Why not use GPS instead?
Why bother with paddles? After all, why go to all the bother and expense of installing paddlewheels and a compass when you could just use a GPS. GPS provides the same information (not actually – keep reading) at a tenth the price and a hundredth the effort. A GPS is already needed for position (which trumps speed and heading), so why even consider the paddle and compass?
For sailboats, if navigation were the only consideration, COG and SOG from a GPS would fill the bill. However, when it comes to using speed and heading to monitor and improve sailing performance, there are several things to consider before you dismiss the idea of using a paddle and compass.
- Current, even in small amounts, has an important effect on overall performance.
- It is not possible to calculate current unless you have both GPS and paddle/compass. Installing a paddle and compass in addition to GPS provides this important piece of data.
- Every tenth of a knot aligned with heading adds (or subtracts) about 2 seconds/mile of rating. The same current athwartship changes your true wind angle (as derived from COG) by 1.5°.
- It is incorrect to assume that inland water (i.e. the Great Lakes) doesn’t have current. Lake currents are unpredictable when compared to salt water currents, and currents of ½ knot and more are quite common (which is 50 seconds/mile). Not knowing what the current speed is and where it’s going can hit your performance hard.
- Since it is so important, knowing the current you’re sailing in can be used to take advantage of or avoid it.
- Sailboats themselves don’t know about current. (Learn more…)
- They perform by interacting with the speed difference between the water they’re sitting in and the wind they feel. Where the water happens to be going is irrelevant to the boat (it is relevant to navigators though).
- In the boat’s frame of reference, tacks are symmetrical; boatspeed and true wind angle is the same on both tacks (except for wind shear).
- Polar and target information is always given in this context.
- Since COG/SOG is relative to land and not water, anything derived from it includes current.
- If COG/SOG is used to calculate true wind speed and wind angle, tack data will be different on opposite tacks, and changes with whatever current you happen to be in at the moment.
- Using polar information and finding the groove on the new tack is therefore much more difficult.
- The inevitable changing apparent performance tend to erode the crew’s confidence that they can control and predict performance.
- When GPS is used instead of a wind sensor, wind direction is assumed to be the difference in heading between tacks.
- Then true wind angle is assumed to be the difference between COG and the last guess at wind direction.
- The biggest problem is that the wind direction guess is always old – minutes old. Wind shifts are not reflected in the assumed wind angle, so performance numbers based on it, including steering to target are meaningless.
- GPS also gives no indication of the magnitude of the true wind, so accessing polars is guesswork.
- If the tack isn’t perfect, the wind direction guess will be bogus.
- Wind shear makes the true wind angle different on the other tack. The wind direction guess will therefore be wrong.
Wind direction is the most important thing to know about when racing. Here’s why. If you only use GPS, you are pretty much up the creek.
The bottom line is, if getting the most out of your boat is important to you, then adding a paddle and compass is the only way to go.
No paddle = no current, wind solution or performance monitoring