Mast Length Ambiguity

[Leopard]

I have a stupid question.  When mast lengths are specified, from where to where do they get measured?

 

From The Baltimore Clipper by Chapelle, he gives:

Mainmast, from heel to hound = extreme breadth x from 2.6 to 2.8

Heads of lower masts = topmasts x from 0.9 to 0.97

 

Now, I have the line of flotation (roughly) and the extreme breadth.  But does the bottom measurement start right at the bottom of the mast, where it goes into it's support, right on the keel (marked A below)? Or does it start at the deck (marked B)?

Does the top measurement stop at the bottom of the head (C), or at the top of the head (D)?

 

I do apologise for how simple this must seem to some of you, but this is my first build and I'm super confused.  I'd appreciate any help or advice.  When I draw it all out in CAD, the different versions of the measurements make a huge difference in what the rig looks like.  Strangely, irrespective of where I choose to measure, I can't quite get the CAD drawing to look quite like the sail plans in the book.  I'm tempted to just scale off of one the drawings that look good (like this one, of Pictou/Herald) and disregard the tables and formulae and ratios.  I'm fairly certain that that way lies some gross errors though.

Edited April 30, 2019 by Leopard

[druxey]

Usually the mast length is specified as overall length. This is from step above the keel to the top of the tenon for its cap. The hounds, however, are at point 'C' on your example.

 

Re-drawn plans (as above) or reconstructed plans can be misleading, though.

Edited April 30, 2019 by druxey

[Leopard]

Hi Druxey,

 

Thanks for the (very quick) reply.  So, just to make sure, the bottom is measured from the very bottom of the mast, where it forms a round tenon which pops into that little block  on top of the keel?

So if the mast length works out to 86' and the mast head to 7'6", that means it's 86' from the very bottom of the mast to the bottom of the head, and then an extra 7'6" to the mast cap, which gives a total "timber" length of 93'6".  Or is it 78'6" from the bottom of the mast to the bottom of the head and then another 7'6" to the mast cap, giving 86' overall?

[druxey]

I'm now a little confused. The 'normal' way mast length is measured is inclusive of the head. The length of head is then marked, down from the top of the mast. However, the table you show states that the measurement is 'heel to hounds', so you need to add the length of the head to that. Not knowing the extreme breadth you are working from, I can't say whether you arriving correctly at 86' 0" or 78' 6"!

[Leopard]

Hahaha, awesome.  Now I've confused someone else as well.

The extreme breadth is 32'.  If I use the middle of the range, 2.7, then I get 86.4'.  And then I rounded down to 86' for some reason.

The main-topmast, hounded is extreme breadth x 0.9 = 31' x 0.9 = 28.8'.  Then the mainmast head is 28.8' x 0.3 = 8.6'

 

These aren't the number I had originally.  And my spreadsheet isn't giving me the correct numbers.  Looks like I got lost somewhere.

I think I'll start a new spreadsheet tonight, re-measure the model, do all the calcs from scratch, and redraw everything in CAD.  Then I'll post what I have tomorrow morning.

[Leopard]

Right, so last night I redid my whole spreadsheet from scratch.  I did this in three ways:

1. I measured line drawings in Chapelle's book and calculated the ratios between the mast lengths and hull length/breadth for those drawings.  I chose drawings that looked good to me.  Then I used those ratios and applied them to my build to get the various mast and spar lengths.  There quite a bit of variation.
2. I used Fincham's tables at the back of the book, which gives ratios to extreme breadth and waterline, and calculated min and max values for each mast and spar.
3. I used Rankine's ratios, which Chapelle says is based on Fincham's tables, to get min and max values for each mast and spar.
4. There's also a bunch of ratios by Marestier, but I didn't have time to get to them, unfortunately.

Then I tabulated all the values, calculated min and max values and drew them in CAD.  There's a massive difference between the two sets.

Below is my table showing all the values that I got off of the line drawings:

 

 

Below is my table showing the values for Rankine and Fincham, with the min and max values for all of them together:

 

And here is the CAD sketch showing the minimum mast layout in orange and the maximum in green:

 

It looks to me like the Rankine and Fincham values are about the same as what I got from the drawings, if I just take the average of everything:

 

Should I just go ahead and use the average of all of these?  Or maybe use the average and then tweak it in CAD (while staying well within the min and max limits) until I get a rig that looks good?  Maybe make the masts slightly too long, to make it the schooner top-hampered, which was traditional.

