Mounting stud vs. 4 hole cleats

[HeadedToTexas]

I had not figured mounting 10" Herreshoff cleats to Escape's gunwales would be so difficult. Seems like a ready made location. As with so many things, there are a lot more factors than first appear. The choice has come down to stud or 4 hole mounts.

Both cleats have very similar dimensions and it comes down to the width of the mounting "feet." The 4 hole type takes four ¼-20 screws or bolts and the stud type has ⅜" threaded studs. Either is typically secured through a backing plate from below with washers and nuts.

While there is plenty of flat space on the gunwale for the cleat, the Mariner 37 has thick and beefy shoulders at that point and that means only two holes can penetrate the gunwale to a space below. The attached cross section diagram shows the problem. When the cleat feet are inboard as far as can be, holes for the ⅜" stud penetrate the space below as do the inner pair of holes for the 4 hole cleat, but the outer pair of holes would have to be secured with lag screws.

The problem with the stud cleats is that the ⅜" holes in the FRP backing plates is only ½" from the outer edge. The backing plate will be epoxied to the underside of the gunwale, but being so close to the edge just seems wrong. The inner pair of holes for the 4 hole design are way off center too, but further from the edge.

The entire structure is foam cored at the points shown, so I will be over drilling the holes and filling with thickened epoxy before drilling the final holes. Pretty straightforward there, but if the answer is 4 hole cleats, what is the proper approach to create optimal "bite" for lag screws?

And yes, I am still wrestling with my spring cleat issue. If you're interested, here is a link to the original thread from July 2022.

 

[rslifkin]

With that mounting constraint, I'd use the stud cleats with as good a backing plate as you can manage.

 

[HeadedToTexas]

So two heftier studs at the center of the cleat but the edge of the backing plate is better than two bolts closer to the middle of the backing plate plus two lag screws into the gunwale?

 

[mvweebles]

I had a similar issue. I went with the single stud. Are you sure the 10" cleat has 3/8" studs? My Buck Algonquin 10" clears had 1/2" threaded studs. Because my caprail was so thick, I went with threaded cleats and purchased 1/2" threaded SS rod from McMaster Carr.

1/4-20 seems pretty puny for a 10" cleat.

Peter

 

[Comodave]

I would not have a problem doing the 2 stud cleat. Just slather the backing plate with thickened epoxy so it is in intimate contact with the deck underside. Then make the plate as large as possible. This is a spring cleat not a bow or stern cleat. Typically the loading on a spring cleat will be lower than a bow or stern cleat. I have used tapped cleats before without any issues, they are like stud cleats but tapped on the bottom for a bolt.

 

[HeadedToTexas]

I already bought the 4 hole cleats before discovering this alignment issue (cart before horse), but I didn't buy the mounting hardware. Could be that they are larger than ¼-20. The supplier told me the studs on the stud mount were ⅜", so I'm pretty sure about that.

 

[HeadedToTexas]

This is a spring cleat not a bow or stern cleat. Typically the loading on a spring cleat will be lower than a bow or stern cleat.

That was my thinking as well, and being a spring cleat, the forces are mostly parallel to the keel which is along the long side of the backing plate. My only concern with the stud type is that the holes in the backing plate will be quite close to the outer long edge of the plate.

 

[Comodave]

But the forces will be pulling against the wider or inboard side.

 

[HeadedToTexas]

But the forces will be pulling against the wider or inboard side.

Certainly true, but also true for the 4 hole type. The outboard pair of screws would receive less force, but probably not that much less as these are spring cleats.

Am I correct in understanding that lag screws into properly prepared and filled fiberglass holes simply are not strong enough for cleat applications?

And I was wrong about the fastener size. The 10" Herreshoff cleats use 5/16" fasteners, not ¼".

 

[HeadedToTexas]

My Dinghy Butler and swim platform cleat installation projects required several over-drilled, epoxy back-filled, then re-drilled holes in order to prevent the foam core deck from deforming and leaking over time. Is that same approach required for the far thicker surfaces of the gunwales for this cleat mounting?

 

[mvweebles]

....

Am I correct in understanding that lag screws into properly prepared and filled fiberglass holes simply are not strong enough for cleat applications?

.......

