Rudder Design and Construction

The rudder of a boat is one of the most important components in determining how a boat feels, as it is the primary means of control for the helmsman.  A rudder that is poorly designed can contribute to many uncomfortable and sometimes even dangerous sailing characteristics.  An unbalanced rudder can contribute to excessive weather or lee helm when sailing heeled over, as well as require significant force to alter or stay on course.  Without the correct aspect ratio and foil shape, the rudder can stall in tight maneuvers and loose steerage at lower speeds. We have taken great care in designing a rudder that is balanced, has the right aspect ratio and is easy to maintain.

The issue with composite rudders with metal stocks, the most common rudder design, is that over time they will leak and get water ingress in the foam core. This will slowly pulverize the core material and result in a rudder shell that will easily break due to the lack of support. The second issue is that if a rudder stock breaks, the boat will flood and potentially sink. This is why we have gone a different route than what most “traditional” sailboats are equipped with.

The rudder of the Offshore 42 is not a new concept, but the design is unusual on a standard production boat. It is a kick-up rudder which consists of a composite blade, pivoting over an aluminum pin that is housed in an aluminum rudder cassette that is fully above the water and transom hung in a V-shaped recess. The rudder placement allows a wind vane to be used and the recess limits the rudder angle to prevent damage caused by too large of a tiller angle. The kick-up function reduces chances of damage when maneuvering in shallow waters or if the rudder hits something at sea.

By structurally separating the rudder blade from the metal steering mechanism, the water ingress issue is fully resolved. Also, the bending moment on the rudder stock is eliminated as there is no rudder stock. Instead, the loads are spread out over a larger area of the rudder structure and therefore less prone to breaking or fatigue.

In addition to the safety advantages, there are also practical benefits to this design. If need be, the propeller shaft can be pulled while the boat is in the water. The rudder blade can be changed out mid-ocean, pretty much regardless of the weather conditions. The structure is very plain and simple, even in the most remote parts of the world, it would be possible to build a new rudder out of scrap material that fits the transom. This is exactly the spirit of the Offshore 42!

The rudder blade is designed so that it is partially under the hull, forward of the axis of rotation. This creates a balanced rudder and reduces the required force to steer, to virtually none. The feel of the rudder can be easily changed by adjusting the vertical angle of the rudder blade, if desired.

 

rudder

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s