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Modifications to Avocet

Don Silsbe

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As many of you know, Ted Johanson (Padre Point) has entrusted me with the care and storage of his lovely Core Sound 17 mk 3 Avocet.  The modifications will focus on organizing the numerous lines that are on this boat, and get them out from under foot. There are other mods on

my list, such as adding a bow roller for an anchor, and moving the centerboard forward to eliminate the leeward helm.  We’ll see how far I get, before we take her to Florida to hang out with the boys and gurls of the WCTSS.


I am posting this work in hopes that I can get some good feedback from the Mark 3 community.  


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I don't want to hijack this thread but I am curious about the centerboard modifications.  As background, here is what I know:

I sailed with Avocet this summer.  We had a pretty difficult reach back to the boat launch, with strong winds and waves intersecting from two directions, slowing boats up.  My boat doesn't point well, but I realized Avocet was doing worse that we were.  Don's a good sailor and he mentioned over the radio that they were having some issues.  He explained later that the centerboard in early CS17mk3 models was too far back, and that in those conditions they were having a hard time keeping on line.  To my eye (and Don and Ted can verify or deny) it seemed that not only were they not able to avoid drifting to leeward, they were also slower than I would expect).


My question is how does the position influence leeway.  I know that generally centerboard placement affects lee or weather helm, but I mainly sail by feel, not by numbers, so more of an explanation would be great.  I'll never turn into a marine architect, but I'm hoping to use this to increase my knowledge of how a cat ketch responds to wind forces.

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I may be biased, but I spent a lot of time getting the holes just right in the comings on Skeena. They look fantastic. 


As for upwind performance, I have the early design with the c-board back. I felt I couldn't reef the mizzen to the second reef point or the boat would have way too much lee helm. Late this summer I realized I could never get the mizzen on the center, which is where it wants to be. To do so with the stock rig requires so much downforce it goofs up the sail shape.  On a few occasions I rigged a line from the aft upwind corner to the sprit to haul the sail up to center and it changed the whole dynamic of the boat in the limited testing I did with it. My next plan is to make a triangular bridal that puts the center point up near the sprit centerline and then up through a block and then down. My challenge is where to go from there as the tiller is on centerline. 


I'm trying to avoid moving the centerboard. That looks like a crazy big messy job. 









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Interesting thought, Steve, on the mizzen.

Richard, the builder of Avocet, made a bridle from each aft corner for the sprit sheet. I’ll see if I can find a photo. Don am I pondered a mod by Gira Gira for the sprit. I’ll try to find that as well.


And, of course, Graham built a boomkin to move the mizzen sheet point aft if the rudder. Others have done this as well. What’s fun for me is that Don is taking on these projects while I just sit at home and enjoy the downhill skiing season. 


I should state that I really enjoy sailing Avocet, more all the time. I’m mostly getting used to the setup I bought from Richard and I don’t have the sailing savvy to know the differences y’all mention. So, I’m really appreciating Don’s attention and sailing smarts. 

But, pizza just came so I need to close this. 😁

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I like the trapezoidal shape, Steve.  Avocet has a bridle that centers the mizzen.  For me, when you over-trim the mizzen, it generates less lift— there is no longer any air flow on both sides of the sail.  Another alternative is to reef the main, and run the mizzen without.  This is what the previous owner did, at least in this photo.  89F09350-C5ED-4930-9BC6-7EB0040D51EA.thumb.jpeg.c6fee61ac16d087f6ec2cc76359d5725.jpeg


@Andy B— I wanted  so badly to keep up with your Sea Pearl!!!  But the tiller needed to be positioned as shown in this photo.  With the tiller in this position, it was generating a lot of drag.



