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Published 27.12.2015 | Author : admin | Category : Free Fishing Boat Plans

Location: South Africa In short, a displacement hull speed is rooted in the waterline. Am I right to think that the function normally referred to as hull speed is related to the length of the bow wave - a wave's speed being a function of it's length? It seems to me that with adequate power (strong breeze, large sail area) all of the friction or wetted surface issues can be overcome but that the length of that wave is the true limiting factor.
On the topic of high aspect ratios generating more lift, why then would a plane like a DC3 or a deHavilland Beaver, two real workhorses with great load carrying capacity at low speeds have such low aspect ratio wing designs relative to a glider? I have read a bit about the Dashew boats recently and have been moored in Newport Beach California for a couple of months where I have seen Deerfoot, some sundeers and a number of Macgregor 65s.
Location: South Africa The nature of the wave system generated around the hull is the stranglehold which inhibits planing and is an important factor affecting the performance of displacement craft. As it moves through the water, a boat's hull produces both transverse and divergent wave system, although only the former appears to affect the resistance of the hull.
A boat's velocity with reference to its wave system and lenght waterline is judged by a Froude number. The quest for good performance starts with the shape of the hull, particular below the waterline. Overhang at the bow causes the bow wave to creeps forward, and because the of the sectional form usually produced by the overhang, the displaced lenght is increased substantionally when heeling. A full bow generates an earlier bow wave, though the same effect would result from a deep forefoot which retains reasonable waterlines forward. Location: South Africa yotphix, here are the photos to demostrate the wave system created by the velocity of a displacement hull.
Location: California To make sure that I understand correctly, Displacement Length is the actual or perhaps, DEVELOPED distance from stem to stern at the waterline?
Originally Posted by yotphix Maybe a dumb question but what better place to ask a dumb question than a room full of smart people!?!
CFD is, of course, an enormous advance because we can now display our almost complete ignorance in full colour!
Originally Posted by Wynand N yotphix, here are the photos to demostrate the wave system created by the velocity of a displacement hull.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Hull Design software I have designed a 4.9m cat on graph paper and I want to design it using CAD software.
Location: Cudjoe Key Fl Tom, I went through this software thing for a number of years, and finally realized the only good boat design software is a large piece of paper and a sharp pencil!
Location: Denmark Personally, I also prefer to do it the old-fashioned way, but I must admit that it is by no means better than using a computer - only slower!
Software for small craft engineering is available, but probably not for craft of the size you mentioned. The price of $150,000 that BillB mentioned is ridiculus, but you must be prepared to spend up to a couple of thousand, though (I should mention here that there are free- and shareware available, too - search for Hullform or PolyCad). Location: MX Hi Tom, Bill is correct up to some degree, be sure of what you are looking for (or what you want to achive with the software results wise), this softwares are usefull but they are not magic boxes that you ask and they respond, so one quick response could be prosurf and rhino, it has worked for me, and they do most of what i need, this is for hull shape and interior detailing, other good one is hullform and rhino, hullform the pro version is quite complete, it may be little bit harder to use IMO, and again this is for hull fairing and lofting, stability (initial with rhino and prosurf) and complete with hullform, other people will be able to give you their opinions.
Location: Perth, Western Australia I have to comment regarding Bill's statements about the high cost and complexity of modern CAD systems.
Similarly, Maxsurf was the system of choice of 7 out of 10 of the syndicates involved in the 2003 America's Cup. I do not disagree that designing with pen and paper is a perfectly valid way of creating a hull shape, but it is slow, difficult to calculate volumetric properties, and inherently inaccurate, requiring the additional step of full sized lofting to create accurate lines to build from.
Rather than imposing a fixed style on designs, I would argue that computer aided design methods have resulted in a greater degree of artistic freedom in the design of hulls and superstructures, particularly on luxury yachts that have gone from relatively simple shapes 20 years ago to a wide variety of more organic shapes, made possible by powerful surface modelling software.
The pic below, a design by Brett Bakewell-White of New Zealand, is a good example, initially modelled in Maxsurf with further detailing and rendering in Vellum 3D.
I must mention again, there is a BIG difference between Design software and Engineering software. Back to the reality of designing craft under 100 feet, which are considered small craft by all marine architects, sure one can figure out what size screws to use by eye, or state what thickness the bulkhead skins should be but I have never seen any Boat Styling software come close to doing this. As far as pencil and paper and clay models, this has worked for a hundred years, and is 100% accurate. On the contrary, Fastship has a relatively small number of integrated tools compared to Maxsurf. On the other hand, the Maxsurf suite consists of many well integrated applications using common files and a common user interface, all developed by my company, Formation Design Systems. Like Fastship, we rely on programs such as ShipCam for downstream structural design and production, as this is an area that we consider to be outside our area of expertise, however Fastship has no equivalent to our preliminary structural design program, Workshop.
