One Ocean describes an internal beam if I am not mistaken. The issues that I have had in the past with internal beams is that the end forms are sticking out the end of the beam with the only attachment being to the last forms with no lateral or support from below. On some boats the end form may be quite long (doubles) and hence the end form can easily be lifted by the down sweep of the first strips and/or pulled to one side. Some people secure the end form to the floor with string to keep it from rising until you have enough strips in place to hold it in place. As for lateral movement, you really need to keep an eye on the end form as you attach strips to make sure it is not being pulled to one side or the other. Many builders have not watched for this only to have the ends of their boat slightly off center and then need to cut away the strips from the inside stems to re-align things. This is why I usually recommend and describe external beams in which you can support your end forms both vertically and horizontally. You can take a look at my web site on the How To page by going to the "Aligning end forms" document.