100 feet aluminium semi plaining hull

[VexCore]

Hi guys.

I am trying to figure out how to shape a semi plaining boat of about 80 - 100 feet so it can go at 18 knotts but still be able to reach a max of 25 knotts. The material of the hull will be aluminium since the weight must be kept as low as possible.
I am new at this, I studied marine engineering but have no previous xp of ship architecture so any advice will be much apreciated. Thanks

 

[TANSL]

For me, without more data, it is not clear that aluminum is the material that produces the structure of minimum weight for a boat of this length and speed. It would be good to make a preliminary study of the scantlings of the hull plating, reinforcements, deck structure and bulkheads.

 

[daiquiri]

Start by designing a 20 ft boat. Then, if it goes well, design a bigger one, around 30 ft. And so on... After 10-15 years of gradually getting more experienced in boat design, you might start thinking about designing an 80 ft ship.
Cheers

 

[TANSL]

I understand what you mean, daiquiri, and I totally agree. But it all depends on what VexCore means by designing a boat (actually he has not mentioned the word "design"). Just to draw the lines plan and calculate the hydrostatic 20-feet boat is as easy as for a boat 300 feet.

 

[gonzo]

The shape is only one of the important parameters. Total displacement and power are equally influential. Each of them affect the other. You can't design one without the others. When you say Marine Engineering, do you mean mechanical systems of a ship?

 

[VexCore]

The shape is only one of the important parameters. Total displacement and power are equally influential. Each of them affect the other. You can't design one without the others. When you say Marine Engineering, do you mean mechanical systems of a ship?

I finished electromechanical engineering ( in 2013 )( to be a marine engineer - onboard ). I do not have any knowledge about the construction process, but the company i am currently working for requested a general arrangement diagram for a 80 - 100 feet aluminium semi plaining power boat... So i am trying to figure out where to start the process. I chose a Yanmar 552 kw engine and will try to build around that... any ideas?

 

[TANSL]

I think I do not understand you, Gonzo, again having trouble with my English. When you say "You can not design one without the others", what do you mean, you can not design displacement without designing power ?. I do not understand because I think those things are not designed, those things are calculated. What I usually design is the boat.
Clarifications, please.

 

[gonzo]

The power plant is part of the design, as is the shape, total displacement, CG, etc. All of them are inter-connected. To start with 552Kw (740HP) is completely unrealistic to make a 100 foot vessel move at the target speed, unless it is a narrow hull with an empty interior.

 

[VexCore]

I received a list of guidelines from my boss like this:

80 - 100 feet long
2-3 screws - 500 - 900 hp
semi plaining hull
3 man crew ( 1 master cabin, 2 crew bunks, 2 toilets/showers)
2 generators - 20kw each ( 1 is standby )
500 - 1000 liter fresh water with water maker
50,000 liter fuel
galley with gas range ( fresh water system )
saloon with small lcd tv/dvd
2000 nm range at 18 knotts
18 knotts cruise speed ( 25 knott max )
light steel superstructure ( welded )
ray marine or garmin chart plotter / auto pilot
radar - 30nm range ( marine radar )
ais receiver ( no transmitter )
SAT dome phone and internet on bridge
vhf / uhf radio / intercom between bridge and cabins
cutlass on bow, tow ring on bow and stern
navigation lights
** aluminium superstructure is an option if weights is too high for steel
** master cabin with small a/c unit ( fans elsewhere )
** weight must be kept low
** endurance ( supply ) for 5 days at sea

As far as i know for now I am the only one working on this, and I have no experience in such things ( until now I just operated and did maintenance on commercial vessels ). Meanwhile they want me to give them a general arangement based on THIS.

Where would you advise me to start? I began to study books of marine design and naval architecture but i need to show them something in 2 weeks time.

 

[gonzo]

Start by reducing target speed to maybe 9 knots and the power could be adequate in good weather conditions.

 

[kerosene]

Is asking for a raise an option if they just gave you a promotion?

Seriously though. I don't think you can be expected to such thing without relevant education/experience. Its a very expensive vessel to create - going through a project with messed foundation is stupidity of extreme level. Feel free to show this to your boss.

And hey - I am an amateur who hasn't designed anything fir real (marine stuff that is). The experienced ones can second the general idea of my post though.

Its of course not your fault but it is the reason why established "expensive" players in developed countries stay in business. Going with a cheap optins result in situations like this.

 

[jonr]

IMO, the best way to start designing a boat is to look at the existing ones that come closest to your specs. If you expect yours to go twice as fast with the same power, you have a problem.

 

[VexCore]

Look, i just need some pointers. I know this is not done like this but hey what can I do. I need to know what is the first step in starting something like this

 

[rasorinc]

Design for 90' with a beam of 26'. Make your bottom beams angle upward at
18.5% off the keel ( 4/12 pitch ) and space them apart 40" on center and run these forward 70' before steepening the pitch for the bow. Now see what you can fit into that using 2 - 800 hp diesel engines. It's a starting point. Make the final pitch of the bow down to the keel at 55 degrees. For some pictures and sizes and layouts for a boat that size Google US Navy
PT boat designs ( WW 2 )

 

[groper]

Look, i just need some pointers. I know this is not done like this but hey what can I do. I need to know what is the first step in starting something like this

What you can do is this- tell your boss you do not have enough information to design anything from a list like that, regardless of your education or qualification.

There is no purpose stated? Is it a fishing boat, a passenger ferry, a submarine??? What does it need to do??????? It is the designers responsibility to determine most of the items on that list, they should not be dictated by anyone except the designer, who determines them based on the operational requirements of the boat.

So you cannot find answers to your questions, because you are not asking the right questions...