1 inch plywood stringers vrs 2x4's laminated on top of one another as stringers

[ED21]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

I'll second Paul's general analysis of I beams.<br />The web serves mainly to separate the top & bottom flanges. Of course it's a bit more complicated than that.<br />I would also be concerned w/ the rot resistance of your typical spruce/pine/fir 2x stud.

 

[BillP]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Mark42, For my next boat project I was thinking about just using old stringers for the form and laying up glass to make the stringer. Only problem I see with that is it will be costly to bulk up for stiffness. <br /><br />Pursuit uses a thin layer of pvc foam under their ply stringers to reduce stress points. I don't know if its necessary but thats what they do. They are building light so maybe it matters. Plenty of other mfgs place the ply straight to the hull and don't have problems so take your pick. <br /><br />YD, I don't work at Pursuit. I was at the plant with a boat owner as his consultant. It was legal deal where he had to get the legal system to enforce warranty. It resulted in them cutting the old deck off and putting it on a new hull. Part of the agreement was he could witness the new hull being laid up. At the same time, I toured the factory to see how they built them. Really not much different from any other production plant I've seen. Boat work is just a hobby for fun now...I'm not up on Novarania. Are they the long skinny outboard hulls with flared bow?

 

[Moody Blue]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Can't resist, have to side with Realgun on this one hands down. The strength of a beam is in its web. The function of the flanges is to prevent side-side bowing of the beam under load and to provide a convienient means of fastening and securing to it. The tension/compression factor also plays into the beam construction but the strength is primarily in the web. Higher loads=thicker and/or longer web. The flange dimension changes very little in proprtion to the web.<br />Bigdad4cyl who ever told you that gluing multiple 2x4's together on edge is stronger than laminated plywood is off their rocker. Don't let them anywhere near a structural project. If strength/stiffness is what you are after then the more laminations the stronger. By glassing the stringers into the hull you add an additional bending resistance by forming an "L" at the hull-stringer joints and across the top of the stringers. As Mark pointed out, if the glass was thick enough you really wouldn't need the wood at all. This thread is getting somewhat off topic so my appologies to Bigdad4cyl.

 

[Realgun]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Pual I would like to oplogize you are indeed correct that the top and bottom are in both tesion and compression. Thats why the use steel reinforcements in concrete. Concrete can be squeezed but not pulled, steel can be pulled but bends when squeezed. Both the webing and the two flanges work in concert to provide the needed strength and to reduce the weight of a solid wood or steel I-beam. The reason a steel I-beam is not used is it is so hard to drive a nail in one that will hold in a wooden structure.<br /><br />I used a small T beam in my boat. this beam is a 1x3 piece of wood that is 24.5" long and a 1 inch x 1/2" x23" piece of plywood underneath for strength. Only because I stepped on the piece of wood and it bent!<br /><br />

<br />The front beam is to hold the floor up where the front of the hatch goes.

 

[alden135]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

I guess we're back to using 3/4 ply and glassing it in huh.Good luck with your project and post some pics.

 

[Richard Petersen]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

I am jumping in to. ALL of you, are all wrong. The beam gets 80% of it's structural strength from the GLUE. the other stuff is just so the GLUE can be fastned and not flex an crack or be crushed at any 1 point.

 

[Bondo]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

I am jumping in to. ALL of you, are all wrong. The beam gets 80% of it's structural strength from the GLUE. the other stuff is just so the GLUE can be fastned and not flex an crack or be crushed at any 1 point.

That's just Flat Out Wrong ..........<br />Unsupported Resins(Glue) has Absolutely No Strength by itself.......................<br /><br /><br />Paul,<br />Realgun is Still Much Closer to Right......<br />I went back to your link,... In order to remove the amount of web like You are saying, You have to factor in the Spacing of Supports(Main Beam),+ Where,+ How Many "Web Supports" are added........<br />You've got to Read All the instructions,... Not just the paragraphs that support Your contention...............<br /><br />Those little 2X3s Don't Carry The Load...........It's the Web ........<br /><br />RodC is also Right..... <br /><br />I also Agree that Dimensional Lumber has No Place in Boat Building........<br />Because of the grain Structure, Plywood is Much Stronger,+ Dimensionally Stabil, compared to Lumber.............

 

[Richard Petersen]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Has any one seen plywood rubrails, sprayrails, skegs, one piece thru the hull keels, coamings, dashboards, etc. Convince the present retro wood boat people that they should not use solid wood. Soild wood can be glued on at least 4 sides safely. Plywood only 2.

 

[Terry H]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Richard Petersen <br />the discussion is about stringers encased in resin on f/g hulls. I think you missed the point. Chief

 

[Richard Petersen]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Your right . I got side tracked.

 

[Paul Moir]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Bondo, I read that page over and over, and I can't find anywhere where it says web stiffeners have anything to do with web holes. And the only thing it seems to me it says about support spacing is that I can't put a large hole near a support. The reason for that because removing web material is going to weaken the beam in shear loading, which is concentrated at the supports.<br />Besides, why do you think they go on and on about not even nicking the flanges, but allow you to blow giant holes in the web?<br />Here's a nice little article that explains the principals of I-Joists: Click here. And this describes the rules a little better (visually), but unfortunately it's in French: Click here. <br /><br />Realgun, I appreciate the concession. But please there in no need to apologise to me personally. I think we're all here for the same noble cause and I don't think you should ever apologise for participating. Now, if you wrote that intending to spare my feelings, I'll tell you that it takes a lot more than I-beams to hurt them.

