Stringer Appeal

Installment XX in the rebuild of a Mako center console classic

We are now ready to make some progress with stringers (longitudinal reinforcing beams on the hull.) The original stringers were marine plywood covered in a heavy fiberglass woven roving cloth and wet out with polyester resin. Holes called “limber holes” were cut to allow water to drain to the bilge. These vintage limber holes are a horror show. A hole saw cut through the beam left exposed wood core. Water migrated in and rotted these areas. The rotten core shows black through the fiberglass. Notice the cracked areas.

These beams bear the brunt of force when pounding through waves. Hard spots and rotted core spell failure.

To remedy this, our task is to grind these stringers off and replace with new. Rotten core has minimal strength and must be extracted. Spot repair and/or sistering in stringers supports is the easiest route with least time and expense. We’re going for the gold- grind the old stringers flush, then replace with foam core stringers. We chose these pre-fabricated stringers by Prisma. Prisma Composite Preforms come in complete sections, ready to wet out. The fiberglass fabric is already bonded to the foam. Just bed in place then wet out.

To spec out the stringers, we carefully measured and snapped extensive pictures of the current hull stringers. Measurements should include:

• angle of deadrise (angle of the hull to perpendicular)
• length of each stringer
• depth of each stringer

We then emailed this info on to the folks at Prisma for technical consultation.

Without stringers, this boat will be loosey goosey. One concern with the upcoming phase will be to maintain hull shape. We must support the hull prior to removing the stringers to minimize distortion. Temporary braces across the gunwales and supports under the hull should maintain hull shape as best possible.

Commonly decks rest directly on hull stringers. Notice this boat has separate reinforcements for the deck, which floats above the stringers. (see 2 remaining nubs in middle) We have the option to replicate this or just mount directly on stringers.

This perspective shows the taper of stringers meeting the rise in the bow.

Thanks for joining us, and please check back for more.

Installment XIX in the chronicles of a Mako classic restoration

We measured out 5 parts 105 resin to 1 part 205 hardener by volume. When metering large amounts, it’s much easier to pour than pump. This is where graduated mixing pots come in handy.

We wet out the first two biaxial strips on the table and transferred them to the boat.

We then proceeded wetting out the 6 ounce cloth, laid it in place and bubble busted once again with the laminating rollers.

Gloves are getting pretty tacky at this point. Layering gloves is the way to go- just peel off a layer and keep on rolling.

We made incisions in the dry cloth at each of the sharp bends of the transom notch. The cuts are needed for the tape to lay flat. To make sure they aligned we marked the port/starboard sides with a permanent marker.

Murphy’s Law- the worst possible time for an irresistible itch on your nose

Bubble busting with laminating rollers.

Holy cow- is that the time? Let’s call it a night. Before heading out, dunk those laminating rollers in an acetone bath if you wish to use them again. Otherwise they become more spreader than roller ;P

-Michael Reardon

Taking the Edge Off

Installment XVII in the rebuild of a Mako center console

By next Wednesday’s session the transom cured rock solid. Our goal tonight was to clean up her top edge so we can layer some fiberglass tape over it. The stiff biaxial cloth did not stay tacked on over the outside of the transom. The cured edges needed grinding back to where there was a solid bond (core to laminate). Great job for this Dyanbrade cut-off wheel.

Almost done grinding stray edges off.

Once all the stray glass was nibbed off, we followed up with the Rotex sander and ETS 125 sander to grind away any remaining un-bonded glass. We also gave all the freshly cured glass a quick wetsand to de-burr it and remove any traces of amine blush. The surface is now ready for TJ and I to cap it with several layers of fiberglass tape. But we’ll tackle that next week.

-Michael Reardon

Inside Skin

Installment XVI in the chronicles of a Mako classic restoration

Prior to our summer break from project Mako, we completed bedding in two 3/4″ sheets of Penske core in the transom. It’s been strategically pickling ever since Our goal now is to encapsulate the transom and move on to the stringer replacement. We’re a long ways from the finish line, so it’s time to get rolling. We’re shooting for this Mako floating pretty next summer.

A quick chalk talk and we’ve got our game plan. Next step - lay cloth inboard of the transom. We again chose 1708 biaxial cloth for inside the boat, two layers to be exact. We wet out with 105/205 West System. 1708 Biax builds bulk quick with lots of impact and load bearing strength. Sounds exactly right for a transom. Prior to layup, we meticulously prepped the surface with the following steps:

• buttered a fillet joint edge into the bottom to make a gradual curve for best bond.
• rounded all sharp edges from top and corners.
• cleaned cured epoxy surfaces with soapy water and a scotchbrite pad to remove amine blush.
• Wiped area clean: on w/ clean acetone soaked rag and immediately off with clean dry cotton cloth in other hand. This step can be omitted over foam core and wood substrates (see surface preparation article)
• Abraded any smooth areas with coarse 80-120 grit sandpaper and dust off (not necessary over any porous substrates.)

