Reverse chines, OB15 way

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OlivierP
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Reverse chines, OB15 way

Post by OlivierP »

Hi all

Quick question, might the reverse chines concept of the OB15 be applied to other designs, say a 17' boat (for instance C17 or GV17) ? I mean by extending the side panel by about an inch at the bottom and filling that extra inch as a reverse chine with epoxy and filler. All before taping, glassing, sharpening etc.

I see that as potentially saving time if you have the intention of adding reverse chines anyway afterwards.

Would that compromise the design in any way ?
Built C17 (app.php/gallery/album/262), GF14, Devlin Bella 16. Sails a 30ft Biloup 89 sailboat.

OneWayTraffic
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Re: Reverse chines, OB15 way

Post by OneWayTraffic »

I don't see it as much easier than filling a dam, and in some cases you might not have room on the hull plywood sheets for nesting. But if you could make it work I see no reason why it wouldn't work.

One advantage of damming against the hull is that you only fill once. OB15 style it seems like you would be filling, rounding, glassing and then filling again to sharpen the edges?

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OlivierP
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Re: Reverse chines, OB15 way

Post by OlivierP »

It sounds simpler to me than a glued wooden chine that I see often built : round, glass edge, cut and glue chine, round, glass, sharpen chine.

Vs OB way : fill, round, glass, sharpen

Alternatively indeed one can build a dam, but isn't the side panel a simpler dam, no extra work and guaranteed flush with the side panel.

Yes it requires 1'' extra width on the panel, ok if the nesting is not too tight.

Thoughts ? Would the designer agree ?
Built C17 (app.php/gallery/album/262), GF14, Devlin Bella 16. Sails a 30ft Biloup 89 sailboat.

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Re: Reverse chines, OB15 way

Post by OneWayTraffic »

Only the designer could tell you if he agrees, but I cannot see any structural issue with it.

If you have the specified layers of tape on both sides then it will have the designed strength. I would suggest that you use a low density filler like microballons if you wish to use less epoxy. A microballoon putty will be strong enough and though lower in shear strength you will have good overlaps onto wood both sides. It will also shape easier and you will need to grind a radius to glass it. Then fill up the little rounded bit with a high density putty later to sharpen the edges. Leave a radius of about 2mm if you want to get paint to stick.

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Re: Reverse chines, OB15 way

Post by OneWayTraffic »

If the nesting allows and you can make it work then it looks like the designer has no issue with it. The CS23 has a similar step chine according to this pinned post:

viewtopic.php?t=63623

pee wee
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Re: Reverse chines, OB15 way

Post by pee wee »

How will the chine be taped? If the sides extend beyond the hull, it's not easy to tape that joint. If you first fill the chine step and then tape, I guess that's okay . . but if you're filling with light weight fillers and epoxy and then taping structural fiberglass over it . . . ? If it all gets covered with biaxial, that could hold it all together. I don't know, and since it's questionable I'd build the hull and add the chine step to it.
Hank

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Re: Reverse chines, OB15 way

Post by BarraMan »

Pee wee has said what I have been thinking, “Sounds like a bad idea to me”! 8O
My reverse chines are made with glassed-over wood dams and epoxy/woodflour mix, built on top of the already structurally finished hull.
I believe they make the boat stronger and they certainly work well.
Last edited by BarraMan on Fri Oct 28, 2022 12:57 am, edited 1 time in total.

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OlivierP
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Re: Reverse chines, OB15 way

Post by OlivierP »

Thanks for the comments. I'm sure add-on reverse chines are fine. Still, I don't see why integrated reverse chines work on the OB15 and would not work on other designs. Yes they have to be filled with a sufficiently strong filler since they become structural. I understand that on the OB15 taping and glassing is all done over the reverse chine. Anyway I'd love to hear Jacques's viewpoint.
Built C17 (app.php/gallery/album/262), GF14, Devlin Bella 16. Sails a 30ft Biloup 89 sailboat.

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Re: Reverse chines, OB15 way

Post by OneWayTraffic »

I’ve seen more than one respected marine architect and Gougeon brothers suggest lower density fillers as an option in joints that will be glassed. If there is enough glass to take the load it doesn’t matter. The fillet is to fill gaps and ensure that the glass transitions smoothly.

Though I would use something heavier there myself. :D

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Re: Reverse chines, OB15 way

Post by TomW1 »

Reverse chines can work on most boats. A builder in Australia built an OB17 with them and did an excellent job explaining in his build notes. Reverse chines work very well in redosing spray and adding some lift on some boats. They can be added to most boats using a dam and a mix of epoxy and either cabosil or fiberglass fibers to make them tougher. One thing to think about is scale, don't make them too high for the length of the boat.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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