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Angle of ship masts

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Hi guys, 

I am currently building HMS Victory and have a small difficulty of a generic nature which needs some help. What is the angle at which the main mast is normally fixed to the deck? I am not sure whether this shld be 90 degrees or slightly inclined toward the stern. Drawings on the plan show the latter but i am bot sure. Thanks for yr help. 

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1 hour ago, dbar1 said:

Hi guys, 

I am currently building HMS Victory and have a small difficulty of a generic nature which needs some help. What is the angle at which the main mast is normally fixed to the deck? I am not sure whether this shld be 90 degrees or slightly inclined toward the stern. Drawings on the plan show the latter but i am bot sure. Thanks for yr help. 

Foremast is vertical, Mainmast is inclined about 1.5 to 2 degrees toward stern, Mizzenmast is inclined about 3.5 to 4 degrees toward stern.

 

Danny

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Moving topic to correct forum.

 

This is for general site questions.

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Hi Danny. Thanks very much for your answer. I appreciate your feedback. You solved my issue😊

Regards,

David

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Masts were usually raked because the weight of the sails is unbalancing and if the mast rakes aft then that helps counteract the added weight. There are apparently some advantages dropping a sail in wind too over a raked mast - but the maths behind that confuses me so I'll take the experts word for it. Also if you have a vertical mast with the sails out then that provides a forward force on the mast which can decrease the effectiveness of the sails. Raking counteracts this force. 

 

Finally a heavily raked mast can help with loading and unloading though this may be more relevant for modern schooner type ships than square riggers. Perhaps some of the experts can chime in.

 

Different masts have different rakes due to the different sail plans each mast would take and thus the forces the mast and sails would apply.

 

Not that you asked but you might have wondered 'why?'

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Hi matrim. Thanks alot for yr reply which gave me some thoughts from a practical perspective. You are right and I agree with yr comments. Someone else gave me a reply to my query and noted that the middle mast shld be 1.5 to 2 degrees towards stern. This makes lots of sense and also goes in line with yr reply.

Thnks and regards

David

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Matrin is heading you down the right path.  Mast Raking is a calculation based on several forces, one of which is the hull design.  If large areas of canvas are vertical to the center of gravity...forward and down forces drive the hull forward and down as well...causing the hull to plunge into the oncoming water.  Instead of having a *trim* path through the water, the hull is pressed down forward...and the vessel plows instead of drives.

Raking the masts several degrees prevents this action and draws the most energy from the sails and translates it forward along the long axis of the hull.

 

Some extreme clippers had extreme rake to the masts and even some schooners had even greater rake...to capture the winds energy and lift and push the hull forward..NOT, cause it to plunge down forward.

 

Good luck.

 

Rob

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Indeed alot of members seem to have a wide theoretical and practical knowlege, something which i unfortunately lack sometimes. Anyway it's good to share.

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Mast rake is also used to adjust the “balance” of a sailing vessel. If the vessel under sail tries to head up into the wind it is said to have a weather helm.  The opposite, where the boat heads downwind is called a lee helm.  Raking the masts changes the geometric center upon which the wind forces act thus correcting the lee or weather helm.

 

There are accounts during the age of sail where Captains changed mast rake or even mast position to improve their ship’s performance.

 

Roget

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Posted (edited)

Glad I could help.  One other note to mention is that hulls with limited buoyancy due to their lines(ie..clipper hulls) forward and aft tend to resist forward down energy..thus resulting in a condition known as *Hogging*.

 

The hulls shape provides more buoyancy amidships due to width and dead rise..where the stem and stern lack buoyancy due to their sharp lines.  So *Plunging* is a greater problem...hence mast rake plays into the calculation....as I mentioned earlier.

 

Yes indeed, there are wonderful people on these pages.....

 

Thanks for piping in Roger...yes *balance* is one of the *Several* forces I eluded too.  This is why you can see that the rake of all 3 masts on a fully rigged ship can all be different.

 

Rob(good luck)

Edited by rwiederrich

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Posted (edited)

Roger nailed it above.  I don't have any experience sailing a square-rigged vessel, but on my little sloop, adjusting the rake of the mast even a little can noticeably change the way she handles.

Below is a relevant excerpt from a message sent by Lt. Stewart, Commanding US Brig Syren to Captain Preble in USS Constitution on 01 January 1804 (during the Barbary War, sourced from the US Navy History of same)...

