Angle iron

[Ad Hoc]

..... The inside angle is bonded with mecjanical fastners 3/8-16 and 5200 to a 1.5" thick plywood backbone. The other 1.25" angle is connected with 3/8 fasteners on one foot centers plus a fastener each side of the cross member junction....

Hmmm .. so those 1.25" angle bars that are 52" are joined together, and not one continuous unbroken span of 104"...is that correct?

 

[fallguy]

A is the other 1.25" angle oriented as a T. It is fastened on one foot centers plus an extra fastener jist under the crossmember and 5200 all along the backbone. Please note the crossmember is the original one we realized was too light.

B is the plywood backbone.

C is a temp cradle that is bending and warping a bit; not part of the boat.

 

[fallguy]

Hmmm .. so those 1.25" angle bars that are 52" are joined together, and not one continuous unbroken span of 104"...is that correct?

no; they are continuous John

 

[fallguy]

Also.. in the above photo; you can see the two angles do not line up perfectly, this is because the ply backer is 1.5" thick and the deck with silencer is 1.25" thick.

 

[fallguy]

This angle can easily be changed to 2" if needed. I can template the holes in wood and transfer them to the 2".

A piece of 2" 316 angle is about $350

 

[Ad Hoc]

Ok... slowly getting to grips with what you're asking/doing.

So, what type size attachment do you have for the Tee that is connected to the angle bar?

 

[fallguy]

Ok... slowly getting to grips with what you're asking/doing.

So, what type size attachment do you have for the Tee that is connected to the angle bar?

Originally, we just gonna bolt it on with two 3/8-16 bolts.

I am pretty sure the bolts would suffice, but the 1.25" flange might bend down overtime or a rough passage. But "pretty sure the bolts would suffice" bothers me, too. I can easily calculate and have the bolt tensile strength.

If I weld wings on the top of the angles; I get a few more bolt locations; say 2 per every 6" and if the wings are a foot long each way; the load is disbursed along 2 feet of the angles flange versus 4".

 

[fallguy]

The tensile rating for each bolt is 5,181 pounds. So they are technically strong enough.

the cockpit panels are screwed all the way around with 1/4-20 stainless bolts and would provide a resistance force as well

 

[fallguy]

The only scary bit would be a slamming force over this span/size/area. It is behind the cabin and a bit higher than the cabin vee, but I suppose technically the area could slam a wave in real bad seas.

 

[fallguy]

For the record, I plan to be super careful about rough seas, but would like to head to Isle Royal on Superior and the seas can get to 6 footers for that 25 mile run easily and of course, no forecast is perfect

 

[Ad Hoc]

Originally, we just gonna bolt it on with two 3/8-16 bolts.

I am pretty sure the bolts would suffice, but the 1.25" flange might bend down overtime or a rough passage. But "pretty sure the bolts would suffice" bothers me, too. I can easily calculate and have the bolt tensile strength.

If I weld wings on the top of the angles; I get a few more bolt locations; say 2 per every 6" and if the wings are a foot long each way; the load is disbursed along 2 feet of the angles flange versus 4".

Errr...ok, but now i'm getting confused.
What is the question then...as it seems you are covering all bases?

 

[fallguy]

Errr...ok, but now i'm getting confused.
What is the question then...as it seems you are covering all bases?

I apologize. I just don't want them to bend under a bunch of people standing in the cockpit. My mind wanders now and then since the slamming concern forward is a little unresolved. The boat is not designed for Bluewater and I need to remind myself of that a bit. It is a category B boat.

 

[Ad Hoc]

No need to apologise, it is your boat and your concerns - and rightly so!
Every boat must be fit for purpose...

Just apply the load add a FoS of 3~4, and then you should be ok.
But as always with structural design, it is about the load paths and supports.

 

[fallguy]

I am just a little uncertain about how to calculate the bending loads. The angle is bolted in two places and is 4" wide. I am sure the calculation is simple, but when I do it, it comes out way too strong versus the 'dan' test bending an iron by hand with a vice grip and a vice..

 

[Ad Hoc]

This kind of structural design is very straight forward and easy to do. But, only with a proper technical dwg showing dimensions/sizes and how the structure is arranged, such as its connection and supports.
Without which, it can only be "general" guidance.

Structural design is like electrical design; in the sense that you follow the electrical path from one wire to the next and so on to see where it leads and what it connects to. The electrical load path - or - the structural load path - is the same; where does it go? Can't wire a boat without the dwg to assist.... well, you can, just not very well or quickly and lots of guess work!