J24 Blog

Filed by: Brian

So Peter and I finally found some time to get down to the boat on a non-racing day to work on re-tuning the rig. We’ve worked on the rig settings a number of times in the last 2 years of owning the boat and have come to realize that it’s a process of continuous tweaking. What’s also helped is the level of understanding we’ve gained each time by starting back at zero and working the rig back up to what we believe is “optimal.”

Now, if you’ve ever tried to find information on tuning your one design sailboat’s mast and standing rigging you’ll inevitably find an avalanche of information available online. A great deal of that information will depend on the brand of sails that you fly, and most of this collective mass of information will prove to be inconsistent or contradictory across all the sources. Hence, it’s taken us 2+ seasons of working on it, and we’re still not quite there… However, once you hit critical mass from all that information intake, some things finally start to knit together.

More insightful information and a neat matrix after the click…

After our recent results in the Tuesday night one-design series at Leschi, we once again found ourselves brainstorming all the possible ways to improve our performance. More time on the water and more fleet races under our belts would help for sure, but the typical questions of whether the boat was setup and prepped correctly always pop up. I dug back into our sailmaker’s tuning guide. This time a couple of statements seemed to pop out differently than before. In the section on rig setup in our tuning guide (Shore sails guide) the author focuses on some details of forestay tension and pre-bend that other guides gloss over. This prompted us to really focus on getting the right balance of the two for our rig.

I think most other guides assume that if you set the mast butt in the right place and set the uppers and lowers to the tensions that they spec that the pre-bend and forestay will automatically be in the right settings. On our boat that was certainly not the case.

This prompted us to re-tune our boat with a single minded purpose of dialing in the right pre-bend and forestay tensions. We started out with this chart constructed with information from our tuning guide. (These forestay and pre bend settings are for Shore Sails.) Note that we left the shroud tensions blank. The tuning guide does give us some as a reference starting point, but it’s clear that you need to find whatever combination will get you to the right forestay and pre-bend settings for your boat. The shroud tensions themselves don’t matter; they are only a tool for getting the other settings correct.

This all probably seems pretty obvious if you already know how a sailing rig works. But when you are new to the sport and all the other tuning info skips this critical point, it’s easy stuck with a bad rig setting. On our boat, when we setup the mast butt in the “correct position” according to the guide, then dial up to the prescribed shroud settings for 5-8 knot wind, for example, we were getting WAY too little pre-bend. So our main would look nice and full on the race course, but actually be too full for optimum speed.

Here’s and excerpt from the tuning guide that describes our situation:

“If the mast butt is positioned too far forward, the mast will have too little pre-bend resulting in a main that is too full and susceptible to backwinding. The headstay will be too tight resulting in a genoa that is under-powered.”

And

“Prebend Light Air
…The exact opposite to overbending can happen in light air. The luff curve in the sail has too much curve in it relative to the mast, or, the mast is too straight. This is much harder to detect than an overbend wrinkle, but it is every bit as disastrous to performance. The visual indicator of this problem is simply a mainsail with too much draft, too far forward, or a knuckle right around the spreader window area. While we want the sails to be full and powerful, we don’t want them to be too full, because an overly full sail creates too much drag. So we have to flatten them a bit.

We could flatten the sail by tensioning the backstay, but we would pull the headstay too tight in the process. We solve this dilemma by pre-bending the mast”

So it’s now Monday afternoon, the boat it sitting with a perfectly tuned rig, and we have one more day to wait to find out if it’ll help or hurt the boats performance in the next race.

I’m counting on a bit more pointing ability and boat speed. We’ll find out tomorrow night.