Best practice suggests this is correct - lag screws are insufficient for cleats. However, given the difficulty of proper installation of thru-hull and backing plate, plus the fact that cleats are usually installed atop a very robust substrate such as caprail protection a hull/deck joint, I suspect screws (vs bolts) are more common than expected. But it really depends on the substrate.

There are some modern screws used in land-based construction that are truly amazing. I have not seen marine counterparts yet. Old school lag bolts required a sizeable hole without much thread 'bite' and were not very strong.

But cleat mounting fasteners are loaded in shear, not tension, so if the stars line up, i would expect screws to do pretty well, at least until the boat gets towed or the cleats are used for a snubber in a storm.

My Dinghy Butler and swim platform cleat installation projects required several over-drilled, epoxy back-filled, then re-drilled holes in order to prevent the foam core deck from deforming and leaking over time. Is that same approach required for the far thicker surfaces of the gunwales for this cleat mounting?

Gunwale is likely the hull/deck joint and not cored. But if there is coring where you mount the cleat, it needs to be epoxy filled as you describe. I would think the stud-style cleats with broad mounting feet would be a better choice as they are less likely to leak, and their broad bases are less likely to deform.

Peter

 

[rslifkin]

But cleat mounting fasteners are loaded in shear, not tension, so if the stars line up, i would expect screws to do pretty well, at least until the boat gets towed or the cleats are used for a snubber in a storm.

In theory, but I'd always account for some vertical load component. Tied to a tall wall or other situation where the lines are led upward from the boat cleats is the worst-case scenario for fastener loading.

 

[mvweebles]

In theory, but I'd always account for some vertical load component. Tied to a tall wall or other situation where the lines are led upward from the boat cleats is the worst-case scenario for fastener loading.

There is a cost/benefit rule here. On many boats in our demographic, properly backing a cleat can be extremely difficult and costly - gaining access through cabinetry is a barrier. At the same time, on many boats (not all), the mounting substrate is some of the thickest and sturdiest on the boat. I realize my Willard is more robust than normal, but the caprail/hull joint section is 3-inches thick. It would take a helluva load to unseat four 2-1/2" x 5/16" screws.

When I replaced cleats, I had a similar clearance issue as the OP. I originally purchased the 4-fastener cleat the OP did only to find that despite my caprail being over 6" wide, underneath clearance was under 2" due to a slight bulwark designed into the hull/deck joint. There was not enough room for the spread of the cleats. For those who have followed my tale of woe with the Hack Team, they installed the cleat anyway in a half-assed manner. I replaced the cleats with the stud style, but had challenges getting a backing plate in place and used oversized (and over-thickness) fender washers, available thanks to McMaster. Is it as good as an oversized backing plate? No, but is it good enough? I have littlr doubt.

Peter

 

[HeadedToTexas]

Yes, my challenge is similar in that the geometry of the gunwale makes using a traditional backing plate difficult. I have easy access to the point where holes penetrate the underside of the gunwale, but it is narrow and off center as I hope my diagram in the original post describes.

It really comes down to this.

1. Cleats with studs that pass through almost 2" of fiberglass (and core?) gunwale but penetrate the backing plate only at its outer edge.
2. Cleats with two screws that penetrate almost 2" of fiberglass gunwale and penetrate closer to the center of the backing plate, and two lag screws that bite in to almost 2" of fiberglass gunwale.

 

[Comodave]

Personally I would absolutely try to avoid using lag screws and would rather go with the 2 stud cleats with a backing plate.

 

[HeadedToTexas]

And you would definitely drill the holes out to ¾”, fill with thickened epoxy, then re-drill at ⅜” for the studs?

 

[mvweebles]

And you would definitely drill the holes out to ¾”, fill with thickened epoxy, then re-drill at ⅜” for the studs?

No. I would drill at 3/8" (maybe 1/2") and use an Allen wrench as a drill bit to gouge out the coring. Then fill and re-drill the 3/8" hole.

Peter

 

[HeadedToTexas]

Interesting. An epoxy wide spot “mushroom” between the inner and outer gunwale walls. I like it.

 

[Comodave]

Check out marinehowto.com. He has an excellent article on how to get the core removed and epoxy filled. I have used the allen wrench to reef out the core around the bolt. Rod has a couple of Dremel bits he recommends for reefing the core out. I bought the bits but haven’t had a place to use them yet.

