Performance difference on starboard and port tack

[joakimharlin]

After one season with our 39i Performance 2008 model we were pretty surprised that is sailed markedly faster on a port tack compared to a starboard tack. The broker rigged the boat but we tightened the turnbuckles at the deck to take out leeward slack. The shrouds seemed to have similar tensions on starboard and port sides and the mast was pretty straight and yet we experienced this difference.

Anyone with similar observations and ideas of the root causes?

Thanks
Joakim

[MalcolmP]

Joakim

are you checking the speed using a GPS? The paddle wheel logs can be slightly twisted so can give a false reading

Malcolm

[Don Reaves]

My SO35 behaves differently on port and starboard tacks. I've always suspected weight distribution differences, as well as minor issues in tuning the rig. But it's hard to know for sure.

I've never gotten a good measurement, because the wind and waves are rarely from exactly the same direction. Since each has an effect on the boat's speed, port and starboard tack will inherently behave differently. But now you've got me thinking about it, and I'll attempt to quantify the differences.

Have you measured whether the mast is perpendicular to the deck athwartships? Shroud tension alone won't tell you this. If you can haul a wire or tape measure to the top of the mast and use it to make measurements to corresponding points on each side of the boat, you can get an idea whether it needs adjustment.

Don

[tean]

Don's suggestion, to check if the mast is upright athwartships is the right starting point. You can simply adjust the main halyard to just reach to the shroud plate on one side and cleat it off, then move across to the other side of the boat and see if it is exactly the same.

If the mast is leaning, it will mean that the genoa will touch the end of the spreaders on one side when sheeted in closer than on the other side. You will be sailing lower (and faster) on one tack and higher (and slower) on the other.

Also when moored up, lay down on your back on the cabin roof and sight up the mast luff groove to make sure the mast is not bent athwartships. Sideways bend in the mast will alter the slot effect between Genoa leech and mainsail from one tack to the other enhancing one tack and detracting from the other.

The genoa cars should be set back the same amount on both sides too (so that all 3 genoa telltales lift together as you luff slowly).

[Don Reaves]

I hesitated to mention using the main halyard to measure the location of the mast because rope halyards stretch. You have to be very careful to put the same amount of tension on the line while making the measurement. It can be done, but you need to be careful.

Don

[MartyB]

The other issue with using a halyard, is many do not come out the center of the mast, most of off to one side! so one almost needs to raise a tape measure with both halyard and actually measure the port v starboard distances.

Marty

[joakimharlin]

Thanks for all tips and suggestions, as regards how the speed was measured I relied on the fixed instrument, i.e. could to some extent be a paddle wheel issue. But I do not think entirely. Next year I'll measure this more carefully also using the GPS speeds over longer stretches. I started noticing this difference late in the season when 'racing' other boats upwind in moderate winds, flat water. We gained on port tacks and fell behind on starboard - also pointed lower. I also suspect that shroud tension differences and mast lean athwartships could be the culprits.

So called winter here in Stockholm, tarp on top and only soil under the keel ...will have to wait till next year.

Cheers
Joakim

[so40gtb]

I have the opposite issue with my SO34.2; it favors the starboard tack. I had the boat yard's rigging crew check it out at launch last year, but they reported no deficiencies.

Since I have to go up the mast anyway after launch in April to troubleshoot and repair the VHF antenna and check out what looks to be a bent masthead fly, I'll perform the suggested measurements and see what's revealed.

Ignoring the apparently misaligned masthead fly and balancing helm/trim by sail behavior only did not seem to resolve the problem last season.

-- Karl

[bacoll88]

Just discovered this forum and am excited already.

Had the same issue on my 39i, pointed higher and faster on starboard. The halyard trick works great expecially when there's a noticeable difference. My rig was leaning to starboard (although it looked straight) a full two inches. Tuned it yesterday and went out with a nice 8 knots. What a difference right away.

Brian

Hudson River

[MalcolmP]

Jul 21, 2009 19:32:54 GMT bacoll88 said:

Just discovered this forum and am excited already.
Brian
Hudson River

Brian

Welcome to the Forum , Glad you found us

also checkout our main site at www.jeanneau-owners.com and also consider registering there

Malcolm

[renegade27]

I also see the same - for my boat port tack is faster. I checked the port/starboard mast lean using the main halyard (with all my weight to stretch) back to the stern pulpit. I've always been taught that the greater distance gives better accuracy.

Are others measuring to the port/ starboard rail or chain plate? Tension on the port and starboard are equal, but I can see how this could be irrelevant.

[MartyB]

Tension can be the same side to side, even if the mast is not straight up and down, so tension is only part of the equation.

I usually measure from a point on the bow back along the rail mark this point and measure this way, that way IF a chain plate is not equal on both sides some how, then I have at least done IMHO a better measurement for side to side.

Marty

[nefes]

Could anyone send me the polar diagram for Sunlight 30? Nefes

[martti]

I got Polar diagrams for my SO 29.2 from local Jeanneau dealer. Maybe one option where to start asking.

Is there place where all those could be uploaded and collected ? Those SO29.2 polar's are attached in one tread and maybe difficult to find if anyone looks afterward.

Br,
-Martti

[so40gtb]

Recently did an exhaustive resetting of rig tensions on my SO34.2, which seems to have lessened, if not eliminated, the boat's favoring of starboard tacking over port.

Despite the yard's claims, my shroud and stay tensions were far from optimal - or symmetrical.

First, I calculated the backstay tensions needed to place the forestay at 15% of breaking strength. I then released the shrouds and set the backstays to the values calculated.

Next, I set the top shrouds at 12% of breaking strength. This may be a bit low, but it was well above where the rig was before I started. The middle shrouds were set to 10%. This takes some of the tension off the backstays, which were left alone.

Last, I calculated the stresses necessary in the lower shrouds for neutral fore-aft forces and approx 8% of breaking strength in smaller, 6mm shroud.

Tacking with the wind in the mid-to-upper teens, my top shrouds were taut windward and leeward, the middle and lower shrouds "just taut" to leeward. Mast bend was smooth on both tacks, though a bit more tension in the uppers may be in order.

More tweaking to do, but progress so far.

-- Karl

[so40gtb]

Despite the report above, I had a mast leaning to port. Some more trimming of tensions in the upper shrouds and backstays seems to have cured this. My upper shrouds are now arount 15% of breakiing strength. The aft backstays are not where they were, but better than where they started. Haven't been out in mid-range winds (15 kt or so) since the last tweak.

[Black Diamond]

I have a 39i Performance, I recently moved the batteries all to the starbaord side under the aft cabin. This moved over 200 pounds to the other side, net differencial, 400 lbs. Lets me put more stuff in the storage locker and still be balanced.

www.radonic.wordpress.com - Blog on our 39i Performance called Black Diamond