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Good day to All,

a quick, probably silly question.

it is worth to install the filler block in between all the bulkheads ? or it`s enough just at the stern and bow.

did anyone attempted to use expanding foam? and if so with what result? any others way to fill the gaps? any tips to share

thank you for your time and have a great day/night

Paolo

HIC SUNT LEONES

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Hi olapa67

My experience: depend on the model. Regarding your model: I would recommend to fill also the final front gap in the bow and to fill at least the three gaps in the stern.

I have no experience with foam, but balsa wood can definitely not be recommended.

Clark

 

 

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If you can mill it to the needed dimensions, an inexpensive source of filling material:

 

in the US,  dwellings are framed using 2x4 by 8' Fir or Pine lumber.  A mega store building supply chain sells it for< $4 each

It is a softwood - evergreen - not difficult on cutting edges.  Pick clear straight stock.  As long as it is not sappy Pine, it glues well.

If you have access, a free supply might be had from a building site from the end cuttings and scrap, if you ask.

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I used balsa as filler for all the bulkheads in my first build (Sherbourne). I found it wasn't very good with glue for the planking, but maybe that was my fault. It doesn't hold nails or other fastenings either in case you are thinking of going down that route. It certainly was better than nothing, though, and extremely easy to shape. I'd go with pine or basswood/lime in future as suggested by Jaager.

 

Tony

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At the bow I filled in the front 4 spaces between the frames with basswood (a variety of sizes as you can see from the pic on my log - page 1).  I felt this would be easier than trying to shape one bigger block.  I then used a dremel with a sanding drum to rough it out and finished with manual sanding.  I think the stern only needs the aft most space filled as the curves here are much more gentle than at the bow.

Basswood is fairly soft and very easy to work with.  It will also hold small brass nails.   I bought a pack of strips, multiple sizes at  a hobby store.  you can find blocks of basswood on amazon too.

 

Jeff

 

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I think there are considerable advantages in planking in terms of no flat spots or dips that have to be addressed when you fill all the bulkheads with balsa, and the only downside is the time required to add the balsa pieces. I'll be doing exactly that with any build where it's possible to do so moving forward.

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Someone a while ago on one of the threads, I don’t remember which tried using expandable urethane foam.  Anyhow, it was not possible to judge how much material to use and the stuff expanded beyond expectations resulting in a mess.

 

Roger

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Posted (edited)

Filling all the gaps is probably not a good idea, although tempting.  On another post (Drazen), someone had filled all the spaces between frames with solid wood.  The problem is that wood will move with humidity, and he ended up with cracks in the planking, especially at points where the filler piece wanted to move and the plywood bulk head didn't.   The lessons from that, at least for me, were:

  1. leave a gap between the filler and the bulkhead.  If not a gap, put a soft layer of cardboard that can flex and shear as the wood moves
  2. align the grain of the filler with the grain of the planking.   Wood doesn't change length much with humidity, but it does change length.   Over-constraining wood structures is never a good thing.

There was also a discussion that the change in width of a plank with humidity for flat grain boards is almost twice that of edge grain.

 

Overall, I would add more bulkheads: fit them in as best as possible then fair them.   This is how "real" ships are built and it eliminates the flat spots when the bulkhead spacing is large and gives more points to tie to when bending around hard curves.   

 

Edited by lehmann

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3 hours ago, Roger Pellett said:

Anyhow, it was not possible to judge how much material to use and the stuff expanded beyond expectations resulting in a mess.

That's an understatement. I've seen more than one full-sized boat's plywood skin and internal parts blown apart by somebody trying to fill an enclosed bow or stern flotation chamber with that stuff. It's like one of those 1950's science fiction "B" movies: The Killer Foam From Hell. It just keeps spreading and spreading until it's done and there's very little way to predict when it's going to stop. It produces a lot of force if it's contained in any way.

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OK first of all thanks everyone for the precious information, put the expanding foam idea on the side. I will fill the bulkheads with wood leaving 1mm gap on one side and glued it only on 1 side of the frame, I hope this will minimized the problem that can be caused by expanding wood due to humidity (this was something I was totally unaware, so thanks again for the tip) I will try to find some basswood although I have already purchased and installed some balsa wood, could not find much on line here in Australia so the choices are to buy overseas, don't know if I can wait for the delivery so I might proceed with what I have. I m still undecided if fill the entire side or only stern and bow.

and then going for my first planking ever. wish me good for that

Thanks again 

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1 hour ago, olopa67 said:

I will fill the bulkheads with wood leaving 1mm gap on one side

That will work fine, however Drazen's problem had little to do with his filler blocks and everything to do with him leaving the model in a basement where it swung from 20% to 80% humidity. That will tear apart just about anything made out of wood, if you put a $4000 acoustic guitar into those conditions it would suffer damage and if you put a Stradivarius there you better have good lawyers because someone is going to be suing you for lots and lots of money.

