Vacuum Bagging Basics Shop Talk

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SHOPTALK Vacuum Bagging Basics Vacuum baggingsmallfiberglasspanelsprovides a higher strength-to-weight ratio compared to hand layup and produces a good finish on both sides. It's the ideal method to fabricate anchorlockers, hatches,tablesandothersmallpanels. M old table with outline of a panel written on the table with indelible marker to act as a cutting template for fiberglass fabric and othervacuum bagging consumables. Typical laminate stack. (right to left) mold surface, inner fiberglass skin, foam core, outerskin, peelplyfabric, breatherbleeder layerand clear vacuum bag. W hilewe prepared oursupplies,we had a helper wax the mold table with a carnauba mold release wax. Five or six applications were required for the first part, one or two for further parts from the same table. Waxes need to harden for a few hours between coats so we allowed two days for this step. We then used the following weight ratios and weighed out our fiberglass materials to determine the amount of resinneededforthecorrectfiberto resinratios:mat35%fiberto65% resin;wovenrovingorwovencloth, 45%fiberto55%resin;stitcheduni- directional/biaxialtypefabrics, 50% fiberto50%resinandprecoating balsa core, 0.5 oz/ft. sq. (150 g/sq. Story and photos by Diane Selkirkand Evan Gatehouse Anchor locker cross-section diagram compares old to new locker volumes. a fiberglass sandwich to the skins. Itprovidesan excellent strength to weight ratio because of the higher glass-to-resin ratio and produces a good finish on both sides of the theincreasedspaceforanewdiesel panel.Asforthenegativesassociated fueltank.Duringthedesignprocess, withvacuumbagging,smallpartsare timeconsumingtofabricatedueto theextraworkinvolvedinvacuum bagging. It'salso more expensive than astandardhand layup becauseofthe additionalcostofvacuumequipment andsupplies.Thetechniquecarries riskofpartialfailureifyoudon'tget yourvacuumbaginplacebeforethe , resinbeginstogelorifyouhavea ) vacuumbagleakthatyoucannot find.Alltheconsaside,thismethod wasthebestSolutionforouranchor lockers. Layup Prep Webeganthelayupprocessbytest- ingour procedures. Before any resin waswetoutorthetablewaswaxed, we stuck down some sealant tape andsomefoamcore.Wedidatrial baggingoperationtoseewherethere Theanchorandfenderlockerson "Ceilydh,"aWood'sMeander40' (12m)catamaranbuiltin1987, hadbeguntorot.Assembledfroma combinationofpaintedandfiberglass ingandweincorporatedthisideainto wealsorealizedthelockerscould doubleascomfortableforedeckseat- Waxing themoldtablewithseveral coats ofwax. wereleaksandthenlearnedhowto fixthem.Then,wedidasecondtest runbylaminatinganon-essential piece.Vacuumbaggingrequiresabit ofpractice,soexperimentationand testrunshelpensuretheoutcomeis successful. -coated plywood, the light construc- tionandpoordrainagehadproven tobeinadequatefortheheavyuse required ofan anchor locker. Additionally,thesizeofthelockers madethemtoosmallforourground tackle.So,ratherthanjustrebuild- ingthemfrombettermaterials,we decidedtocompletelyredesignthe lockersfor multi-purpose use. Thenewlockersweredesignedto be bigger and have better drainage. Locatedinthemiddleoftheboat, these lockersare inthe optimal loca- tionforheavyobjects.Catamarans are more sensitive than monohulls toexcessweightintheendsofthe boat,sowedecidedtousesomeof Diagram ofvacuum bagging system the design. Usingourdesigndrawings,we prefabricatedthelockerpanels. Prefabricatingthepanelsallowed muchoftheworktobedoneina controlledenvironmentofftheboat andmeantthatthebuildtimeinthe boatyardwasreduced.Althoughthis wasarelativelysmallproject,althe panels were vacuum bagged. The bottomsofthelockersaresubjectto wave impacts and the extra strength ofavacuumbagged,coredpanelare benefits. Whendecidingifvacuumbagging issuitable for a project, consider the followingpros.Vacuumbaggingisthe bestwaytosecurelybondthecoreof Airbleedvalve Forthelockers,weusedaflatmold m)resin.Hereareafewexample surface.Wemarkedouttheoutline calculations:12ozofmat=12ozx ofeachpartonmoldtablewithan (0.65/0.35)=22oz(6248)resin; Optionalsecond pressuregauge Pressure gauge Vacuum pump indelible marker. Usingthis outline, weusedanOlfafabricrotarycut- ter to cut the fiberglass fabrics that formedtheskinsandthenuseda utilityknifetocuttheshapefromthe Corecellfoamcore.Ifthecoreisnot predrilled,itmustbepuncturedto allowairtoescapefromtheoutside reinforcing skin. We drilledholesevery 3" (75mm) apart, about 1/16" (lmm) diameter. Sealing tape 24oz of biaxial = 24oz x (0.50/0.50) =24oz(680g)resin. BaggingTechnique Whenwewerereadytobegin,wecut outthevacuumbagplastic,thepeel plyandthebreather/bleederlayer. Thevacuumbagneedstobeatleast 12" (300mm) wider than the part on each edge. The other layers were cut to the size of the part. We applied a Vacuum bag Breatherlbleededlayer -Peel I Insidefiberglassskin Outside fiberglassskin (top to bottom) Any excess bag material requires a pleat; To form a pleat in a vacuum bagapplyashortamount ofsealingtape to theperimeter tape, inside thepleat, then fold over the top of the short length of sealing tape; seal the bag against the short length ofsealingtape,pinchingitoffatthe top;sealthebagagainst theshortlengthof sealing tape at the bottom corner; finished pleat. 1"(25mm) wide outline of masking tape to the mold surface, about 6" (150mm) away from marked outline ofthe part. This protected the area where the sealant tape will go from epoxy drips. D IY boat owner 2006-2 (www.diy-boat.com) 1-888.658.2628 Suctioncup A O 4F 41 Vacuum Bag,,' DIYboatowner2006-2 (www.diy-boat.com) 1-666.658.2628 Moldsurface 0 D iagram of laminate stack and vacuum bagging materials.

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