Turbo-ing
Part 3

by Chris Cochran of Morrelli & Melvin

This summer I’ve discussed numerous ways to turbo a boat, attempting to bring hope to the people who want to power up their older racing boats, and to the guys that race slow boats with no realistic intentions of buying a faster one anytime soon. Up until now I have covered keels, rigs and rigging. So for the stunning conclusion of the Turbo-ing saga, I’ll discuss just about the only remaining characteristics you can change for a boat; the rudder, hull shape and deck layout.

Rudder
The rudder probably should have been included with the keel in “Turbo-ing Part I”, since they sort of have a symbiotic relationship. However since that article was already becoming too lengthy, the rudder got the shaft. But don’t let that fool you…a new rudder could be just as worthwhile an investment, depending on the style and age of the boat.

Chances are that your modern racer or racer/cruiser already has a deep, high-aspect rudder with a carbon shaft, which would not be necessary to upgrade. But some older racing boats, and even some newer cruiser/racers, sport a low-aspect foil with a heavy stainless steel shaft. The benefits of this type are low cost, low draft and to some extent, durability. But these rudders are usually on the heavy side, and could afford to gain some performance enhancements in terms of lift and drag.

So let’s assume that you have a cruiser/racer, which has a trapezoidal rudder with a solid, stainless steel shaft. A replacement rudder would probably be something like a high-aspect elliptical or “butter-knife shaped” foil with a carbon fiber, rhomboid rudder shaft. The carbon shafts are roughly 40% lighter than their stainless predecessors, so the obvious benefit is getting weight out of the ass-end and reducing the pitching moment of the boat in waves. A refined planform shape with higher aspect ratio will produce sideforce faster (that is, at a lower angle of attack), which reduces the amount of rudder angle required and subsequently reduces the amount of induced drag produced. As always, there are some drawbacks to consider. For one thing, carbon fiber isn’t cheap, and a carbon shaft could be roughly 2x as much as a stainless steel one. Also, carbon shafts are usually hollow (due to the manufacturing techniques), which forces them to be slightly wider than a stainless shaft for the equivalent strength & stiffness. This means that the rudder bearings might need replacing, and that the actual rudder would be slightly thicker than if a solid stainless shaft was used. If you remember from “Yacht Design 101: The Deal on Keels”, a thicker foil shape will create more form drag, but will also resist stalling – a compliment to the higher AR foil which might induce stalling at low speeds.

Hull
Modifying an existing boat’s hull can be a risky maneuver, mostly due to the uncertainties in predicting how the hull contributes to sideforce, total drag, balance, etc… And because of the potential cost, it probably isn’t worth the risk. Nonetheless, some people go through with it, and some fast boats have been reborn as a result. As far as I have seen, the most common modifications have been made to the bow and/or stern, while some hulls have been lengthened in the middle, or even completely replaced below the sheer.

A traditional raked bow can be blended into a plumb bow, increasing the waterline length (upwind sailing potential), but also increasing wetted surface and adding forward buoyancy. Increasing buoyancy is not necessarily a bad thing, especially if the boat is prone to nose diving in waves, but it will affect the boats longitudinal balance, and will probably need to be corrected with some sort of longitudinal shift in the center of gravity. Another way to compliment this would be to reshape the transom – widening it for downwind surfing capability, or adding a transom scoop to gain wetted length. I don’t consider myself an expert in IRC, but I do know that hull overhangs play a part in the determining the TCC, so modifying a boat’s overhangs will probably have a rather large impact on the rating. Luckily, IRC allows a few trial ratings, which could be compared against VPP results to determine if the modifications are “worth it”, before proceeding with any changes.

A recent popular trend in hull modifications, and probably the most extreme, is to use an existing deck and completely remodel a new hull beneath it, a la the latest Nicorette or Margaritaville. While this would give you the greatest flexibility in terms of design freedom, it would be the most expensive type of modification. But assuming you use the same deck hardware, rig, keel & rudder, it should be far less than buying a new boat.

Deck Layout
The deck layout is the type of upgrade which might not bring direct speed increases, but will probably make the boat much easier to handle, thus allowing the crew more time to focus on boatspeed and tactics. Deck hardware has become lighter & stronger in the recent years, with the use of carbon and high strength plastics (and yes, it has become more expensive), and corresponding deck layouts have changed as a result.

For older racing boats, and for some modern production racer/cruisers, the original deck hardware probably isn’t the best stuff out there anymore. For example, genoa tracks can usually be upgraded from the pin-stop style to the block & tackle style, similar to a traveler, which is adjustable under load. Those annoying self-tailing genoa winches could be replaced with the wider body 3-speed racing winches, with the faux self tailing top-cleats on them. The old-school array of mast base winches could be replaced with blocks that lead the halyards aft, and distribute them to the cabintop winches via deck organizers and clutches. Additionally, the cabintop winches can be replaced with 4-speed winches, with a wide drum (spinnaker trim) at the bottom and a narrow drum (halyards) at the top. While replacing hardware on the cabin top, it might be worthwhile to replace the generic halyard stoppers with clutches. As halyards become more high-tech, they tend to become smaller and harder to grip, so it’s usually necessary to upgrade the clutches & jammers along with the lines. I could go on and on for another few pages talking about deck hardware upgrades, but the long and short of it is that unless the boat is a modern racing boat, it could probably benefit from a deck hardware overhaul. And as I said earlier, it may not make straight line boat speed any faster, but it will probably make the round-the-course time faster.

Final Remarks
As a designer, I think it would be great for everyone to sell their old race-boats and buy new ones. But as a realist, I know that not everyone has the resources to buy brand new boats, so the obvious next best thing is to upgrade their existing boats. I hope this recent series of Turbo-ing articles can open some people’s eyes to the types of upgrades that are available. For everyone’s convenience, I have included a summary of the various modifications, including some of the pros & cons for each one. So instead of complaining that new boats are too expensive and that your current boat is too slow, consider making some changes, support your local naval architect and boat yard, and have them done already. And lastly, go out and have fun racing your “new” boat.