 

You'll have more success protecting your model by controlling the environment than you will by reinforcing it at every step against movement if you live in a harsh environment like that. You don't want any significant movement if you want it to survive, reinforcement just delays the inevitable if it's put through regular significant humidity swings. This is true of anything precision made out of wood. 

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Hi Olapa67 and all the others,

I would be interested if anyone has problems with changing wood length due to changing humidity. My first model (Soleil royal, Mantua) was finished 1998 and was moved to various places in the meantime. I could not detect any damages.

 

Regarding the filler blocks: thanks for initating the discussion.

Clark

 

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On my 14 Gun Brig  Fair American build, I used bass wood to fill the forward/after bays in the hull assembly.  Fairing was done with course sandpaper wrapped around a large dowel.  After fairing, this added support was a real help in planking.

 

Regards,

Pete

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2 hours ago, Clark said:

Hi Olapa67 and all the others,

I would be interested if anyone has problems with changing wood length due to changing humidity. My first model (Soleil royal, Mantua) was finished 1998 and was moved to various places in the meantime. I could not detect any damages.

 

Regarding the filler blocks: thanks for initating the discussion.

Clark

 

The worst case of this I have seen in the forums here is Trussben Swan in the scratch build section.  He had to rip out months of work and redo the entire midsection of the framing due to changes with humidity.  Page 15 of his build log. 

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I have not tried it myself, but I have heard of using extruded foam, the kind sold as sheets for insulation, as filler blocks.  It doesn't have the same issues with changes in humidity that wood has.

 

Jeff Betcher

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The extruded foam does, however, have an issue with temperature changes! As the temperature changes, the foam expands and contracts, and when it re-expands after contracting, it does not return to its original size. It can end up, over time, as much as 2% smaller overall. Yes, this is documented in the manf. data sheets. This was pointed out in a Model Railroad forum, as many build their layouts out of this material. I measured some old sheets that I was given, and they are indeed 1/4" shorter than the original 96". These sheets came out of a Southern USA garage, and probably spent 20 years sitting in there, with the large temperature swings that would be expected.

 

This would probably not be a big factor in our models, but I did want to make you aware of it.

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I have used expanding foam in a previous build of mine. after expansion and completely dried I pressed on it, apply another layer so that it became slightly solid. I did not try to glue the planks on it (gues CA will melt it) but it served as a base for the planks to lay, supporting planks especially in tight turns. nice and easy method but really sticky and messy :-)

mehmet

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You will never know what will happen to a model in the future, but as was noted above, any structure made from wood is not very forgiving with respect to dramatic changes in humidity. That's a fact of nature and there will be other parts of the model than the hull that are likely to suffer. So, as long as you are in control of it, try to keep it in the same kind of environment.

 

Plywood is made to counteract exactly that problem by having layers of grain running cross-wise. Hence, you could use pieces of plywood as fillers. Not so easy to work, however, Otherwise, a fine-grained not too hard tropical wood will do as well. Making the filler pieces just as thick as needed and running the grain along the ship, as noted before, will minimise the force the filler pieces can excert on the framing.

 

In general, it is a good idea to use a wood that is a hard or softer than the plywood bulkheads, but not much softer. If the wood is too soft, such as balsa, fairing becomes more difficult and you kill the effect that you are trying to achieve - to make fairing easier. If the wood is too soft you will get a sort rippling effect, the harder bulkheads protruding. If the wood is harder than the plywood, you are going to have a tough time working it down.

 

Many years ago I built a steamer-model with bulk-heads sawn from brass sheet and filled the space between them with an acrylic foam. This is essentially foamed-up acrylic glass and made by the manufacturers of PLEXIGLAS. This foam is very stable and doesn't shrink. It is used e.g. in aircraft construction.

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wefalck: Out of interest I thought I'd find out where to buy acrylic foam in the UK. I can't find any sites, including Plexiglas, that talk of acrylic foam except in relation to acrylic foam tape. I found a reference to syntactic foam as another name for acrylic foam in a paper on flexible acrylic foams as a carrier for speciality tapes.

