Rudder end-plate?

I have a Montgomery M-23 Cutter. See:
http://msog.org/models/m23new/m23_thumbs.cfm

The transom-hung rudder on this boat extends perhaps 8-9" below the fixed keel when the centerboard is up. While my current sailing ground (Potomac & Chesapeake) are mostly soft mud AND I'm almost always sailing with the CB down, I wonder about the wisdom of shaving off that rudder to make it equal to (or slightly less than) the keel and affixing an end-plate to the rudder. Bolger swore by them, but I think he found them most useful in extremely shoal draft boats.

Thoughts?

Jerry W
sailing out of Port Kinsale on the lower Potomac

 

Welcome to the forum.

You'd be much better off with a kickup style of rudder, which can attach to the gudgeons you currently have.

 

that might work for a boat that does not heel, but on a sailboat you run the risk of lifting most of the rudder out of the water when heeled over.

also, it will be operating in the turbulent flow off the keel and center trunk, the extra length on the rudder is likely there to get part of the rudder below the disturbed flow coming off the keel and hull.

You might be able to get make it shoal draft with two shorter rudders, angled outward about 10-15 deg on each end of the transom. it would keep a rudder in the water better, and they would be in the less disturbed flow field far way from the center line. This would also give you some reduncacy if you damage one of rudders as well.

A simple high aspect ratio rudder is more efficient (less drag) than a shorter end plated rudder anyway.

 

This boat is a wholesome cruiser, so the twin rudder arrangement, though it addresses the issue, is (IMO) a bit more then necessary. Kickup rudders are well proven, with many production boats employing them as well as custom designs. Most of my design include a kickup rudder. End plates work, but not as well as a deeper appendage. A kickup lets you have your cake while you eat it too.

 

I would wait until you actually have a few episodes that indicate there might be a problem and then think about it.

Then again, searching 'rudder problems' on your site brought up a guy who ran into some sand and ripped out some of the rudder supports and he wasn't happy. You could make it a kickup or possibly substitute some breakaway (plastic) type of bolts in the supports.

 

Any shoal draft boat with a fixed rudder deeper then it's belly, is destined to tear out the gudgeons at the very least, if not destroy the blade too. I think it's way too easy to design a kickup, cassette or other style of rudder, that can protect itself in a strike and frankly foolish not to. The very nature of shoal craft means, the bottom is a clear and present danger, so not offering some level of security in this regard isn't particularly reasonable.

 

PAR's last post (#6) sums up the worst-case scenario. I've uploaded a photo to Flckr of my rudder. It's at:
http://www.flickr.com/photos/75439007@N06/12133226376/

Clearly visible is the aft cut-out in the rudder so it can swing clear, or nearly so, of the boomkin. Twin rudders are probably out of the question with this big appendage on the transom.

Since the boat is out of the water for the winter...and the rudder is at my house, I'm gonna take all the lines/measurements off it and ponder the fabrication of a kick-up rudder. For now, the safe thing will be "when in shallow water - keep the CB down!".

Appreciate the responses!
Jerry

 

For those in need of a harder working rudder , the end plates do work for low speed better control.

I have seen them made out of angle SS (1 1/2) and bolted to the end of the rudder to create a T and faced so the open side of the angle iron is touching the rudder , creating a diamond when installed.

No idea which installation creates more force when slow turning .

 

Using your existing rudder blade, you can cut it off, through bolt some aluminum plates to each side and reinstall the cut off lower portion, with a pivot bolt. I usually rig an automatic down haul, by way of an "over center" bungee cord, typically rigged behind the pintle straps.

Attached is a very simple kickup, but shows the basics. This is for a much smaller boat, but the concepts transpose. If you look closely, you'll see a lanyard hole on the upper forward corner of the blade, where a bungee is attached, lead up along the leading edge of the rudderhead, behind the pintle straps and cleated. On this design I've run the lanyard in a groove, but you don't have to and instead of a bungee, I've spec's a spectra line to an auto release cleat.

 

Thanks PAR

Thanks for the drawing PAR. I think I shall leave the present rudder as is and simply build a new rudder based on the principles of the design you graciously provided. That way, if I ever decide to sell this boat, the next owner will get the original [unmodified] rudder plus a proper kick-up rudder. I built, and still sail, a little Bolger "Nymph", so a new kick-up rudder should be within my grasp!

Thanks all!

Jerry

 

The drawing I've provided is quite old and originally hand drawn. I use a different set of shapes now for the top of the blade and of course the blade plan form, though most of it remains the same. I radius the top of the blade to match the arc it'll swing through as it raises and lowers. This allows a more uniform "contact patch" between the blade and the rudderhead or cheeks, bracketing the rudderhead. All in all there are lots of little differences between the latest ones I've done and this one, now that I look at it.

 

Welcome to the forum, Jerry! Small world sometimes...I'm straight across the river from you and Port Kinsale Marina is one of our regular river stops.

Crewing a friend's Swedish Maxi, with its deep draft and fixed keel, out off Tall Timbers for many years, I have an appreciation for the constant "battle with the bottom" that you alluded to. ;-)