Swing keel in heavy seas.

[jfrench]

So far, I've only sailed my swing-keel Cat in rather calm conditions on the Chesapeake Bay, but I got to wondering about the swing keel's motion under the hull when the boat encounters seas heavy enough to make the hull pitch up and down. Unlocked, the keel's weight is going to tend to keep it pointed at the bottom, while the hull pitches up and down around it. If the hull pitches down far enough, the keel will hit its maximum limit of extension, then begin to move with the hull, until the hull begins to raise. Now we have the beginning of an oscillation. On the next pitch downward, the hull and the keel could conceivably be moving in opposite directions, causing it to hammer against the fiberglass. It seems to me that the keel and hull could get to flapping around a fair amount in seas only 2 to 3 feet high.

I don't see the keel locking bolt being much good at keeping a 550 pound keel fully extended with the boat pitching up and down, although it might dampen the swinging action.

Depending on tides, it's perfectly possible to have 2 to 3 foot seas on the Bay while winds are a manageable 20 knots. Thunderstorms can cause similar and greater waves and are a common occurrence in the summer. It could really ruin a weekend if the swing keel punched a hole in the bottom two miles off shore, or pulled three or four of it's little mounting bolts out of the hull.

Is there any published limit to what the swing keel hull can safely handle? Any history of sea worthiness, or lack thereof?

 

[littlescoop]

I dont use the locking device it does nothing but make the manufactures covered by a law suit...I have had my boat in 8--10foot swells and never ever felt unsafe...Its all about what you feal good with

 

[txtowman]

You will be fatigued before the boat will.

I had mine in a nasty blow in corpus christi once. the boat was fine.

 

[paphman]

We sail ours on Lake Ontario, and have bveen out in some nasty waves. We do not use the lock-down and have never had a problem with the keel. I think you would have to pitch the bow way up into the air before this could be an issue. At that point I think you will have alot of other thinks to worry about.

Dale

 

[Jackdaw]

If you are under sail, the lateral loads on the keel will keep it wedged solidly in the truck. You could not move it if you tried.

 

[kpgraci]

When I was looking into buying a swing keel boat I was reading some of the manufactures literature (not sure which one) and the boat was only considered self righting if the keel were locked. That makes sense, in case of a knockdown the keel could retract.

 

[watercolors II]

Keep a little tension on the keel cable, by letting the cable go slack you allow the top of the keel to stop against fiber glass. At this point you only have a couple points holding the keel in place, the keel bolts and the keel weight resting against the glass hull. A little tension on the cable will eliminate the metal up against the keel trunk and some of the weight will be carried by the cable, turing ball and winch. In this position I believe the cable will absorb much of the keel shock by it stretching rather than the keel bolts and keel trunk carrying the whole load.

The keel hangs back about 30 degrees from vertical by measuring one of Catalina’s own technical drawings of the keel. If the keel hung vertical the keel would react as a pendulum as you stated, oscillation would occur. Sailing up the face of a wave to an angle of 30 degrees the keel would become totally un-weighted and swing in the vertical, this is where the lock would help in adding a little friction to the weightless keel. 30 degrees is steep and 40 degrees is?

My boat off the trailer and elevated to a height high enough too allow the keel to drop the whole way down to this 30 degree angle the keel creates so much downward force that I can not physically budge the bottom of the keel backwards and I consider myself a little stronger than the average 160 lb. guy.

 

[jfrench]

<<The keel hangs back about 30 degrees from vertical>>

Ah ha, a key point. Some smart engineer did that on purpose! By resting the keel at that angle, it is always pre-loaded with probably about 200 pounds of its weight for stability. I should not have to worry in the moderate weather I encounter. If I ever experience 40 degree pitch I still won't have to worry, I will have died of fright prior to the keel breaking off!

 

[littlescoop]

There you have it all ........so go sail and dont worry let her ride the waves and bring you happyness