{"id":6684,"date":"2009-09-07T09:00:21","date_gmt":"2009-09-07T14:00:21","guid":{"rendered":"https:\/\/setsail.com\/?p=6684"},"modified":"2009-09-07T08:08:15","modified_gmt":"2009-09-07T13:08:15","slug":"speed-length-ratio","status":"publish","type":"post","link":"https:\/\/setsail.com\/speed-length-ratio\/","title":{"rendered":"Speed Length Ratio"},"content":{"rendered":"

\"Wind-Horse-11-knots-3\"<\/p>\n

Over the past year we have posted photos of various craft and their bow and stern waves as an indicator of efficiency. This is judged in terms of Speed Length Ratio (SLR) or the boat speed divided by the square root of the waterline length. In the photo above, sent to us by a cruiser in Scotland, Wind Horse<\/em> is doing her normal eleven knots. She has an 81 foot waterline, the square root of which is nine. Dividing eleven knots by nine gives us an SLR of 1.22.<\/p>\n

<\/p>\n

\"Wind-Horse-11-knots-3-2\"<\/p>\n

As you can see from the photo above there is not much bow wave (and we are full load here or about 44 tonnes\/92,000 pounds).<\/p>\n

\"Wind-Horse-11-knots-3-3\"<\/p>\n

The same is true aft. A nice clean release off the transom with little magnitude to the stern wave.<\/p>\n

Virtually all commercial vessels and displacement yachts operate at a SLR of around .9, or for Wind Horse<\/em> a little over eight knots. This would be more efficient for Wind Horse<\/em> in terms of mileage, but because of a variety of factors we have the option of cruising at eleven knots, in a vibration free and quiet environment. We can do this for in excess of six thousand nautical miles because of the factors which we have described in other articles on the website.<\/p>\n

To recap these critical factors for efficient cruising include:<\/p>\n