Chesapeake Double with Mk 3 Sailrig - handling question

I'm building a Chesapeake Double with the Mk 3 sailrig. Has anyone built this combo, and if so, how does it handle? Is there a tendency to round up or fall off?

The reason I ask is because I'm replacing the aka-mounted leeboard with a daggerboard in a through-deck case. I need it to be strong, and the aka mount isn't strong enough. I'm trying to determine the best place to mount the case. My three options are 1) inside the front cockpit; 2) between the forward laminated deckbeam and the forward aka; and 3) alongside the front cockpit on one side or the other. The position inside the cockpit has the disadvantage of being wet and in the way. The positions ahead of and alongside would be through the deck and would allow them to be sealed off from inside the boat.


Any ideas out there? Any experience?


6 replies:

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RE: Chesapeake Double with Mk 3 Sailrig - handling question

Hey Deltaguy,

If I understand what you're attempting, then the only person that can really help you is John Harris.  The exact location of the point of lateral resistance is extremely important to locate with respect to the combined center of effort of the sail(s).

John is a busy man, and normally these kinds of tweaks are commissioned then offered as an option to the general public later.  For example, a SCAMP builder wanted a yawl rig instead of a lug.  This is a little more design work, but is still in the same ballpark.  The builder happily paid Mr. Welsford and now you can build a SCAMP yawl.

There's obviously a lot of effort into building a boat like this, so I would hate to wing anything that important.  However, if I was going to do so, I'd just locate the daggerboard/slot/case perfectly laterally athwartship from the leeboard, making sure the longitudinal surface areas stay centered.

Good luck with your endeavor and keep us posted.

RE: Chesapeake Double with Mk 3 Sailrig - handling question

The relationship between the sail's center of effort and the leeboard's center of lateral resistance determines how the boat handles. That relationship should not be changed when you go to a centerboard.

Going from a centerboard to a leeboard is tricky because the leeboard has to be at the widest beam, but going from leeboard to centerboard is much more forgiving.

It should be at the same lateral location as the leeboard. So a line orthogonal to the centerline from the leeboard will show you exactly where you need to put the centerboard trunk. The tricky part now is the structural support and convenience.

If you put the trunk behind the line you'll have weather helm, in front and you'll have lee helm. If you have too much weather helm and can't move the centerboard forward, a small foresail can help. Conversely, a small mizzen sail can eliminate lee helm.

Good luck,



RE: Chesapeake Double with Mk 3 Sailrig - handling question

   Thanks for the feedback from both responders. That's exactly what has been concerning me. I can get a good approximation by finding the center of effort on the sail and center of lateral resistance. Between the front cockpit and the foreward aka would be the same relationship as the aka mounted leeboard. But the Mk 3 is a bigger sail, and the center of effort may be a bit further aft.

John sent a picture with the case inside the forward end of the front cockpit. The problem with that is that daggerboard cases tend to spit a lot of water. I think I may be able to seal it off, though. That location makes me suspect that theres some rounding-up tendency with the Mk3 sail and the leeboard in the original position. A post I read by a guy in a Chessie 17 (I believe) with the Mk 3 sail and the aka-mounted leeboard who mentioned that he had a hard time keeping the boat from rounding-up adds further to that suspicion. 

I'll figure this out. :)


RE: Chesapeake Double with Mk 3 Sailrig - handling question

I've successfully used foam to stop centerboards from spitting.



RE: Chesapeake Double with Mk 3 Sailrig - handling question

   I believe that the sailor with the Chesapeake 17 was using a rudder much too small for sailing, and that caused his problems.  John had the same problem at first, wrote about it in his blog about the SailRig, and designed the new SailRig rudder as a result.  Standard kayak rudders just aren't large enough to counteract the force of the sail, and as a result cause rounding-up.

RE: Chesapeake Double with Mk 3 Sailrig - handling question

A blanaced rig is the goal. But a weather helm is a better problem than a lee helm.    

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