Idea 21

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Idea 21 is the latest development of my family of small plywood & epoxy sailboats plans for homebuilders: it was quite a time since I was thinking of an evolution of her smaller 19 footer sister, so I finally take the decision to publish this new plan.

The goals of this plan is simple: add interior volume, simplify the work for homebuilders switching to a complete plywood & epoxy radius chine hull, enhance slightly the sparkling performances of Idea 19, keeping the sailboat very balanced and suited for sailors ranging from enthusiast beginners to experienced seamen.
 
 
 

Let’s start form the hull: chined hull on a small light sailboat has a simple reason to exist: it gives more stability to the sailboat when heeled, much more than a round hull similar sailboat. I managed to keep a very low wetted area of the unheeled hull, in order to achieve a good pace in light air and avoid excessive drag. Stern sections are quite flat to gain speed downwind (idea 19 has been clocked with speed steadily in excess of 15 knots).

Bow sections: experiences on racers showed that “knife-blade” bows may give you less resistance, but the price to pay is high in terms of buried bow sailing downwind, so I decide to provide this plan a large U-shaped section on the bow; sails provide the sailboat plenty of power to defeat the small amount of added drag. 
 
 

 

Sailplan: I have a very good starting point with idea 19, so we’re doing small adjustments and no revolutions: square top mainsail, 7/8 fractional rig , very wide single swept spreaders, no backstay, deck stepped mast with sturdy section, 110 % J jib, code zero, jennaker hoisted on swinging retractable bowsprit, and a good amount of sail area. 
 
 
 

 
 
Keel and ballast: idea21 have a solid hard wood cored & unidirectional glass epoxy laminated lifting keel, with a NACA optimised profile and a low resistance hydrodynamical shaped 280 kg lead bulb bolted on the keel tip; it can be made by a homebuilder, no need for professional welder; the fin area is on the low side, speed will help generating the required lift without adding too much drag. Keel case is in 20 mm thickness plywood and epoxy laminated glass reinforcements, and it’s perfectly waterproof while sailing. 

Cockpit: was one of the strongest point in IDEA19, we simply keep the same arrangement and dimensions, so we have a really huge area for the crew and a simple and sturdy building in plywood panels epoxy glued on a structure of bulkheads and stringers. 
 
 
 
 

Interiors: here I focussed on several upgrades; I decided to split the project in two versions (so two different sets of plans, you have to specify on order), “sport cruise” or “racing” ; both versions have 4 berths, a classic V berth on bow and two quarter berth after; in the cruising version cabin is 55 cm longer, giving wider interiors, enough room for a separate toilette and more comfortable after berths ; in the racing version we have a marine toilet (there’s room for a Jabsco compact one) under the bow V-berth; inner height is 1.65 m in both versions. Interiors plywood panels are detailed on plans. 
 
 
 

How to build the boat: we chose the plywood & epoxy resin “radius chine” technique, as for Petrel 28 and Hirundo 750, so the hull planking is in okume marine grade plywood ; planking the hull is quite fast, and the internal structure of the boat is made by plywood bulkheads, floors and solid wood longitudinal stringers, all glued with epoxy and strengthened with epoxy laminated glass tape, assembled on a cheap wood scaffold, keeping the hull light, sturdy and quite easy to build for homebuilders; the goal is to keep the total weight of the 19 footer, raising the ballast fraction of the sailboat at the same time. Cristian Pilo.