Your description is a little sketchy, but, I doubt that the centerboard had anything to do with it. If the boat was handling well at first, with the rail in the water, then the centerboard was probably down at that time.
Centerboards are designed to not come up by themselves, unless you hit something, and, if you hit something hard enough to raise the centerboard, you would probably have noticed it. I don't know anything about your son, but most kids (not all) who were just learning to sail with their dad would probably not think to raise the centerboard without being told
to do so. I doubt
that your son raised the board without you telling him to do so, or without him asking you first.
You lowered the jib
, because the wind was too strong, but then you raised it again because you thought the windspeed had decreased. I strongly suspect that was a mistake. Inexperienced sailors often have difficulty in judging windspeed, because they don't completely understand how the wind behaves in relation to a sailboat. When you lowered the jib
, the boat's speed through the water would have decreased greatly, and that would decrease the apparent
windspeed (but not the actual
windspeed). It would feel as if the windspeed decreased, when it really didn't. You probably only thought the wind had declined. Also, you might have sailed through a brief lull in the wind, and not realized that a lull is usually only a temporary condition of relatively brief duration.
In any event, when you raised the jib
again, the boatspeed increased, and the apparent windspeed increased, and you found that the boat was overpowered, just as it had been when you first furled the jib
When you raised too much sail area in too much wind, the boat became instantly overpowered. It tried to accelerate, but sailboats are somewhat slow to accelerate, and it couldn't cope with all the energy that its sails were creating, so the boat heeled excessively, the rudder was overpowered by the forces on the sails, and the boat either broached or at least rounded up suddenly. That's probably what stripped the slugs off the mainsail. As they get older and a little worn, plastic (or nylon or monel, or whatever they are) mainsail slugs can break fairly easily. Once they start to break, it's best to replace them all.
So, what should
you have done? Your first instinct was that the wind was too strong for the amount of sail area, so you decided to reduce sail area. That was the right thing to do. But, you furled the jib and tried to sail on the mainsail alone. A sailboat can sail well on the mainsail alone, but it will be at a significantly reduced speed. Since you already knew
that the wind was too much for the main and 110% jib, you shouldn't have re-raised the jib. Instead, you should have tucked in a reef in the mainsail. By doing so, you would have greatly decreased the tendency of the boat to heel, and the forces on the sails would have been more balanced,
forward and aft of the boat's center of effort (it's pivot point). That would have reduced the amount of power being generated by the sails, which is what you want to do when the boat is overpowered. After you reefed the mainsail, then
you could have re-raised the jib, because that sail configuration probably would have been well-balanced under the conditions.
You said you sailed the boat previously on jib alone, and it sailed well, but not this time. A sailboat can sail off the wind just fine with only a jib, but it can only sail to windward if it has some
sail area aft
of the center of effort. That part of the sail area pushes the stern to leeward, which, in turn, causes the bow to point toward the wind. When you sailed the boat previously, you might have only been sailing off the wind, or you might have been sailing with a big overlapping genoa jib. A big genoa jib will usually provide enough sail area aft of the center of effort to help the boat sail to windward.
As others have said, a sailboat generally needs a balance
of forces forward and aft of the center of effort to sail well. With only a 110% jib, the boat didn't have enough sail area aft
to help the boat point to windward.
My suggestion is, avoid the temptation to sail the boat with only one sail. Sailboats are designed to perform their best with two sails. They can
be sailed with only one sail, if you're only
sailing off the wind, or if you use a big genoa, but that's really not the best choice. As the windspeed increases, try to reduce the area of the jib and the mainsail so that you maintain a balance