[wefalck]

I am not sure what you are heading for, a reconstruction of a particular ship ? With the hull dimensions you should be able to constrain the spar dimensions better. A lofty rig normally requires a deep hull or a very broad hull in order to give stability. So for a medium deep hull compared to length and breadth one would not expect the upper end of mast length. For your CAD-example my feeling says that the sail-plan should be somewhere between the two extremes - one is grossly over-canvassed and the other one too small for the ship.

It may be also helpful to look not only at the proportionate dimensions, but to go a bit into the physics and compare the meta-centres of the sail-plan and the hull, the resulting levers and righting moments, and their relative position along the longitudinal section. The textbooks you quoted should give instructions for this. This would help to further constrain the sail-plan, though you will have an equation with perhaps to many unknowns/degrees of freedom still.

[Leopard]

That's a really good idea.  I'll see if I can calculate the center of buoyancy, center of gravity and center of sail pressure.  I have some formulae for that.

 

As to the particular ship, well, this is a banned kit.  I bought it for my nephew but ended up starting it myself (he builds plastic car kits and my wife didn't think he'd be too impressed to get a box containing a few sheets of wood and one sheet of instructions).  As far as I can tell it's a scaled down copy of the AL Harvey.  I've looked at all the AL Harvey build logs on MSW, but I couldn't find any mast lengths or ratios anywhere, and I'm hesitant to scale off of photos.  I'm not too concerned about being historically accurate; even my time period is loose - anywhere from 1800 to 1850 works for me.

 

So yeah, I'm using this build to learn as much as I can and then, after I finish it, I'll start a build that I can post a log of.  Perhaps something like one of Chuck's kits for the barge, pinnace or longboat.  In the meantime though, I'm still planning on doing my best on this one and not rush through it and neglect it.

 

But that's a really good idea.  I think I'll have to take some measurements, loft a 3D hull in CAD and do some math.  I know roughly what the ship is supposed to weigh, I can calculate mast and sail weights and there are formulae for center of pressure in the book.  Or I can just take the average of the above values be done with it.  It certainly sounds like that's what the original builders of the Baltimore Clippers did, just sort of look at other examples and copy some of the distinguishing features from memory.  Which is pretty much how they ended up with such extreme rigs and hull shapes.

[druxey]

The largest results look massively oversparred! I suspect about half-way between the two extremes the truth may lie.

[Leopard]

So... it turns out that measuring a hull is a bit more difficult than I had imagined.  I can draw the thin in CAD, I can do all the math, that's not really a problem, but getting measurements that are accurate enough to mean anything is another matter.  I tried to make a jig that's basically a flat plate with coordinates, mount the hull on a stand and then use a dowel sharpened to a fine tip, mounted on a block of known height and then trace horizontal lines around the hull.  The idea was that I can then get 3d coordinates for a bunch of points on the hull and transfer that to CAD.  Unfortunately, plywood is not as flat as precision-ground cast iron.  And it's difficult to constrain the tip of a dowel mounted on a block of wood, so you never really know where it is.

 

So, anyway, I decided to just take the average of all the values, draw it out and then adjust what doesn't look quite right.  This rig below is the average mast and yard lengths:

 

I cut the picture off at the waterline, since that's how Chapelle did it in all the other pictures on the book.  Here is a collection of ones that I like:

Looking at these, I think my square sail yards can be a bit longer.  I think the main top mast can also be just a smidge longer.  I'd like the bowsprit angle to be higher than shown, but that's pretty much determined by how it fits into the model itself.  I'll have to see what, if anything, I can do there.  Maybe cut off the bottom corner where it mounts to the deck, making it look like it passes through the deck.  The rest of them look good to my eye.  Maybe the gaffs can be a touch shorter.

 

What do you guys think?

[JerseyCity Frankie]

The rig height was a variable because there is a range of risk verses safety involved in adding more canvas to a given hull. Baltimore Clippers were known for their speed due in part to being recklessly overcanvassed. But Baltimore Clippers were intended for speed and those who sailed them accepted the risk as the penalty for greater speed. Conservative ship owners would sacrifice speed for the safety of a shorter rig, as they would also sacrifice a more efficient (and faster) hull shape in order to have a hull that could hold more cargo while traveling slower.

