Didi Mini
Radius Chine Plywood Mini 650

Didi Mini radius chine plywood Mini 650 boat plans
Mike O'Neill's "SCM", previously "Warlock"

Low budget performer

~ Economy of plywood

~ Radius chine hull, stitch & glue cabintop

~ Round bilge from sheet material

~ Amateur or pro builders

~ Fixed or canting keel

~ High performance racing on a tight budget

~ See our Kits Page for pre-cut kits and foils

~ Visit South African Didi Mini kit construction project

~ Advice and tips in Builders Notes

~ Sailing photos ~ Sailing video ~ Flickr Album

~ See the Didi Mini Mk3, with updated hull and rig



Credit Card

Boat Sites


"Warlock" is in the water and sailing

Comments from crew for her first sail, Wednesday 10th September 2003.

~ Rick Nankin, North Sails ~

Potent little boat. She is most impressive even at this early stage of her life.
The boat appeared stiff to windward and very bouyant over the waves. Reaching and running she just took off easily and planed with the kite up fantastically. The rudder just followed the boat and the helm was light and responsive.

~ Pete Shaw, Sparcraft South Africa ~

Beware!! This little boat could become more addictive than coke in Amsterdam. What a sea trial!
The boat performed really well upwind and simply took off downwind. The layout all seemed to work pretty well apart from a few minor tweaks that need to be done, but nothing major. Credit to all concerned.

~ Andrew Edwards, Project Manager ~

Sailed this evening, wind NW about 15knots, little girl picked up her skirt and took off, easy 10knots on a reach, planes easy and effortlessly......

Didi Mini radius chine plywood Mini 650 boat plans

Didi Mini radius chine plywood Mini 650 boat plans

This is the scene at Bayfront Center for Maritime Studies at East Dobbins Landing in Erie, Pennsylvania. Under the capable eye and hand of Director Jim Stewart, hundreds of youths are working together building a Didi Mini as part of a community project. They come from many schools and juvenile placement facilities in the area and they come with little or no boatbuilding experience. Here their project is seen with a group from Walnut Creek Middle School fitting the radius section of the hull skin.

Mini 650 or Mini-Transat boats attract great interest worldwide. Tiny but costly offshore yachts, they give spectacular sailing, and are generally beyond the ability of most amateur builders. Commissioned by a client who wants to build a reasonably competitive boat himself, this design is our contribution toward reducing the cost of these boats.

Detailing is based on the series of radius chine plywood designs that started with my DIDI 38 "Black Cat", and was followed by the DIDI 34, Didi MG30 and DIDI 26.

Design principle is simplicity and to the Mini 6.5 Class limits. The initial design has a fixed keel and conventional water ballast, as well as single aft daggerboard for tracking downwind. We have added a canting keel & forward daggerboard to the package, so that builders can choose the option that suits them. Linked twin rudders are steered by central tiller.

Keels are hollow aluminum fabrications with through-bolted beaver tail ballast bulbs. The fixed keel has optional trim tab. Both keels are supported by the hull structure by means of an internal aluminum box frame. The fixed keel has an integral post to transfer some of the keel loads through to the deck structure.

Didi Mini radius chine plywood Mini 650 boat plans
The Didi Mini of Enrico Manuretto nearing completion
in Italy.

The deck layout is a fairly conventional 3-winch arrangement. The smaller headsails sheet to the top of the cabin and are led to the cabintop winch. The larger headsails and spinnakers sheet to the cockpit winches. Tweeker lines replace headsail tracks.

We have sold nearly 60 sets of plans for her, as at Dec 2005. Drawings include full size Mylar patterns of the backbone, bulbs, rudders and daggerboards. Optional full size Mylar patterns for the bulkheads are also available.

Pre-cut kits are available from various suppliers. Click here for supplier contact info. Kits vary from bulkheads with hull & deck skin through to almost everything needed to complete your boat. Please clarify with suppliers what is included in their prices.

Click for material list or drawing list.

We have made some modifications to the design, as from January 2004. The stepped stern has been replaced by a deck extending to the transom, moving the mainsheet track aft and giving more cockpit space. A small mound has been added over the emergency hatch, allowing it to be mounted higher above the water. At the same time the rudder linkage has been changed to improve the geometry of the rudders. The drawings below show the Mk2 version.

We now also have a cruising version of this design, the Didi Cruise-Mini. It has a smaller rig, optional lifting keel, more accommodation and more headroom in the cabin. It is more suited to those who want good performance but a simpler boat with a bit more comfort.

Didi Mini radius chine plywood Mini 650 boat plans

Didi Mini radius chine plywood Mini 650 boat plans

Didi Mini radius chine plywood Mini 650 boat plans

Didi Mini radius chine plywood Mini 650 boat plans


LOA 6.50m (21'4")

LWL 6.45m (21'2")

Beam 3.00m (9'10")

Draft 2.0m (6'7")

Displ to DWL 1050kg (2315lb)

Displ light 850kg (1874lb)

Ballast 320kg (705lb)

Waterplane area 8.75sq.m (94sq.ft)

Immersion rate 90kg/cm (504lb/inch)

Wetted surface 11.8sq.m (127sq.ft)

Sail area (main + jib) 40.6sq.m (437sq.ft)

Sail Area/Wetted Surface 3.43

Sail Area/Displ 40

Displ/length 109

Prismatic coef .54

Block coef .44

Fineness coef .67

Righting Moment @ 30 deg 835kgm (6040ft.lb)

Righting Moment @ 60 deg 1060kgm (7667ft.lb)

Righting Moment @ 90 deg 540kgm (3905ft.lb)

IG 8.62m (28'4")

ISP 11.62mm (38'1")

J 2.585m (8'6")

P 10.435m (34'4")

E 3.7m (12'2")

Mainsail 30.27sq.m (326sq.ft)

Solent Jib 10.33sq.m (111sq.ft)

150% Genoa 16.67sq.m (179sq.ft)

This design is dimensioned in both metric and imperial measurement systems.


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This page was updated 30 July 2018

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