 

That led me to look up syntactic foam on Wikipedia, where it says:

"Syntactic foams are composite materials synthesized by filling a metal, polymer, or ceramic matrix with hollow spheres called microballoons or cenospheres or non-hollow spheres (e.g. perlite). In this context, "syntactic" means "put together." The presence of hollow particles results in lower density, higher specific strength (strength divided by density), lower coefficient of thermal expansion, and, in some cases, radar or sonar transparency. A manufacturing method for low density syntactic foams is based on the principle of buoyancy.

The term was originally coined by the Bakelite Company, in 1955, for their lightweight composites made of hollow phenolic microspheres bonded to a matrix of phenolic, epoxy, or polyester."

So I looked up syntactic foam suppliers, and their offerings include rigid, high strength composites of epoxy resin and hollow glass microspheres. Would this be the material you refer to? It's probably very expensive.

Would it be very different in properties to the generally available PVC foam or foam board, which sounds similar to polyurethane foam and is very crumbly in character?

Tony

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Posted (edited)

The brand-name is Rohacell and it is made by Evionik Industries, formerly Röhm GmbH in Germany, who are the inventors and producers of PLEXIGLAS: https://www.rohacell.com/product/rohacell/en/

 

To be honest, I don't know exactly, how Rohacell is made, but to my knowledge it does not contain cenospheres, but is just the co-polymerised acrylic and acrylimide resin. It is seem that the monomers are heated to 170°C, whereby they begin to foam an polymerise. It is a true foam, not sponge, meaning that the bubbles are not connected and, hence, the uptake of humidity is limited.

 

I would know, where to buy the stuff in the UK. I was lucky that my late father worked for a the pharmaceutical daughter company of Röhm GmbH and that at that time I had easy access to everything related to PLEXIGLAS. In Germany PLEXIGLAS and Rohacell are sold in small quantities by shops catering for the builders of architectural models. I didn't check the prices, but it certainly is more expensive than the common 'styrofoam'.

 

The pores of Rohacell are very fine and the surface of the sheets or blocks is quite smooth. It can be easily and cleanly cut with a knive or any saw. I can be cleanly sanded with sharp edges. The dust is a bit messy, at it is very light-weight. The sheets are somewhat brittle and thin sheets can be easily broken into pieces.

 

Unlike 'styrofoam' it is not dissolved by the common contact cements. To the contrary it can be glued very well with these, CA cements, or cements for acrylic glasses.

 

Once I have the current project finished, I am planning a somewhat innovative approach for a small-scale model, where I will cut the frames from PLEXIGLAS, fill the spaces with Rohacell to aid fairing and incease stability. The hull will then be planked with either strips of styrene sheet or of phenolic resin sheet. I am not such great fan of styrene, but it can be quasi welded to the PLEXIGLAS frames using ordinary styrene cement or dichloromethane.

Edited by wefalck

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    When I first saw this posting of this topic, I was reminded of seeing that in the March/April issue of Ships in Scale there was a short article on converting POB construction to solid hull construction by Robert Brandt.  In his article, he described his method of using foam blocks to fill in between frames allowing him to use a single layer of planking that would have continuous solid support and eliminate the problem of hollow spots in between frames.  (Something quite important if you intend to use a natural finish rather than painting the model.)

    He thought that by using extruded polystyrene foam for his blocking, the ease of cutting and shaping the blocks was easier than using wood.  As an added bonus this would add very little in terms of weight.  The excellent compressive strength of this type of foam doesn’t hurt either.

    Shown below are the illustrations of his method that were shown in his article.  (Currently being reviewed by my assistant.)

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     A version of this type of foam that is readily available throughout North America is Dow Blue Styrofoam.  STYROFOAM™ Brand Insulation is the original extruded polystyrene foam insulation, invented by Dow and first manufactured by them in 1941.  Dow's blue colored extruded polystyrene Blue Board's closed cell structure and lack of voids resists water and water vapor penetration thus protecting underlying materials from water damage. 

    This product is also available in several sheet sizes and thicknesses and is relatively inexpensive.  It does however, require the use of a particular type of adhesive, as some types of adhesive will dissolve the board. 

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here is my solution about filler blocks expanding problem due to humidity. not sure if it will work and if i wasting my time but i ll give it a go.

the idea come after i saw concreter  cutting the cement slab to avoid cracking. so i cut with a small saw  blade the filler blocks after i had installed to create a small gap so that the wood have a bit of freedom if it need to expand.

i ll let you know in 10 years if it worked or not 😁😁😁

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