The Ship Model Forum

yes i was thinking of priming to, i presume gray color.

I have one its transparent, so not much of use i guess. The other is epoxy grey. What kind would you suggest? There is also available in the shop, car body primer thin and and thick, good for correcting micro chips. Which one you suggest?

Mike:

What I have used, both on autos and model ship hulls is the grey "Primer Filler". This fills in small depressions, bubble holes and sanding scratches. In addition it really lets you appreciate the contours and any changes needed. Wet sanding with very fine sandpapers will bring a perfect surface for the final paint.

Best regards! Tom

I sprayed the filling primer over the hull. Although there's still work to be done I hope by this Sunday that it will done along with bilge keel fitting

Mike:

Pretty fast work which should be an example to anyone dithering about building a scratch hull!

Regards: Tom

Thanks for the encouraging once more. And i will probably need it.

While test fitting the bilge keels i noticed one thing, hull could not sit straight. Have seen that actually weeks ago but for unknown reason i didnt bother. So while i bent and noticed something kinda horrified. The hull was touching the table only with bow and stern edges.
I remember that keel was totally straight and paraller to the table with full contact on it. I really can't tell why the ship got this obvious hogging effect.
Then i looked at the previous hull and noticed that there was the same problem. So i went back to plans to check but all model and online plans i found are calling for a flat bed hull. However the front half part of the model has an 1 to 2,5mm gap as you can see in the photo which must be corrected.
First i trimmed the stern a few mms and added wood acrylic putty pefore apply bondo. Then forward, i added a 2mm balsa fillet and a 1mm trianlge piece right after the bow. I layered wood filler and let it try. I hope tomorrow i can sand add bondo and correct this final, i hope, issue.

Mike:

I think that the shrinkage of the putty and fillers is on the hull bottom but not the deck, causing a slight hogging. This would be exacerbated by the slightly compressible foam material and lack of a rigid sheathing over the ribs. I have been fighting issues with materials in the 3D printing world. It's a matter of judgment. Good Judgement is acquired by experience, experience acquired by bad judgement.

Cheers: Tom

I think I would have used a longitudinal aluminium plate as a 'keel' plate - along its plane it would be very difficult to bend and you have always a good datum to which you can sand.

On a much smaller scale, or rather size, some 35 years ago I made a PoB (Plating on Bulkhead) hull with a 0.5 mm brass keel-plate and 0.25 mm brass bulkheads slotted into it. The spaces in between were filled with a special acrylic foam-board (kind of foamy Plexiglas from the same company). It was easy to sand down the foam-board to the brass frames and to fair it with a thin layer of auto-putty. The surface quality, however, was not so important, as the hull was to be plated with embossed 0.1 mm copper-sheet, simulating the rivetted in- and out-strakes.

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Eberhard

Former chairman Arbeitskreis historischer Schiffbau e.V. (German Association for Shipbuilding History)

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Some foams, body fillers and glues generate quite a bit of heat while curing. This can cause thermal expansion, especially with plastics. Usually there is a larger volume of these materials on the upper part of the hull than at the bottom around the keel. Uneven expansion could easily hog a hull while the materials are curing, and the result would be permanent hogging.

Just one more thing to consider while constructing a hull!

For example, the Coefficient of Thermal Expansion (x 10-6 K-1) for a few materials is listed below:

Douglas fir 2.3 (parallel to the grain)
Steel ~12
Aluminum 23
PVC 52
Polypropylene 150

Aluminum expands 10 times as fast as Douglas fir, PVC aboutt 20 times, and polypropylene 65 times as much (for a given temperature rise). Plastics expand 2 to 6 times as much as aluminum. Expansion forces are very great in uncompressible materials. Fastening these different materials together in a structure that will be exposed to significant heat (from any source) is a sure way to cause it to self destruct!

Phil

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A collision at sea will ruin your entire day. Aristotle

My model was completed some 30 years ago and for the time being I did not observe any problems, but the model is only 40 cm long. Problems aggravate obviously with longer models.

The discussion now become theoretical, as the colleague has already completed the (2nd) hull, but the sagging probably could also be prevented by having an aluminium (or carbon) tube running internally the whole length of the ship, but not attaching it, so that it can move with temperature changes. Another, more esoteric method could be to install internally anti-hogging wires/ropes, much like chains they used on shallow draught river-craft in the old days. With chosing the right material they would expand/contract together with the hull.

