John R. Coil

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  • in reply to: help needed for noob – updated #38014
    John R. Coil
    Participant

    Are you asking about trying to estimate weights of a completed hull?

    You can assign skin thicknesses and also material densities; however, it seems that the version of DS I use (not the latest) projects such thicknesses outwards , altering the displacement and hydrostatistics of the hull. The effect is not necessarily large; but, when I was still assigning hull thicknesses, and once I figured it out, I disabled the data for hydro statistics unless looking for hull shell weight.

    It has been a while since I used any hull thickness, though, so maybe things have changed.

    in reply to: POWER CATAMARAN #37908
    John R. Coil
    Participant

    Hi,

    A trick you might use is to create a separate horizontal intersect layer with lines where your stations are. This should pass through the side of the hull you consider good. It may help to temporarily move the hull to be centered on the Y-axis. With resolution at its highest setting then use the intersect command to put new lines into the intersect layer. These points represent where your hull on the good side was passing through the intersect layer.

    You can use these values as basis for the opposing side.

    But since that side has a hard corner it may help to add a new hull line just below the hard one by using the intersect layer as above, just lowered a bit. This would help you reproduce the shape of the hull on the good side a bit more precisely.

    EDIT: just realized my misspeak. Rather than “stations” it should be “control points”.

    in reply to: Offset Surfaces to the inside of the hull #37395
    John R. Coil
    Participant

    It took me a while to realize that DELFTship adds thickness to the model, and if it had not been for an accident in assigning plate thickness (missing decimal point) who knows how much longer it might have taken?

    I must admit that I’m quite curious about changing surface normals, something I had not even considered possible, much less doing (I missed that in my skimming of the manual) until reading your post. [/Homer Moment]

    Thanks for that! ๐Ÿ™‚

    I would that I could return the favor and give you an actual solution besides suggesting trying undersizing your model just enough so that the added thickness brings the now unseen outer surface up to where it should be, but by then you might as well have exported it to AutoCad … though I guess you might try using scale once you’ve got it looking right … but unless you are using a uniform thickness shell (it could happen) that isn’t necessarily much of a solution either. ***

    I wish you well and will return to see what someone who actually knows may tell you.

    *** For example, per Gerr scantlings rule the .8″ thick topsides ply on what I’m currently playing around with would give (4-0.0667)/4 = 0.9833Y and (39.9167-0.1333)/39.9167 = 0.9967X) and saving that as a different model. Of course THAT gets anyone trying this into the whole: well the sheer strake is 0.9″ and plank below BLH – see the formula in the fiberglass section of the book for how high above the waterline that is – is 1″ thick except for the garboard which is 1.1″ and the 3.1″plank keel … but, hey, that’s what lots of added tiny hard chines are for, right? So my proposed so-called “solution” is more like another form of self abuse … which should be just about right coming from someone wanting to design and someday build their own 40′ boat…. ๐Ÿ˜‰

    in reply to: Show me your ships! #37388
    John R. Coil
    Participant

    It’s a Houseboat!

    For a while now I’ve been toying with the idea of a sidewheel yacht with the wheels nestled between stabilizing amas (roughly 10% of displacement) and a somewhat narrow, 7-to-1 LBR, shallow draft hull. In larger boats (say 70′ or more) this actually seems to work well, and allows for a huge party deck on top of the main cabin (the roof line for this deck is level to the bow), aft of the pilot house. Going by the DELFTship power estimates, even assuming just under 64% propulsion efficiency between a assumed piddling performing feathering wheel and lackluster diesel-electric, such a boat seem to offer very good economy for a cruising speed of 10 or so knots with some modest dash potential.

    Unfortunately I can no more afford a 99′ yacht than I can … well, a LOT of things. Even, sadly, this 39’11” scaled down concept (well, most likely I can’t … pity no one I know is tearing down a century old barn made of native live oak).

    You may note that it isn’t a paddlewheel but has twin Glen-L style electric drives made from outboard bits. Shown are the props for 15 kW motors, their housings possibly hidden beneath some bench seating. The 10″ prop for this power is also the largest that could be put under the boat without resorting to deeper protective skegs. DELFT calculations say this would give me about 10.6 kt max and 9.2 kt cruise (80%), again about 64% efficiency (just because assuming “mediocre” seems a way not to be the-bad-surprised if it ever were built).

    I would like to thank J.Sass for the outboard model from which these details were cut and scaled.

