Oars: A working paper

This paper is devoted to oar mechanics, materials, etc., especially as applies to the oars to be used with Viking longships. It will be developed and added to over time - readers are encouraged to submit comments, corrections, and additional data. Initially the primary intention is to provide at least some basic data where previously none has been available.

OAR WEIGHT (12' oars)
Laminated spruce oars (made by Kerry Eikenskold)                             approx. weight  8 lbs
Oak oars (made by Jim Lande)                                                             approx. weight 14 lbs

OAR  HORIZONTAL PULL FORCE
Measuring the pull exerted on the loom of a laminated spruce oar during power strokes
8 lbs of pull force              easy stroke
10 -12 lbs of pull force     standard stroke
15 lbs of pull force            power stroke (not easily  maintainable for long periods) ,
20 lbs of pull force            maximum stroke likely to be used in normal circumstances (e.g. getting underway quickly from dead stop  -- quickly exhausting)
25-40 lbs of pull force       Emergency circumstances stroke

The laminated oar blades are significantly narrower than the oak oar blades. That doesn't automatically translate into differences in the force applied to pulling the two types of oars, because the same amount of force must be exerted on each type of oar regardless of blade size  to produce the same "equal and opposite reaction" in motion of the ship. Essentially, rowers will have to pull their oars with X amount of force over Y stroke distance to get a specific amount of  movement by the ship. Wider blades do allow the same amount of force to be exerted in a quicker or shorter stroke in some circumstances, but when rowing in unison, especially with mixed oars, it becomes very difficult to measure and calculate the different amount of pull required between the oars. (E.g. as anyone who has rowed as part of a crew knows, it is possible to exert anywhere from near zero effort in pulling an oar by just putting it in the water and letting it be swung by the movement of the ship, powered by the other rowers, until it is taken out of the water for the next stroke, to pulling with maximum possible effort,  reducing the amount of effort required of  the other rowers or increasing the speed of the ship.)  Once the ship has gotten under way and has momentum, maintaining that momentum/speed  is much like pushing a swing; once going, only a comparatively small, set amount of force has to be exerted in each push to maintain the pace and distance (the period) of the swing. That set amount can be exerted by one hand, two hands, one person, two people, three people. As long as the combination of pushing force and length of push remain the same, it makes no difference how much of the force comes from which hand(s) or person(s), and so it makes no difference if the pushing hands are big or small. So too in rowing; eight rowers with wide oar blades will need to exert the same amount of combined force per stroke cycle of specific time period as eight rowers with narrow oars, to move the ship at the same speed. Thus, the wide blades are able to exert more force in the same stroke cycle, but in normal rowing they will not necessarrily do so. Crude observations/measurements produce a guess on my  part, that there may be a tendency to exert about 10%- 20%  more pull force when using the oak oars when the majority of the crew are using the laminate oars, just because the weight of the oars makes one feel like they should be pulled a bit harder. Thus, if those rowing with the laminate oars are pulling at 8lbs, an oak oar rower keeping pace may be using 9 or 10 lbs.

There is probably slightly greater "slippage" (oars moving through the water rather than transfering all motion to the boat) with the narrow blades, and indeed, I have noticed small vortexes below the surface when the narrow bladed spruce oars (and the experimental PVC oar with blade width about equal to that of the spruce oars) end their stroke, but none with the oak oars. I assume those vortecies indicate slippage. However, once up to speed,  when in the lower force of stroke range,  the slippage factor with the Sae Hrafn is probably only in the single digit, or very low double digit,  percentages. (Although we have the perception of moving the oars through the water, the objective is to have the oar tips remain as stationary as possible while the ship does all the moving.)   When going against a current or wind, the movement of the ship is slowed, but whether there is greater slippage in such circumstances, I have yet to determine.

OAR VERTICAL RAISING/BALANCE FORCE

(This is where things get interesting)

To raise the oars out of the water and hold them balanced on the oar port while swinging them forward to recover for the next stroke  requires

Laminated spruce oar                                                      4 lbs of downward force on the loom

Oak oars                                                                        12 lbs of downward force on the loom

That gives a raw figure of 3x more force needed to lever the heavy oars up out of the water and hold them clear of the water during the recovery stroke. But the passive weight of my arm supported by just resting my hand on the loom when near my chest at the end of the power stroke, balances about 2 lbs of the upward force being exerted by the oar at the loom. Obviously, my arm weighs more than 2 lbs, but it is mostly supported by my shoulder. Subtracting that 2 lbs from the force needed to be exerted downward on the loom,  gives us:

Laminated spruce oar                                                      2 lbs of downward force on the loom

Oak oars                                                                        10 lbs of downward force on the loom
 

