Angle iron

May I ask why you don't bolt the crossmember T directly to the plywood beam? All it would take is welding a bracket at the end of the T. One flat bar 2-3feet long with triangular gussets (wings as you call them) top and bottom. Then you screw directly to the ply trough the other angle iron, and you can also screw the top wings to it. This way any slamming loads are taken by the bolts in shear, you don't load up one leg of the 1.25" angle only.

On another note may I ask why this angle iron construction instead of a (ply)wood or composite one?

 

there is a floating plascore panel that is carried by the angle

bolting the crossmember to the ply would be possible; unfortunatet they are already too short for that and I have spent a small fortune on these parts already

When I started this project, I had no idea a composite panel was an option. Keep in mind this setup allows the cockpit to be taken apart so the boat can be hauled on a semi.

 

I understand they carry a floating panel and that it's removable for disassembly (screwd or lashed down I suppose). I can also imagine the 316 angle was not cheap. What I don't understand is your choice of angle iron instead of glueing a triangular wood or foam batten to the hull and beams and glassing them over. The center spine could have been a triangular plywood or foam/glass beam.

What is to short for bolting to the ply? Right now you are bolting the centerline T upper bars to one side of the angle bolted to the ply crossbeam. You would actually have to shorten the centerline T's lenght to be able to fit a flat plate in there.

 

So, you are suggesting a couple of new ideas I had not considered.

Keep in mind this is a prototype. And with all prototypes; some risk of change is present.

I am grateful for your comments.

This idea of using a high density foam core is curious. I have another place on the build where I want to install a wood deck and have been wrestling with how. What foam core density and glass arrangement can support bolting where you want to flange a near vertical face? A 20mm high density foam cleat would need to be glassed on the bottom and bolt pressures can delam it rather easily. I had considered making all glass cleats for there. My inexperience shows, eh?

Also, you are suggesting I cut the two angles under the ply to install a flat plate that is beefier. If I did so, the top of that plate would be 1.5" below the deck and the deck is 1.25" with silencing. So in order to make that work; I would have to router out the plywood enough to glass back over it and make the connection. This could work, but is it needed? I, first, wanted to know the raw strength of the existing connection. The flat cockpit panels offer resistance to bending of the tee.

What really forged the irons idea is the fact the back iron is strapped to the beam. It just made sense then to build it all from steel then.

Had I built a ply or foam step for the cockpit at the plywood; it would have eliminated two angles. But required some sharp inside corners I am not certain how to build in composites. I suppose the flat panel could have accounted for radiused landings (thinking out loud).

You ready for the real fun? I really am not a fan of the metal.

However, can an 88" long composite beam 2 1/4" - 2 3/8" deep achieve 5/8" deflection under 1500 pounds load for the same or less weight and allow bolting to it within 1/4" of the top? Not trying to sound like a smarty pants if it does. The beam has a 3/4" arch, too. My gut tells me no. It could be an I beam configuration. It won't work in 5 pound foam. Those I beams are strong; not that strong. We are for an aft, so I suppose the beam depth is not as critical either. The cabin base is a good 5"-8" deeper than the bottom of the iron angle now.

I am a certain distance in with this method. The cockpit panels, for example, are nearly finished and they have a 1-1.25" high density glassed in edge that would limit moving connecting points for composite radiuses on a major change now.

Thank you for contributing. I wish I had the discussion sooner.

 

It should be noted the crossmember also still connects to the angle at the aft side. The best I can come up with there is to add wings to crossmember top flanges.

Can anyone answer my original question on how to calculate the strength of the lower lip of an angle iron?

I have been using the thickness of the iron, 1/8" and the distance the force is applied over 4" and I come up with 1/2" square inch of stainless.

I grasped at straws and used 70,000 psi tensile for the stainless and come up with 35,000 pounds, but that is flat dumb wrong.

 

Trying to explain my ideas better here. Take 2 of the pictured bracket plate, weld to the end of your 2" T crossmember. One with the gussset on top over the arms of the T, the other one mirrored with the plate under the leg (or fold one piece of steel plate to the desired U shape). Bolt the bracket directly to the plywood. Sheer is taken by the bolts, size accordingly.

