19m semi displacement / planing hull "Port service boat"

Thank you very much for that hull information Sir. But my hull being of aluminum, I am expecting a displacement of about 20 to 25 tonnes max. I will have to consider my hull accordingly.

But the problem here being of complying with both the planing and semi displacement regimes, I am trying to find a hull suitable for that purpose.

Thanks for your help.

 

Hi Devu De Goa,
You should argue more flexible.
The defining factor for a choice of model is not only the material of the hull.
I know many projects which was manufacture from different materials on one model.
For model which I offer, if not we shall scale, the draft will be changed only.
At Displacement=25t draft=0,833m; LCB=5,789m; VCB=0,567m and Cb=0,415; Cwp=0,782; Cx=0,666
If to accept VCG=70 % Depth=1,7m then we shall receive GMt=2m
At smaller displacement the conditions for planing are more good and smaller power of engines also will be necessary for an output on planing.
If you will write principal dimensions from yours GA, I shall make process of scaling of this model and if you want - and a body line on dxf.
______________________
NA Razmik Baharyan

 

It would be interesting to know the reasons why the characteristics should be changed:
LOA 18.98 m to 17.57
Beam 5.50 m to 5.96
Draft 0.94 m to 1.2
Displ. 25 tons to 51.85 tons

In addition, to change them would not require a process of scaling but a related transformation.

 

Hi Devu De Goa,
I do not understand what for you Loa=18,98m instead of 19m, but I have complied with your solution and scaled model. The following sizes were received:
Loa=18,98m; Boa=5,50m; Depth overall=2,7m; Transom depth=2,473m
LCB=12,707m from zero; VCB=0,576m
At Displacement=25t in sea draft=0,844m and Lwl=17,025m
Cb=0,408; Cwp=0,779; Cx=0,663
The beginning of the coordinate system on Orca3D is in the bow.
I publish the changed files and calculations of Hydrostatics.
The body line has made on Shape Maker because looks better than on Orca3D.
There is only one variance - the beginning of the coordinate system on Shape Maker is on the transom, in the stern. Model too most as in Orca3D and too it is scaled.
Next time I shall write as to calculate velocity and power.
_________________________
NA Razmik Baharyan

 

Hi Devu De Goa,
If I was in your place here is how would satisfy requests of your teachers from university in Liege:
Time is a request the vessel to be maintained in two modes - semi-displacement and planing, it means that the service speed is necessary to be in a broad band.
If you will select more high-power engines and will make the project with such hull form that planing with this capacity automatically follows was received that these engines will be quite sufficient on capacity that the vessel was moved with smaller velocity in a semi-displacement regime.
Differently on which example of model I offer to use, if we shall select two engines capacity 900kW for each, the total power 1800 kW will suffice enter on a mode of planing velocity 45kt.
See at the file for calculation Planing Analysis with Orca3D.
There you will see the following:
1. From 20 up to 31 kt including we have a semi-displacement regime of floating at
Fnv = 1,928 - 2,989 <3
Dynamic trim = 4,72 - 4,64 deg
Total propulsive power = 748 - 1158 kW
2. At 32 - 39 kt we have mode of planing with
Fnv = 3.086 - 3.761> 3
Dynamic trim = 4,55 - 3.77 deg
Total propulsive power = 1194 - 1474 kW
But the vessel will be unstable, there is a hazard from Porpoising.
3. At 40-45kt we will have stable mode of planing without peril from Porpoising.
Fnv = 3,857 - 4,339> 3
Dynamic trim = 3,67 - 3.2 deg
Total propulsive power = 1522 - 1789 kW
In calculation parameters which are incorporated will see on a picture, i.e.
Displacement = 25t /alloy of aluminum / and VCG=1,7m; LCG=LCB = 12,678m
You can change location of the propeller and the angle of the shaft axis or speed range and itself to make calculation on Orca3D, for that I publish also the file which differs from previous that two of surfaces - bottom and a spray rail, are pooled in one general and in the bow extremity of the bottom a new series of control points is added.
If is that vague - ask!
________________________
NA Razmik Baharyan

 

Wish you all the best
1. Have you considered a catamaran? Large deck space, high stability. Comparatively low resistance.
2. If you are thinking of a monohull, from the froude numnbers, you can expect a hump in resistance around 16-17 knots . That's a guess. you can use Savitsky pre-planing method to assess resistance.
3. Where do you intend to do the model tests? Go for as big a model as the tank can manage - accuracy will be higher.
4. Before going for model tests, two things are advised. First o the fairing well. Second, do a cfd analysis if you can. You can try out several hull forms before deciding on the one for model test.
5. Keep angle of entrance low.
6. You may use bow strips and a stern wedge.
7. Flow to propeller is all important issue.