Thus, it requires, at most, only marginally more effort to move the ship a given distance pulling a stroke with a heavy, wide-bladed oar compared to a laminated spruce oar, whereas it requires 5x as much effort to lift the heavy oar out of the water and keep it clear of the water while swinging it for the next stroke, with that effort being nearly equal to the amount  which will normally be expended when an oar of either type is in the water and moving the ship. (If we want to play mathmatical games to come up with sensational  but meaningless statistics like we so often see thrown around here in Washington, we can calculate that for someone with heavy, Popeye-like, forearms,  which we will assume have 4 lbs of passive balancing weight, the figures become 0 lb and 8 lbs -- meaning infinitely more times the effort required to lift the oak oars clear of the water compared to the spruce ones.... )

The extra effort required to use the heavy oars under normal circumstances  thus comes primarily in moving them when they are out of, rather than in, the water, and that extra effort makes rowing with the oak oars roughly the caloric equivalent of rowing 50% -100% additional distance or time with the lighter oars (e.g. two strokes with the heavy oars require as much effort as three strokes or four  with the light ones). Fortunately, the pull/power and return/recovery strokes require the effort of somewhat different sets of muscles, so the arms of the rowers using the heavy oars probably won't give out quite as quickly as might be assumed from that total effort calculation.
 
 

POSSIBLE ADJUSTMENTS
In addition to weighing almost twice as much as the laminated spruce oars, the oak oars have a balance point approx. 70 inches from the loom end (i.e. they will balance naturally at that point, very close to the midpoint of the oar) , as compared to approximately 60 inches for the spruce oars -- both types normally contacting the oar port at about 40 - 42  inches from the loom end.  Reducing the size of the blades on the oak oars is a way to both reduce the weight of the oars, and shift the balance point  back towards the loom, thus reducing the force/effort needed to lift and balance them out of the water. If, as indicated above, the blade width makes little difference once underway and up to speed, narrowing the blades will not reduce our normal rowing speed nor  the maximum speed which we can attain. An alternative is to weight the looms so less force is needed to lift and balance the oars out of the water even while making the oars heavier -- adding to the overall weight of the oars won't significantly add to the force needed to propel the ship. Weighting does pose some potential problems that need to be considered/overcome e.g. a weight could cause an oar to be so heavy as to sink rather than float if dropped in the water.

EXPERIMENTAL OAR COUNTERWEIGHTS
Since the above was written, two each of two types of oar counterweights were fabricated and tried. One type consists of cast lead strips coiled into narrow spirals with center holes sized to fit over the shaved down ends of the looms but so that they will not slip down further on the oars. The other type consist of concrete cast into short lengths of 4" dia. PVC pipe, with the concrete cast over a removable core that left necked-down holes so that the weights ride mainly over the full diameter part of the oar but will not slide further down the oars. These weights are all in the 4 lb. to 5 lb range. Their designs allows them to slide off before, or as, they hit the oar ports when emergency "ship oars" or "throw oars" commands are being executed. Everyone who has used them agrees that they make rowing with the heavy oars much less tiring. The concrete weights are sightly more convenient for most people to use because the lead spirals of the other design need to be positioned so as to miss the rower's legs, while the PVC pipe of the concrete ones generally can clear the tops of the rower's legs. The final design will thus probably be lead, cast in a manner similar to the concrete, with the greater density allowing a more compact weight e.g. < 3" diameter.

___________
STILL TO COME:
Oar structure and stress calculations
Oar materials strength data
Calculating our maximum possible rowing speed
 
 
 
 

Journal -- Call for articles/papers

An online journal of medieval transportation and technology is being created in connection with the Longship Company Ltd web site to provide a venue for publication of articles concerning the Viking era (usually considered circa 700-1100 CE -- but for the purposes of this journal also extending through the Norse "age of exploration" which continued a few centuries longer) and geographical range or the Vikings (i.e. from the Caspian on the east, North America on the west, Spitsbergen and northern Greenland on the North, and the northern coast of Africa on the south). Of particular interest will be articles related to construction, operation, and maintenance of the single sail square-rigged ships of the era, and similar vessels of preceding and succeeding eras that provide additional insight on those used by the Vikings.

The goal is to create a scholarly journal that contributes to knowledge of the Norse and those with whom they came into contact, their times, their technology, and their accomplishments. To that end, articles will go though a process of review -- somewhat less formal and extensive than that for a strictly academic journal -- adequate to verify that sources, data, methodology, etc. meet basic standards. The primary guidelines for articles are only that they be written in a clear style (e.g. uncommon technical, historical, Scandinavian language, or otherwise esoteric terms should be defined/explained either parenthetically or in foot/end notes); preferably they should focus on specific subject areas rather than being broad overviews, with perhaps the exception of surveys/analyses of existing literature or research; and they should strive to add to knowledge of the relevant subjects either by original research, new analysis of existing data, or factual/logical refutation of misconceptions based on outdated information or sloppy science/scholarship. The format will evolve depending on article submissions and reader response.

