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    DodgyGeezer
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    Member No.#1291
    RegisteredπŸ“…18th Dec 2010
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    Recent Posts
    πŸ“ EeZeBilts From Keil Kraft
    6 days ago by DodgyGeezer ( Sub-Lieutenant)
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    Here is a Shapeoko 2 - my eShapeoko is a similar machine - cutting steel. You will see that you need a decent spindle motor, which is not surprising. But the framework is adequately rigid.

    I have over-specced what I have to allow for expanding for future use. I would not be surprised to find that a machine which was limited to cutting balsa, plastics, obeche and light ply (which would cover the vast majority of marine modelling) could be sold for less than Β£100. Unfortunately, there are too few customers to make it worth designing such an item.
    Milling 316 Stainless Steel in my Shapeoko 2
    ▢️

    machine
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    πŸ“ EeZeBilts From Keil Kraft
    7 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "....but would have to be a bit more powerful/stronger build even for Jelutong....."

    You can cut steel with a Shapeoko (slowly!) so long as you have the right spindle and cutter. It's designed for a DeWalt or a Makita - I would use a Dremel clone when cutting something like ply - and a stronger tool. But then it would be much noisier. Using a model boat motor is unusual, but I have shown that it works with balsa...

    cutter
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    πŸ“ EeZeBilts From Keil Kraft
    7 days ago by DodgyGeezer ( Sub-Lieutenant)
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    Other disadvantages include the requirement to add expensive safety precautions to the work area - and I believe that some of these things need cooling water?

    I am happy with a self-built eShapeoko that just hums quietly behind me in the spare bedroom - I'm not so sure I would be happy with 100W of incandescent power hanging from a half-stripped bolt, some gaffer tape and a couple of paperclips in the same place... πŸ€‘βš‘
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    πŸ“ EeZeBilts From Keil Kraft
    8 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "...I'd rather cough up a bit more and know that I could do something with it!.."

    Quite right!

    When buying, people need to understand the important features of a product, and with new technology it is easy for the advertisers to conceal these.

    For a CNC cutter, stiffness is very important, particularly if you are going to cut metal. The machine must not deform appreciably when it puts a strong force on the workpiece.

    It also needs adequately powerful stepper motors to put that force on. and, of course, it needs to move the cutting head to all parts of the workpiece. I was interested to see that the spec states 'max travel distance' - I would have expected it to say 'max cutting dimensions', and wonder if these are less than the figures quoted.

    At least we can specify a cutting area ambiguously, so that modellers can understand what they are getting. I would guess that 1ftx1ft cutting area would be fine for most aeromodellers, while 1ftx1yd is more what boat modellers want. But it is easy for an individual to chose.

    Motor power requirement is harder to define - it depends so much on the leverage designed into the mechanics. Screws have more advantage than belts, for instance. And if you are only count to cut softwoods you can get away with much less power than cutting steel! Usually I would like to see the steppers having between 5000 and 10,000 gfΒ·cm of torque - though that is a 'piece of string'.

    Rigidity is even harder to estimate. You can get some feel when the seller says that this machine will not cut metals, or 'is an engraving machine'. The other indicator is weight - rigid machines are going to be much more massive. If the frame is light it will bend under stress. Though if you are using a laser...

    machine
    product
    machines
    engraving machine
    softwoods
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    πŸ“ EeZeBilts From Keil Kraft
    8 days ago by DodgyGeezer ( Sub-Lieutenant)
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    There doesn't seem to be any complaint about the machine fundamentals in those reviews - their problems are with understanding how to use it, and the quality control and packing. In fact, one said that the quality of the parts was 'very good'.

    Nothing was said about some of the most important aspects of the machine, which I have extracted below:

    Max travel distances:
    X: 160mm
    Y: 100mm
    Z: 45mm
    Repeat positioning accuracy: 0.1~0.05mm (no load)
    Max material depth: 30mm

    Something that can only do 4" max dimension parts is very limiting! That positioning accuracy would be ok for load, but they spec 'unloaded'? I know that will depend on the material and cutter, but I would like a better understanding of the stiffness than that...

