Tumblehome

Tumblehome (pronounced tuhm-buhl-hohm)

(1) In naval architecture, an inward and upward slope of the middle body of a vessel; of the sides of a ship: To incline or slope inwards, to contract above the point of extreme breadth.

(2) A conceptually similar shape applied, in reverse, to the upper body of an automobile.

1828: A compound word, tumble + home.  Tumble was from the Middle English tumblen (to fall over and over again, tumble), frequentative of the Middle English tumben (to fall, leap, dance), from the Old English tumbian, from the Proto-Germanic tūmōną (to turn, rotate).  It was cognate with the Middle Dutch tumelen and the Middle Low German tumelen & tummelen.  Home was from the Middle English home, hom, hoom & ham, from the Old English hām (village, hamlet, manor, estate, home, dwelling, house, region, country), from the Proto-West Germanic haim, from the Proto-Germanic haimaz (home, village), from the Proto-Indo-European tḱóymos (village, home), from the root tḱey-.  The (rare and probably extinct) alternative spelling is tumble home.  Tumblehome is a noun; the noun plural is tumblehomes.

The meaning of the word tumblehome has been well understood from its first appearance in the early nineteenth century but the origin has never been obvious.  Shipbuilders had for centuries been using variations of the design for a number of reasons but the first known instance of the word dates only from 1828 and then without explanation, suggesting the term may already have been in common use, at least within the industry.  An 1848 reference from a shipwright does however hint at some sense of novelty, noting “… the upper works usually incline towards the middle line, or as it is termed “tumble home”.  The word “tumble” to refer to the sides of ships appears to have been used at least as early as 1687 but the compound tumblehome seems not to have emerged for another hundred and fifty-odd years.  The idea always summoned was of the imagery of the sides of a ship “tumbling down” the slope created but why “home” was added remains a mystery, the assumption being it was based either on (1) an association with certain domestic architectural styles of the time (2) the romantic notion of the sea, to which the tumblehome falls, being "home" for sailors or  (3) the idea of a dilapidated house in the throes of "tumbling down", fallen bits an pieces accumulating at the bottom.

Big ships and fast cars

In automotive design (upper), the term is applied when the width of the cabin (cockpit or glasshouse) reduces as the height rises.  Although curved glass in the side windows of cars began widely to be adopted in the mid-1960s, thus creating a mild tumblehome effect, the term is applied only when it is sufficiently severe to be apparent to casual viewers.

In naval architecture (lower), the geometry is reversed, a tumblehome define as a hull which flares out as the sides approach the waterline.  Although in some vessels, the effect is barely detectable by the naked eye, it’s a technical term and applies to all hulls which dimensionally qualify.  The opposite, the classic shape for ships’ hull, is called the flare.

USS Brooklyn, 1896.

Tumblehome, unless taken to extremes, was functional in that it improved stability in warships under sail; sailing ships heel (they tend to lean over when moving) and tumblehome reduced this.  At the time, the biggest contributor to a warship’s mass on the upper decks was the guns and a tumblehome design, moving the centre of gravity lower, allowed armament to be maintained or even increased without further loss of stability.  Additionally, there was the benefit of making it harder for boarding parties to climb aboard.  In commercial shipping, vessels were long taxed on the basis of the square footage of a ship’s deck and fat ships with a pronounced tumble carrying the same freight but taxed less, were attractive.  Government fiscal policy thus influenced and distorted design and engineering principles in the same way tax arrangements of windows affected architecture and those on cylinder bores (adversely) affected engine design.

Lamborghini LP500 Countach prototype, 1971.

The Countach had one of the most extreme implementations, the angle meaning it was possible for only part of the side-window to be lowered but at least the Italians were more thoughtful than the Germans; in 1954, facing a similar challenge with the side-glass on the 300 SL (W198 1954-1957) gullwing, Mercedes-Benz simply fixed the panes, ventilation provided only by small quarterlights.  Neither flow-through ventilation or air-conditioning was available so driving in a gullwing could be hot and sticky experience and there's a reason they're sometimes seen being driven (at low speeds and not on public roads) with at least one door open. .  The tumblehome is used by high-performance cars because of the aerodynamic advantages it confers, reducing frontal area an allowing the curve of the greenhouse to be optimized for air-flow, lowering resistance.  Because of great advances made during the late twentieth century, refinements to tumblehomes no longer deliver the 3-5% improvements in a drag coefficient (CD) which once was possible, engineers now pursuing factional gains.  The origins in cars however lay in the quest for more interior space and for mass-market vehicles, bulging out the sides gained the odd vital inch and the technique, combined with curved side glass, has become almost universal although there has been the odd deviation.  Stylists are predicting tumblehomes are likely to become more exaggerated as sides need to be bulkier to meet more rigorous side-impact regulations and roof-lines are lowered slightly in the quest to reduce drag.

Lindsay Lohan in tumblehome blonde wig.

What professional hair stylists call “the tumblehome” is a triangulated shaping which is most cases can’t be achieved without an expert application of product and when sported by models on photo-shoots, it’s common for the angles and an illusion of volume to be achieved with engineering no more complex than a sheet of cardboard (cut to suit) being attached with hairclips to the back of the head.  The look can however be achieved with synthetics which can be persuaded sustainably to behave in a way human hair naturally resists and Lady Gaga (b 1986) made a tumblehome wig a signature feature of her “Fame Monster” period (2009-2010).  With natural hair, a tumblehome with hair a little shorter than that of Lady Gaga’s wig is sometimes technically achievable given the right hair and a generous use of product the sideways projection would be noticeably less.

Lady gaga in Fame Monster mode.

The tumblehome style with the exaggerated elongations al la Gaga is rarely seen and usually represents a lot of work.  However, many take about as much effort to avoid the similar geometry of the “pyramid head”: a triangular shape with a flat crown area which flares to a wide bushy shape at the ends.  A function of length and weight for those with curly hair, pyramids happen usually when the strands are of almost uniform length and the curls tend to “stack”, the weight meaning the roots sit flattest on the scalp while towards the ends where the effective volume (hair + space) is greatest, the curled strands move sideways, unlike the behavior of straight hair which is purely downwards.

Lindsay Lohan with pyramid head, Saturday Night Live, 2004.

Stylists recommend layers as the best tactic to minimize the triangulation, the strategy essentially to create longer, diagonal layers to frame the face, meaning the remaining curls “sit into each other”.  What this does is simply physics, the layering on the surface reducing the weight, increasing the percentage of the volume on the crown area and although some are resistant, the best results will probably be achieved if the hair is cut dry because it will be presented at its natural weight.  When wet, the moisture content will disguise the extent of the left-right movement and exaggerate the up-down.  The shorter the layers of course the more effective the amelioration but this can be too radical for some so clients need to be turned into realists.