A Matter of Efficiency

by Howard Rice

As a former racing sailor and lifelong cruiser, I have had the opportunity to use and appreciate both ends of the sail rig efficiency world, these being high aspect and low aspect ratio types. Over time I have for the most part evolved toward the low aspect ratio end of the spectrum as I see advantages inherent in the type.

Sail rig efficiency is but one aspect of the boats we sail so for the sake of keeping this simple I'll put hull shape, keels, and centerboards aside and just focus on the sail rig aspect ratio question. I figure sail efficiency is the percentage of the wind energy put into a rig that comes out as a useful or desired performance, in my case cruising. I am not an expert, self-proclaimed or otherwise, just an observer of all manner of watercraft and a sailor. I do rely on my experiences and know this might sound a bit cheeky in a world chock full of experts (real or not) who believe in high-aspect triangular sails as "the way" so bear with me as I take a closer look.

Recently I ran into someone who elected to fire away at my choice of gaff-rigged yawl as opposed to Bermudan or Marconi rig for a small boat voyage I made down the Strait of Magellan and beyond. I chose and built the rig to suit the place I was exploring but he would have none of that. He was all about schooling me on the modern high aspect as being, "The way." His conviction was set in concrete and rather firmly at that. He emphatically told me I had made a poor choice in spite of my informing him how well the rig had performed and performs to this day. I asked why he was so emphatic and so he explained. "The Bermudan high aspect ratio rig is the hands-down global choice used by more boats than any other, therefore it must be the best." Hmmm, I thought. He continued, "The Bermudan is the most efficient upwind. For that matter, he continued, it is also the best downwind and in the event of the need to claw off a lee shore the rig has it hands down for any cruising sailor plus there is no gaff like you have to bonk you on the head." Hmmm, again with the caveat thought that I had to agree about the best upwind bit.

At one time I was an all-in racing sailor who devoured everything in print on the subject of performance. I have raced both around the buoys and long distance. For a very long time, I was all about the Bermudan rig as the best all-around just like my new acquaintance. It had to be if it was the choice for the fastest race boats. I firmly believed this as one of my first boats was an antique yet wickedly fast gaff-rigged Abeking and Rasmussen 22 square meter, the Vegesark (gaff rigged due to a modification resulting from a broken mast). I had fallen prey to a sort of group think or herd mentality believing the high aspect rig was the best choice for all sailors regardless of the type of sailing they did. Commercial yacht and small boat marketing by in large supported this premise.

Advertisements often touted features of the latest hot race boat design including the "High aspect ratio sail plan for excellent performance." I noted that with some exceptions this same tout of high aspect Bermudan or sloop configuration benefit spilled over to the marketing of many cruising and day sailing boats, both large and small. However, I can't recall any specific benefit for the cruising sailor being highlighted. When you boil it down the Bermudan rig is excellent upwind but the old saw goes like this, "gentlemen don't sail to weather" but when they do I believe a well-conceived low-aspect rig will do the job just fine.

Illustrations courtesy of Roger Barnes, The Dinghy Cruising Companion

Let's take a brief look at the term "Aspect Ratio" before I proceed with my argument that low aspect may be better suited for many small cruisers and day sailors. In general terms, it means length-to-width ratio. Aerodynamicists use the term because it is a good descriptor of the lifting-line theory applied to wings of a known span. In other words, the Aspect Ratio or AR is the wing span divided by the chord or thickness.

Here is a bit of aerodynamicist gobbledygook for fun. To define a variety of wing planforms our aerodynamicist friends measure AR as the ratio between the span of the wing and its chord. However, since wings like sails are rarely uniform along the length of the span they are most commonly calculated by dividing the square of the wing span by the wing area. Sailors on the other hand calculate AR this way. We square the height of the sail and divide by its area or we calculate the AR by dividing the height by the length of the foot of the sail.

So what good does this head-scratching do for us? Does it relate to or have an impact on efficiency under sail? For the airplane designer the AR calculation plays a major role in the design process, it's not everything but it is a huge factor in designing a wing form. It has everything to do with attempting to achieve less drag and more lift while minimizing the negative impacts borne of designing a thick heavy structure in the attempt to increase the aspect ratio. For us, waterborne folk's knowledge of what AR means can help us choose the right rig for overall sail rig efficiency, which includes ease of use, performance defined as speed under sail on all points, and how we use our boats.

High-aspect sails tend to have more lift for the area of the sail much like the long slender dare I say sexy wing of a sport plane. Lower aspect sails (generally square sails, gaff, lug, etc) offer more power with workhorse wing shapes akin to a thick chord plane wing of a Piper Cub or other classic tail draggers. Like the aerodynamicist, sail rig designers labor and head scratch to find a balance between these extremes.