    You can get machines with cutting beds of 12" for between Β£100-200 on ebay - but I think boat modellers would be better off getting a 36"x12" Eshapeoko or similar. Base cost of that would be Β£300, plus Β£100 for motors and controller...

    machine
    cutter
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    πŸ“ EeZeBilts From Keil Kraft
    8 days ago by DodgyGeezer ( Sub-Lieutenant)
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    A brushed 775 motor? Standard 'Johnson Can'. Cheap and powerful, for power drills - a bit more powerful than I am using. For cutting curvy balsa shapes, as aeromodellers do, it would be ideal.

    Most modellers cut shapes that are long and thin. The only problem for marine modellers is that we typically require shapes that are about 36"/1m long, while aeromodellers rarely look for aerofoils which are longer than 1'/30mm. And the longer the base of a cutting machine, the more it will cost...

    aerofoils
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    πŸ“ EeZeBilts From Keil Kraft
    8 days ago by DodgyGeezer ( Sub-Lieutenant)
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    ".... I have also been looking on utube at DIY CNC Machines using old DVD Drives and an Arduino board...."

    You can probably make a machine for nothing out of scrap if you know what you're doing - but I wouldn't advise a beginner to learn that way!

    The issue is getting the precision of movement together with enough stiffness to be able to apply adequate force when cutting and not have the structure bend.

    For modelling, we have an advantage in that many of our materials are thin and easy to cut, compared to typical professional requirements. A common cutting tool is a Dremel - which we often have, and you can see that a model boat motor can easily cut balsa - and probably light ply...

    DVD Drives
    Arduino
    machine
    model boat motor
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    πŸ“ Water Jets
    8 days ago by DodgyGeezer ( Sub-Lieutenant)
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    Decent printers are still a bit expensive for home use, and the technology is advancing - I'll wait until it slows down and becomes cheap...

    For early warning of possible modelling disturbance, I use these things https://www.ebay.co.uk/itm/Wireless-Motion-Sensor-Doorbelll-...

    Very useful when you're in the workshop and the postman calls...
    https://www.ebay.co.uk/itm/Wireless-Motion-Sensor-Doorbelll-Chime-Detector-Entry-Alarm-Alert-With-2-Sensors/143236146237?_trkparms=aid%3D333200%26algo%3DCOMP.MBE%26ao%3D1%26asc%3D59227%26meid%3D8708e097eed3447dad1a775dd19293a0%26pid%3D100008%26rk%3D2%26rkt%3D12%26sd%3D352280192113%26itm%3D143236146237%26pg%3D2047675&_trksid=p2047675.c100008.m2219
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    πŸ“ EeZeBilts From Keil Kraft
    8 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "....I am looking forward to the next stage....."

    There will now be a short intermission while I sort out other things, and I suspect that a build will start sometime in September. Or later!

    In the meantime, this thread has introduced a number of issues apart from describing the egg-box structure that Ernie Webster used in the KK EeZeBilt series. It suggests that if CAD packages are used for model boat design then the plans created can readily be shared with other modellers over the Web, and shows that personal CNC machines costing a few hundred pounds are a useful supporting workshop tool for this process.

    Any comments on the above points would be read with interest!

    machines
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    πŸ“ Water Jets
    9 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "...DG if you have a 3d printer you must have the design software for it too - otherwise its useless ..."

    I said I 'can get one printed'. Dodgy Geezers can call in favours from all sorts of places! And not only plastic deposition machines either - stereo lithography or selective laser sintering (if you want to 3-D print in tungsten) would be available through university contacts. As would design modification...Though, given how long it took me to get a pair of rather specialist gears lapped the last time I wanted a set, I would match RN's comment in saying that I wouldn't hold my breath!

    3d printer
    design software
    deposition machines
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    πŸ“ Water Jets
    9 days ago by DodgyGeezer ( Sub-Lieutenant)
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    a fee is required for some of the water jets - but not yours. I suppose you could add another bearing. I've downloaded it and can get one printed, but I'll wait until I've seen the ebay ones...
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    πŸ“ EeZeBilts From Keil Kraft
    9 days ago by DodgyGeezer ( Sub-Lieutenant)
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    All the hard work would have now been done, if I had got the waterjets and had finished designing the stern. We will have to wait for that, as well as a delivery of balsa... But I have a couple of spare sheets of balsa and a few final parts, so I can give you a short sample of how things will go on from here while the machine is cutting them.

