Since I do my first RG 65 project , decided to take advantage and make a step by step how to do a project using Freeship.
The first thing a designer must make when starting a project is to research what already exists in similar boats and make a summary of data dimensions, weights, etc. Eventually over time we will form the project in the head and we have more or less the dimensions and weights, but we can also get off the ground and then this research is essential.
The Project should start by selecting the maximum beam, beam on the waterline, the hull draft, prismatic coefficient, wet surface, position of the LCB and LCF, the forward freeboard, freeboard aft.
Naval Architecture and Data Base page, here on the blog, which appears in the menu up there, you can see the meaning of these quantities.
The RG 65 has the following characteristics, according to my research:
Maximum Beam – 0.13 m to 0.18 m
Beam on the design waterline – 0.10 m to 0.17 m
Total weight – 0.7 kg to 1.1 kg
Bulb – 0.3 kg to 0.8 kg
Freeboard Fore – 0.05 m 0.07 m
Freeboard Aft – 0.02 m to 0.04 m
Hull Draught – 0.03 m 0.06 m
Prismatic coefficient – despite not having data on Cp, is between 0.52 and 0.58
Wet area – another difficult of knowing, I have a reference that is around 0.05 m² and 0.07 m², unreliable.
Let us define the following measures to begin our project:
Length – 0.65 m
Beam – 0.13 m
Draught – 0.04 m
The Freeship can be obtained here: http://www.hydronship.net/index.php?lang=en
If by chance you fall into a page with something in Russian, at the top of the page has a British flag, click on it and you goes to the English page, but this link is already in English.
The software is developed by a Russian. It is identical to Delftship but has a little more recurses. If you use Windows no problem, if Linux, use the program in the Wine environment.
The problem using Freeship is that it is not so accurate for small boats, the calculations are rounded and has zero value. What do I do to solve this problem is to design a boat 10 times bigger, so I’ll make a boat with a 6.5 m long, 1.3 m in breadth and 0.40 m draft, ie I’ll work on a boat on a scale 10 / 1.
For values calculated by the software for my RG I divide by 10 the linear dimensions, areas by 100 and volumes by 1000.
Open Freeship and click on File -> New and you will see the screen:
The dialog box, comes already populated with some data and others in blank as Length , Beam , and draft that I fill up with data that I picked up.
The first two lines already filled with 6 and 5 which are the points of the control net of the hull form. The higher the numbers the harder it is to work, leave these values, which define the shape well, in the future you can raise them. Choose meters in the last row.
After filling in the dialog box, click on √ in green at the top of the box and you get the design of your boat:
Sure, the colors of my screen are not like yours, because I went to File -> Preferences and choose those colors as standard to help explain better, but the design is the same.
If you look closely you will see the drawing lines of the boat and a green mesh with green dots at the intersections of the mesh. These points are those 5 and 6 of the previous dialog box. You change the shape of the hull designed by clicking and dragging these points, which are 5 * 6 = 30 points.
I invite all interested peoples, to participate in this post with suggestions, data, comments and doubts. Only adding we will be better, in all senses.
The Freeship window consists of 4 minimized windows and arranged side by side in the order used in technical drawing:
side view = Profile View,
seen from above = Plan View,
front view = Bodyplan View
and a window to show the boat 3D = Perspective View.
To view each of these windows in full screen just click the maximize button in the window. If after you click the minimize button, the window back to its place, minimized.
If you click the mouse right button in each of the windows will open the dialog box:
The box blue line is for you make a new window if you happen to click the wrong button to close the window, just open the box and choose the vacant window, it returns the same way it was before, that because in reality you are working in 3D and the windows are only views of a 3D object, closing the window does not alter the object.
Camera and Line Mode is to use in the Perspective View.
With Mode you can render the boat in four ways:
Wireframe – just lines, such as now,
Shade, which is a rendering showing the immersed and emerged parts in color, you can change the colors in File –> Preferences
Gaussian Curvature and Zebra Shading put the colors according to the degree of curvature of the hull form.
Camera are ways to see the figure. You can use any you wish.
Background image is the line for you to insert a background image in the window, Print to print and Save Image to save the instant window like figure.
The zoom can be done through this window but the most practical is to click the left button on the window, outside the lines of the drawing, and drag up to increase or down to decrease.
The menu Visibility:
Control Net – serves to make visible or not the mesh. Click to see how it looks, to go back to see the mesh, use the menu again.