    Abandoning the paddlewheel for this boat was done because having them with a 5-to-1 LBR main hull (and more supportive amas) and properly wide wheels made the thing look ponderous, though not necessarily unattractive, and would have also added a lot to the cost of construction as well as weight (besides, long ago I decided that for this length and smaller using a quarterwheen trimaran/pontoon arrangement works best in terms of internal layout: the engine bay and head being nestled between the wheels leaving the rest of the cabin open, extending over the wings a few feet, and still managing to keep the profile down a bit).

    You may also note that the amas are unattached. This is because I’ve yet to decide on the style of wing. For a boat like this something industrial, maybe even an exposed painted truss, might look suitable. I’m not really committed on wing style and thus none is shown. Not even to having the amas at all (the program indicates only needing 10 kW motors for the above speeds as a true monohull), truth be told.

    EDIT: just realized a mistake with the power assumptions. Previously I’d got in the habit of thinking about the genset end of things and not the motor driving the wheel. Looking at the motor end of things that means their power could be 10% less than stated above. Okay, not a huge difference but at least it allows the resistance calculations to be somewhat rosy and it not matter as much.

    in reply to: Dave Gerr’s formulas in a spreadsheet #37387
    John R. Coil
    Participant

    Necroposter Alert!

    Did a search on “scantlings” and this was what came up. I too have this very nice book but am interested in scantlings for wooden boats. In particular I like the notion of fiddling with the siding and molding of framing dimensions to arrive at something that can be cut from commonly available lumber. For example, by playing around with low-profile frames a boat with a Sn of 1.6 can get by with 1.75″ molding x 3.5″ siding (24″ on-center) that can be cut from easily obtained 4×4 (3.5″ square actual) DF posts and still not seem to break his scantling rules for frame construction (a quick look-see at Lowes and locally available post showed a pleasantly high percentage with the grain in a favorable alignment, not even close to a majority but also far from rare).

    But what I’m really wondering is if anyone has ever seen or heard tell of a system of scantling rules for “instant boats”?

    in reply to: Longitudinal center of buoyancy % #36949
    John R. Coil
    Participant

    Hi, based on my efforts to tweek hulls so LCB and LCF are as close as possible to each other it seems that these are given from the aft, not the bow, when the default settings are use.

    in reply to: For those modeling Classic Sailing Ships #36324
    John R. Coil
    Participant

    The Rudder ( http://books.google.com/books?q=editions:0AFLRE72WVBqg_pA4QmHg298dbxdrJeXs3GVeEDO-A-Z7LtbLpOlYoMI&id=Krc6AAAAMAAJ )

    The classic magazine of all things boat related is actually available on Google Books as PDF downloads by year at the above link.

    Most years from 1901 to around 1922 are available and there are LOTS of gems therein.

    Like importing from lines? There are hundreds of examples of power and sail given.

    And you will also find articles on how to build such classic boats as Seawren (a 14′ catboat) or the 25′ yawl Sea Bird and her larger 38′ sibling (both of which may be adaptable to plywood construction!). Many power boats and runabouts too if you want inspiration for something that really looks classic.

    Also articles on design and building of boats in general that at a glance have real merit to them and which, while they may be old, may still be very useful.

    Innovations that we may think of as recent seem not so recent as well, and I could point to articles by C. Andrade Jr. as examples. In the 1901 yearbook he talks about a “new type” of hull he actually patented that seems no less than a scow upended to show how he could think outside of the box (this one reminds me of a SWATH with its pontoons cut off … and there is a later iteration by someone else that raises the centerline of the scow out of the water to make a even more SWATH-like catamaran). Then too there is a “Speed House Boat” he built called Parakeet which was enlarged from the lines of Viper as that runabout appeared in The Rudder as a how to article … said ship looking ever so much like the much later Wyoming designed by Bolger for efficiency rather than speed. As a side note: if anyone knows anything about or can find information on how Parakeet worked out I would be fascinated to learn what became of that experiment.

    There are also more poignant moments as a story detailing the launch of Hood as a no compromises battlecruiser and pride of the fleet … “poignant” in light of knowing how that story ended.

    John R. Coil
    Participant

    While the program ably handles matching lines there is an issue with tables of offsets because the points you enter are control points rather than actual points โ€” i.e. it draws the station based on the location of the control points but not necessarily through them. This leads to the model shrinking somewhat relative to what you want.

    I have been fighting this very bugaboo too, though to a lesser extent since I’ve been building developed hulls out of the intersections of sheer, chine, and sidewall profiles that are themselves developed BUT the way the program works only the end points in a line are REALLY just where I want them without fudging the control point locations.

    To match offsets for a round chine hull I would recommend first inputting your data as indicated and then export a set of offsets based on the model so generated. You may be able to employ scaling on individual waterlines or sections to get things closer but just moving the control points a bit is probably what you’ll be doing before long. Repeat as needed.

