I had been avoiding this thread like the plague for fear that it would devolve into an irrational expression of personal bias, but find that it has actually stayed pretty civil. In any event, there were a couple of points that I wanted to address:
Early on Boatman 61 suggests that the cats that flipped were old ones like Catalacs, Iroquois etc., due to the narrow beam. Talbot refers to the warranty that Tom Lack had against raising a hull
on his Catalacs and isolates the Iroqouis as it was 'designed by a dinghy
Let me start by providing some information about the designer
of the Iroquios - J.R. (Rod) Macalpine - Downie. He was not merely a 'dinghy sailor' but rather, was quite possibly the pre-eminent designer
and performance cats of his time. Rod's 'Thai Mark 4' won all six races of the 1962 European One of a Kind Regatta
. He followed that with 'Lady Helmsman', which won the first IYRU International Catamaran
Challenge in 1963; indeed, as I recall
his designs went on to win that presitgious cup for seven consecutive years. He was an incredible pioneer in the design of performance cats and his Lady Helmsman included the world's first rotating wing mast
. His 'Crossbow' catamarans won 5 consecutive 'Player's Fastest Sailboat' trophies with a top official speed of 41 knots, albeit one was unofficially clocked at at 60 knots in 1984. He and his partner Reginald White also teamed up to produce two hugely successful offshore racing
catamarans for Robin Knox-Johnston, including the 70 foot British Oxygen.
The Iroquois was perhaps the first performance cruising cat and its emphasis was decidedly on the performance end of the spectrum: it had relatively light displacement
, a fine entry and modified u-sections aft, a relatively high SA/D ratio, boards rather than LAR keels, a relatively high bridgedeck for a 30 foot cat (which in turn raised the Cg and the Ce of the sailplan), and a trampoline forward rather than the solid foredecks in vogue on cruising cats in the 60's.
The resulting boat was very fast indeed - I believe that one may have actually won the Round Britain race
in the late 60's. Unfortunately, it was early days for production catamarans and many thought that they could be sailed as hard as self-righting monohulls, or the non-performance oriented Prouts and Catalacs of the same era. Really it is no different than some of the 'modern' performance cats such as Chris White's Atlantic series: while they carry a LOA/BOA ratio of in excess of 50%, their huge SA/D ratio means that they need to be reefed early. A couple of years ago one capsized, in significant part because her crew were flying too much sail for the conditions.
The attack on narrow beam is also a bit simplistic. Yes, the ratio of beam to length is an important factor in reducing capsize
. However, there are many others:
1. LWL - just as with a monohull
, a cat with a longer waterline will be more roll resistant that a shorter one, all things being equal. It is worth noting that many of the early cats that capsized were much shorter than the typical cruising cat of today.
- just as with a monohull
, transverse stability increases with displacement. Again, many of these early cats were not only short (typically, 28 to 34 feet overall), but also had much less displacement than most current
3. A solid foredeck, as was used in most early Prouts and Catalacs, also increases the risk of pitchpoling as it allows seas to break on the deck
, with the potential of burying a bow. Furthermore, if a hull
is lifted it allows a greater underbody area for winds to catch and continue the roll over into a complete capsize
In spite of these disadvantages, incredibly few early Prouts and Catalacs capsized or pitchpolled. This is in spite of the fact that they were produced in relatively large numbers (I believe that the Prout brothers alone produced around 1000 cruising cats) and over the decades, many have completed (and continue to complete) successful ocean crossings, etc. Why did neither the Prouts nor Tom Lack ever have to pay out on their warranties against capsize? There are a number of factors that led these boats, in spite of their relatively narrow beams , short LWL's, low displacement and solid foredecks to remain capsize resistant:
1. Cg (center of gravity). A lower Cg increases resistance to capsize and most of the early Prouts and Catalacs had much lower Cg's (due in part to lower bridgedeck clearance) than the current
crop of catamarans. It should be kept in mind that beamier cats need
increased bridgedeck clearance as tunnel width is a huge factor in slamming: eg., a 12 foot tunnel will allow 50% more water
to enter the tunnel and come into contact with the bridgedeck than a boat with an 8 foot tunnel. Furthermore, a narrower tunnel allows a greater 'slick' effect, or shading by the windward bow for entry of seas into the tunnel. Finally, just as a relatively narrow Jeep or off-road vehicle can 'straddle' boulders or surface irregulaties better than a wider one, so too can a narrower tunnel allow a cat a better chance of 'straddling' surface irregularites in the sea.
In the result, a cat with a 50% wider tunnel needs at lest a 50% higher bridgedeck clearance (and many naval architects suggest that as beam exceeds 50%, the actual ratio and not just height increases). Accordingly, the Cg of the vessel also rises up and this reduces transverse stability.
2. Ce (center of effort) of the sailplan: Again, making use of the 'lever principle', a higher Ce for the sailplan increases the risk of capsize. As the bridgedeck gets higher, so too does the sailplan. This problem is compounded in many current cats by the use of flying bridges (eg, the Lagoon
44 and 45) which place the boom itself extremely high off the water
. So too, the flat-top mains that are currently in vogue also operate so as to raise the Ce of the sailplan and reduce transverse stability. Compare this with the relatively low rigs on many of the early British Cats (the Iroqouois excepted); consider the 'Prout rig' - a cutter
rig that was oriented more fore/aft, rather than up and down and one can immediately see that the Ce of the sailplans was much lower than virtually any current cat.
3. Windage - The greater the windage, the greater the risk of wind
or wave assisted capsize. Consider the high, slab sides of the design of most current cats against the earlier Birtish cats (in part in order to gain headroom
, as well as because the bridgedecks must be higher) - again, wind
and waves from abeam have a greater area (and less aero/hydo dynamic shape) to operate on. This also increases the risk of capsize.
Consider the following: what is more likely to sway side-to side in a cross-wind, or to roll over in a sharp turn, a sports car wih a low center of gravity and an aerodynamic shape, or a bus? Even though the bus is much wider, its higher center of gravity and greater windage due to slab-sidedness and height, all reduce transverse stability. Of course, in a catamaran
we must also add the much higher Ce for the sailplan of the new catamarans.
Simply put, to suggest that only older, narrower cats can capsize is incorrect. Furthermore, one must always remember that beam is only one of the factors that relates to lateral stability, or resistance to capsize.