So i decided to dust off my very rusty CAD experience. Found an old copy of solidworks that I had and decided to remodel the plans for the Mehoshi Maru. The primary reason for picking the Maru is because the original plan had 1 keel and I wanted to split that in to 2 parallel keels running most of the length of the ship . Isometric view You can see that frames 3 and 12 actually join with 3 keel pieces each. Each keel is intentionally half an inch longer on the joining ends to provide a full joint with the rib. The midsections of the ribs are also not removed (similar reasons, and it also keeps the part complexity lower) This is looking directly down on the assembly The keels and ribs are notched to fit together From this view you can see one of the problems I need to address: Carl's plans aren't designed for jointing the subdeck into the tops of the ribs, rather theyre designed for the subdeck to be on top of the ribs - so my ribs are too short and need to be re-dimensioned before I can build the subdeck components. Thats ok though, because I didn't constain their heights properly originally and so with the exception of 4 - 10, they all have differing heights. I am concerned that the the aft keel is too thin - this is supposed to be a single screw, single rudder vessel, but the aft keel is only 1/4inch material - If you put a stuffing tube through that I'm a little concerned there wont be much left there... This is an image of how Carl's CAD build (looks like ribs, keel and subdecks are complete here)
Wow that's some cool stuff. I might have gone one more rib in on the front and back sections just to give it a bit more strength.
I thought about that, but for the moment I'm just mostly replicating Carl's original rib layout. They're 1/4inch ribs, the mid-section ribs (about 3 - 13) are spaced 2 1/16 inches apart - the aft ribs have a little more spacing between them as-is. If I cram them in closer to fit another rib I might run afoul of the penetrability requirements. I'm already thinking the stern might violate them: from the tip of the stern to the aft-edge of the aft rib is only 1 1/4 inches, so 1inch of impenetrable stern material would leave only 1/4inch gap between impenetrable and rib - not sure of the legality of that - Maybe someone can enlighten me?
No, I mean to extend the front and rear sections longer to attach across two of your existing ribs down the centerline. It would keep these "module ends secured to the main frame better. Right now they only attach at one anchor point making them weak.
Ah, i see now. That might be a good plan. I was thinking that the cap rail/subdeck jointing in would lend sufficient strength to the assembly, but perhaps not.
Nothing to be lost by a little overengineering. I'll add your suggestion in with the next round of changes here. I can always cut off the extra if it proves to be in the way (but why would it, its a 3ft long unarmed cargo ship, space isnt exactly at a premium)
What do you think of Solidworks and what sorts of files can it export. I'd love to be able to do some cad assisted designing but don't have any experience or cad tools at this point.
I like it, but my only modeling experience has been from Solidworks and later Maya (definately not for CAD, ugh). I am by no means a profesional though - about 5 years ago I took a quarter long class on CAD modeling with Solidworks and thats about it. Its definately not cheap - my copy is an old one that I gleaned off of a friend of a friend who no longer had a need for it - there's no way I could afford to throw the money at a new license for the latest versions. I think non educationals are around $4,000 per seat? Learning curve wise, I dont think it was that dificult, but I also had instruction and labs/course assignments, etc that I learnt from. There are books and tutorials available though. I'm honestly not sure of its export list, as I've never migrated a file out of it. This is the list of file types it can save as. I believe the newer versions support more as well, and there are plugins to more export options I think.
Hmmmm. sounds like it will work but would rather spend that kind of money on more ships, or more likely on a down payment on an additional garage which is needed so I have space for more ships... Thanks!
Student licenses are $100 I think - if you know any students, but they're limited in some features, can't recall what exactly. There are other more grey area to illegal means of obtaining it, but I'm not going to reccomend pirating software to anyone, especially not in a public forum. If you jsut want to play with CAD stuff without investing monetarily there are freeware CAD utilities out there, some are reasonably good I'm told. Unsure of their suitability for producing ribs or outputting to a CNC Mill though (if you happen to have one, which I dont )
Update - Made some progress today. Redimensioned some of the aft ribs and fixed a error in the keel dimensions. Heightened and notched the tops of the ribs to accomodate a rail. Also took Iceman's suggestion and lengtened the bow and aft keels to extend one rib further in to provide additional support. Also ribs 2 and 11 have cross members now to fill the gap between the different deck levels. I'm pretty sure I need to use wider material for the aft keel though. Its 1/4inch right now and it seems that a stuffing tube is about 1/4inch OD. Oops.