 

Hi Devu De Goa,
I dispatch the file of the model on program Maxsurf Modeler.
So now you can enter in Maxsurf Stability and to make the tanks, hydrostatics, intact stability and unsinkability.
Correctly that in Maxsurf Stability there are not criteria about stability under Rules BV, but also that there is very much to you will help.
Look how to start if not you know:
<http: // www.boatdesign.net/forums/design-software/how-start-work-maxsurf-stability-55794.html>

Very much it is pleasant to me Maxsurf Stability. In it there is all about calculations on the Ship theory. There hydrostatic curves are shown in one general diagram as against Orca3D and it is pleasant to me more.
Certainly, it is necessary to calculate still Windage Area and to indicate location of critical points of downflooding, but I think that to you all this is familiarly.
I wish you good luck and success.
_________________________
NA Razmik Baharyan

 

Hi friends,
Probably this model is not pleasant of Devu De Goa.
Likely the similar model of a planing Motor Yacht will be necessary for other student. So that it is lost nothing and not for nothing it is made. Will suffice only to scale on X-axes, Y and Z or to use the function Parametric conversion on a coefficient of fineness or on displacement - see the program Maxsurf Modeler.
To complete business up to the extremity has made the following:
1. Has changed location started the coordinate system of model in Shape Maker - now it is in the bow /see the IGES file fig 1/
2. Has a little bit corrected outlines of frames of the bottom in the bow - now they are straight-line with deadrise /see fig 1/.
3. Has made a new Body lines on dxf on the new coordinate system in Shape Maker - see fig 2. Thus the Bodyplan is shown in two versions - about a frame space 500mm and 100mm.
4. Has made the Table of offsets on Shape Maker for version about a frame space 500 mm - see fig 3.
5. Has made calculation of hydrostatics with Shape Maker - see fig 4.
6. Has made export with IGES file from Shape Maker in Rhino - see fig 5.
7. Has made calculation of hydrostatics with Rhino - see fig 6.
8. The file of Rhino open in Maxsurf Modeler - see fig 7.
9. In Maxsurf Modeler has made calculation of hydrostatics - see fig 8.
Index 1 I mean those files for which started the coordinate system is in the bow.
Now you can compare outcomes of hydrostatics for DWL.
With it I finish this model. I hope that it has liked you.
____________________________
NA Razmik Baharyan

 

Hi friends of Boat Design,
For those from you which "V" figurative outlines of the bottom without rounding in CL prefer, I was changed the surface of bottom in Rhino, was made new calculation of the speed-power and then import the Rhino file in the Maxsurf Modeler.
You can see that ` s all in the attached files.
The outcome of calculation was shown that the draft will be increased a little - from 0,843m on 0,855m in sea by displacement 25 t and the ship have a possibility to go on planing at a stable mode /without porpoising/ still at 39 kt for which is necessary a power 1474,5 kW. For speed 40 kt it is necessary a power 1523 kW, and for 45 kt - 1793 kW.
That is it is possible to draw a conclusion that the total power 1500 kW for the two engines is enough for a good speed 39-40 kt.
_________________________
NA Razmik Baharyan

 

Dear Sirs,

Sorry for the late reply. It was a very hectic week.

Before going any further with the lines of the vessel, I have roughly worked out the structure of the vessel. Kindly find attached the structural drawing. Next, I am doing a preliminary weight and LCG estimation for the vessel.

One that is done I will come back to the hull and redo the planing calculation.

Also included in the same file is a general mid ship shape of the vessel. Here I have taken the idea from @Rabah's work. But I am not using his work directly for two reasons:
1. That will amount to plagiarism in academic work, which will disqualify me in this semester.
2. I do not understand why his upper chine is so high. If it has to deflect the spray at say a draft of about 0.9 meter, it should be about that height.

So, keeping in mind his shape I have tried to make a new shape. I do not know if something like this already exists. Would like to know the advantages and disadvantages of that.

I am keeping a flat surface of about 500 mm at the baseline which should provide a small stable planing surface at all times. Then there is a dead rise of about 15 degrees and a second chine at about the expected draft of the vessel.

I would like to know your comments about this design.

Also, those who are experienced in structure of aluminum hulls may please comment on the structure so that I can revise it accordingly.

Best Regards,
Devu

 

@Rabah

Thank you Sir for all the effort you have put in. I can not use that work directly. But am learning a lot in the process.

