One tack faster than the other

[Davidasailor26]

I've noticed that our Oceanis 37 seems to sail faster on starboard tack than port but I can't figure out why. I noticed it during our last couple races and at first thought maybe is was just the effects of current. Our chart plotter records all of the NMEA data it receives so I've looked at our average speeds close hauled for the last year, and sure enough starboard averages about 1 kt faster through the water and .25 kt faster over ground. The paddle wheel is mounted just to starboard of the keel, so I'm thinking that as the keel generates lift on starboard tack the transducer may be in the low pressure side of the foil where the water speeds up, but that doesn't account for the speed over ground difference. The boat seems to sit level at the dock, and I've noticed the difference regardless of the fill level of the water tank under the aft port berth. Any thoughts on causes I may have overlooked?

 

[kbuckley]

Is the mast centered? You can check quickly by pulling the halyard tight to the toerail on one side and then cleat it off and move it directly opposite to the other toerail and see if the halyard is still tight against the rail.

 

[Scott B]

Is the mast centered? You can check quickly by pulling the halyard tight to the toerail on one side and then cleat it off and move it directly opposite to the other toerail and see if the halyard is still tight against the rail.

I saw a video on this and they used a person on a bosun chair to put a heavy but equal weight on the halyard to give an accurate measurement. You can put uneven pressure pulling by hand and will give different results on either side.

I had the same type of problem and was able to adjust the mast to reduce the difference in speed on opposite tacks.

 

[kbuckley]

Good idea!

 

[JRacer]

Agree that checking the mast side to side is first. But here are a couple other thoughts.

Hanked on jib or roller furler? Wondering whether the entry to the jib is consistent from one side to the other?

Certain that the jib tracks are the same distance from the centerline from one side to the other?

 

[Davidasailor26]

Thanks for the ideas everyone. I'll check the mast with a weighted halyard the next time I'm there. It was stepped by the dealer at the start of last season, so it is possible that it's a bit off.

JRacer, we have roller furling for both jib and main. The jib is in the starboard track and the slot for the main is offset to starboard. I guess it's possible that this is causing some amount of disturbance over the sails that's more harmful on port tack than starboard?

 

[Captn TJ]

Before you go through a lot of mast trimming make sure it's not the way the transducer was mounted. I'd check the speed with GPS to rule that out