I should also correct the impression you give that Maxsurf is for small craft and Fastship is for big ships.
Location: Cudjoe Key Fl Andrew, now that is the reply Tom is looking for, among the rest of us!
You may want to consider drawing and fairing your hull in a CAD program, not a hull design program. Originally Posted by Mr Efficiency OK, that is a lot, so would the transom be the greatest contributor to the increased resistance ? Take boats of same weight, same length but different hull shapes - displacement and planing.

Originally Posted by Alik Take boats of same weight, same length but different hull shapes - displacement and planing.
Originally Posted by Ad Hoc If same length, and same weight (displacement), then the length displacement ratio is the same.
Originally Posted by Alik Provide resistance curves for two boats with same DLR, but one with displacement hull, another one with planing shapes. Location: spain Gee guys, while you are thinking about it the whole world is sailing past you !!! Originally Posted by Mr Efficiency I am particularly interested in a power cat in this regard, where chines will be immersed from well forward. Therefore, with regards to the resistance of sailing vessels what does induced resistance, heeling resistance, centre of effort and centre of lateral resistance, not to mention the aerodynamics and wind direction etc have to do with power cats?
I have a lot of such calculations done for few boats (from pre-design studies of semi-displacement craft); actually I was doing such comparison just 3 days ago for 60' powercat hulls. All variations of hull shape have very very minor effects and differing at different Froude numbers. Been doing it for over 20 years?shape plays such a minor roll only button pushers with software debate the ?differences?. Please note, that graph #3 is from sailboat, which, if highly optimized for planing, is still designed keeping in mind low speed performance too. Please also note, that Tasar in itself is also not strictly optimized for displacement sailing. The book with different calculation methods is now not in the same room as me, so I cannot present calculations at the moments notice. Originally Posted by Perm Stress To be accurate, 20 years of experience is not an argument. There are other mistakes evident, but I do not want to discuss it as it is clearly not worth any discussion.
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Location: Rockport, Maine & Rochester Hills, Michigan So transom immersion doesn't matter?
Than it is necessary to row it with transom immersed and with bow down trim and transom out of the water.
Location: Australia TAD's graph, if accurate, indicates that at slightly below hull speed, say 5-6 knots, resistance is about 50% more for the full planing hull versus the displacement hull of similar proportions. I would say there is a lot of amateur designers around boats, and some of them produce nice and good working designs. Location: Thailand This is sample of design study made last week for selection of hull shape for power catamaran. It should be noted that for lighter catamarans intersection point between red line and rest of lines (i.e. Originally Posted by Alik This is sample of design study made last week for selection of hull shape for power catamaran. Originally Posted by DCockey How was the data generated: tank test, CFD, software tools, ???
Is a narrow hull with a fine and low angle entry able to achieve higher speeds than a wider blunter hull? Is there a site or book anyone could recomend to a lay design enthusiast to help me understand such things?
Is that perhaps because the advantages of high aspect ratios where poorly understood 50 years ago? It pays to maximize displaced LWL, thus enhancing the hull's capability of generating a longer wave system by a bow wave which forms earlier and a stern wave which extents as far aft as possible. I have some photos somewhere that shows a model of a displacement hull and its wave system created from low speed to max disp speeds. I understand it will take a while to design it on CAD but I am deternined to design the catamaran using CAD software. And there is the added benefit that the software can do the calculations for you (hydrostatics, stability etc.) much, much faster than if done by hand. The only reason why I'm considering purchasing CAD software is because all the most successful companies in the world, whether it is to do with yachts or to do with cars are using Cad software. Maxsurf costs as little as $700, yet was used to design the hull shape of Mirabella, the world's largest single masted yacht.
Each one of these syndicates could afford to choose whatever software they liked, and in many cases they were sponsored by major CAD vendors, yet they chose to pay full retail price for Maxsurf.