    Another alternative is to import VRML from a program like Hullform that does draw its lines through the control points you enter (though in the case of Hullform faring a rounded station with more than 4 control points is often tedious slogging). I think Hulls may also draw lines through the indicated points and there is a specific import feature for that program.

    in reply to: Swath or Catamaran Model #35959
    John R. Coil
    Participant

    If you go to the design database on this site you’ll find both a wave piercing cat and a swath under multihull.

    John R. Coil
    Participant

    I recommend this from Eric Sponberg for an assortment of useful calculations and a clear explanation of their application.

    http://www.sponbergyachtdesign.com/THE%20DESIGN%20RATIOS.pdf

    Also, while these are not calculations this http://www.diy-wood-boat.com/Ergonomics.html#name2 seems to be somewhat useful.

    in reply to: transom and deck #35716
    John R. Coil
    Participant

    At this point I’d recommend just adding a new face where the transom goes to the model rather than try to trim the curved surface down. The hole you’ve created has the same curvature anyway.

    It looks nice. Be sure to post it in show me your ships when you’re done.

    in reply to: transom and deck #35706
    John R. Coil
    Participant

    Yep.

    in reply to: transom and deck #35704
    John R. Coil
    Participant

    Even IF you had been pesty โ€” and you haven’t been โ€” I’m not likely to loose patience: I take care of both my grandmother (who’s getting surly with age) and a handicapped sister (who’s a twerp).

    The “problem” is likely that there aren’t enough corresponding CPs in the curved surface to leave behind a transom.

    At this point I’d suggest either ditching the curved surface and create a new face for the transom from the existing CPs on your hull and deck. It will have the basic curved shape you want. Since you’ve probably got a 3rd control edge on this curved surface look to see if any CPs were inserted along it when you did a layer intersection with the hull and deck. If so โ€” and there aren’t corresponding CPs on the hull/deck (you will need to move the curved surface to check), write down those values and manually insert them on the hull/deck before you form any new face … that way you can better replicate the control edge(s) that helped to define to shape of the transom’s curve.

    The alternative would be to manually create a matching set of CPs to the hull/deck in the curved surface. Which wouldn’t necessarily be hard (just start by dividing your interior edges and moving the new CPs around to match) โ€” if you do this it may be easier to move that layer a set distance away from the rest of the model so you don’t have problems selecting the wrong CPs on the hull/deck rather than your transom.

    The advantage of the former is ease.

    Turn on the option to see interior edges, if it isn’t already on, and see if any sort of criss cross pattern of lines has developed on your new transom. If one has AND you can also see it when your view is set to the render mode(s) (if not, don’t worry about it) you will need to break the transom’s control face up by connecting some of your CPs with control edges. Since the transom’s surface was defined with a vertical surface curved in the horizontal plane it is probably best if any control edges you add are as near up and down as you can get. These will break up the face and prevent some, if not all, of the criss cross effect (assuming any was visible).

    in reply to: desing #35703
    John R. Coil
    Participant

    Yeppers. Over in the design database there’s a downloadable file called the Loyalist that, when you set the hull and deck to transparent (in Edit>Layers>Dialog), you can see what one person did.

    in reply to: transom and deck #35700
    John R. Coil
    Participant

    It sounds right that you’ve got to find intersections twice since you’ve two layers (hull and deck).

    What I’ve found in my own experience is that when you intersect with multiple layers like this (I’ve usually got multiple layers too) is that near the transitions between layers the program does not necessarily create all the control edges you may need on some layers. I would guess that this is because some CPs which may have been used to help create subsequent faces in a different layer (like a deck fit to a hull) are co-joined to the later face but are actually a part of the earlier. For example, “Move” your deck up a foot (which you can always undo) and you’ll possibly find it assuming a humped shape as the CPs that are really part of the hull remain where they were but the control edges between them and the deck also remain. While I’ve not qualified the program’s behavior exactly it seems that it will miss putting that last control edge into the “newer” face in a different layer that connects to the CP in the “older” face in the original layer. The CP needed is usually there, though, as it was inserted as part of finding the intersection between layers for that layer.

    So before I start deleting excess I find it necessary to create these missing control edgesย โ€”ย their presence stops the program from deleting more than I want it to.

    Sometimes you can have one of these missing control edges that is really small because of where you were intersecting layers โ€” say if your curved surface passed very close to, but not exactly through, one of your CPs on the sheer line. If you find you’ve a problem area that wants to delete too much zoom up on the problem area after you undo the delete and see if there isn’t a missing tiny control edge to deal with first.

    I hope that helps.

Viewing 15 posts - 1 through 15 (of 39 total)