comparison of monohull against catamaran

[amohammadbeygi]

Hi,

Which of the A.M. hull form is suitable for a passenger boat with 12m length with 35 pax and 30 Knots speed ? any idea for comparison creiteria?

Thanks in advance
A. M. Beygi

[charmc]

The answer to the specific question is: both are suitable. There are many touring, party/head boat, and ferry boats in service with both hull types. In general, a catamaran would tend to be more stable, although any boat of that size will roll. The term "monohull" encompasses many designs, many of which would be suitable.

I don't guess that is enough. If you give more background information and specific details it might enable more meaningful responses.

[amohammadbeygi]

thanks for your responce,
I would say, suppose the budgetory cost for boath type is the same.
I think the monohull type has more advantages than catamaran, for example the lower engine power, lower weight, lower resistance, lower maitance cost, more engine room space and .... Is not it true?!

regards,

A.M. Beygi

[charmc]

A. Mohammed,

The things you have stated are all true....of either type of hull. What I mean is that, in my experience, there are monohulls that are more economical than catamarans, and there are catamarrans that outperform certain monohulls.

Some very general statements:
1. A monohull design with a length-beam ratio of about 3:1, having a fine entry forward with a narrow forefoot and some flare to give the bow fullness and deflect spray, and a shallow vee or flat bottom aft, will perform well at displacement speeds and at moderate planing speeds, say about 15-20 knots. At those speeds it would likely prove more efficient than a catamaran hull. At higher speeds, a well designed catamaran might be able to operate with slightly less power for the same speed, therefore better fuel efficiency, and might be able to better maintain speed in choppy water or the kind of steep swells seen in shallow coastal waters.

2. Those statements above are very general, and the key is a well designed hull for the service you desire. The specific design is more important than the general hull type. The qualities you mentioned as advantages for a monohull "might" be true... of a good design. To further complicate matters, 30 knots is a speed at which many catamarans begin to show advantages over "conventional" monohulls. I am not qualified to recommend a specific design, not being a designer or a naval architect.

One way to answer your question: since you seem to feel more comfortable with the idea of a monohull, start a new thread on this forum asking where you can find information on monohull designs suitable for the service you describe. Are you planning to purchase an existing vessel or have one built? If having one built, ask for recommendations on designs. There are many small ferries and passenger launches in service like you described, so there are, I am sure, a few designs that have proven to be good for this purpose.

Good fortune in your search.

Best regards,

Charles McAllister