Plastic ship 'hull rigidity'

Thanks, Tracy!  Good information to have.

I have a minuscule amount of experience compared to you folks, but using Tenax really worked well in 'welding" both halves of the 1:350 DDG Kidd I just started. It has 2-3 internal braces, which are useful as you manipulate the hull; the plastic is on the thin side, it really buckles a bit if you grab it near one end.

It's just the Smooth-On that my local Hobby shop carries from time to time. I chose it mainly due to the availability and fact that it's a 1:1 mix ratio.

Hi Tracy,

What type of resin do you use?  Is it polyurethane? And, where do you typicalloy purchase your resin from? 

I saw this technique described in Mike Ashley's book as a way to add a solid "chunk" inside the hull for mounting attachment.  It wasn't clear where or what type of resin to use for this.

Thanks in advance.

Cheers, Rick

Tracy White wrote:

I only use CA as a putty, and only in limited applications (other than for PE). I don't like the long-term strength of it nor issues with it hardening within a couple of days to something harder than the plastic... makes it harder to work with. I generally use a combination of tube glue and liquid cement; Tube glue for some of the ares I need stronger bonds and liquid cement on longer, less structural seams.

....And you still have breakage, cracking and distortions along the seams?  Well, I guess I just have no explanation then..... Must be lucky! I have noticed that comapnies use different strengths of styrene in their kits.... The Nichimo kits were always very soft, but that mostly affected trimming flashing, etc....

searat12 wrote:

I've just had a thought, which may or may not be applicable.... All you folks having problems with hull seams, are you using CA glue?

Liquid cement. IMHO, the plastic Trumpeter uses is very soft.  I prefer the stiffer styrene found In Tamiya kits.  I also really like the styrene made by Evergreen.

I had a warping problem with a 1/720th Italeri Nimitz-class ship I built.

I removed the optional lower hull since I intended to make the model a waterline one. I opened the flight deck elevator doors and added some simple styrene sheet "hanger decking" so that I could show a plane or two through the openings. I also added a couple of styrene sheets to keep light from shinning through hull openings where light shouldn't show. The rest of the basic assembly was by the kit instructions.

When the model was finished, the bow and stern had drooped enough that I couldn't mount the hull flat on the base I'd selected for it. After some selected language, a couple pieces of tubing and drilling a couple of holes, I mounted the model slightly above the base. It worked, but the warp was there.

Probably should have mounted the hull and covered the base at the beginning, but obviously I hadn't counted on any problem.

I only use CA as a putty, and only in limited applications (other than for PE). I don't like the long-term strength of it nor issues with it hardening within a couple of days to something harder than the plastic... makes it harder to work with.

I generally use a combination of tube glue and liquid cement; Tube glue for some of the ares I need stronger bonds and liquid cement on longer, less structural seams.

I've just had a thought, which may or may not be applicable.... All you folks having problems with hull seams, are you using CA glue?  I only use CA where it is necessary (resin and metal parts), but otherwise just use the same good ol' airplane glue that has been around for years and years.  It actually melts the plastic a bit and makes a very strong and flexible bond once it has hardened thoroughly.  Even in the case of hull halves that were slightly distorted (there was another string earlier regarding a 'Titanic' model being converted to WW1 camo that illustrates this sort of thing well), if you simply airplane glue it and clamp it, when it hardens there is no problem (and not much need for putty either, certainly not for any sort of structural integrity).  I have always found CA glue to be fiddly and unreliable, with no torsional strength whatsoever, and thus avoid using it if possible (and I can see if you use CA for bonding slightly distorted hull halves, you would have a lot of problems!).....

I had to do the same thing with my conversion of the Revell USS LEXINGTON (CV 16) to the USS HANCOCK (CVA 19).  I seperated the Revell sailing ship style hull below the waterline from the upper hull, then have begun grafting the lower hull from the Lindberg USS YORKTOWN (CV 10).  Besides the slow grafting process (described several years ago in FSM, grafting the Revell Forrestal lower hull onto a Revell USS MIDWAY), I found that I had to provide internal bracing along the sides of the hull for the graft to take.  It is working, but it is time-consuming.

Bill Morrison

I have experienced very annoying hull parts seam separation problems when the kit parts' fit isn't good.  This is especially a problem when the hull seam is along the waterline.  1/350 Trumpeter kits have this problem, 1/350 Tamiya kits do not because their hulls are molded in one piece (except Enterprise CVN-65).

For example, on a 1/350 Trumpeter Yorktown CV-10 I am building, the upper hull parts do not fit well with the lower.  So, when the upper hull parts are fixed to the lower, the seam is under internal pressure.  Any handling or pulling of tape after painting tends to pop open the seam spoiling the finish.  It's happened four times and is really tough to repair properly.