The designation of the journal as "scholarly" should not be taken as in any way as exclusionary as to authorship of articles. Rather, it is intended to uphold a tradition of true scholarship in which quality and validity of work, rather than academic or professional credentials, are the primary consideration. As with many other fields, this is one in which dedicated amateurs and those who are self-educated in the subjects can make valuable contributions. The editorial function will be to ensure that articles meet the standards of, and follow the basic methods for, serious research --providing help to any authors who may be unsure of how to structure and present their work. Similarly, the review process will seek to have the reviewers, if they find any factual or technical errors or other weaknesses, provide suggestions as to how such can be corrected by the author so as to allow acceptance of the article. It is hoped that the concept of "scholarly research" will not intimidate or deter anyone from contributing to the journal; something as simple as a one or two page article on some previously not fully understood aspect of a particular craft technique of the Viking age, based on archaeology-by-experiment carried out during a couple of evenings at a kitchen table after appropriate background research, would be very welcome as a submission to the journal.

In addition to publishing formal articles, the journal will be a place where questions deserving of scholarly attention can be posed, and where attention can be drawn to information or potential sources of data that may be of benefit to other researchers. Given the proliferation of some total nonsense related to Vikings and the medieval world on the Internet, which is so baseless and lacking in validity that it does not warrant refutation by major articles, the journal will serve as a place on the Internet where that sort of erroneous information can be identified as such, and those attempting to use the Internet for research on the subjects can be directed to sources on or off the Internet where reliable, factual information is available. The journal will provide for feedback on articles and related matters by publishing email letters concerning them. At this time it is not planned to create an interactive reader forum as part of the journal due to the range of subject areas likely to be covered. Instead, authors will be encouraged to specify forums elsewhere on the Internet devoted to their particular subject areas where they would like to see their articles discussed and are likely to participate in those discussions.

Your comments, suggestions, inquiries, and, most of all, article submissions are encouraged

Initiating editor

(Journal as yet unnamed)

email
journal@longshipco.org

The Oar Rack Controversy

In the category of questions deserving scholarly attention: two images are presented below relevant to an ongoing discussion within the Longship Company concerning oar racks on Viking ships. Among the matters under debate are whether oar racks were commonly used or rare, and whether there is any evidence for racks of a "Y" or similar configuration.

Reproduction quality leaves much to be desired, but the first image shows five Y-shaped uprights (actually tridents) in the ship, and the second shows something(s) rigid (depicted by cross-hatching) running horizontally alongside the mast, supported by uprights fore and aft. I (the journal's initiating editor) have been party to the oar rack debate, but ran across these images totally coincidentally in the course of unrelated research, and do not purport to know with certainty exactly what these carvings depict. However, having some knowledge of primitive art and the techniques of primitive artists, the following observations are offered: When depicting things actually seen and/or familiar in their lives, primitive artists tend to minimize or drop unimportant or unimpressive details, while those things which are considered most important or which visually impress the artists are included and given prominence. When depicting the number of things seen, numerical accuracy is almost always adhered to in cases of one or two items unless perspective hides one or more, in which case the hidden items may or may not be shown, and is usually adhered to in cases of three items, but can not be depended on above that point except that more than three items are unlikely to be depicted as three or less. Thus, in both images below, the artist obviously either knew the items being depicted were important enough, or was sufficiently visually impressed by them, to include them in his not very detailed carvings. In the case of the five Y-shaped uprights we can be reasonably sure there were more than three such items sticking up in the ship, and in the case of the other image, that there was one upright fore, and one upright aft, of the mast, which may have been in line with the mast or else offset to port, and in the latter case there would be the possibility of a second set on the starboard side not shown due to the artists perspective. (Images current unavailable - will be restored soon)

Anyone knowing of extensive and/or definitive research having been done on the subject of oar racks is asked to send the journal a citation of that research. If no such definitive exists, the journal would welcome copies of any additional images of ships created during the Viking era, or citations of historical or archaeological works, that show/mention the existence or absence of oar racks (or what appear to be oar racks) on Viking ships. (If someone has access to a collection of Viking era produced images of ships comprehensive enough to produce meaningful data, a statistical and descriptive analysis of them relative to the question of oar racks would be an excellent subject for a brief article for the journal)

(Images are from Helge Ingstad's book, Land Under the Pole Star. Copyrighted material reproduced under the terms of Section 107 of the copyright law governing fair use for non-profit educational purposes of criticism, comment, news reporting, teaching, scholarship, or research.)