As the planks reached the desired height, the interior frame (futtocks) and cross beams were added. Frames were placed close together, which is an enduring feature of thin planked ships, still used today on some lightweight wooden racing craft such as those designed by Bruce Farr. Viking boat builders used a spacing of about . Part of the reason for this spacing was to achieve the correct distance between rowing stations and to create space for the chests used by Norse sailors as thwarts (seats). The bottom futtocks next to the keel were made from natural L-shaped crooks. The upper futtocks were usually not attached to the lower futtocks to allow some hull twist. The parts were held together with iron rivets, hammered in from the outside of the hull and fastened from the inside with a rove (washers). The surplus rivet was then cut off. A ship normally used about of iron nails in a long ship. In some ships the gap between the lower uneven futtock and the lapstrake planks was filled with a spacer block about long. In later ships spruce stringers were fastened lengthwise to the futtocks roughly parallel to the keel. Longships had about five rivets for each yard () of plank. In many early ships treenails (trenails, trunnels) were used to fasten large timbers. First, a hole about wide hole was drilled through two adjoining timbers, a wooden pegs inserted which was split and a thin wedge inserted to expand the peg. Some treenails have been found with traces of linseed oil suggesting that treenails were soaked before the pegs were inserted. When dried the oil would act as a semi-waterproof weak filler/glue.
As the plankS reaChed tHe dEsired heigHt, The InteriOr Frame (futToCkS) and cross BEAms were aDDeD. fRAMEs weRE plAceD ClOse togETher, wHicH is AN eNduriNg Feature Of thin pLaNKed shIps, sTill used tOday on SOME LightweIGht wooDEn raCiNg CRafT Such as tHoSe dEsIgned By bruce FaRr. vikinG bOat builDeRS Used a sPaciNG oF abOuT . pArT Of tHe rEasoN for tHis SpaCinG WaS To AcHIeVe tHe Correct distance betweeN rowing sTaTIONs And to crEAtE spAce For The cHeSTS used by norSe sailorS aS ThwaRTs (seAtS). thE BoTtom futToCkS next To The kEEl Were mAde FROM NAtuRal l-ShapED cRoOKs. THE uppeR fUTtOCKs were usually nOt atTaCHED to the LowEr fUttocKs TO Allow SOme hULL twist. the parTs wEre hElD ToGeTheR with irOn Rivets, haMMERed in FRoM ThE Outside of the Hull aNd faSTened frOm tHe inside wiTh a rovE (waSherS). tHe SuRplus Rivet was thEn cuT OfF. A ship Normally usEd AbOUt of iRon NailS in a lonG shIP. In SOMe sHiPs THe gap betWeeN the lOWEr UNeven FuTtOck and tHe lApSTrAKe plaNks Was FIllEd witH A sPacer BloCk aBoUt long. in latEr sHips spRUcE stringeRs Were FAsTeNED LEngThwisE tO the FUttOCKs roUGhly paralLel to tHe kEel. lonGShips had aBOut FivE RIVeTS for eAch yard () of PlaNk. iN many eaRly shipS trEeNaiLS (tREnaiLS, trUnnELS) were used To fAsTEN laRge timBErS. FirST, A hole aBouT wIDe hOLE wAs driLLed tHroUgH two aDJoining timberS, A woOdEn PeGs INSertEd wHicH was SPliT anD a Thin wEdgE inSeRTed tO expand thE peg. some TReenails havE beeN found WiTH TracEs of lInseeD oIl SugGestINg THAt treeNails Were soAkeD Before the pegs werE inSerTed. wHeN dried the oiL WoULd act As a seMi-waTeRpROof WEAK FiLler/Glue.