Thinking the thermal expansion problem through, I would be a bit worried about such big hull just puttied. It may be worthwhile to give it a thin skin of glassfibre matting soaked in some suitable and compatible resin. The glassfibre would take up the strains from the expansion.

_________________
Eberhard

Former chairman Arbeitskreis historischer Schiffbau e.V. (German Association for Shipbuilding History)

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I have started already repairing the hull. I just read all the interesting answers. Now there is already a layer of filler and a balsa panel. I l already gave a second coat and start sanding. I know that filler over filler with burned foam works ok. I did it in a few spots. I will let the hull rest for at least 24-48 hours and see later how it goes. Wood filler is totally harmless and can be sanded easily while the final apperance is quite smooth. I saw another Greek guy here made a patrol boat with foam, but covered the hull with 0,30 mm styrene plus i dont recall what kind of putty he used.

A learning experience for all of us. The hulls I have done were wood over wooden ribs with only skim coats of other materials. Missouri, (1:192) has a thin coat of fiberglass, the thin stuff model airplane constructors use. Putties and fillers only in very thin section to correct minor hull defects. An exception would be the current LSM hull which is made from aluminum, originally some 60 years ago. But that's a smaller model.

An interesting characteristic of some plastics in very cold temperatures is they shrink and remain shrunk. I had a Weaver scope on my rifle when I lived in the Arctic mountains. The plastic adjustment equipment shrank and stayed shrunk in the -40, -50 temperatures. I sent the scope back to Weaver and they very kindly machined new parts of aluminum for me and changed the design of the scopes. I had a fan belt shatter like glass at -70 when starting my car!

For ship models, living an indoor life with a controlled temperature makes life easier. Large RC types face more sophisticated challenges. An original model I made in the early 60's or ARL 12 lived for many decades in my parents ambient temperature attic, survived despite it's alloy hull.

Keep plugging away Mike!

Sometimes issues show up only decades later. I just participated in a restauration experience exchange seminar at the Musée de la Marine in Paris and they had an about 3 m long tanker model in their workshops that showed some delamination at the hull - they didn't talk about this model, but it appeared to me that under the paint there was some kind of sheathing that had become detached from the wooden(?) hull. Just as you see wooden veneer becoming detached from wooden furniture as the glue fails, when the wood 'works'.

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Eberhard

Former chairman Arbeitskreis historischer Schiffbau e.V. (German Association for Shipbuilding History)

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Situation is a bit funny. I recently started restoring my old 1/700 collection built 25+ years ago. They remained as I left them except they have more dust.



It is also noticeable that bridge deck was built in the same way. No issues whatsoever. I built it after finishing filling my first hull, some months ago






Seems that if improper materials combined in a larger scale then problems are bigger

Indeed ...

_________________
Eberhard

Former chairman Arbeitskreis historischer Schiffbau e.V. (German Association for Shipbuilding History)

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Which tanker?

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Pascal

•Battleship Bretagne 3D: https://vu.fr/FvCY
•SS Delphine 3D: https://vu.fr/NeuO
•SS Nomadic 3D: https://vu.fr/tAyL
•USS Nokomis 3D: https://vu.fr/kntC
•USS Pamanset 3D: https://vu.fr/jXGQ

Did not pay attention, sorry.

_________________
Eberhard

Former chairman Arbeitskreis historischer Schiffbau e.V. (German Association for Shipbuilding History)

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I continue the hull repair. Added a 2nd layer of balsa at center. I tested and hull seatted perfectly on the base. Tomorrow early morning will do a bit of work before go office. I work double shift now to make up for the lost time.

Mike!

Persistence is a wonderful tribute to possess in any endeavor. Keep plugging away! For many decades I have had thin styrene adhere perfectly to wooden bulkheads.

Tom

So I did all corrections that required and primed again the hull. I used a safe method. Wood filler over not wooden surfaces then glazing putty spreaded with finger just to give a smooth surface. Need to fill in a few bumps additionaly not much work.
I contact an old member on FB. Seems his an expert on doing fiberglass hulls from mould. He offered to answer all my questions. I have been researching this for every day this week. Thinking of using the existing hull to make a proper glass one.

Most of the work is done, tomorrow will check for small flows then polish the hull