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Old 01-10-2017, 06:00 PM   #321
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Something doesnt sound right. What's your Sn you are using for the equation?

Calculation is not specifically for wood stringers
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Old 01-10-2017, 06:07 PM   #322
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I usually agree with this, but there are composite manufacturers who advise otherwise....its an interesting debate.

http://www.hexcel.com/Resources/Data...ite_Repair.pdf


Maxie,
That pic of the stringer looks like a good method of construction. I especially like the "stringer pad" that lays under the stringer and beveled at 45 degrees.

I like tabbing wide to narrow but really dont see a distinct advantage either way.
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Old 01-10-2017, 06:15 PM   #323
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Something doesnt sound right. What's your Sn you are using for the equation?

Calculation is not specifically for wood stringers
18 ft LOA (tip to transom) x 8ft beam x 3.5ft deep = Sn 0.50
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Old 01-10-2017, 06:48 PM   #324
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18 ft LOA (tip to transom) x 8ft beam x 3.5ft deep = Sn 0.50
Sn looks right. something in your math. I came up with 2.08" wide. Half that for height.

I should have hesitated before posting the formulas or at least prefaced it before hand by saying Gerrs calculations in this book are more suited towards larger vessels ,workboats commercial craft etc. It didnt dawn on me until I saw the unusually low Sn calculation his formula yeilds.

Would they work at the dimensions and laminates calculated? I would say so.

But for practicalitys sake maybe not
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Old 01-10-2017, 07:13 PM   #325
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Sn looks right. something in your math. I came up with 2.08" wide. Half that for height.

I should have hesitated before posting the formulas or at least prefaced it before hand by saying Gerrs calculations in this book are more suited towards larger vessels ,workboats commercial craft etc. It didnt dawn on me until I saw the unusually low Sn calculation his formula yeilds.

Would they work at the dimensions and laminates calculated? I would say so.

But for practicalitys sake maybe not
I think you are correct that they would work and it kind of puts in prospective how easy it is to over design something. Keeping in mind that work boats and commercial boats are usually moderately powered. Im sure there is a lot to be learned in the rest of the book that would help understand how and when to use the formulas he came up with.
Thanks

I realised after reading your post 2.08" wide that i mixed up the height and width.

Last edited by surv; 01-10-2017 at 07:16 PM. Reason: additional info.
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Old 01-10-2017, 08:00 PM   #326
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The new $270. Grinding room works great!

Thanks for the inspiration Gerald.
D
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Old 01-11-2017, 11:02 AM   #327
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Maxie,
Thanks for the reply!

Other then building/repairing a few fish boxes I have little experience with foam core construction. After seeing the pic, I was curious to find out if foam core specifically required a narrow to wide tabbing schedule.
D
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Old 01-11-2017, 02:01 PM   #328
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It shouldn't matter what you use for a core, ie foam or plywood, that would determine wide to narrow or narrow to wide........the repair type may do that, ie grid vs hole repair vs transom and whether or not you follow the West System or Geralds methodology as to the glass orientation and the resin rich line at the end of each layer. I've seen tabbing done both ways on older boats coming from the factory and they've all held...if your calculations as far as failure is that close because you're balancing every ounce of weight vs strength like an Americas Cup Yacht, then you're too close to the edge anyway for a typical fishing boat in my opinion....plus I use epoxy so I'm not worried about elongation issues. Its a good discussion.
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Old 01-13-2017, 09:07 PM   #329
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Last week I posted that I would be doing some testing on a new product and I'd try to get some video of the process. Well here it is. But first, let me warn you, it's NSFW. If your boss catches you nodding off you could get fired. You've been warned.


The reason I wanted to post this video is because so often I see stuff posted about the "horrors" of polyester resin. "Epoxy, you gotta use epoxy" is what you see written on so many forums it's almost comical. Epoxy is great stuff. It's just not need most of the time. It's my experience that polyester is more than adequate for most composite constructions (and repairs for that matter). I hope this video will at least give a hint as to the relative strength of composites in general and polyester in particular.

To give you an idea of what is going on, we build products for the telcom and utility industries. This unit we are testing is called a below grade enclosure (BGE) or utility vault. You can commonly see these at street corners. They look like a hatch in the sidewalk. These things are basically big hollow boxes that are used for junction points and excess cable storage.

The basic dimensions of this BGE are 61" long x 31" wide x 36" high. The top is divided in two across the width making two 30" x 30" lids. The parts are made with a few different materials. The common glass is 1708 biax and 102 oz quadraxial. Well, the quad is maybe not so common but it is E-glass. We also use a product called Saercore. It is a product made for VARTM and infusion type processing. The version we use is constructed with a polypropylene flow media sandwiched between 4.5 oz CSM layers.

We do an infusion on these prototype parts with a polyester resin. Later, when we are in production, we will switch to VARTM in matched molds. After the parts are demolded and trimmed, we bond them with a vinylester bonding adhesive.

