lehmann

In North America we have nitrocellulose lacquer, which is solvent based.  Lacquers are fast drying, so the solvents are very strong (very volatile), so you will want to avoid it since you have asthma. 
Varnishes are technically resin and oil based, so there is no nitrocellulose in the mixture.  
Shellac flakes are dissolved in ethyl  alcohol and heated to make it liquid.  As Kurt mentioned, it can be purchased pre-mixed.  Shellac is the basis for French polishing, so you may be able to find it following that path.  It is also the traditional method for finishing musical instruments.
 
As a simple alternative, try diluting white glue with water.  Brush it on, let the mixture soak in for a few minutes and then wipe the excess off.  The water will raise the grain, so sand after it dries.

In North America we have nitrocellulose lacquer, which is solvent based.  Lacquers are fast drying, so the solvents are very strong (very volatile), so you will want to avoid it since you have asthma. 
Varnishes are technically resin and oil based, so there is no nitrocellulose in the mixture.  
Shellac flakes are dissolved in ethyl  alcohol and heated to make it liquid.  As Kurt mentioned, it can be purchased pre-mixed.  Shellac is the basis for French polishing, so you may be able to find it following that path.  It is also the traditional method for finishing musical instruments.
 
As a simple alternative, try diluting white glue with water.  Brush it on, let the mixture soak in for a few minutes and then wipe the excess off.  The water will raise the grain, so sand after it dries.

Are your difficulties related to laying out  or marking the ports, or from cutting them out?  (or both?).  
 
I have found over the years that accurate marking is the key to good results and the best way to mark is with a knife, not a pencil.   With a line scribed by a knife, you can carve, file, sand right to the line, and you'll end up with straight edges and sharp corners.  The smaller the scale, the more critical this becomes.  

Are your difficulties related to laying out  or marking the ports, or from cutting them out?  (or both?).  
 
I have found over the years that accurate marking is the key to good results and the best way to mark is with a knife, not a pencil.   With a line scribed by a knife, you can carve, file, sand right to the line, and you'll end up with straight edges and sharp corners.  The smaller the scale, the more critical this becomes.  

Are your difficulties related to laying out  or marking the ports, or from cutting them out?  (or both?).  
 
I have found over the years that accurate marking is the key to good results and the best way to mark is with a knife, not a pencil.   With a line scribed by a knife, you can carve, file, sand right to the line, and you'll end up with straight edges and sharp corners.  The smaller the scale, the more critical this becomes.  

Are your difficulties related to laying out  or marking the ports, or from cutting them out?  (or both?).  
 
I have found over the years that accurate marking is the key to good results and the best way to mark is with a knife, not a pencil.   With a line scribed by a knife, you can carve, file, sand right to the line, and you'll end up with straight edges and sharp corners.  The smaller the scale, the more critical this becomes.  

The Taig lathe is easy and fast to change from metal to wood and vise versa.    First, just slide off  the tail-stock.  The carriage for metal working and the tool rest mounts for woodworking just slide on/off on the dove-tail base.  
 
There is a wide range of speeds that can be quickly changed on the stepped pulley from the motor.    The Taig web site lists 520-5200 rpm.
 
The gibs on the metal working carriage can be set up quite tight without any sticking for the whole range of travel, so the setup is very rigid.  As for the rigidity of the base, I used my circular saw setup to cut some nylon sheet a few weeks ago - a tough cut - but, even when the belt was slipping there was no vibration or chatter. 
 
Length of the bed is 15 inches, but the distance between centers is 9.75 inches.  
 
As for the reference to alchemy, the lathe cannot covert  wood into metal, but it does transform base square stock to perfect rounds.

The Taig lathe is easy and fast to change from metal to wood and vise versa.    First, just slide off  the tail-stock.  The carriage for metal working and the tool rest mounts for woodworking just slide on/off on the dove-tail base.  
 
There is a wide range of speeds that can be quickly changed on the stepped pulley from the motor.    The Taig web site lists 520-5200 rpm.
 
The gibs on the metal working carriage can be set up quite tight without any sticking for the whole range of travel, so the setup is very rigid.  As for the rigidity of the base, I used my circular saw setup to cut some nylon sheet a few weeks ago - a tough cut - but, even when the belt was slipping there was no vibration or chatter. 
 
Length of the bed is 15 inches, but the distance between centers is 9.75 inches.  
 
As for the reference to alchemy, the lathe cannot covert  wood into metal, but it does transform base square stock to perfect rounds.

