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Optimal Bowsprit Angle


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It seems to me there should be exactly one optimal bowsprit angle for a specific ship in specific weather conditions, and then one for the weather condition of most concern.  Authoritative sources such as Marquardt (page 26) note ranges for a bowsprit angle (e.g., 30 to 36 degrees, 25 to 30 degrees with the range varying over time), and further indicate that a cutter's bowsprit is near horizontal.  The closest I have come to actual guidance is a comment in a manual that the angle of the rigging to the masts needs to be in a certain range, which might impact the bowsprit angle.

 

Does anyone know of a formula source or table for an optimal bowsprit angle?  I am looking at a 1783 launched Royal Navy Brig and several similar brigs.

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This is an excellent question! I will throw out also that the pitching motion of the ship must be taken into account. Maximum pitch needs to be known to avoid the jibboom plunging into the sea. Broadly,  A sailmaker and rigger would be juggling a LOT of math calculations and these would be driven by the Center of Effort of the entire rig, since the headsails job is to effect this imaginary point in space above deck by countering it-or altering it- with the collective Center of Effort of the headsails. These same considerations would be in play in determining the size and shape of the Spanker, for the exact same reasons. So the factors effecting the Steev of the Bowsprit are also effecting the angle of the Spanker Gaff. The higher off the water the tip of the Bowsprit, the higher the center of effort for the headsails will be.

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I imagine the pitching motion of the ship is effected most by waterline length, the longer the waterline length ( or maybe call it Beam to Length ratio) the less pitching. It seams to me that the more modern a ship, the more shallow the Steev of the Bowsprit. And I’m guessing-GUESSING- this is due to the greater hull lengths achieved through time. Older ships appear to have much steeper Bowsprits? However the cutter rig appears to always have a very shallow Bowsprit despite a short Beam to Length ratio. But cutter headrigs are very odd things...

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Like everything else aboard ship there are definite trends in the development of rigging.  The steeve of the bowsprit initially was much greater and gradually became lower over time.  At first the bowsprit was intended and used to rig bowlines to and so it needed to be very high to give a proper lead to those lines.  It started to become more of a supporting structure for the fore mast, and so longer, when additional sections were added to the fore mast to increase sail area, but it still retained it's high angle.  Next the spritsail top mast was added to increase head sail area and the bowsprit steeve started to come down.  Additional lowering of the steeve of the bowsprit was done to increase the head sail area when stay sails and jib sails were added following the era of spritsail topsails.

 

I believe that most of the changes that occurred were due to trial and error on the part of shipwrights and captains and only adopted generally when shown to give some advantage in real world use.  For example, the spritsail topsail was eliminated because it proved to be too cumbersome and useless on most points of sail and the benefits derived from it were able to be provided by triangular stay sails and jibs.

 

Regards

Edited by popeye2sea
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This has all the makings of a fascinating lecture. I could imagine someone trying to document the degree of Bowsprit Steeve on every vessel for which data can be obtained and then build a presentation that would show the many influences that would arise over time to guide the shipwrights decisions about the angle. Factors as mentioned above by Henry. Whenever I’ve gotten involved with a sailing vessel I’m always eventually reminded how every individual part of the vessel is subtly effected by every other part of the boat. You can’t isolate anything aboard and say that it’s independent. If you perform some task at one end of the ship it will have subtle effects all over the rest of the boat.

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I think shipwrights just fudged it.  Probably you need a 3d model and to run myriad simulations in lots of weather conditions.  I can see one height being best for a chase in good weather, and yet another being better in other seas (ignoring trysails and no sails for bad storms).  So, first you would have to prioritize speed/safety and and normal condition handling vs. bad condition handling.  Then, with that to set values, run the computer.  A lot of math involved.

 

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With our modern mind-set, which is framed by efforts to increase utility and efficiency, we tend to analyse artefacts in that way, which may be rather misleading. Our ancestors had much less capacity to predict due to the absence of the concept of a 'model' and the lack of methods to quantitatively measure e.g. performance. They may have observed that certain features work better than others and these may then have been slowly adopted - but, as a ship is made up of many different components that interact with each other, such new feature may not have worked everywhere and all the time. Errors or underperformance can be costly in an economic sense or in armed conflict. Hence shipbuilders and seamen were conservative, they preferred to err on the safe side. I gather for every successful innovation that has been recorded in history, there were scores of less successful ones that have sunken into oblivion.

So the question of an 'optimal' bowsprit angle can only be answered, if one sets a range of boundary conditions. We can guess the boundary conditions of old, but often we cannot be sure. Traditions and customs can be very pervasive boundary conditions that are not accessible to modern rationale. So, most often we can only observe the facts and can only speculate on the 'why' by trying to understand the 'how'.

As to the near-horizontal bowsprits of the late 18th/early 19th century cutters: this may be due to the fact that they often had a running bowsprit, which would be more difficult to manage, if inclined. Also a horizontal bowsprit increases the area of foresails.

As to the pitching: the pitching movement is not only determined by the length to breadth ratio and absolute length, but also by the amount of buoyancy in the bow and stern. A ship with good buoyancy at the ends and flaring bow-sections tends to have shorter, but perhaps harder pitching movements and keeps the 'head out of the water'.

 

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Jeffrey

This may be an easy way out, and specific to one or two vessels.   Zephyr 1779 (14 gun brig) drawing   https://collections.rmg.co.uk/collections/objects/85176.html     If you download and print the drawing you can measure the angle pretty accurately for that brig. You can compare it to Swift (8 gun brig sloop), 1783 as well.   https://collections.rmg.co.uk/collections/objects/84645.html

 

Allan

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37 minutes ago, BANYAN said:

Underhill also discusses the angles of the bowsprit in his book "Masting and Rigging the Clipper Ship and Ocean Transport"; may be worth a read.

 

cheers

 

Pat

 

 

Perhaps you could share a brief synopsis of his conclusions before we all rush out and buy the book?  :)

Edited by Gregory
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I am glad you asked as I seem to have gotten myself confused (reading far too many books at the moment while sorting the spars for my build).  I am building a Gun Despatch Vessel steam-screw sloop which had an Aberdeen style bow and the steeve , when measured from the horizontal of the WL, was 15 degrees.

 

It was Goodwin "The Construction and Fitting of the English Man-of-War" page 174 that provided the guidance I wrongly attributed to Underhill (memo to self - check before posting next time :) )  - basically, 25-30 degrees for ship-rigged vessels - smaller classes closer to horizontal.  I dare not state more as this book is still in copyright and, sorry, I will need to check with moderators how much can be cited re copyright.

 

I used underhill to get averages of the steerve angles, and angles of the caps for the 1850s, as he has many accurate drawings of clipper ships of many designs; hence my subliminal association.

 

cheers

 

Pat

Edited by BANYAN
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Jeffery, a little later than what you need for your period build, and Gregory for info, the only formula/rule-of-thumb I have found is for clippers (I knew I had seen something somewhere in my reading :) ) .

E. Armatage McCann in his series of articles published in the  Model Ship Builder magazine (originally in the The Ship Modeller magazine), titled "Rigging of Clipper Ships" - part 3, page 10 provides:

"The steeve was 4 to 5-inches to the foot" using the length the bowsprit extending from the bed to the cap.  Note this was for clipper ships of the 1850s.

 

cheers

 

Pat

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