An interesting note on these parts is that the thickest laminate is only about 1/4" thick. Most areas are about 3/16". The geometry is somewhat like a single skin boat construction with stringers and bulkheads. Stringers on the long sides of the box and bulkheads in the lids. That is about all I can say about the part. Some of the information is proprietary.

The tests are pretty involved and the video only shows a quick glimpse of what we are doing. We test to the design test of 22,500 lbs for ten cycles and then we check deflection at load. The allowable deflection is 1/2" and we are generally seeing deflections of less than 3/8". In the video, you can see the 2" dial indicator we use for deflection measurements. After the design test, we then we do a load test of 33,750 lbs. The load is distributed through a 1" thick 10" x 20" steel plate. Just imagine six full sized pickup trucks pressing down on a 10 x 20 plate. I've actually tested up to 40,000 lbs. It really is quite impressive how this bit of glass and resin can hold up to the equivalent of half a fully loaded tractor trailer and not break.

Now, as I alluded to at the beginning of this screed, the video is pretty boring. No explosions. No car chases. No fancy women. Just plain old boring testing. What it does show is how strong fiberglass laminates can be. When I pan to the laptop, you can see the readout for the load cell. In the future I may be able to post something that fails. That might be a bit more exciting.

So, without further ado - the video.


Last edited by OReely; 01-15-2017 at 05:50 AM. Reason: added info
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Old 01-16-2017, 07:59 AM   #330
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I don't think anyone questions the making of a part using Poly resin...its been proven effective for many many years on parts/boats....the reason why epoxy is usually recommended (myself included) for a repair is the same reason you used vinyl-ester bonding adhesive to put your polyester parts together...the VE's and Epoxies are better adhesives than the Poly's...they are not required for making a part, but they are better suited for the bonding part.

That video brings back memories from the testing labs back in school...pretty cool
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Old 01-17-2017, 11:09 AM   #331
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Good morning gentlemen ( it's morning here ), I didn't pick a good job to post daily progress on, everything that could go wrong has. The weather's been terrible, low temperatures and high winds and then the next day we have high 30s, rain, and high winds... I was struggling a little with the shape or my perception of the shape to the point that I was a little frustrated when I stepped back far enough to realize that the boat has a 2° list to the port.. bad move on my part to have not figured that out sooner.
I built up six layers of 1808 and three layers of mat ( 1808's overlapped at the centerline ), I ground after each session of two 1808's and then did three layers a 24 ounce roving alternated with mat to get the shape close. Slid my pattern in place and then hung a 1 x 0.25 x 12' piece of stainless steel on the stem to check my accuracy ( the straight line of the stainless steel doesn't lie ).
Thursday afternoon I cleaned up my taper around the perimeter and laid two more 1808's that extend all the way out to the edge of my grind ( but did not lap around the stem ), 2 1/2 hours after that laminate I ground again and put on a single primer coat of micro balloons, resin and gelcoat.
Friday morning I knocked down the primer ( 16 grit on a 9 inch and 24 grid on an 8 inch ) and applied three coats of gelcoat with a roller. While that was kicking off I finished prepping the stainless steel, drill and countersink, put some polish on the portion that sticks above the waterline. Two hours after rolling on the gelcoat I hit it with the 24 grit and an 8 inch and then finished with 80 grit and fastened the stainless steel strip...
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Old 01-17-2017, 11:35 AM   #332
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The stem shot that I posted was blurry ( wrong photo ), this one's better.

Edit, that one doesn't look all that great either, I'll get a better one but if you zoom in my shape is good.
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Old 01-19-2017, 06:15 PM   #333
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Looks well done to me Gerald! Good work.

A whiskey plank for us today!



Here you can see the red highlited areas which we will get cnc routed molds we can pull glass parts off and graft into the hull instead of trying to shape the openings by hand.
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Old 01-19-2017, 08:54 PM   #334
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Congrats on the "whiskey" plank!

The cnc router makes it so easy its almost cheeting! j/k Those are some tough radius' to figure out.

Thanks for the pics.
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Old 01-19-2017, 09:00 PM   #335
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Gerald i didnt say anything when you posted your pics but I need to. That looks great! You did an excellant job of rebuilding the original shape of the keel. I know that wasnt easy. Nice work.
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Old 01-19-2017, 10:24 PM   #336
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Looks great Gerald! I'm sure you have one happy customer.

Can you tell us a little more about "fastening" that stainless steel strip?
D
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Old Yesterday, 09:53 AM   #337
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Quote:
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I don't think anyone questions the making of a part using Poly resin...its been proven effective for many many years on parts/boats....the reason why epoxy is usually recommended (myself included) for a repair is the same reason you used vinyl-ester bonding adhesive to put your polyester parts together...the VE's and Epoxies are better adhesives than the Poly's...they are not required for making a part, but they are better suited for the bonding part.

