Striving for a Stronger Boat Cleat

Posted by Ralph Naranjo at 03:20PM - Comments: (3)

Ralph Naranjo
Ralph Naranjo

For maximum strength the cleat is generally oriented at angle to the direction of pull.

Casting metal parts has been a technology in use for at least 6,000 years, and it remains the preferred approach when it comes to manufacturing sailboat cleats. Modern investment casting yields smooth symmetrical surfaces in need of less polishing. The approach can be used with zinc, aluminum, bronze, and stainless steel. Zinc, though often found chrome-plated on low-end powerboats, is too weak a metal to be used for cleats on a sailboat. Aluminum alloys are light and relatively strong as long as the casting process has kept void (air bubble) content to the barest minimum possible.

One of the biggest challenges with aluminum alloy cleats is their galvanic interaction with the stainless-steel bolts that secure them to the deck. Bronze and 316 stainless steel castings are heavy, but they are also stronger and less prone to corrosion issues. The shape of a cleat carries real significance in a variety of ways. The first and most important is how the configuration locks a line in place yet still allows a crew member to control the easing or snubbing process.

Cleats with abnormally long horns and two bolt attachment points allow more line to be wrapped around the appendage, but these “long-horn” cleats also present increased leverage on the base and more vulnerable end points.

The four-bolt open pattern of Herreshoff-style cleats affords greater support, and their shorter horns are less vulnerable. Some cleats come with an in-line, three-bolt pattern that offers significant strength in one direction but very little on an angle that’s perpendicular to the bolt alignment. All cleats rely on good engineering practices when it comes to how they are installed.

Those retrofitting or upgrading their boat’s deck cleats can greatly improve the installation with a little attention given to topping and backing plates.

The former is a carefully cut and painted piece of G-10, or homemade FRP layup comprising three to five units of woven roving and mat laid up on a smooth waxed surface. The solid glass laminate ends up about a quarter-inch thick, and using a cardboard template, is cut to well exceed the cleat’s bolt pattern footprint.

The exact shape of these topping and backing plates depends upon available space and deck shape, but the underlying principal is to provide a load-spreading capacity both above deck and below. The topping and backing plate are best bonded in place with a gap-filling epoxy putty prior to cleat attachment.

When the epoxy putty has cured, the cleat can be fitted, holes drilled and a sealant used on the fasteners during the installation. If a raw balsa or low-density foam core is exposed in the newly drilled holes, the extra time spent “hooking out” a half-inch perimeter around the hole and filling it with epoxy putty will pay off in the long run. Be sure to plug or seal the bottom of the hole before filling the holes with epoxy putty. Once it cures, re-drill the holes and install the cleat.

For related articles: see 

Practical Sailor Takes a Close Look at the State of Boat Cleats

Trouble Free Deck Hardware Installation

A Better Way to To Mount Deck Hardware

How Big Does a Backing Plate Need to Be? 



Comments (3)

IMHO aluminum cleats should not be made for nothing other than dectrived purposes. Whose than that I have seen hollow aluminum cleats on larger boats power and sail. The shock strain on cleats can destroy all but the most solid s s cleats.

Posted by: Captain Bill | April 8, 2018 7:33 PM    Report this comment

Since most DIYs use epoxy, and because mat does not go limp with epoxy (only polyester and vinylester resins dissolve the binder), I wonder if 17-ounce biax is not a more user friendly DIY material for this sort of project. It is easier to wet out and easier to fit, and still provides great strength. Some grades come with a very thin mat on one side, which makes bonding even easier. Cut the glass to shape, lay up 4-8 layers on a polyethylene cutting board, roll to eliminate bubbles but leaving it just a little resin rich, and then transfer the wet layup to the surface and roll it down. In this way it is bonded into place and will better distribute the load with less material than if a separate plate was used. I've pre-wetted a lot of glass in this way. At least that seems like the best reason for laminating to me.

Yesterday I paddled around the harbor, touring marinas, and I saw quite a few broken cleats from this past winter. I told it was the result of extreme tides and boats tied too short. Perhaps if they had followed Ralph's advise they wouldn't have a boat all scratched up on one side. Tying smart with springs lines is another solution.

Posted by: Drew Frye | April 4, 2018 4:44 PM    Report this comment

Yup, a stout-looking Herreshoff-style aluminum cleat on my 1984 Sea Sprite 34 failed while moored in a storm last fall. (Wind and waves were strong enough to lay the boat on its beam ends, with bare poles.) The aluminum failed near a 5/16" stainless bolt, but the other three bolts held, as did a similar cleat with a backup line to the mooring. Take the problem seriously: there was no obvious sign of incipient failure before it broke, and had it been a two-bolt cleat I think the whole thing would have gone. I'm replacing both cleats with bronze from Spartan Marine.

Posted by: Surrymark | March 29, 2018 10:17 AM    Report this comment

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