Didi 27 Retro

Radius Chine Plywood Classically-Styled Sportboat

Didi 27 Retro radius chine plywood sportboat plans

Performance with Classic Looks

~ A Gentleman's sportboat

~ Developed from Didi 26

~ Economy of plywood radius chine method

~ Round bilge from sheet material

~ Professional or amateur builders

~ Modern Marconi rig

~ Fixed or lifting keel options

~ High performance with Classic good looks

~ Pre-cut kits and foils

~ Flickr Album



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This design commission was inspired by the Didi 29 Retro. Both were developments from our popular DIDI 26 sportboat trailer-sailer design but the two Retro sisters are very different in purpose and execution.

Most of the hull is the same as the DIDI 26, with some obvious differences. For starters it has a plumb bow instead of the slightly raked stem of the 26. The more springy sheer curve was achieved by adding bulwarks that are 100mm (4") high in the bow and taper down to normal toerail height in the aft half of the length. This improves safety for working the foredeck but allows crew to sit comfortably on the rail alongside the cockpit. (Gentlemen don't sit on the rail but their crew sometimes do.)

Being longer than the Didi 26, the sterns of both the 27 and 29 are extended to achieve the extra length. Whereas the 29 Retro has a counter stern, with the bottom sweeping up to a raked transom, the 27 has a flatter and more powerful stern that ends in a radiused vertical transom. This will give the 27 greater downwind potential in strong wind planing and surfing conditions.

Didi 29 Retro radius chine plywood boat plans

Didi 29 Retro radius chine plywood boat plans
3D images of Didi 29 Retro with cabin as designed.

The Didi 27 Retro is not your run-of-the-mill cruising trailer-sailer. My client wanted a simple dayboat, with only a pair of bench seats down below. I included a double berth in the bows to allow for camp-cruising when sailing those beautiful backwaters of Chesapeake Bay and similar areas. With 4 berths down below and the addition of a boom tent over the cockpit for more space, she can give family fun in warmer weather. There is space under the cockpit to stow a camp stove, small Porta-Potti and personal gear.

We have two keel options, a bolted fixed keel and a lifting keel. Both keels use a casing that is full-height between hull and deck, adding strength/stiffness and also allowing for later conversion from fixed to lifting or vice-versa if needs change. The keel foils are laminated hardwood sheathed in fibreglass and have a bolted lead bulb.

Steering is by tiller to an inboard spade rudder in a lift-out casette that allows steering when partially lifted. Aside from the benefits for getting into shallower water with the lifting keel, it makes for very easy rudder servicing without taking the boat out of the water.

Didi 29 Retro radius chine plywood sportboat plans
Accommodation of lifting keel version

The standard sailing rig for this design is a square-top fractional Marconi configuration, with asymmatric spinnaker on an extending and pivoting bowsprit. It is a modern and powerful rig that will give sparkling performance. For those who prefer, we can also make the cruising gaff rig of the Didi 29 Retro available, as a straight transplant with only minor adjustments.

No allowance has been made for a motor. An outboard can be mounted on a transom bracket. A well in the cockpit for an outboard motor will also work but is not included in the drawings at present.

Didi 29 Retro radius chine plywood boat plans
Deck plan of fixed keel version

Didi 29 Retro radius chine plywood boat plans
Cross-section at front of cockpit.

Didi 29 Retro radius chine plywood boat plans
Side view of hull.

Construction uses the radius chine plywood method, which produces a round bilge hull shape from sheet material. Amateurs with little and even no boatbuilding experience have built good boats with quality finishes to this range of our designs. This one uses a plywood backbone that slots egg-crate-fashion through plywood ring-frames and bulkheads.

The Didi 27 Retro will be a fun boat for performance sailors, with the added benefit of camp-cruising the family or close friends.


LOA 8.35m (27'5")

LWL 7.55m (24'9")

Beam 2.50m (8'2")

Draft lift keel 0.5/1.7m (1'8"/5'7")
Draft fixed keel 1.7m (5'7")

Displ to DWL 1500kg (3306lb)

Displ light 1050kg (2314lb)

Ballast 435kg (959lb)

Waterplane area 9.87sq.m (106sq.ft)

Immersion rate 101kg/cm (565lb/inch)

Wetted surface 13.8sq.m (149sq.ft)

Sail area (main + Genoa) 46sq.m (496sq.ft)

Sail Area/Wetted Surface 3.34

Sail Area/Displ 35.47

Displ/length 97

Prismatic coef .54

Block coef .40

Fineness coef .66

Headroom 0.94m (3' 1")

This design has metric and imperial measurements.


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This page was updated 10 January 2019

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