Calculating Speed of a Boat for Dumbo - Help Needed

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SUMMARY

The discussion focuses on calculating the approximate speed of a catamaran hull boat designed by the user, Tai. The hull dimensions are 150mm x 100mm x 620mm, with a total weight of 8.5 kilograms. The propulsion system consists of two bilge pumps capable of moving a combined total of 84 liters per minute. To estimate the speed, the user is advised to consider the drag force and apply the formula P = 1/2 ρ v³ LW Cd, where drag coefficients must account for viscous, wave, and profile drag.

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  • Understanding of fluid dynamics principles
  • Familiarity with drag coefficients in marine applications
  • Basic knowledge of power calculations in propulsion systems
  • Experience with catamaran design and performance metrics
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Tai
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Hi everyone,

I'm hoping for some help in calculating the speed of a boat I am planning to build, I'm not looking for a precise speed just an indication of what it is likely to be to ensure the pumps I would like to use are powerfull enough.

The boat is a catamaran hull with the hull dimensions 150mmx100mmx620mm (per hull), the remainder of the boat will be above the water line. Overall the weight will be 8.5 Kilos, the propulsion system I would like to use is made up of two bilge pumps, each bigle pump is capable of moving 42 litres a minute so combined 84 litres per minute. The pump output pipe is 19mm in diameter, which i guess fits into the equation somewhere...

Is someone able to tell me an approximate speed in either kph or mph? I don't even have a clue where to begin :blushing:

Thanks in advance,

Tai
 
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You need to determine how the drag varies with speed. Then for a first approximation, you relate that to the power output of your engines:

P = \frac{1}{2} \rho v^3 LW Cd

Bear in mind that your drag coefficient would have to include viscous, wave and profile drag terms.
 

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