The Sea3Pio is a trailable day-sailer or camp-cruiser for use on relatively protected waters. I drew her for a client who signed up for the classes that I led at the WoodenBoat School in Maine, building the Naskeag 16. He was impressed by the accuracy of fit of the hull panels that were cut by CNC and the relative ease of assembly with this method of construction and considered it suitable for his proposed project.

Construction of main hull and amas is multi-chine plywood over bulkheads and stringers, with stitch & glass chine joints. Deck construction is similar, with additional framing at bulkheads and other structure to properly support the weight of crew where needed. Scantlings are to ISO requirements, with 4mm hull skins over 6mm bulkheads. The centreboard casing is full-height between the cockpit sole and hull bottom, built from 9mm plywood. The casing is also the cockpit drain. Centreboard controls are at the front of the cockpit, below the compaionway.

The amas use similar construction. They are canted 10 degrees, to be close to upright under sail. They have toe-in of 2 degrees to reduce wave action interacting between the hull and leeward ama, also helping with the heading to windward.

The folding system uses two different sizes of aluminium tubes, with the smaller tube sliding into the larger tube. The tubes are supported by aluminium carrier frames with plastic bushes that can be machined from Starboard or 3D printed. Sailing beam is 4.35m [14'3"] and trailing beam is 2.5m [8'2"]. When folded, the amas tuck partially under the wings of the main hull.

The rig has a rotating wing mast that is built from douglas fir bead & cove strips, with a solid trailing edge for screwing a sail track. It is built in two halves inside female formers, glassed on the inside and outside. It is solid at top, bottom and at shroud attachments. It is stepped in an aluminium tabernacle with a tube that pivots on a lateral axle, to allow raising/lowering from aft. A smaller tube is buried into the foot of the mast and rotates inside the larger tube on Teflon bushes, allowing the mast to rotate. The two tubes are the same sizes as the sliding beams.

Deck Plan

3D with amas extended for sailing.

3D Folded for trailing

She has an easily handled fractional sloop rig with fully battened mainsail. Standing rigging is arranged to allow the mast to stand without the amas in place although the shrouds to the amas must be in place for sailing. Shrouds are angled aft to eliminate backstays. The forestay is wire to allow a furler to be used and the shrouds are Vectran. While she has a lot of stability, provision is made in her sail plan for reducing sail considerably for use in a blow. The asymmetrical spinnaker is tacked to a retracable sprit and will be hoisted on a top-down furler.

The rudder blade is the pivoting type, controlled from the tiller, to allow beaching. Auxilliary propulsion is by means of oars, single skull or a small outboard motor.

Sea3Pio is designed to be a safe and lively boat to sail singlehanded or with a crew, ideal for comfortable gunkhole cruising in relatively protected waters.

Follow these links to print a material list or a drawing list for this design.

LOA 6.39m [20'11"]

LWL 6.2m [20'4"]

Beam sailing 4.35m [14'3"]

Beam trailing 2.5m [8'2"]

Draft 0.16/1.38m [0'6"/4'6"]

Lightship displacement 370kg [815lb]

Half load displacement 610kg [1344lb]

Mainsail 15.33sq.m [185sq.ft]

Genoa 10.59sq.m [114sq.ft]

Bruce Number 1.51

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