Drive-thru Stringer Installation

Installment 29 of Mako Restoration

Day two of the Prisma visit, and we're ready to finish up - this post we're installing the stringers. The previous day we completed the stiffener installation, and it cured hard by the time we returned the next morning.
Those stiffeners installed fairly easy since it lay higher in the hull on the flats. Installing the stringers is more challenging; the stringers are closer to the keel, and span complex angles and turns up forward. Getting a flush fit can be a head scratcher. But we have a plan of attack.




Having Scott and Mike from Prisma onboard for this stage was an incredible boost. Their experience and expertise guided us easily through the process without sweating insignificant details. Together we dry fit the stringers to the hull.

The upsweep in the bow was problematic; it caused the stringers to bridge. For a perfect fit we'd need to shave the underside through trial and error, or trowel out some thickened bedding compound. Either option would eat up valuable time. But Scott reminded us the load is actually carried through the fiberglass not the foam. The foam core simply secures the fiberlass laminate shape from deflection, thus giving it exponentially more strength. A simple relief wedge cut out of each stringer gave a sufficient fit. It worked for this boat because the deck floats above the stringers not on them. The relief cut hinged the stringer with the bend to achieve adequate hull contact (though not perfectly flush.) We laid it out and everything looked shipshape. Mike hopped in the boat and TJ and I suited up to work the laminating table.


We're again using epoxy to glass in the stringers since the earlier stages were completed with epoxy also. (Polyester resin is the common go-to for this, but should only be used when bonding to a polyester based hull.) With temps in the 60° range, we're going with 105/206 slow mix to get the desirable work time.
We passed the first sections into Mike and he set them in the hull. Notice the index marks on the transom for alignment. Mike kept a tape measure onhand to assure alignment.


This job is best done with several sets of hands. We wet out on the table, making sure the spun polyester backing (aka Trevira™ or Duraspun™) is completely saturated and the quadraxial cloth has a translucent soak of epoxy.
We fed Mike a steady supply of epoxy so he could complete the wet out. He kept a laminating roller and chip brush on-hand, along with a healthy layer of gloves to peel away as needed.




Where the stringers butt together, Mike covered the joint with 6" wide strips of quadraxial cloth.







Wood strapping and some old fashioned gravity helped tack these stringers in place while curing. Be sure to add a poly sheeting barrier to keep the wood from bonding to the stingers. We sat heavy 5 gallon pails atop the wood for pressure.





Where the deadrise (V) is steep, Mike drilled some drywall screws through the spacing planks into the stringer to keep them from sliding down.

With all the stringers set in and wet out, Mike stepped out of the Mako and hung the "do not disturb" as we stepped away. A few tie in strips to the transom will finish the job up. (included in next post)

Skeleton Crew

Installment 28 of Project Mako Relaunch

We're ready- time to regenerate bone structure in this old Mako. Last week we kicked the project in overdrive ; we needed to laminate enough hull strength in time for a very important visit. This next phase brings in a couple of expert stringer installers. Scott Lewit and Mike Canfield will be joining us from Prisma Composite Preforms in Melbourne, FL. They're here to guide us through installing stringers.



Scott and Mike are specialists in installing foam core stringers. Prisma supplies foam core composite hull reinforcements to many of the major OM boatbuilders. This modular boatbuilding concept is drawing the attention of many recreational boat restorers like ourselves. They offer a whole line of foam core composite reinforcements to structure any composite boat. The guys arrived at the JD workshop Tuesday afternoon. By mid-day Wednesday, using their prefab components, we completely installed new stringers and stiffeners in a few hour's work. It was easy. We're sold on it's value- huge savings on time and labor.



First step is to dry fit the stringer sections to the hull. The preform hull lumber ships in 4 ft lengths, so we butted several to gauge the run. We looked foremost at the deadrise angle. The stringers come in 3 deadrise options, 15°, 18° and 26°. Ideally stringers should be perfectly perpendicular. This presents a squared horizontal top to rest the deck on. The Mako 19 is different. Instead of landing the deck on stringers, she was built with a suspended deck. A suspended deck floats above the stringers through it's own support structure. Since the deck doesn't land on the stringer, a few degrees of deadrise slop is no problem in our new stringers.



Most boats will require some deadrise angle fine tuning. Mike showed us how to square up the stringers to vertical. Option one, Prisma offers deadrise converters, angled shims the stringer sits on top of to make it plumb. The other option is to shave away foam til the stringer sits perfectly up and down. To measure the cut, simply tip the stringer until the top measures level (using a combination level) and measure the gap. Mark this height on opposite side and shave that material off. Now that you have a mark, the easy way cut this:

scribe the gap height on the longer side of stringer, the side in contact with hull

draw this height the length of the stringer

then score the fabric with a razor knife, peel away cloth tabbing

next, looking at the cross section, draw a line from mark to opposite bottom corner

cut the foam with a hand saw.

