Jaager

Nu, unless you developed a magnetic attraction for the subject.
 
I wrote that to make a point. 
The point is:
with a wood ship model kit, all is never lost if you make a mistake. With wood, the same (or most often) better components can be self manufactured.  The barrier to scratch is more imaginary than real, unlike with a kit of molded plastic pieces,  

For WL bread and butter, I think that shaping the end grain of plywood would be a perfectly awful experience.
Your provided prices are a sign of sanity over there.  It is still about twice what we pay for similar.
It takes things back to doable for the OP.

Nu, unless you developed a magnetic attraction for the subject.
 
I wrote that to make a point. 
The point is:
with a wood ship model kit, all is never lost if you make a mistake. With wood, the same (or most often) better components can be self manufactured.  The barrier to scratch is more imaginary than real, unlike with a kit of molded plastic pieces,  

Nu, unless you developed a magnetic attraction for the subject.
 
I wrote that to make a point. 
The point is:
with a wood ship model kit, all is never lost if you make a mistake. With wood, the same (or most often) better components can be self manufactured.  The barrier to scratch is more imaginary than real, unlike with a kit of molded plastic pieces,  

For WL bread and butter, I think that shaping the end grain of plywood would be a perfectly awful experience.
Your provided prices are a sign of sanity over there.  It is still about twice what we pay for similar.
It takes things back to doable for the OP.

A search of SD's previous content yields this  " I bought 3 kits the Syren, the Marseille (C. Mamoli 1/64 kit), and the HMS Victory cross section."
Based on posts, I am guessing that Syren was the first build.
I suggest not giving any priority to the planking ambition for a while.  Since your shortcut on acquiring experience did not lead to the result that you wished,  why not follow as tried and true a course as there is at present to get up to speed?
 
The Model Shipways Shipwright Series  has a fairly low entry fee.   The finished models are attractive, small,  would look good on library shelves (in their separate "glass houses") and being boats, would give you the chops to build the boats that every large vessel carried.
 
Your model of Syren is made of wood.  It would not be difficult to acquire the raw materials to either backup to the stage where things went bad,  Or duplicate the whole K&K from raw materials and build a Syren v.2 that has superior materials.

For WL bread and butter, I think that shaping the end grain of plywood would be a perfectly awful experience.
Your provided prices are a sign of sanity over there.  It is still about twice what we pay for similar.
It takes things back to doable for the OP.

B and Q do a clear pine board, 1.2m x 400mm x 18mm for around £30.
2.4m is £50
Is the tug wider than  400mm?  Other than that most builders merchants have a timber section.
Would not a good sheet of marine ply be suitable? A 2.4 x 1.2 x 9, 12 or 18 mm would be around £30-50 respectively.
Just chiming in here😉

A search of SD's previous content yields this  " I bought 3 kits the Syren, the Marseille (C. Mamoli 1/64 kit), and the HMS Victory cross section."
Based on posts, I am guessing that Syren was the first build.
I suggest not giving any priority to the planking ambition for a while.  Since your shortcut on acquiring experience did not lead to the result that you wished,  why not follow as tried and true a course as there is at present to get up to speed?
 
The Model Shipways Shipwright Series  has a fairly low entry fee.   The finished models are attractive, small,  would look good on library shelves (in their separate "glass houses") and being boats, would give you the chops to build the boats that every large vessel carried.
 
Your model of Syren is made of wood.  It would not be difficult to acquire the raw materials to either backup to the stage where things went bad,  Or duplicate the whole K&K from raw materials and build a Syren v.2 that has superior materials.

A search of SD's previous content yields this  " I bought 3 kits the Syren, the Marseille (C. Mamoli 1/64 kit), and the HMS Victory cross section."
Based on posts, I am guessing that Syren was the first build.
I suggest not giving any priority to the planking ambition for a while.  Since your shortcut on acquiring experience did not lead to the result that you wished,  why not follow as tried and true a course as there is at present to get up to speed?
 
The Model Shipways Shipwright Series  has a fairly low entry fee.   The finished models are attractive, small,  would look good on library shelves (in their separate "glass houses") and being boats, would give you the chops to build the boats that every large vessel carried.
 
Your model of Syren is made of wood.  It would not be difficult to acquire the raw materials to either backup to the stage where things went bad,  Or duplicate the whole K&K from raw materials and build a Syren v.2 that has superior materials.

OK    The lumber is planed.  When you buy an off the shelf 1" board, it is probably 3/4" thick.  You are paying for the wood chips.
I advise accepting reality.  Buy the off the shelf boards.   Get a board wide enough to do half of the hull. Glue port and starboard at the midline.
Measure the actual thickness and loft your WL to match what you can get.   Find out which builders lumber yard or building supply is used by your local contractors.
Get what they use.  No Net,  visit in person.  The on-line guys seem to be real sharks.

Basswood is not a species for you.   It is a North American species.  It is our substitute for Lime/Linden.  And it is a poor one at that. 
 
Your lumber yards do not play nice,   your Pine is an import from here.  You don't want it under those conditions.
It looks like your substitutes are English Cedar  or  European Douglas Fir.    Look at builders lumber yards.  Go with domestic species.

