DRAGONFLY Trimarans User Forum

What are the common causes of this? I tried tweaking sail trim and tack angles, but seem to consistently go faster (8kt in 12kt true) on starboard tack than on port (6.5kt in 12kt), close hauled. Helm felt neutral on both tacks. Swell was ~1ft and from the same direction as the wind. I have a few theories but don't know how to test them, any ideas appreciated:

1) Asymmetric sidestay length. I measured the rope portions of the side stays to be the same when I tighten them, but this doesn't mean the wire side stays are exactly same length. I guess I could go up the mast and measure them directly - any other way?

2) Centerboard not pointing straight. There is some sideways play in the centerboard housing, could that be the issue? I guess it could affect leeway but why the water speed?

3) Water speed sensor is located about 1 foot to starboard, just in front of the saildrive. Not sure here, the main hull is not anywhere close to being above water there.

4) Unevenly positioned amas/akas. This is obvious the hardest problem to fix if true, but how can I measure it?

5) Asymmetric sails? The tape-drive part of the sails is on the SB side, could they have stretched so differently?

Anyone else has this?

Think I have experienced something similar.

My solution was to mark the rope controling the tension in the side stays - so I have a mark that shall be in the same position on each side.

And lets add: 6) mast rotation - does the mast rotate into the same angle on both tacks?

/.-)

Did you measure the tension on the rig with a Loos gauge?

I would start there- see what the tension on the rig and backstays on the starboard side. Seems that side is sailing better than port.
Then measure the port side - adjust accordingly to match the starboard readings.

If you balance the rig accordingly, you can eliminate that from the list.


Let us know the outcome.

Ted

My guess is that tension should be pretty similar even if length is uneven. In other words, small changes in geometry don't change tension too much (port tension should be roughly same as sb tension, because most tension is in the vertical plane). With the 26' beam and 55' mast a .5 foot shift off center in the masttop would result in <1% difference in tension. I also don't have a loos gauge, which costs $150+

I will try to make more direct geometry measurements today, using the main halyard.

Alas, this is not a rotating mast.

Ivan,

Are you measuring all this with electronic means, i.e. wind angle and speed through water/over ground?

If so, there are a myriad of error possibilities.
Current can affect sog, wind angle might not be perfectly calibrated, speed through water might not be linear, waves can affect it etc.

If the mast is vertical when the boat is unfolded and in still water (easily measured with a level or a plumb bob), have fun sailing and don't worry about it.

Hey Steve,
Speed through water. I need to add more observations through more conditions I guess.

If you were on the boat and saw it it would bug you to no end, I am sure.

So far the shorter bottom stay wires seem ok, only one (starboard one) is 1/8th of an inch shorter than the other.

measuring sidestays resulted in a tie -- port and starboard within .5 inch of each other. Also the boat manual specifically says "you don't need to get it exactly equal when tightening the backstays"... more testing needed. Thankfully another Mexican cyclone is passing by...

If the speed is not measured with a gps, I will first incriminate the speed sensor.