Is it stable enough for a powerboat?

Size of tank: for planning boat, I would put at least 3-5 hours of run at full power of engines. For semi planning, I would recommend 5-7 hours minimum.

So take engine power, calculate the consumption and define volume of tank.

 

vazer, I have two questions to you.
First, which hull do you choose?

Second, how will you register your boat? As I understand in Croatia all boats above 2.5m should be registered (it seems to be a bit harsh btw), and you should produce evidence of seaworthyness for registration. What does it consists of in Croatia, and how will you obtain it? I have obtained the information from here:
http://www.dubrovnik-guide.net/croatiaboating.htm#boat_registration
According to that page, foreign vessels shall also have certificate of seaworthyness, which would mean that if I would decide to bring even a kayak there, I should have such a certificate (sounds really crazy).

 

You can find a more complete guideline document at the site of Croatian Ministry of Sea, Transport and Infrastructure: http://www.mmpi.hr/userdocsimages/2005/041231-guidelines-registration.pdf
Any craft with a CE certification can be registered in Croatia. Vessels driven by oars (kayaks, beach canoes, pedal boats) are exempted, of course.

 

Alik

Engine, power, consumption, calculation....I know that, I am asking if someone out there have similar experience, is it safe and is it OK to fit tank of this size (82 gallons) in the 20 ft boat, is it tank this size to big for 20 ft boat regardless of engine, or can I fit on the boat of this size mer cruiser 3.0 with alpha one leg gen II and 82 gallon tank

probably I can, but I do not wont to build and look like tanker

 

Then you have asked the wrong one!

There are experts around here to tell you the right way, Daiquiri; Ad Hoc, Mike Johns, Matt Marsh, to name a few. Our young Hungarian (bold) novice is not the one to assist!
Sorry to blow a bubble.


I hate these "know it all novices" coming here and screw new members!
By no means that guy is able to even tell you the basic parameters you would need to accomplish your task!
But shows up as if he would know anything about the business.

Tunnels, Magwas, Questor, and the like, are not part of the industry, have nothing to supply, and are a real danger for a amateur searching advice here!

Be aware, this is a open Forum, you may get what you pay for!
Sometimes, (you have to figure when) it is all proper advice, sometimes it is just profile neurosis!

My opinion, not my 2 c.
Richard

 

hehehe apeks 1, for what you are taking me...

...for Forest Gump

 

Richard (Apex1), Alik, E. Sponberg, Baeckmo, Daniel Skira, Willallison, Guillermo...

 

daiquiri

come stai, where you been on ferragosto....istria

 

I have been on board friend's old Windy 22 powerboat this summer. A 200+ Hp Merc sterndrive and 250 liters (67 gallons) of fuel. We rode smoothly at around 30 kts with 5 persons on board. Your fuel capacity is about 20% higher, which means about 50 more kilos of fuel. 5 persons on board are too much anyways - just throw one of them in the sea and it should work.

 

In Rovinj, the second most beautiful city at the Adriatic Sea.

 

daiquiri

i am asking about that 82 gal tank because i would like to have range with mercruiser 3.0 (130hp) at least, let say from Dubrovnik to Crotona (golfo di taranto) plus 50 miles reserve (20kts cruising speed),

also, i would like to go from Dubrovnik to Bari and back without refueling and still have plenty of reserve

 

Leaving me out I would agree with your list.

And I have some severe opinions about experts.

A shipwright, done well all life long, like Skira, Nortje, Radcliffe, is twenty times the value than a well established boat builder like me.

But these values are not seen and adored any more.

Good for us, we must not provide that.

Regards
(best regards in this case)
Richard

 

vazer, if You are talking about 20kts of cruising on 20-footer, then You are on planning boat...

 

I have attached the resistance calculation output for the hull variations designed so far.
Before calculation I have set the draft of each boat such that the displacement should be 1 ton.
I extracted the hull, set max speed to 30s, and did nothing else, as I don't exactly know what is what
I hope that the results are comparable. They may not be accurate, because maybe more should have been tuned here, but hopefully they are inaccurate in the same way.
Any comment on
- how one can come out with a meaningful amidship deadrise,
- which is the most accurate spray strip influence calculation method for each of these hull forms
- about the applicability of this resistance calculation method
are welcome.

I believe I can come out with midship area above waterline if I try hard enough

Regarding roughness coefficient, after some research I have found that this may refer to the Gauckler-Manning coefficient (http://en.wikipedia.org/wiki/Manning_formula ). This is given as 0.0004 (0.4 * 10^-3) as default. However in the page http://www.engineeringtoolbox.com/mannings-roughness-d_799.html I have found much higher values, even for plastic they give 0.009. So what would be the correct value there for an epoxy coated hull?

The first one (neptune3) is the "original" 5 strake version.
The second one (neptune4) is the same but with 3 strakes.
The third one (neptune5) is the flat bottomed, one chine version.
The fourth one (neptune_flat) is the all-flat version.

I hope this helps to choose the hull.

 

Why are You using this Sedov's method? it is 60-70 years old; the results are based on flat plates and thus not realiable. Use Savitsky for planning mode.