Ladder steps

[allanyed]

I believe typical modern stairs have a vertical spacing of 8 inches.  I have been looking for information on the distance from tread to tread on ship's ladders.  Looking at high res contemporary drawings of Africa and Ardent in the 18th century that I enlarged to full size on my drawing program, the height from tread to tread  varies from about 9.5 inches to 11 inches for the various ladders.  I found a paper on Georgian stairs (https://georgiangroup.org.uk/wp-content/uploads/2018/05/Georgian_Stairs_by_N.Burton-s.pdf) that is interesting but it only states that the distance is to be no less than 5 inches and this is regarding buildings, not ships.     

If anyone can share any contemporary dimensions or "rules" regarding the height between treads and other dimensional information for British ships in the 17th and/or 18th centuries I would be grateful.  

TIA

Allan

 

[bruce d]

Hello Alan,

HMS Assurance, 1747. G5896 in Dansk Museum. Very precise drawings of stairs/steps, perhaps good enough to take a scale reading? Here is the link to allow you to get better resolution: - "https://ao.sa.dk/ao/data.ashx?bid=31918097"

 

 

Edited July 28, 2021 by bruce d

[Mark P]

Good Evening Allan;

 

I have never seen anything which gives guidance on the vertical spacing of ships' ladderways for this period. I think that the best thing would be to go with the plans. I have checked a couple of the plans I have at full size, and the spacing seems to be around 10". 

 

All the best,

 

Mark P

[allanyed]

Bruce,  Thank you very much!!   I did the same thing with six very high res contemporary drawings from the Wiki Commons site which has hundreds of high resolution contemporary drawings  and they are all the same, that is, none of them are the same.  They vary nearly two inches from one ladder to the next on any given ship that I checked.  The drawing you posted is not as clear as those that I checked on the Wiki site but I was able to bring the Assurance drawing up to full scale on my CAD program and from what I was able to discern it has the same variation in spacing from tread to tread, from under 9" to over 10", thus no consistency from ladder to ladder.  

 

Thanks Mark.  I agree the average is somewhere around 9.5 to 10.5 inches based on the half dozen internal profiles I checked.   I suppose the spacing may have been to create a number of steps in a given vertical spot such that the spacing was the same on that specific ladder.  The problem though is that if anyone ever tries a set of steps with one spacing and then another ladder with a different spacing, it can lead to stumbling.  Even one uneven step is an uncomfortable situation.    I agree that relying on the drawings is a good way to go and has been what I have done in the past.  It was just one of those things that was an oddity for me and for which I could not find a specific number.

 

Allan

[druxey]

I agree with Allan; about 10", but slight variations depending on total rise without any uneven step in the run!

[Dr PR]

In modern US ships the number of treads in a ladder (vertical or angled) depends upon the vertical length. This is divided to give a number of equal spaces between the treads (top of treads) somewhere around a foot (12 inches). This can vary between about 10" to 13" between treads, with the bottom tread on vertical ladders as much as 18" above the deck. Angled ladders tend to have the same spacing from the deck to the top of the lowest tread as the rest of the treads. Blueprints usually don't actually give the spacing, but just give the height of the bottom step from the deck and the distance from the top step to the deck above, and show some number of treads and say "Equal Spacing." The rest is left up to the shipyard.

 

I suspect ladders have always been made this way. You have a space to fill with steps and you want them spaced in a reasonably familiar way. The fact that the spacing differs from ladder to ladder doesn't matter. Take my word for it - I climbed all over ships at sea with varying tread spacing and never had a problem missing steps. But it is important for the spacing to be equal on a given ladder. Also, the lowest tread should not be too close to the deck - that can cause tripping. And the top tread should be about the same spacing below the upper deck as the tread spacing in the ladder, but often is shorter if necessary to get appropriate spacing between the other treads.  You don't have trouble finding the deck above the ladder when climbing - it is wherever your foot lands. - again, I speak from experience!

 

Well, if you are climbing a ladder in the bow while the ship is pitching in high seas you may find yourself catapulted into the air just as you reach the top step with the ship dropping out from under you and then have momentary difficulty finding the deck, but gravity quickly remedies that!

Edited July 29, 2021 by Dr PR

[jud]

Only one way to adhere to a lift per step standard without having an odd step at the top or bottom is to adjust the length of the slope. Many times that option is not available and step height must be adjusted, not a problem for an experienced seaman to adjust to, it is the odd height at the top or bottom that causes problems, so keep them all the same, those using them will adjust.