The Taig lathe is easy and fast to change from metal to wood and vise versa.    First, just slide off  the tail-stock.  The carriage for metal working and the tool rest mounts for woodworking just slide on/off on the dove-tail base.  
 
There is a wide range of speeds that can be quickly changed on the stepped pulley from the motor.    The Taig web site lists 520-5200 rpm.
 
The gibs on the metal working carriage can be set up quite tight without any sticking for the whole range of travel, so the setup is very rigid.  As for the rigidity of the base, I used my circular saw setup to cut some nylon sheet a few weeks ago - a tough cut - but, even when the belt was slipping there was no vibration or chatter. 
 
Length of the bed is 15 inches, but the distance between centers is 9.75 inches.  
 
As for the reference to alchemy, the lathe cannot covert  wood into metal, but it does transform base square stock to perfect rounds.

The Taig lathe is easy and fast to change from metal to wood and vise versa.    First, just slide off  the tail-stock.  The carriage for metal working and the tool rest mounts for woodworking just slide on/off on the dove-tail base.  
 
There is a wide range of speeds that can be quickly changed on the stepped pulley from the motor.    The Taig web site lists 520-5200 rpm.
 
The gibs on the metal working carriage can be set up quite tight without any sticking for the whole range of travel, so the setup is very rigid.  As for the rigidity of the base, I used my circular saw setup to cut some nylon sheet a few weeks ago - a tough cut - but, even when the belt was slipping there was no vibration or chatter. 
 
Length of the bed is 15 inches, but the distance between centers is 9.75 inches.  
 
As for the reference to alchemy, the lathe cannot covert  wood into metal, but it does transform base square stock to perfect rounds.

I have the Taig lathe, with both metal and wood working accessories.  With the vertical slide, it can do the work of a small milling machine.  Very rigid, and vibration free.    To make it a bit more easy to use, I've added a digital scale to the carriage travel.  I've also built an saw arbor and table so it doubles as my circular saw http://modelshipworld.com/index.php/topic/11441-turning-a-lathe-into-a-table-saw/.  
 
I also have a large Delta woodworking lathe.  While in theory it could be used for modelling work, you'll need to get a chuck for holding small pieces as it's not possible to work with a spur drive, even a tiny version, for small diameter work-pieces.

I have the Taig lathe, with both metal and wood working accessories.  With the vertical slide, it can do the work of a small milling machine.  Very rigid, and vibration free.    To make it a bit more easy to use, I've added a digital scale to the carriage travel.  I've also built an saw arbor and table so it doubles as my circular saw http://modelshipworld.com/index.php/topic/11441-turning-a-lathe-into-a-table-saw/.  
 
I also have a large Delta woodworking lathe.  While in theory it could be used for modelling work, you'll need to get a chuck for holding small pieces as it's not possible to work with a spur drive, even a tiny version, for small diameter work-pieces.

It appears, based on the position of the one gun port and hawser hole relative to the other gun ports that there is a change in the elevation of the decks at the point.   This is seen in the picture and the two drawings.  Is the forecastle a "split level" relative to the decks in the waist?   There could be some construction detail that ties this staggered wale to the deck shelf.
 
Another question:  is this really a wale, or just a plank (wale or not) painted black for aesthetic reasons?  To my understanding, the wales are a set of planks, not a single line.  
 
Lastly, I not certain that wales are always continuous.  I've studied a few plans that seem to show cuts for gun ports.  

It appears, based on the position of the one gun port and hawser hole relative to the other gun ports that there is a change in the elevation of the decks at the point.   This is seen in the picture and the two drawings.  Is the forecastle a "split level" relative to the decks in the waist?   There could be some construction detail that ties this staggered wale to the deck shelf.
 
Another question:  is this really a wale, or just a plank (wale or not) painted black for aesthetic reasons?  To my understanding, the wales are a set of planks, not a single line.  
 
Lastly, I not certain that wales are always continuous.  I've studied a few plans that seem to show cuts for gun ports.  

One observation that has been missed is that the width of the strips is equal to the vertical distance between the ratlines.  Or, more precisely stated, the distance between the knots.  As long as you can set the strips level, there is no need to use a paper grid.

From the CD of data and drawings of the USS Constitution (available from http://store.ussconstitutionmuseum.org/collections/books-models-modeling).
 
Plate size:                         14 inch x 48 inch
Number of plates:              3400, in 28 rows
Number of nails per plate: 120 to 150
Weight each plate:             6 lbs   
Thickness, based on density of 0.324 lb/in3 = 0.0276 inches
 
At a scale of 1:48, the model plate thickness "should" be 0.00057 inch.  
 
