Paravanes: An Alternate or Backup Stabilizing System for Trawlers
Bluewater has her paravanes deployed. Photo: Milt Baker
One key to successful long-distance passagemaking is ensuring maximum comfort and safety of the crew. A factor that contributes to fatigue on long rides is excessive motion. Granted, sometimes heavy seas make some level of pitch and roll unavoidable, but both hull design and specialized systems can minimize the motion.
Roll stabilization is now quite common on full-displacement trawlers, but there are two different ways to accomplish the task — active-fin stabilizers and paravanes. The former are wing-like appendages attached to the hull below the waterline and they move like the control surfaces of an airplane to minimize roll. Paravanes are also wing-like but they are not part of the boat’s structure and are instead towed alongside the boat, below the surface of the water.
Milt Baker’s Nordhavn 47, Bluewater, can quiet the rock and roll in two ways. The first line of defense is the active fin stabilization system from Naiad, which was installed on the boat before delivery. The second anti-roll system aboard Bluewater is the paravane system that relies only on a couple of electric winches and the practiced deployment and recovery techniques that he and his wife Judy use.
Paravanes look complicated, with all of the poles and rigging installed, but actually are quite simple. The system involves two “flying fish” made out of metal and weighing about 40 pounds each, for a boat of Bluewater’s size. These are hung from outrigger poles about 15 feet below the surface of the water, well outboard of Bluewater’s midships rail (see photo).
As the boat moves through the water, paravanes resist being pulled up through the water by the rolling movements of the boat. Since one is deployed on each side of the vessel, rolling motions are damped, often by as much as 60 percent of what an active fin-stabilization system can achieve.
Copyright © 2008 by OceanLines
Tom,Thanks for your article on paravanes. Question: How critical is the inboard placement of the paravane boom? For example, could the swivel point be amidships instead of on the side of the hull? I am considering a design for a round hulled displacement trawler in which the in board end of two paravane booms would be placed nearly on the fore and aft center line at the base of the mast. The base fitting would be such that the booms could be swiveled 90 degrees aft and do double service as light cargo booms.
Any thoughts?
If I remember my principles of the lever properly, (and there is no guarantee of that) then you want to righting force to act as far away from the centerline of the ship as possible in order to gain greatest effect. That increases the moment-arm and the force applied. Given that, you would NOT want the base of the arms to be amidships, since there would be little or no moment-arm to act as a lever. Let’s see if we can get a naval architect to weigh in on this. After all, I am not a REAL naval architect, I only play one on TV (sorry, always wanted to say that).
Tom,
Thanks for the imput…I suspect you are right, but just as a devels advocate I have to ask: wouldn’t the triangle formed by the mast and the staby boom function the same whether the horizontal leg of the triangle was formed by a single long boom from the mast to the point of attachment for the fish or by a shorter section of boom and the the rest of the ships structure? Seems like the line of force would ultimatly be transmitted to the center of boyancy, either way.
Thanks for your help