You are left with a perfectly level stringer. Shaving foam will shorten stringer height, reducing structural support, so be sure you have height to spare. If not, the angle converters are a better option.






If there is a sharp deadrise, keeping the stringers in place can pose a challenge. We cut some boards as spacers in advance. These will maintain the stringer spacing and we will suspend weight on them til cured.

Cutting the stringer to transom angle

1. measure the stringer distance. We left the full length 4' sections intact up forward and opted to shorten the aft stringer.



2. After marking the distance, cut the cloth face with a utility knife



3. Also cut the tabbing quadraxial cloth with scissors



4. Use a hand saw to cut foam



5. Place stringer against transom and measure the gap. Most transom angles will see the gap up top. Mark that measured distance on the BASE of the stringer to make the angle agree.




6. Connect the dots from top corner to the measured distance




7. Again, cut first with the razor knife and peel away all attached fabric.



8. Finish the cut with a hand saw

The resulting angle should fit flush to the transom.


All prep work complete, it was now time to wetout. We installed hull stiffeners first, and returned to the stringers next day. Prisma offers a great carbon topped hull stiffener that adds significant hull strength while adding very little weight.

We prepped the area with a light 36 grit sanding to add tooth and shake off any amine blush.

On the laminating table, TJ and I wet out each 4' piece with West System 105 and 206 Slow hardener and passed them into the boat. Mike set the stiffeners in place and chased bubbles with a roller. He kept a small batch of epoxy on hand to saturate any remaining areas. Where the stiffener pieces butted together, we overlaid tabs of quadraxial cloth.

We finished the wetout in less than an hour. We'll cap the forward ends and tab the back into transom sometime later. For now, time to let the stiffeners cure and come back tomorrow for stringers.

More Bulk - 24 oz

Installment 27 of Mako Restoration

The time is near! TJ and I are suited up for an all out blitz to whip this hull into shape. Help is packing their bags, they're touching down at TFGreen next day for our scheduled stringer installation. With hustle and some extra late nights we already completed laminating a layer of 36 oz quadraxial cloth. Tonight we're not leaving til a complete 24 oz lamination is in this hull! Stick around, it promises to be exciting...

We have a 35" wide roll of 24 oz /yd² cloth with a standard 0°-90° weave. This cloth also includes the same polyester Trevira™ backing as on the Quadraxial cloth. It will bring this boat up to and beyond it's original hull stiffness. We overlapped strips across the boat to counter the fore & aft overlap of the Quadrax layer. Same coverage area as the quadraxial layer, looking for 3-5" of overlap, and butting it right up to the chine on the sides. We again used West System 105 with 206 slow hardener.

Dry cut all cloth in advance to assure fit.

We split the foremost bow strip in two, allowing overlap each side of the keel.

One last thought before jumping in. Make sure that flimsy hull is in alignment. Any warp and twist will cure permanently to shape, making one odd boat. Everything looked plumb, it was time to roll.


Tackle the diciest section first- we began in the bow. The wider cloth made this stage messy. A bit of strategy is required, since you must lie in the steep hull you are wetting out. Sitting in the bow, I aligned the dry cloth. I folded one panel in half, wet out the back and stuck it forward then chased out the bubbles. Hinge it the other way, resin the back, and flip the aft half in place. Not too difficult. Now the same steps on the port side while I sit on cloth that is mostly dry. I returned to wet out on top last; here it gets tricky.

TJ passed in a fresh mix of epoxy. I poured the resin over-top the cloth to starboard and spread it with squeegee or chip brush, and chased out any bubbles. Switched to the port side and now there's nowhere dry left to sit. I pulled the dry cloth from the next aft section and set it underneath me. Laying on this dry "mat," I wet out the port side and chased out bubbles. Gloved hands made the best bubble chasers in tight spots. There's no helping this one, it's a messy job. Just tried to keep it off any skin. Epoxy is itchy stuff.



Funny angles and limited workspace took time to laminate. So meanwhile, TJ brought the epoxy aft and began wetting out the stern. Now we both had room to operate and planned to meet in the middle.







We opted to spread the resin in the hull as opposed to on a table. The Trevira™ backing received a thorough wet out first and then we set it in place. Mixing, pouring, spreading. Good tunes. We found our groove. A few hours flew by. TJ progressed steadily forward from the transom while I worked back from the bow. Once you start this job, gloves covered in resin, there's no stopping til it's done. Murphy's Law, itchy nose, Itchy Nose, ITCHY NOSE, someone please scratch my nose!



Down to the last and final strip. This was the biggest challenge, no where dry to hide. We strategically saved the strip just behind the foredeck step for last. That nice cross beam was support to lay and brace on. Some slipping and sliding but we made it happen. Laminating rollers on extension handles worked great for final touches from a step ladder.

Surprised by the late hour, it was time to close up shop, boost the room temp and head home. This was one of our longest nights. We headed home happy, deadline met and promises kept. Next step stringers! This boat is coming together.