We then placed the cloth inside the transom dry and traced the contour with a sharpie

The cloth cut was 5″ beyond the transom contour to tab it over, around and under all connecting surfaces. Alternatively, you might cut the transom fabric exactly to size and then tab the perimeter with cloth tape.

With gloves and tyveks donned, I mixed up enough 105/205 at the 5:1 ratio to wet out the first layer. I spread a thin layer over the penske core with a chip brush to fill porosity and make sure there is no resin starved spots. Meanwhile TJ used the remainder of the batch to wet out the first 1708 over a laminating table. Once all the cloth was visibly wet out (translucent) we grabbed either end and transferred the slippery, sticky mess over to the transom. Easy now- one slip and this could get very dicey. The cloth should be laid with the chopped strand mat on the inside and biax weave on outside for best results.

This woven biaxial pattern faces out, (”laces out Dan!”) random mat faces core.

The thinking is random oriented mat fibers hold more resin and make the best mate to rough surfaces. Thus, mat is the go-to first layer over core and 30 year old woven roving to prevent a resin-starved weak bond. Nobody wants that oh so evil word- DELAMINATION- oh the horror! 1708 integrates mat one side, cloth the other, making it an excellent base. With the sharpie outline showing proud, we stuffed the cloth like a bedsheet into place aligning the black outline to the contour. We then chased out bubbles with some laminating rollers to minimize air entrapment.

It’s amazing how messy transferring wet cloth to the inside of a transom can be. Best advice, be prepared to throw away whatever layers you’re wearing; but before you do, check out how your shirt stands on it’s own the next morning- cool!

The 1708 does not drape well, as evidenced in the photo below.

No matter how well you tack it down, expect some cleanup with a grinder and cutoff wheel once this stuff kicks. Vacuum bagging is best option. The vacuum bag process sucks the cloth in place while it cures, negates air entrapment, and prevents cloth lifting away. With the complex turns in this form though, we opted out of vacuum bagging on this step.

As we left her to cure overnight we noticed it’s awful quiet round here- music! - knew we forgot something. The radio’s coming back next week. Once dry, we’ll have a rock solid transom, cored with high density, high strength foam (penske) and reinforced with 2 layers of 1708 on both sides of the core.

-Michael Reardon

For our devoted following, we could list a thousand excuses for the long hiatus since our last spring post.
But a picture is worth a 1000 words and excuses are for, ummmm, well, these two guys. Our apologies.

Here’s what TJ and I were up to that kept Mako progress at bay…

Now back to our regular scheduled program…

Transom Bevel

Installment XV in the chronicles of a Mako classic restoration
We returned the next morning eager to see how this old boat accepted her new core. The Penske core sandwich buttered with epoxy cured nicely, the clamps securely held everything in position. We removed the C-clamps and exterior 2×4 board handily. The bond between the new core and the old outside laminate skin was rock solid. Unavoidably, some epoxy ran through the bolt holes of our 2×4 clamping setup. Excess epoxy also drizzled down from the top. Thus our temporary clamp was also accidentally bonded rock solid to the inside in a few spots. It needed persuasion from the multimaster with an ecut blade to cut through the bond and free it up. We resisted the urge to tear the board free as the penske material is only a dense foam. The E-cut made a surgeon like incision which solved this problem perfectly.

This evening involved prep work in advance of the next stage, laying-up cloth inside the transom. We will lay 1708 biaxial cloth over top to the inside of the transom. To assure optimal bonding between old and new, a taper of 5:1 surface area to laminate thickness is recommended. We used a rotex orbital sander with coarse grit discs to grind the bonding area. [Beveled area pictured above, the tan area along the top of transom.] We rounded the top edges slightly and will add some thickened epoxy. Our goal is to fair any sharp edges to a smooth transition- this makes better bonding surface for the cloth.

Traces of epoxy oozed over night leaving a slight hollowing under the core bottom edge. Some epoxy thickened with high density 404 filler and cabosil remedied the voids under the core edge. With this same mix, we laid a fillet joint bead along the entire transom to hull edge. The back of a spoon or a gloved fingertip is all that’s needed to create the concave fillet. The fillet shape forms a nice easy curve for cloth to adhere, which is our next step.

Gravity brought low some epoxy from up on high. Epoxy run is an inherent problem to both bonding and hand-layup of vertical surfaces. We filled the voids along the top corners with the same blend of epoxy thickened with high density filler. The remaining thickened epoxy we spread across the top transom edge to complete a nice smooth transition- like icing on a cake.

