at that point in time. This is the point at which I would put the wing deck into the water, thereby converting Doulos into a barge with two very large and deep keels. The boat is actually designed to operate this way when I have to. This case requires very large diameter propellers, which convert into very efficient propellers at more normal displacements. It is only because of the variable speed fluid power transmission that I can consider such a large displacement range. While I would not normally want to run at more than about fifty tons, every commercial fisherman strongly desires the ability to really overload his boat. I wanted for Doulos to at least be able to tolerate this abuse, should I ever have the opportunity to abuse her in that way. No fisherman could ever pass up such an opportunity, and I would be no different. :-) Of the designers who guarded their designs too closely to be of use to me, when they saw my numbers based upon Gerr, their reactions were all the same. They believe that these numbers show the power requirements to be much too high. That, of course, is nothing more than a gut feel to them, since none of them have the particulars about Doulos. It is clear to me that they all believe that they could design a passage making powered catamaran that performed much better than these numbers would indicate. I have no doubt that this is true. I have a good idea as to how I could also do the same; but then I designed this boat for commercial fishing and not for recreational passage making. The objectives are very much different. None-the-less, it does not make a half bad passage maker. That was actually part of the reason that I selected a catamaran design for a commercial fishing boats. I had hoped that it could also make passages economically, and I believe that it will. >With these clarifications, we'll have some excellent data with which to >make some good comparisons! What other clarifications would we need? +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ :: Paul and Cindy Kruse :: KJV Joh 14:27 Peace I leave with you, 165 South Kenneth Court :: my peace I give unto you: Merritt Island, FL 32952 :: not as the world giveth, give I unto you. E-mail: plkruse@iu.net :: Let not your heart be troubled, 407-453-6206 :: neither let it be afraid. :: +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++