 

"The 27th we sailed and kept company with the United States Brig Argus until the 29th.  At midnight, a severe gale of wind came on with a tremendous sea that hove the Syren on her beam ends and filled her waist full of water.  We got her before the wind, knocked out some of the ports, and freed her decks.  The jolly boat was stove to atoms and lost.  Nothing but strong gales from the westward, with heavy squalls (that prevented our carrying any sail but storm stay sails) prevailed from the 2nd of December to the 12th, during which time we were driven considerably to the eastward and all my officers sick but two young and inexperienced midshipmen."

 

Later in port...

 

"I immediately commenced the necessary repairs that the Brig requires.  She leaks very much in her upper works, which has damaged some of the provisions and other articles.   I am therefore under the necessity of caulking.  Her rigging we take this opportunity of overhauling and also to shift her main mast further aft, which it requires, and feel confident it will much improve her sailing.  I left at Leghorn Robert T. Spence, Midshipman, whose mind had been for some time deranged.  He is a son of Mr. Spence, Purser of the Philadelphia".

 

Cheers,

 

Keith

Edited by el cid

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Mast rake is also a matter of fashion as the centre of gravity of the sailplan can also moved aft during the design or building phase, thus moving aft the fulcrum that acts on the hull and makes it dive into the sea. It is noticeable that a pronounced rake was fashionable from around the mid-1830s to about the mid 1850s. The 'true' clippers of the late 1840s to late 1850s, though having comparatively little bouyancy forward, mostly did not have very raked masts. The rake seems to have been also more pronounced on schooners and some brigs than on barques and full-rigged ships.

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Correct me if I'm wrong but I think the more strongly raked masts on smaller ships was influenced by the fast that the faster you try and push a displacement hull through the water the more it will resist and the more power it will take to make it go faster. Every hull has a 'natural' speed through the water and up to that point it does not take much power to reach that speed. This factor is primarily based on hull length. As a rule a longer hull will travel through the water at a higher speed than a shorter hull. Hull shape is also a factor but not as much as length. The above of course is a very simplified and general rule. In reality it becomes a little more complex, the stuff that keeps marine engineers employed.

 

At any rate a fast small, (short) ship will reach hull speed much easier than a longer, larger ship, as it is lighter, and can carry proportionally more sail than a larger heavier ship of the same design. But their hull speed is much lower than a larger longer ship so the faster they go beyond hull speed the greater the resistance at the waterline. As sailing ships derive their power from their sails that are elevated above the water line this pushing power will cause the ship to plow. The bow will drop and the stern will rise. Some of this is overcome with proper ballasting and trim. Stories of sailing ships going from stodgy to fast sailing ships are rampant, and in most cases it was just a matter of how the Captain ballasted and trimmed the ship.

 

So when we look at profile drawings and pictures of small ships we see that they tend to draw much more water in the stern than the bow and that the rake of the masts tend to follow the keel angle rather than the deck. Some designs are even more radical and will have additional rake even over the keel angle. The net result though will be that at speed the mast(s) will be much more vertical than at rest. This mast rake is also more pronounced in many cases of fore-and-aft rigged ships than square rigged vessels. It was not very common to see heavily raked masts on larger ships until the large Clipper ships started being built.

 

Interesting discussion.    

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A displacement hull driven by sails cannot go beyond the theoretical hull speed you mentioned, raked mast or not. Sails just cannot supply enough energy in order to overcome the cavitation effects at the end of the hull that would develop. Before towing-canals and the theoretical foundation (e.g. Froude) were developed, ship designers experimented by feel and looking for examples in nature. As you noted, it is the combination of design and implementation parameters that determine, whether a given ship is fast or not. Changing this combination by trim, for instance, can change the performance rapidly.

However, as I said before, raking masts can make a particular ship faster, but not necessarily so - but it certainly makes it look faster, which can be important in both, a naval and a commercial context. A fast looking ship is likely to attract more business. This is why the ocean-liners of old were given raking funnels.

At a time when ship designers experimented with waterlines, where the main breadth was above the middle, i.e. that had very sharp, even hollow lines forward, raking the mast may have brought the centre of gravity of the sail plan closer to the centre of gravity of the body plan, thus reducing the tendency to dig in. The same could have been achieved by stepping the mast further aft, but then the mast would have come to close together, partially blanketting each other.

