Building a Corsair CR13

[Brocky]

Hello everyone, I have started building a CR13. The panels are cut out and glued together, frames are cut out, and all the edges have been sealed with a couple of coats of epoxy, and best of all I've made only a couple of mistakes. While I've been waiting for glue to set, I've been following all the threads to do with this boat, and I have a couple of questions that the Boat Builder Central people may be able to help me with:

1. I brought up the question of a centreboard instead of a daggerboard in the questions before building section, and after some good advice from Jaysen decided to defer a decision till after I started. The place where I buy all my boatbuilding supplies from, and who rebuilds sailing dinghies for customers really thought a swinging centreboard is a good idea, especially with the many shifting sandbanks where I will sail, and where they all sail. The question came up in a thread in 2009, and Jacques offered to send the centreboard design plans for a C12. It must be a similar design. Is it possible for you to send me these plans?

2. I would like to use a gunter rig on the boat. In a thread in 2014 Jacques offered to send the plans for a gunter rig for an OT16, which would suit the CR13. Can those plans be sent to me also?

If there is a cost, I am happy to pay it for these.
Ian

[Reid]

Hello everyone, I have started building a CR13. The panels are cut out and glued together, frames are cut out, and all the edges have been sealed with a couple of coats of epoxy, and best of all I've made only a couple of mistakes. While I've been waiting for glue to set, I've been following all the threads to do with this boat, and I have a couple of questions that the Boat Builder Central people may be able to help me with:

1. I brought up the question of a centreboard instead of a daggerboard in the questions before building section, and after some good advice from Jaysen decided to defer a decision till after I started. The place where I buy all my boatbuilding supplies from, and who rebuilds sailing dinghies for customers really thought a swinging centreboard is a good idea, especially with the many shifting sandbanks where I will sail, and where they all sail. The question came up in a thread in 2009, and Jacques offered to send the centreboard design plans for a C12. It must be a similar design. Is it possible for you to send me these plans?

2. I would like to use a gunter rig on the boat. In a thread in 2014 Jacques offered to send the plans for a gunter rig for an OT16, which would suit the CR13. Can those plans be sent to me also?

If there is a cost, I am happy to pay it for these.
Ian

Brocky,

I sent you an email with some attachments that you are referring to. Hope this help.
Good luck on the build!
-Reid

[Brocky]

The build is progressing well, but I am at the stage of making some decisions about the mast and sails. I am going to use a gunter mast instead of the usual bermuda rig and Reid sent me plans for one from an OT16. I am looking for some advice on which sails should I get. Should I use the ones for the OT16, the ones for the CR13 and make the mast higher or some other sails that fit the dimensions of the masts? I have a set from aa old Heron dinghy. I also would like to lift the boom a bit higher so I can duck under it, and not have it whack me on the head. Is that a good idea or does that upset the balance of the boat? Is it critical to keep the original sails or doesn't it matter too much? Any advice would be helpful.

[Jaysen]

Sails are about aligning the COE from the sails with the COR of the dagger/center board more than fitting them to the mast. Since you are making the CR13 with the standard mast stepping location, I would use the CR13 sails to reduce the offset from planned COE. This will keep you in balance and make your boat more enjoyable.

If all that is Greek… yep. Sailboats have lots of jargon.

COE == Center of Effort
COR == Center of Resistance

[Brocky]

Thanks for your thoughts, Jaysen. OK, so I've spent some time researching those terms and their meaning in the sailing context and now have a grasp of what you are talking about. I ran it past my mechanical engineer youngest son and he got the whole concept in about 5 seconds - it took me about 2 hours with explanation, but at least I managed. The CE is marked on the sail plan for the OT16 but not on the CR13 unfortunately, and from what I have read, the COR (some call it the centre of lateral resistance) is about the centreboard. Even though I have used a pivoting centreboard instead of a daggerboard, I put it in the same spot in the hull, so it should be the same. OK so I keep the sails original, what about the idea of lifting the sails up a bit, about 8 inches higher? Will that upset the balance a lot, I assume it will a bit? I would really like to do that as I'm nowhere near as fast and as flexible as I once was. I suppose shortening the mainsail a bit at the top is a bad idea too eh?

[VT_Jeff]

I want to raise the boom on my racy c&c 29 to reduce head wackages, but my thought is to just treat it like an inverted reef as opposed to moving the whole sail up, and thats the approach i would take if i were you. You'll lose a little power in light air and reef lafer when the breeze freshens. If you understand sail twist then you'll know that the wind at the top of the mast is faster than at the boom, so adding sail higher up will have a bigger effect than you may think, along with the increased spar weight higher up. Would need to be balanced and may indeed move the ce some.

Of course, its subject to the "try it and see" rule. You may just end up with a slighlty wilder ride, more healing, more weather helm etc, but i'm sure it will still sail.

[Jaysen]

Basically what Jeff said. Reduce sail from bottom up, not “raise the trim top”. The former minimizes change to CE the latter maximizes it. The change to CE also reduces the effectiveness of CoR on dagger/center board.

If CE is easy to visualize by drawing a line from each sail corner to the mid point of the opposing line. Where the lines intersect is CE. Map out your planned changes and you’ll see the problem pretty quick.

[Brocky]

Wow, doesn't this get complicated fast. I spent some time researching 'sail twist' online and it seems that as well as considering varying sail angles and different wind speeds up the sail, apparently I have to consider the Coriolis Effect and which hemisphere I'm in! Only kidding.

Ok, so if can just make sure I'm understanding this correctly, if I want to go through with this change, instead of my thought of taking 8in off the top of the luff and then lifting the whole show up thus causing instability, I should take it off the bottom of the luff, as if I'm doing a permanent reef, and lift the foot and boom up 8in. I plotted the CE of each potential change on the mail sail as you both suggested, and your one sees almost no change in the CE, and it would also mean almost no change in the combined CE of main and jib It will reduce the area of the mainsail by 5 sq ft from 102 to 97. As to the extra spar weight as mentioned by VT_Jeff, I was going to increase the height of the yard of the gunter rig and not the mast. It is smaller and lighter than the mast so should help a bit. All this to reduce wackage (what a beautiful word).

[Jaysen]

Helmet and wrapping the boom in foam might be simpler and make for some interesting conversations later in the day!

[Brocky]

Haha. That is what I am trying to avoid. I take it then that I have understood you correctly?