Show both sides – used to show or not both sides of the hull, see the figure below with the option thrown Both sides:
If we click the right button in the Perspective View window and choose the option Mode -> Shade, take a look:
You can not see very well the picture, then use the the Perspective view window maximize button and use the buttons located below and to the right of the window to move the window , with them you can put the hull in any position:
To return just click the button to minimize the window, back to the window with 4 views.
Other lines in the menu is to see or not the various lines of design – Grid Stations, Buttocks, Waterlines. Click them and see what happens. To re-activate the lines use the menu again.
The menu line – Hydrostatics features places (or remove) the values of some hydrostatic properties of the hull, it is interesting at times when you want to modify the hull form and instantly see the variations in these quantities.
In this menu and other menus there are some lines that do not work in version Free. Work only in paid version.
There are several icons on the toolbar that facilitate these functions menu:
Just click on them and see what they do. To return to what it was before click the button again.
If you find interesting to have your drawing colors as my drawing, then go to menu File – -> Preferences and set the color as mine, to change the color click on the current color:
Let’s take a look at Menu -> Calculations and see what are the values that the boat has for the main quantities that we need to control in the project.
Clicking in menu → Calculations opens a dialog box with :
Intersections – later we will use this feature
Hydrostatics – Click on it, clicking this sub menu you can access a box with the leak points.
Leak points are grid points that indicate where the mesh has no continuity like at the top of the hull at the height of the deck and in the transom. Check the light green mesh points, these are the leak points. These leak points are normal and not have to worry about them, however if by chance there is a leak point on the centerline of the boat the program will not do the calculations and you have to fix it by putting the value of y equal to zero. When you click a green dot (light or dark) of the mesh a box appears giving the point value of x, y, z . If any point on the centerline of the mesh is not at y = 0 is a leak point and you have to change the value of y in the box to zero.
As we do not touch at any point of the design click a point on the center line and check the box with x, y, and z and see that it has zero value for y. When we click on it change to red
The axes have the following direction:
x -> source (x = 0) in the stern and the positive direction is to bow.
y -> source (y = 0) on the center line, positive direction to the left (Portboard)
z -> source (z = 0) at baseline (Base line) positive direction up
You really do not have to worry about the box of leak points, click OK. If the page show the calculations with all data is because everything is OK, if you see a dialog box saying it was not possible to calculate, verify which point of the grid center line is not with y = 0, correct and return the menu page of the calculations, will appear the calculations (unless you have more points with y non zero, but there’s just see what is not, and put y = 0).
This window gives the values of the main hull dimensions and magnitudes of hydrostatics on the draft of the project we set at the opening of the project, that first dialog box.
Let’s see some highlights of this window:
Water density – 1.025 t / m³ density This is for salt water and we need exchange it for fresh water that is 1.000 t / m³. We design the boat for fresh water because the condition is worst. Let’s just make this change:
Go to Project menu and then click on Project Settings and click on the tab Hydrostatics and change Water Density of 1.025 to 1.000. Click also in the box: Enable automoving model to baseline
Back to the Menu Calculations to open it again with the calculations:
. Beam over all – in spite of setting a maximum breadth of 1.3 m, mesh is formed with 1.292 m, it is inherent in the creation of the mesh, the process that generates the mesh. Not much difference to what we thought, remembering that our RG 65 has a beam that is 10 times smaller than 0.1292, a difference of only 8 / 10 millimeter of beam we want.
Displaced Volume – 0.859m ³ – Volume of water displaced by the hull, is equal to the volume of the submerged hull. The weight of water displaced equals the weight of the boat (Archimedes’ Principle)
Displacement – 0.859 tonnes (in fresh water the volume is equal to the Displaced Volume because the density of freshwater is 1.0 t / m³). This greatness is one of the most important because it shows us that the our boat to be at the design draft 0.4 m should be weighting 0.859 t.
Here I must pause to explain the following:
Did the number that represents the weight in tonnes, in this scale 10:1 we are using, is the same number as our boat would have on RG 65 in kg, so if this boat in the window has 0.859 tonnes displacement, our RG 65, had a displacement of 0.859 kg if built in scale 1:10.
If by chance the GR 65 that we are trying to build is to have1 kg we need move the mesh, changing the shape of the hull to increase the volume submerged to the displacement to be 1.0 t. This is the advantage of letting fires the icon that shows some of hydrostatic quantities on the screen, let’s stirring in hull form and instantly see that the displacement value was.
