Monday, January 10, 2011

DiDi 34

DiDi 34 "Nandi" on launch day. Note the powerful keel (to match the rig), the deep rudder, long waterline, fine bow and clean lines of the hull. The high freeboard makes a dry boat with generous cabin volume, while allowing an exceptional reserve stability (AVS 140+ !!). Nandi was built singlehandedly by Nick Fairley over two years, working in spare time.

Nandi sailing out of Hout Bay for Cape Town in fresh winds during one of the early club rallies. She was often sailed double handed by Nick (owner/builder), and myself.
Tall, uncomplicated rig and nice clean lines
 Nandi pacing a Farr 38/40 under Chapmans Peak. Note the single transom-hung rudder remains fully immersed even during a fair angle of heel.
cruising back from Vulcan!

Of all the boats we are likely to cover in this blog, the DiDi 34 is clearly one of the best overall designs I am aware of. I have been involved with this particular boat since day 1 - "Nandi" was built by my great friend Nick Fairley. I have also sailed it many times and in many conditions, and witnessed the construction from start to end.

DiDi 34 is one of Dudley Dix's DiDi range of performance keelboats designed for radius ply construction. They are fantastic all-rounders with impressive performance, cabin space, safety, good handling, and great looks. Equally impressive is that the designs are simple, strong, use no fancy materials or parts, and are actually designed for home/kit construction. The design-to-build element is actually quite a touch of genius, and the kits are very well designed and accurately cut.

How does Dudley achieve all this, and what makes these boats so unique? No doubt Dudley could explain this all a lot better than I can, but the elements that have impressed me include:

1. Powerful rig and keel, combined with fairly hard bilges, give these boats lots of power whilst remaining suitably light. The Didi 34 displaces about 4T, of which a full 2T is lowdown in the (bulb) keel. The beam justifies a fair bit of height in the freeboard and coachroof, which also adds cabin room, whilst achieving a class leading stability profile. See diagrams below:
2. Dynamically, the DiDi 34 also excels. The deep fin keel, combined with a deep transom-hung rudder gives it sharp response on the tiller. The hull profile is sufficiently rounded to keep the rudder immersed at all times. The hull shape makes fair allowance for comfort and seakindliness without giving much away in terms of waterline length and planing ability, and she makes a good offshore racer or cruiser. Notable in many Dix designs is the station of the engine - usually just aft of the keel, forming a useful galley counter and enclosure. This allows maximum buoyancy in the bow and stern, whilst keeping the engine very low as well. Similarly, the fuel tank is situated right over the keel, in an epoxied wooden tank, which doubles as a saloon table. This all helps to keep the weight low down and midships, benefiting power, seaworthiness, and her light, simple and cheap . . . Accommodations remain very practical. Diagram below:

3. Build Philosophy - possibly the thing that appeals to me most is the approach of avoiding expensive materials and complex rigs. Carbon fibre is not required anywhere. A simple 2-spreader standard-section mast is used. Single tensionable backstay. Tiller steering, plywood rudder. Marine ply hull and bulkheads with radius chines. Lots of glue and epoxy, but GRP overlays not required (wood is stronger and does not require fairing like GRP). Fuel tank made of epoxied wood - its perfect. Savings in cost and weight, no rust to worry about, easily bonded to hull. Wood as a building material - modern marine ply, correctly used and epoxied, is in fact as good as a high-tech building material, with amazing strength ratios. It does not suffer rot, rust or osmosis if properly epoxied. It feels good, great to work with and repair, and has good insulation as a bonus. Rig design does not make use of highly stressed chainpates or stays, and the dominant mainsail leaves moderate loads on the headsail and winches.

How does she sail?
DiDi 34 is best on longish offshore courses. I have seen her outrun a well-known Simonis 35 on one occasion over a leg of about 15 miles from Cape Town to Hout Bay, and hold a very hot professionally crewed, very high-tech L34 for an equal distance in False Bay 9bearing in mind that Nandi was being sailed with plain club sails, a #2  roller furling headsail, and shorthanded. 7.5-8.5 knots is common in moderate conditions. Round the cans, she needs weight on the weather rail, but is easily handled with a crew of just two in the cockpit. Single-handing would be a bit more challenging on short courses, but quite possible assuming a roller-furling headsail, tiller-pilot and stackpack on the main. She is a remarkably dry-boat in the cockpit, and gives a decent ride on a beat, with little pounding. Off the wind she is quite steady and simply flies. She keeps moving in light airs, excels at 12-15 knots, wants 1st reef at about 20. Sails quite well under jib alone, if desirable.