The thinnest copper sheet I've been able to find is 0.002 inch.  
 
I'm working at 1:96 scale, so my main conclusion is that overlapping the plates will create too large of a step ( , so I intend to cut the plates narrower and shorter by the amount of overlap and just place them side-by-side.  This is probably why the strip method works so well.   I was also thinking of cutting a shallow rebate in the planking so the step at the top of the coppering is not so noticeable, but then I realized that the thickness of the top-sides paint is probably thick enough to hide the step.

I bought one on eBay.  Good ones are not cheap, which is amazing considering the general demise of manual drafting and the availability of cheap digital calipers.  However, after examining their construction, I can see why they're not cheap - if there are errors in certain lengths and positions then the scale settings will be off enough to be very exasperating.   They are a very different animal from regular dividers.  
 
There are some plastic versions available - I have one of these as well, but I think they are more for artists to scale a picture rather than for drafting.  The major limitation of mine is that the ratio is adjusted by moving the pivot to holes of fixed locations so that ratios of only 1:1, 1:2, 1:3 are possible.
 
I use them fairly often, and not just for model building.   As others have said, if you're working a kit boat, you won't need proportional dividers.   But if you're mashing drawings from different scales, they're a real time saver.  
 
As a poor-man's option if you only have standard dividers, I've attached an example of a grid I use for a converting between 1:72 and 1:96. I used a CAD program, but you can make a satisfactorily accurate version by hand.
 
72_96Scale.pdf
Set the dividers on the dimension on the 1:72 drawing Place the dividers on horizontal base line Pivot from the right point of the dividers  Set the dividers to span up to the diagonal line The dividers are now at the distance needed for the 1:96 drawing

I bought one on eBay.  Good ones are not cheap, which is amazing considering the general demise of manual drafting and the availability of cheap digital calipers.  However, after examining their construction, I can see why they're not cheap - if there are errors in certain lengths and positions then the scale settings will be off enough to be very exasperating.   They are a very different animal from regular dividers.  
 
There are some plastic versions available - I have one of these as well, but I think they are more for artists to scale a picture rather than for drafting.  The major limitation of mine is that the ratio is adjusted by moving the pivot to holes of fixed locations so that ratios of only 1:1, 1:2, 1:3 are possible.
 
I use them fairly often, and not just for model building.   As others have said, if you're working a kit boat, you won't need proportional dividers.   But if you're mashing drawings from different scales, they're a real time saver.  
 
As a poor-man's option if you only have standard dividers, I've attached an example of a grid I use for a converting between 1:72 and 1:96. I used a CAD program, but you can make a satisfactorily accurate version by hand.
 
72_96Scale.pdf
Set the dividers on the dimension on the 1:72 drawing Place the dividers on horizontal base line Pivot from the right point of the dividers  Set the dividers to span up to the diagonal line The dividers are now at the distance needed for the 1:96 drawing

I bought one on eBay.  Good ones are not cheap, which is amazing considering the general demise of manual drafting and the availability of cheap digital calipers.  However, after examining their construction, I can see why they're not cheap - if there are errors in certain lengths and positions then the scale settings will be off enough to be very exasperating.   They are a very different animal from regular dividers.  
 
There are some plastic versions available - I have one of these as well, but I think they are more for artists to scale a picture rather than for drafting.  The major limitation of mine is that the ratio is adjusted by moving the pivot to holes of fixed locations so that ratios of only 1:1, 1:2, 1:3 are possible.
 
I use them fairly often, and not just for model building.   As others have said, if you're working a kit boat, you won't need proportional dividers.   But if you're mashing drawings from different scales, they're a real time saver.  
 
As a poor-man's option if you only have standard dividers, I've attached an example of a grid I use for a converting between 1:72 and 1:96. I used a CAD program, but you can make a satisfactorily accurate version by hand.
 
72_96Scale.pdf
Set the dividers on the dimension on the 1:72 drawing Place the dividers on horizontal base line Pivot from the right point of the dividers  Set the dividers to span up to the diagonal line The dividers are now at the distance needed for the 1:96 drawing

From the CD of data and drawings of the USS Constitution (available from http://store.ussconstitutionmuseum.org/collections/books-models-modeling).
 
Plate size:                         14 inch x 48 inch
Number of plates:              3400, in 28 rows
Number of nails per plate: 120 to 150
Weight each plate:             6 lbs   
Thickness, based on density of 0.324 lb/in3 = 0.0276 inches
 
At a scale of 1:48, the model plate thickness "should" be 0.00057 inch.  
 
