about Speed & Power

[horumbou]

sorry does somebody know the Orca3D can be use in calculate the speed & power which the hull has tunnel?
the propeller will be inside the hull(side view)

and i feel confuse that when we calculate the hull , we just select the surface below the chine , the planning surface ,
can use that to cal. the disp. LCG VCG....etc.
now these all  about the splited  planning surface but not the total hull surface,
 i feel confuse that won't be affected to the result?

stupid problem~ thanks!


Btw,the Orca3D's annotation(for recording the  ship assistant's parameters)
have some bug ,the item "sheer Heigh" will automatic add "ft"(or another length unit) behind the word, but actually this is scale

and the tree layer manager sometimes the icon have some wrong

[lleibman]

Horumbou,

The Orca3D planing hull powering prediction is based on the semi-empirical approach of Savitsky. As noted in the Orca3D help file, "One important consideration when using the Savitsky method is that it was developed for prismatic hulls, meaning that the hull is a prism of a pure wedge shape. These hulls had linear sections from keel to chine with constant deadrise (no warp), and no strakes or rails. HydroComp [the supplier of the planing hull prediction library for Orca3D] has developed and implemented a number of modifications to the Savitsky method for warped hulls, as well as for hulls of non-linear sections with strakes and rails."

That said, Orca3D will allow you to perform a planing hull prediction for a hull with tunnels, however, the influence of the tunnels will not be directly accounted for. You can account for the influence of the tunnels both on resistance, by entering an appropriate resistance margin, and on efficiency by entering an appropriate propulsive efficiency during the calculation. However, these numbers are input to Orca not computed by Orca.

I would urge you to review the Orca3D help file section on speed/power analysis for additional information.

Thank you for the other comments. We have addressed several of these types of issues for the next release. We will review your comments internally to make sure they have been addressed.

Larry

[horumbou]

thanks for lleibman  help,
i know that is a self-experiential method,but
what i confused is that when we set the value for the Weight,VCG,LCG,
can select "From Design Condition",but just use the hull(splitd from chine)

the help say:
Note: the weight, LCG, and VCG can be automatically filled in by Orca3D
if a design condition is specified after the planing surface is split (if necessary) from the hull surface by clicking the From Design Condition box.

so it just use splited hull not the original ship hull ,
that weight and VCG LCG values all caculated from splited hull~
don't need to use real ship hull that makes me confused~

ex: 
that's what i do in my model

defind the design condition(float plane 1.28 select all surface but deck)

original
(this by speed & power)
weight:56192.53 kgf
LCG           13.976m  (but from _AreaCentroid is 12.79 why not be equal??)
VCG              1.72m  (from _AreaCentroid)

calculate _AreaCentroid from all surface(transom & hull but no deck and mirror them)
so the LCG VCG can be know~

after split
defind the design condition again (float plane 1.28 select all surface but deck)

weight :44480.61kgf
LCG :    12.95 m   (but from _AreaCentroid is 12.64)
VCG      0.75  m    (from _AreaCentroid)

also calculate  _AreaCentroid(splited transom surface ,splited hull surface and mirror them)

thanks for help so much~

[lleibman]

Horumbou,

The design condition should be defined to include all hull geometry that is "wet". This would include the planing surface as well as the hull sides above the chine. If you split the hull surface after defining a design condition, you must redefine the design condition after the split since Rhino creates new surfaces (again including the hull sides).

When running the planing speed/power analysis you only select the planing surface below the chine because that is all that is relevant to the planing analysis. However, if you want to get the weight and centers value by clicking the "From Design Condition" button, it will be using the surfaces you selected as part of the design condition which should include the hull sides. Note that if you know the weights and centers you can just enter them manually. You don't have to use the Design Condtion to get them. Also note that the VCG value is generally not the same as the vertical area centroid.

Regards,

Larry

[horumbou]

very thanks!
i find i make a very stupid mistakes~
help,it says after splited must redefine the hull...so i just select the splited hull..ha ha

thanks u again!  i will check the results with the towing tank experiment's value~