Big piece or small? - Sail Magazine

Big piece or small?

"Many books on fiberglass repair, including one of yours, have drawings showing how to lay up cloth and mat over a tapered repair area, like a hole. The repair always begins with a small piece of cloth at the bottom, and as the layup continues, the pieces get larger. This makes sense to me, because a layup schedule doesn’t depend on just one interface bonding. Going from smaller to larger would
Author:
Publish date:

"Many books on fiberglass repair, including one of yours, have drawings showing how to lay up cloth and mat over a tapered repair area, like a hole. The repair always begins with a small piece of cloth at the bottom, and as the layup continues, the pieces get larger. This makes sense to me, because a layup schedule doesn’t depend on just one interface bonding. Going from smaller to larger would seem to suggest that you are matching the shape of the tapered hole you are repairing. However, one epoxy manufacturer suggests a laminate schedule that begins with the largest piece and finishes with the smallest. Which approach is the right one for laying up material to cover a hole, stringers, and so forth?"

-- Jeff Field, Greenville, South Carolina

Don Casey replies: I’ll answer by quoting from the newest edition of my This Old Boat, which will be available in stores this summer: “You may encounter conflicting guidance—including in the previous edition of this book—on whether to apply the largest piece first or the smallest piece first. Here is the definitive answer to that question. If you are using either polyester or vinylester resin, put down the largest piece first. This will be mat, and it will give you the best bond to the underlying surface. If you put down the smallest piece (also mat) first, the next layer, which will be cloth, will not have mat between it and the existing laminate beyond the perimeter of the underlying piece. This will make for a weaker bond.

“If you are using epoxy resin, the order of the laminates does not actually make any difference in the strength of the repair for reinforcing or bonding. Small first tends to yield a neater appearance where the repair will not need to be faired. But where the larger layer drops over the edge of the one beneath, you may have a problem with creating a void and with the thinner epoxy resin draining through. This is avoided by laminating in a large-to-small order. The relatively recent development of epoxy-compatible mat also makes a large-to-small schedule using mat between the cloth layers a possibility.

“When filling a depression or doing reconstruction, the intuitive order is small to large, but the problem here is that we are trying to replace cut-away or ground-away fabric, and the new fabric, except for the bottom piece, will attach to the original material only at the perimeter—in effect, a butt joint. So the largest piece should go into the cavity first to maximize the surface area of the secondary bond. After that, all subsequent laminates bond to this first piece and each other on a molecular level, but applying them in a large-to-small order still maximizes the mating surfaces.

Related

01b_WALKING-KEDGE-OUT-cmykpromo

Getting More Use From Kedge Anchors

If you are cruising, you need at least two anchors on board for the simple reason that you must have a backup. Imagine having to slip your anchor on a stormy night with other boats dragging down on yours, or having your rope rode severed by some unseen underwater obstacle, ...read more

SailAwayCharter

How-to: Navigating on a Bareboat Charter

So you graduated from navigation class where you practiced dead reckoning, doubling the angle on the bow and maybe even celestial nav, and you now feel well prepared for your first charter trip. Well, you won’t be doing any of that on vacation—not past the first day, anyway.Most ...read more

04-Turtle-rescue

Turtle Rescue in the Vic-Maui

Strange and often wonderful things can happen in the course of an offshore sailboat race, and one of the strangest and most wonderful things we’ve heard of recently took place during the 2,300-mile 2018 Vic-Maui race, from Victoria, British Columbia, to Lahaina, Hawaii.It ...read more

dorcap-open-blue

ATN Inc: Dorcap

COOL SLEEPYou’re fast asleep in a snug anchorage, forehatch open to catch the breeze, when you’re rudely awakened by a sneaky rain squall. Now you’re not only awake and wet, you’re sweltering with the hatch closed. Sucks, right? That’s why ATN came up with the Dorcap, an ...read more

HIGH-RES-29312-Tahiti-GSP

Ask Sail: Who has the right-of-way

WHO HAS RIGHT-OF-WAY?Q: I sail in Narragansett Bay, which is a relatively narrow body of water that has upwind boats generally going south and downwind boats generally going north. When sailboats are racing, the starboard tack boat has the right-of-way over the port tack boat, so ...read more

albinheaters

Albin Pump Marine: Marine Water Heaters

IN HOT WATERSweden’s Albin Pump Marine has introduced its line of marine water heaters to the United States. Complete with 130V or 230V AC electric elements, the heaters can be plumbed into the engine cooling system. They feature ceramic-lined cylindrical tanks in 5, 8, 12 and ...read more

03-squalls4

Squall Strategies

Our first encounter with a big squall was sailing from San Diego to Ensenada, Mexico. We left at 0200 to ensure we’d get into Ensenada before our 1300 haulout time. The National Weather Service had forecast consistent 15-20 knot winds from the northwest, which was perfect for the ...read more