Tuning the rig on a Precision 21? someone please explain

[eaglecreeksailor22]

I read someplace that a P21 delivers poor performance if the rig is not tuned/balanced. I know that using a Loos's gage
to adjust standing rigging is needed. But with a furler how to do that, I do not plan to race on a regular basis but would like the boat to sail well. I did sight up the mast groove and adjusted to a straight sight line, other than that nothing else. Advice and suggestion welcomed. Thanks, Rich.

[Brian N.]

Hi Rich -
I don't have a P21 but from my time on the forum (old and new) this topic has been discussed many times. Foremost, as you mentioned, the mast must be straight side to side, accomplished by shroud adjustment. Rake should be slightly aft by just  couple of inches at the top of the mast (this is what I inferred from previous older threads).On the P165 it is barely an inch or so. Mast bend is accomplished with your backstay and to some extent the shrouds and halyard tension. Mast bend of course varies with conditions. More directly to your point, is the tension on your stays. In general piano string tight is too tight, and in moderate conditions (8-12 knots) the tension on the leeward side shroud should not be slack, but "soft". I have no idea what the Loose gauge readings should be, but they measure the tension in a "static" state without wind pressure. Tuning your boat's rig is a compromise with the average sailing conditions. If you were in a one design racing fleet, it would be critical and an ongoing process for each race. For the average sailor, "close" is good enough. I keep my rig fairly loose as summer sailing here is generally in light winds. By loose I mean it takes moderate hand pressure to bend the windward shroud while reaching, but not slack on the leeward side. Hope this clarifies things a bit.

[JGrahamK]

There is a good discussion on how to tune the rig in the "New Trailer Sailors Guide to the Precision 18." This is book is useful for your P21 as well as other Precision boats. It's available for free at https://www.precisionowners.com/ScottBook.htm

[pgandw]

In addition to the Loos, a tape measure will help you get the same result consistently.  Using duct tape, I attach the loose end of a 30+ft tape measure to the main halyard.  I hoist the loose end up to the top, and use the measurement to the stern chain plate to set the mast rake, using the forestay and the swept upper shrouds (backstay is left loose during adjustments).  ODay Mariner racers have documented their base settings for the rest of us to use.  In the case of the Mariner, mast rake also has a profound effect on the amount of weather helm you have.

I then use the tape measure to the shroud chain plates to make sure I have the mast centered - much easier than crawling and craning and sighting up the mast in my old age.

Fred W
Stuart 19ft Mariner #4133  Sweet P

[Brian S]

You can also download Selén Mast's tuning guide from here: https://support.seldenmast.com/en/technical_info/rigging_instructions.html It's the "Hints and Advice" section. My word of caution on this, though, is that for my '84 O'day, I think their recommended rig tension is far too much for the design of the boat, it not being a racing specific design, and tensioning the rig they way they recommend puts too much tension on my mast step and chainplates. 

There is a lot of debate, and debate I've had myself, about mast rake. I think the best way to figure mast rake is to go out and sail in some consistent wind up to 10 knots, and see how the boat feels. If there's too much weather helm, slack off the uppers and backstay, and take up on the forestay. It's there's lee helm, or the boat doesn't head up reasonably quickly, slack off the forestay and take up the uppers and backstay. (For boats with swept spreaders, which the P-18 has. I don't think the P-23 has swept spreaders.) There is no measurement for rake for boats that don't have an aggressive, established racing class, where people will play around with rig settings and share their results. Pgandw (Fred W) above suggests a rake measurement from an O'day Mariner. That won't help with a Precision 18 in any way, as they are completely different boats.

Be cautious with adjustment of the lowers. They are used to keep the mast in column side-to side. Sighting up the mast from the base, you'd be able to see if it was bending out to one side or the other. If you tighten your lowers equally too much, you can pull pre-bend out of the mast. For small boats like ours, my sailmaker said we should have about 3/4" of pre-bend (mast bending forward) which helps the main set, as well as helps prevent a mast inversion (where it bends aft.)

So, my tuning procedure is as follows: Using either the main halyard, or as suggested a tape measure brought up to the head of the mast (would use a surveyor's tape for this), make sure the mast is straight side to side by measuring to the chainplates. Then sight up the mast to make sure no bulges side to side using lowers to correct for this. Pull main halyard down the back of the mast to visualized that there is roughly 3/4" of pre-bend, primarily using backstay for this. (I'm careful about backstay, because on my boat too much backstay tension makes the mast above the hounds look like it's kinked aft, and that doesn't look good to me.) Make sure forestay and lowers feel fairly tight. Then go sail, and tune for weatherhelm, ideally so helm isn't heavy, and you get what looks like about 6º of weatherhelm (tiller 6º off the centerline), as controlled by mast rake. You want a little weatherhelm to have the rudder give a little lift to windward when close hauled, but not enough weatherhelm to cause drag and slow you down. In stronger winds @12-15 knots, have the rig tight enough that when close hauled, the leeward upper is loose, but not moving around.