The complex form of the top corners will prove challenging to rebuild. We have ground out taper here and still have a bit more grinding to get the correct ratio for a proper bond. Our first layup in this area will focus purely on encapsulating the transom core. We will address the gap in the gunnel in a later step. Bridging that gap will require placing some temporary mold to lay wet-out cloth over.

The final consideration before the glass layup is assuring the surface is clean from contaminants. We will cover this in the next post.

-Michael Reardon

Installment XIV chronicling the rebuild of a center console Mako classic

Battening Down the Penske

With Tyvek suits donned we’re ready to roll, like NASA storming down the street to capture ET (unfortunately, camera couldn’t catch TJ’s glowing finger trick) Thus far we’ve ripped out all the old rotten stuff, prepped the transom, filled the voids with thickened epoxy, added a layer of biaxial cloth, and now we’re ready to replace the core. For core we’ve cut out two 3/4″ Penske sheets, equalling 1-1/2″ total core thickness.

We mixed up neat epoxy using the standard fast hardener and 105 resin. We spread this on both sides of the first Penske core sheet to fill in any porosity. We’ll do the same to bonding side of the second Penske panel before installing it.

Just before setting the first core sheet in place, we mixed a batch of thickened epoxy. This we troweled approximately 1/8″ thick on the boat where core edges meet hull, and thinner along the inside of the transom skin. The remaining thickened epoxy we distributed evenly over the joining faces of Penske core once the first panel was in place. The thickened mix assures a strong adhesive bond.

We needed a large clamp to secure everything. A couple of boards thru-bolted with long hex cap bolts and fender washers on either end did the trick. This kept the core in place under moderate pressure until it cured. (We cut the boards and pre-drilled them beforehand.) A liberal wax application to the bolts permitted removal post-cure. Though the inside board lay against dry core, a little epoxy slop inadvertently worked in there. Plastic sheeting would have prevented the board from bonding to the core wherever epoxy oozed. This occured to us in after thought and we later needed the multimaster to pop the inside board free. The bolts passed through the entire clamp setup. We drew tight the 4 hex nuts in sequence, a few turns of the ratchet per bolt to maintain even pressure. The pressure from our makeshift clamp squeezed out any excess epoxy.

Much of the thickened mixture displaced any remaining voids along the bottom base of the core, working to our advantage. We squeegeed away where necessary. Lastly, we braced the top edges with C-Clamps (with plastic sheeting in between). This entire setup was then left untouched to cure overnight.

- Michael Reardon

Installment XIII in the reconstruction blog of a 1973 Mako center console

We mixed up several batches of West System neat epoxy (no additives) and wet out the 1708 cloth on the table. There is a science to estimating the amount of epoxy needed to wet out cloth. We don’t make any pretenses to be scientists; our formula= mix many small batches til we don’t need anymore. We gently squeegeed it over the surface with a single edge spreader and let the cloth soak in the epoxy. Typically the cloth will become translucent as fibers soaks up and bond to the resin. This did not hold true for the biax, but more on that later.

Transfering the wet-out cloth to the transom is most certainly a messy two person procedure. An alternate method is to bring dry cloth over and wet it in place.

Once aligned, we chased out all air from under the cloth using laminating rollers and spreaders.

Notice the Biaxial cloth does not wet out completely clear. In hindsight we learned that styrenes in this “mat type” fiberglass cloth do not bond with epoxy as they do with polyester resin. (Biaxial is woven cloth one side and mat on other side.) Engineers at West System acknowledge this quirk between mat type fiberglass and epoxy in their literature. They also state it does not negatively impact the finished composite strength (from extensive testing). Yet any mat based fiberglass wetted out with epoxy will be less conformable (i.e. harder to drape over a shape) than the same mat cloth using polyester resin. Wow, who knew? Certainly not these two guys. Also, if this were a critical application where it needed to be clear, biax and epoxy should not be your mix of choice (i.e. a cold molded hull where beautiful mahogany shows clear through). Lucky for us, biax and epoxy are fine in this hidden and flat application. Henceforth though, I think we’ll stick to regular 4 to 8 oz cloth compatible with epoxy.

With the biaxial cloth in place, we’re now ready to bed in the core.

- Michael Reardon

Mixing It Up

We’ve moved the boat over to a nice clean and warm workshop for the epoxy application. 60 degree or better room temp is what we’re after. For this whole process we’ve got a wealth of resin and hardener onhand. We also have a cache of mixing pots, mixing sticks, single edge spreaders, fillers, latex gloves and tyvek suits.
The transom area received one last go over with wire brush and vacuum. (See “Preparing Laminates” for more info.) Then we wiped it clean with acetone, let it flash off, and wiped dry with a clean dry cloth. We measured out the resin and hardener into separate graduated mixing pots, and then mixed them together. (Isolating resin and hardener during the measuring process allows us to recapture overpours. An alternative is pumping from the calibrated measuring pumps, but this proves tiresome and slow for large volumes.) We added a 50/50 mix of high density filler and coloidal silica until it was thickened to a peanut butter consistency.We layered on several pairs of gloves so we could peel off a layer without interupting workflow as the epoxy becomes tacky and tools stick. We then used spreaders to fill the epoxy mixture into all sharp angles and hollows, with a fillet joint bead lining the hull to transom joint. Our goal is to ease any sharp angles for the biax cloth, which we will layup in our next step.

