Jaager

Do you need the flags to be showing the effects of wind?  If it is the rectangular flat version, then the dynamic effects that vector provides are not needed.
A raster based graphics program should do. Straight lines will work.  I work at 1:48 for plans and the short segments that make a hull cross section be facets instead of a smooth curve, still work for me.
GIMP is free, PhotoShop is subscription,  PaintShop Pro is low cost,  and Painter is too expensive unless you want to use a computer to actually paint a picture.

Yellow PVA (e.g. Titebond II) has gap filling properties.  PVA fixed with wood flour from the same wood has even more. 
With the task of filling the outer perimeter gap between POB moulds - for to give support for planking and allow for needing only one layer:
Avoid Balsa at all costs. 
Basswood comes (or used to come) in packs of sheets 1/32 - 1/4" on line or from mega craft stores.  Easy to work but kinda dear on wallet damage.
Construction Pine from ~Home Depot or Lowes (Slows as my framing contractor in the Blue Grass called them)  2x4,  1x4, even thinner -easy to cut, soft put sturdy - avoid sap/resin stock.
 anyway, no one will see it,  so as long as it stays bonded in place, close enough is good enough.
If you paint, fillers take care of gaps.
If it is wood with clear finish,  as tight a tolerance as your skill allows.  If a piece does not measure up, toss it into a scrap box and start again.  You will know and you will always know if you just settle.  almost no one else will notice or know that it is less than perfect,  but you will.
editorial:
decks - make the caulking seams under scale and if the vessels is before 1860 - color it Walnut, not black  Drake's well was 1859.

Note that the old guys used circumference, not diameter there is a factor of 3 difference.
pre iron and steel  - bark brown (Walnut) instead of black is less garish.
 
diameter is easier for us -  It is easily measured by counting the number of rotations of the line - tightly packed - in a inch distance along a dowel. the diameter of the dowel does not matter
1/rotations x pi = circumference

Yellow PVA (e.g. Titebond II) has gap filling properties.  PVA fixed with wood flour from the same wood has even more. 
With the task of filling the outer perimeter gap between POB moulds - for to give support for planking and allow for needing only one layer:
Avoid Balsa at all costs. 
Basswood comes (or used to come) in packs of sheets 1/32 - 1/4" on line or from mega craft stores.  Easy to work but kinda dear on wallet damage.
Construction Pine from ~Home Depot or Lowes (Slows as my framing contractor in the Blue Grass called them)  2x4,  1x4, even thinner -easy to cut, soft put sturdy - avoid sap/resin stock.
 anyway, no one will see it,  so as long as it stays bonded in place, close enough is good enough.
If you paint, fillers take care of gaps.
If it is wood with clear finish,  as tight a tolerance as your skill allows.  If a piece does not measure up, toss it into a scrap box and start again.  You will know and you will always know if you just settle.  almost no one else will notice or know that it is less than perfect,  but you will.
editorial:
decks - make the caulking seams under scale and if the vessels is before 1860 - color it Walnut, not black  Drake's well was 1859.

Yellow PVA (e.g. Titebond II) has gap filling properties.  PVA fixed with wood flour from the same wood has even more. 
With the task of filling the outer perimeter gap between POB moulds - for to give support for planking and allow for needing only one layer:
Avoid Balsa at all costs. 
Basswood comes (or used to come) in packs of sheets 1/32 - 1/4" on line or from mega craft stores.  Easy to work but kinda dear on wallet damage.
Construction Pine from ~Home Depot or Lowes (Slows as my framing contractor in the Blue Grass called them)  2x4,  1x4, even thinner -easy to cut, soft put sturdy - avoid sap/resin stock.
 anyway, no one will see it,  so as long as it stays bonded in place, close enough is good enough.
If you paint, fillers take care of gaps.
If it is wood with clear finish,  as tight a tolerance as your skill allows.  If a piece does not measure up, toss it into a scrap box and start again.  You will know and you will always know if you just settle.  almost no one else will notice or know that it is less than perfect,  but you will.
editorial:
decks - make the caulking seams under scale and if the vessels is before 1860 - color it Walnut, not black  Drake's well was 1859.

https://www.stewmac.com/Luthier_Tools
StewMac is on the high side as far as price, but they have quality tools - if a bit specialized and limited their being focused on luthiers.   I have no association other than being a customer.
They also use email advertising - a lot.
 

https://www.stewmac.com/Luthier_Tools
StewMac is on the high side as far as price, but they have quality tools - if a bit specialized and limited their being focused on luthiers.   I have no association other than being a customer.
They also use email advertising - a lot.
 

