Saved from the Junk Pile!
Part IV: Damage Repair, New Stringers, and New Transom
For those of you just joining us, to date the deck of this viper has been removed along with every piece of wood that it contained, including the core, stringers and transom. I have constructed a jig that will support the hull until the deck is reattached, as well as supporting the two molds that are built into it (the mold for the pad is cut out of a piece of mica laminate. The mold for the side damage was cast off another Viper). Excess material has been ground away to a clean flat surface throughout the entire hull. Using a circular saw & sawzall I have removed 6 ft. of the pad and the majority of a previous repair that looked a little scary. I cut out the pad because I wanted to make it flat instead of concave and I also wanted to remove the hook. Instead of using glass and filler on top of what was already there, I had decided to cut it out and start fresh with a flat clean surface and solid glass. After cutting out the old pad I will be adding 1/4" to the pad height to bring the nose down (theory: I want to improve the hang angle). My Viper's bottom should be flat and hook free, with the correct layers of glass in the most critical area. After grinding the perimeter of the cutout areas on the underside of the hull (just 2 inches around will aid in the blending process later) and coating the mold surfaces with 4 layers of PVA (mold release), the hull is ready to be placed in the jig. With little effort it lines up perfectly, the hull is then screwed into the jig at various points around the perimeter of the holes I had cut (every 1.5 ft).
I have opted to use un-waxed polyester resin for this project for a variety of reasons. 1) The cost ($95/5 gals). 2) it is the same material the hull was constructed with. 3) it can be recoated without grinding (as long as the surfaces are smooth). 4) it will provide a good bonding surface for the gel-coat. The initial order came from a local supplier (Dyna-grout 631-242-3366,Warren) consisted of the following: 3 - 5gals un-waxed polyester resin, 1 qt TFA (tack free additive), 3 bottles of MEK (hardener), 3 yds. of Fabmat 24 oz roven with 1 ½ mat backer, 1 - 100 lb roll of 1 ½ oz mat x 50in., 15 yds Bi-Axial 12oz roven/3/4 mat x 50in., 1 bag of Cabosil, 1- 3-35cc MEK dispenser.
FABMAT is a product manufactured and trade marked by Fiber Glass Industries Inc. According to the manufacturer, "Fabmat consists of a roving base layer to which a controlled quantity of chopped strand is deposited and chemically bonded. This process minimizes the binder content insuring fast wet out and ease of handling. FABMAT is ideal for hand lay up molding, resin infusion process, SRIM, RRIM, and SCRIMP processes. End users have complete compatibility with Polyester, Vinyl Ester, Epoxy, and Polyurethane resin systems."
Woven roving is similar to, but much heavier than fiberglass cloth. Woven roving is a coarse, open-weave, heavy fabric recognized for its easy handling and high strength. Woven roving also wets out easily and provides high tensile and flexural strength in laminates.
Bi-axial cloth is a non-woven, double-biased fabric that has two layers of yarn "stitched" in place, oriented + and - 45 degrees to the horizontal axis. This material is approximately one and one-half times stronger than comparable weight conventional cloth.
CABOSIL "is a material also referred to as colloidal silica or cab-o-sil and is an excellent thixotropic agent which is used to control the viscosity of mixed epoxy systems. Can be used alone for a very smooth, non-sagging, high strength mixture or combined with bulking or fibrous agents to make them non-sagging."
With the hull in the mold, cleaned and prepped I was ready to start on the two areas removed.
I should have cut the
areas out as an oval instead of a rectangle.
The oval makes a continuous edge and is easier to blend.
The edges are tapered as depicted in the diagram below.
This is done so that every layer is bonding to itself and also a piece of
While blueprinting my brother's Viper bottom, I cast a fiberglass mold for the repair area, constructed the mold for the pad and built the jig. The two molds were screwed to the jig and are supported right off his boat.
To begin the repair, the molds are glassed using the schedule
depicted. The first layer 3/4 matt and cabosil on the edges is not shown.
