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.
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|
|Fibreglass (fabric, tape, epoxy, fillers, etc.)||537|
|Cleats/towing pad eye/bolts/backing plates||100|
|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|
- New Zealand's 'boat-building capital' is Auckland. As I was building in Wellington, some 800km [500 miles] away, almost everything marine-related in the table above incurred a freight charge to get it to me, and this has been included in the figures above.
- The 'Sundries' figure is quite large. Most of this went towards building the main jig and temporary frames, as I used new timber for all this work (my scrap pile didn't have much that was big enough or true enough for this project).
Building Jig, Bottom Panel & Keel
- Building Jig: I added 100mm to the height of each station upright to give me a little more clearance to work with. I also erected my jig on a pair of saw benches so I could work more easily around the base of the hull to start with. Once the lower planking had been installed, I dropped the jig down to the ground so I could access the interior of the hull more easily.
- Bottom Panel: JohnW suggests tracing the offcut from one side of the bottom panel to make the other side. I found it easier to plot the offset for both sides, as I felt that the kerf left by my jigsaw would make the resulting shape less accurate than if I'd simply plotted both sides.
- Keel: This is located 2.5mm on the port-side of the centreline (not 5mm, as hinted at in the plans). The 60mm-wide keel batten plus the 65mm-wide keel packer will then lie exactly on the centreline (where the mast foot should be).
- Keel: After gluing in place, I used my circular saw to cut a pilot slot for the centrecase. This pilot slot was slightly under-sized and was enlarged with a flush-cutting router bit once the centrecase was installed.
Frames, Transom, Stem & Stringers: Construction
- Frames: I found that it pays to do as much assembly 'on the bench', rather than 'on the boat'. This includes cutting notches for the stringers and keel, and attaching all doublers [reinforcing layers] and battens. Most of the battens support some element of the sole [floor] and are shown on the plans to be unbroken runs of timber - it's only later, when you're locating the rest of the sole supports, that you realise that most battens need to be notched. Notch the battens as part of your 'on the bench' lay up.
- Frames: I used several laser-cut jigs and router templates to shape my frames. I'm very pleased with the accuracy and 'purity' of the shaping provided by these jigs and templates.
- Frames: I made my temporary frames out of 12mm [½"] MDF - anything thinner would not have been rigid enough. Don't forget to notch these for the stringers and keel (and locate reinforcing blocks accordingly).
- Transom: It pays to have a very clear mental image of how the various parts come together at the transom - as well as the triple layer of ply (one solid panel, with a doubler on both sides), the stingers and outer skin of the boat join here too. For example, I cut stringer notches into the solid panel and inside doubler, but not the outside doubler, such that the end of each stringer is 'capped' by the outside doubler. The outer skin on my hull overlapped the whole transom, but if I'd made the outside doubler larger it could have overlapped the outer skin, which to my mind would look better and be stronger.
- Stem: I made the jig for my stem out of a sheet of MDF with cross-sections of Ø25mm [1"] dowel glued-and-screwed onto it. With glue on everything, I wound in the clamps I was using to pull the laminations into the jig, and, with 90% of the bend in, the entire jig exploded - it was just too weak to handle the forces involved. I had to back up the dowels with 100mm x 50mm [4" x 2"] timber in the end. In short, build your stem jig solid.
- Stem: Note the 75mm-deep rebate at the end of the stem where it joins the keel. Stagger you laminations to save having to cut the rebate. Put a couple of nails through the stack of laminations (just behind the 'rebate' and in a line across the width of the stack) before bending in order to hold their positions relative to one another.
- Stem: I left my stem on the jig for a couple of weeks after gluing it up. The stem offsets are laid out on a 100mm grid, and I marked the outside of my stem with the 100mm grid whilst it was on the jig so that I had some points of reference once the stem was off the jig. I also fitted the lower 50mm-thick reinforcing block whilst the stem was 'on the bench', rather than 'on the boat' (the other two blocks need to be positioned relative to the stringers, so are best fitted after the stringers go on).
- Stringers: accurately ripping long lengths of timber is painful without industrial-sized equipment. I bought my planks rough-sawn and had them planed/thicknessed for NZ$48 and ripped for NZ$25. This is one job that is worth every cent to outsource.
- Stringers: After ripping, I clamped all of my stringers together and marked them at 200mm [8"] intervals so I had reference marks to work from once they were 'on the boat'. These marks were very useful in ensuring that the stringers and frames met at exactly the same places on both sides of the hull.
Frames, Transom, Stem & Stringers: Erection
Free Laser-Cutter Designs: Jigs And Router Templates
- John Welsford's 'Houdini' dinghy design page
- Laser-cut router templates - another page on this web site that details the use of laser-cut router templates, including templates specific to this project
- Cyborg CNC - fool-proof NACA airfoil cutting/shaping.
- The Lemouix Dream: Houdini Boat Construction Project - Peter Black's building diary, with photos
¤ Copyright 1999-2023 Chris Molloy ¤ All rights reserved ¤