newbie here, hull design Questions

Who here has a cad system or hull design program that can show how adding tunnels would effect a hull?

 

Welcome to the forum.

There's no software package that can teach you to design and engineer something, unless it's an education course in the disciplines you desire, in which case you may or may not need the assistance of CAD. This said, if you have design experence, you can run various analise subroutines in software package(s), that will offer insight into advantages and disadvantages of some shape decisions you've made. Simply put, you can develop tunnel shapes that are better than others on a given hull form, but you do need an understanding of the principles involved, so these comparisons can be relevant and hopefully meet SOR targets.

 

it is true that no generic software package is available for public access. I know an institution/also designers who are using a custom CAD system for design and simulation.

 

It would effect a hull in many different ways, but most of the information that you could get from some commonly used 3D cad software will be the change in longitudinal (and vertical) position of the centre of buoyancy of your hull, because you are basicaly substracting part of the volume from the hull.
There are few basic rules of thumb used in designing of propeller tunnels, most of them are noted in this paper by Mr Donald L. Blount;
http://www.boatdesign.net/forums/at...2693-prop-pocket-design-propeller-tunnels.pdf.

Hydrodynamical effects, like change in efficiency of propulsion, are much harder to calculate, even with more advanced CFD softwares, because it would require modeling hull and prop, combining them, then making calculation, which is again usually in idealised conditions, and ommits a lot of details like air drawing, behavior in waves, etc...

There are lot of people that are making their hulls with stern tunnels, but the design of them, as always includes many opposing design decisions, and designing one for a specific boat would probably be to much...