"Skin" is followed by 2 layers of 24 oz roven w/matt side down.
This was allowed to dry; a quick cleanup grind, and layers 3 & 4 of 1
1/2 oz matt were applied. Cabosil powder and resin are mixed to a peanut butter
consistency to fill any voids that would be created upon application.
The fiberglass will never bend at a perfect 90 (see Diagram 2).
Always have a batch ready while glassing.
With the patches complete the areas are blended and
ground smooth. Note: Once the hull is out of the jig more glass will be applied to
finish the topside of the repair.
I have decided to put the stringers and transom in before the core. This should strengthen the hull, but will make it harder to seal the edges of the bag (more to work around) when vacuum bagging it. Exterior grade multiply wood is purchased for the stringers and transom, finished on both sides. Yes, wood. I believe it’s stronger than a composite stringer system. Check the following chart for a strength comparison of various core materials:
The hull will be light enough and it’s going to be carrying a massaged V6 Merc. As long as the wood is completely encapsulated and any screws are properly sealed this will never be a problem. The stringers and transom will be ¾ MultiPly ($100 per sheet 4x10) and the floor will be ½” multiply ($80 /sheet - from Roberts Plywood, they will ship anywhere). The stringers will go entirely to the transom instead of stopping at the well, 10 feet in length. I am also adding gussets on either side for additional support. The original stringers never completely tied in to the transom, often causing the area in the transom cavity to break. I have decided to tie it all together to add rigidity and strength. The splashwell on the deck prevented the center stringers from being any higher. Adding the outer stringers gave the added height I was looking for and will also serve as the back seat base. The transom will be two layers of ¾” MultiPly, which is glued and screwed together. Using a straight piece of wood in the valley where the floor will lay, measurements are taken every foot to design the stringers. For even better accuracy, you can lay a small flat block of wood on the bottom next to the stringer material, and with a pencil laid flat on the block and its point against the stringer, slide it along the length so that the pencil scribes a line which will mark a perfect outline of the hull for which to cut out of the bottom of the stringer material. The stringers are actually curved on the bottom to fit the hull and straight on top to meet the floor. The stringers, gussets and transom are all cut and fitted together prior to any glass work. Once they were fitted a router is used to roundover the topside. The fit should be as close as possible to prevent large gaps. The cabosil is good for small voids, however too much will weaken the area.
A 20" Offshore midsection will be mounted flat on the transom. I have made the transom 5" taller than original (an estimate). Before the transom is drilled we will hang the motor and determine the correct height. This will be done before the deck is painted, should it need to be cut it down. The final height will be determined by the prop shaft height in relation to the pad. More on this later.
The transom and gussets are glassed in first using two layers of 1 ½ oz. mat as a bed, cabosil to fill the voids and clamped in place. Once cured, a quick cleanup grind, vacuum, and the stringers are tabbed in. Square blocks are used to hold the stringers square. These are screwed in place and will be removed once the stringers are set. Again, two layers of 1 ½ oz mat are laid down, the stringers are set in the hull and then cabosil is used to fill the voids. Note: light grinding is only to knock down the burrs and blend. Once the stringers are dry the blocks are removed and two layers of 24 oz Roven w/mat backer are used to glass the stringers, gussets, and transom to the hull. Additional layers will be added to the stringers throughout the recore so this should be sufficient for now Stay tuned for the recore, Next!!
Since I will be vacuum bagging this one, a few other items were needed for the next step: 1) a vacuum system (Piab pump supplied by Mark C., thank you). 2) 25 yds peel ply (Release Ply A 46”x yd). 3) 25 yds. breather fabric 4oz.x60in/yd. 4) 1/2 in. contoured Balsa 2x4 SHEET, all supplied by Fiberlay (www.fiberlay.com). I used 3m masking film for the bagging film, purchased locally, but suggest you purchase it from Fiberlay along with the fittings to pierce the bagging film (to attach vacuum lines).
If you have any questions, please contact Chris at Boatmender@aol.com