Join Date: Apr 2006
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"why the boat might have been slower on the port tacks."
Actually, it is not unusual for a boat to be *slightly* faster on one tack than the other. Especially on budget-priced boats, the rudder and keel may not be installed perfectly true and the keel often isn't faired perfectly symmetrically, especially after years of pervious owners. But that's a difference of a fraction of a knot, something to bother racers not stop the boat dead.
"One thought that comes to mind is there may have been a current and the GPS was showing us the current speed. " Probably on the nose. The GPS shows your speed over ground ("SOG") not your speed through the water. You need a regular knotmeter with an impeller in the water to read actual speed versus the water. Consider this:
If you are in a car moving down the road at 30mph...that's like being in a boat moving through the water, and the airflow is analogous to the current moving the water, for our purposes.
Now, stick your hand out the window, fingers together, palm faing you, fingers forward. Your hand/palm/fingers is pretending to be the keel. When the keel is facing straight ahead, into the current, it simply slices through. But pivot your wrist a boat--swing the keel at an angle to the wind--and WHAM, your whole hand moves over.
In the same way, if your keel gets sideways to the current, your boat can be pushed sideways--and that's often not the direction you are trying to go in. And usually not "symmetric" for your purposes of tacking against the wind.
That's where navigation and tactics for racing (or even "We're cruising but we'd like to get ashore for dinner tonight") get more complicated. You need to find out the local currents, if there are current charts in any detail for your area. And then check the charted water depths, because local changes in depth (shallows) will change currents. In some places there will be reverse eddies, too.
Trying to figure out the real net effects, the totals of land shadows on the wind, shoals and currents, wind shifts, and getting the best boat speed OVER GROUND for all of that, is part of why racing can be more like a chess game than just watching the grass grow.
All the rest, hull differences, rig not vertical, crew weight, etc., falls into "tweaking". The gross difference, probably is from the current, as you suspected. If you don't have a knotmeter and can't install one for now, you can still time your speed through the water by throwing a piece of popcorn (biodegradeable, fish & waterfowl food) off the bow and timing how long it takes to get to the stern. A little basic math on speed/vs/distance, and that's how it was done before knotmeters. Still works.