My speedboat hull design!! need some feedback from you experts

[Dutcher]

I'm designing a developable planing hull witch i want to build from aluminium.

Some specs:

Deadrise at transom: 18 degr.
Deadrise midship: 22 degr.

hull length aprox. 5.5 meters
hull (transom) breadth aprox. 1.95 meters. (overall: 2.05 meters)
Displ. not established yet but i quess plus/minus 500-600 kg.
LCG and wetted surface area also not established yet.

I want to put an outboard (130-150 Hp) on it.

I attached the linesplan views of the hull.

What could you experts say about the design (shape) taking into account the specs above?

And when i got the LCG and Displ. how should i go on to get the best results?
Are there any rules where to put strakes?

Thanks for any feedback







Michel

[Dutcher]

No one?

[SeaSpark]

Hoi,

I do not know very much about speedboat design, i do know it is very hard to tell something about hull shape from perspective views only. The isocurves in your pictures also distort the look. The bottom picture seems not to relate to the top three.

It is not hard to create a lines plan in Rhino, if your drawings look more proffesional, you will get more proffesional response.

[Dutcher]

put the linesplan there

[yipster]

cool lines, variable deadrise is gambling without specs, bow perhaps some more flair? how does it look in perspective views?
than again i'm not an "expert"

[Dutcher]

yipster thanks for replying, you said exactly what i was thinking.


Therefore i hope somebody could tell me how to move on when i finished the
design and established data as LCG, vertical CG and displacement together with the hullshape to get reasonable results.

I have acces to software to calculate roll stability, waterlines and trim but this is only in displacement position so i have little exact (theoretical)knowledge about planing hulls.

Am i wrong thinking that i get trouble with the developability of the aluminium plate with a constant deadrise? at least much more tension in the plates?

Yipster what would you like to see in perspective the overall model or the linesplan?

[Dutcher]

bump-

[yipster]

i like to see some renders of the overall model, devellopment checks you can do in freeship, planty on aluminum on the forums etc but you got to do it yourself and "bump" isnt doing it...

[wdnboatbuilder]

I agree with yipster need more flair and flam in top sides or you will be wet.

[tom28571]

Shouldn' try to judge too much from a lines plan but I see nothing obviously wrong with the lines. The bottom design does most to determine whether the boat will be dry or wet. Hard chines contribute to dryness as do chine flats like those you show. I dont think adding flare will do much except when in large waves that the bow actually plunges into. Most wetness is due to spray climbing up the topsides as in a roundbottom hull or windblown spray which is almost unavoidable unless the boat is fast enough that the spray converges aft of the hull.

The buttocks look completely flat aft so I assume the hull is a monohedron from about 60% of WL to transom.

The plan view shows the waterlines, the profile shows buttocks and end view shows sections. Having all three in the same views would likely help visualize what is going on.

[fede]

Hi Dutcher,Tom is correct,nothing wrong in your lines,this shouldn't be really called a variable deadrise in my opinion since 4 deg.from transom to midship is not much of a variation.
You should try to consider the kind of performance you are looking for,carefully check for potential instabilities (porpoising in particular),18 deg at transom could be not enough if you are looking for a comfortable ride at speed in rough waters,it's perfectly ok if you are looking for good performance and don't mind some beating.
If very high perf is what you look for I would not mind about flare...as Tom posted,chines will do the job plus with rough seas you would be jumping from wave to wave more than "cutting" the wave.
Also, a very important part of a high perf boat is played by strakes and LCG location,the LCB/LCG relation is very important also,of course, try to keep VCG as low as possible...(duh)
If you want to get in deep with high speed design get Renato Levi's books,SNAME small crafts cd and Blunt Papers.
A new book is out called high speed hydrodynamics that should be very well done.

[im412]

my advice would be to google locally australia and new zealand to see what they are doing in aluminium ..it is a popular material here
http://www.google.com.au/
http://www.google.co.nz/

[Dutcher]

hey Fede,

Mentioning the books was very helpfull, in the past i searched the internet for books but i didn't really know wich book would be usefull.

I have no intentions to ride the boat at sea but only at rivers and lakes so the deadrise of 18 degr. would be reasonable i guess.

I also was planning to put strakes on it but i have to figure out what the best position would be.

Yipster,

I'll give it a try but i'm not that much of a renderer so don't expect to much from it, and of course i'm willing to do it myself.

[tom28571]

Originally Posted by Dutcher

hey Fede,
I have no intentions to ride the boat at sea but only at rivers and lakes so the deadrise of 18 degr. would be reasonable i guess.

Unless you will encounter some fairly rough water in those rivers and lakes, you may not need so much deadrise. There is a price to pay for deadrise in more power required, more weight, less stability, higher fuel use, higher minimum planing speed and more wake. The last one can make for upset neighbors in small areas. I consider a lot of deadrise aft of midships a negative factor in general enjoyment of a boat unless it is needed for rough water conditions.

[Dutcher]

Tom,

You got a point there, the only big waves there are the wakes that come from other ships (yachts and commercial vessels) but they can be large too.

therefore i want a certain degree of smoothness in the ride when i'm just cruising.
That i need some extra power i have to take for granted i think.

I already went out there with other aluminium boats with +/- 12 degr. deadrise and sometimes thats a fairly rough ride.

that is actualy the reason wy i came up with 18 degr.

Do you think 18 degr. could work for me in above mentioned conditions?
(sry for asking that much but i got no expirience with higher rates as 12deg.