Conclusions
While it is recognized that only extended service evaluation will tell with certainty whether the vessel as constructed is fully capable of withstanding the stresses and abuse of continued service operation, some conclusions may be made concerning feasibility of constructing larger plastic vessels, and the suitability of available materials and current techniques.
1. Materials as selected - glass cloth, glass mat, thixotropic polyester resins, and honeycomb and C.C.A. core materials - are entirely suited to production of relatively large plastic boats.
2. Materials and techniques used, while satisfactory, are not necessarily the most suitable now available. The rapid growth of the plastics industry and the continual development of new and improved products is such that refinements to existing techniques could be made which would result in savings in costs, and there is the distinct possibility that revolutionary advances may be made in the not too distant future.
3. The size limit for plastic vessels using this construction is not approached at the 60 foot length.
4. Strength studies in connection with ExMSB-23 indicate that laminate strengths are far in excess of the stresses to which these laminates will be subjected. This points the way to further savings through use of lower quality laminates.
5. Substantial savings in time and money are possible through substitution of a male mold process for a female mold process in fabricating sandwich type hulls in this size range (40-60 ft).
6. The inherent rigidity of the sandwich type hull shell is such that it is unnecessary to provide a complicated cradle to support the shell after mold removal and until the internal structural components are in place.
7. Sandwich type hulls, properly designed, require little or nothing in the way of additional framing beyond bulkheads, keel, and engine girders.
8. For hulls having considerable compound curvature, honeycomb cores are far superior in ease of application to rigid foams. Rigid foams are ideal for applications where shape is not a factor such as cores for keel, deck beams, and studs.
9. There are several questions which need to be answered before it will be possible to design plastic vessels which may be built at lowest cost and which will more fully utilize the advantages offered by reinforced plastics. These are:
(a) What are the effects of service abuse on sandwich constructions?
(b) To what extent can the strength gained through monolithic construction be balanced by use of lower strength core bonding systems?
(c) What should the value of core bond strength be in terms of core shear strength in order to allow for fatigue considerations?
The following might be termed "qualified conclusions" because they are based in part upon study of some of the aspects of single skin construction rather than upon actual experience with this type of construction.
10. It is desirable from a cost standpoint to utilize sandwich construction rather than single skin - conventionally framed construction, since honeycomb is faster and less costly to install than equivalent framing.
11. It does not seem that a single skin hull without framing would have sufficient rigidity to allow handling after separation from a male mold, except at the cost of providing a cradle so complicated as to amount almost to a female mold.