The first few CS17.3’s were built with the c/b in this position, including Avocet.  Once B&B realized what was going on, they moved the c/b forward 10”.  Basically, by design, the lateral resistance of the boat should line up with the lateral force that the sails apply on the boat.  When they don’t line up, you get windward or leeward helm.  This easy to say in a few words.  It is much more difficult to get it right on the drawing board.  With a c/b boat you can cure windward helm by pivoting the c/b rearward.  Leeward helm is more difficult to correct.

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@PadrePoint— While you were eating, I found a photo of Gira Gira.  B9A52978-E7CB-49A4-ACD8-42E8D08BAACF.thumb.jpeg.a4d2251e94597842fff7b36589f64fe8.jpeg

Incidentally, today, I bought the electrical conduit to try this out on Avocet (and maybe do it on Local Honey, too.  It does require running the mizzen sheet forward, up the sprit, and down to a fairlead/cam cleat on the thwart.  Fortunately, Avocet is already set up this way.  57CD6EFB-3F28-44F7-9FC4-E934CDB62BE7.thumb.jpeg.84a90b2c41de4f8675c623c457b39aca.jpegLocal Honey started out this way, 2797F7B1-E699-4724-BFDD-1EF9FD82A5D0.thumb.jpeg.0a9f83659dd4fbad28a78757d4a43200.jpegbut eventually I went with the mizzen sheeting shown on the plans.  I might need to switch back, it this works for preventing outboard motor fouling.

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Nice work Don!  Your cut out shape looks great.


I agree with Don that if you pull in the mizzen too close to centerline you will no longer have good airflow on both sides of the sail.   I watch the tell tails; if I pull in the mizzen too far, the tell tails no longer stream straight back, they are angled back. 


Let out the mizzen by as little as 1 or 2 inches until the tell tails start streaming straight back.  I'm not saying the mizzen shouldn't be pulled in hard when sailing upwind (Graham and Alan recommend the mizzen be sheeted in a little bit more than the main), just remember to check the tell tails when you do.  

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I started on the bow roller.  Here, I’m gluing a triangular plate underneath the deck.  Next, I’ll add a knee.


Since it is cool outside, the anchor locker is a mini-sauna.675C1BC6-9907-4AC6-85C2-BD70C4F5864B.thumb.jpeg.eb7409263af07fc0341d8eb1d905ab89.jpeg


Once the way is clear, I want to ask y’all’s opinion on roller placement.  There are a few options, all good.

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Don, I've been working on installing a anchor roller as well.  I plan on angling it to port with the cleat fasteners going through a backing plate in the anchor well.  B&B angled theirs to stbd and their cleat goes to a backing plate in the cabin (they show that in their CS17.3 tour video), so you may want to consider their layout as well.   Here is my rough draft setup:












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Thanks, Amos.  The shape of your plate is exquisite!

 I was also thinking of tilting it to port.  There are fewer lones on that side— more available space.  The problem I cant’t get past is how to work around the support knee.  My roller is narrow, and has holes in the same location that yours does. My current solution is to attach the wooden base plate with through-bolts, and attach the roller to the plate with short 3/8” bolts and T-nuts.  What’s your plan?


Also, is a 1/2” thick knee substantial enough, or should I go thicker.?

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I plan on through bolting the anchor roller through the bowsprit and breasthook (I don't have a knee to work around; my breasthook is 2.5" thick and fiberglassed in). 


 I'm a little confused on your knee thickness question:  is the knee already installed or are you installing one?  Is there anyway to get at least one through bolt if you angle the bowsprit a little bit more?

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Currently, there is no knee.  I have a choice of adding a 1/2” or 3/4” thick one.  One is shown on both Graham and Chief’s boats in those videos.  Also, there is even less room on a 17 for packing this all in.  So, my current plan is to go straight with the roller (like Graham did), put the cleat just to port of the tabernacle (like you did), through bolt the base plate, straddling the knee, and using T-nuts to attach the roller to the base plate.  Before I do, I want to make sure I can get those beefy T-nuts in stainless.  I would also appreciate hearing from others, before I glue in the knee.

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