Undergraduate NA Project: Catamaran

[ejasmudar]

Hi, I'm a final year undergraduate student of Naval Architecture. My Project is to design a catamaran. All the parameters are left to me.

So, I'm thinking about a water jet powered Ferry/Cruise/Luxury Yacht plying in the Singapore-Malaysia/HongKong Area.

I need help and advices from the experienced guys here. Is it feasible to do a Luxury Yacht Project (we have only 4 months)? What will the hurdles that I'll have to face, design wise?

How do I decide on the design speed to be achieved/no of pax/etc? Can you recommend a better route?
These are the first part of the project design, for the next week. I hope you guys can help me out.
Thanks

[ejasmudar]

I've progressed since last post. Now I've fixed my main particulars as
LBP: 24m
Breadth: 8m
Demihull breadth: 3.2m
Depth: 2.4m
Draft: 1.6m

Speed: 35knots

Cb: 0.5

Now my next task is to generate a lines plan. But I've no idea how to go about this. I've heard about Wigley and NPL series but where do i get charts/tables from which to generate a hull???
Pls help.

[gonzo]

That does not make sense. If your halfbreath is 3.2 the beam is 6.4. If you put the hulls together the overall beam is 12.8. Also the draft is excessive. For a final year graduate, you don't seem to have the basic knowledge of boat design.

[DavidJ]

No need to be mean.

I don't have much experience with catamarans but from what I can tell the numbers look to be similar to existing vessels. These guys have many catamarans of similar lengths and the beams and drafts seem to be within range:
http://www.incatcrowther.com/Display...n&VesselID=286

Hull series are a good method for designing a hull for students. If you can't find one that works for you try contacting companies who design or build similar vessels. When I did my final year design project in university I contacted several designers. Some people said their designs were proprietary and they couldn't give me any drawings. However, three companies did send me drawings including lines plans. I chose the one that was closest to my requirements and then modified it to suit (the biggest change was to switch from twin screws to a single prop and therefore I needed to create a bigger prop aperture).

Some quick googling on Wigley and NPL:
http://www.fdsfiles.com/webmanuals/h...ody_method.htm

http://www225.pair.com/magic/ftp/Max...t97_couser.pdf

Good luck.

[gonzo]

I am not being mean. He claims to basically be a Naval architect.

[ejasmudar]

Thanks for the quick replies.

Gonzo, I can see where you misunderstood me. By demi-hull breadth, i did not men half breadth. Demihull breadth (b) as opposed to Overall beam/breadth (B) is the full breadth of a single hull in a Cat. That way, 3.2 + 3.2 gives 6.4m which gives a seperation of 8-6.4= 1.6m, which gives me a seperation ratio of 0.2

So far, i have managed to satisfy most of the requirements/restrictions put forward by Insel and Molland in their 1991 RINA technical paper.

ie, Required Value vs My Value
Seperation Ratio: 0.2 - 0.24 vs 0.2
Cb: 0.4 - 0.55 vs 0.5
L/b: 6 - 12 vs 7.5
b/T: 1 - 3 vs 2.042

Let me tell you how i went about fixing these values.
First , i decided on the no. of Pax. Then i obtained parent ship data and plotter B/D L/B, etc I fixed my B from seating arrangement and got L from L/B.
The got D from B/D. After fixing Sep. ratio, i got my b.

But, all through out this project we students make the stupidest mistakes; for eg, a friend of mine, while presenting his findings, on stage, found out that his demihull breadth was negative, due to a mistake in the order of subtration while getting b from Sep. Ratio. So, it is very probable that I will also be making such stupid mistakes and I hope you guys can point it out to me and help me out.

DavidJ, thanks for the advice. I will try contacting the local shipyards here or somebody from the NET. those links you gave will shortly become useful when I'm about to do my resistance and powering calculations. But for now I need to get hold of some NPL tables or charts. Or like my seniors before me did, I can take the stock design I get from Free!SHIP and scale it to my dimensions. Is that OK?

[Leo Lazauskas]

Originally Posted by ejasmudar

So far, i have managed to satisfy most of the requirements/restrictions put forward by Insel and Molland in their 1991 RINA technical paper.

The program "Michlet" includes some NPL hulls as examples. If you are really stuck to find the offsets of an NPL hull try that program.

Better still for your purposes there is an example of the NPL parent hull, NPL100A, available for download from the Delftship web site.

Be aware though, there are five incorrect entires in the table of offsets of the parent hull in Bailey's report, "The NPL High Speed Round Bilge Displacement Hull Series", Resistance, Propulsion, Manouevring and Seakeeping Data, RINA 1976. The example on Delftship used the incorrect entries as markers. The errors are quite small. Good enough for students!

Have fun!
Leo.

[ejasmudar]

Leo, From the delftship website, ion the models section>multihulls, there are only 9 models, of which none are NPL round bilge series.
And i can't find a download link for michlet though their site points me back here.

Atleast is that Bailey Paper available online? I can refer to it directly then.

[Leo Lazauskas]

Originally Posted by ejasmudar

Leo, From the delftship website, ion the models section>multihulls, there are only 9 models, of which none are NPL round bilge series.
And i can't find a download link for michlet though their site points me back here.

Atleast is that Bailey Paper available online? I can refer to it directly then.

Michlet 8.07:

http://www.boatdesign.net/forums/att...ity-mlt807.zip

The NPL100A is in the Naval section at the Delftship site.

I don't know if Bailey's paper is available on-line. Your University might have copies of RINA Transactions.

Regards,
Leo.

[gonzo]

A ratio of 1:2 beam/length is average for cats.

[ejasmudar]

Thanks Leo,
Got the NPL hull in freeship. I scaled it to my length, breadth and draft. I also moved and mirrored it to get twin hulls. But the problem is, the Cb is around 0.3 and I want it to be around 0.5. I tried hull transformationbut I'm always getting transformation error. What to do?

[capt vimes]

probably you will find some answers regarding freeship in this thread...
Modeling boats in Freeship-The techniques of Using the sofware

or at least you could post your questions regarding this software there...

[Leo Lazauskas]

Originally Posted by ejasmudar

Thanks Leo,
Got the NPL hull in freeship. I scaled it to my length, breadth and draft. I also moved and mirrored it to get twin hulls. But the problem is, the Cb is around 0.3 and I want it to be around 0.5. I tried hull transformationbut I'm always getting transformation error. What to do?

I don't know much about Freeship so I can't help.

You could try manually changing the hull shape (using the NPL100A as a starting shape) to get something with CB=0.5.

Good luck!
Leo.

[ejasmudar]

OK, so my project guide advised me to take a planing hull as my fn is greater than 1. So, NPL is out. Now my plan is to take one of the stock designs given with freeship and modify it (it has only cb of 0.2).

I've tried for data about the USCG planing hull series for catamaran but couldn't find anything.

[ejasmudar]

Ooh, If i use a planing hull, the trim will be high during higher speeds right? So, wont this affect passenger comfort? How can this be overcome?