Overall, a great boat for club and offshore racing, occasional cruising, and weekend excursions. Its great all-rounder with no vices. Actually a great design to benchmark against.

Does she have any drawbacks? Not really. She's not a classical heavy long-keeled cruiser though, nor a high-tech carbon-mast 4-spreader racer, but wont be embarrased in either role, on a far lower budget. If there was a prize for value-for-money allrounder, she must own it! The thinking-man's sportsboat . . .

For detailed info on the design see

Dudley's Commentary on the DiDi 34/38 follows below:

Didi 38 
I started on this design while sailing the 1993 Cape to Rio on Nick Taylor's Shearwater 39 "Ukelele Lady". I wanted a fast and light boat that I could build myself in the 3 years between races. I sometimes suffer from seasickness, so I took great care to design a boat that would be comfortable despite being light. That meant that it had to be fairly narrow to have an easy motion.

It was to be cold moulded wood for economy and to be suitable for me to build as an amateur. It took a year before I had money to start the project but 2 years was not enough time to do it, so I had to come up with a way to speed up construction drastically. I fell back on my staple radius chine metal designs and adapted that hull form to plywood construction. Aside from speeding up the build it also pulled the material cost way down. Against dire predictions from all and sundry in the boating world and media, we were on the start line in January 1996 after starting the build in January 1994.

"Black Cat" proved to be very fast offwind and a joy to sail on all headings, with a light helm unless pressed very hard. The slippery hull and tall fractional rig make it very fast on all headings on flat water in light breezes. It is a design that like to be pushed hard rather than treated gently. In common with many modern designs, the flattish bottom forward of the mast doesn't like to be sailed upright in lumpy water, powering her up to generate heel softens her ride and makes her more weatherly.

I have sailed her through a few storms in mid-Atlantic and in extremely rough seas as only the Cape of Storms knows how to generate. She has always felt safe and solid despite having a 12mm lightweight plywood skin throughout. Of her 4000kg displacement in measurement trim, a full 50% is ballast in her deep bulb keel. This, combined with her high cabin structure, give her stability characteristics that will right her from the worst of knockdowns.

To date we have sold plans for nearly 70 boats to builders from South Africa to Siberia, USA to Vanuatu.

Didi 34 
I drew this design as an entry in the SA Yachting Design Competition in 1995. My radius chine plywood concept was not yet proven but I decided to use the same method of construction. I did not know at the time that the whole aim of the design competition was to arrive at a new GRP small cruiser/racer that the boating industry could promote together. My wooden boat was out of the running from the start but it has proven to be a really nice design. We have sold more than 40 of these to builders worldwide.

The Didi 34 is more moderate than the Didi 38, so it is a bit finer in the stern and has a bit more emphasis on cruising. The result is a boat that is capable and fast on all points of sail, with reaching being her strong point.

When designing her I also aimed at making her a more modern and more offshore capable version of the CW975 design with which I had won the Cruising World Design Competition in 1979. To that end, the interior layout is very similar and she has the same rig. I had enjoyed sailing my own CW975 "Concept Won" for many years in short-handed races and cruising single-handed, so wanted to bring her ease of handling into the Didi 34. The Didi 34 became a more all-round-capable boat, whereas the CW975 is an extremely fast boat for running/reaching but lacks a bit when beating, both of which result from her flat bottom and multi-chine hull form.

The HBYC boat "Nandi" was built by owner Nick Fairley from a kit that was supplied by Roy McBride of CKD Boats. The kit was cut using a CNC router to provide accurate components, including bulkheads and all panels of hull and deck aside from the radiused areas. I have not seen "Nandi" but from what I hear Nick built her to a good standard. She has been doing well in local racing.