Sizing Bridle Eyes

Just used the Wing Guy..

 

aahh ok...so not actually representative then. Since many caveats given by WG.

You need an actual dwg of what you are proposing, not a sketch, but an actual dwg, showing actual sizes, thickness, materials etc..
Otherwise, it is just speculative of what you can or cannot do.

Once you have that, the options tend to answer themselves out...but the objective needs to be clear...the objective being..what the structure/joint is 'designed' to do.

 

very fair; unfortunately, I don't even have a piece of paper or a mechanical pencil and ruler as am on vacation for awhile...

I can draw something about March 28 unless I run out and get stuff, but can't measure the boat angles either...

The loading, based on vessel alone is 5200 pounds if we use the drawing from BK and the longest bridle length. So, in the simplest context; seems like I should be trying for about that, but rx suggested much lower numbers.

I'd like to know what I need to do to withstand 5000 pounds load at that angle from the bridle drawing.


changing subject for a second..

The bow eyes are in an overbored and epoxy putty refilled hole and they would be pretty strong, but the local core is also only M80 and so I added a 12" piece of butterflied stainless to help with any lateral forces. The backing plate is about say 28 square inches and so I figured (perhaps incorrectly) that the bow eyes would also support some load. the external butterflied section is about 1" of ss and 12" long, so I guessed they might help spread the load in an emergency to to say half of half of pi times 12" or say 3•pi or lets say 9.5 square inches which was only to help keep from tearing out the hull in an emergency tow..But I was really guessing at it all. A mostly straight pull on the bow eye of half the vessel using 5000 pounds and the backing plate is 178psi which was close to the core compressive ratings of the m80. The butterflied piece and a quarter of it is like pi/4 x 12 or say around 10 sq in.. The M80 core only has compressive strength of 145psi though, but the lateral forces would never be the full vessel weight. The local core is m80, but maybe about 10 layers of it and each bedded into epoxy with two layers of 1708 (600/225) tapes on the outside and more than that on the inside. The bow eyes are probably stronger than the plate, but the plate area has the opposing force of the trampoline netting.

I realize most of what I am saying is jibberish, but was my best attempt.. It would be so nice to understand the real ratings of the bow eye. I set it up as an emergency tow point or a place to secure the hulls for transport and it was really expensive and custom made. They eyes are like 10" long threads to go through enough layers of core to get to 2" wide inside. I seem to recall about 10 layers of 12mm and a bunch of epoxy putty. I barely have any extra threads inside after the backing plate which I think was 3/16 or 1/4".. Anyhow, I knew they were not very strong on any side pull intuitively..thus the butterflied piece which only serves to spread load.. If the bow eyes were tested hard; they'd likely fail sideways first (intuitively). I wish the local core were heavier now...

sorry about my grammar here; wrote when I was too tired to see and edited in the night

 

ps

When I made the holes for the bow eyes, I used a piece of copper supply pipe to maintain the hole as a pilot when I did the overbore and refill. I did have to work them a bit, so they are not perfect. I bedded them in 5200, but probably should have used epoxy putty..point is the holes would probably start to fail after hours on a hard anchorage unless the 5200 serves as a shock absorber... anyhow, worth noting

I really 'felt' like the bow eyes would work for towing when I built them. Maybe I could jist bridle there..

 

So, I want to bring this thread back to life.

I am wondering whether I can rebuild the netting beam in carbon and the fixtures as well AND make them strong enough for the bridle eye AND the beam fixture and clamp. The clamp could be the existing stainless one.

Before getting too deep into the idea about rebuilding the bracket in carbon; is it just a silly notion to build something complex like the bracket shown on March 15 amended to include a bridle eye in carbon?

If carbon is silly, I will do the drawings for the part; and do some drawings to determine loads and see if it can be made in aluminum as well.

The boat was launched and we have some better weight data now as well.

Thanks to all the contributors thus far. Some of this is rather daunting to deal with, but now I even have a bridle to use and real boat weights, etc.

My goal will be to anchor this boat in a hurricane and survive...bend not break might mean aluminum is best for the bracket..

 

This is now adding another layer of 'complexity' then.
Since to survive at anchor during a hurricane, is a significant amount of load. Way way beyond what the beam is most likely designed for.
If your goal is to anchor and survive a hurricane, i'd recommend a totally separate fixing for this.

I designed specific typhoon bollards for a series of high speed catamarans that we designed that operate in HK.
The same objective...when a typhoon hits, they anchor them and ride out the storm. But the loads imparted to the vessel, require major structure, not little bolt on beams.

 

The netting beam is bothering me.

It is either 6061 or 6063 aluminum, from memory, that latter. And 1/4" thick wall, 4.5" od. It is a hair under 12' long. And it is accidently double the specified wall thickness, my error on ordering. It weighs 43 pounds or so and as far forward; I would like to cut its weight to half to help provide for anchoring moment. It was polished and anodized and really expensive. If I redo it, probably getting painted..

I think to build in carbon and end up at 12 pounds is probably not worth it. So leaning heavy to aluminum; despite the carbon dream. It will be super hard to fab to 0.125" wall....lotsa turns

I had the bridle designer tell me to use soft shackles, but I really hate the concept.

Another poster here gave me a knot combination to use that I need to investigate further.

But I do need to be prepared for a hurricane. I am not an insane fellow, but I would like to keep my boat out of a direct hit from a big one. This means I might be on the boat in really bad winds somewhere firther away.

The too beefy, too heavy netting beam is strong, but the core at the hull would probably shear if I anchor off it.

Bottom line is I need to reevaluate the section and be prepared for anchoring in high winds.

Wondering out loud about using the beam and the cleats..and maybe even my tow eyes in some combination.