Mast Horn Cleat


Well-Known Member
'Wuz wondering about using an adhesive to bond the cleat to the mast. Is 3M's 5200 up to the job? Went here and found a lot of choices available: :oops:
Joining metal with adhesives

Aluminum forms a protective oxide finish within seconds of "roughing-up" the surface. You'd have to put the adhesive on immediately after preparation—then slap the cleat on the mast and clamp it. Just remember to align the cleat with the mast cap. :confused:

The idea being, to eliminate drilling holes altogether. Though I'd be tempted to wait 'til it's set, then drill one hole for a pop-rivet. The innovative "aDP" pop-rivet might have a future here. ADP Rivets - Colored Blind Rivets Made in the USA (Makes its own backing-plate!) :)

It wouldn't hurt to wrap a piece of coarse sandpaper around the mast, and hand-form the cleat base into a matching concave shape. I have some 24-grit sandpaper. :eek: (Need gloves to handle it!)

I'll be back at my three Sunfish "haven" in two weeks and might give an adhesive a try.

[puts on my day job structural engineer hat]
drilling a small pilot hole should not significantly weaken the mast cross section. traditional checks on the member's gross, or full, cross section are against the material yield strength, and net section checks are against the material rupture strength (often 15% higher, or more, than yield strength) - so while the pilot hole does cause a small loss of net section, the higher rupture strength compensates for it.

if failures are occurring at that location, I'd hazard to guess it is primarily due to years of corrosion, not the small loss of net section from the pilot hole. the bending and shear stresses on the mast will be highest down near the deck, so that would mean the higher you mount the mast cleat, the better. granted, the 48" limit makes it difficult to reach the cleat to de-rig if you're standing in the water.
Other advantages of the mast cleat: The mast cleat reduces the down-thrust of the mast and, I believe, makes the boat easier to tack in light air. It also reduces the tendency of the the base of the mast to grind through the bottom of the mast hole and cause leaks or even structural problems, a problem made worse if you get beach sand inside the mast hole. I have seen some Sunfish that have been sailed without a plastic base cap on the bottom of the mast, and the raw metal edge of the mast acts like a cookie cutter as it rotates from tack to tack over time. That said, if you use a mast cleat for the halyard, be sure to run the slack end of the line through the deck eye and cleat it off loosely to avoid having the entire rig fall out of the mast hole in a capsize.

For the last few years, I have used a small, open ended clam cleat rather than a horn cleat and this rig works fine even when I use the slack end of the halyard to make a boom vang.

Alan Glos
Cazenovia NY
Any "insult" to the mast can be expected to cause trouble.

My mast broke in a very strong wind; however, I couldn't find any significant corrosion at the break site. (No different there, than the rest of the mast). I suspect that an overloaded mast can break at roughly the same location on any Sunfish. If an "insult" (corrosion- or drilled-hole) is added, expect that hole to be the site of a break. Higher cleats would be safer for the mast.

Later Sunfish were equipped with an internal sleeve, which can be retrofitted.
View attachment 30436
(This mast had no cleat).

This is about where my mast snapped last year. I had no cleat installed or drilled holes.