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“Tech Talk” …



Our new Commodore has asked if I would write a column for this newsletter on technical subjects. Hopefully, there will be some benefit to you and your boat. So this column begins.

As past Commodore, I should introduce Commodore Cathie Coultis to you. She has grown up with Albergs under her feet as the boat she now sails was her parents’ and so she really knows Albergs well. She has also done a considerable amount of racing out of QCYC on the Toronto Islands and has been a part of race crews for other owners as well. She and her husband John keep the boat in one of the most picturesque harbours in Ontario at the tip of the Bay in Picton. Cathie has worked in various boat-related firms and so has a considerable network of people that she knows in the sailing community. You will see some dramatic changes within our association, I am sure. I am looking forward to these changes and with our support, a continuing, excellent Great Lakes Alberg Association.


As for tech topics … I thought it would be a good place to start with two of the three very weak points on the Alberg 30s. There are still hulls with these original problems still being sailed. Those three points are;
  • chainplate bolts
  • rivets in spars
  • gate valves

There is no trick to replacing the bolts in the chainplates. You need 5/16” (or 3/8” if you want oversize) stainless steel (SS) bolts of appropriate length (so take the old ones with you on the trip to buy the new ones), and an appropriate drill bit and drill to increase the hole size in the knees and chainplates. Make sure you have a solid shoulder on the bolt where the contact with the chainplate occurs. NOT THREADS as in the originals. It helps to have a drill press to drill the chainplates but that is not absolutely necessary. You will need a clamp or two to clamp the chainplate to a solid surface if you hand drill them to the bigger size. Drill the chainplates and knees and then replace the chainplates on the boat. You have 7 to do. If the holes look very out of round and worn, you might want to consider replacing the chainplates too.

The rivets in spars are another weak point and it is consistent throughout Alberg boats, 22’s and up in size. If there is any play in the spar end caps or any oxidation on the rivet the possibility exists that the forces on the sails can shear the rivet and then you have a problem of a loose boom and a luffing sail thrashing about your head. To prevent that, all that is needed is to replace the rivets with cap screws or short bolts, 1/4” x 1/2” x 20. I have found that fine threads are quite difficult to cut by hand in aluminum and so I have used course threads. The measurement of the bolts just mentioned means the bolt is 1/4” in diameter, 1/2” in length and has 20 threads to the inch, which is the NC or national course standard. If fine threads had been specified, it would be 24 NF as the spec and that means 24 threads per inch, the National Fine standard.

To cut threads one requires a tap or die. A tap cuts threads inside a circle and a die cuts threads on a rod. There are also three different styles of taps depending upon the use and restrictions of the job. The most common tap is a tapered tap and there are plug and bottoming taps. The tapered tap is used when there is ample space below the hole to allow for a gentle cut to begin and then the cut tapers out to the full thread by the time the full diameter is achieved. This taper runs out to about 5/8” on a 1/4” tap. A plug tap is much shorter on the taper (so much more difficult to start the threading process) but still relies on some space on the exit or it will not cut to the bottom of the hole. A bottoming tap is square and thus requires a start with either a taper or plug tap and it cuts threads close to the bottom in a hole that has no exit.

Taps and dies have a specific tool to hold the cutter, so tap handle or die holder. Since we are wanting to cut threads in the circle (hole) left by the rivet, we need a tap and tap handle and since we want to use 1/4 - 20 bolts, we need a tap for 1/4” and 20 threads per inch, the specs for that can be as short as 1/4 NC. There is also a specified drill size for every tap and there are schedules that suppliers have for you to reference so that you get the correct drill size. Often the tap will be sold with the correct drill. The process is to drill the hole and then tap the threads. Put the tap in the handle and tighten the holding jaw. Now, use it as you would use a screwdriver or wrench. Since you want a bolt square to the surface make sure you hold the tap perpendicular to the surface and turn it clockwise with some pressure down into the hole. You do not want the tap to slip without cutting on the first turn so the first turn is a bit careful. After that, you continue to press some force down on the tap and turn a second revolution. At this point, you will have some shavings coming off the hole surfaces and into the small hollows in the tap. As these get longer and bigger, turning the tap gets more difficult. Reverse the tap by turning counterclockwise and this will break the cutting from the surface and they will fall out of the hollows so you can continue threading the hole. Continue again with clockwise rotation and every turn and a half or so, reverse just enough to cut the shavings and go clockwise again until you have the tap turning very easily which means you have threads all the way through. That is all there is to tapping a thread. The process also works in epoxy.

The end caps of the boom and the masthead fitting are riveted in and it is easy to replace these rivets when the mast is down and the boom is off. It helps to hold the end caps in a vice if one is alone but a second pair of hands can be sufficient. There is ample room on all out end caps to use tapered taps. When you use dissimilar metals as in SS and aluminum, it is best to add an isolator so that the two metals do not contact each other. There are products available that you brush onto the threads of the bolt for this purpose and as little as 0.003” is enough to do the job.

Gate valves will be discussed in my next column. I suggest that if you cannot wait for that column and/or have a problem you want answered or discussed, please post it up in our GLAA chat forum, “Cockpit”, or e-mail me directly. Thank You.

Don