If by chance I want my RG 65 with a weight of 700 g = 0.700 kg, the boat of the screen should have 0.700 tons of displacement and I have to decrease the volume of the submerged hull by modifying the shape of the hull through the grid, moving in grid points.
Prismatic coefficient – 0.5287 This value is good for light wind where the boat does not reach the maximum speed he can achieve, personally I not use prismatic coefficient down like this, I use 0.55 or up. Take a look on the page Naval Architecture in the Blog Menu to see the text about prismatic coefficient. The prismatic coefficient has a relation on the wave resistance which together with the frictional resistance are the most important resistances.
Wetted Surface – 5.153 m² (our RG 65 would have a wet surface of 0.05153 m² – dividing the value of the screen for 100 because it is area). This value, with the data I have is reasonable to good, here, would be interesting if someone was in possession of data from RG 65 wet surface (area of the hull in contact with water) could add something.
Longitudinal Center of Buoyancy (CB) – 3.144 m Here we have an indication that the center of gravity of the volume, local application of Buoyancy, which is the resultant of the forces of water pressure that pushes the hull up, is at 3.144 m from astern. This data is one of the most essential since it indicate that we need have the resulting centers of gravity of the weights, that make up the total weight of the boat, to be exactly at 3.144m to the stern, for the boat to be exactly on the design waterline.
Longitudinal Center of Buoyancy (CB – Center of Buoyancy in %) = – 3.496 % (negative value because it is aft midship section ), is the percentage of the distance from the Center of Buoyancy to midship section to the length of the waterline project (Total Length of submerged body), is an important aspect to the resistance of the hull in the water. I think a value between -1% to -2% would be better. To change this current value would have to put more volume to forward, shifting the Longitudinal Center of Buoyancy to forward.
Waterplane Center of Flotation (CF is the center of gravity of the waterline area) = 3.018 m, personally I like to keep close to the CB, little aft, near the middle of the boat
Well, seen these figures now I need:
1 – If I want to do a RG with 900 g, so my project will need have a Displacement = 0.900 t, and I will have to increase my volume by increasing the stations area in the immersed part.
Here lies a good conversation – of course, the lighter the boat less the resistance, however a very light boat means a bulb with less weight and thus less righting moment to put the boat at an angle of heel to have a good efficiency of the sail.
Here is the X of the RG 65 equation.
What is the weight of the bulb to be chosen? What is the length of the keel?
Imagining that all boats have an equal weight of hull (smallest possible) what would be the ideal total weight of the boat? In fact, towards the end when the project gets closer is that I will choose the final weight of the boat, for now we leave it with 0.900 kg or 900 g or 0.900 t for our design.
2 – To increase the prismatic coefficient to 0.55 or more we need decreasing the immersed area of the station with the bigger immersed area and increasing the area of the other sections immersed areas and I can also utilize this to increase the volume to 0.900 m³.
3 – When I’m make this, increasing the volume, I would prefer to increase the volume forward of the midship section, in the fore part of the boat, so that my LCB and LCF to come more closer to the midship section.
4 – In the same time I will stay alert to changes in the values of the wet surface for not increase and even decrease it, if possible.
We need change the position of the stem and the aft part of the hull also.
Before we start to modify the shape of the hull will look at the running resistance of the hull Freeship launched.
We go to the Calculations menu and clicking on Resistance and then in Delft Yacht Series or Holtrop-88 for Sea Ships and we have to fill in various data and we now need to talk about speed.
The fastest speed that a displacement boat (because the force that pushes up is arising mainly from water displacement made by the hull) can achieve is given by:
Vmax = 1.34 * √ (length waterline in m / 0.3048) (knot)
The hull on the screen has a length of waterline 5.256 m :
Vmax = 1.34 * √ (5.256 / 0.3048) = 5.56 knot
Well, as we have set the maximum speed to put in place in the dialog box – end speed – we will establish 6.0 and establish 10 calculations of resistance in the range 0.0 – 6.0, then Step = 0.6.
In the next part of the box – Hull – We mark the option – Extract data from current hull and put 0.4 in Hull Draft option instead of 0.000 now, as we just do nothing in keel and rudder let’s stay as is, and hit the calculator at the top of the dialog box:
We see that the graphic appears the running resistance of the boat and if we clicked on Results we have:
In the figures above we have the input data
Here the numerical results of resistance
By the results we see for speeds above 4.8 the recommendation of a Prismatic Coefficient Cp = 0.55 or more are confirmed but the calculations indicate an ideal position for the Center of Buoyancy – CE – of – 3.2%, so the different I guess, but as the project grows we will see how this percentage will evolve.
