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[npomeroy]

deleted due to accidental "post" before finished - will start again:

[npomeroy]

I am planning a scratch-built Damen 1907 tug boat, 1/32 scale (600 mm long).  https://media.damen.com/image/upload/v1655733874/catalogue/tugs/stan-tugs/stan-tug-1907/product-sheet-stan-tug-1907.pdf (Damen require an email to view this).The hull is hard-chine and I was intending to make a frame from laser cut 3mm ply and cover with 1mm ply sheet. Initially I drafted the ribs to be built the same as some of the Billings boats, one side at a time attached to a flat surface that represented the mid-vertical-longitudinal plane. It should be possible to cover each half with ply sheet and the 3D shape would be stable. But this structure would need to include cross pieces under the deck. These would need to be partly removed in order to access the internal space to install motors and other mechanical parts.
So alternatively I am thinking of building the framework as a single unit keel-up, with no deck cross pieces. The build surface would be slightly curved as per the deck profile. I would incorporate a deck margin (say 20mm wide) to help keep the shape. So my question is:  Would this structure have 3D stability after the hull sheets were glued on? Perhaps steam curving the hull sheets would be helpful, and/or laminating a second layer, especially as the 1mm ply may be fragile in collisions.

Cheers
Nelson

[1967Brutus]

So my question is:  Would this structure have 3D stability after the hull sheets were glued on?

Cheers
Nelson

I think it will, but it depends on the cross-section of the frames. For safety, I would cut the frames to include a decksupport serving as crossmembers to prevent the sides from flexing out, until the hull is off the building board, and only remove them once you need the access. For example after the deck has been fitted. The deck will make the hull a box like structure.

[npomeroy]

I think it will, but it depends on the cross-section of the frames. For safety, I would cut the frames to include a decksupport serving as crossmembers to prevent the sides from flexing out, until the hull is off the building board, and only remove them once you need the access. For example after the deck has been fitted. The deck will make the hull a box like structure.

Thanks Brutus.  As you say, it depends on the rigidity of the cross members. I am hoping that if I include a (say) 20 mm wide frame, i.e. like the deck with the centre cut out, then that should hold the lateral shape. Also, when the two main sheets each side are on, there should be a sort of monocoque rigidity, although I can not quite visualise the forces. I would like to include a longitudinal member at the chine join on the side of the hull, but drafting the 2D shape with the double curve may challenge my plotting in Inkscape.


Cheers
Nelson

[tonyH]

You can get a twisting force in the hull from minor differences in wood thickness, wood hardness etc in the ply and the stringers and even the amount of glue, so watch out when you first remove the hull from the building board and prior to putting the decking on.

[1967Brutus]

You can get a twisting force in the hull from minor differences in wood thickness, wood hardness etc in the ply and the stringers and even the amount of glue, so watch out when you first remove the hull from the building board and prior to putting the decking on.

It would help, to place the hull in an adjustable jig of sorts, such that any warping out, BEFORE fitting the deck.
Once the deck is in place, the resultig box structure should be virtually warp-free, even if there is a deck opening.

But I suspect that wetting the hull planking before glueing on the frames will take away a lot of the tension, and prevent or at least strongly reduce the planked hull from warping when taken off the building board.

[npomeroy]

It would help, to place the hull in an adjustable jig of sorts, such that any warping out, BEFORE fitting the deck.
Once the deck is in place, the resultig box structure should be virtually warp-free, even if there is a deck opening.

But I suspect that wetting the hull planking before glueing on the frames will take away a lot of the tension, and prevent or at least strongly reduce the planked hull from warping when taken off the building board.

The "planking" will be just two major sheets each side. Indeed if I steam them to an approximate curve first it should reduce tension. Also since the sheet (already purchased) is only 1mm thick, I may laminate a second layer, with epoxy, after applying to the frame. This should "lock in" the curvature as well as add impact strength.


