Stringer Appeal

Installment XX in the chronicles of a Mako classic restoration

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.

Transom Wrap-up

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

Over the Top

Installment XVIII chronicling of the restoration of a classic Mako runabout

With prep work completed last week, we're ready to cap the top edge of the transom with fiberglass. We planned out a schedule of various cloth to encapsulate the transom top. To cover the top edge precisely, we cut 4" biaxial tape in 2" strips to lay down first. We then cut two progressively wider strips of 6 ounce boat cloth.

Sizing up some lighter cloth that will drape the hard corners.

2 layers of Biax tape first covered with 2 increasingly larger widths of 6 ounce boat cloth

Love these little electric shears. They cut through any cloth without making a frayed mess or destroying the weave.

2 layers of biaxial tape and 2 wider layers of 6 oz cloth laid out in order on the table

Let's get ready to roll. Gloves are a must for this part.

All joking aside, pumps become tedious when measuring large volumes. Pull em out and pour by volume.

"Hey, quit pointing that thing at me."

All 4 layers of cloth are laid out in order. Spreaders, a couple of laminating rollers, mixing pots, resin/hardener, mixing sticks, extra gloves - check. Looks like we're ready- let's wet this stuff out!

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.

A Midsummer Interlude

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...

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.

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 2x4 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 2x4 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.