C19 in Richmond, VA

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Dan_Smullen
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Re: C19 in Richmond, VA

Post by Dan_Smullen »

Thank you all for the spirited opinions, advice and debate. At the end of it all, this is what I've got. Pure speculation, but visualizing the compressive force required to fail the top of the fir stringer cap, after 1/2" ply is laminated atop, is hard for me to do.

Reducing the height of the tanks, or filling the tanks at the console were the only options to avoid this condition, but both of those seemed less appealing than an speculative calculations about compressive strength as compared to the unladen weight of a European swallow.

More suspect than this stringer, is my virgin stitching and glueing performance early in the build. :lol:

I think my puzzle joints are more likely to fail than this stringer. Of course if they all fail at once, I will ask the forum to warn all who follow, and to remember me as I sink into the drink.

Photo below taken during the most recent planning/decision making session. I will have one to share with anyone who wants to take a boat ride and help me field test the stringers!

8346

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cape man
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Re: C19 in Richmond, VA

Post by cape man »

I'm in!
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OneWayTraffic
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Re: C19 in Richmond, VA

Post by OneWayTraffic »

I wasn't thinking about compressive strength at all. I'm willing to bet that that is solid, and far in excess of whatever force you apply standing on top of it.

I'm more thinking about the boat wanting to bend globally as it slams into or falls off a wave. That force is resisted by the stringers, that now have a hole near the top of them. That force will get focused into that cut out, by how much depends on just what section modulus is effectively left. I don't know enough about the precise situation to say anything for sure.

Anyway that's all I've got to say about that.

TomW1
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Re: C19 in Richmond, VA

Post by TomW1 »

I said my piece and there is not enough wood at the top to prevent breaking of the stringer if it hits multiple hard waves over time. I would at least take some 12oz and tie the top of the cleats to the lower part of the stringer. Right now I could snap the wood that is left with my two hands. Adding the 1/2" deck over my knee. I have worked with woods all my life and know where and how to place things for strength and durability. This has been discussed many times and shown and I believe is shown in the How To's. You must not reduce the strength of a stringer or a frame when running anything through them. The normal is like 1/3 down or 1/3 up. Peter in building his CS25 in Curacao had to reroute many of his tubing runs.

Well I have given you an idea on how to strengthen it. I don't like it, but it may keep your boat from breaking up.

Sorry I have been off line, my computer was hi-jacked and I just got it back today.

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

OneWayTraffic
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Re: C19 in Richmond, VA

Post by OneWayTraffic »

I said I'd enough to say, but I will quote others.
viewtopic.php?f=12&t=16798&start=320
Cracker Larry wrote: Tue Jul 14, 2009 5:06 pm Peter, I just posted this in another chase tube thread, wanted to make sure you see it so I'm just going to copy it here.
TomW wrote:
Also always put the cutout in the center of the wood this leaves the strongest beam.

The building notes say to cut the chase holes as high up the frames & stringers as possible.This ensures that the maximum amount of wood is against the the hull,where you want it to be. on the panga the frames are quite deep, so it may be more academic, but on the fs17 I am building the frames/stringers are shallow, so it becomes more important.
Steve
I agree with Tom. From an engineering standpoint any I Beam or joist carries the load on it's top and bottom surfaces only. One side is in compression, the other side in tension. The center of the beam has no load. If you read any building codes concerning drilling holes for conduits in floor or ceiling joists, or I Beam timbers, it says that all holes must be drilled in the center 1/3 of the beam and not exceed 1/3 the height of the joist. And building floor joists don't get the flexing that a boat stringer does!

Photos like this really worry me, Peter :?

Image

Not only is the load bearing portion of the stringers cut away, but there are several cuts right across from each other :help: This boat will hinge/ flex at that midships point and suffer very early hull failure.

Peter, you really need to pull out those chases and rebuild the stringers. I'm serious :cry:
Cracker Larry wrote: Tue Jul 14, 2009 6:15 pm Kick it where you want, do what you like. Please do ask Jacques. But as an almost certified marine surveyor, I'd flunk it. All 4 of those stringers are weakened in an athwartship plane. The boat will break in the middle over time. Stringers should never have a notch in the top of them, or any kind of step or change of level. Nothing but a straight line across the top, bow to stern. Sorry, please don't shoot the messenger :help:
jacquesmm wrote: Wed Jul 15, 2009 3:54 pm I missed that.
Cracker Larry is correct: those cuts seriously weaken the stringers.
The chase tubes should go, as much as possible, through the middle of the stringer height.
You need 3", minimum 2 at the bottom and 1 or 2" plus the whole thickness of the cleats at the top.

