What drives the cost of a multihull?

The cost is basically the cube of the length.
But you can change that by choice of materials/complexity and you can make it much higher by choice of modern inconveniences - kitchen, radios, generator, refrigerator, tv, etc.

 

The modern mantra that it is pointless to build a boat because your materials and labour will be lost on resale is a very large pile of bovine manure! I'm afraid designers and professional boatbuilders come thickly smeared with the stuff. They have to stress investment, finish and resale because that's what most of their clients want. They don't mention that the annual upkeep on a gin palace will more than compensate for the loss in resale.
Amateurs need to stick to the principle KISS KISS KISS. Watch your costs and enjoy what you are doing. Hell I've had more fun balancing on a log than riding around in a friend's very expensive speed boat. There's nothing like the pride of being able to say it's all mine.
Regards Harry

 

You missed one of the obvious costs, that I personally can vouch for greater than cubic increase -

3) Consumables and support structures and admin
Cost of gear to shelter, roll over, move around the hull(s)
Sanding, cleaning gear and chemicals and tool costs
Launching and associated transport costs
Registration, insurance and associated costs
Electrical charges, premise rental, etc etc

 

ThomD, the surface area actually increases with the square of the dimensions, but of course building a physical surface requires adding thickness to the surface. But that's why my first naive thought was that costs of the hull should increase as the square of the dimensions rather than as a cube or possibly more.

RWatson, good point about the "hidden costs". For a 20 ft boat you can tow it around on an inexpensive trailer. Double it to 40 ft and you likely need the experienced help of the boatyard to launch it, and at 80 ft I suppose you need professional help.

 

Figuring costs on displacement rather than length gives a better idea of materials expenses. Rig costs need to be considered by performance, righting moment and area. A heavy cruiser has different needs than a raceboat etc.....

 

Multihulls will always be more expensive than monohulls. 30% of the weight of a monohull shell (at worst) comes in the form of a bolt on keel which in relative terms costs nothing. All the weight of a multihull shell will go through the builders hands

A multihull is much wider than a monohull so usually has to be built by the water. And waterfront property/taxes are very high, if available at all. So the overhead costs for a multihull builder are higher than for a monohull

One major reason the French did so well in developing their boatbuilding industry in the 1980's was that the French government supported their industry with subsidised waterfront factories

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Good point about premises close to the water Richard.

In fact, many new builders tend to ignore the cost of building shelter totally. This is a major factor in the success of many builds, especially as the sizes of the boat increases.

If you want to have a boat in survey, the first thing the authorities look at, is what your premises as like. Weather damage and weather affected processes can ruin a boat long before any launch date.

 

Modern materials and methods have largely eliminated " shade tree " boatbuilding. Anything over about 18ft will probably require the construction or hire of a shelter. That's assuming that you are willing to leave the car out in the weather for the build.
Professionals can estimate their costs etc pretty accurately, amateurs can't. My best advise is that the build will take longer and cost MUCH more than you think. Be warned and prepared!
And the best of luck to you. Regards Harry

 

I think this seems relatively accurate to me. I'm building an 18' tri and I could go as big as 22' or so at home, but I wouldn't attempt anything bigger without moving to a real commercial shop space. And the expertise and tooling to do a great job on fiberglass layup with larger and larger projects gets much more expensive. Even on my small boat it's very hard to ensure that every part is done correctly and accurately.

And there is a learning curve. I'm certain that I could build a second boat in half the time of the first. And probably build a better boat too.

 

Jetboy,

Have we ever see the boat you are building? I would like to.
~18' Tri is what I keep thinking about, forever.

 

It's a Scarab 18 with a number of my own changes. Mainly I'm changing how the beams mount so that they are bolt on rather than integrated, and I'm building in honeycomb/glass/epoxy.

Not much to see yet. I have two ama shells off the frames and taped and almost ready at this point. I just put the final two extra layers of glass on the bows this weekend in a the few hours I had to work on them. If I get some time next weekend I should be able to get all the bulkheads in and if thing go well get the decks put on and ready to fair.

I was hoping to be sailing this fall, but I had a busy summer and just haven't had the time to spend on it I had hoped. Things are looking a lot better for the winter to get it finished up by spring. Now that I've got a nice 20' table to work on and have learned a lot about materials and how to work more efficiently I think the main hull will go pretty quick.

 

We all know someone here who can attest to that.

In fact he recently stated he could have saved $100,000 by having a pro build his cat for him.

 

An amateur should be able to get a good idea of materials costs, the designer sends the list usually. Where and how to get the best prices he might not do as well and he is at a disadvantage in figuring the labor. Adding a larger multiplier for experience level should help. The newbie has to times his best estimate by 10 and the pro by 2. For home builders appropriate technology should be considered as well. For many craft a polyethylene shelter is enough but for infusion builds and exotic laminates a building with temperature and humidity control starts looking nice. That is when the overhead really starts to go up. The pro builder lottery joke has the builder say when asked what he'll do with the winnings. "Well, I guess I'll keep building boats till the money runs out."

 

I have my doubts. There are a lot of failed projects that went into huge cost overruns, costed by 'professionals'. Anywhere from The Anzac naval frigates, to Greg Normans luxury yachts that nearly sent the boatyard broke. The stories from government projects all over the world would give anyone grey hairs.

The only professionals that are spot on with costs are those doing a long production run, or a certain 'type' of boat where all the 'unknowns' have been revealed.

There is no reason that an amateur cant be as accurate as a full time builder - and I know for sure that a lot of the full time boat builders cant add up to save themselves.