 

About the composite cleat. The foam or wood is just a core, the stress is taken by the layers of glass that are over it and extend onto the hull (or cabinsides or beams). This is just like building a top hat stringer but instead of a rectangular section it has a triangular section (rounded corner so you can lay the glass over). This cleat is basicly part of your hull like a gunwhale. Then you drill oversize holes, fill with thickened epoxy and redrill for the fastener. You could tap the thickened epoxy, embed a nut or drill the hole completley and use a nut on the underside (or any other arrangement you like, lashing with dyneema, studs, etc.).

The centerline fore and aft beam can be T, I or box beam. I would do a triangular hollow box beam where the top flange is flat (to support the deck panels) and the centerline of the sidepanels (the apex of the triangle) forms a parabolic curve. That gets you the most stiffness for the least amount of material (weight) since the beam tapers at the ends. A straight hollow rectangular box beam is just as effective and easier to build. Such a beam can be made to not have any measurable deflection under your proposed load. Fixing it to the transverse beams or cabin would be with a gusset plate like described above or other methods like suitable sockets, etc. depending on the actual configuration.

 

I did an Excel spreadsheet calculating the force that would take an angle iron to failure on its lower leg. For my situation, we used 30,000psi for the yield strength of 304 stainless and a cantilever beam calculation. The calculation we used is Yield Strength = m*c/I. The result of the calculation is the 1.25" leg would deliver a strength of 500-540 pounds, which is less than the design desired. By using the calculator, I could determine that putting wings on the crossmember would extend the B and get me to the 1000 pound number rather easily, but that includes no safety margin. To get to a safety margin, I can either use thicker angle or apply wings to the crossmember. Rumars idea is also not a bad one had I started in with it earlier..

 

Fallguy,
The beam that you have built using 1/4 inch by 2 x 2 angle forming a T is an extremely poor profile as far as minimizing the amount of deflection at the center point of the beam for the amount/weight of material that you have used.
This 88 inch 'beam' will weigh over 50 pounds.

This is all a basic overview AND by basic I will not get into a bunch of equations or units, ie inches to the 4th, or inches to the 3rd etc, as the discussion will get complex

If you take a piece of wood with measurements of 2 inches by 6 inches. If we orient the 6 inches vertically, and apply a load in the middle, it will deflect less than if you orient the 2 inch vertically and apply the
same load. So for the same weight of material, you minimize deflection just due to the orientation of the wood. There is a neutral axis in a symmetrical cross section that is midpoint between the edges. The further that you have material away
from the neutral axis, the lower the STRESS which results in less deflection. With an unsymmetrical cross section, ie either one piece of angle or two pieces made into a "T", the neutral axis is closer to the horizontal flange.
So if the distance from the neutral axis is smaller, you will have more deflection

You have made the assumption that you need to calculate the "strength" of the lower lip.

Assume for a moment, a beam with no deflection or at least an extremely small deflection. The end points of the beam, bolted to the 1.125 angle, would provide a 750 pound load, vertically down, ie shear only. At the end points
of the beam there will virtually no moment forces producing moment stresses. (Vb excepted) So taking your .125 inch leg x 4 inches long, your shear stress at the cantilevered leg is about 1,500 psi, much below the shear strength of the material.

Will there be some induced bending moment? A bit but due only to the deflection of the beam. We know intuitively that when the center deflects downward, that it will curve toward the end points and try to pull the lip downward.
But will it? While the lip of the 1.125 inch angle is only .125 inch thick, it will be bolted to the 1/4 inch beam angle making the horizontal thickness .125 + .250 or 3/8 of an inch thick PLUS it is also has a 2 inch by 1/2 inch vertical flange
from the 2 inch by 1/4 inch angle times 2.

