Short-cut URL for this page: https://chrismolloy.com/houdini.

My project for Winter 2009 was a home-built dinghy. After a fairly brief web search I settled on the Houdini design by New Zealand-based John Welsford (JohnW). This page will chart my build progress and will hopefully capture a few hints and tips for any prospective builder out there.

First up is a critique of the information and support that I've had from JohnW with regards to this design. I wish I'd had more of an idea about this aspect before I'd got started as I've experienced a major 'expectation gap' between what I thought I'd get and what I actually got. I've enjoyed building Houdini, and think she's a sweet design, but 'fore-warned is fore-armed' on this project...

Information And Support

The information and support from JohnW has five components: the plans; the written instructions; JohnW's boat-building book; the web forum; and direct e-mail to/from JohnW. The following may read like a bit of a moan, but it's intended to give prospective builders a bit of clarity around what they can expect from JohnW, rather than to scare people off giving one of his designs a go. Hard-core JohnW fans may want to look away now...

The Plans: The plans consist of five photocopied A1 sheets. Ostensibly these are 'scale plans', but I found them to be otherwise. The inconsistencies between stated scales and enumerated dimensions are not uniform, which rules out any error from the photocopying process. Instead I believe that the original drawings have been updated with newer dimension values (as a result of corrections coming out of actually building the design). Unfortunately the drawings themselves have not be updated to match. This is irritating on several fronts, not least because many dimension values are not stated, or are scattered across multiple sheets and boat parts, leading to much derivation of dimension values (by adding up various numbers) instead of simply being able to measure off the plans directly (which is what 'scale plans' are for). Sometimes leaps of logic have to be applied as well.

A good example is the offsets for the stem. The numbers stated on the plans are useless as they are. You need to understand that they are laid out on a 100mm grid, but this is not stated anywhere. A 200mm grid is specified for the bottom panel offsets on another sheet, so you need to apply this bit of knowledge to the stem offsets (with an adjustment of 200mm to 100mm). The scale of the offsets specified on the horizontal axis seems to be dead on 10:1, the default scale of most of the plans, but the scale of the offsets specified on the vertical axis is a little smaller (e.g. the 975mm dimension is 95mm in the drawing). No dimension is specified for the full extent of the stem along the horizontal axis, as it is for the vertical axis (975mm), but it looks to be about 475mm, assuming you use the 10:1 scale. The rebate that connects the stem to the keel measures 7.5mm @ 10:1 (on sheet #2) and 15mm @ 5:1 (on sheet #3), which seems to work out to be a consistent 75mm. Unfortunately the keel piece it marries to is 100mm in length (as specified in a text note on sheet #3). So which one is correct?

This is an extreme example, but it does give you a flavour of what you can expect to have to muddle through - fun, if you like detective work/using your calculator/fudging bits; not so fun if you just want to worry about the woodwork, knowing that the plans are clear and consistent.

The Written Instructions: The written instructions consist of 4½ A4 pages. This is broken down into: ½ page 'index to plans'; 1 page materials list; 2¼ pages of building instructions; ¾ of rigging and sailing advice. If you thought 2¼ pages of building instructions for an entire dinghy is a little on the brief side, you're not alone - it's more of a list of (18) steps. To be fair, most of the build is a 'follow your nose' affair, but some bits would have benefited from a little more detail.

JohnW's boat-building book: JohnW has written a boat-building book (Backyard Boatbuilder: How to Build Your Own Wooden Boat) to support building his designs. It's definitely worth a read, but whatever you do, don't buy it unless you have to - it contains little actually useful information.

The book is split into two parts: general building advice; and a set of chapters, each dedicated to a specific JohnW design. Most of the general building advice chapters can be summed up in a few sentences (e.g. 'Chapter 2: Understanding The Material' - summary: "Use marine-grade plywood"), although one or two are useful. The design-specific chapter dedicated to Houdini was a lovely story about a week-long sailing trip around the Hauraki Gulf - a highly inspiring story, that got me chomping at the bit to have my very own Houdini, but absolutely zero help in actually building one.

I've compiled a summary of the general building advice chapters below.

The Web Forum: A Yahoo! group (jwbuilders) exists to support the community of JohnW-design builders. I have been a member of many web-based communities, but this was my first Yahoo! group. The community is very active and reasonably helpful, but the Yahoo! group format is woeful. It is mostly a giant e-mail-based question-and-reply store, where each reply contains a copy of all the preceding text on the topic. This means that 90% of the content is duplicated many, many times. Searching for stuff in here is just awful. A lot of good information is buried in here, but good luck finding it! As a result a lot of questions are asked over and over. And as most forum regulars get sick of answering the same questions over and over, you only get a reply if your question is novel. I asked many questions in the forum and got zero replies - the silence seemed to suggest "search harder" or "it's in the plans, just look closer", but who knows. It's worth noting that a good number of my questions were Houdini-specific, so perhaps there were just too few active Houdini builders in the forum when I was an active member. One highlight is that JohnW himself is a very active member of this forum.