Edge bending is trying to take wood into a shape that is against its nature.  Some species take to this better than others.  A lot of the species supplied in kits - look to be brittle - as well as having out of scale pores.  One of the better species for serious bending is Holly and stock that has been infected with Blue Mold will work just as well .   I suspect that infected Holly is not available commercially.  Accepting it makes self harvesting an easier proposition than insisting on snow white stock which requires cold season harvest and immediate placement into a kiln.  Commercial white Holly is becoming very expensive and the color matches nothing that was used on an actual ship.   I have seen Basswood or Lime taking a serious bend.  The grain, color and pore structure are spot on.  Those species are too soft, fuzzy, and friable for me, though.
 
Looking at the build in your link,  the wale does not seem to edge bend all that much.  The run of the planking appears to follow that of the wale, and not the rail.  The stern is planked with short runs of planking with little edge bending.  A ship that got into wave action requiring serious strength at that upper stern location would be in more trouble than strength there would help.

Edge bending is trying to take wood into a shape that is against its nature.  Some species take to this better than others.  A lot of the species supplied in kits - look to be brittle - as well as having out of scale pores.  One of the better species for serious bending is Holly and stock that has been infected with Blue Mold will work just as well .   I suspect that infected Holly is not available commercially.  Accepting it makes self harvesting an easier proposition than insisting on snow white stock which requires cold season harvest and immediate placement into a kiln.  Commercial white Holly is becoming very expensive and the color matches nothing that was used on an actual ship.   I have seen Basswood or Lime taking a serious bend.  The grain, color and pore structure are spot on.  Those species are too soft, fuzzy, and friable for me, though.
 
Looking at the build in your link,  the wale does not seem to edge bend all that much.  The run of the planking appears to follow that of the wale, and not the rail.  The stern is planked with short runs of planking with little edge bending.  A ship that got into wave action requiring serious strength at that upper stern location would be in more trouble than strength there would help.

https://www.stewmac.com/Luthier_Tools
StewMac is on the high side as far as price, but they have quality tools - if a bit specialized and limited their being focused on luthiers.   I have no association other than being a customer.
They also use email advertising - a lot.
 

POB filling between moulds?  The material will be hidden.  It does not need to be pretty.  If there is a gap, use paper or cardboard to make up the short fall.  Liberal use of PVA will stiffen the paper. 
A right angle square, a piece of 1/2" plywood, and a sanding block will stand for a poor man's disk sander.
 

This particular tool has been said to be a Chinese copy of a domestic tool, that may have done in the original company.  It may look neat'o, cool'o  but a home made version will cost less and do what you want.   Tooth on the gluing surface is good, so 100/120/150 grit will cut fast and leave a surface for PVA to bond with.

I build POF and am a bit biased on terminology.
As a side note,  what you ( and most everybody) call bulkheads are actually molds.  Subs have bulkheads,  some steel ships have bulkheads, Chinese wooden ships have bulkheads.  Western wooden ships did not have bulkheads.  They certainly are not frames.   What you (and everyone else) call the keel is actually a central support spine.
I have never built POB, so this is theory.  How I would try to rectify this:
1.  This curve is the natural shape that your piece of plywood seeks.  Anything that you do only to it  (bend it back with steam or heat) is likely to be a temporary fix. It will still "want" to bend.  You can clamp it to a baseboard and use the planking applied while clamped to hold the shape.  But when removed an twist force will be on the glue joints of the molds and inside planking - forever.  It may or may not hold. 
2.  If the molds have not been glued,  there is a stronger fix.  Scab a long streamer on each side of the central spine.
Remove the black area on each mold.  Get a couple of long sticks of straight hardwood ( 1/4" x 1/4"  or 1/4" x 1/2" or substantial size ).   Drill holes thru the sticks and central spine all along the length.  Use threaded bolts, washers and nuts to fix the sticks and central spine together.  Make sure this assembly is dead straight.  Remove the assembly.  Glue the molds to the central spine.  Slide the sticks thru the holes along the length and glue the sticks to the spine.  Check to make sure it is still dead straight.  The bolts can be removed and bamboo skewers glued thru the holes.  You just need a drill bit that is the diameter of the skewers.
 
3.  The holes in the molds remove some of the bonding surface between them and the spine.  Short pieces of SQUARE wood can be used to reinforce the bond.  Eight pieces per molds.  Just do not block the path of the straightener sticks.
 
