the trailer as shown in fig1 and 2 is basically comprised of a static frame which is mounted over the trailer wheels and a moving apparatus mounted atop the static frame which serves to move the hull - carrying cradles laterally in and out between two possible modes . the static frame 10 includes a centerline beam 12 which extends into a neck 14 which mounts the socket 16 of a conventional trailer hitch . the centerline beam 12 has mounted to it at spaced intervals primary transverse beams 18 which terminate in webbed gussets 20 to support overyling secondary transverse beams 22 . these last mentioned beams extend out and abut with longitudinal outboard beams 24 which are brought together at their foremost portions by connecting yoke 26 which slopes downwardly toward the front to mate the outboard beams the lower midline beam 12 . triangulation braces 28 may be included in the design , and leaf springs 30 stabilized by crossbar 34 connect to rocking beams 36 which mount the dual axles . the frame also mounts a rear bumper 38 . the frame as thus described is obviously subject to considerable variation in engineering detail , but the embodiment set forth above , constructed principally of i - beams , provides an adequately strong , static frame mounted the wheels 40 and serving as a framework for the attachment of the apparatus described below . central to the entire operation of the trailer , both physically and conceptually , is the traveling beam 42 which lies immediately above the static centerline beam 12 . some means is required to permit this traveling beam to move longitudinally relative to the static frame , and as shown this means is a set of roller tracks 44 which are shown as four in number . these roller tracks are also used in another application which will be detailed below , and are illustrated in fig6 through 8 . these tracks each have a u - shaped frame 46 which is made of a heavy steel , and as each track is required to limit the motion of an i - beam therethrough to one dimension , a number of rollers are used in each track . a pair of bottom rollers 48 support the bottom surface of the lower plate 50 of the i - beam and three staggered upper rollers 52 engage the upper surface of the lower plate 50 to prevent the upward escape of the i - beam which will be attempted with considerable force by the traveling beam . staggered cooperatively with the upper rollers 52 are three vertical axis rollers 54 which center the i - beam by riding on the edges of the lower plate 50 . it can thus be seen that once the i - beam is captured in a roller track 44 , it can slide through longitudinally but is otherwise immobile . turning again to fig4 a roller track 44 is shown having a modified bottom 56 which clamps onto the top of the centerline beam 12 . the other three rollers mounting the traveling beam are similarly attached in longitudinal alignment so that the traveling beam is free to move forward and aft along the four restraining tracks . again referring to fig4 the upper flange 58 of the i - beam 42 mounts upright pivot pins 60 , each of which mounts in journaled relation a clevis 62 retained by a nut 64 secured by a cotter pin 66 . the clevis straddles and secures the web of outrigger beam 68 with bolts , welding or other suitable means , this structure being best shown in fig5 . these pivot pin and clevis arrangements are provided in mated pairs as shown in fig4 as are the outrigger beams 68 which they pivotally mount to the central traveling beam 42 . fig2 provides a good view of the attachment of the outrigger beams to the central traveling beam . two pairs of outrigger beams 68 are shown in the drawing , although it is possible and probably desirable to have more than two , and even as many as four or five to support a heavy vessel . again referring to fig2 each of the outrigger beams 68 is captured by one of the roller tracks 44 which in the case of their relation with the outrigger beams serve as guides 74 which are pivoted to the underlying outboard beams 24 . this structure is shown in fig7 wherein the frame 46 of the roller guide is retained by a nut 70 on a stud 72 which is welded to the outboard beam to permit free rotation of the guide 74 supported on a thrust washer 76 . the roller structure described above securely but relatively frictionlessly restrains the outrigger beam to longitudinal motion . returning again to fig1 and 2 , it can be seen that as the traveling beam 42 proceeds forward or aft , the outrigger beams 68 move outwardly according to the path indicated in fig1 . in the collapsed position of fig1 the foremost end of the traveling beam is close to the very front of the trailer and the outboard ends of the outrigger beams are substantially aligned with the static outboard beams 24 and the distance between the outer ends of the outrigger beams is close to the legal maximum width of a vehicle permitted on the highway . at a point near the ends of each of the outrigger beams 68 is a beam