– You {Expensive} Beauty –

Beware the Pitfalls of the Designer/Builder

The finished product. It looks and goes really well but so would my 19 year old car with this much money spent on it.

Last year this magazine published an article I wrote regarding a self designed and built 35’ power catamaran (Issue #145 July/August 2017). Some months ago, I advertised the boat for sale, expecting some interest from prospective buyers and I have been surprised by the interest in the boat. Surprised not so much from four enquiries from potential buyers but surprised by the many ‘boaties’ that have approached me in various marinas asking all sorts of questions (and expressing very positive comments about the boat) and by six enquiries from like-minded designer/builders of similar craft.

The marina ‘boaties’ asked questions like “who designed it?”, “are you going into commercial production?”, “how was it made?”, “how fast is it?” and “how much does it cost?”. The builders asked more technical questions about hull shapes, displacement, etc. and I have spent considerable time emailing replies and photos taken during construction.

Interestingly none of the builders asked about costs or time taken to build the boat! So, I thought a follow up article was warranted, if only to try and settle some possible misconceptions about designing and building your own.

Nearing the end – showing 'shoes' fitted under aft hull areas made to suit 25" (635mm) transom height. They give increased buoyancy aft and flat run to outboard power units.

I am actually a great believer in people doing their own thing and ‘having a go’ and I do not want this article to stop anyone from trying but I feel that my experience with this project can serve as a useful point to ponder from a practical perspective, particularly if a prospective designer/builder has little boat building experience. I should note here that this is my ninth boat build, my third design and my first power boat.

The total cost of my build is just over $K300. This includes all materials and fittings, shed rental for five years and a petrol allowance of $K5.I actually spent much more than $K5 on fuel because the build took longer than expected and because I had a 130km return drive to the build. I originally budgeted $K215 for the project and I have had some experience at costing these things!

As for my time designing, sourcing and gathering materials and making the boat I spent a little more than 5000 hours. Note that this does not include travelling to and from the build site. If I paid myself $50 per hour that amounts to another $K250 but I do not expect any monetary compensation for my time. Note that a similar semi production power cat such as a Prowler or Argus E35 costs about $K600 new when equipped to the same standard as mine. A sobering thought!

Completed shell first time out of the shed. It may seem like a milestone in the process but still about 2000+ hours to go! Changes to hull profile evident.

It may seem initially to be financially attractive to self design and build but it will almost certainly be

a) More expensive than you think (budget x 3 might be close!)
b) A lot longer in time than you think
c) Needing on-going design and problem-solving inputs, and
d) Extremely hard on your patience, wallet and your partner!

The good news is that not everybody gets the chance to design and build a thing that looks good and performs to expectations. The satisfaction of verifying your work is priceless if you can do it. I suppose that buying and modifying a used boat to your requirements can also be rewarding and would most likely be cheaper but since I did this with a pair of Turissimo hulls I am not so sure! The original hulls were modified fore and aft. The bow profile was dramatically changed and the transoms extended and modified. At the back I added ‘shoes’ under the hulls. These provided a flat run aft to the outboards, increased the buoyancy by about 120kg each side, flattened out the aft rocker in the hulls and, together with the bow modifications increased the waterline length by about a metre. The depth of the shoes was dictated by my desire to have 25” transoms and the shoes tapered forward by about 3.5m to fair into the hull profile. I used ply, 440g double bias glass and epoxy for both ends.

Almost all of the cabin structure and cockpit is made from 15mm divinycell/440g double bias/epoxy composite and 15mm polycore/800g double bias/epoxy panels make up the bridge-deck floor, some internal doors and foredeck.

Main cabin showing helm area, demountable dining table and out to cockpit. Helm seats are refurbished car seats, super comfortable in marine vinyl. On far right of picture is one of the front door electric actuators that give access to the foredeck.

All up weight, with three passengers and half full tanks is about 3600kg. This is about 1000kg lighter than semi-production cats of similar size and explains the superior performance I have obtained with 2 x 90hp four stroke outboards.

The interior of the boat is simple but luxurious with foam backed marine vinyl used extensively for interior lining, seats etc, except for faired and painted galley and ‘bathroom’ areas. It looks and feels upper class and never fails to impress visitors, especially women.

I now have about 50 hours only on the engines but that includes operating in both bays near Melbourne and two trips between them in Bass Strait, one trip in 25kt winds and 2.5m seas. The boat has performed faultlessly. Each of the Bass Strait trips were 80nm and the first took 6.5 hours and 85 litres of unleaded (average 12.5kts), the second took 5 hours and 101 litres of fuel (average 16kts). One little trip of 10 miles was done at 8kts with rain and wind against tide conditions producing a short 2’ chop and I have to report that it was really very pleasant in the comfy cabin while using only 8 litres of fuel for the entire trip. In fact, at 13kts the boat uses 13 litres per hour and at 20kts about 35 litres per hour. Excellent fuel consumption for a 35’ boat!

Port hull looking forward through galley to bunk area. Induction cooktop lives in sliding drawer beneath microwave.

Two improvements to the original design are underway. The rear duckboard will be widened by about 600mm to make fishing easier and some sort of spray minimisation will be added as dried salt spray on the unwiped areas of the extensive window area make viewing difficult especially if cruising in the mid-teens or above speeds. This is my first power cat design and it is not perfect. Like all boats it is a compromise but it has proved to be very soft riding with no banging like that associated with planning designs. It is also comfortable and economical with excellent manoeuvrability and performance. If you must you can email me at This email address is being protected from spambots. You need JavaScript enabled to view it. for details. Now, all I have to do is find a buyer.