Resistance prediction for a large B/T

[pavel915]

I usually use Holtrop and Mennen modthod, Series-60 etc for resistance Prediction. But the boat we are now designing is of a B/T =6 which is not compatible with Holtrop and Mennen or Series 60.

Particulars of the boat are:
Lwl=40
Bwl=8.4
Draft=1.4
Cb=0.5
Service speed=12 knots

Would you please tell me if there is any other method for resistance prediction for boats of this dimensions?

[Perm Stress]

Try Fung prediction method.

it works well with high B/T.

[pavel915]

Thanks a lot for your reply.

Can you please give any paper which describes Fung Prediction method?

[b1ck0]

I think this is what you need

[pavel915]

Thanks a lot bicko,
But in my boat, the transom is not immersed, so will my boat be still compatible with fung method?(As I came to know that this method is for transom hulls)

[b1ck0]

I can't give you an answer to this question because I simply don't know. Sorry

[pavel915]

Its okay b1ck0, your helps were appreciable,

[baeckmo]

Pavel, what is the L/B ratio and the slenderness ratio (L/(Displ)^0.33)? It might be possible to find something useful if we change perspective!?

[pavel915]

baeckmo,
my boats L/B =5 and slenderness ratio= 6.75 (displacement =220 m^3)
Sorry I did not understand what you said by " It might be possible to find something useful if we change perspective!?"

[Leo Lazauskas]

Originally Posted by pavel915

baeckmo,
my boats L/B =5 and slenderness ratio= 6.75 (displacement =220 m^3)
Sorry I did not understand what you said by " It might be possible to find something useful if we change perspective!?"

NavCad has several empirical resistance prediction methods. Have you looked at what they offer to see if any apply to your vessel?

All the best,
Leo.

[baeckmo]

Originally Posted by pavel915

baeckmo,
my boats L/B =5 and slenderness ratio= 6.75 (displacement =220 m^3)
Sorry I did not understand what you said by " It might be possible to find something useful if we change perspective!?"

What I meant was that you are looking for a solution that primarily satisfies the "B/T"-criterion. If we instead take a look "from another angle", say slenderness ratio, we may come up with something useful.

Since slenderness ratio is a primary factor regarding resistance in this speed range, while B/T is more of a secondary factor, a search among methods based on slenderness may be a better start than to use B/T.

[pavel915]

Thanks baeckmo,
your words are now clear to me.
nice to know the info that slenderness ratio should be my criterion.
I will study that what method may suite my boat with that criterion but would you please suggest me any method for the slenderness ratio of my boat?(as you are more experienced one)

[pavel915]

Leo,
If the slenderness ratio is the criteria, in what range of slenderness ratio michlet will be good?

[Leo Lazauskas]

Originally Posted by pavel915

Leo,
If the slenderness ratio is the criteria, in what range of slenderness ratio michlet will be good?

Unfortunately, Michell's thin-ship theory has nothing to say about the slenderness ratio. It requires the longitudinal hull slope to be small.

Apart from Navcad, you could also see what standard empirical formula are available in Maxsurf.
Good luck with your search!
Leo.

[pavel915]

[quote=
Apart from Navcad, you could also see what standard empirical formula are available in Maxsurf.
Good luck with your search!
[/QUOTE]

Leo,
Thanks for your answer.
Yes I have access to those softwares. But I think a better explanation can be got by the papers which were published for those method, than the softwares. I am trying hard to search those papers. I like that I have those papers and I make my own program or spreadsheet for the methods and in that case I could be more confident when I predict resistance.