plate clamp 78 which supports an upright axle pin 80 journaled in a bushing seated in a suitable bore shown at 82 in a cradle element 44 . each outrigger beam supports one such cradle element and each cradle element in turn supports a plurality of rollers 86 positioned to accommodate the hull , indicated in phantom at 88 , of the vessel which the trailer will carry . the cradle elements for each individual hull are longitudinally aligned and maintained parallel and spaced by longitudinal spars or struts 90 to define complete cradle assemblies 92 . it can now be readily imagined by viewing fig1 and 2 that the entire cradle assemblies 92 , each comprising the component cradle elements 84 with their pivotal attachments to the outrigger beams and the longitudinal spars 90 , can be moved from a retracted position indicated in fig1 to an expanded position indicated in fig2 by moving the traveling beam 42 aft to the position of fig2 . as can be seen in fig2 the ends of the outrigger beams protrude slightly beyond the edges of the cradle assemblies , and it is for the purpose of minimizing this overlap that the axle pins 80 are slightly outboard of the center of each of the respective cradle elements 84 . these pins could of course be positioned otherwise relative to the center of the cradle elements with the commensurate gain or loss in the flushness of the outrigger beam ends with the cradle assemblies when in the expanded position of fig2 . numerous means of moving the traveling beam forward and aft are of course conceivable , but the simplest and probably the most economical in manufacture is represented in the drawings by a forward windlass 94 and a rear windlass 96 . of course a single windlass with a looped cable could be used to achieve bi - directional movement as could a rack and pinion arrangement . out of respect for economy of weight the minimum strength required to make the trailer functional would be provided . inasmuch as the period of minimum stress on the outrigger beam 68 as well as the remaining structure would occur during the shifting between the modes shown in fig1 and 2 because there would be no highway jostling or jolts from hull alignment when loading the vessel onto the trailer or of , minimum beam strength can be provided if some reinforcements are incorporated into the design at the two extreme modes of use shown in fig1 and 2 . this is accomplished in part by the utilization of outrigger beam pads 98 best seen in fig4 which compensate for the eccentric pivoting of the cradle asemblies 92 by supporting the cradles beneath the center of gravity or even closer in when the cradle assemblies are in their completely expanded mode . this occurs because at that position the cradle elements 84 are each parallel to and immediately above their respective outrigger beams so that they will slide over the chamfered - edged pads 98 to be supported during the launching and hauling out operations . a similar chamfered inboard support cradle is mounted on a supporting pedestal atop the traveling beam so that mating inboard arms 100 and 102 would slide over the edges of the pad to provide support for the weight of the hulls in the cradle assemblies during the critical time when the hulls will be transported and in need of the maximum support provided by the trailer . it can be seen from the drawings of fig4 that the static and moving frame structure of the trailer is disposed immediately above the trailer wheels . this configuration results in the allowance of the maximum legally permissible width of the collapsed double - hull structure with their supporting cradles . for this reason it is unlikely that it would be possible to lower the overstructure of the trailer to a position between the wheels to obtain a lower profile . however , it may be possible to do this with the outboard beams 24 , although an obvious sacrifice in moment arm will be made because the high moment arm provided the heavy hulls in their expanded position will produce greater strength demands on the outrigger beams , the static outboard beams 24 , the traveling beam , the centerline beam 12 , and all the structure holding these beams together . by putting the entire mechanism above the wheels , the trade - off is of course a high profile of the trailer and a possible increase in the difficulty of manuevering the trailer in the water beneath the boat during launching and hauling out . it is the design of the instant invention to provide a road - worthy trailer which is capable of effecting , by a single motion of a single operator , the expansion of a pair of catamaran hulls into launching position , and the collapsing of the same hulls into a configuration sufficiently narrow to permit the trailing of the boat on the streets and highways of the country . obvious modifications of design are possible within the overall goals herein set forth , and any such modifications would fall within the scope of this description and the appended claims below .