This page includes information on the tuning of a keel-stepped rig. If you are looking for information on a boat with a deck-stepped rig please click here.
There are many helpful tuning guides around, giving the forestay length, and calibrations for each element of the forestay, diagonals and verticals of the shrouds. However, even in a one design, these guides can be difficult to put into effect for the first time. And how do you set up the rig on a boat where a tuning guide has not been written. So below is my way to get the rig fundamentally correct – a position which keeps the mast safe, and sail set-up efficient. It’s the method used when setting up a new boat.
The first thing to do is to get the mast standing firmly enough to hold the mast up without swaying about, but not enough to bend the mast at all. Using a central genoa halyard, ensure that the mast is vertical by comparing the halyard to each chainplate in turn until you are happy it is upright. Now we make sure the lower 1/3rd of the mast is 90 degrees to the waterline. You need to stand off the boat, side on to it, and judge by sight that it is standing perpendicular. You may need to alter the forestay, the mast foot and/or partners. In one way the keel stepped mast adds a complication, in that there is an additional adjustment at the partners, but its easier to get the lower mast standing upright. Tighten the lowers until firm and check again that the mast is perpendicular. Firm up on the caps, until firm, and D2s as well if you have a double spreader rig. Again, from off the boat, the lower mast should still be perpendicular, with the upper mast is now beginning to bend back.
If all is well firm up all the bottlescrews, a couple of turns at a time, each time checking the lower mast. As you firm up the caps, the mast will be bending more, and trying to bend the lower mast forward, and you need to tighten the lowers to bring it back to perpendicular. As you get to about the right V and Ds settings, check the mast is upright and in column in a sideways plane. If not tighten up the V or D that affects that “panel” of the mast, until the mast is completely straight.
From off the boat, you should have a nice even bend coming of the perpendicular lower 1/3rd of the mast. The bend now should be even, mast bending gently backwards, and the curve of the spreader tips equally forward. ( note that a very stiff mast may not get this “equal curve”, with mast being the least curved “side”, but that is OK, and is quite common with carbon masts). For the first time apply a moderate amount of backstay, and firm up the caps. (putting on backstay slackens the caps and makes it easier to tighten – letting backstay off slackens the lowers if you need to change them). Let the backstay off again and check the side view. With backstay on the curve of the mast increases, whilst the spreader tip curve reduces. Put the backstay full on, and the make sure the spreader curve has not gone into the same direction of curve as the mast. This should not happen under any circumstances, and more forestay tension will be required to stop this happening – the mast is overbending. This basic approach may take a bit of iteration to get right, and could take some time. Once there, and the rig tight, and the mast is a good shape, then you need to go sailing. With a good wind pressure, look at the mast and it should be upright in the lower 1/3rd (side to side this time) and perhaps bending away slightly to leeward in an even curve. But the leeward shrouds should not be overly slack – this means that the cap shrouds are a bit slack, and should be tightened. This is easy to do on the leeward side, say 2 turns on, then tack and do the SAME to the new leeward shrouds. When you have done this, ensure again the mast is upright and even side to side. Once back in the dock, get off the boat and check the lower 1/3rd for being perpendicular. Don’t rush all this, it can take a few sails and tweaks to get it all right, but once it is, the rig will be safe and secure, and efficient when sailing.
When happy with the results, measure and log your settings – they are repeatable year after year, very quickly and easily. Bring your genoa halyard to the mast and cleat it when firmly level with the upper edge of the lower black band. Swing this out to the forestay and mark your forestay/racing foil or furler foil clearly and indelibly. Measure from here to the deck below the forestay pin. Log this. Shrouds – If you have a Loos gauge, measure each in turn and record. If you don’t count the threads showing out of the top of the bottlescrew, or using a verier gauge to measure from the upper to lower stud of the rigging screw for each shroud.