Bolbous Bow design theory

[Guest625101138]

Originally Posted by designz

Sandy,

Thank you for your reply. While I fully appreciate the limitations of bulbous bows I also know they have other benefits (apart from having a very narrow speed range). You also did not ask why I was asking this question nor to what application I intend to put the vessel. So with respect you did not answer my question.

Do you know a mathematical formula for calculating the optimal size of a bulbous bow (for a given size and expected velocity)?

Leo Lazauskas has posted a version of Michlet/Godzilla with 20 shape functions at this web site:
http://www.cyberiad.net/michlet_betas.htm
It arrives at some interesting shapes. And you can probably get it to produce a bulbous bow as a minimum drag configuration if the conditions are right.

Leo also posted the attached in.mlt file for Michlet. This is Wards Optimal hull and basically produces no waves at the design speed. It has a very interesting bow.

So armed with this you may be able to produce a minimum drag bulbous bow for your application.

I have not played with the 20 shape function to see if it would arrive at a bulbous bow. It was certainly producing some interesting sterns for the case I was considering.

There is also a thread titled "Michell v CFD and EFD: Round 2007" that Leo monitors and I am confident he can answer your question or at least advise the route to take. I know he has proposed simple methods to achieve the same result but not something I have taken notice of.

[designz]

Rick,

Thank you for the reply, - I will investigate this with considerable interest.

Regards,

Christopher

[Guest625101138]

Originally Posted by designz

Rick,

Thank you for the reply, - I will investigate this with considerable interest.

Regards,

Christopher

Christpher
The ward hull is scalable. I have scaled longitudinally and there is a point where the wave drag drops to zero and obviously at higher speed than the hull given in the in.mlt file. I have not checked scaling in other dimensions.

The Ward hull is not the minimum drag hull for given displacement but it has virtually no wave drag. It might find application in low wash situations.

The 20 shape function hull produced by Godzilla can be quite distorted but this aligns with results of CFD generated hulls I have seen proposed for ships. They can be lower drag for given conditions but not something you would want to build or are practical to build.

There is some nice comparison photos of the influence of bulbous bows here:
http://boatdesign.net/forums/showthr...hlight=bulbous

I have modelled these things in Michlet but for the type of slender hulls I use they offer very little, if any, benefit.

Leo can certainly point you in the right direction.