Bulb Quest Again...

[Torrey]

heiii... its me again....
n stiil having a lots of question about bulbous bow

i'm having a research about bulbous bow and using a model
after i have got all the data... there is something i noticed

when the ship model have no load... in lightweight condition
the speed for the model with bulbous is slower than the ship without bulbous

what i want to ask is ....
how does the bulbous effect for a ship with bulbous when she is sailing????

thanks ...
i will be very gratefull for any information

[jehardiman]

That is correct, the residual drag for a hull with an exposed bulb is higher than that of the parent hull. Additionaly, there is also more wetted surface.

Think of it this way, the bulb only lowers residual resistance when it is submerged so it can effect the "normal" bow wave pressure gradient. In this condition the residual resistance is reduced more than the wetted surface drag is increased. Otherwise a bulb is just a poorly shaped entry with added wetted surface.

[Torrey]

thanks for the reply

my quest must be a basic question... sorry..
cause i am lack of reference here....
n this bulbous thing is a new knowledge for me

i have another question
does the bulbous not only effect the residual resistance but also effect the frictional resistance.. cause by using the bulbous will added the wetted surface

give some opinion about that
thanks alot

[RANCHI OTTO]

This kind of bow named "SV Bow" was developped by the Maierform Group and gave resistance reduction in fully loaded condition as well in ballast depending on Frounde number and block coefficient.

[jehardiman]

Torrey;
Yes the bulb effects both the residual resistance (lowers) and the frictional resistance (increases wetted surface).

Ranchi Otto;
I saw some of that data a long time ago. As I recall (class discussion) there was some question as to what was going on here because of inconsistancies in the measurement of LWL, Rn, and half entrance angle. Which is why it only reduces resistance in some cases. Seems to work best at high block shapes fitted with ellipitical bows as I recall.