Preliminar power for catamaran

Hello all,

I hope this thread is well placed here, if not, please let me know better one.

I'm currently in the process of define the power requirement for a small catamaran (less than 5 m length), with an electric propulsion.

Could someone share with me any information (formulae, estimation, method,...) to make a early estimation of the power?

Thanks so much all in advance

 

The estimation is based on the resistance of the hull at the target speed. Can you post the basic dimensions and speed? By the way, the estimation of power will be the same regardless of whether it is electric, gas, or sail.

 

Thanks for your interest @gonzo , I know the basics about the resistance for the hull, in particular with Holtrop & Mennen approach, but I would like to know if there is a better procedure in the case of catamarans due to the differences in the hull.

The dimensions (aprox.):
Length: 5 m
Breadth: 2.7 m
Draught: 0.9 m
Speed (max): 10 kn

 

The interference between hulls may create a higher resistance than just adding the two hulls indepently. The method you refer to is based on accumulated data, which is not likely to exist for small catamarans. Is there anything significantly different from catamarans of similar dimensions?

 

The Holtrop-Mennen method is only valid for monohulls. It's not valid for small catamarans, nor for large catamarans (let's not confuse people). It's also not valid for all types of monohulls. It was studied for boats with certain hull coefficients and within certain ranges of the Froude number. Length alone doesn't seem to be a factor limiting its application.

 

No, just the small size. I tried to make an approximation of the power using similar ones but I didin0t find enough to make a solid database for interpolation; that's the reason for asking for any kind of formulae or method.

 

I know, Holtrop & Mennen comes from an study of an extended list of vessels and its valid for some kind of characteristics, but for this kind of vessel (multi hull) I'm completely lost

 

Maxsurf, you may be familiar with this app, it has procedures for those calculations on catamarans.

 

Which of those method implemented in Maxsurf Resistance Module do you recomend me?

 

The slender body method is specific to catamarans.

 

What is the displacement?

 

I'm not pretty sure due to the design is in progress, around 900-1000 kg

 

Ok, to put this into context.
At roughly 1000kg, your LD (length-displacement) ratio is 5.0. This is on the low side. Very draggy for its length. So lots of power to get through the hump.
Not ideal...you need to increase this LD ratio...i.e less weight for same length.

 

Thanks for your insights. This parameter mentioned is obtained by your own or its theoretical.
Please, don't misunderstand my question, I just want to know where the information comes from.

 

The parameter is called "slenderness ratio", and is a major influential factor on hull resistance. It is the ratio between water line length and third root of the displaced volume in consistent dimensions (m and m^3). In the case of a catamaran with a wide tunnel compared to the separate hull beams, the slenderness ratio should be checked for each hull. In your example the SR is then ~6.2, which is quite ok, resulting in a low planing hump.

Most scientific reports on resistance testing today refer to the SR as a nondimensional "loading value".