I used a single Suunto compass with adjustable tacking bands for many years, and then switched to two Suunto jr compass's for reasons below. I found a single compass worked great on flat water, but to confusing to use in the ocean. The tacking angle on flat water was normally 90 degrees, but in the ocean always changing between 90-115 degrees on a TheMightyHobie18.

It became confusing in the OCEAN when the waves would NOT come from the same direction on the race course as the wind during the day. The waves continually change their height, angle and spacing in relation to the boat's sailing angle throughout the day, making one tack's VMG appear on the compass better on the other tack constantly change. The sea state/angle changes during the race, the tacking angle can be 50 degrees off the nose on one tack, and 60 on the other, then as the waves build/change AGAIN to 50 and 65 equals 115 degrees.

Sea state/wave angle affects your tacking angle. On the race course in the ocean with no land bearing, when your compass shows a 5-10 degree change you need to know if this change is due to the wind OR sea state/wave angle, because when you tack your compass reading will be WAY OFF due to sea state and wave angle on the other tack. The sea state/wave angle can change with proximity to the shore. The wave height, angle and distance between waves can change due to depth of water which could vary over the race course.

For me, there were to many constantly changing variables involved adjusting the tacking angle in short course coastal racing trying to figure out why it changed from one tack to the other due to sea state/angle, OR did the wind change? A compass that can adjust the wind direction for each tack is needed to compenstate for the sea state/angle on each tack, or two compasses would be more accurate. I'm not saying it can not be done with one compass, but it takes a lot of racing PRACTICE, and to know when NOT to use the compass. Then, throw in a variable cross current, and as it has been said many times before, "keep your eyes out of boat".

To selfteach some things what to look for when you keep your head out of the boat try a racing simulator.

For long distance sailing using a VMG reading (velocity made good) on a GPS is better tool to use when deciding which tack it more expeditious.