This first step will fill voids so that in our final bonding step, when the core is clamped in under pressure, there are no voids. Clamping will squeeze out any excess epoxy which will then be removed.We mixed several small batches to complete this step. Large batches hold heat from the resin/hardener exotherm and will surely kick before you can apply it all. Should the epoxy “kick” in the pot, you’ll feel the heat building in the mixing pot, and the epoxy balls up like chunky cookie dough as you spread it - not good. To forestall the heat buildup we could chill the resin beforehand or disperse the mixed epoxy in a flat pan, but it’s easier- with less waste- just to mix in smaller portions.

We focused attention under the transom top edge and in the complex top corner where gunwale, transom and hull meet.

Once this step was completed we moved immediately to wetting out the biaxial cloth.

- Michael Reardon

Installment XI in the Mako rebuild project blog.

Core Strength

TJ and I have reached a major turning point - so far it’s all been destruction to this old Mako. Now we’re ready to build! After a fair amount of elbow grease cutting, grinding and chiseling out the old rotten core from the transom, we’ll begin preparations to bond in new core.
Step one - we need a template for the new core. A large cardboard box worked well for this. Matching the exact core shape is a challenge since we destroyed the old core. We approximated the shape by first clamping the cardboard sheet lightly to the outside of the transom. We traced the exterior contours for a rough, oversized shape, too big to fit inside. Then we pared away excess to fit the inside the boat. An easier approach would be to drape a simple cloth over the inside and trace it with a sharpie, but we used what we had. Matching every intricate imperfection would be extremely tedious. We didn’t sweat the details too much, any voids will be filled with thickened epoxy. We will ultimately bed our core into place with thickened epoxy, like a brick in mortar.

With a satisfactory fit of the template, we traced the shape to new core. We selected a sheet of 3/4″ Penske board. Penske, properly known as Airex PXc board, is high density urethane with glass fibers mixed in for reinforcement. A sheet of Penske is structurally strong, shapes easily and is impervious to water. Unlike traditional plywood, this core will never rot! We managed two transom cutouts onto one 4′x8′ sheet. Sandwiched together it will give us a total core thickness of 1.5 inch. To scribe the cut, we used a Festool Jigsaw. The jigsaw style seen in the picture is the barrel grip. I prefer this style to the traditional top handle for lightness and scribing blind underside cuts.
We dry fit our core cutouts to the transom. A little grinding was required on high spots. We also trimmed the top to approximate the old core height - slightly less than the outside skin.

Now, I’d like to say removing the old core came off without a hitch- but I can’t. We punched through the outside a time or two in the process and those need some touching up. A
proper patch would suffice, but we opted to bullet proof the transom with one layer of biaxial cloth. This will go in place just before the core installation. Biax, also called 1708, is great stuff for structure applications. But before you go ahead and jump on the biax train too, you may want to read on in future post to see how it worked with epoxy. These pictures show our cut of the cloth.

We used these electric shears to cut the cloth and man they’re awesome. One of those simple things that makes life so much easier. A little battery powered gadget that sounds like an electric toothbrush. You can lay the cloth over a shape and cut it out without manipulating it and distorting the weave. If you have alot of cloth cutting to do, it’s worth it’s weight ten times over for the savings on damaged cloth!

The old Mako made a trip for the the next phase. We were blessed with access to a heated building in winter! The unheated warehouse posed a problem for resins to cure. Cold temps can be overcome by very fast hardeners in a pinch, but it’s a give and take. Very fast hardener will accelerate cure in cold temperatures, but epoxy cures much stronger in temperatures above 60 degrees (the warmer the better). The cure strength is much happier in a warm workshop. Come summertime mother nature will take care of the heat for us, but for now this workshop is a blessing.

Before calling it quits for the night we did a few last odds and ends. We tried out the biax cloth for fit and made some diagonal slices to fit it into the odd corners. Next we etched the whole bonding area with a wire brush and course sandpaper to add a little tooth for bonding. We then cleaned the inside thoroughly with the shopvac. Placed a few bandaids with painters tape to show our sympathy for the wounds we had inflicted, then we filled all those old screw holes and damaged spots with thickened epoxy. Content with how things looked, we retired to our favorite pastime - standing back for a gam session with a beer in hand, talking about “what we should really do next is…”

-Michael Reardon