What I should have done was reinforced the hull while I had access to the hull interior after joining the upper to the lower but before fixing the hangar deck.   At the time during the build process I failed to anticipate how often and how severe the seam pops were going to occur so I felt no reinforcement was needed.  Now that the kit is largely done, it's too late to reinforce the hull and seam pops will likely continue.  Doh.

 

 

The Heller 1/400 scale 20th century warship series had it right concerning supports for the seam between the port and starboard halves.  They simply had two or three rectangular flat beams cemented fore and aft (maybe midships) across the halves. Nothing more was necessary.  Their system worked well.  I do not see how the current system of placing many athwartship bulkheads inmproves upon Heller's simple system.

Bill Morrison

Hmmm!  I don't recall ever having a bad joint on the bottom of any hull, but perhaps that may be due to my habit of gluing in a fair amount of ballast (which could well have the same effect as resin, or styrene, or whatever), and of course, I don't travel about with my models at all (once they are finished, they are on the shelf).  Also, most sailing ship models have a very substantial keel with plenty of contact surface to grip with, which might also be a mitigating factor.....

A note of caution on the resin.   Most polyurethane resins generate heat when the set.   Limit the volume of resin used.  Pour several thin layers as opposed to a thicker one.   Warping will occur. 

I have a Panda Burke with an unintentional oilcanning along the waterline due to resin in the lower hull

Tracey White makes a good case for adding additional rigidity, I like the idea of pouring resin in the bottom myself.  Sounds easier than cutting styrene to fit in spot locations.  Come to think of it, I've seen several models which over the years have appeared to 'release' their PE railings, and perhaps minimizing any flexure would mitigate that.

When done right it makes a lot of sense, particularly on long, two-piece hulls. If you've ever had a bad joint on the bottom of a hull, adding stiffness there will help avoid flexing that will cause putty to crack.

On my Trumpeter CV-13 Franklin build, I used Mr. Dissolved putty and was confused as to why I kept getting pock marks along the seams ... I later figured out that the plastic joints were flexing and the flexing was compressing and then releasing the putty, damaging the bond with the plastic and then popping it out on the next compression.

I usually pour a layer of resin in the bottom of my injection-molded hulls once they're aligned and glued together; it helps keep the hull more rigid AND gives me a good solid material to drill into for mounting. In the case of my Trumpeter Hood the hull is wide and flat enough at the bottom to have four posts in a diamond formation, but in a ship such as San Francisco the hull needs the extra substance to prevent the plastic from cracking due to loads where the pedastals are mounted. Rigidity helps prevent distortion from those loads from expanding to the point that it distorts decks that might have PE attached.

Thanks for the thoughts.... I just find this quite odd!  In the Aoshima 'Atago' the hull has seven half bulkheads for a model that is only 23 inches long, and the Kongo and Nagato have a fair few more and they are full bulkheads (and Nagato is molded in quite thick styrene as well!).  I have built some other kits from other producers of a similar size without any internal bulkheads or other strutting without any problems, but then again, my models are not asked to travel around much (once a hull and deck are glued together, they form essentially a 'box girder' structure)!  First time I have incountered this sort of internal work was with the Hasegawa 'Mikasa.'  In that particular case, the full bulkheads primary use appeared to be as mounting points for the secondary guns, and I suppose that was a fair enough purpose, even if a bit 'overkill.'  But now I see the same thing in a lot of other kits and am wondering if this really is because someone somewhere has noticed a problem with a lack of rigidity, or whether this yet another 'artifact' from the CAD process, or whether it was just done on one kit, and a lot of other model companies have decided to copy the idea just because it looked like a good idea for some reason...... Puzzling!

Occasionally, I found myself adding some styrene to the hull give the deck something to align with and glue to, but never for structural reasons.  Recently, while building the Glencoe NS Savannah, I found myself adding bracing to achieve proper hull shape -- the hull halves tended to warp inward around midships.  I'm a bit nervous about heating plastic, but decided that adding the bracing then warming the hull with a hair dryer to relieve some of the residual stress might work.  Perhaps something to consider is the fact that over time and with some exposure to heat, the model could warp or charge shape.  Don't know if this has ever been observed.  But if a kit mfgr gives you the parts, I would install them.

The only ships that I needed any hull bracing for were the 1/400 scale Heller battleships and the larger Heller sailing ships (Cap Horn and Preussen).  The only bracing that I used came with the kits. I see no real need to brace the Nagato, the Aoshima Japanese heavy cruisers, or the Tamiya kits.

Bill Morrison

 I am one of those who chose to build in some braces to the hull of my 1/350 Tamiya New Jersey. The ship is mounted on a 33" plank of red oak, standing on 4 brass tubes which have a screw up the center. Even with that mounting, when you picked up the board, the ship ever so slightly can flex. I just thought that the extra bracing was a good insurance policy. The hull also has four wood blocks that the screws draw into. The model has been taken to a number of shows and military displays and it comes home in one piece so I am satisfied in why I took this extra step.