Best Regards,
Devu

 

@Bijit Sarkar

Dear Sir,

You have raised some very important queries, I will answer them one by one:

1. Have you considered a catamaran? Large deck space, high stability. Comparatively low resistance.
In this project I am focusing on the planing monohull design as it is something which I always wanted to learn. It is a very specialized field so I want to be good in this field.

2. If you are thinking of a monohull, from the froude numnbers, you can expect a hump in resistance around 16-17 knots . That's a guess. you can use Savitsky pre-planing method to assess resistance.
Yes a hump is expected at that speed, but using the hull shape which @Rabah proposed, I am able to get the vessel planing at about 13-15 knots. Will try to get the vessel planing before the hump. I hope that should help. Kindly advise.

3. Where do you intend to do the model tests? Go for as big a model as the tank can manage - accuracy will be higher.
University of Liege has a towing tank.

4. Before going for model tests, two things are advised. First o the fairing well. Second, do a cfd analysis if you can. You can try out several hull forms before deciding on the one for model test.
The size of the model and fairing will be probably taken care of by the Professor because they may be using some 3D machine for that.

5. Keep angle of entrance low.
Yes I have taken your advise and reduced my angle of entrance, as you will be able to see in the structural drawing I have provided.

6. You may use bow strips and a stern wedge.
Do you mean for the model? I am not sure if I can provide that much detail for the model. Will discuss this with my Professor.

7. Flow to propeller is all important issue.
Okay. Will take care of this when I fair the lines.

Thank you very much for the valuable comments.

Best Regards,
Devu

 

Scantlings : after a very preliminary study, I would like to comment on the following:

1.- Central zone about 7 m from the stern:

• The thickness of the bottom plate may be reduced by 2 or 3 mm
• The inertia of the bottom frames could be greatly reduced and, a little, too, their area to shear.
• The bottom longitudinal (90x12) should have a lot more inertia

2.- Bottom girders could only go between frames 3 and 9.

3.- Watertight bulkhead frame 10 :

• The panel may be 3 or 4 mm thick.
• The vertical reinforcements could be similar to the bottom longitudinals

This must be taken with a lot of reservations, but it wants to indicate that it is probably necessary to make a finer calculation of the scantilings.
NOTE : Design category "D.- sheltered waters"

 

Hi Devu,
Let's see what the experts write for the model which I offered to you. G.M.Novak in the book „ Motorboat, boat and motors in problems and answers”-1977, has shown model of a vessel with two spray wedges in drawing 19. It concerns to double-duty outlines.
The upper spray wedge is on levels static WL of full displacement.
Lower - on levels expected WL of planing with allowance for running /dynamic/ trim.
What will be effect from these spray wedges?
Thanking of them at movement in modes of floating and transfer to gliding it is a little decreasing of running trim.
It is applied on motorboats by length L> 8 m at major external loads in the seas or oceans.
Now we shall think as the model which I prefer will work.
I will be not sure that maximum displacement of your project is 25 t. I expect that it will be more, that is static DWL will pass between two spray wedges. In such situations this model quite meets the requirements about double-duty outlines.
At draft more than 0,9 m /e.g. by more displacement/ in the initial phases of floating only the upper spray wedge will be turn down the spray by the side when the mode planing starts.
Except for that „At sharp heel, for example on circulation, the upper bilge - the spray wedge enters into water and due to the hydrodynamic lift force originating on its lower face, and also to sharply increased volume ensures an increment the Righting moment. ”
When the vessel will pick up the speed up to the operational then it will glide only on two surfaces - bottom surface and down spray rail then the spray will be deviate by the side due to the lower spray wedge.
Which you offer model is similar of the model with double-duty outlines with addition outlines of type sledge in CL /see the file with combination outlines/.
Whether this model will work well? Whether there are feeble parties? Yes. We shall see what for:
The breadth of the gliding plate it is necessary to take up to the first bilge, that is only the flat segment of the bottom in CL. Your gliding plate is received narrower than in my model. That is at the equal main sizes and at equal displacement higher power will be necessary for you that the vessel started to glide.
If you want advice from me - I would remove the flat segment in CL and would make such a profile of the frame /see the file with monogedron outlines/-from one or two longitudinal planing steps.
On relation of the spray wedges - you can accept version only with one in the joint of the bottom with the side. Usually second from above apply at a higher side.
__________________________
NA Razmik Baharyan

 

Hi friends,
I ask to excuse me dear readers of the forum of my small mistake in the view of the stern extremity of the model`s deck. Has already corrected - and files.
_________________________
NA Razmik Baharyan