Weather Criterion

[santoo]

Aha!!

Thanks Perm Stress,
"How far up did you made your superstructures weathertight?", All window and door are weathertight. But, there are some hole for blower device.

My boss will never change the shape and dimension of superstructure.

You know a ship like passengers ferry which have so high of superstructure, but she can sail with legal...

How about ratio of weather lateral area with displacement?

Thanks...

 

[Perm Stress]

The question really was more like "how many tiers of superstructure are made weathertight?". In principle, (wild generalization tough) if all the superstructure is sealed, and CG is only reasonably (not wildly) low, the ship could be made uncapsizeable, like those all-weather lifeboats that RNLI employ around Britain.
Is it possible to relocate that blower hole one or two decks higher?
I am not sure if lateral wind area to displacement ratio is of much significance in itself... there are many other variables involved.

 

[santoo]

Ok OK Ok...
thanks perm...

I already try to including superstructure to maxsurf model, for hydromax (analysis).
and that's look more stable...
But still so critical,
is that cause of VCG value which so high?
i have try to recalculate the position of G point, but still become so high...

Thanks perm, u open my eyes...

Do you have any email address?
Hope we can be best friend, You are from Lithuania, and i am from Indonesia.

isn't that useful knowledge is knowledge that is transmitted?
hihihi...

 

[Perm Stress]

What is the source of weight and Center of gravity information?
Nothing will beat detailed weight calculation here. I do not mean counting every bracket. I mean counting average weight of every bottom, side, deck, deckhouse side with stiffeners. Then web framing and bulkheads. Then all the foundations for engines, generators, mooring winches... . Then add some 10% for all the forgotten stuff.
Then interior fit-out (just ask a interior supplier company for average weight of all the fit-out for m2 of cabins). And so on with all the major weights.
Provided nothing mayor is forgotten, weight and CG will be more or less accurate. As a rule, weight and CG estimations tend to be optimistic (too light weight and too low CG).
But it is much better than guessing and significantly better than statistics from other vessels.
With multi-deck superstructures of big ships it is customary to make top few (or most) layers from aluminium. Even if steel is used, the higher up the superstructure, progressively thinner plating and lighter framing is used.
Hope this will help.

 

[santoo]

Noted perm... Noted....
Thanks for your reply....

 

[Alik]

Santoo, I belive You are making mistake by assessing HSC using IMO intact stability code. For HSC there is input of windspeed; play with that and get weather criterion comply; then limit operational windspeed.

Pls look at HSC Code, they have their own intact stabiliy assessment methods, including wind gust, roll, high speed turn and passenger crowding. Also pls try to read the code before using software.

 

[santoo]

thanks for your reply Alik,

i already read the code first before running my software. I use BV HSC code.
And i was used his rules..

Maybe u can give me any reference please, because i afraid i make a mistake.

Thanks for your respoun..

 

[Alik]

In HSC annex for stability assessment there is a formula for wind pressure, it depends on wind speed. Reduce windspeed and get compliance for weather criterion. Then, limit operational conditions to obtained windspeed.

Another option - You can work with roll angle; try to reduce it.

I doubt if You can do too much to increase GM of boat if yard is not willing to change the structure. I also doubt that making deckhouse watertight will help as it will cause much heavier structures, closings, etc.; it will definitely reduce initial stability.

 

[santoo]

ya ya ya ya,,,,
I'll try this one first,,,,

So my vessel has a specific operational area,,,,
hm hm hm,,,,

Ok Ok, i'll try,,,,

Thanks Alik...

 

[Perm Stress]

With all the attention to details and high-end stuff, the elephant passed by unnoticed.
Operation area restriction normally mean less stringent criteria for stability, weather criterion, and so on...

 

[Alik]

I believe if operational windspeed is reduced from, say 25m/s to 20m/s it will still be OK. Need to reduce class of vessel, but it is not really important for HSC which are only designed to make passages up to 4 hours long, according to HSC Code.

 

[ekamarine]

I assume that you know where this boat will work. If you have no chance to change design, it's easier to modify the criteria a little bit. You can try to reduce wind pressure which will let design succeed the criteria.
Of course achieving all with changes on design is the way to make a good hull but if you are sure that the boat will not run in extreme weather conditions, no need to satisfy the criteria for Beaufort 10.