 

[bruce d]

Here is the detail from the Assurance drawing that I thought might be most helpful:

 

 

In it, the two ladders in close proximity connecting the same two decks have different numbers of rungs. I believe you have a free hand.

[allanyed]

Thanks again Bruce, very much appreciated!   

Allan

[Jaager]

There is a strict code for houses.  The width of the tread, the height of the tread - there is a strict formula.   We have a learned expectation and it is almost instinctive.   When steps are being used at night, with poor or no light, and the whole structure is moving, often irregular motion.  The more extreme motion occurring when the pressure to move quickly is most intense,  it would be a bad idea to have unpredictable tread intervals.    

[allanyed]

Jaager, yes there is a strict code today.  But, based on the research done on the Georgian staircase article, it was not the case back in those days.   And based on the inboard profile drawings I've had a chance to study, it was no different aboard ship.    Me thinks that building codes, both marine and land are a good thing!!! 😀   

 

[Peanut6]

What I have to share is based upon my facilities drafting days of yore.  It doesn't directly apply to ships, of any era, but I can't see how the logic could not be carried over.  Yes there is a strict code for stairs.  But it does have flexibility built into it in order to handle all situations.  There is a min/max for tread depth and a min/max for riser height.  What those numbers are have escaped me after all these years.  The number of steps, odd or even, is not a factor.  The key factor is that the riser distance must be consistent for that particular flight of stairs.  This distance is to include the surface you are standing on to the top of the first step and the surface of the last step to the destination surface.  There are other factors that affect rise and run in a flight of stairs but I won't go into that now.  The one consistency I've seen in all the build logs I've read is the inconsistency in the distance from one deck to another.  Not only between ships of different eras, but within different types of ships within the same era to even the decks within the same ship.  IMHNO (In My Humble Newbie Opinion) I would think that if one would follow the guideline of a consistent riser distance of a "realistic stride/step to scale" you couldn't be faulted.  I'd bet that is the "general rule" the shipwrights of old followed.   

[allanyed]

Kev,

If I am understanding you correctly, when closely examining and measuring the distance from step to step, that is exactly what the contemporary drawings show.  While one ladder is different than the next, the spacing is consistent for the steps on any given ladder, be it 9 inches  or 10.5 inches or something between.

Allan

[druxey]

Kevin: The rule of thumb is one riser depth plus one tread width totals approximately 18". So a six inch rise, 12" tread, etc. (Sorry, you metric folk!) This applies to flights of stairs, within certain parameters. Ladders, being steeper, are another matter. Around 10" spacing seems average.

[CDR_Ret]

My two cents, which basically corroborates what has been stated previously ...

 

The following information is abstracted from pages 316 and 317 of The American-built Packets and Freighters of the 1850s: An Illustrated Study of Their Characteristics and Construction by William L. Crothers.

 

In the mid-19^th century, the spacing of ladder rungs and stair treads was dictated by the natural step of the average 5-foot, 8-inch man (according to Crothers—a value he never provided!).

 

Vertical ladders for accessing deckhouse roofs had equally-spaced rungs. The distance between the upper rung and the roof surface was the same as between the lower rungs, to avoid creating a surprise and misstep when accessing the roof. The lowest rung was at a variable distance above the deck, but could be a larger step than the space between the other rungs. Stringers were at least 4 inches deep to provide toe room at each rung. If the upper end of a ladder ended at a coaming, the upper rung (or tread) was at the same height as the deck outside the coaming, again to avoid tripping or other surprises due to height differences.

 

Inclined ladders (stairs) had treads that were closer together than vertical ladders. However, all treads were equally spaced—from each other, from the lower deck, and from the upper threshold. This is so the user experienced the same drop and rise whether descending or ascending. The number of treads was determined by the height between decks and the inclination of the stair. As the stair angle from the horizontal decreased (became less steep), the vertical distance between treads decreased, and the width of the treads increased. Again, the reference for these dimensions is the length of an average person’s step or pace, but no absolute value was given.

 

Stairs and ladders were made for the specific location where they served and were not interchangeable.

 

Often the lower ends of the stringers of inclined ladders/stairs were cut plumb with the deck (“dubbed off”) below the lowest tread to eliminate a tripping hazard.

 

While the era Crothers discusses is several centuries after the OP’s interest, I imagine these principles were more or less followed from the earliest times simply due to their practicality.

 

Terry