    We want to cut parts out of a 4"x36" balsa sheet so I draw up the boundaries, and fit the parts in at appropriate places (fig36). The sheet is oriented vertically, because that's how my CNC machine wants to see it, and the top right corner is positioned at 0:0, so I know where my origin is.

    Then I remove all the lines that I don't need to cut. Because I have lined up the long straight edges with the edge of the balsa, I don't need to cut along them. I don't need to cut the boundary lines either - so I have a rather odd drawing for final cutting as at fig37.

    From now on we don't need to look at any more drawings. I save just the bits I want to cut as a .DXF file - which is a standard CAD drawing format. Then I take this file and input it to a free software package called 'DXF2Gcode'. Which, you will not be surprised to hear, outputs instructions for cutting those lines in G Code, which is a standard language for controlling cutting tools. The language looks like this - my comments in brackets:


    G90 (Absolute programming)
    G21 (units in millimeters)
    G17 (We are working in the XY plane)
    G40 (Cancel automatic tool radius compensation.)
    G49 (Cancel tool length compensation.)
    G28 (go to the pre-programmed Zero position directly over the balsa sheet)
    G92 x0y0z0 (Set this position to Origin Zero. All distances will now be measured from here)
    G0 Z -10.000 (drop the cutting tool to height -10mm - just above the balsa)

    (*** LAYER: Layer1 ***)

    (* SHAPE Nr: 2 *)
    G0 X +0.000 Y -68.551 (go to the first place to start cutting)
    F60 (set the feed rate to 60)
    G1 Z -15.400 (drop the cutting tool through the z axis to height -15.4 - this cuts almost completely through the balsa, leaving just a thin web underneath to hold the part in place)
    G1 X -25.258 Y -68.525 (Move the cutting tool along the x,y axis to cut the first line)
    G1 X -25.255 Y -65.350 (Move the cutting tool along the x,y axis to cut the second line line)
    G1 X +0.000 Y -65.350 (Move the cutting tool along the x,y axis to cut the third line)
    G1 Z -10.000 (raise the cutting tool along the z axis out of the balsa)

    You can easily learn the basic commands - but you don't need to as DXF2Gcode just creates a working cutting file for you.

    Next, you put some balsa in the machine, turn it on and send the G Code commands to it. This is done with another free software package called 'G Code Sender'. The names are quite descriptive! I enclose some photos of what happens next, and a 'media file' (video) which, as you know, you download by clicking on it, and then clicking on the miniature little blue square on the top left of the screen. As you can see, there is very little dust with a thin cutting tool, and the sound from a 12v motor running at 10v is low. This was recorded with a camera within a foot of the cutting tool...

    After that, it's just an evening of taking the parts out of the balsa sheets, assembling them and gluing up...

    sheets
    machine
    CNC machine
    balsa sheets
    camera
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    πŸ“ EeZeBilts From Keil Kraft
    10 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "Perhaps DG is the best one to answer this -"

    Dunno why - my boats will sink like anyone else's if they fill up with water.

    Partly it's horses for courses - don't sail a boat with a low freeboard on the choppy side of the lake where the waves break over the bow. Fast boats which deflect water away might get away with it - slower displacement hulls where the water creeps up the side won't. Google 'Coandă effect' for a more technical description of the reason water sticks to surfaces. Tugs usually have heavy ballast and are more likely to have waves breaking over them than to ride up and over them. And sealing a deck effectively is going to depend very much on the way it's designed to fit on the hull...

    Adams of Adamcraft fame in the 1950s used to stretch clear plastic 'clingfilm' over the decks of his open boats (it was invented in '49!) to keep the water out, and you might find that trick useful if you have to have a removable deck. The clingfilm would go underneath the deck, of course...

    Sinking is less of a problem with EeZeBilts (though the Beaver with its heavy ballast would go down). They are made of many watertight compartments. If your boat doesn't have such flotation support, try using expanded foam in all the spare cavities. I do this in my boats, partly as a safety measure, partly to deaden the motor sound and stop the decks from 'drumming' and partly because I mount batteries and radio equipment in it. Here is a shot of a PT Boat with removable centre deck, which is happy in heavy waves - you can see the foam blocks...

    boat
    radio equipment
    decks
    batteries
    PT Boat
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    πŸ“ EeZeBilts From Keil Kraft
    10 days ago by DodgyGeezer ( Sub-Lieutenant)
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    My first printer was an ICL line printer, in 1979 http://www.chilton-computing.org.uk/gallery/ral/orig/r18088l...

