I own a 1992 two cabin. It seems to strange to even me, but there is absolutely no doubt that I get much better performance on a starboard tack than on a port tack. The difference of about 1/2 a knot is obviously to everyone. Can anyone think of a logical explanation?
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Starboard Performance
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 jeffneedle |
Starboard Performance |
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Posts: 8 05/22/06 17:13:56 |
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lakandjc |
Starboard Performance | #1 | ||
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Posts: 144 05/22/06 17:48:24 |
Jeff:
Do you mean more speed or higher pointing or less helm, etc? Speed may be influenced by the knot log placement which on our boat is not in the center. On one tack there may be turbulence that would affect the log reading. I know ours certainly reads different on one tack or the other. Just a thought... James White Star #450 Puerto Vallarta |
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CaptNorm42 |
Re: Starboard Performance | #2 | ||
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Posts: 617 05/30/06 20:32:52 Moderator |
GPS Speed Over The Ground would be another test. Would get most accurate results if could tack straight up or down current so it is not a factor in the speed.
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Norm Perron, Hull #600/2 cabin, Aphrodisiac, Marina del Rey, CA |
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tinolanza |
Re: Starboard Performance | #3 | ||
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Posts: 212 05/31/06 23:50:36 |
Dancing Dolphin has always performed better on a starboard tack both in terms of pointing into the wind and boat speed. We are usually 0.2 to 0.5 knots faster on starboard. I had our rigger check the stays to make sure they were tuned and balanced. Another thought was the weight distribution, i.e. the galley, made for ballast on the starboard side (she is a 3 cabin model). The location of the knot meter is an interesting possibility. It is mounted slightly to starboard which would put it closer to the surface on a starboard tack. Does this mean more turbulence? I must give this some thought.
Tino Lanza, Dancing Dolphin (#739/3 cabin pullman, Westlake Village, CA)
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oscar |
Re: Starboard Performance | #4 | ||
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Posts: 475 06/01/06 06:42:31 |
If you imagine the impact of moving the rudder just a few degrees, you can imagine the impact of keel alignment, a much llarger surface, and also keel symmetry. With all due respect to Catalina, I bet none of our keels are aligned perfectly, and/or perfectly symmetrical. I wonder if the slight improved/degraded performance on one tack versus the other has something to do with that.
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ragtime |
Speed on different tack | #5 | ||
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Posts: 133 06/01/06 07:13:22 |
I think another possibility is that when the transducer is not on the centerline it is at a different depth on each tack. The speed of the hull passing through the water would be different at different depths because of the effect of the bow wave and the water itself is therefore also moving. The movement of the water due to the bow wave would be greatest at the surface and less at lower and lower depths. Maybe that would cause a slight difference in the apparant speed.
Gerry Ragrime C42 108 |
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jerrygagerman |
Re: Speed on different tack | #6 | ||
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Posts: 71 06/01/06 09:36:16 |
Our knotmeter, reading through the transducer, generally shows one half to three quarters of a knot faster when on a starboard track. However, the GPS SOG is the same when on either tack. Therefore, I would guess that off-center placement of the transducer is responsible for the variance.
Jerry Gagerman Current Sea two cabin #431 |
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captrick |
Re: Starboard Performance | #7 | ||
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Posts: 195 06/01/06 16:24:06 |
I've noticed a difference in both knotmeter and SOG with starboard tack consistently 0.5-0.7 kt faster. The current in SM bay makes interpreting the SOG difficult. But I have been racing on another 3-cabin and we consistently maintain or lead the pack on stbd and slip behind on port tack. Baffling.
Rick 704-3 |
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tinolanza |
Re: Starboard Performance | #8 | ||
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Posts: 212 06/01/06 17:42:24 |
Another possibility that would account for the performance difference is the offset backstay. Wouldn't this would favor the starboard tack?
Tino Lanza, Dancing Dolphin (#739/3 cabin pullman, Westlake Village, CA)
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yorkrose |
Re: Starboard performance | #9 | ||
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Posts: 261 06/01/06 18:20:28 |
Well, just to add a little variety, we consistently see up to 0.5 knot better speed on port tack. The paddlewheel speed and the GPS agree fairly closely on either tack.
The backstay is still located in the standard location, and the boat has a slight heaviness on the starboard side due to a generator set. Both of these conditions might favor starboard tack. There may be some asymmetry in the hull, the keel, the rig, or the sails, but I have not been able to figure out just what would cause the speed difference. Regards, Gene Fuller Yorkshire Rose, C42 #870 |
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470catalina42 |
Starboard performance | #10 | ||
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Posts: 58 06/01/06 18:36:56 |
I think that the location of the knotlog impeller is the reason for most of the difference in speed readings. The impeller is lower in the water on starboard tack, and the water in that area has to travel faster to get to the stern. Bernoulli's principle works for water, too.
However, I seem to point higher on starboard tack than I do on port. I wonder if the difference is the location of the luff groove in the furler. Because the UV cover is on the port side of the genoa, I use the port side groove to give a more gentle bend to the luff when rolling it up. This makes a more efficient airfoil shape on the luff on starboard tack. Could this be significant? Norman Duford Fortune Cookie Mark I, 3-cabin Fin |
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