Good to see someone pick up the Mehoshi Maru project. The original ship hasn't seen much use for years now, although it's been refit for combat again. Nick, allow me to address some of your questions. 1) The thickness of the stern keel was something that I considered for a long time. The original model Mehoshi Maru that I based the CAD model on had a 3/4" skeg, which was quite easy to drill a hole for a stuffing tube, but that had a deletrious effect on water flow over the rudder, and thus hampered maneuverability. So I set about finding ways to make a better skeg. I found two solutions. You could either mill a slot in the skeg, and put a stuffing tube in the slot, or you could build the skeg up using a 3/16" plate sandwiched between two 1/32" plates. Either way, I figured that a straight thin-wall brass stuffing tube would work fine, because it wouldn't be very long (reducing friction concerns) and a few drops of water leaking through a propshaft (about 1 drip per minute is what I encountered) is the least of a transport skipper's concerns. 2) I CAD-modeled the Mehoshi for WWCC Big Gun combat, which has different penetrability requirements than Fast Gun and some other Big Gun formats. The WWCC calls for up to 2" at the bow, up to 2" at the stern, and spaces between ribs are measured edge-to-edge, not center-to-center. Fast Gun measures by % penetrable area of length, and a few Big Gun clubs measure ribs center-to-center instead of edge-to-edge. I don't remember if I checked the ribs for compatibility in other formats, but since WWCC is one of the strictest clubs then you're probably OK. Better be on the safe side and check, though. For further information and ideas on the Mehoshi, take a look at my construction thread on the PUMA class transports. The Pumas share many of the same features as the Mehoshi, and even a few improved techniques. PS: those of you looking for CAD, I suggest you take a look at Alibre. It's a solid-modeling CAD that's almost as powerful as Solidworks. The free version is almost as powerful as the pay-for version, they only turned off certain advanced curve-drawing features and limited the number of objects in assembly mode. And, almost as important, it's (relatively) cheap and goes on sale frequently. I investigated pirating CAD, but caught a virus and a bunch of spyware instead. I also used student versions of SolidWorks, but found that student-made files cannot be opened by regular versions after my CAD class was over.
I should have done this math earlier, but for some reason I didnt. IRCWCC requires no more than 15% impenetrable - The ship is roughly 35inches from fore to aft, 15% of that is 5.25inchs of permissible solid material. 15 ribs at .25inches each is 3.75 inches against the limit, leaving 1.5inches for the bow and stern zones. I had planned to put 1.75 inches of impenetrable in the bow (to join up against the foremost rib to technically be the max 2inches), and whatever needed in the stern (up to the 1 inch). That would put me over solid material budget by .5 inches after the bow + however much went in the stern. Any one with suggestions? I could use less solid material in the bow, none in the stern. I could remove some midsection ribs and stretch their spacing out to 3inches each...
yeah I'm coming up with 9 ribs 1/4 equal perfect amount. If you reduce it, it will make an easier build. It sucks as far as loosing ribs but makes it lighter also. You can go with 18 1/8th ribs but that probably is too much work and not worth it. It's a small boat so lighter probably is better.
Well, ribs 4 through 10 are all exactly the same, so I could lose a few in there without any real loss in hull definition. If i took 4 of them out, (leave ribs 4, 7 and 10), that would drop my total rib thickness to 2.75 inches, leaving 2.5 inches for the bow and stern. The biggest problem with this though is that it would leave 6.5 inch gaps without ribs in the most likely to be hit section of the vessel. I could also remove 4, 6, 8, and 10, which would reduce the gaps to about 4.3 inches each. (pictured below) - this would result in minimal hullform loss without need to refigure rib dimensions. I could place a bracer across the 3 keel pieces in the bow to reinforce the joinery there if need be (since there would no logner be 2 ribs attached across it). If I started pulling other ribs I'd probably have to shift rib locations around and interpolate new rib forms, which is more work than I had wanted to do for this ship.
For propulsion, I would recommend a 1.25" three-bladed or four-bladed prop, and either a 280-size motor with 5:1 gearbox, or a Mabuchi RS-365SH motor direct-drive. Any combination of the above should get you up to even Fast Gun speeds. On rib spacing, I generally like to have as few ribs as I possibly can. If the Mehoshi's stepped decks didn't step where they did, I would have used a smaller number of 3/8" ribs instead of the 1/4" ribs currently there. If you need to keep hull strength up, though, have you considered substituting 3/16" or 1/8" ribs for the 1/4" currently there?