4.  Rather than Balsa, consider using Pine to fill the outer planking edge between the molds.   Assuming that you do not have power tools,  a hand fret saw. planes, knives and sanding block will do.  Select Pine in 1" thickness is easily found. There may also be thinner stock of solid Pine.   Cut out the shapes, glue up the layers to fit between the molds, and do as much shaping as you can before fixing them between the molds.  You are unlikely to be lucky enough that a sum one 1" layers will be a tight fit between the molds.  The outer surface does not need to be continuous.  Cardboard or what ever is to hand can be fitted between a layer to make up the difference.  It does not need to reach the outer shaped surface.  You just want the unit to be a push fit between the molds.

one more thing - avoid 3-wheel bandsaws - most can be very cranky.

My Rikon 14" uses a 142" circumference blade.  The spec literature allows 1/4" to 1"  for blade width.  I did not look too hard, but I did not find any 1/8" x 142" blades for sale.
It is strong enough to tension a 1" blade, but I gave up on expecting a wider blade to improve resaw tracking and use 1/2" blades.  I think the frame is steel.  It is heavy enough that I hired it assembled, delivered, and adjusted.
 
I never gave much thought to what 9" / 10" / 14" /18" really referred to.  The 9"/10" are smaller bench top.  The 14" is a large free standing.  The 18" is really large free standing.   It appears that 9" - 18" is the theoretical maximum height of cut - the upper housing to table distance.  I think that the upper blade guide reduces the actual distance possible.   I don't think that I would care to try to get 12" diameter log thru - too heavy, too unwieldy, way out of scale.  I do not build full size furniture or guitars so wide, thin boards are not something that I need.  2" wide is generally enough and 4" is my upper limit.  It is the power and precision in cutting and tracking that requires a 14" saw.  If you want frustration, try using a bandsaw that will not track for resawing.

My Rikon 14" uses a 142" circumference blade.  The spec literature allows 1/4" to 1"  for blade width.  I did not look too hard, but I did not find any 1/8" x 142" blades for sale.
It is strong enough to tension a 1" blade, but I gave up on expecting a wider blade to improve resaw tracking and use 1/2" blades.  I think the frame is steel.  It is heavy enough that I hired it assembled, delivered, and adjusted.
 
I never gave much thought to what 9" / 10" / 14" /18" really referred to.  The 9"/10" are smaller bench top.  The 14" is a large free standing.  The 18" is really large free standing.   It appears that 9" - 18" is the theoretical maximum height of cut - the upper housing to table distance.  I think that the upper blade guide reduces the actual distance possible.   I don't think that I would care to try to get 12" diameter log thru - too heavy, too unwieldy, way out of scale.  I do not build full size furniture or guitars so wide, thin boards are not something that I need.  2" wide is generally enough and 4" is my upper limit.  It is the power and precision in cutting and tracking that requires a 14" saw.  If you want frustration, try using a bandsaw that will not track for resawing.

My Rikon 14" uses a 142" circumference blade.  The spec literature allows 1/4" to 1"  for blade width.  I did not look too hard, but I did not find any 1/8" x 142" blades for sale.
It is strong enough to tension a 1" blade, but I gave up on expecting a wider blade to improve resaw tracking and use 1/2" blades.  I think the frame is steel.  It is heavy enough that I hired it assembled, delivered, and adjusted.
 
I never gave much thought to what 9" / 10" / 14" /18" really referred to.  The 9"/10" are smaller bench top.  The 14" is a large free standing.  The 18" is really large free standing.   It appears that 9" - 18" is the theoretical maximum height of cut - the upper housing to table distance.  I think that the upper blade guide reduces the actual distance possible.   I don't think that I would care to try to get 12" diameter log thru - too heavy, too unwieldy, way out of scale.  I do not build full size furniture or guitars so wide, thin boards are not something that I need.  2" wide is generally enough and 4" is my upper limit.  It is the power and precision in cutting and tracking that requires a 14" saw.  If you want frustration, try using a bandsaw that will not track for resawing.

I have both a 9" bench top and a 14" bandsaw.   The 9" is a model that MM sold for a short period of time. I am not sure if it was manufactured in China or Taiwan.   I use it exclusively for scroll cutting.  I use 1/8" blades and it is fortuitous that it uses a readily available size blade:  59.5" .   It also will mount a Carter Stabilizer, which greatly enhances scroll cutting control.   I would choose a more powerful motor, given the option.  I only scroll cut sorta, maybe close to the line.  I use a drum or disk sander to get to the finished shape.
 
