Details on drop and swing keel

Hello community,
looking for information on support and spacing of moveable keel on 27' or bigger sailboats. I am not lazy and have and still read all the boat books I can access.
But here are some details eluding me:
Each moveable keel transmits lateral forces, weight and momentum into the hull.
Easy movability even with organic fouling and rusting if steel is used must be assured.
Obviously a certain play is essential: on the box containing retracted keel,
the pivot bolt and the part where the root of keel is socketed to the hull. (when down)
Here are my question:
What are the clearances on those points and areas?
How is wear and tear affecting these dimensions?
Is the keel part locked or secured when down; or just dangels around by gravity?
Are there any wearsurfaces to take up gap and need to be replaced within
keel pocket?
Seen some pictures with swingkeels dropped down when on the hard, but details are hard to find. Please help;thanks
Mik

 

Most swing keel arrangements are fairly simple engineering, eg steel plates sliding in slots in cast iron ballast or slots in timber or grp structure. I think you will find clearances of 3 to 5mm fairly typical, I have seen people using a sail batten to poke out jammed grit which gives you an idea. If you have small clearance it can jam with grit or even just mud, larger clearances can still jam, but with larger stones!

My own boat has a swinging ballast keel but it is a smaller boat than you are thinking of. I have it arranged so that when it is fully retracted it still projects a couple of inches below the hull, I think that helps stop it getting jammed with debris but it needs strong pivot etc since the keel can have to take the full weight of the boat plus inertial forces if it bumps on the bottom with the keel up. I also have rollers built into the keel and roling on the sides of the casing rather than just sliding parts, this works well but may be more complicated than really necessary.

If you hope that the boat will be self righting then a ballasted swinging keel must be locked in the down position in rough weather but in shallow water and more benign conditions I would release the locking mechanism to avoid damage if you run aground.

John

 

Thanks John, good info.
The design I am involved in, will feature hard rubber guides/seal
around where the retractable foil meets the fixed keel stub.The ballastbulb on the end of keel will ensure no direct contact with gravel and sand at the replaceable seal ;hopefully!
But I am wondering if any sliding/wear surfaces in the pocket at the inside are needed, to prevent too much looseness.Hydraulic ram is doing the lifting and alignment stress needs to be considered.
cheers mik

 

Plenty of room in the case with teflon, Nylon whatever bearing striips, little clearance on a pivot pin for a swinging keel and no lock required for a swing keel, just a stop. The case can be sealed and all under the waterline with sealing plates over the pin ends and a pipe for the cable/chain hoist.

Marine growth is a pain, jamming down is the usual problem, gravity helps the jammed up scenario. Haulout often and design access into the case.

Vertical sliding are harder, need more room for the case and are more prone to jamming, usually arange for the bottom of the case to be a tight fit on the keel and packers at the top otherwise it clunks around too much, the case usually extends to the deck level.

Loads on the bearing surfaces and pins can be high and are worth calculating so you know that things are safe.