The Tridarka Raider

A Trimaran for Coastal Vagabonds

Sail Plan

The Sliding Gunter Batwing Cat Rig

Class Rules for Sail Rig

Any sail design is usable with the following restrictions: 

  1. There must be at least one mast.
  2. There cannot be more than two masts
  3. The combined sail area of the main and mizzen (if present) cannot be more than 115 sqft.
  4. A jib and or reacher is allowed not exceeding 84 sqft.
  5. A spinnaker is allowed.
  6. Mast or masts may be stayed or unstayed.
  7. A minimum of three reefs must be included.
  8. Builder assumes all risk.
Wizard and I discussed many sail plans including the NorseBoat's; the Sea Pearl's; an inexpensive, unbattened sprit-boomed leg o'mutton with rotating-mast reefing; a jib-headed, boomed & battened sail looking pretty similar to the current gunter; Wizard's pet roller-reefing standing lug, a used beach cat rig, a 505 sloop rig, and several others. 

Finally I asked permission to buy the NorseBoat rig for production use on the Tridarka Raider.  When the answer came back - NO (who can blame them), we designed our own but without the fancy curved gaff.

The rig shown will be the primary rig unless competition shows another rig to be superior.

So why this rig?

1.  Fast Cruiser - We need to be thinking of this boat primarily as a fast cruiser, where safety, reliability, and ease of handling in a wide range of conditions are higher priorities than straight speed in round-the-buoys afternoon racing.  WaterTribe events (and adventure cruises) don't cancel as day races often do when the wind gets up in the 20's and 30's.  The boat needs to be efficient and handy when shortened down for hours and days on end in heavy going; low drag, low center of gravity - and for that the first best thing you can do is shorten the mast.  This also explains why the aspect ratio is rather low compared to similar boats.

2.  Weight Distribution - This gunter rig's mast is about 27" shorter than that of an equivalent jib-headed rig, so it's lighter, with a lower center of gravity.  Of course the gunter's yard weighs something too (about 1.5 lb. depending on material and stiffness), but this weight is lowered with the sail in reefing, so that with the first reef down, the gunter's total heeling moment us about the same as the tall rig with 1 reef.  With 2 or 3 reefs the gunter has less heeling moment than the tall rig with 2 or 3 reefs.

3.  Aerodynamic Drag - The short yard of this rig is comparatively lightly loaded, therefore quite skinny.  It's set inside a sleeve in the head of the sail, which creates an airfoil-shaped fairing around and behind the yard, that rotates and twists with the sail.  Most of the yard exists in the turbulent lee of the round-section mast anyway, so, to a degree that there's any difference, we'd expect the gunter rig to have slightly less air drag than the equivalent tall-masted sail plan.  This is definitely true when reefed, when the naked top of the jib-header's mast will be sticking up 2 feet higher into the fast wind 20' above the deck.

Windage under bare poles riding out a squall or anchored on a lee shore, deserves consideration too; the shorter mast trailing shorter halyard falls has a small but noticeable advantage.  In passing we'd also note that a shorter mast is of course easier to step or strike.

By the way, we're not talking here about a rotating foil-section mast, which was judged to be too complicated and fussy for this boat's mission.  From the beginning the boat's spec was for a simple, reliable unstayed pole mast that can be dropped in its step, then forgotten.

4.  Good Batten Geometry - The sail shown has its battens all peaked well up and meeting the leach of the sail at close to right angles, which spread the greatest area of sail efficiently with the least stain on the sailcloth, least weight of battens and gear, and least stress on batten end fittings.  When lowered the yard folds aft to lie neatly on top of the boom, releasing leach tension so the battens can relax.  If the same batten geometry where used on a jib-headed sail (as it is in Hobies and other beach cats, for example), the battens wouldn't flake out on the boom when lowered, but would be held up off the boom by the triangle of sail above the topmost batten.

Beach cats and day-racing dinghies get around this problem by releasing the sail entirely from the mast groove when lowered.  Unrestrained, it then billows all over the place and tries to escape overboard and becomes a sea anchor.  A pain in the neck you can live with in sheltered water on a sunny afternoon, but not acceptable in a shorthanded coastal cruiser.

A good cruising rig, particularly in a light capsizable boat, ought to come down under its own weight when the halyard is let go.  Few full-battened rigs do, but with a bit of spray wax this one should.


Sail Plan Notes (only a portion shown here)
Subject To Change
Refer to Plans for Building - The entire rig will be available for sale.

Mast is tapered carbon fiber engineered by manufacturer to the following spec:

  • Length overall 231"
  • Bury 28"
  • CE above the step 139"
  • Max righting moment 11,000 lb-ft
  • Round cross section
  • No track
  • Integral masthead sheave for main halyard, hard wearing finish
  • Attachment points for headsail rigging 
  • Sealed top and bottom

Mast step tube built into hull.  Inside diameter 3/16" larger than greatest diameter of mast. 

Mast boot is conical canvas or rubber seal to keep water out of mast step tube. 

Yard is tapered wood/carbon/epoxy.  Fits inside sleeve in head of sail, lashing from peak cringle of sail through hole in top of yard.  No other holes.  Bottom of yard floats loose in sleeve.

Halyard ring on yard is smallest diameter S.S. ring available with 1/4" diameter stock; built into yard with carbon fiber sleeve.  (Alternate: Serve (lash) tightly to yard at opening in sail sleeve using heavy seine twine.  Lashing may be varnished or coated with contact cement if desired.)  DO NOT drill holes or otherwise weaken the yard to attach this ring, or it will break.  Halyard runs out through this ring when slackened, allowing yard & battens to lay down flat along boom when furling sail.  When halyard is taut, ring pulls yard up parallel to mast.  Yes it does work.

Boom is T-section wood/carbon/epoxy.  Alternative is anodized aluminum or carbon tube.

Three battens are full length pultruded fiberglass or carbon to sailmaker's recommendations, in open ended batten pockets.

Three reef points using slab reefing.

Optional reacher with sail area of 84 sqft.

Optional spinnaker.


Adventure Races
for Sailing:
 
WaterTribe Everglades Challenge

WaterTribe Ultimate Florida Challenge