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Turbo-ing
by Chris Cochran of Morrelli & Melvin
Last month I started discussing the topic of modifying, or “turbo-ing” existing boats, either for all-around speed gains or to better suit the prevailing sailing conditions. The previous focus was bout keel upgrades – what the options are, what is required to make those changes, etc… This month I’m going to continue the turbo-ing topic and discuss some possible rig modifications, in lieu of, or to compliment the new keel. Upgrading the rig can be one of the most effective ways to turbo your boat, in terms of straight-line boat speed. This can be done in many different ways, such as adding the capability of mast-head sails to a fractional rig, or replacing an aluminum rig with a lighter (possibly taller) carbon one. If modifying your mast isn’t in the cards, there are some more subtle options out there, like replacing wire rigging with rod (Nitronic, PBO, carbon, etc…), replacing wire backstays with synthetic rope (vectran, Kevlar, etc..), adding more roach to your mainsail, upgrading to a (longer) spinnaker pole, etc... Just like when modifying the keel, there are certain rig changes that will work better for particular boats. In keeping with the theme from the keel upgrade article, we’ll look at three different types of boats and figure out what kind of rig modifications would benefit them.
The performance problem for Boat A is that since it’s so heavy, it needs a lot of sail power to move in lighter breeze. But since the boat has an emphasis on cruising, it was designed with a small, easy to handle sailplan. The cure for this guy would be a taller rig, preferably made of carbon fiber since the boat could stand to lose a few pounds. A taller rig would carry more sail area, which would give the boat more horsepower. Since the rig is taller, it would also raise the sailplan’s center of effort, which would increase the heeling moment caused by the sails. But this is OK, since the boat probably has plenty of righting moment to begin with. Boat B is already going fast enough, and always seems to be sailing on its ear. Obviously, a taller rig is not necessary. But this boat would benefit from a carbon fiber rig. The weight savings would be pretty significant - a carbon rig is usually in the realm of 60% the weight of an equivalent aluminum rig. And since the rig weight plays has a large influence in the vertical center of gravity (VCG), reducing the weight will lower the VCG, translating into greater righting moment. So the ULDB flyer will now have better righting moment (without changing the keel), allowing it to stay powered up without excessively heeling. Boat C is essentially an older medium-displacement one design boat, which sports an aluminum rig and fractional spinnakers. Its goes upwind like a bat out of hell, but lags on the downwind run, especially in light air. The remedy here would be to increase the downwind sail area, but not the upwind area. Using an oversized spinnaker pole is a good start, and it wouldn’t require much modification to the rig, if any. An even better bet would be to keep the oversized spinnaker pole and add a masthead halyard for the spinnaker. But bear in mind, this would require some modifications to the top of the rig – probably by beefing up the top mast section, or adding jumpers and masthead shrouds.
To get an idea of how these modifications will increase performance, let’s look more closely at Boat C. The accompanying figure represents 3 different rig/sailplan configurations for a 35 ft racing yacht. Configuration #1 is the original boat, with a fractional spinnaker and a standard spinnaker pole. Configuration #2 utilizes an oversized spinnaker pole (increasing the spinnaker area by ~21%). Lastly, Configuration #3 uses the same spinnaker pole as Configuration #2, but adds a masthead spinnaker, increasing the area another 15%. A simple VPP analysis indicates that the extended pole is 4% faster downwind (VMG) in 6 kts TWS, and only 1.9% faster in 20 kts TWS. The masthead configuration, on the other hand, is 9% faster downwind in 6kts TWS, and 4% faster in 20kts TWS. So this is telling us that if this boat is raced in a light-air venue most of the time, the mast-head kite would most likely be beneficial, depending on the rating change. But since the extended pole only increases performance a small amount, the rating change probably wouldn’t be worth it. If you don’t feel like modifying your rig, there are a few minor upgrades you can still do to increase performance. Changing the standing rigging is a good place to start. If your boat doesn’t already have it, rod rigging is a good upgrade to look into, although you will have to replace some of the tangs and spreader fittings in addition to buying the rod. If you are upgrading from 1x19 wire to Nitronic 50 rod rigging with a breaking strength of ~8000 lbs, you can shave off 16% of your standing rigging weight and reduce the diameter (reducing windage) by 20%. Invest in pultruded Aramid rigging and you can get rid of 80% of the weight, in addition to reducing the diameter by 11%. The same goes with your backstay(s). Replace your 9/32” wire backstay with 5/16” Vectran and lose 80% of the weight, with only a slight increase in windage. But before you get too excited, you should realize (especially by now) that the lighter it is, the more expensive it is. An upgrade to Nitronic rod wouldn’t be too terrible, but a complete upgrade to PBO or Aramid rigging will cost a pretty penny. A good upgrade for fractionally rigged boats is a larger roach mainsail. This will add sail area to the top of the rig, where the wind is stronger, and increase sail power both upwind and down. A properly designed sail is also dynamically responsive in gusts, spilling the air out of the top of the sail to automatically de-power the boat. One issue is that most big-roach mains will get in the way of the permanent backstay when tacking/gibing. In this case you would have to add a flicker (the batten at the top of the mast the automatically clears the backstay during tacks & gybes). If you want to go nuts with the roach, you can add a multihull style mainsail, seen more and more on monohulls, and convert your single wire backstay to a split rope backstay – one for port tack & one for starboard tack…just think of them as masthead runners. Unfortunately, most rig modifications will yield a rating change. Depending on the rating rule and the type of modification, a VPP will be needed to determine whether the modifications will actually be worth the rating hit. For instance, if an oversized spinnaker pole gets an extra -3 seconds in PHRF, yet the VPP indicates that its only 2 seconds/mile faster, than its probably not worth the modification. A naval architect/yacht designer would be able to assist you with your options and help you determine if they are worth it. These are just a few of the many modifications you could make to your rig. Depending on the type of boat you have, it could be a costly, time consuming upgrade, or you can luck out and it won’t take much more than a new sail and some new rigging. So now that we’ve looked into keel and rig modifications, the only thing left is the rudder, deck & hull, and I’ll get to some of those next time. |
