Stabilized or not?
Posted on 26 May 2010
Written by Peter Swanson
Lacking sails and rig, power cruising vessels must achieve stability either through a form-stable hull or mechanical stabilization systems.
This is an area in which it pays to listen carefully to salespeople and current owners, then note the vessel's performance during sea trials.
While usually ensuring a greater degree of comfort than non-stabilized vessels, any conventional passive or active stabilizer penalizes a boat in terms of speed and fuel consumption. Form-stable hulls vary in their effectiveness, but have the advantage of solid-state technology - that is, they have no moving parts to fail. All catamarans are inherently stable, while several monohull trawler builders claim varying degrees of form stability, including American Tug, Great Harbour and Nordic Tugs. The more form-stable the hull, the less effective the use of mechanical stabilization.
Towed passive stabilizers (paravanes, "flopper stoppers") offer low-tech reliability. No electric or hydraulic power is needed and they can be repaired or replaced wherever there is a welding shop. They work best on displacement hulls and there is no drag penalty when they're out of the water.
Passive stabilizers do require skill and practice to deploy and take in. They can't be used in shallow water and the drag obviously slows the boat and increases fuel burn. They are optional on Nordhavns to 52 feet, Kadey-Krogens and most custom steel boats, and they can be retrofitted on most displacement vessels.
Deployable at the flip of a switch, active stabilizers are effective at diminishing roll by up to 75 percent. Multiple failure points affect reliability, and as an appendage to the hull they may be fouled by lines and debris. Again, drag slows the boat and increases fuel burn. Nearly all displacement and semidisplacement monohulls may be fitted with active stabilizers, though Great Harbour is an exception. And they don't work on catamarans.
In addition to active and passive fins, a third alternative has been brought to market in recent years and that is gyro-stabilization, such as the system made by Seakeeper (www.seakeeper.com).
See related stories:
- Cracking the trawler code
- Understanding the math
This article originally appeared in the June 2010 issue.