For the round-the-buoys racing sailor, getting off the start line like a scared cat ahead and in clean air can translate into arriving at the weather mark first and this critical first beat often leads to a high placing at the finish line. Hence the need for optimizing weather ability. A higher aspect ratio rig will equal more available power off the start line, greater potential speed, and most importantly high pointing ability. In the case of round the buoys it's all about the weather leg first and foremost so the length of the leading edge of the head sail and main sail is critical for getting out ahead right at the start, allowing clear air and the potential to get ahead and cover another boat or much of the fleet. If we keep the sail the same height and add width (a longer foot) we likely don't get any more power upwind. Perhaps we get less. If we start two identical boats at the gun, one with a high aspect ratio rig and one with a low aspect rig, both with the same sail area,the higher aspect ratio would in most cases be first at the weather mark. Then the magic of the low aspect rig comes into play off wind with less hassle borne of not having to pull out, hank on, and hoist a larger head sail such as a genoa or spinnaker. The low-aspect sailor with the longer footed main and a big square chunk of sail area simply eases sail and off she goes.

High-aspect ratio rigs tend to have a narrower performance groove upwind than low-aspect ratio rigs. For optimal performance with a high-aspect rig the helmsman who can focus with knowledge of lifts and headers, while sailing at the edge of a breaking luff on the head sail will be fast. The low-aspect rig will be more forgiving as the optimal performance groove is typically more than a little wider. The real point to this statement is that most low-aspect rig sailors aren't racing around the buoys, but if they were a well-conceived low-aspect rig may be a big surprise at the weather mark. As mentioned, the real pay-off comes after rounding the weather mark and easing sail letting the powerful barn door of a sail do its thing, whether sprit, lug, or gaff rig. The high-aspect rig sailor will need a large head sail or a spinnaker to make up for the lack of sail area aloft when heading off wind. In addition, tall high aspect ratio sail rigs will produce power upwind and that power will often lead to excessive heeling before it's time to reef. Excessive heeling may look good but in reality, it doesn't lead to greater speed, just the opposite is true. A lower aspect rig with a shorter mast and lower center of effort will stand up longer and thus maintain speed.

Many high aspect ratio rigs tend to be sloops (Bermudan) and with two sails a solo sailor can have a handfull handling all that cloth when raising, lowering, or changing sails. A lower aspect rig in the form of a gaff-rigged cutter or yawl, for example, offers the solo sailor an advantage given that each sail is smaller in size and typically sails don't need to be changed out, only reefed or struck. Sail rig selection for the cruising sailor often comes down to "Just what is the maximum size sail you are willing to deal with?"

I happen to love the gaff rig as it offers more sail area for a given length of the mast as do most low-aspect rigs. For a given sail area the mast can be significantly shorter than a Bermudan. This can mean that the mast can be stronger and will require less complex rigging. The strength and stiffness of any column are inversely proportional to the square of its length. In general terms, a mast that is twice as long will fail with only one-quarter of the load, which means it has to be four times as strong or very well stayed often with spreaders and even jumper struts. This dividing up of the mast area into sections supported by appendages introduces more stress, greater potential for gear and fitting failure, more cost, and of course more maintenance.

In conclusion:

If windward sailing is of paramount importance, then of course the Bermudan rig has much going for it. However, for most of us who make cruises of short or long-duration, planning is key and good planning should aim at as much off-wind sailing as possible. Of course, if we go off wind and have to return to a launch site we will likely have to sail upwind, yet hard on the wind, hair-on-fire sailing generally isn't in the mix. A well-conceived, low-aspect rig including those varieties with a proper head sail and sufficient head stay tension will go to weather with the best all day. If your boat's keel, daggerboard, centerboard, or leeboard and hull shape are properly designed and coupled with a well-tuned, well-handled low-aspect rig, your boat should perform incredibly well on all points of sail. This performance will deliver a more relaxed sailing experience, less hardware, a shorter spar, potentially smaller sails, all in all, a better day on the water.

For most cruising or day sailing, keeping things simple and strong is wise. A simple rig is easier to use without the need for winches and wire halyards. If sails are set on mast hoops or laced, then life gets even simpler and costs lower. So for this sailor who cares as much about how he gets there as getting there, low-aspect rigs are a fine choice because they perform well, and dang they do look good. See you out there! •SCA•

Visit Howard’s website, the Pocket Yacht here.