Pippins
Member
I have seen a few posts here on mast cleats and wanted share my thoughts and how I do mine.
Materials: Aluminum or Nylon cleat, long grip aluminum rivets, spare sunfish mast or 2.25" tube, one tube slightly smaller in diameter 1.5" or so, and self adhesive sand paper.
I like to use the 4 inch aluminum Schaefer horn cleats. The base of the cleat should be sanded to match the profile of the mast. If you do not do this, the cleat will put high tensile loads in fasteners with any side load and might eventually work the fastener loose. I put self adhesive course sand paper on a mast and hand sand the back side of the cleat to match the profile of the mast. This is tedious but should take less than 10 minutes or so. As a final step I like to put another piece of the same sandpaper on a smaller diameter tube and take a few final passes on the cleat to ensure the center of the cleat is not proud and if anything slightly recessed. This helps ensure the cleat is stable on the mast and hopefully will not lever itself out.
For fasteners I use long grip aluminum rivets that have a grip length that matches the required length of the combined mast and cleat. The rivets in this example from McMaster Car and are 3/16 inch aluminum with a grip length of 0.75 to 0.85. These have a tensile and shear strength of 310 and 500 pounds (respectively) which in my experience is enough for the application. Higher strength rivets are available as well. For $20 shipped you can have 100 of them to share with your sunfish sailing friends.
Many people here are putting stainless (-.50V) fasteners into aluminum (-.95V) spars. This turns your mast into the sacrificial anode in a galvanic experiment. The .45 volt potential difference between them is three times the accepted potential difference in a marine environment. You will not find any spar maker in the world that will tell you its ok to put a stainless fastener directly into their aluminum spar. I do believe that there are some monel alloys can be used into aluminum but which alloys is beyond my knowledge without research.
Using threaded fasteners into a thin walled (0.083" wall thickness) mast is also not good idea. There is not even close to enough thread engagement to consider this an acceptable joint design. The threads in the aluminum mast in this situation will be your limiting factor for strength. There is no industry accepted specification that you use to justify that short a length of engagement for this application and load. If I was going to use a threaded fastener I would put a block of wood on a temporary stick and use it for a backer.
These thoughts come from my tinkering with sunfishes, and my professional experience as a marine engineer. Will a stainless screw work into a Sunfish mast? Clearly it will, I just wanted to share my thoughts on what I feel is a better option.
Materials: Aluminum or Nylon cleat, long grip aluminum rivets, spare sunfish mast or 2.25" tube, one tube slightly smaller in diameter 1.5" or so, and self adhesive sand paper.
I like to use the 4 inch aluminum Schaefer horn cleats. The base of the cleat should be sanded to match the profile of the mast. If you do not do this, the cleat will put high tensile loads in fasteners with any side load and might eventually work the fastener loose. I put self adhesive course sand paper on a mast and hand sand the back side of the cleat to match the profile of the mast. This is tedious but should take less than 10 minutes or so. As a final step I like to put another piece of the same sandpaper on a smaller diameter tube and take a few final passes on the cleat to ensure the center of the cleat is not proud and if anything slightly recessed. This helps ensure the cleat is stable on the mast and hopefully will not lever itself out.
For fasteners I use long grip aluminum rivets that have a grip length that matches the required length of the combined mast and cleat. The rivets in this example from McMaster Car and are 3/16 inch aluminum with a grip length of 0.75 to 0.85. These have a tensile and shear strength of 310 and 500 pounds (respectively) which in my experience is enough for the application. Higher strength rivets are available as well. For $20 shipped you can have 100 of them to share with your sunfish sailing friends.
Many people here are putting stainless (-.50V) fasteners into aluminum (-.95V) spars. This turns your mast into the sacrificial anode in a galvanic experiment. The .45 volt potential difference between them is three times the accepted potential difference in a marine environment. You will not find any spar maker in the world that will tell you its ok to put a stainless fastener directly into their aluminum spar. I do believe that there are some monel alloys can be used into aluminum but which alloys is beyond my knowledge without research.
Using threaded fasteners into a thin walled (0.083" wall thickness) mast is also not good idea. There is not even close to enough thread engagement to consider this an acceptable joint design. The threads in the aluminum mast in this situation will be your limiting factor for strength. There is no industry accepted specification that you use to justify that short a length of engagement for this application and load. If I was going to use a threaded fastener I would put a block of wood on a temporary stick and use it for a backer.
These thoughts come from my tinkering with sunfishes, and my professional experience as a marine engineer. Will a stainless screw work into a Sunfish mast? Clearly it will, I just wanted to share my thoughts on what I feel is a better option.