As a result, few of todays professional designers still do things by hand, and more and more use computer systems such as Maxsurf, and are more than satisfied with the results. Maxsurf and the like, are fine programs for small craft, and making beautiful displays, BUT they don't ENGINEER the boat! Remember you the draftsman are creating the exact cut lines this way, the computer is always off by some. Proteus, the authors of Fastship, rely on GHS (by Creative Systems) for their hydrostatics and stability, NavCad (by Hydrocomp) for their resistance and propulsion, the US Navy SMP program for their seakeeping analysis, and ShipCam (by Albacore Research) for detailed structural design. Maxsurf is used by shipyards of all sizes, including installations in 5 of the biggest shipyards in Japan - Mitsui, Mitsubishi, Kawasaki, IHI and Sumitomo. Admittedly, in Maxsurf you can set the tolerance to which curves are calculated, and the default is 0.2mm.

User ID - guest, password - guest) and you can access our FAQ, manuals, and tutorials for all programs. I still draw the basic shapes by hand and transfer them using points into Ashlar-Vellum Graphite ($995). Hull shape plays such a minor roll it is not worth considering; except for those looking at endless decimal places in their computer software print outs!
Note that at Fn=0.3 (that is comfortably below hull speed) Skiff (yellow line) has ~26lbs and Tasar (blue line) ~12lbs of resistance. If this hull was designed without any regard for low speed qualities, would its resistance be some 20-30 % more as it is now, when below hull speed?
So, her resistance (per pound of displacement) below hull speed is also somewhat more as if it was designed for displacement sailing only. Statement like this could be used to support value of some real argument, but do not prove anything by itself. Meanwhile they should have re-calculated residual and frictional components of resistance separately.
With sketches of general hull shape, only to have an idea of hullform variation involved, not to enable anyone to copy your designs. Last time we outsourced CFD calculations and got the resistance predictions that were 20% lower than actual. However, because of different hull shapes, this is not always true - therefor actual hull speed can varies from about 1 - 1.6 times approx theorotical hull speed. High aspect ratio's generates more lift that low aspect ratio's - ever wondered why a glider's wing is so narrow and long?
Software that they have actually developed from scratch in-house consists of Fastship and Maestro, their excellent structural analysis package. The enclosed photo is one of the most recent vessels constructed using Maxsurf and Workshop, one of the largest container ships afloat. If you think you can cut and build more accurately, you can always set the tolerance finer.
On the other side, planing boats are usually light, and with powerful engines, and it is not easy to notice, whether your engines are using 5% or 15% of their rated power.
There is no sense to study effect of hull shape on resistance if DLR of compared options is different. If this is published in serious research paper I would look at results; once it is published in amateurish book for sailors - no need to pay attention to that pseudo-science. Red line refers to sharp chine shapes with submersed transom (about 85% of middle area); rest of lines refer to round bilge shapes and stern with slightly submersed transom.
I believe they would make it narrower still if they can find a way of attaching them safely to the fusalage! When I look at the seething mess of splash, spray and white-water around a fast-moving ship, I think of the great simplifications needed to make the problem mathematically tractable. I have experience with computers but have only used very basic design software before for other reasons. So if these companies that have turnovers of ?500 million, then they must be doing something right!
Any SHIP BUILDING software costs many thousands of dollars simply because in itself, it is huge. I am not using the software to design a 80ft yacht, I would be using it to design a 4.9m catamaran. When it looks good on screen, I plot it out on D size paper and take a long hard look at it, just as I would by hand.
Clearly in the presence of headwinds that would be whittled down to much less than 50%, but it is a significant figure for consideration, if resistance is directly proportional to fuel consumption, which I assume it is, very nearly so anyhow. Any competent professionally trained naval architect can tell you shape plays such a minor role.
After all the required simplifications and excisions are made, are we really justified (or sensible) in using sophisticated techniques? I calculate the areas of the hull sections using the 2D Analysis tool, then I input the areas, waterline halfbreadths and vertical centers of the areas into a spreadsheet to calculate the hydrostatics. Of course there are plenty of dedicated displacement hulls with hard chines, though not with a straight run aft.
I am well aware that DLR is major factor of resistance in interested range; so let's fix it and compare the rest. Allowable stress for the same material is different for different structures, applications etc..
Your desire, dream or belief to the contrary will not change the existing and known laws of hydrodynamics, despite your protestations. I just want a hull design software that will let me produce a professional hull shape with no major problems, but I don't want to spend thousands on the most high tech software out there. This works fine for small boats and you have the CAD program to detail the rest of the boat, which is really the bulk of the design anyway. If we compare that to a hull form that is a long wedge, we have a lower pressure (but along a longer length) with the same pressure loss at the stern.

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