[Dr PR]

Leopard,

 

I went through the same process to determine mast lengths for my current build of a revenue cutter, post #52:

 

 

I found the length of the main mast heel to hounds on American Baltimore clippers to be 2.6 to 2.8 times the extreme breadth, while on British ships it was only 2.3 (probably for normal square rigged ships). But the American vessels did carry a larger top hamper.

 

The head (the part above the hounds to the top cap) is 0.25 to 0.45 times the extreme breadth. Look at sail plans of ships similar to the one you are building to determine a suitable head length. The heads are usually the same length on both masts.

 

Total mast length is heel to hounds + head.

 

Drawings show the main mast height above the deck (partners to top cap) to about equal to the hull length, or maybe a bit longer. The "partners" are where the mast penetrates the main deck. In this respect your masts may be a bit too short, at least on American schooners.

 

The fore mast is 0.9 to 0.97 times the total length of the main mast.

 

The fore and main top masts tended to be about the same length, and are typically about half the length of the lower masts.

 

The mast diameters from Fincham's rules are a for full square rigged ships, and are bit large for schooners. Underhill says in "Masting and Rigging the Clipper Ship and Ocean Carrier" that schooner masts are only about 4/5 the diameter of masts for full square rigged ships. The fore mast on top sail schooners carried greater weight and was typically was larger diameter than the fore and aft rigged main mast.

 

Both Underhill's "Masting and Rigging the Clipper Ship and Ocean Carrier"and Mondfeld's "Historic Ship Models" have tables and formulas for mast diameters and tapers that agree closely.

 

After making your calculations compare your results with Marestier's data for a ship of about the same length as you are planning. In the end, you are right that there was a bit of leeway in determining mast heights and sizes, so anything reasonably close will do.

Edited August 11, 2019 by Dr PR

[BANYAN]

Not to confuse the situation further, but I think it depends on the era the ship was built.  According to Robert Kipping and John Fincham (both published books on Masting and Rigging in 1854), masts in that era (mid-19th century) were given as hounded and headed lengths (deck/partners to the hound stop, and then the masthead length..  The housing (below the deck) was not given and depended on where the mast was stepped.  As this period was during the emerging 'steam' period, many Mizen masts were stepped on the Orlop as the screw shaft was in the way and prevented stepping it on the keel.  Also, many ships were also moving to the use of an iron-cage or cradle style of stepping in the boiler rooms (these were quite large) so that the steam and heat did not interfere / burn the mast housing.  These started to appear as early as the very early 1830s- thumbnail image of NMM image ZAZ6753.

 

 

cheers

 

Pat

Edited August 11, 2019 by BANYAN
Additional info.

[Dr PR]

Pat,

 

Thanks. The period and type of ship is important.

 

The calculations I made were for the Baltimore clipper and revenue cutter schooners of the late 18th century and early 19th century. They were based upon Fincham's 1829 tables and Marestier's schooner descriptions included in Chapelle's "The Baltimore Clipper."

[Leopard]

Hi Phil,

 

Thank you very much for the thinking through all of this so clearly.  I went through your numbers and they seem to correlate well with what I have, especially taking into account the British vs American mast lengths.  Mine are a bit shorter, but then again, I'm partial to the Royal Navy.  And my schooner's painted black, with a yellow/ochre stripe in the Nelson chequer.

 

Since my build comes out of a banned kit, I can't show you what the masts look like in situ, but I can show you this picture, since this is all scratch-built from maple dowels I got at Woodcraft:

I've since stepped the masts, glued on the cross-trees and and topmasts.  Then I went overseas for a working holiday and now I'm building a ropewalk.  While away, I sketched out every single line in the standing and running rigging, including all the hardware.  Now I just have to finish the ropewalk, make some rope and start rigging.  I've made all the deadeyes, but I have a few blocks to go yet, before I'm done.  These are all from scratch as well, btw.  The kit didn't contain any blocks or hardware.  Cheap far-eastern rubbish.

Here's a couple of maple deadeyes.  That vernier is in millimeters:

 

 

 

[Dr PR]

Nice work on the deadeyes. And making your own ropes! Good practice for the next build.