by Scott Welty
Cruising by Sail Definitions:
1. Repairing your boat in exotic ports all over the world
2. Long stretches of relative peace and boredom separated by brief moments of abject terror
3. Not being able to go the direction you want to go.
In this article I’d like to deal with the third definition (while I’m currently “enjoying” definition #1).
So often we have a decent wind and, sure enough, it is right in our face for where we want to go. The sea conditions are choppy. What do you do?
Motor straight into it with bare poles.
I see many Lake Michigan sailors take this approach. When they discuss their day they’ll say, “you know we just wanted to get there”. I find this the most uncomfortable attitude to put the boat in. Let’s face it, these are rotten power boats by design! A long day of hobby horsing and crashing the bow (which is up higher when on the motor) into the chop is not a fun day. There is nothing wrong with motor sailing but let’s not forget the sailing part!
Motor with the main
Two things will happen if you raise the main and keep the motor on. 1. The motion of the boat will be calmed by the damping effects of the main moving through the air. 2. If you can bear off a little to keep some pressure on the main your speed will increase AND your motion will be even more sailboat like and less hobby horse like. But we want to GET there and now we’ve had to bear off to keep the pressure on. Ah Ha! Remember, since you are having maybe an uncomfortable day, you don’t care how far you sail; or you care how long you sail. So the question becomes as it often does in sailing and in this article: How much direction would you give up for how much gain in speed?
In this case let’s say that going dead into it in some chop you are only making an average of 3 knots. This is not unreasonable on our Catalina 30. She’ll do 5+ knots on the motor alone but heavy chop and head wind will knock this down considerably.
So we raise the main and bear off until the main fills and we get some push from it. Now we want to sail from A to B but we are going to bear off and sail a new direction. The new velocity has to have the same or better ‘velocity made good’ (VMG) to make this worth it.
Your VMG is just your velocity projected back onto your rumb line. As seen in figure 1, the more you lay off the rumb line the faster you have to go to have the same VMG.
As the graph in figure 2 shows…Raise your sail and bear off, brother! For example, if you bear off 20 degrees and can get your speed up to about 3.15 knots or greater you are going to be more comfortable and get there in the same time or SOONER!
Of course you might turn off the engine and raise all sails and start tacking in true sailor fashion, “clawing your way up the coast” as Hornblower would put it. Now at the best you are going to be 45 degrees off the wind. It is still the same graph you just want to look at angles around 45 or 50 degrees. (see figure 3)
As expected this requires a more significant increase in speed to about 4.2 knots but this ignores any leeway. There is nothing wrong with keeping the engine on, though! If the boat is in a more comfortable condition, you are not pounding into the head seas AND you get to mess with your sails - go for it! For me it sure beats the heck out of chugging straight into the slop.
Sailing Down Wind
The other extreme is being on or close to a dead run. If you fly a spinnaker or go wing and wing the question is about the same. If I’m not so comfortable with the wind dead aft, but that’s the direction I want to go, how much gain in speed for how much I run up? Maybe I run up until I can get on a broad reach. The question is geometrically a little trickier because it is not symmetric as it is when you are tacking. When you tack your VMG would be the same on either tack if you are tacking through around 90 degrees. When you jibe you would have a long run on a starboard tack keeping the wind at let’s say 120 degrees relative to the boat. Then you’ll have short run on the other tack to get the wind to be 120 degrees on the other side of the boat. See figure 4.
The graph in figure 5 shows by what factor you have to increase your speed for how much lay-off angle. Each curve is for a different wind direction to the rumb line. For example. If the wind is 10 degrees off of your rumb line (figure 5) and you lay off 20 degrees, you have to increase your speed by a factor of about 1.1 times what you were doing heading right for your mark. So, if you were doing 5 kts going for it you have to go 5.5 kts or better to make it worth it.
What we quickly see from the graph is that with the wind way behind you, you are almost certainly going to do better by running up 5 or 10 degrees. This turn only requires about a 5% increase in speed. At 5 knots you have to be able to increase your speed to 5.25 knots or better to make this course worth it. This does NOT take into account time spent jibing the boat. Certainly the longer the total run the less this matters. For cruisers, where a long down wind leg might be several miles the time taken to jibe is totally ignorable.
So, cruisers, yes we DO want to get there but that may mean being a clever sailor and aiming the boat where you don’t want to go!
Scott taught high school and college physics over a 30 year career which included a 4 year stint at Chicago’s Museum of Science and Industry. An avid Lake Michigan sailor, Scott and his wife Sue Budde retired from their respective jobs in June of 2005, sold their house, cars and most possessions and struck out to try their hand at the cruising life. Their goal is to get their Catalina 30 sailboat from Chicago to the Florida Keys and beyond.