OK    The lumber is planed.  When you buy an off the shelf 1" board, it is probably 3/4" thick.  You are paying for the wood chips.
I advise accepting reality.  Buy the off the shelf boards.   Get a board wide enough to do half of the hull. Glue port and starboard at the midline.
Measure the actual thickness and loft your WL to match what you can get.   Find out which builders lumber yard or building supply is used by your local contractors.
Get what they use.  No Net,  visit in person.  The on-line guys seem to be real sharks.

Basswood is not a species for you.   It is a North American species.  It is our substitute for Lime/Linden.  And it is a poor one at that. 
 
Your lumber yards do not play nice,   your Pine is an import from here.  You don't want it under those conditions.
It looks like your substitutes are English Cedar  or  European Douglas Fir.    Look at builders lumber yards.  Go with domestic species.

Basswood is not a species for you.   It is a North American species.  It is our substitute for Lime/Linden.  And it is a poor one at that. 
 
Your lumber yards do not play nice,   your Pine is an import from here.  You don't want it under those conditions.
It looks like your substitutes are English Cedar  or  European Douglas Fir.    Look at builders lumber yards.  Go with domestic species.

I don't think it would be significant in that case, either. We must remember, though, that the USN specs for ship models were designed (and later written) for ship models of WWII vintage and newer, so six foot long models weren't all that unusual. A modern-day aircraft carrier at 1:96 would run around ten and a half feet long.
 
I must confess that after checking it, I discovered my recollection of the USN model mil specs was "bass ackwards." They prohibit gluing the two halves of lifts cut together at the ends in models of less than 12" maximum beam! They only require hollowed lifts for models with more than a 12" beam.  They say that on hulls of less than 12" maximum beam they require that "...hull lifts shall be cut to the full body shape; lifts shall not be cut in halves, thereby creating a glue seam along the vertical centerline of the model." This would suggest that hollowed lifts were at the builder's option in hulls with less than a 12" maximum beam as long as the lifts were built of a solid piece of wood, and mandatory for hull's with a greater than 12" maximum beam and hulls over a 12" maximum beam could be glued up of two pieces along the centerline. That would tend to make sense because mahogany or basswood lift stock wider than 12" isn't all that easy to come by.  All and all, ship modelers would do well to aspire to following the Navy's specifications. 
 
Actual text of USN ship model contract specifications:
 
Hull
Hulls shall be built up in lifts of clear, first-grade mahogany or basswood; doweled and glued together with water-resistant glue. The wood shall be completely free of knots, checks, and sap pockets and shall be thoroughly seasoned. Models over 12 inches beam must be hollowed for reduction of weight The hull shall be composed of the least number of parts necessary to achieve the proper shape. An excessive number of glue joints shall be avoided. On models less than 12 inches beam, hull lifts shall be cut to the full body shape: lifts shall not be cut in halves, thereby creating a glue seam along the vertical centerline of the model. The lifts shall conform accurately to lines of the vessel as shown by the plans. A stable, durable, flexible body putty may be used in moderation to fill gaps.
 
Nautical Research Guild - Article - Specifications for Construction of Exhibition Models of U.S. Naval Vessels (thenrg.org)

I was spotting you the work needed for lofting of the WL on the tug.   I purposely have set my focus to end at 1860.  I am buried under by all of the choices as it is. Including steel would put me into a  positive feedback loop.  I do think that the transition steel vessels up until 1914 contained some very interesting and bizarre subjects - almost totally ignored.
 
I missed the part about the two part bilateral symmetry.   Perhaps the reason is to have opposing tension.  Lifts from a single board may allow a bend: crook/crown?  I have always assumed that the hollow requirement was to reduce the damage caused by changes in humidity.   With wooden ship models of vessels before 1860,  the difference in weight that being hollow produces seems like it would not be significant.   For a CVN, or BB at 1:48 the difference would be significant.  But then a CVN could probably carry HMS Victory 1765 on davits as a very large lifeboat.

I was spotting you the work needed for lofting of the WL on the tug.   I purposely have set my focus to end at 1860.  I am buried under by all of the choices as it is. Including steel would put me into a  positive feedback loop.  I do think that the transition steel vessels up until 1914 contained some very interesting and bizarre subjects - almost totally ignored.
 
I missed the part about the two part bilateral symmetry.   Perhaps the reason is to have opposing tension.  Lifts from a single board may allow a bend: crook/crown?  I have always assumed that the hollow requirement was to reduce the damage caused by changes in humidity.   With wooden ship models of vessels before 1860,  the difference in weight that being hollow produces seems like it would not be significant.   For a CVN, or BB at 1:48 the difference would be significant.  But then a CVN could probably carry HMS Victory 1765 on davits as a very large lifeboat.

For those of us who build wooden sailing ships,  the plans come with WL.  Rather than doing any lofting, the WL from the plans determine the lift thickness.
The hollow insides are a requirement from the USN museum. 

The Birch is the outside layer.  It is for looks.   It should work as long as it does not get wet.
There is a Birch ply for boat building. The liner ply are not junk and the bonding adhesive is waterproof.   An extreme that you do not need and unlikely to be anywhere as thin as you want.
 
