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Rudder repairBy Tom Pawlak
A typical spade rudder for sailboats is made up of two fiberglass skins that define the shape of the rudder, a metal mandrel that is an extension of the rudder post, and foam core which bridges the space between the skins and mandrel. In order for a rudder like this to work properly, its fiberglass skins must be attached to the core and the core must be attached to the metal mandrel. Side loads on a rudder exert compression loads on the core which transfer into the mandrel. If the components become detached, the rudder can deflect excessively and eventually develop cracks in the fiberglass skins.
Causes of rudder failure
Through normal use, rudders go through a lot of stress. With every turn, the skin on each side is subject to a cycle of compression and tension. Years of sailing can accumulate a lot of these fatigue cycles. Shock loads, groundings, competitive sailing and a rudder that may have been under-engineered all contribute to rudder failure.
Additional damage, at least in northern climates, can be caused by freezing water. A slight leak at the top of a fiberglass rudder will allow moisture to enter. A drop or two of water per day adds up over time. Once inside, the water will freeze during the winter. When it freezes, it expands and can crush the foam core and, in some cases, cause the rudder to delaminate and even split apart. It may take several seasons for a problem like this to reveal itself. Our tech staff gets many calls about this kind of damage from boat owners in northern climates.
A common place to find damage is at the top of the rudder where the skin meets the rudder post. The core and fiberglass skin surrounding the post are repeatedly compressed against the post. The result can be a gap along side of the post, allowing excessive movement and permitting water to enter along the post.
Reinforcing/repairing the top of the rudder
A small gap around the rudder post or tube is not considered serious and can be sealed with a flexible sealant to keep water out. Left unsealed, the gap may allow water into the rudder, leading to extensive damage later.
As a rudder ages and additional fatigue cycles accumulate, stress cracks may develop in the fiberglass laminate around the rudder post at the top of the rudder. These cracks usually radiate from the post into the surrounding fiberglass, often beginning at the glue joint where the two fiberglass halves of the rudder meet. If the cracks are limited to this glue joint, they can be cleaned out with a broken hack saw blade or rotary grinder and glued back together with epoxy thickened with a high density filler.
If the cracks at the top of the rudder radiate into fiberglass beyond the glue joint, the cracks need to be properly repaired. This is accomplished by grinding out all of the damaged fiberglass and replacing the removed material with fiberglass cloth and WEST SYSTEM® Epoxy. At the same time, reinforce the joint between the rudder post and the fiberglass rudder top by cutting away a band of fiberglass and core around the post and filling the gap with epoxy thickened with high density filler.
It's not a bad idea to reinforce the top of the rudder in this way as a precaution, when the rudder is out of the boat and you are making other rudder repairs.
Accumulated stresses can lead to cracks in other locations on the rudder. A common skin failure on an aging rudder occurs in the area where the metal mandrel inside the rudder ends. These stress cracks show up on the sides of the rudder about two thirds of the length down from the top. The damage may be isolated to the cracks in the fiberglass skin or problems may go deeper.
Delamination can occur anywhere in the rudder but will most likely show up in this same area where the metal mandrel inside the rudder ends. The stress cracks and delamination can go unnoticed for a season or two and the problem may not be identified until water begins weeping from the rudder after the boat is pulled from the water.
When delamination is discovered, drill a few small holes to drain any water that may have accumulated inside the void. Tap on the outside of the rudder to identify the extent of damage. Debonded areas will have a distinct dull sound compared to undamaged sections. Use a pencil or permanent marker to identify the boundaries of damage.
There are two approaches one can take to restore strength to the delaminated area. The first and easiest option is the drill and fill approach. The second option involves removing the fiberglass skin in the debonded area, repairing the core, gluing the skin back in place and structurally repairing the original cracks in the skin if any and the cuts made in the fiberglass skin to gain access to the core.
Drilling and filling
The drill and fill method is the easiest of the two repairs. It involves fewer steps but takes more time to complete the repair because of the longer time required to dry out the wet core before the repair can be attempted. The repair may not be as reliable as the second method because there is no opportunity to inspect or prepare the delaminated areas inside the rudder for optimum bonding. Even so, this method has worked well when the damage is not too extensive.
Removing the skin and repairing the core
Most repair facilities use the second option and cut off the fiberglass skin in the debonded area. They remove and repair the voided core before gluing the rudder skin back in place. This method allows the rudder to be repaired over the period of days rather than weeks. It is also a more reliable repair because you get to see what you are bonding to. Surfaces can be dried quickly and thoroughly, and damaged core can be removed and replaced with new core.
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