Well, let’s work in the hull shape, so, close the window and maximize the Profile View:
To set the zoom window, to get the whole picture in the window, click the left mouse button and drag it up or down.
As we have seen, the longer the waterline length is, the greater is the boat speed, by this we need increase the waterline length as much as possible.
We will do this by placing the stem in the vertical and lowering the stern of the boat.
The stern I do not down totally, let it be slightly above the waterline so that when the astern boat wave forms the stern not to bury causing vortices that increase resistance.
To modify the stem, just click on each grid point on the stem and put x = 6.5 and give a return, see:
And see, as the displacement has already increased – displ = 0.87 t .
Come to the stern. Click at the lowest point of the grid in the stern and drag down to where I want to:
Immediately I see that my displacemente go to 0.89 t.
This figure also shows that to move the mouse with the points we lost a little accuracy in position, this point moved with the mouse should be with x = 0 because the point is at stern, yet, but it is at x = – 0.0071 or aft of the aft limit, in this case is just going into the box and put x = 0.
Let’s take a look at the resistance calculations to see the progress of our new boat:
By increasing the length of the waterline we modified the relation Lwl / BWL and Cp :
(LWL = length of the waterline project and BWL = Beam on the waterline project, Cp – prismatic coefficient)
As we increase the length of the waterline and the volume immersed not increased in the same proportion the prismatic coefficient decreased.
Cp = Immersed Volume / ( Max Immersed Sectional Area * Design Waterline Length )
Also with the increase of Lwl the ratio Lwl / BWL soared.
These two effects prevent Freeship formulas for calculating the resistance by Delft because with these new values our boat is outside the dimensions of the formulas are valid for use.
For this reason the Freeship shall calculate the resistance by Holtrop.
Formulas are the problem, you can not compare now the calculated values of resistance with that we calculated before because the calculation processes are different.
A real boat from 6.5 m in length have beam in average 2.8 m, a relation Lwl / BWL = 6.5/2.8 = 2.3. Ours has to Lwl / BWL value 6.5/1.093 = 5.94.
Our boat have sometimes differents proportions compared with real boats.
We can use the Delft calculations if our bean would be at least 1.3 m for BWL and Cp at least 0.52. Our Cp is 0.474.
Then we have no possibility to know if we are changing for the worse the resistance of our project each time we modified it.
And no point in making the project within the parameters for Delft because we do not know the resistance of the boats that lie outside the geometric relations valid to use the formula, which may have a lower resistance.
Hence the need for the designer to know the resistance of RG 65 boats out there, but we do not know.
And then the project becomes a lottery.
We will then begin modifying the shape of our boat to make it stay the way we wanted him to stay, the way we think a boat RG 65 and later take a look at resistance
We will now hit the contour of the hull, put a freeboard compatible with our RG 65, changing the number of stations rising to 11 which is what we normally use to make a RG 65, put waterlines in multiple 0.05 m in order to have data calculation for choosing the final weight of our boat.
To change the number of stations and water lines and change the spacing between them will use the menu Calculations -> Intersections
Let’s click on the Stations icon – the first icon, and pops up the dialog box:
Click the trash and the list of stations disappear, then clicking on the + N and a dialog box appears asking you to put the spacing you want for new stations, we put 0.65 to stay with spacings between 10 stations:
We click OK and the new window showing the position of the 10 stations :
Let’s change the waterlines, click on them, the third icon:
We click on the trash and then N + and appears in the dialog box to put the spacing you want, where 0.05 m:
We click OK, and the position of our new waterlines appears.
Maximize the Profile View and adjust the design within the window to see the heights of the water lines and keep them as reference :
Let us now set our edge of the hull. I will choose for our RG 65 3.5 cm freeboard aft and fore 5 cm which corresponds to 0.35 and 0.50 m in our design.
For this I will click on the grid top spots and bring down the line of the hull to stay where I want.
You can see the dialog box coordinates of the point I moved, he is at Z = 0.8935, as I want a freeboard of 0.50 and have a draft 0.40 the Z should be with 0.90, but there is only going to hit 0.90.