The Mahogany that you can get is not really Mahogany.  Real Mahogany was timbered to near extinction fairly early in the 20th century, so it is a protected species.  I would look real hard for something else.
Most everything called Mahogany has open pores.  This means that it is scale inappropriate if it is on view.
 
Going to a builders supply and getting clear Pine would be a low cost option.  If their thinnest project boards are too thick,  make friends with a serious woodworker and see if he would turn Pine 2x4's or 2x6's into sheets that are your target thickness.
 

There is such a thing as sawn frame POF and I guess what you have drawn could be considered to be that.  As fat as you have it drawn, it does not meet the spirit of what POF is though.  You are not after a hull that represents what POF is intended to show anyway, so dealing with definitions  is not relevant.
If you scroll cut that pattern from a Pine plank, it should do what you are after.  If you use a plank of 1/2 the thickness and cut twice as many "frames" but with half if them having an opposite grain orientation, when glue bonded in pairs, it may greatly reduce any breakage.
 
If you use a pattern with alignment holes,  doing it as pairs -  one of the pair could be two pieces - Vertical grain - meeting at the "Y" axis in the center of the keel - two pieces for that frame.  The other be two boards meeting at the "X" axis about halfway up.  The result would be three pieces for that frame.  It would be much easier to cut out the pieces.   Bamboo skewers as dowels = idiot proof orientation if you plan it well.
 
 
That is essentially the Hahn method.  It may be overkill for a hull meant to float.

First:  this is not a frame. It is a mold.  The first Italian POB mfg used a term that translated as "bulkhead".  Those parts are not bulkheads.  Western wooden ships did not have bulkheads. Chinese seagoing junks did have actual bulkheads.  But with POB there are no actual frames.  There are no parts that should be called "frames".
 
That the grain for a mold has to support a curve covering as much as 210 degrees is the reason that plywood was first used to make them.  From an esthetic point of view, plywood is a wood product, but not actually wood.  Now another semi synthetic  material: MDF is used by some mfg.  
 
For actual POF, the frame should be made up of timbers.  The timbers should have grain that matched the line of the shape where it lives.    The original builders used compass timbers where there were curves.  This is not really practical for a scale model.  It can be done, but it a lot of work, a lot of luck, and a lot of waste.   An end grain to end grain bond has almost no strength.  A single frame is a breakup waiting to happen.  A pair of frames with timbers that half lap the butt joint of the partner and glue bonded together is very strong.  This is what a 'bend' is.
 

I am not really sure just what you mean by sliding lid, but I am imagining a sheet of wood fixed between two rabbets.  It slides in the rabbets.  At best, only 50% of the plane can be open.
A roll top could maybe get you a 90% opening.  Instead of a single sheet, the movable part would be slats with rounded edges and bonded to a tough fabric.  The rabbet would need to have a navigable curve and continue down the back.   In any case, the rabbet is a dado cut on a table saw or a straight bit router cut..

For POF,  Pine is a low cost wood to use for frames that will be hidden.  It works as well as is needed.
I dislike Basswood and its tendency to be fuzzy and for the fibers to roll make it a poor choice for frames from my perspective.
 
For POB, either Pine or Basswood will do.  For reasons that seem good but really are not,  Balsa is favored by many.  It is certainly soft and seems like it would be easy to remove what is not wanted.  But Balsa is ugly to work.  It does not plane, rasp, file, or sand nicely.  It is fibrous and wants to tear.  A sharp edge will want to dig in and stop a cut.
 
Most POB modelers who do fill all of the gaps between molds use a horizontal orientation for the filling wood.   A disk sander makes it easy to get a tight fit between molds.  The down side is that the shaping is done in situ.  Major wood removal is done on the whole hull. 
I recommend  the filling be done with the wood mimicking actual frames in orientation.  The inside can be left fat enough for Bamboo skewers to be used to join and orient a stack of layers.
The mold shapes can be used as the pattern and a disk sander can be used for shaping the individual slices.  Then joined using the Bamboo and final shaped .  Then slud into the gap between their molds.  A throw away end piece can be used to make up the difference in thickness for the mold with the pattern on the other side.  The holes for the Bamboo dowels make orientation easy, so the identical pattern can be on both ends.  If the sum of the layer thicknesses come up a bit short, poster board can be used to shim the difference.

The Birch is the outside layer.  It is for looks.   It should work as long as it does not get wet.
There is a Birch ply for boat building. The liner ply are not junk and the bonding adhesive is waterproof.   An extreme that you do not need and unlikely to be anywhere as thin as you want.
 
The Mahogany that you can get is not really Mahogany.  Real Mahogany was timbered to near extinction fairly early in the 20th century, so it is a protected species.  I would look real hard for something else.
Most everything called Mahogany has open pores.  This means that it is scale inappropriate if it is on view.
 
Going to a builders supply and getting clear Pine would be a low cost option.  If their thinnest project boards are too thick,  make friends with a serious woodworker and see if he would turn Pine 2x4's or 2x6's into sheets that are your target thickness.