From the Drawing Board
By John Welsford - Hamilton - New Zealand
Pet Theories on Seaworthyness
I have been involved in a debate on one of the Yahoo forums about seaworthiness in small craft and had sent off a reply to a protagonist of very narrow beam boats, his opinion based upon references in C A Marchaj’s
book Seaworthiness the Forgotten factor. Now that was written in part
as a response to the disastrous 1979 Fastnet race in which many lives and boats were lost. The basis of the research is the type of racer, mostly between 30 and 45 ft long and intended primarily for short haul coastal racing with occasional use for cruising. Compliance and Speed within handicap rules are the most important things for the designers. Not necessarily seaworthiness as the handicap rules were not necessarily sympathetic to the features that produce a seaworthy boat.
My opponent had asserted that the Sharpie native to the Chesapeake bay and Carolina banks was the most seaworthy of small craft. I would agree to a certain extent, in that it is particularly suited to its home environment and use, but wanted to make the point that there are other environments and uses . The wrong boat, in the wrong place is not going to give good results.
I thought that some of the points I was labouring to make about seaworthy hull forms might be of interest, so here is my latest posting. More or less, I’ve added a bit.
“ I cant find, in Marchaj, (and I have Sailing Theory and Practice, and The Aerohydrodynamics of Sailing buy the same author) any more than a suggestion that narrow beam is one of several key factors in reducing roll.
I can, though, find references (across the three books) to other boats that evolved in really rough places.
Now I accept that people will look out over Chesapeake Bay and the Carolina banks at times and wonder that I dare suggest that this is not as tough an environment as places like the Bristol Channel, the English Channel ports and the Brittany coast for example. But those latter are on the lee side of the North Atlantic weather and current systems, have huge tidal currents and a very high proportion of gale force winds.
They also all of them have deep water in most of the boats operating areas.
The sharpie is peculiar to the Chesapeake and the area south, all shallow waters, bars and flats. The weather has the moderating influence of a large continental mass and its on the windward side of the weather systems so has light and moderate weather for a large enough percentage of the year for a boat that will stay home in bad weather to be economically viable which is not the case in the ports above.
I hear your comments about 6/1 beam length ratios, and in fact use that for the flat bottoms in my small boats, but with very rounded and flared sides to add stability. I note that the 6/1 ratio may have originated with Chapelle who found that it was common among the flat bottomed sharpies, but noted that as the vee bottomed Nonpariel and round bilged Presto Sharpies began to be built the beam gradually became wider.
I think that 6/1 beam length ratio issue is about waterflow around the chines rather than anything to do with roll stability or resistance, and note that Bolger for example has been able to go wider by having much more rocker.
I draw small boats for a wide range of climates, environments and uses, and don’t like drowning my clients so spend quite a lot of time researching historical and contemporary designs to see why they evolved to be what they are, how that relates to the conditions that prevail, and monitoring the performance of the boats that are built to my designs.
In my research I look for an environment similar, or slightly worse than the one I am designing for, and in the case of New Zealand where I live the best corollary is that area around the south of England, the area from the French Atlantic Coast down past Portugal, Western Ireland and Scotland and also the Caribbean where small keel fishing boats were highly developed and very seaworthy. There are also good examples of very seaworthy small boats from the Western seaboard of Scandinavia,
Colin Archers famous rescue boats being only one group of examples.
All of these areas have high proportions of high onshore winds, the Caribbean included. Relatively shallow waters where the whole several thousand miles of wave fetch builds up onto a continental shelf and is exacerbated by very fast currents against the tides, and fishermen who don’t eat unless they are out there fishing.
The configurations that come up repeatedly in those areas once the local style and decoration has been stripped away is a very powerful boat (I am talking 18 to 28 ft long here) about 3/1 beam, sometimes more and sometimes less but never far from that. They have long, relatively shallow keels, most have built down garboards and slack bilges, low but large rigs, and long waterlines for their lengths. They are relatively heavy, but are sailed singlehanded a lot, and are expected to be handy enough to fish the lobster and crab fisheries in among the rocks and reefs long the cliffs of their home ports. To claw back out to sea in some of the weather that these guys fish in requires a very capable boat with lots of power.
Interestingly there are strong similarities here between the cross sectional shapes of these boats and the Contessa 32 that Marchaj found to be a shape highly resistant to capsize. Even stronger connections can be made between the likes of Lyle Hess’ Falmouth cutter range of boats and the much older but legendary International Folkboat.
You could take one each of the indigenous fishing craft that I mention from France, one from UK and one from the Bahamas and put them each one into the others environment and they would perform very well. But even Commodore Munroe would have sat by the fire and grumbled about the weather if asked to sail his Presto off Falmouth on a bad day. Inside Falmouth harbour in a gale, maybe but not out in the really nasty stuff.
I know that he ran river bars regularly, and that the waves in those situations are pretty dramatic, but suggest that like Dave and Mindy of Paradox fame, he was smart, showed good seamanship and sat and waited for the right conditions. The one thing that the shallow Sharpie has that the others don’t, is an ability to retain control when surfing which would certainly help in a big following sea as long as the person on the helm was fresh and strong.
I do appreciate the Sharpie, but believe (from experience as well as
theory) that the Sharpie is a creature of her environment and is particularly well suited to that. A Falmouth Quay Punt with a draft of about 5 ft will not work in the Sharpies home waters, but that does not mean that the Sharpie is of necessity the more seaworthy, just better evolved for its environment.
Some useful references:
Marchaj - Seaworthiness the Forgotten Factor
Marchaj - The Aerohydrodynamics of Sailing
The Chatham Directory of Inshore Craft
Chapelle - American Small Sailing Craft
Bolger - 30 Odd Boats
Leather - Colin Archer and the Seaworthy Double Ender