You see clearly that the grid lines passed over the points below, so I’m going down all the points below before continuing:
Now I can lower all the other grid top points:
Let’s minimize the Profile View and see how is the appearance of our boat:
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:
Let’s see the menu: Mode -> Gaussian Curvature.
Right click in the Perspective View window and select Mode and then Gaussian Curvature
The perspective is red with some blue spots and some green parts. These blue stains indicate locations of the hull where there are bumps, we say that these stains are not fairing and is then necessary to take them away moving the mesh points near it so it gets all red, see below figures:
Finally, the entire hull fairing:
The choice of displacement
The lower the boat total weight the lower hull resistance. Let’s imagine that everyone can make the lightest possible hull, weighting, say 350 g, I do not know what the real value.
Let’s assume that this boat has a bulb with 500g and is positioned at 0.30 m below the waterline.
We can separate the righting moment of the hull into two components, the moment due to buoyancy, moved from its position when the boat is in heel and the moment caused by the bulb when it is withdrawn from the vertical of the boat because the heel.
The moment made by buoyancy should not vary greatly from one boat to another because the short length of RG 65. Suppose that all boats have more or less the same value for this moment.
The bulb moment will be M = Weight of bulb * Q * senα
Q = bulb CG distance to design waterline center line
α = angle of heel
So our keel bulb generate a moment M = 0.5 * 0. 30 * senα = 0.15 * senα (kg * m)
Well, what would be the distance for a bulb with 300 g did the same moment?
0.50 m as M = 0.3 * 0.5 * senα = 0.15 * senα (kg * m)
And our boat would shift to a much smaller displacement, from 850 g to 650 g with much less resistance.
Obviously this can be an exercise with weights and measures exaggerated, but the operation is this.
What about the keel?
The keel must have a certain area to generate a lateral force capable of counterbalancing the power side of the sail made by the wind. We then need keep the area of the keel. If our keel was 7 cm for width and 0.30 m long (area 2.1 cm * m) the new keel can be 4 cm wide and 0.50 m long (area = 2.0 cm * m). This new keel may have even greater efficiency than before due to the higher aspect ratio. But everything has a limit.
Thus the design of the RG 65 must take into account this aspect, and then must be studied for several displacements because each competition depend on the statistics of wind speed and so we can use a particular bulb and keel, so, a given displacement.
Thus an RG 65 must have (more or less, I have not deepen into the calculations in this math, but it is just a warning for this detail) about 3 bulbs and each bulb about 3 fins.
Obvious that for light winds the light bulb and shorter keel and for very strong winds the heaviest possible bulb and the longest possible keel, are the two extremes.
Due to know the area of the sails, we can do some calculations and determine which bulb and keel for each wind.
Obvious that nature is not mathematics, but who knows the region knows for sure what the wind speed is more constant.
This is the solution for x GR 65:
1 – A hull optimized for various displacements
2 – A suitable family of keels and bulbs.
So that our procedure these days, we worked only one displacement, in fact has to be done all over again for about four displacements mainly: 0.7 kg, 0.8 kg, 0.9 kg and 1.0 kg and 1.1 kg may . In reality we have to do several projects with various options and choose the best, which has less resistance for the various displacements.
To study the moments of keels and bulbs family that is appropriate to use in RG 65.
Let’s take a look at what can be done about a family of keels and bulbs:
We see that up to 0.15 kg * m we can use the 300 g (0.3 kg) bulb with fin length 0.30 m to 0.5 m, from there you can use the 400 g (0.4 kg) bulb with keel length of 0.5 m and 0.4 m after we can use 500 g bulb with fins from 0.45 m to 0.50 m prioritizing the bulb of lesser weight.
The problem, at least for me is knowing the data of the moments in sail as a function of wind direction to choose the best bulb and how far the keel can be increased without introducing problems such as low efficiency or other problem. Anyway this worksheet clearly shows the problem (and solution).
One doubt: will be the 0.5 m keel feasible, 0.5 m is efficient for RG 65?
If is feasible, who uses 4oo g bulb with keel less than 0.4 m is penalizing in 100 g the total weight of the boat and who uses bulb keels 500 g in less than 0.4 m is also penalizing in 100 g.
Also obvious is that research on the dimensions of the sail is extremely necessary, it can greatly help in the solution.
Other restriction is that we’re just optimizing the boat for stern wind because we do not have a software for optimize the boat in heel.