I know that some production boats have that type of cuts in the top of the stringers but it is wrong.

Browndog
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Re: C19 in Richmond, VA

Post by Browndog »

Dan,

When building the FS 19, there were a number of instances where I asked for advice, got none, then proceeded as planned only to get a bunch of Monday Morning quarterbacking from some of the forum participants after the fact.

In all cases it hasn’t made a difference.

The boat is looking great, you’re making good progress. Looking forward to helping you coat the boat in fish slime at some point in the not too distant future.

Dan_Smullen
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Re: C19 in Richmond, VA

Post by Dan_Smullen »

Browndog wrote: Tue Apr 20, 2021 7:20 am Dan,

When building the FS 19, there were a number of instances where I asked for advice, got none, then proceeded as planned only to get a bunch of Monday Morning quarterbacking from some of the forum participants after the fact.

In all cases it hasn’t made a difference.

The boat is looking great, you’re making good progress. Looking forward to helping you coat the boat in fish slime at some point in the not too distant future.
Roger that, BD. Thanks. I remember reading about your spray rails. The advice, I believe, is well intentioned.

The decisions we make aren't made on whims, but after much mental deliberation and risk calculation. At some point, it's time to go and to not look back.

Chasing big red drum on the Eastern Shore this time next year is not out of the question!

OneWayTraffic
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Re: C19 in Richmond, VA

Post by OneWayTraffic »

Of course at the end of the day, it's your boat. I've made decisions with mine that others may disagree with, and always thought it through too.
Keep in mind however that sometimes issues take years to show. If it were mine, and I was married to having the tubes through there, I'd probably put ply on top and raise the sole. The C19 like my 17 has a deep cockpit. That way you can have your cake and eat it. Nearly everybody who has built a boat wishes they had done that. :D

Either that or design something on top of the sole to reinforce it. Glass in a beam to retain the cooler, or put a seat there, tabbed in with biaxial, or just some extra UD glass or CF running longitudinally on top of the sole in that place. On top of the sole so it's far from the neutral axis. That will cost almost nothing in time or materials. Sealing in the PVC tubes with glass and gflex won't cost much either and will allow the PVC to assist in the structure.

Anyway, it's been great to watch a C19 go together in real time. I'd take you up on your offer, but what with the cost of international travel these days, you'd need to offer a lot of beer!

Dan_Smullen
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Re: C19 in Richmond, VA

Post by Dan_Smullen »

Solutions! That’s what’s it’s all about!

Onward to the forward bulkheads and hatches!

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VT_Jeff
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Re: C19 in Richmond, VA

Post by VT_Jeff »

OneWayTraffic wrote: Mon Apr 19, 2021 7:35 pm I wasn't thinking about compressive strength at all. I'm willing to bet that that is solid, and far in excess of whatever force you apply standing on top of it.

I'm more thinking about the boat wanting to bend globally as it slams into or falls off a wave. That force is resisted by the stringers, that now have a hole near the top of them. That force will get focused into that cut out, by how much depends on just what section modulus is effectively left. I don't know enough about the precise situation to say anything for sure.
Just discussion for the sake of gaining knowledge at this point.

My impression:

I highly doubt Dan was referring to compression from walking, he was referring to the same compressive force you are: wave pounding, applying a force to the outside of the hull, which will be transferred, eventually to the cap/sole. In a I-Beam, the web component experiences sheer forces, the flanges bending forces. The sheer forces are distributed evenly throughout the web-depth, they are not concentrated at the top or bottom like in a "normal" beam. In a normal beam, the top and bottom experience tension or compression with a bending moment, the center neither, which is why holes need to be at the center. In an I-beam, it's not the case. A hole will weaken the web but the location of it, depth-wise, makes little-to-no difference.

As always, more than happy to be proven wrong, as my ONLY goal in this entire enterprise is to learn.
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