    Rather like this one, but orange, since I was working on an ICL 2900 system https://en.wikipedia.org/wiki/ICL_2900_Series
    http://www.chilton-computing.org.uk/gallery/ral/orig/r18088l.jpg
    πŸ”—
    https://en.wikipedia.org/wiki/ICL_2900_Series
    πŸ”—

    line printer
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    πŸ“ EeZeBilts From Keil Kraft
    10 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "...You can create the element, or Icon (also known as "Shapes" in some programs), by grouping the vector objects...."

    Luxuuury! Now we used to have to draw the vector on the CRT with a graphics pen, move it with a tracker ball to an analysis section, change it into an EBCDIC file and print out the resultant data on a dot matrix. Then our project manager would beat us to death with a daisy-wheel before we went home...

    And you tell this to the modellers of today and they won't believe you...!
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    πŸ“ EeZeBilts From Keil Kraft
    10 days ago by DodgyGeezer ( Sub-Lieutenant)
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    In the 80s they built software to last! Cue 4 Yorkshiremen sketch...

    In 1988 they did not have much concept of elements - only vectors...unfortunately the current version of my package (which I am sure will do everything) would set me back around Β£1,500 for the cheapest item...

    The only way I could handle this would be to manually type text comments at all places. Which would involve writing a book...

    software
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    πŸ“ EeZeBilts From Keil Kraft
    10 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "...Each element can also be labelled with this reference..."

    Ah - you are using a CAD package developed in this century. Mine has the copyright date '1988-1995'.... I am a vintage enthusiast...πŸ˜€
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    πŸ“ EeZeBilts From Keil Kraft
    10 days ago by DodgyGeezer ( Sub-Lieutenant)
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    That sorts the version issue brilliantly. You only have one result.

    The advantage of doing things with CAD is that they are infinitely replicable and amendable, and can be converted into physical entities with no work. But version control with things which can easily be reproduced with slight differences is something that is rarely appreciated until you are drowning in the swamp...

    CAD
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    πŸ“ EeZeBilts From Keil Kraft
    10 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "....or multi-page drawings with an incremented dwg / variation number...."

    I tried that. I got multiple different drawings with no clear idea of which one had the latest version of which feature...😭

    Actually, what I do is not too bad. I work across the screen, left to right, adding stages developing the plan. At each stage I am working on several varying features - these get developed down the page. So you can look at a page and say "I'll have one of those bows with that stern.." - but if you don't keep to this positioning things become difficult and you end up going to a new version...


    "...I thought you meant at the stage of assembling to prove the drawings ..."

    The advantage of doing it on CAD is that there is little need to prove the drawings - if it fits on the screen it will fit in real life. Ideally, I should learn 3-D cad and then I can virtually assemble and look at clearances without any need to cut materials at all...

    version
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    πŸ“ EeZeBilts From Keil Kraft
    10 days ago by DodgyGeezer ( Sub-Lieutenant)
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    Ah - the great advantage you have there is that you are dealing with physical items. There is only one final output.

    I am working on a screen where there are going to be multiple versions of many items - all fairly indistinguishable without careful measurement.

    In a proper software development environment there are rigid procedures for making changes, specialist packages for storing and controlling them, and a whole department of staff for change control.

    My rule is that I usually work from top left to bottom right....
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    πŸ“ EeZeBilts From Keil Kraft
    10 days ago by DodgyGeezer ( Sub-Lieutenant)
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    Now we are on the home straight! We have a drawing, a reasonable structure, and we can start pulling out the detail.

    It's at this stage that I usually confuse myself completely, since I will make numerous slight alterations to put bulkheads and formers in better positions for several reasons - internal layout, better strength and balance.... and I end up with several dozen slightly different hull designs, each of which are slightly incompatible with numerous slightly different bulkheads, and I then lose track of which parts go with which others...

