Foil Ratio

[oldsailor7]

One can cut the "Gordian Knot" by putting a pivotting CB in a sealed CB case, fully controlled from the coclpit, as in the very successful Biccaneer 28 Trimaran.
You could put the CB in any position you wanted---including so far forward that the boat wouldn't sail at all. Ideal for "Parking" the boat for lunch during a pause between races, etc:
However the greatest thing was SAFETY. If you went aground the "Down" control line simply pulled out of the plastic jam cleat and the CB folded backwards,--- then could immediatly be re-set.

[Gary Baigent]

Stick with your dagger board Caiman, don't listen to OS7; I agree with just about everything he says ... but disagree when it comes centreboards and daggers. Daggers are better shaped, better performing, better for leak problems, better for cleaning ... and if you have an elliptical tip, the dagger too, will also pop up if you ground. Tou can hear it coming, light scrape, scrape, whoops, lift that board.

[oldsailor7]

Originally Posted by Gary Baigent

You can hear it coming, light scrape, scrape, whoops, lift that board.

----lol.

Not when you are as Old, Deaf and Slow, as I am.

More like Bump. Crash, Oops----wet feet.

( No offence Gary. )

[tspeer]

Originally Posted by caiman

Can anyone tell me how to compare the lift to area on foils please?eg if a 2 square metre 0012 foil fully immersed produces X amount of lift,what size would a 0015 foil have to be to produce the same X?Everything else being equal.I am trying to figure out the relative sizes of a rudder/dagger board combination.
I apologise if this has been done before.
Cheers

Changing from a NACA 0012 to a NACA 0015 section will not significantly affect the amount of lift in the linear lift range (below stall). The thicker section will have a little higher maximum lift and more profile drag. So it becomes a tradeoff - the thicker foil will give up a little speed, but be a bit more tolerant in situations like coming out of a low-speed tack.

The depth of the board and rudder will have a bigger effect on the drag.

[oldsailor7]

For a multihull where the higher speeds enable lower AOA situations, I have much preferred an NACA 0008 section for Daggerboards. At speed this section has lower drag in real life.
0012 and 0015 sections are better for Rudders, as the trade off between drag and lift is more beneficial when turning and the rudder is at a higher AOA..

[caiman]

I've got to admit,that if given the choice,I'd opt for a CB rather than a DB.Caiman lives on a drying mooring which only has enough water to get at with the foils down,for 2 hours before, and 3 hours after HW.With the foils up,I can add another hour either side of HW.However,control is on a par with a floating Frisbee.The present set up makes the rudder totally non liftable when the tiller is rigged.As a break from the forth coming sanding,I intend making a bracket that will make the rudder properly liftable.I only have access to mild steel,but if the idea works,I can get one made in Stainless.
A lot of the harbours in Cardigan Bay are drying harbours.The Mean Spring tidal range is about 4.5m.Going aground is a fact of life here.There are a few fin keel monos,most are bilge keel.
Cheers

[oldsailor7]

Caiman.
With your sailing situation as you describe it, an under slung rudder, like the alternate spade rudder on the B24 is not the best idea.
If you had a high aspect ratio rudder, sliding (like a daggerboard) in a hinged case it would be better, as you could lower the rudder blade as required and it could still rotate.

A better idea is a pivotting rudder blade with a semicircular head, in a rudder stock where the blade can be controlled by Up and Down lines led thru plastic jam cleats so that you can hold the blade down in deep water and pull it up to be only as high as the bottom of the hull when in the shallows. If you did run aground with the blade down, it would pull the Down line thru the plastic jam cleat thus protecting the rudder blade, allowing sailing on with the blade tilted back, and still giving some semblance of control.

My Buccaneer 28 had a relatively low aspect ratio Spade rudder as standard. In practice we had no problems with it even though we often sailed the boat up the sandy beach (and in the Toronto harbour lagoons, up the grassy banks), as the keel of the boat grounded firmly and the rudder didn't touch bottom. If it did, we never had a problem, because of the designers stout steel tubing post and pivot tube. Your situation is a bit different.

[caiman]

Hi OS7.Thanks for the ideas on rudders.I'm fairly confident that with a bit of fettling I've got the kick up system sussed.The tiller is attatched to the front of the rudder yoke, by sliding the square tube of the tiller, over the square bar welded on the yoke.This was fine except that it 'locks' the rudder down.If the rudder touches,it rotates the tiller into the cross beam and jams.Also,without the tiller rigged,the square bar welded to the front of the yoke has gouged the deck when the rudder is raised.By mounting the yoke facing backwards,and making a hinged bracket,I reckon I can surmount that one,I've had the stock milled over the holiday, and got some steel together today.We will see
What are the thoughts on using carbon tube for a rudder stock?Or are there any other alternatives to Stainless?
Cheers

[oldsailor7]

All the rudder stocks i've ever had on my boats were made of wood.

[caiman]

I have now put 400miles on the new rudder,and can class it as a success.I am now in the middle of making a new dagger board.My Lee helm has gone,as has the 'self servo' effect.I now have very slight weather helm.I want to thank all of you who have contributed to fixing my boat.I hope that I am able help someone,somewhere, in a similar way.
Cheers.