 

[BillP]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

I presume I-beam stringers aren't necessary or every boat out there would have them. There may be some boats out with I-beams but not many. It seems to me the bottom of the boat and the underside of the floor connected to the stringer prevent torsion...if they don't, the sizing is too small. Its nothing like building joists that have one side supported every XX feet...even with decking on one side. <br /><br />Glue. In the surfboard mfg biz we used to cut the foam blanks lengthwise and glue them back together for additional strength. We used regular polyester resin pigmented (to show a colored glue line) as the glue. Just doing this made a notable difference in keeping boards from breaking in half or flexing. Glue lines were approx 1/16" thick by the time they soaked into the foam and three glue lines were normal. That made a 3/16" thick x 6"+- thick "stringer" of resin.

 

[Richard Petersen]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Paul Moir. Thanks for the French LVL beam. As they state very clearly, all the load is divided and carried at the tiny 4" over the supports. The glue and wood chips there are carrying the full loads.in a 4"" area. Engine weight is spread over the length of our stringers. NO comparison to the 2 applications. Our point loads are the engine mounts.

 

[Bondo]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Paul, I understand the Theory,+ Application of Lateral Beams.............<br /><br />I also know for a Fact, that if 98% of the Web is Removed, The beam Will Break or Bend Exactly Where the Web Is Removed..............<br />Whether Steel or Wood, The Web supports the weight,... Remove it,+ the Flanges Will Not carry the load......<br /><br />I didn't learn this from a web page,... But from real life experince..........<br /><br />BillP is Right, We're not using I beams in our boats,.. But,... We Are creating Structure, By glueing the Stringers to the Hull, Then adding a couple of Bulkhead pc.s,+ Glueing,+/or Screwing the Floor to the tops of the Stringers......<br />We've created several Boxes, hence Strength thru Structure..................<br /><br />And, In the Surfboard senerio, It's Still Not Unsupported Resin.....<br />The resin soaks into the foam... <br />So, It's a Combination of Resin,+ Foam that create the Resin Stringers.........<br />And, Yes,.. That's a Strengthening Structure............

 

[alden135]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Well bigbad4cyl, looks like from the direction this thread has gone in you'll need to have a structural engineer stamp your plan and pull a permit with the local building inspector.

 

[BillP]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Even though it was overkill for strength, I used 3/4" ply for stringers so it had enough end grain area to screw the floor down on. A flange on 1/2" would have worked but I did't go that route. Being it was on the ply's edge I used 3" long screws with epoxy to secure the floor.

 

[crab bait]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

when i built my last boat.. the stringers were 5/8 ply ( ab doug fir ext) with 1 x 2 mohog strips epoxied an srcewed to the top an bottom edge of the ply stringer .. one side only.. to make into an I-beam persay.. <br />but i overkilled an did it to both sides of each stringer.. top & bottom to each side.. 4 lenghts of 1 by per each stringer..<br /><br />amazin' the load bearin' of an I-beam..<br /><br />also it was great for construction also.. gave a good glue an screw surface with the top & bottom mohog surface..

 

[bassman1]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

I agree with Bondo, I beams will give even with none of the web removed. I know from experience as a contractor.

 

[Paul Moir]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Bondo - I suspect we may have a misunderstanding here. I originally took issue with Realgun's post because he seemed to imply to me that the web material was the primary load carrying part of a wooden I-joist, and the purpose of the flanges were entirely secondary. He seemed to confirm this with his second post.<br />I don't mean to say that cutting holes in the web doesn't greatly impact the ultimate shear strength of the I-joist (clearly it does), or that it doesn't make the beam some more flexible. What I am arguing is that the flanges are providing by far the stiffness of the beam. Otherwise, the logical extreme would be that you could replace the web with popsicle sticks without any loss of strength and stiffness.<br />The example of the I-joist is ideal for this since it is a composite of solid wood (the flanges) and A manufactured panel. The OSB web has extreamly low tensile strenght (~1500psi) verses the straight grained flanges (~5000psi along the grain, and lots of sinches). So if you were to cut the bottom flange in the middle between the two supports, the OSB would immediately begin to tear. However, if you were to cut the bottom flange close to one of those supports, the beam may not fail at all since the bottom isn't in much tension there, and the superior shear strenght of the OSB material will support the load. <br />So what I'm left to wonder is what exactly you ment in your first and second post, about Realgun being closer to right. And I'm hoping that through my gusto I led you to belive that I thought that the web provided no strength or stiffening at all. Which I don't.<br /><br />Also - I'm using web pages as convenient references for all of us. Don't think I have no experience with these things. I just think references are more convincing than saying 'I saw it', since my credibility with you is limited to my postings on this site.<br /><br />I would like to thank you though for explaining the relavence of this to those who don't see it. EDIT: And I would also like to appologise for turning this post into a book! I was trying to be breif - believe me.

 

[Realgun]

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

Re: 1 inch plywood stringers vrs 2x4's laminated on top of one another as string

I have a ? <br /><br />So plywood is good and solid wood is bad. Correct?<br />For various reasons. Weight and strength being the top 2.<br /><br />Thats what was asked and We all got WAY off topic here. <br /><br />BigBad we (please don't be mad guys) humbly suggest you replace the stringers with ply just as the MFG did. <br />But you can seal them better!!!