    However, here are some examples of the output from this stage. The superstructure base(fig32) is going to have to be made from parts as I mentioned earlier. The bulkheads (fig33) can now all be drawn with their slots and tabs, ready for assembling into the classic egg-box on the sub-deck (fig34). The front formers and the keel are taken off the drawing, again with tabs drawn (fig35)...

    There will be quite a number of other parts to be drawn and made - the transom and other flat sections of the stern, the triangular bulkheads under the subdeck, the trapezoid plates which go to make up the funnel and mast, and other details like the anchor well. Almost all of these parts will be uninteresting rectangles with dimensions taken off the drawing, so I am not going to list them all down here.

    The full set of parts, however, will be needed when it comes to the cutting stage, because we will be trying to get as little wastage as possible from the balsa, and sneaking little triangular formers into all available gaps on the sheets. I will take a bit of a break now, because I need to get the water-jets delivered before doing the final stern design - and I am running short of balsa, so I will need more of that!

    I may cut a few parts on a sheet of 1/8" inch as an illustration. To do this you simply arrange the parts you want into a 4"x36" rectangle, load the cutter with a 4"x35" balsa sheet and send a file describing the parts to the cutter over a USB link. We will cover the software used and the stages of converting the drawing file to cutting instructions at that point...

    trapezoid plates
    cutter
    sheets
    software
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    πŸ“ EeZeBilts From Keil Kraft
    12 days ago by DodgyGeezer ( Sub-Lieutenant)
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    A little aside now, for the superstructure.

    We can now draw a bit more detail on the superstructure, and shift it onto the hull to check how large an access cavity we have. If it looks too small we can always use part of the deck, but this looks as if it should be big enough. See fig27. I still don't know how I will hold it on - magnets perhaps, with a locating dowel?

    Then we start measuring in just the same way as we did the bulkheads - base and height. This will give us the angles at which the superstructure walls are placed - most boats have these vertically upwards! Fig28 shows the cross-sections of the superstructure at 4 places, where the joints are.

    Now we have a base shape and a top shape - we can draw these in as fig29. The vertical lines mark where the walls change their angle - these have to be in line top and bottom. How easy to check with a CAD package!

    Imagine the superstructure base and top - held apart by those cross-sections. measuring on the diagonal line gives us the shape and size of the sheets which will be needed to cover it. Here they are drawn as fig30.

    Finally, we have the roof with the bridge wings, and the upper roof of the bridge proper. They are drawn out as fig31, and immediately you can see that they are too big to be made from a 4" wide sheet of balsa. We may need to add parts on - or make them from plasticard? The base is also too big for a single sheet - that will need building in parts...

    I still need to think about the actual construction, but now I have the shapes I can work out how they will be assembled and attached to the hull...

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    πŸ“ EeZeBilts From Keil Kraft
    13 days ago by DodgyGeezer ( Sub-Lieutenant)
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    We just need to draw the superstructure and bulkheads, and then we can start estimating how much balsa will be needed. Next, arrange the lines to fit on the sheets with minimum wastage, and point the output at a CNC machine.

    Then all you have to do is glue it together and paint...

    sheets
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    πŸ“ EeZeBilts From Keil Kraft
    13 days ago by DodgyGeezer ( Sub-Lieutenant)
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    Not a problem - it's easy to modify drawings in CAD. I'm not sure it needs much change anyway...
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    πŸ“ EeZeBilts From Keil Kraft
    13 days ago by DodgyGeezer ( Sub-Lieutenant)
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    Ah - now I was assuming that the strip was where the chine was... the Visbys have got quite a pronounced chine around that shape...
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    πŸ“ EeZeBilts From Keil Kraft
    13 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "....So I hope you don't take this the wrong way.

    When I made the hull it was reasonable easy.

    It seems to me that there are two issues hear.
    Firstly the Bow section.
    Secondly fitting waterjets...."

    I am always happy to discuss model boats with other designers!

    Looking at your sketch, it seemed to me that the bow unit had all the chine curve in it. The chine on this boat actually starts to curve quite a way from the bow. Would that mean the boat was actually being made in two halves, rather than a long box and a short bow section?

    I think your original design will fit a water jet very well - but I need to see what the product is like before deciding to use it - or not...

