Capsize Moment Comparison www.trisailing.com

There are many factors that influence a boat’s righting moment.  Rig height and waterline are the main two factors.  There are many others: 

Flotation of the hull and the amas:  The main hull on Corsair trimarans flares out from it’s narrow waterline width.  As the hull is submerged a progressively wider section of hull (with greater flotation) is pushed under water.  This is also true for the amas.  Comparatively Adagio has a lot less flotation in the hull and amas.

Rocker line of the hull:  Corsair tris have considerable rocker in their aft section.  This will cause the bow to come up as speed increases thus decreasing the possibilities of burying the bow.

Narrow hulls at the waterline:   This increases the acceleration of a Corsair Tri.  The easier it is for a boat to accelerate the less the capsize moment.  This is why when sailing off the wind the loads on the rigging of tris are lower than on keel boats of comparable lengths.  If the forces of the wind are easily transformed into acceleration there will not be as much of a capsize moment in a gust.  The chances of rig failure are less in tris. 

The ability to place crew weight far aft:  Four 200lb crew members placed far aft will place a down ward load of 24 thousand foot pounds on the stern of a 31 foot boat as it starts to pitch-pole

Rig rake angle:  While the raked back rig of Adagio will decrease the chance of a pitch pole is initiated.  If the bow digs in once the rig becomes vertical it actually increases the capsize moment compared to a  rig which  began vertical and is now exposing less of itself to the wind.  If you watch a  windsurfer doing a forward loop which is essentially an aerial forward capsize.  At the apex of the jump the rig will be raked aft as far as possible to increase exposure to the wind as it becomes vertical.

Rig design:  A square top main will twist off at the top spilling wind in gusts. This combined with releasing the main sheet will generally save tri which is nearing capsize.

A bow sprit.  Placing the tack of the spinnaker or screacher further forward will decrease the chance of burying the bow.  If the spinnaker is sailed with several feet of tack line released allowing it to rise even more wind is spilled keeping the bow up. 

Asymmetric spinnakers: tend to be blanketed by the main as a boat begins to capsize downwind.

The deck netting’s permeability:   To the wind.  Some multihulls have strap netting which may provide more windage which could increase the capsize moment as a boat starts to go over.

Corsairs and F-Boats are certainly the most tested tris in the world.  As is clear by the many factors that will affect capsize moment (I am sure there are others) tris will probably capsize because of several combined reasons.  When sailing a tri in powered to over powered conditions it is important to remember the factors over which you have control.   When in doubt let it out

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	Crew weight:  keep it to windward.  If you are sailing down wind in heavy air you may consider having one personas far back as possible strapped in.  Be sure if one person moves to leeward only one person does so.  Thee guy on the foredeck will not need your help,  Be sure one person is not going forward into the cabin as another is going up to the bow.  It sounds basic but I have seen many sailors that are not at all aware of how crew movements affect their boats.
	Sail area.: Should you reef now?   What sails can you quickly reduce?  It is important to practice reefing in lighter area.  Reefing is done with the jib in tight and the boom traveler all the way out.  Having the most sail up is not always fastest.
	Sail trim: be prepared to release all sheets.  If you have self tailing winches do not use the self tailer use a cleat.  A cleat is quicker to release.
	Tack Line:  If the tack line is let out a bit in overpowered conditions it brings the bow up by spilling some wind off the foot of the chute and creating upward lift.
	Gear:  Where are you storing your heavy items:  If you left your anchor in the anchor locker in the bow the anchor with wet line will weigh at least 50 pounds which will be an increase of 1500 to 2500 foot pounds of  downward force depending on the part of the main hull on which you are planning.
	Point of sail:  When sailing downwind If you sail slightly lower angles in the puffs your speed may drop but you are going further down wind.  If you manage to surf down a wave face it also takes load off your rig reducing the capsize moment.  The forward force of the wave balances the forward force of the gust on the rig.  Riding waves is also fun!!!
	Mast rotation:  One quick way to reduce sail area down wind is to bring your mast to center.  This also moves the center of effort of the sail slightly aft.
	Increased windage:  If your furled screacher is raised this is not only weight aloft but it is also windage.  In strong winds as the sail begins to unfurl the windage further increases until it rips.
	Water in your rolled screacher:  placing a Velcro strap very tightly around your screacher right at the bow will decrease the amount of water that enters the rolled sail.  You may also want to fold the rolled screacher upward and strap it to the bow pulpit about one foot above the deck before it runs aft.  This will create a step which should stop the sail from filling.  This weight is crucial because it is on the bow.