Building Hours for Multihulls

There's a well bantered saying that for trimarans you have to build five hulls, for cats only two. Trimarans require more time on the structure but usually have less detail in the interior fit-out. There’s only one hull with livable spaces and certainly a lot less interior surfaces to finish. Accordingly we can assume the total build time is similar for cats and tris and other factors come into play rather than the number of hulls. 

In choosing a design you might also argue that a for a given level of performance you can build a significantly smaller trimaran. That argument probably wont wash well with a family setting out on a world cruise with a bunch of water toys and a galley that would be the envy of most restaurant owners.

In one respect trimarans are easier to build than cats. Everything is at a suitable working height for most of the project and the beams and floats can be easily moved around the factory space. A cat calls for a lot climbing once you’re working at wing deck height. Aside from the comments above a trimaran optimized for racing with a very spartan interior could come in well under the build time of a similar sized cruising cat.

Using flat panels can significantly reduce build time, possibly by around 20%, maybe even more.

One designer claims his 38’ LOA cat can be built from a DuFlex kit in 4000 hours. This may well be the case, but I expect it applies to a well planned project using experienced workers and maybe a fairly basic fit-out. It would be helpful if the designer provided more detail, like the level of experience of the builders, the stage of completion, the quality of the finish, the extent of fit out, and maybe a few photos. 

For a 40’ cat using a kit I would generally expect more like 6000 to 6500 hours. Without a kit and using more conventional methods probably more like 8000 hours.

To give some idea of the variability that’s possible, a well organized and experienced professional builder might complete a one off 60’ cat to a high standard in about 16000 hours. In contrast it is common for a large professional yard using female moulds and infused laminates to estimate between 45,000 and  50,000 hours for a similar boat.

Right; DuFlex panels being bonded in ATL's heat press.

The glue join cures in about ten minutes. The panels are slid forward to the next join and the individual parts are cut out of the panel assembly with a jig saw, then stacked ready to be assembled to the boat. If the parts are not to be used immediately they may be left attached to the panel until needed.

Below; There was a time when the designer would have given the builder a table of offsets and the builder would have painstakingly  lofted the boat and all its parts full size on the workshop floor before transferring the definitions to patterns and then the actual parts.

Today the parts get made directly from the designer's cutting files. Does that mean boats get built a lot more quickly these days? See Designer's Footnote at the end of the article.

Apart from whether a kit is being used, one of the biggest variables is in the quality of the finish, both inside and out. Yes, we all want a nicely finished boat but if you're not building from female tooling at least some amount of fairing is unavoidable. A DuFlex kit and other panel building methods will substantially reduce fairing time but it will still require a certain amount of filling and sanding both inside and out.

Below Left

This is what your boat looks like possibly just a few days after your kit has been delivered. Composite parts stacked against the wall ready to be separated and assembled.

Below right

This catamaran topside panel was taped up, prep'd and and painted on the inside prior to being fitted to the boat. The unpainted areas have been left to allow for bonding to the bulkhead and floor panels. This is a major step forward in minimizing interior finish time.

Below: The level of finish of this Barefoot 40 catamaran is quite exceptional, even in places that are unlikely ever to see a human gaze. Apart from the fact that it's a boat it wouldn't be surprising to see it roll off the assembly line in the Ferrari factory in Maranello

Interior of Chincogan 52 Soul tastefully finished with judicious use of timber laminate and trim. 

The hulls were female moulded and required no exterior finish work, but the interior was hand faired and painted at the expenditure of a significant portion of the total build time.

•Finishing composite surfaces is a big deal. Look at ways to minimize fairing time. Use pre-laminated panels that require a minimum of fairing work.

•Plan the project so you can do as much work as possible at working height on the workshop floor. Keep the workshop clean, tidy and organized.

•Employ professional teams for fairing and painting. They know how to get a better finish in less time and they waste less material in the process.

•Keep the laminating work fair and tidy from day one so a minimum of finishing is required.

•Use third party components wherever possible. Longerons, Daggerboards, Rudders, Forebeam etc.

A friend of mine who used to build boats in Australia now builds the same boats in Asia.

I asked him how much the build hours had changed. 

He told me he now doubles the allowance for build hours.

When I asked him why this is the case he thought for a few moments and then told me that in the early days of the business he was mostly full time on the shop floor working side by side with the other workers. 

If you're a professional boat builder you probably have a pretty good idea how long your team is going to take to complete a particular project, especially if it's similar to one you've done before. Otherwise there's not a lot of resources available to refer to. There's no text book. No online app you can download, no consultancy that can figure it out for you. The variables that apply are daunting.

Not all builders keep good records of build hours, and its not an easy thing to do if parts of your team is moving between different projects from day to day. And the builders who do keep good records are not likely to want to share them with the public.

But let's have a stab at this anyway.

On the table below I have plotted out suggested build hours for the Raku Catamarans going through the build process step by step. You could apply it to to the Sensori catamarans as well - but maybe reduce the numbers by 15 to 20% because the deck equipment is much simplified and there's no rig. How did I come up with those numbers? Not by a very scientific method.

If you're in the boat building business estimating the hours reasonably accurately is critical and this can best be addressed using your own experience, expertise and a detailed set of plans with a comprehensive list of surface areas, laminates and reinforcing materials. 

It is common practice for builders to charge the deck equipment and fitout on a cost plus basis. This arrangement avoids the risk of the builder having to charge a high figure to cover unknowns and it helps to minimise the risk to the owner of the project going over budget. 

Designer's footnote.

I sometimes reflect on the fact that we spend so much more time on the design work now than we did thirty years ago. Not just a bit more - but a very significant multiple of hours. That's in spite of the fact that we were working then with tech pens that used to clog up and sometimes bleed onto the mylar film which then required the ink blotches to be scratched off with a scalpel blade. Pocket calculators were cool technology at the time and a big one with a lot of functions was a bit of a "look what I have" item..

With that level of technology you couldn't grab a text block and resize it, or move it to another drawing. You couldn't correct a typo with a click of the mouse. It was a delicate operation of scratching and patching. You couldn't copy a reinforcement detail from another boat and paste it into the drawing. You couldn't send a drawing to a builder by loading it to a Drop Box folder. You had to drive into town, get it printed, go to the post office, roll it up into a tube and send it off.

Yet it all seemed to go so much more quickly.

I think a similar thing may have happened with boat building. We have wet-out machines wonderful CNC facilities, and an array of other digital devices. No more full size lofting on the workshop floor and all of those complicated shapes needed for the building forms or the various composite components get delivered on the back of a truck ready to assemble.