Boat Mooring Cleat Sizing
From time to time we are asked the question ‘What sized mooring cleat to I need for my boat?’ It surprised us to find that this information does not seem to be generally available, or at least we struggled to find it.
So, as we have a good range of boat cleats available for sale, we decided to gather some information to answer this question. Of course there are lots of places where cleats are used on boats, from flag poles to halyards to mooring cleats, but here we are focussing on mooring cleats.
So Why Does It Matter What Sized Mooring Cleats I Have On My Boat?
Larger cleats are stronger than smaller ones, and they come with holes for larger and stronger fixing bolts. Also the larger the cleat size, the more able it is to accommodate larger mooring ropes – we will talk more about that aspect later.
So there are obvious advantages to having larger mooring cleats, and not really many down sides at all. The balancing factor, of course, is having a sense of proportion, and having plenty of room to fit your mooring cleats without interfering with other deck hardware, or your tread space.
Our Survey
In 2024 we conducted a survey to establish a trend of boat length vs cleat size. The survey covered a total of 27 boats, a mix of sailing and motor boats, ranging from just under 15 feet to just under 45 feet. A graph showing the results of the survey is shown below.
Boat Mooring Cleat Sizes
Modern boat mooring cleats tend to come in fairly standard sizes, 100mm, 150mm, 200mm and 250mm with some small variations on these cleat lengths. In our survey the smallest cleat lengths, used as mooring cleats were 150mm in length, and with a few exceptions, the largest cleats tended to be 250mm in length for boats up to 35 feet in length.
Some of the largest vessels had cleats of length 300 or 350mm with a large ‘sole plate’. Most boat mooring cleats were made from 316-grade stainless steel in styles similar to those shown below:
Click on any of the cleats images to find out further information or purchase.
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Boat Cleat Materials
Most of the boats in our survey were current models, and it was interesting to see that the vast majority of cleats were made from stainless steel. It is note-worthy that the recent and current trend for stainless steel cleats represents a change from those used in previous eras. In the 60’s, and 70’s it was common for many boat mooring cleats to made from aluminium, for example many Westerly boats had aluminium cleats.
We can explain this change in trend, towards stainless steel cleats, as a result of a burgeoning manufacturing capability in the far east for investment-casting of 316-grade stainless steel products.
Most ‘chunky’ stainless steel components to be found on modern boats originate in China. The process involves casting the components using an investment casting process (lost wax method), which gives quite an accurate and repeatable casting process. The cast components are then polished to a near ‘mirror finish’ which is important to their corrosion resistance as well as their looks.
Cleat Attachment & Under-Deck Reinforcing
Which ever size and style of cleat you choose, it is also important to consider the under-deck reinforcing. As-built your boat should have reinforced areas under the deck where the original mooring cleats were attached. If adding cleats where none were before, steps should be taken to ensure adequate reinforcing and load-spreading underneath the deck.
A typical deck cleat mounting is shown below:
Typically, underneath the deck material, there will be a load-spreading core material. This can be marine-ply, Tufnol, or other non-compressible material - there are many choices. The core material is bonded to the underside of the deck and further reinforced with layers of fibreglass. The fixing bolts for the mooring cleat, clamp through all of the structural elements, and are tighened with Nyloc nuts and penny washers.
Cleat Size In Relation To Rope Diameter
Another factor, when choosing a cleat size, is what size mooring ropes you want to use. There is a commonly quoted 'rule of thumb' that the cleat should have a length of 1 inch per 1/16 inch of rope diameter. As an example a 1/2 inch rope would want an 8 inch cleat. Putting this information into metric, and rounding the rope diameter to the nearest commonly available size, gives the table below:
| Cleat Length (mm) | Maximum Rope Diameter (mm) |
| 150 | 10 |
| 200 | 12 |
| 250 | 16 |
| 300 | 18 |
Mooring ropes are most of made of polyester, constructed either as 3-strand or a braid-over-braid construction. Both types of rope construction are well-suited to mooring lines, the 3-strand has the advantage of being easy to splice. It is often convenient to splice an eye into the end of the mooring line for easy attachment to your mooring cleat.
Examples Of Mooring Lines
3-Strand Polyester Line. Can be easily spliced to make a permanent eye (loop) in one end. Available in 6mm, 10mm, 12mm, 14mm diameters. Click on the image below to find out more or purchase.
Braid Over Braid Polyester Line. Available in 6mm, 10mm, 12mm, 14mm diameters. Click on the image below to find out more or purchase.
Putting It All Together
By way of a couple of examples, putting together the information above on typical mooring cleat size, and mooring line size
Example 1: 24ft Boat
- Typical mooring cleat size: 200mm
- Typical mooring line diameter: 12mm
Example 2: 32ft Boat
- Typical mooring cleat size: 250mm
- Typical mooring line diameter 14mm
