How do I hide a method so it's not called by programmers but still usable in code?

public class Ship

public bool Validate()
{
//validate properties only found on a ship

FurtherValidate();
}

public abstract bool FurtherValidate();

public override bool FurtherValidate()
{
//validate properties only found on a lifeboat
}

public class Ship
{
    public virtual bool Validate()
    {
        //validate properties only found on a ship
        return true;
    }
}
public class Lifeboat : Ship
{
    public override bool Validate()
    {
        base.Validate();
        // lifeboat specific code
        return true;
    }
}

protected abstract bool FurtherValidate();

protected IValidator FurtherValidation { private get; set; }

public bool Validate()
{
//validate properties only found on a ship

    if (FurtherValidation == null)
        throw new ValidationIsRequiredException();
    if (!FurtherValidation.IsValid(this))
        // logic for invalid state
}