I have some concerns regarding the pointing ability of my sun odyssey.(tack angle 110 degrees) I believe if is due the set up of the standing rigging and mast alignment. Can anyone help with settings such as rake and prebend. The forestay has an excessive amount of sag in light breezes (under 10kn) The leeward shrouds rattle at around same wind strength. I'm aware that I will need to tension the rig approx 15%. The boat does not have an adjustable backstay and is a mast head rig. previous sailing experience on a Beneteau 40.7 (part owner, raced on east coast of Australia) and on an Etchell
maybe Hoppy will pop in here, he has an SO40 down under somewhere.......not sure what his settings are set at. My older 85 Arcadia, I use 15% for the most part, with winds over 20 knots solid, I like 20%. I find as little rake as possible gives me the least amount of weather helm. Make sure your spreaders are level to slightly up. I send someone up the mast with a tape to get both ends the same distance to the deck. I literally make a mark on the deck using a sharpie pen, that i can use for ALL the measurements I need from the mast to deck. I make this back from the tack with a tape also. SO both sides are the same distance from that point. Try to satay with in 1/8" to no more than 1/4"......swag about 2-3mm max 5mm port to starboard etc.
Sorry to say that I am clueless when it comes to rig tuning. Mine was performing very different on tacks until I had a rigger do some tuning.
I did find this in the owners manual and maybe it is some help.
TRIMMING An agent has proceed to the first adjustments and cable tension. After few trips you will have to do the final adjustment to obtain a correct rectitude in transversal; it is also important to keep the mast rectilinear in longitudinal when sailing. Therefore, it needs compensation adjustment along side; a first bending of the mast in longitudinal is required : the middle of the mast bended forward and the head afterward. The bend must be the half of the mast section.
COMPENSATION ADJUSTMENT: 1 - This is a pushing spreader rigging, so you will have to stretch the upper shrouds before the backstay. 2 - Stretch tighly all the rigging ( the rigging must be a little bit loosely when sailing with 15-20 knots). 3 - When a perfect transversal and longitudinal rectitude has been obtained, ease t h e both side aft lower shrouds with 2 turns of bottlescrew. 4 - Finish longitudinal adjustment by stretching tightlier the backstay bottlescrew to obtain a good stability of the forestay when sailing by 15-20 knots. Fasten with pins all the bottlescrews and keep this trimming during all the sailing season.
May I suggest that your forestay sag is the first problem, and the most important to attend to first. With excessive forestay sag, the sail draft will be too deep and too far aft, and no amount of fine tuning will make a difference to balance or pointing, or even rounding up in a gust.
Hoppy's post is right on topic, first understand your rig. Slowly adjust that slack out of the shrouds a turn or two of the turnbuckle at a time on each side, until you have the mast straight, vertical side to side and perhaps a slight rake aft and light tension all around. Then, either use the Selden method with a tape measure or eventually get a Loos gauge for your wire size, and tension up a little, keeping the mast straight. Some tension on the shrouds, combined with the spreader pushing action and the lower shroud tension will start to tighten the forestay. Similarly with the upper spreaders. With a Masthead rig, you will also need a little tension on the back stay(s), again using the turnbuckle, to add a bit more tension to the forestay. When you are happy with it all in those light winds, you can then use a Loos gauge, or the tape measure again, to tension it all a little further to get the full recommended tensions for higher wind strengths. You can't fully eliminate the sag, but you can get it back to near what the sail maker anticipated when the curve of the luff was cut.
When you have the forestay sag minimised to your satisfaction, you can have a good look at the sail and decide whether it still has a satisfactory shape, or is somewhat stretched and baggy. If you are not sure, take a wide angle picture, looking up from deck level near the boat centre line, and take it along to discuss with your sail maker.
With minimal forestay sag and a good sail shape, then all those finer adjustments will make for a race winning margin in a close race, but without it, they won't make a useful difference. I think we will all be interested to hear how you go, and how much you can improve that tacking angle.