All About Water Ballast Systems

  • Advantages of Existing Internal Water Ballast Systems
  • How Water Ballast Increases Boat Speed and Comfort
  • Advantages of New External Water Ballast System
  • Stability and What Hangs In The Balance

  • External Water Ballast System

    Advantages of Existing Internal Water Ballast Systems

    Many new high performance racing and cruising sailboats are being manufactured with built-in rigid internal water ballast tanks to improve their upwind performance, without sacrificing downwind performance.  This is accomplished by filling the windward ballast tank with water while going upwind to stabilize the sailboat, and emptying the ballast when going downwind for less weight.  Reducing the angle of heel not only increases performance but also increases comfort and safety similar to sailing down wind.  The cockpit is much more comfortable and you have a safer working platform, especially on the fore deck.  Below deck tasks such as cooking, using the head or sleeping (in improper sea berths) are made safer and easier in heavy seas.  Even when just day sailing with friends and family it becomes more comfortable -- everyone likes a nearly level boat!  Reefing is also minimized by stabilizing the boat in moderate conditions and not having to depower the sails.

    Examples of  internal water ballast manufactured into high performance cruising sailboats can be found in Roger Martin's 40 foot Gray Wolf, with the following advantages:

    "with winds westerly at 15 to 18 knots.  Our initial angle of heel, close reaching with full main and 120 percent jib, was near 10 degrees.  This all but disappeared after Rodger scurried below and switched on a Rule 3600 pump to fill the windward ballast tank.  Our speed subsequently increased by a knot, to say nothing of our comfort level."  "Each port and starboard tank holds 262 gallons (2,240 pounds)."       CRUISING WORLD magazine June 1997, page 91.

    and also, in Steve Dashew's 80 foot Beowulf:

    "Beowulf's 7,500 pounds of saltwater ballast, stored in side tanks, reduces heeling by 8 degrees and adds several knots to boat speed".     CRUISING WORLD magazine August 1998, page 36.

    How Water Ballast Increases Boat Speed and Comfort

    Water ballast works by reducing the angle of heel on a sailboat.  This makes the keel, rudder and sails increase their projected profile and lift in the horizontal direction (less downward sail pressure), generating greater driving and tracking forces that make the sailboat go faster.  It also reduces leeway (side slipping) and the resulting (hull form) drag.  Although there is additional drag from the hull with the added ballast weight, it is minimal when compared to the gain (also in water line length).

    Modern sailboats that are light and have flat under bodies gain the most performance from water ballast since they are capable of going beyond their normal hull speed when planing.  Speeds beyond hull speed are generally achieved going down wind in brisk conditions having a good driving force, when the sailboat's bottom sections are kept flat on the water for planing.  The driving forces on a reach or upwind are not as direct, making the sailboat heel, no longer presenting the flat bottom sections of the vessel.  Adding water ballast on the windward beam while on a reach reduces the heeling angle, which again presents a flatter bottom for planing and increases the driving forces which make the sailboat go faster.  Heavy displacement sailboats have a substantial gain in performance with water ballasting, although they are limited by their hull speed.

    Light modern cruising sailboats also tend to have a harsh motion in heavy seas.  This can make it uncomfortable and difficult to perform normal tasks on ocean passages, with excessive heeling only aggravating the situation.  By adding additional water ballast weight on the windward beam, rolling and tossing are dampened and more velocity is sustained through oncoming waves.  With slower and less internal movement, as well as angle of heel, one has a more comfortable and safer sea kindly ride in heavy seas, with less time spent at sea with the added speed.  Also, water ballast can be placed on both sides of the sailboat to reduce rolling at anchorage or on one side to remove the vessel from a grounding.

    Advantages of New External Water Ballast System

    The new external water ballast system attaches to most sailboats in seconds without alterations, and can be moved from one rail to another or from one similar size boat to another.  This system provides all the advantages of internal water ballast for any existing sailboat.  Attempting to add  internal water ballast tanks to an existing boat would require major reconstruction and take up valuable internal space, even when not in use.  External water ballast also provides better performance with the ballast held further outward which has a greater stabilizing force for the same quantity of water.  External water ballast requires no active pumping for the emergency release of water on the leeward side of the boat and is also compliant with the 10 degree (heel) static rule for offshore safety (both sides 2x10°=20°).

    Disney's water ballast bags.

    Disney's water ballast bags, Sailing World.

    Home page for Maxi Marine external water ballast system.

    Stability and What Hangs In The Balance

    As mentioned earlier, reaching speed is directly related to the heeling angle of a sailboat.  Some expensive high-tech solutions involve lightening the sail rig by the use of  Kevlar® sails and carbon fiber masts, or use of bulbed keels to lower the center of gravity.  To measure the effect of  weight loss from the rig, project the center of the weight loss straight down from it's location as shown on the diagram to the right.  On the other side of the center of flotation (CF), measure the stabilizing force of the keel or movable ballast, i.e., water ballast, crew, etc..  Removing 200 lbs. from the rig with the boat heeling 15 degrees would have the similar effect of adding 200 lbs. to the keel, or only 100 lbs. on the beam rail.  Adding water ballast or crew on the boat's rail is the least expensive and most dramatic stabilizing force, especially within the optimal heeling/performance range for the modern sailboat.

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