 

[HeadedToTexas]

Excellent article. Thanks Dave.

https://marinehowto.com/sealing-deck-penetrations-to-prevent-core-rot/

 

[OldDan1943]

ATs have a vent opening at each cleat which indicated there is some sort of backing plate.
One day I will remove the vent cover and look.

 

[Comodave]

Excellent article. Thanks Dave.

https://marinehowto.com/sealing-deck-penetrations-to-prevent-core-rot/

Rod has done a great job with the website. I really enjoyed reading all of the articles.

 

[mvweebles]

Rod has done a great job with the website. I really enjoyed reading all of the articles.

He sure has. I laughed when the opening paragraph said he'd heard of people recommending a bent nail to hollow out the core; and he wondered if the people who recommended that had ever actually done it. I confess, I have not, and he was right to call folks like me out. Great info on exactly what tool and bit to use.

I really marvel at people like Rod (and Comodave) who have so much hands on experience.

Peter

 

[Comodave]

I never used a bent nail but I have used allen wrenches and cut the short side down. It is kinda a pain because you need to reef out all the core. With the allen wrench it takes a while to chew it all up. Rod recommends a Dremel bit for reefing the core out so I bought the 2 he recommended. But I haven’t needed to reef out any core since I got the bits so I don’t know how well they work. But they look like they should work just fine.

 

[psneeld]

He sure has. I laughed when the opening paragraph said he'd heard of people recommending a bent nail to hollow out the core; and he wondered if the people who recommended that had ever actually done it. I confess, I have not, and he was right to call folks like me out. Great info on exactly what tool and bit to use.

I really marvel at people like Rod (and Comodave) who have so much hands on experience.

Peter

I have in the old days (used a bent nail) and it works if you know what you are trying to do and a little trial and error applied....and Ron is correct that some cores may be resistant to all but certain tools.

A nail can be similar to an allen wrench if you don't have one handy...or a complete set of professional tools that you amass after years of doing a project here and there but eventually wind up doing a lot of them and buy all the right tools.

 

[Circumnavigator]

.... Typically the loading on a spring cleat will be lower than a bow or stern cleat.../

That depends.....


If you dock by dropping a spring line on a cleat on the dock and then idle forward with the rudder hard over away from the dock to bring the stern in, the spring line will be heavily loaded. On Fintry we could move the dock if we weren't careful.



If there is a current going by, the spring may also be more heavily loaded than the bow and stern, which usually see only wind loads.


The loads on these fastenings are all in shear, save for the times you are at a high fixed dock at the bottom of a big tide. In shear the fat screws into the wood are almost as good as the through bolts, so I think I'd go with the four fastenings. Two 3/8" have a little more meat than four 1/4", but I like the fact that the load is more distributed. While you certainly should use a hefty backing plate, it will actually see very little load. Drill the holes tight -- you want to give the fastenings as much side support as possible.



Jim



Sweetwater -- Swan 57 sloop on which we circumnavigated 1995-98
Fintry -- x Royal Navy Fleet Tender -- owned 2003-2022, 20,000 miles including trans-Atlantic
Morning Light -- Webbers Cove 42 single screw trawler 2021- ?

 

[Comodave]

I was thinking that he wanted to use the cleat for tying up at the dock and not springing on and off the dock. Then the loads could be quite high.

 

[HeadedToTexas]

The only springing on or off our dock I have done is with the forward spring cleats. Those are factory installed and look beefy, but I am only guessing at the backing plate as they are all glassed in below deck.

I expect these new midship spring cleats will carry mostly spring lines when tied along side docks. Not a lot of current here in the Great Lakes, but we will be in the land of tides and current eventually.

I already have the 4 hole cleats and was all set to order the stud cleats. And note that the 4 holes are for 5/16" fasteners, not the ¼" as I had originally posted.

 

[Circumnavigator]

Four 5/16 fastenings are significantly beefier than two 3/8, so that reinforces my opinion that you should go with them.


Jim

 

[rslifkin]

For the 4 hole cleat, I wonder if instead of using self tapping screws for 2 of them, could you install some kind of strong threaded insert to screw them into?