Cheers
Nelson

[John W E]

hi there


I have put a link on from a build of a Tid tug which is in the masterclass part of this forum.    You may just have seen this build but I have put it on in case.   It may help you.    The difference being is, the hull skin is planked in broad stripped planking.  I have seen a lot of people do this where they cut the plywood into approximately 25mm wide strips - for ease of planking.   Somewhere on this Forum there is a guy who does this method, but, he double planks the hull so that the 2nd layer of planking covers the first layer of the plank's joints.  He also uses a waterproof PVA glue rather than epoxy.   Then, when the hull is rubbed down, he gives it a coating of Epoxy resin, without any matting. 


I would personally use a building board as previously mentioned - this would prevent any twisting in the framework.    If you have a look at any builds from people who are building from kits, say Billings, the method that is commonly used is frames are fitted to a solid deck then the keel is added to the frames.   This creates a solid and stable framework.    What you are trying to do may not create a stable framework by leaving an unsupported area.   This is where a building board would come in useful to support the unsupported areas of frames.


This is my two penneth worth.


John
TID TUG (modelboatmayhem.co.uk)

[npomeroy]

Hi John.  Thanks for the comments, and that link is really useful. I'm not sure what you mean (or in which plane) is the "unsupported area". I was intending to build on what is essentially an inverted deck. It would not be quite flat because the deck has a slight curve, which I would duplicate with a stepped build base.

[ChrisF]

My Faireys are obviously different to a tug but I build inverted. My bulkheads/frames are a mixture of those with cross-members and those without but for the latter I include them before the addition of the hull skins and then cut them out where not required or for access for the later parts of the build. Once the hull skins are on the structure is stable.

[dodgy geezer]

Ernie Webster's 'EeZeBilt' technique, illustrated here:   http://eezebilt.tk/making.html  is of interest.

The system gives a stiff internal framework based on two horizontal flat sheets, the deck and the chine line. This contrasts with Les Rowell's Aerokits eggbox structure using extended vertical superstructure sheets, or Phil Smith's Veron central box with added external formers.  While the EeZeBilt system was originally intended for small boats of around 1ft, it can easily provide hulls in the 2-3ft range, and the largest one I have made is 42". Others have gone further...

At the larger sizes the implied straight chine line might be a problem, but I have found that it is easy to either kink the chine sheet or curve it upwards to produce the proper bow shape. The RAF Crash Tender in the 50+ range even has reverse kinks to produce the double bow chine curvature of the Vosper hull. Several others also have curved deck lines. So long as there is a flat chine line at the rear of the hull to pin to a building board, a datum exists which can be used to build all the other shapes to - much like packing up a wing half to produce dihedral in the aeromodelling world...

[Circlip]

And don't forget the "Adamcraft" use of a bulkhead support/alignment jig for upside down hull construction.


  Regards  Ian

[John W E]

Hi there Nelson


I suppose the correct answer to your initial question, nobody can give you a defined answer - i.e. will it or will it not work - but, we have all to try something different in our modelling hobby to see if our idea works.   I would suggest  - try your method i.e. maybe try using very thick cardboard for your frames as a trial and if that looks good/showing signs of possibly working - then try it out using plywood.


As a lot of us modellers on this forum come from 'the stone age'    where we use building boards to build our models on.


I am putting a link on here - to an excellent build - although it isn't a tug, it is a warship HMS Ocean.   Look how he constructs the outer planking.   Modellers who can manipulate plywood in this way always amazes me.   In theory plywood shouldn't bend like this.


Go right to the end of the build and have a look at the big open spaces he has created in the deck.


john


HMS Ocean Scratch Build (modelboatmayhem.co.uk)

[dodgy geezer]

......
As a lot of us modellers on this forum come from 'the stone age'    where we use building boards to build our models on.

.........

Building boards?  A nice chunk of Yellow Pine, a workbench and a chisel should be good enough...

[npomeroy]

Thanks for the various comments and links.
Some admirable projects there.


Nelson.