When in the later 1850s the hulls became longer and the sharpness more evenly distributed between the forward and rear section, the need for raking masts disappeared.

One should also distinguish between naval and commercial practices. Commercial ships need to be able to maintain a steady speed across all weather conditions in order to achieve short travel times, i.e. the average speed is important, while for naval ships often the top speed is the important criterion.

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Posted (edited)

While I do not disagree in general, If you do some math, (Again I stress in over simplified form) you come up with some numbers that discount the fact that sailing ships could not exceed hull coefficient or design speed.

 

Without going into a bunch of math formulas on wave forms and drag here are some commonly accepted numbers for hull speed.

                       

20 feet

25 feet

30 feet

35 feet

40 feet

45 feet

50 feet

 

6.0 knots

6.7 knots

7.3 knots

7.9 knots

8.5 knots

9.0 knots

9.5 knots

100 feet             13.4 knots

75 feet               11.6 knots

125 feet             14.9 knots

175 feet              17.7 knots 

While these numbers only partly take into account beam, depth, and length of the hull they are still relatively accurate, or at least they were in the mid to late 1800s. As can be seen it is not only possible for some ships to exceed hull speed but in small ships can become quite common. Not so much in larger vessels as the power required to overcome drag and wave length becomes more than the power source can provide, (wind). Of course these numbers are routinely exceeded with modern day ships with hundreds of thousands of horsepower available but that is not what we are talking about.

 

I included the last number as I read in one of my books that one of the faster speeds logged by the Constitution was in her escape from Annapolis in 1861. When she hit open sea according to that book she reached the speed of 13.5 knots. the Constitution was known as a fast ship for her time and while not exceeding hull speed, 13.5 knots is pretty fast even for ships of a much later design. I am not a big clipper fan so I do not have similar accounts for ships like the Cutty Sark or Thermopylae and ships of that era but it is possible that they may have exceeded hull speed at one time or another. 

 

I agree that ship design was done in many cases more by what 'looked right' and what worked in the past for similar ships built by the same yard. In some cases you also had to take into account that a ships design was also heavily influenced by whoever was going to be the first captain. Again take into the building and sailing characters of the Constitution, President, Vs. the United States. 

 

I also agree that military and civilian ships experienced different design factors when built from the keel up as such. But at the same time there was considerably more crossover than there is today that allowed many ships built as merchant ships to fulfill the role of warship as well, especially when it came to smaller ships like Sloops, Cutters, Schooners, and Brigs.

 

 

Edited by lmagna

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If mast rake helped to prevent a downward driving force on the bow, how does one explain the rationale for negative (forward) rake of the fore mast on some ships.

 

Regards,

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Posted (edited)
3 hours ago, popeye2sea said:

how does one explain the rationale for negative (forward) rake

I am not trying to say that the rake of the mast is designed to prevent the downward driving force of the ship. I reality I don't think that it can be prevented, and the rake was an attempt at establishing a dynamic mast angle that was more an effort to achieve a fully upright angle when the ship was actually under way and the hull started raising in the stern and coming down in the bow. Something that could not be prevented and would increase with speed and wind force.

 

As for the forward rake of the foremast on some ships I am at a complete loss. I think that I have only seen the practice on larger Frigates and ships of that sort but then again I have never done research in the matter. I was was hoping that some people with real sailing experience, better yet, tall ship experience would chip in and bring real life knowledge to my theories. It is entirely possible that what I am saying is completely full of hot air.   

Edited by lmagna

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No need to qualify.  I just thought you may know the reason for the forward rake.  I have never heard an explanation for it, either.

 

Regards,

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Posted (edited)

Interesting discussion folks.  I am currently researching, drawing up and building a 1:72 model of HMCSS Victoria - built 1855 at Limehouse Docks in London - she was based on contemporary RN Gun Despatch vessel lines but modified for a more sleeker (longer and less-wide) by her designer Oliver Lang.

 

Her masts were extremely raked with the Fore - 5 degrees aft, Main -10 degrees aft and Mizzen - 15 degrees aft - and yes I have 'triple' checked these even superimposing a photograph of her over the profile plan.  She was also known as a fast ship easily attaining 13+ knots at sea (in the right conditions) and having achieved 14.5 knots over the measured mile during her sea trials (under sail alone). She was a Barque rigged vessel to Royals only and standard topsails  - not the 'split' (upper and lower topsails) used in the clippers etc.

