RG 65 Design with Freeship – 6

Well now I will begin to change the hull shape by clicking and dragging the points in view of the following:

1 – put the CB to the foremost, keeping close the CF

2 – seek to increase Cp decreasing the midsection immersed area ( I do the midsection immersed area the maximum immersed area ) and increasing immersed areas of other stations

3 – Put volume forward in the hull above the waterline project to difficult the bow down

4 – reduce the volume of the hull above the waterline, aft, to prevent excessive floatation aft that help the sinking of the bow when in heel

5 – Place the sections immersed aft more flatter (it’s one of my studies)

6 – Try to make the sections in such a way, often referring Calculations, for I have the smallest possible wetted area

7 – increasing, if interesting, the beam on the design waterline to enter into a relationship Lwl / Bwl that is suited by the Delft formulas

I will making images from time to time and place here:

How I want diminish the volume aft, above the design waterline, I will introduce a chine in the height of the hull design waterline.

For that I click with mouse in the two line segments near the wl that pass to red, then go in menu and click on Edge → Crease and the chine is done, after, I move the mesh points so that the top of stations are straight:

Let us look at the design, minimizing Bodyplan:

You can not say that it is a simple conventional RG 65, but so off-beat that is that I need say – just a study – and will be builded and tested – only after checking the inclined waterlines :

Let’s flatten the end of water line:

Of course I always have, when modifying the lines, gone on Calculations -> Resistance to see how the shapes are influencing the resistance, let’s see how it is right now:

Let’s see how the current results are compared to the previous one, since I raised the beam in the water line and the calculations are being made by Delft:

.                                               Before                      Now

CB Position                            -3.5%                     -2,241%

Cp                                           0.5287                      0.5290

WL beam                               1.055                           1.299

Wetted area                          5.15 m²                        6.59 m²

Displacement                        0.859 m³                    0.953 m³

Lwl/Bwl                                4.982                              4.78


v = 4.8 knot

. .                       Rf             Rr           Rt            Cp optimum                 % CB optimum

Before               49.4         48.1       97.5                0.55                                -3.22

After                  61.4           26.5      87.9               0.50                                -2.88

Before do any conclusions, we must realize that the displacement increased, then the resistance must increase. Further on we will see how we put these data in the same displacement.

The frictional resistance (Rf) increased with the increase of wetted area

The residual resistance (Rr) which is composed mainly by the wave resistance collapsed

The total resistance, due to the large drop in residual resistance, lowered.

With the new hull form the Cp suggested by the Delft fell from 0.55 to 0.50% and suggested %CB fell from -3.22 to -2.88

Remembering that the current displacement penalizes the current results, if we compare this hull in a displacement = 0.859 m³ possibly will have much less resistance.

Here a picture for diagonals.

These lines are the intersection of inclined planes with hull and show (a little) the shapes of the inclined waterlines ( I use a Lisp program in Autocad to do the inclined waterlines ), we can do diagonals using Calculations → Intersection in the same way as we do for new stations and new waterlines:

New post only monday  —>  Continues !!!!!!!!!!!


About Fred Schmidt

Engenheiro Naval interessado em projeto de veleiros radio-controlados. Naval Architect interested in RC sailboats design
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