The Sarah Design

Over the years I have done a fair bit of sailing. I grew up in southern Tasmania. My family have always owned boats, beginning with dinghies of various classes, and later cruising yachts, ranging from an 18 foot pocket cruiser to the current S&S 36. We cruised the Tas east coast extensively, and even did a Sydney Hobart in 1994. Deb has been out a few times on the family yachts, usaly when doing the rellie run at Christmas. We have done a couple of Whitsunday charters.

When we started talking about taking a sabbatical for a couple of years I realised that Deb had been a bit spoilt by the Seawind 1160 we had charted in the Whitsundays. She loved the light and airy above waterline saloon and fully protected cockpit. Also another feature of cats is their ability to totally isolate the engines (and their smells) from the accommodation. Although not especially prone to sea-sickness, I knew she would rather do without the typical diesel boat type smells prevalent in comparable monos, with their engines within the hull.

Building and sailing Selah is a joint adventure. Deb by nature is courageous and supportive, and has confidence in my ability to make good choices about the boat. I wanted to make sure she would be as comfortable as possible and feel safe. I also knew that when cruising full time, the majority of time is spent at anchor waiting for the right weather pattern for the next leg of the journey. In this regard catamarans are hard to beat as a cruising platform, providing apartment like accommodation for the times we will be in port.

Financially we could not afford the half million plus price tag for a production cat, which led to the idea of building. I knew of the Easy family of designs by Peter Snell from Queensland, so I logged onto their site and was immediately drawn to the Sarah design.

The original Sarah at launch, Calboolture river, QLD.
The protected cockpit
Stern steps, targa bar and cockpit. Bridgedeck clearance is 600mm.

Designing a cat is a numbers game. Much like aeroplanes – every design parameter is intrinsically linked. If one characteristic is altered it affects the others. For example, wider hulls give more internal space; seemingly a good thing – except it that space is filled up with more “stuff” which adds weight, which in turn needs more sail area, which means heavier rig equipment, which means more stresses on the hull structure, which in turn means heavier engineering which means more weight, which means bigger auxiliary engines … and so on.

The Sarah design is an evolved design with moderate easily driven hulls with light weight but rigid specifications. A proper sailing boat, only requiring moderate sail area to keep her moving in most wind conditions and small outboards for auxiliary power. She is based on a series of designs with over one hundred boats of the same family on the water, spanning twenty years.

The especially clever thing that Peter Snell has done, is that he has managed to keep these basic parameters, while at the same time, by designing around standard material sizes, keeping waste material down to the minimum. For example, all the bulkheads and frames are based upon the standard 1220 x 2440 plywood sheet. The 22 degree stem means no timber lengths exceed 12 meters, which means only one scarf joint is required for the chines and stringers. Many of the hull and deck components are full, or lightly trimmed standard panels. This is no mean feat, and helps to keep building costs and time down.

Sarah number one under sail, en-route to New Caledonia, Western Pacific.
Master bedroom.

There are two basic categories of cats. “Enclosed Bridgedeck” and “Open Bridgedeck”. Selah is of the enclosed type. This means that the span between the hulls, is used for accommodation. The trade-off is that the hulls have to support the weight of a substantial bridge-deck floor and accommodation. Also, in order to provide headroom in the saloon, the bridge deck is placed lower, closer to the water, which at times induces wave slamming. This places an inherent limitation on a cats ability to sail quickly to windward. Properly designed cats are built to withstand this, but often the humans find the noise and motion stressful, and choose to slow the boat down for comfort.

The other limitation of cats is pay-load capacity. Selah’s will not be able to carry the same amount of water and fuel as similar size monos. This will necessitate more frequent visits to marinas and fuel depots. To maintain the benefits of a cat, she must be kept as light as possible.

Mono visitors to my building site have sometimes expressed surprise at the apparent lightness of the construction. I explain that there is a different mindset with cats. Rigidity is achieved through engineering, not mass. With monos, hull failure is generally a catastrophic failure, relying on pumps to stop the boat from sinking.  Cats have natural redundancy by nature of their design. They do not carry ballast to pull them down. Selah is designed with buoyancy enclosures. Each hull is separated into four separate watertight zones, with full height bulkheads. In addition, I will be ensuring the below waterline bilges in the accommodation area (the largest zone) are watertight between the bulkheads. The cabin floors will effectively be a second skin. If for example, a hull is holed by hitting a container or floating log, water ingress will be contained to the immediate zone. She will not sink. With two rudders and two engines there are options in case of failure of any one of these critical components. Even if we cannot get her back to port she will be habitable, until assistance arrives.

The other safety consideration is the possibility of capsize. Cats are not self righting. Selah has a width to length ratio of 50%. This means her inherent stability is immense. Instances of cruising cats capsizing are very rare. Also as previously mentioned, her rig is moderate and mast height low for her length, which keeps her centre of gravity low. Most importantly though, with modern weather forecasting there will be no reason for us to be at sea when we shouldn’t.