# Powerboat trim angle study

Hello to everybody,

My name is Zeus, I am a naval architect from Uruguay, working in the UK at the moment.

I am really interested in predicting the trim angle of planning hulls, because in my office we do this with old Savitsky’s equations (forgive me dear Sav!), but I would like to try which are the results with CFD.

So, I would like to invite all the people interested in the project to work together and try to solve the problem.

I don’t know anything about CFD, but I can help with the hull, naval architecture and later to compare the results with the old Savitsky equations.

Maybe, first it would be better to simulate one of Savitsky experiments, and then try with a different hull.

Let me know your questions, of course the project will be public, so everybody can learnt from it.

Many thanks!

5 Likes

Very nice idea, I’m in.

I propose that as a first step you show us an example case done with equations, in order to analyse the phenomena and the kind of simulation we can make. If you have seen this done in CFD before, an example of that would be very useful also.

Second, you can select the Savistky experiment we will use as a benchmark and show it to us, alongside the reference results, so can we build the simulation and plan the posprocessing to extract the relevant data.

Greetings.

Hi @zgaryulo, Hi @ggiraldo,

excellent - interested in this topic as well. @zgaryulo do I get you correct, that the quantity that you want the simulation to predict is the angle the boat has with respect to the horizontal axis? So the boat can not be fixed in the domain, but free at least in rotation across the lateral axis? So looking at the graphic below, you’re looking for \tau ?

If that’s correct, we’ll probably need to work with the 6DOF model. In the other topic over here the boat is fixed withing the domain, so \tau is prescribed and not computed.

In any case, what we’ll need to do is upload a model of the flow domain, as SimScale is not yet capable to build an external flow mesh with a split face inlet to allow for both water and air entering the domain on the side. I did this briefly over in Onshape:

Let me know if you’re fine with me making the Onshape model public - then you could work on it as well.

As a side note: Middle of next week, there will be some improvements to SimScale with respect to multiphase flow analysis (@jprobst currently busy with this). So I’ll wait until then and run the first analysis and make my project public, okay?

Looking forward to this!

David

Thanks @ggiraldo and @dheiny for your interest in the project, I am looking forward to work with both of you.

First of all, I could send the original Savitsky’s paper to anyone interested in the matter, you only have to ask for it.

I have examples done with equations with my own excel file, the results are something like this:

Unfortunately, I don’t have any CFD examples of this at the moment.

Here are some pictures of the boat that I would like to study, and the hull lines drawing.

The thing is, original Savitsky’s paper was done for prismatic hulls (same deadrise angle, single chine hulls), nowadays, hulls are double chined with warp (variation of deadrise angle with lenght), people continue to use the method with some minor modifications, but it would be interesting to study the problem with CFD to see the differences.

Before trying to solve this complex problem, we could try with one of Savitsky’s prismatic hulls first, at the moment I am looking for results and geometry descriptions of the hull used in the test, so I can model this in Rhino (and the domain also) and then run the simulation.

1 Like

Please send the paper to me at guillegiraldo@gmail.com

Hi @zgaryulo,

yes, the paper would be great. Could you post a link to it here? I think first reproducing the known application with a prismatic hull is a great approach. That way, we can validate the sim setup and then apply it to the new hull you’re designing.

Interesting to see you using Rhino. Is there a specific reason for it?

Best,

David

Hi David,

I don’t know how to upload the file here in the forum (shame on me), but if you give me your email I’ll send it to you, and also another paper with a recent tank testing from Southampton University, because I can’t find original Savtsky’s results…

In naval architecture and yacht design Rhino is a must, because it’s easier and faster than other softwares, SolidEdge, Solidworks or Catia, are used only in big projects (generally speaking).

Hello everyone!
Zeus, it’s a GREAT Idea.
I am also a Naval Architect with similar interest in CFD so I am IN!
I think we need the solid model we can mesh and COG with the correct displacement of the boat.
Because as you know, the position of COG in relation to the center point in which dinamic lift acts, is crucial for the trim.
And also for resistance…
But I think the real validation of this CFD analysis is possible if we have some basin model testing results…

Welcome aboard!

I have some results from a tank testing that I would like to discuss with you, please give me your email so I can send you the paper.

I couldn’t find Savitsky’s results, but we may use Series 62 of Blount, if I remember well, the geometry of the hulls was described very well in that paper.

@bkocijan - excellent!

once you’ve got the geometry that you suggest for the initial validation step, it would be great if you simply put it into a public SimScale projet and post the link here. I’m happy to set up the first baseline simulation, from which we can start tweaking! @gholami will be the go to guy once we model the boat free floating. In a first step, I’d probably start with having it fixed. I think I’ve mentioned that often in this forum - I’m the “crawl, walk, run” type of guy when it comes to simulation

Best,

David

Hi! Here is the link to the project:

https://www.simscale.com/projects/zgaryulo/powerboat_trim_angle_study_1/

The geometry is very simple, very prismatic:

The loading coefficient is around 6 (Ap/V^(2/3)), the CG is around 35.5% of the Lp (chine length).

The weight of the craft is 6855 kg.

These are the results expected from my Savitsky analysis:

Any doubts, please send me a message.

1 Like

Hi @zgaryulo,

awesome - excited to get started. I’ll get back to you soon.

Best,

David

I took the hull geometry and modeled the domain in OnShape, imported to Simscale and meshed for a laminar simulation. Links are:

If you look at it, I am having an issue with the mesh. The region refinement for the fluids interface is producing this triangular refinement outside of the region box. I don’t know why this happens, and I have tried many variations on the region box and this always happens. Maybe David can help me with this?

Hi @ggiraldo,

mhm - you mean this here, right:

I’ll take a closer look and will get back!

Best,

David

Forgot to mention - nice mesh setup!!

Wow guys you don’t waste time!

But I think we should do a turbulent simulation.
We should use the Re mentioned in the paper Zeus suggested.
I suggest we use omega-SST turbulence model, what do you guys think?

@zgaryulo : Which model did you choose?

@dheiny

Exactly, that’s it.

And thanks (I got inspiration from the Free Float Boat simualtion project)! Hope we can fix it and start simulating.

@bkocijan

I agree, we should make turbulent simulations. Will add boundary layers to the mesh.

@dheiny

Could you find something in the mesh?

2 Likes

thanks a lot for following up. Unfortunately no progress on my end yet - I’m planning on working on it again this weekend.

I also saw that @Zoran is doing interesting stuff over here: https://www.simscale.com/projects/Zoran/v1hull_fs/ - very interesting model + mesh! How did you generate the mesh?

Best,

David

Dear all,

I am now pursuing a career as naval architect while developing new skills in FEA and CFD. I really happy to meet the experts here to learn from. Also, I am excited to collaborate with you if I may.

@zgaryulo, do you mind to send me the papers, the old and recent, to rpmuayyad@gmail.com?

Best regards,