That video brings back memories from the testing labs back in school...pretty cool
While I agree with you that VE and epoxy resins are better adhesives, my point was that they are not necessarily needed to do most repairs. Provided adequate bonding area, polyester can be used with great success to make repairs. I really do like VE. I've often posted in favor of polyester when budget is a driving factor and stepping up to VE if one could swing the modest upcharge.

Epoxy, on the other hand, is something that gets too much praise, in my opinion. It's not that I dislike epoxy, on the contrary, I think it's great when used in the proper context. It's the simplistic idea that epoxy is the only thing that will keep you and your boat from joining Davy Jones down in his locker that gets under my skin.

Maybe not in this particular thread, but many threads on THT (and other forums) have posters (certainly not you) extolling the virtues of epoxy resin and the surety of calamity if polyester is used. Reading between the lines, I can often tell the poster has little or no understanding of the products they are promoting and/or discounting.

Today, most boats are built with DCPD polyester resins. One of the issues with DCPDs is a short open window, generally no more than 24 hours. Since boats are often built over a number of days, those windows close and the surface needs to be prepped (by grinding) to get good adhesion. If this is done on new polyester construction, why wouldn't it work on a polyester repair? The answer, based on my experience is that it will work.

A final point before this soapbox collapses out from under me. You mentioned my use of VE bonding adhesive. I have several reasons for using VE adhesive. It's a better glue (as you and I have both stated). It has a higher elongation than polyester. I have minimal bonding surfaces in this particular product. Cost. The loads being applied.

Among my reasons, minimal bonding surfaces was most important. Where the loads are concentrated, the bonding surface of the supporting structure is just shy of 2". This is a real challenge as fiber engagement over such a short span is ultra important and that is where elongation comes in. The VE adhesive can do a better job of getting all the laminate in the contact area working. I'm putting forces on this product that a boat would never see. If the bonding surfaces were bigger, or the loads were lower, I would certainly consider polyester adhesive.

The bottom line is I choose materials that will do the job (with a significant safety factor). I could "overbuild" but why? That's just spending more for no real added value.

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Old Yesterday, 10:19 AM   #338
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While I agree with you that VE and epoxy resins are better adhesives, my point was that they are not necessarily needed to do most repairs. Provided adequate bonding area, polyester can be used with great success to make repairs. I really do like VE. I've often posted in favor of polyester when budget is a driving factor and stepping up to VE if one could swing the modest upcharge.

Epoxy, on the other hand, is something that gets too much praise, in my opinion. It's not that I dislike epoxy, on the contrary, I think it's great when used in the proper context. It's the simplistic idea that epoxy is the only thing that will keep you and your boat from joining Davy Jones down in his locker that gets under my skin.

Maybe not in this particular thread, but many threads on THT (and other forums) have posters extolling the virtues of epoxy resin and the surety of calamity if polyester is used. Reading between the lines, I can often tell the poster has little or no understanding of the products they are promoting and/or discounting.

Today, most boats are built with DCPD polyester resins. one of the issues with DCPDs is a short open window, generally no more than 24 hours. Since boats are often built over a number of days, those windows close and the surface needs to be prepped (by grinding) to get good adhesion. If this is done on new polyester construction, why wouldn't it work on a polyester repair? The answer, based on my experience is that it will work.

A final point before this soapbox collapses out from under me. You mentioned my use of VE bonding adhesive. I have several reasons for using VE adhesive. It's a better glue (as you and I have both stated). It has a higher elongation than polyester. I have minimal bonding surfaces in this particular product. Cost. The loads being applied. Among my reasons, minimal bonding surfaces was most important. Where the loads are concentrated, the bonding surface of the supporting structure is just shy of 2". This is a real challenge as fiber engagement over such a short span is ultra important and that is where elongation comes in. The VE adhesive can do a better job of getting all the laminate in the contact area working. I'm putting forces on this product that a boat would never see. If the bonding surfaces were bigger, or the loads were lower, I would certainly consider polyester adhesive.

The bottom line is I choose materials that will do the job (with a significant safety factor). I could "overbuild" but why? That's just spending more for no real added value.
Thank you Roger, I too am irritated when polyester gets an unwarranted bad name. I've spent much of my career repairing boats with polyester and refuse to accept that that is folly.
I post projects on this thread not to highlight what I can do, but to highlight what can be done with polyester, I'm a boatyard type mechanic, nothing special, projects like these are done all around the world. In these projects I hope to show good workmanship and how to get it done with polyester...
Gerald
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Old Yesterday, 10:24 AM   #339
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Looks well done to me Gerald! Good work.

A whiskey plank for us today!

.........
Congratulations kln, your crew is growing
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Old Yesterday, 10:26 AM   #340
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Looks great Gerald! I'm sure you have one happy customer.

Can you tell us a little more about "fastening" that stainless steel strip?
D
Thank you, just drilled and tapped 1/4- 20 fasteners and a little 5200...
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