The thinnest copper sheet I've been able to find is 0.002 inch.  
 
I'm working at 1:96 scale, so my main conclusion is that overlapping the plates will create too large of a step ( , so I intend to cut the plates narrower and shorter by the amount of overlap and just place them side-by-side.  This is probably why the strip method works so well.   I was also thinking of cutting a shallow rebate in the planking so the step at the top of the coppering is not so noticeable, but then I realized that the thickness of the top-sides paint is probably thick enough to hide the step.

Roger,
They are available from Lee Valley.... http://www.leevalley.com/en/wood/page.aspx?p=32681&cat=1,50230.  Now,  $36 CDN, though.  I have the set and they're very nice.  I bought these instead of LV's miniature spoke shave.

From the CD of data and drawings of the USS Constitution (available from http://store.ussconstitutionmuseum.org/collections/books-models-modeling).
 
Plate size:                         14 inch x 48 inch
Number of plates:              3400, in 28 rows
Number of nails per plate: 120 to 150
Weight each plate:             6 lbs   
Thickness, based on density of 0.324 lb/in3 = 0.0276 inches
 
At a scale of 1:48, the model plate thickness "should" be 0.00057 inch.  
 
The thinnest copper sheet I've been able to find is 0.002 inch.  
 
I'm working at 1:96 scale, so my main conclusion is that overlapping the plates will create too large of a step ( , so I intend to cut the plates narrower and shorter by the amount of overlap and just place them side-by-side.  This is probably why the strip method works so well.   I was also thinking of cutting a shallow rebate in the planking so the step at the top of the coppering is not so noticeable, but then I realized that the thickness of the top-sides paint is probably thick enough to hide the step.

From the CD of data and drawings of the USS Constitution (available from http://store.ussconstitutionmuseum.org/collections/books-models-modeling).
 
Plate size:                         14 inch x 48 inch
Number of plates:              3400, in 28 rows
Number of nails per plate: 120 to 150
Weight each plate:             6 lbs   
Thickness, based on density of 0.324 lb/in3 = 0.0276 inches
 
At a scale of 1:48, the model plate thickness "should" be 0.00057 inch.  
 
The thinnest copper sheet I've been able to find is 0.002 inch.  
 
I'm working at 1:96 scale, so my main conclusion is that overlapping the plates will create too large of a step ( , so I intend to cut the plates narrower and shorter by the amount of overlap and just place them side-by-side.  This is probably why the strip method works so well.   I was also thinking of cutting a shallow rebate in the planking so the step at the top of the coppering is not so noticeable, but then I realized that the thickness of the top-sides paint is probably thick enough to hide the step.

Roger,
They are available from Lee Valley.... http://www.leevalley.com/en/wood/page.aspx?p=32681&cat=1,50230.  Now,  $36 CDN, though.  I have the set and they're very nice.  I bought these instead of LV's miniature spoke shave.

Wood has a low thermal expansion coefficient - meaning the size does not change much with temperature.   However, the temperature of the air affects the amount of water vapor in the air (relative humidity), which will, over time, change the moisture content of wood.   As a result, you may see changes in the size of the wood if you leave it in the garage at different temperatures.  
 
Cabinet makers have long know to store wood at the same moisture content as it will eventually be used.  In most houses, that's about 6% - 8% moisture content.  Since, it takes time for the moisture content of wood to change, the first thing  to do is keep your wood supply in the house, not the garage.  Second, if you can, keep the model in the house when you're not working on it.  
 
There may be another trick - over-dry the planks before putting them on the hull.   As the planks come back to equilibrium moisture content, they will swell slightly, closing up the seams, just as planks on a real ship swell when the hull is put in the water.  There was a comment earlier that this may cause the planking to buckle, but I doubt it.  
 
FYI, a version of this trick is used by chair-makers to securely hold the bent backs into the seat.  The ends of the back are shaped slightly over-sized to the holes in the seat.  The backs are then dried in a small oven, just heated by light bulbs, to perhaps 2% moisture content.  With the slight shrinkage that occurs the ends now fit (snugly) into the holes, but when the moisture content comes back to 6%, the end is solidly locked in place.  
 
So, if you're too impatient to wait for the planks to dry, make a small oven above a light bulb (or perhaps a heat lamp or a halogen).  The drying time would be pretty fast for pieces as thin as planking and you may get the added benefit of over-dried planks.