רצ"ב מאמר ותיק על ויכוח
ב: BOATDESIGN.NET In 1986 we integrated what we call the "Chamfer panel" into the design work for a 10.6m (35') LOA open bridge deck cat which we were designing at the time and which was to become the Alfresco 1060. The chamfer is quite simply a 45û bevel between the bridge deck and the inboard hull side and our original intention was to create a more uniformly stressed structure by minimising the loadings on the hull to bridge join but it had a surprisingly beneficial effect on the motion of the boat in a seaway and significantly improved access into the hulls when applied to bridge deck catamarans. At the time there were two of the Alfresco 1060's building side by side and one of the owners elected to employ the straight bevel (chamfer) as designed while the other rounded it out, effectively creating a large diameter radius between the hull and the bridge. When the two boats were sailing side by side it was possible to detect a distinct difference in the motion of the two boats in short lumpy conditions, with the boat which employed the chamfer as designed demonstrating a more even motion as it encountered wave action. The chamfer panel effectively has a dampening effect on the motion of the boat and this is especially noticeable in quartering and beam seas. When the rising wave encounters the chamfer, the wave acts to lift the boat slightly and if the wave is large or steep enough to strike the underwing it will eventually do so with less force and create a minimum of vertical acceleration to the boat. A steep beam sea is potentially the most uncomfortable sailing environment for a catamaran, with wave forces at 90û to the hull side often creating a sharp jerky motion. The inboard hull side causes most of the problem here as waves are effectively trapped in the corner created by the hull side and the bridge. In this situation the horizontal accelerations are dampened in a similar fashion to the vertical accelerations with the chamfer panel lifting the hull and easing the wave under the leeward hull. The structural form created by the use of the chamfer panel was ideally suited to the integration of composite technology to produce an evenly stressed structure which was also simple and economical to build. Unidirectional glass fibres are laid across the bride deck and splay out down the inboard hull side, thereby removing the highly stressed corner join which is otherwise formed, and effectively distributing the loads from the main bulkhead into the adjoining structure. In 1989 we were commissioned to design the Azure 37 production catamaran (also known as the G37) and in this case the chamfer was a major attribute to the design quite apart from it's structural and sea keeping advantages. The chamfer panel allows the steps into the hull to be moved closer to the hull centreline, thereby making access from the hull into the bridge a reality without having to stoop and without having the upper coach house extend too far across the boat thereby stealing valuable deck space and limiting access to the foredeck.