The 14" has more bells and whistles.  High quality guides and a lever to release the tension.  It also has a 3 hp motor.  It is used for resawing, both planks and logs.  I would not even attempt to mount a 1/8" blade on it.  But that is below what is even listed as a choice and not available anyway. 
 
Factors that I consider important decision:  the more powerful motor,  a blade size that is easy to source,  a quality machine if 14"
 
A bandsaw is going to use up steel blades,  For resawing dense hardwood steel blades do not last all that long.  If you do a lot of cutting, the amount spent on blades will approach what you paid for the machine.  I find carbide blades to be more cost effective,  but bimetal blades are even more cost effective.  Buying an economy machine will probably leave  you with a machine that uses up blades more quickly and any supposed savings will be more than reversed in additional outlay on blades.
 
For the 9"  only steel is available and cutting frame timbers can use a couple per ship.  Bosch makes Vermont American and I ran into a batch that was so dull that I may as well have tried cutting using the back edge.  I now only trust Olson, they just cost more.
 
A bandsaw is by far the more efficient and safer way to resaw.  
I scroll cut 0.15" - 0.25" stock  for the most part and a bandsaw with a sharp blade will do the job fairly quickly and the work does not chatter.

I have both a 9" bench top and a 14" bandsaw.   The 9" is a model that MM sold for a short period of time. I am not sure if it was manufactured in China or Taiwan.   I use it exclusively for scroll cutting.  I use 1/8" blades and it is fortuitous that it uses a readily available size blade:  59.5" .   It also will mount a Carter Stabilizer, which greatly enhances scroll cutting control.   I would choose a more powerful motor, given the option.  I only scroll cut sorta, maybe close to the line.  I use a drum or disk sander to get to the finished shape.
 
The 14" has more bells and whistles.  High quality guides and a lever to release the tension.  It also has a 3 hp motor.  It is used for resawing, both planks and logs.  I would not even attempt to mount a 1/8" blade on it.  But that is below what is even listed as a choice and not available anyway. 
 
Factors that I consider important decision:  the more powerful motor,  a blade size that is easy to source,  a quality machine if 14"
 
A bandsaw is going to use up steel blades,  For resawing dense hardwood steel blades do not last all that long.  If you do a lot of cutting, the amount spent on blades will approach what you paid for the machine.  I find carbide blades to be more cost effective,  but bimetal blades are even more cost effective.  Buying an economy machine will probably leave  you with a machine that uses up blades more quickly and any supposed savings will be more than reversed in additional outlay on blades.
 
For the 9"  only steel is available and cutting frame timbers can use a couple per ship.  Bosch makes Vermont American and I ran into a batch that was so dull that I may as well have tried cutting using the back edge.  I now only trust Olson, they just cost more.
 
A bandsaw is by far the more efficient and safer way to resaw.  
I scroll cut 0.15" - 0.25" stock  for the most part and a bandsaw with a sharp blade will do the job fairly quickly and the work does not chatter.

I have both a 9" bench top and a 14" bandsaw.   The 9" is a model that MM sold for a short period of time. I am not sure if it was manufactured in China or Taiwan.   I use it exclusively for scroll cutting.  I use 1/8" blades and it is fortuitous that it uses a readily available size blade:  59.5" .   It also will mount a Carter Stabilizer, which greatly enhances scroll cutting control.   I would choose a more powerful motor, given the option.  I only scroll cut sorta, maybe close to the line.  I use a drum or disk sander to get to the finished shape.
 
The 14" has more bells and whistles.  High quality guides and a lever to release the tension.  It also has a 3 hp motor.  It is used for resawing, both planks and logs.  I would not even attempt to mount a 1/8" blade on it.  But that is below what is even listed as a choice and not available anyway. 
 
Factors that I consider important decision:  the more powerful motor,  a blade size that is easy to source,  a quality machine if 14"
 
A bandsaw is going to use up steel blades,  For resawing dense hardwood steel blades do not last all that long.  If you do a lot of cutting, the amount spent on blades will approach what you paid for the machine.  I find carbide blades to be more cost effective,  but bimetal blades are even more cost effective.  Buying an economy machine will probably leave  you with a machine that uses up blades more quickly and any supposed savings will be more than reversed in additional outlay on blades.
 
For the 9"  only steel is available and cutting frame timbers can use a couple per ship.  Bosch makes Vermont American and I ran into a batch that was so dull that I may as well have tried cutting using the back edge.  I now only trust Olson, they just cost more.
 