If you have doubts, discordances, concordances, if you see some wrong, please let us know, go to comments in the end of the page, is very important for all that want know something else, principally I 🙂
I modified the hull form for improve performance in three displacements – 0.8 kg, 0.9 kg and 1 kg and I passed the drawing to scale 1 / 10, to length stay with 0.65 m, the hull form was slightly different from the last drawing posted here.
To move to the actual size, length 65 cm, just go to menu Transform -> Scale:
In Autocad with a routine Autolisp I did the design of heeled waterlines for the angles 10⁰ 20⁰ 30⁰ and 40 ⁰:
It look good without excessive strain on the immersed side.
I’ll do hydrostatic calculations, also with a routine Autolisp in Autocad, especially seeing – displacement, wetted area, the longitudinal CF and CB and prismatic coefficient, checking whether these parameters behave well laid:
– Does not increase the wetted area
– CB should move ahead or stay where it is
– Ditto CF
– Do not change too Cp
I believe, judging by the inclined waterlines from above that there will be no surprises.
The calculation of the final resistance was:
I would ask peoples who have followed these posts during those days to give me a feedback and if in doubt, think that something is wrong, make any comments, make suggestions etc, feel free, because I want to learn and know what people thought of these posts.
Once I check the hydrostatic inclined magnitudes , I’ll put here, it should take a little time and I do the Freeship .fbm file available for all who want to build or study the design, just send e-mail or use the comments.
The calculations in heel:
0,0008 m³ –> 800 g : at 20⁰ the draught is 0.03 m, at 30⁰ is 0.027 m, at 40⁰ is 0.020
0,0009 m³ –> 900 g : at 20⁰ the draught is 0.032 m, at 30⁰ is 0.03 m, at 40⁰ is 0.022
0,001 m³ –> 1000 g : at 20⁰ the draught is 0.034 m, at 30⁰ is 0.032 m, at 40⁰ is 0.024
The LCB variation is practically tenths of mm, that if is not so wonderful is reasonable by the rush that I’m making my first RG 65
– Wetted Area
The wetted area variation is not good, tends to increase significantly , the second RG 65 will be more worked
The Cp are with good values increasing with heel which means that increase as velocity increase, what is good.
Well, I’m going to do my first RG 65, who follows me? The Freeship .fbm file is available for anyone, just send me an e-mail .
About RG 65 Keels and Bulbs
What I conclude about RG 65 keel and bulbs is that I need choose both correctly because I can penalize the displacement. With this figure we see this clearly:
Considering that I can have a efficient keel with 0.5 m (and upper?) we can see that:
– never use bulb with 400g weight with keel less than 0.375 m
– never use bulb with 500g weight with keel less than 0.400 m
Yes, have the intermediary bulb weights.
Beside the fact that we do not have exactly the sails moments exists what we have nowadays: a minimum bulb and a minimum keel and a maximum bulb and a maximum keel (efficient ?) and with this alert we are with more data to choose the better. Choose the wrong bulb weight or a wrong keel height is penalize the displacement and by consequence the resistance.
And I see that the goal is do a hight efficient big keel, that will lead to lower weight bulb and lesser resistance.
Where is the CG ?
Keel and bulb positions
Formulas and datas:
D6 = volume from Freeship
D7 = LCB from Freeship
CGs = like pictures in previous post
F12 –> F19 = column D * column E
F20 = Sum F12 –> F19
D21 = Sum D12 –> D19
D22 = F20/D21
D25 = D6-D21
E25 = (D6*D7 – D21*D22)/D25
D28 = D25+D21
D29 = (D25*E25+D21*D22)/D28
The problem is: where is the keel and bulb positions.
The keel has need to be according the sail area CG and the bulb CG need to be in accordance with the others CG weights in manner that the total x CG must be in the same LCB position.
As bulb is fixed in keel we have this compromise too.
Stipulated the lead distance between sail CG area and CG immersed area we can try a multitude of mast, keel and bulb positions (the bulb CG has a position interval along the width of the keel ).
Changing the data in column E (distances from stern) for mast and keel the spreadsheet give the bulb CG position
With the spreadsheet we have now a mathematical help.
We can change the mast and keel positions in column E and see if the bulb position is compatible with keel position.
You can strange my mast position but my rig is una rig (cat rig ?)with mast aft.
The cells D28 and D29 are to check if the CG weight positions adopted are in accordance with D6 and D7 data from Freeship.