lifting rudders

[David King]

Hi 

I am having to replace my rudders due to beaching damage. 

I would like to make them from composite materials to keep them light and also be able to lift them as my boat is on a drying mooring. So my question is has anyone designed a system they are willing to share, so I don't have to reinvent the wheel. Any ideas or comments please.

Regards

David

[Andrés]

Boatsmith has fitted lifting rudders in the T8m. You can see it in

http://wharrambuilders.ning.com/photo/albums/boatsmith-tiki-8m-day-...

I don't like the gap between the rudder and hull (it can catch underwater ropes), but I see that BS has changed the design, see

http://tiki8m.blogspot.com/

[David King]

hi Andres,
thanks for the reply. I had thought of hinging in the same way, but it would add another metre or more making them exposed in high winds when dried out and damage in shallow marinas.
My thoughts are to construct the blades the same shape as the originals but to make a head stock of stainless steel with a sliding fixing to allow the blades to rise vertically by 600mm.
the blades will have a hinge sized gap between the hull and blade and end at the base of the skeg so no rope problems.
My fears are that the blades may not have enough lateral strength being fixed at the top section only.
what do you think
David

[Andrés]

I'm sorry but my english is not very good and I don't undestand well your idea. You can make a rudder to be of a pivoting type, a lifting type or a combination of both. I think you want the last option, which is the most complicated.

Ian Farrier has this type of rudders in his trimarans, but I think is a little high tech (you can see it in  http://www.f-boat.com/f-33/f-33newfeatures.html); there are other types in Crhis White's  book "The cruising multihull".

Also you can find interesting the following thread

http://wharrambuilders.ning.com/forum/topics/rudder-lashing-issues?...

If you keep the skeg and you don't want to increase your rudder deep, then I think that the lifting type is the best option.  You can see an example of this type in this beautiful M. Tennant cat

As you can see, the case of the rudder can be made very long and strong connected with three hinges.

[David King]

hi Andres,
your English is fine. The rudders in the photo are the type i a. thinking about.
I will be drawing plans a d will send them to you.
David