A bandsaw is by far the more efficient and safer way to resaw.  
I scroll cut 0.15" - 0.25" stock  for the most part and a bandsaw with a sharp blade will do the job fairly quickly and the work does not chatter.

If your emphasis is on accuracy, a band saw isn't going to be a machine where you'll readily find it. On a band saw, "accuracy" is dependent more upon the operator's skill than anything else. If "tight curves" are anticipated, certainly at modeling scales, a good quality scroll saw is the tool for the job. The "tightness of curves" or "minimum radius of cut" of a given band saw blade can cut is dependent on the width of the blade. As indicated on the chart below, a 1/8" wide band saw blade will only cut minimum radius of 3/16" and, while I've never seen a 1/8" band saw blade, I expect it's a rare bird indeed. I expect it would require a band saw designed to do such fine work. On a standard 14" band saw, I expect a 1/8" blade would be quite prone to breaking. A scroll saw, on the other hand, is capable of cutting radii equal to half the width of the blade itself. 
 
Blade Width (Inches) Minimum Radius (Inches) 1/8 3/16 3/16 5/16 1/4 5/8 3/8 1-1/2 1/2 2-1/2 5/8 4 3/4 5-1/2 1 7  
 
It's a matter of preference, price point, and space available, I suppose, but, in my opinion, small bench top band saws aren't really all that practical. A good scroll saw will serve much better for short radius cutting, although perhaps with slightly less throat depth, which generally isn't an issue with tight curves. A table saw will cut straight lines easier than any band saw, too. For larger work, however, a "standard"  14" or larger band saw is really required and is also capable of accurate re-sawing if properly set up. As to which one to buy, the price points are generally indicative of quality. As with many stationary power tools these days, the retail distributors all sell essentially the same models, all built at the Revolutionary People's Patriotic Machine Tool Collective somewhere in China, but there is a difference in fit and finish, depending upon the distributor's specifications. When it comes to things like band saws, the used market is also worth checking out. It's not unusual to see quality machines in decent condition selling used for a fraction of their original price. Neither is it unusual to find older machines which are of much higher quality than the models now selling new.

POB filling between moulds?  The material will be hidden.  It does not need to be pretty.  If there is a gap, use paper or cardboard to make up the short fall.  Liberal use of PVA will stiffen the paper. 
A right angle square, a piece of 1/2" plywood, and a sanding block will stand for a poor man's disk sander.
 

This particular tool has been said to be a Chinese copy of a domestic tool, that may have done in the original company.  It may look neat'o, cool'o  but a home made version will cost less and do what you want.   Tooth on the gluing surface is good, so 100/120/150 grit will cut fast and leave a surface for PVA to bond with.

Wondercutter is the product name.  It looks to me as though the target material is too limited in density and thickness for it to provide much use for scratch building.

POB filling between moulds?  The material will be hidden.  It does not need to be pretty.  If there is a gap, use paper or cardboard to make up the short fall.  Liberal use of PVA will stiffen the paper. 
A right angle square, a piece of 1/2" plywood, and a sanding block will stand for a poor man's disk sander.
 

This particular tool has been said to be a Chinese copy of a domestic tool, that may have done in the original company.  It may look neat'o, cool'o  but a home made version will cost less and do what you want.   Tooth on the gluing surface is good, so 100/120/150 grit will cut fast and leave a surface for PVA to bond with.

POB filling between moulds?  The material will be hidden.  It does not need to be pretty.  If there is a gap, use paper or cardboard to make up the short fall.  Liberal use of PVA will stiffen the paper. 
A right angle square, a piece of 1/2" plywood, and a sanding block will stand for a poor man's disk sander.
 

This particular tool has been said to be a Chinese copy of a domestic tool, that may have done in the original company.  It may look neat'o, cool'o  but a home made version will cost less and do what you want.   Tooth on the gluing surface is good, so 100/120/150 grit will cut fast and leave a surface for PVA to bond with.

Bottom line, there isn't anything that even comes close to the Byrnes saw and you do get what you pay for. With the "also-rans," you pay a little bit less and get a lot less for your money in quality and accuracy, not to mention resale value, if you ever want to sell it. They do cost money, but if you are cutting your own strip wood, it won't take too long to pay for itself, particularly the way pre-cut stock is starting to cost these days, when you can find it. Just throw your pocket change in a Mason jar and watch it add up. Save a buck here or there as you go along. You'll have enough saved up in short order. Particularly now, when we're all "locked down" and aren't spending any pocket money, anyhow.