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    πŸ“ EeZeBilts From Keil Kraft
    13 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "...I have just googled "Tumbledown" to find out what it meant as it is the first time I have heard of it..."

    If you googled that you would have found yourself in the Falklands war. The word to look for is 'tumblehome'. 😊

    The sub-deck is about water-level - but the jets will have to clamp onto the bottom skin. Your original stern design looks as if it was made for them...

    My concern is that if the input drive shaft is below water level then we may have a slight leak. So I'm proposing that the jets go in a compartment of their own, and that the drive motors are a bit distant - much like the Visby class, in fact...
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    πŸ“ EeZeBilts From Keil Kraft
    13 days ago by DodgyGeezer ( Sub-Lieutenant)
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    For a simpler hull I would have done all the hard work now - for this one I might need to go back and start from the beginning if I find it doesn't work.....

    But anyway, here is the next instalment. From the plan and elevation views (fig20) I can take all the data about where the sheets cross, and where tabs may need to be put in. These are then marked and the egg-box structure (fig21) is just taken away. Easy to do this with a drawing package!

    So we are left with cutting lines for the top deck (fig22), the sides of the internal box (fig23) and the sub-deck (fig24). The decks are made with two balsa sheets to obtain the width. I have included a rear bulkhead (fig25) and a front former (fig26) to illustrate where these will go.

    Note that we now have much of the hull shape, and we haven't even specified the keel (which will need a few more tab cutouts from the sub-deck). For eezebilts the keel is often made in two parts - above the sub-deck and below. I am expecting assembly to follow this route:

    1 - add bulkheads and box sides to subdeck.
    2 - when glued, add front formers and keel top, and bend bow up.
    3 - when glued, turn over and add keel bottom and bottom formers.

    Since the keel is not relied upon to add a lot of strength, it could just be a single sheet of 1/8" balsa. But I note that Martin used multiple sheets of plasticard to build his keel, and am wondering whether two bits of 1/8" should be glued together...

    Another thing we do at this point is check that the measurements of any large items don't exceed the maximum size of a sheet of balsa. And we can do a bit of thinking about where each item will come from - slight size adjustments might mean that we have less wastage when it comes to cutting...

    P.S. - actually, two pairs of centre tabs are not going to be needed, since those bulkheads will just be connected straight to the outside of the box and there need be no internal division. It's slips like this that make me end up putting out incorrect plans... 😭

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    πŸ“ EeZeBilts From Keil Kraft
    13 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "Still think that the sides should be the eggbox sides - and the bottom v slope incorporated into the frames meeting a small part of the keel in the centre.
    Martin - were you thinking of the old principle of tumblehome when you created the upper chine ? - or was it just for effect ?
    .....
    One thing puzzles me however as to how you will mount two drives or a single one for that matter. Double would have to lean in towards each other surely causing a steering problem and single how do you cope with the V. "

    Good questions! To which the answer might be 'Search me!"....

    The upper chine is simply part of the 'stealth' shape. The boat should have no vertical surfaces which would just bounce radar waves back to the sender. They either get deflected into the water or up into the air.

    Note that this means that an aircraft might get a fix when flying at 90 deg to a surface which is angled upwards. But maintaining the fix will be difficult - if the aircraft varies from a 90 deg course or the boat alters course the fix will be lost.

    I wondered about the V as well! Might depend on the waterjets. If I can tilt the pivot angle then all is fine. If the angle isn't great then it may be fine. Maybe I'll have to flatten the hull at that point?

    I have left the stern out of the plans for the moment, since things will depend on what these jets look like. I will probably build the boat with a space for a conventional prop and a pre-slotted keel for use if anything goes very wrong...

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    πŸ“ EeZeBilts From Keil Kraft
    13 days ago by DodgyGeezer ( Sub-Lieutenant)
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    "...jet units are really good for maneuvering but you will need to make a reversing bucket which is what gives you reverse (obviously) You can stop a boat on a dime and spin a boat from full speed by just dropping the reverse bucket and spinning the wheel (causes the stern to lift and pivot on the bow. Would work well on a Huntsman etc. ..."

    Hmm....how well does it work on a boat who's prototype is 250ft long? That was why I was thinking about a bow thruster. Just a reversible water pump with nozzles at each side of the bow. But it will be an experiment...

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