So long as the bolts will carry shear flow loads and minimal loads due to the beam deflecting, you do not have to be concerned with the lip "bending and causing issues"

Another issue here is that the type of end conditions, ie where the beam attaches to the wall/structure impacts the deflection. And this imposes some guess work as the 1.25 inch angle is bolted to say plywood whose strength is
significantly below steel. If your 1.25 angle was welded to a solid steel backing then you can assume loads corresponding stresses and deflection would produce call it "A" series of values. If you assume the end conditions to
be simple end conditions, the you will have different values for loads, stresses, deflection. Call it "B" series of values. As the plywood backing attachment will offer some rigidity to the 1.25 angle, AND if you could determine
some percentage of the how to allocate the portions, I would expect that the load, stress, deflection calculations would be somewhere between the "A" series of values and the "B" series of values

That being said.
I have never ran across any calculations that would specifically show leg deflection due to loading as you are looking for.

I am only guessing here in that you have made an assumption that the 1.25 leg will act as a pure cantilever beam and that this leg will fail due to loading. Not taking into consideration that the beam bolted to the 1.25 angle
will stiffen the lip of the smaller angle.
IF your calculations are correct and there is a 5/8 inch deflection without a FS, the leg "downward bend" will be limited by the stiffness of the main beam.

So we are back to the main beam poor design, or usage of material and possible issues with the 1.25 angle attachment to the plywood being able to carry the required loads without the plywood deflection

So as a summary
The smaller angle lip will support the shear forces but will be limited by the attachment of it to the plywood
The lip will not act as a cantilevered beam due to the bolt connection
If I understand it from the discussions, you will have a panel that will drop in to the pocket and this will carry some of the load. It pretty much has to or your 52 inch span between your three beams, is excessive.

If I had started this from scratch with an unhampered budget, I would have had an unequal angle formed to attach to the plywood. say 3 inches by 1 1/2 inch legs 3/16 inch thick. The 3 inch leg going
against the plywood and 2 rows of bolts/screws *** for attachment. The beam would have been of a taller height which would have made the beam lighter, ( getting material away from the neutral axis) and minimized
the deflection.

*** a single row of attachment bolts will permit the angle to wobble along the axis of the bolts. If you create two parallel lines you limit this type of situation which could result in failure over many loading cycles

 

Thank you.

Yes, we used a cantilevered beam and we did neglect to account for the thickness of the attached section in the calculation. I am a bit convinced, however, that we are dreadfully light. Suppose someday I catch a 500 pound fish and four large men are standing in the middle of the cockpit, for example..!!

And, yes, you are correct, had I thought this through a bit more, I could have build a composite beam that would have had the 3/4" rise in the middle, and if I need to do lose some weight someday, I will have a good place to start. The center beam cost me $400 to get two pieces of steel shipped and probably $250 to get fabbed. I could have built the thing in coosa for less, but we would still have connecting points, so the coosa would have needed some T or means to connect to the other plane.

I just know if I get a vice grip and grab the angle, I can bend it with my own strength and that scares me a bit...'dan test'

the quoted portion confuses me

 

I was guessing that you were assuming that the leg would act as a cantilever just by your wording. When you grab the leg with vise grips, you create a large bending moment in the cantilevered beam, but with the bolting the two pieces
are treated as one, (so long as the fasteners can carry the loads) and basically (except for a small bit of deflections of the leg due to the deflection of the main beam) the shear will really be the focus of determining strength.

Also I was not aware that you were aware of I, M , c etc but seeing your excel spreadsheet, I realize that I over simplified the explanation. Sorry about that,

Re the ***
Say you are installing a flat plate to another flat surface and the substrate is weak, ie wood behind steel. If you run a single line of bolts, the flat steel plate will over time be able to wobble back and forth due to a few possibilities
Shrinkage of the wood will allow movement, the screws/bolts will lose their compressive loading allowing some space between the steel plate and the wood. To try to reduce a premature failure, looseness, if you stagger the bolt line,
when the plate is tilted, the twin bolt line will resist the wobble.

 

Ahhh. I understand.. Many thanks. I have a similar situation with my beam socket cabin mountings. They are all in a line and that wobble could occur. Only trouble is staggering them makes them a bit off in the socket, but I think I will probably add at least a couple in the offset after your contributions here.