Rudder Calculation

[Leanangle]

Does anyone have any information relating to calculating the rudder sizes for a semi displacement boat?

[dave-the-diver]

Suppose there must be calculations, but suspect I would be tempted to make it so it looks a bit on the large size, then be prepared with one of these:

Underwater Jigsaw

HTH

David

[J3JCV]

Is there no other examples around you can copy, I'm sure it is a fine art to getting it exacly right so a Naval Architect will have to get involved, however if its a popular boat you may just be able to take dimensions of one in a local boat yard.

I think the shape as opposed to the size ( as long as it is in proportion to the vessel) can have the worst event for vibration etc.

[mickrick]

You should also consider the position of the blade on the rudder stock. i.e how much blade forward and aft of the stock. It will affect the balance.

I once changed the rudder blades on an 82ft motor yacht. She wouldn´t hold a steady course running downwind in a bit of a sea.
I had the blades cut off the stocks, and some new larger ones fabricated and welded back on.

The difference was chalk and cheese! I did however get the profile from the yard that built the boat.

Can you not contact the yard who built her?

[tr7v8]

Get a copy of John Teale's book "How to Design a Boat" just looked in there & there is a graph of lateral area to rudder area.

[Ayahuasca]

I read an article in a US yachting magazine that interviewed several sailboat designers about their views on rudder design and they all used different methods that seemed to be rules of thumb.

[Leanangle]

Cheers. The Graph in Teal book give quite a large area for the rudder, would this be for a yacht or powered?

[tr7v8]

Leanangle said:

Cheers. The Graph in Teal book give quite a large area for the rudder, would this be for a yacht or powered?

I suspect it is for WAFIs