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what was found initially

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Tom v.d Brink


Right so as explained a preliminary simulation was done on a cad modelled outrigger.

the outrigger resembled the hull as I had run in 2003 or better explained

a model near an eagle SG with just details changed to better suite saw performance.

Off course a cfd simulation is always just an approach to reality.

the software needs a lot of computer power to run even a simplified model.

therefore the model had to be simplified and some things could not be simulated completely.

The concessions that were made to suite the cfd software were:

-the simulation assumed a model to have a symmetry plane in the longitudinal direction.

* As we simulated on the rudder side this means a hull would pretend to have two rudders

* The carburettor only had a fuel intake side.

* No fuel and water lines were included in the model

- the software did not take into account any interaction between a liquid and a gaseous fluid.

* chosen was that no water would be simulated only the airflow.

* the water surface would be represented by a moving flat surface

- no surface roughness was applied.

* this means that all boundary layer flow will likely remain laminar for a longer length on the model before attempting separation.

it will reduce the model's air resistance but as it is applied to all surface the component drag scale to the overall drag will still be valid.

- the model was mainly tested at the target 100mph speed it would have to achieve. only a few lower speeds were run but they shall not be discussed here.


So a lot of things did not yet scale to reality yet.

despite that effort was made to enhance and study in more detail the components that were included in the simulation

when discussing simulation results the question is always how detailed was the mesh of the model.

so great effort was made to detail the mesh round surface and straight edges.

the simulation was run in various mesh settings to achieve optimal convergence at the end of the calculation.

this was a long and lengthy process but does give the project proper validation.


after several simulation runs some primary conclusions were made to describe the components of the model causing aerodynamic drag.

the total component of the aerodynamic drag was made up out of three major components besides the tub. in following order they were

the round sponson boom 37%

the open engine 21%

the sponson 20%


this was with the traditional sponson shape. however another run included a different sponson shape and

the boom resistance as well as the sponson resistance increased to 42% and 24% respectively.

The amount total aerodynamic drag is as many have already claimed not as high as a potential hydrodynamic drag.

but to people who are trying to get the all the speed potential from their boat i would say it is significant enough to notice.



well now that we know what our major players are for aerodynamic drag next up will be a study of these parts individually and their relation to the

drag and stability of the boat. starting with the biggest component the booms.



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