 

Just for interest.

 

cheers

 

Pat

Edited by BANYAN

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Hi Pat

An interesting vessel to be sure. From what I was able to look up she did indeed have a noticeable rake on her masts. As I said before I have very little knowledge of ships of the Clipper era and I can find no listing of the hull dimensions, especially the waterline length so I can not fit her into the chart and see how close she came to the larger ships numbers, but I am almost certain that she never exceeded her hull speed just as wefalck stated in his post. 

 

I think we still need a marine architect!

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Might I suggest that, when discussing ship design pre-1830, the contemporary record offers abundant discussion of the lack of appreciation of the role of science as opposed to trial and error in British (and American) ship design.  The French and Swedish were more advanced in theoretical application.

 

A modern Naval Architect would be applying modern scientific and mathematical knowledge to vessels where that knowledge was not available during design.  Essentially, retroactive application to show WHY something worked (or didn't), but NOT proving why it was done.

 

I would suggest a visit to what I have found to be a very readable and comprehensive discourse on the topic in "Ships and Science" by Larrie Ferreiro (and original sources, many available on the interwebz, listed therein).

 

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Thanks Wayne

 

I suppose I was being a little lazy in saying it would be nice addition to the conversation to have a Naval or marine Architect explain the scientific codification behind the evolution of a certain practice, rather than buying and reading the explanation already provided by a navel architect in book form for myself.

 

Looks like I will be adding yet another book to my reference pile so that hopefully I will be able to provide the answer next time the question comes up. 

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Posted (edited)

A side effect of a dramatic Mast Rake on a square rig is that the location of the Sling of the course yard needs to move farther forward in order to avoid having the yard laying directly on the Mast. The hole in the top to accommodate the Sling on the Brig Niagara, for instance, is way up forward near the forward rim of the top, far enough out so that the yard suspended below is free and clear of the Mast.

B4E5670B-D8D8-4867-B44C-3844F8C22D75.png

C0B17B0F-33B7-4EF9-BA05-F95003900E92.png

Edited by JerseyCity Frankie

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On 6/15/2018 at 10:13 AM, lmagna said:

I am not a big clipper fan so I do not have similar accounts for ships like the Cutty Sark or Thermopylae and ships of that era but it is possible that they may have exceeded hull speed at one time or another. 

The clipper Sovereign of the Seas reached the highest daily rate and fastest speed recorded for a sailing vessel of 22 knots.  Mast raking was popular with the clipper design.

 

Rob

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Posted (edited)

Thanks Rob

Still doesn't really answer the raked mast question but using Froude's formula above, and a guesstimate of 225' waterline she is the first large sailing ship we have found that has exceeded the formula for hull speed.

Edited by lmagna

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From what my 40+ years of studying the clipper design has revealed to me, is that, to some degree mask rake coupled with the hulls entry and exit features was part of the experiment in gaining the most speed from the vessel.  There are examples of clippers with zero fore and main mast rake and only 1 degree on the mizzen...while other designs employed over 2~3 degrees on the fore and main and more then that on the mizzen.  Smaller schooners and Baltimore/Boston clippers had an excess of 5 degree rake.  Designers employed these extremes because the forces were balanced between hull design and forward action  provided by the energy captured by the sail plan.

In many instances rake was perceived by captains/designers as the essence of speed.  Coupled this with extreme hull designs and you achieved speed.  The commodity bringing the highest dollar value(At the time).

Many theories were formulated during the time when speed was the goal and many experiments followed...some with results and some not so much.  But as I've mentioned earlier, many forces are acting on the hull to propel it through the water on an even keel, and many forces are acting against that goal as well.

 

I'm sure somewhere, someone has penned the cumulative answered as to why.  I've tried to explain some reasons.

 

Rob

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Posted (edited)
1 hour ago, rwiederrich said:

I'm sure somewhere, someone has penned the cumulative answered as to why.  I've tried to explain some reasons.

Hi Rob

 

I doubt anyone without a degree and a few additional years of research under their belt will be able to do better. 

 

All we will probably be able to conclude is that the practice was quite common well into the early 18th century or sooner and that it was apparently more intuitive than scientific. It certainly proceeded the Clipper era by a considerable time span.

 

Edited by lmagna

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