A couple of pieces of forum advice I've seen many times are variations on "don't worry, it'll work out - there's little that extra epoxy can't fix" and "embrace the ambiguity in the plans - it makes for an individual boat". Keeping the former in your mind in times of stress is very helpful, but I take issue with the latter - I'd rather individuality came about by choice, rather than "ambiguity in the plans".

E-mailing JohnW directly: I had occasion to write to JohnW three times. He never once replied. Enough said.

The basic upshot of all this is: expect to get this project done without much help. It is very doable, but it could have been a less stressful experience with a little more information and support (and particularly with accurate, 'to scale' drawings, which would have supplied answers to all of my questions to JohnW and the web forum).

In closing this section, let me restate that "I've enjoyed building Houdini, and think she's a sweet design" to temper the seemingly negative critique above.

The Book

Here's a quick summary of the 'general building advice' chapters from Backyard Boatbuilder: How to Build Your Own Wooden Boat by John Welsford. It is worth noting that a second edition of the book is due out late 2009 and has purportedly been revised and updated.

Chapter 1: From Simple Beginnings... - An inspiring introduction, but no help as far as building goes.

Chapter 2: Understanding The Materials - Use marine-grade plywood.

Chapter 3: Adhesives - Use epoxy, if possible - with special mention of West System products. Resorcinol/Aerodux glue can also be considered.

One correction concerns John's claim that Resorcinol/Aerodux is not gap filling - my Aerodux box states that it is "a boil proof and weatherproof gap filling adhesive". Epoxy + fillers is the ultimate gap filling adhesive, however.

Chapter 4: Tools - Basic hand tools are sufficient. Regarding powertools: a jigsaw and circular ('Skil') saw are required; an electric plane and router are desirable. Buy top-grade sandpaper by the roll.

Chapter 5: Basic Joining Techniques - This is a very useful chapter and well worth studying closely.

One correction concerns John's advice about epoxy thickeners/fillers - he refers to using either low or high density fillers for bonding and filleting. If you look at the West System Filler Selection Guide you'll notice that the 404 High-Density Filler has a relatively low rating for "Bonding with Fillets", and that the 407 Low-Density Filler is only a little better. What you want to be using is the 406 Colloidal Silica Filler (and if you only want to buy one filler type, this is by far the best all-rounder). Their 411 Microsphere Blend (not currently listed on their web site) is a mixture of hollow spheres and colloidal silica, and could be worth a look as well.

Chapter 6: Plans - How to transfer offsets to your plywood - pretty simple really, but worth a glance if you've not done this before.

Chapter 7: Construction Methods - Details of 'traditional' building techniques (i.e. a fully load-bearing frame, with a skin to keep the water out). Not applicable to what you'll be doing overall, but some useful details that are relevant to JohnW designs.

Chapter 8: Taped Seam Construction - Details of more modern building techniques (i.e. using fibreglass and plywood to virtually do away with the need for a frame). Not applicable to what you'll be doing overall, but some useful details that are relevant to JohnW designs.

Chapter 9: Doing It My Way - A synthesis of the two previous chapters, as they relate to JohnW designs. Most of the really useful/practical stuff is in the earlier chapters.

Chapter 10: Making It Look Right - Tips on shaping and painting things to get them to 'look right'. Worth a read, but mostly common sense stuff (e.g. put lots of curves in, rather than corners and straight lines; don't make the paint scheme too busy; etc.).

Chapter 11: Camping Equipment - Of interest, but no help as far as building goes.

Time-Lapse Video Of Build

A time-lapse video of building my Houdini. Shot at one frame every 15 seconds, and run at 30 f.p.s. (i.e. 8 hours of work = 64 seconds of footage). Note that this video only captures the assembly - fabricating all the parts took place in my shed, and was not captured on video.

'Houdini' Dinghy Build, pt. 1: In this episode we go from zero, to having the keel, frames, stringers and king plank assembled. The first 10 seconds or so is a bit wonky as it took me a few attempts to get all the time-lapse settings right - hopefully I can re-cut this bit from the original footage and re-upload it at some point.


In NZ$, including GST, incurred May - August, 2009...

Marine plywood (BS1088, Meranti) 746
Silver Beech (rough-sawn) 487
Planing/thicknessing/ripping 73
Fibreglass (fabric, tape, epoxy, fillers, etc.) 537
Resorcinol/Aerodux 120
Screws/nails/bolts 438
Rudder gudgeon/pinion 65
Cleats/towing pad eye/bolts/backing plates 100
Anchor 45
Undercoat, 1 litre 65
Top coat, 1 litre (white) 60
Includes materials for the main jig [building platform] and temporary framework, plus laser-cut router templates, pattern making gear and random other stuff 505
Total (to date) NZ$3241

Budget Notes

Building Tips

Building Jig, Bottom Panel & Keel

Frames, Transom, Stem & Stringers: Construction

Frames, Transom, Stem & Stringers: Erection

Free Laser-Cutter Designs: Jigs And Router Templates