Developing design criteria

Lets consider design criteria as were mentioned previously in the post about the Design process. I thought it might be helpful to examine one simple to understand criteria that has major design implications; SPEED.

First we need a frame of reference. All of us who sail would be pretty pleased if we could count on making a steady 8 knots in our cruising monohull sailboats, at least I know that I would be. As an example, we sail a Tartan 3700. It has seen 9 or 10 knots on occasion, but realistically when averaging all points of sail the boat is a 6 knot boat. Off course how the boat is sailed has a lot to do with speed. We sail under full main and 120% genoa up to about 28 knots. That may be pushing too hard, but when winds build we find it often easier to sail through it to our destination than to reef. If expecting more wind than that, well we usually hang out where we are with the dogs and enjoy an "Extra" day.

The next boat I spend a lot of time in is a Pursuit 2560 walk around with a big block Volvo Penta duoprop sterndrive. The boat pretty comfortably runs 25 to 30 knots. I burn around 100 gallons of gas on an average days of fishing. For the distances we run to fish that boat is really about the minimum in both boat size and speed. When it starts to get nasty out on the water 14 knots is much more the norm. In fact I have come to realize that most boat owners, especially power boat owners, trade up to larger boats so that they can run more comfortably in marginal weather. Sailboat owners seem to trade up in size to get more accommodations or a faster speed in any given wind.

The third boat I am in regularly is the torpedo stern launch that is shown on my website. The speed that it runs at is about 8 or 9 knots; and it does so comfortably in virtually any seas. It has an easy motion more like a sailboat than a powerboat. Fuel consumption is miniscule compared to the average powerboat, and filling a ten gallon tank only once or twice a season is really a joy.

Why do I describe these three very different boats? Because they are very different boats! You must know how you are going to use a boat to know if it will meet your needs. And you must be honest with yourself. If I lived on a place like Bass River on Cape Cod and wanted a boat for cruising up and down the river after dinner each evening, well then I would be spending my boating time at 6 knots in a no wake zone. If I was looking to fish east of Chatham for Bluefin Tuna every weekend during the season, well then being able to cover water more quickly becomes a necessity.

Speed is more complicated than this though, and determining how fast you need to go means nothing without simultaneously considering other major criteria. Is it a sailboat or a power boat that you are looking for? Is the boat for fishing, quiet evening cruises, or multi day adventures? What areas do you wish to use your boat around? If cruising, how many days do you have to use the boat in a row? How far do you hope to range? If you keep your boat on the Cape and never have more than four consecutive days to use it, and you want to cruise regularly to Newport Rhode Island or even Shelter Island in New York then you begin to develop an understanding of just how fast you "Need" to go.

Maybe the decision ends up being between a cruising sailboat and a cruising powerboat. Some people say "I'm a sailor" and hold the line, yet their lives don't allow them the time to go and see the places that they enjoy visiting. So let's talk about speed with relationship to sailboats and powerboats.

I would be ecstatic to be able to average 8 knots on all points of sail in our Tartan 3700. Yet like many people I would probably consider cruising in a powerboat at 8 knots to be painfully slow. Why are we like that? Consider 8 knots directly into the wind. Talk about making a difference on cruising westward into the usual south westerly blow here in Vineyard Sound. Don't get me wrong, I am not advocating for cruising powerboats over cruising under sail, you just have to be realistic about your goals to make sure you end up in the right boat.

Personally, I love to sail. I also love to explore new harbors. I would like to see more powerboat designs that can travel efficiently at ten knots with style and grace just as I would like to see more sailboats that can sail comfortably at 15 knots.

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