Chotu's Advanced Running Rigging Thread (lots of pics)

[Cavalier MK2]

Dyneema does creep a bit under use and temperature changes so adjusting provisions will be needed. You can research rigging sites for that info.

[Chotu]

just to be clear about creep:

“Creeping or chewing-gum properties

Dyneema® behaves like chewing-gum: if it is subjected to continuous significant tension; it stretches incessantly and permanently. It is this irreversible elongation under static load that is called “creeping”. Nevertheless, the risk of creeping occurs only if the rope is used beyond 20% of its breaking load. If you are overcome by the fear of going beyond that fatal 20% limit, rest assured! That threshold is never reached with “regular” working loads, which remain at around 10-15%. Basically, unless you are racing in the Vendée Globe on a 60 foot IMOCA, you will never have to worry about creeping”


https://shop.inorope.com/en/project/...urce-of-worry/

[Cavalier MK2]

Check out the Rigging Doctor site for a good explanation of Dyneemas coefficient of thermal expansion. It is odd in that it contracts in heat and expands in cold. I use the stuff on my running backs and other items, probably lifelines next.

[rslifkin]

The thermal expansion thing is likely to be the biggest pain in this application. Personally, I'd be inclined to see if there's a fab shop in town that can weld flanges onto a couple of pieces of aluminum pipe to make additional bracing along the lines of what you've got. I'd probably leave the existing braces in place, then add an outward angled brace outboard of each one or maybe an X brace (with another outboard upright) if space permits. An X brace in the center might be ideal, but if you need good access to the dinghy through that space it won't work (and stiffening the roof enough to make up for that lack of support shouldn't be too hard).

[Chotu]

too ugly, unfortunately. no others catamarans need to do this. i need wire/rope and even that isn’t amazingly pretty to look at. lol

[Chotu]

Originally Posted by Cavalier MK2

Check out the Rigging Doctor site for a good explanation of Dyneemas coefficient of thermal expansion. It is odd in that it contracts in heat and expands in cold. I use the stuff on my running backs and other items, probably lifelines next.

it’s pretty odd isn’t it? Interesting that it works the reverse of what we would think.

It’s currently holding my mast up. My shrouds are dyneema

[s/v Jedi]

Search for “Hollaender Speed Rail”. They have that in 1.25” IPS which is 1.67” outer diameter, schedule 40 pipe in 6061 T6 aluminum with anodized finish, which has a 45,000 psi tensile strength rating. They have very robust fittings for them, incl. ones that use 4x 1/2” bolt.

If I do a quick math, this pipe is 0.66 square inches of material in cross section so tensile strength of the pipe is 30,000 lbs which should be enough for that 7,000kg load mentioned before with a safety factor of 2:1.

Of course these supports don’t get the full load.

Now here’s the thing with SpeedRail: the fittings come with set screws. These should be discarded and instead the fittings should be through-bolted.
Also, and Chotu won’t like this, they should be glued as well and the right product is the thickened G-flex epoxy from West or similar.

[rslifkin]

Originally Posted by Chotu

too ugly, unfortunately. no others catamarans need to do this. i need wire/rope and even that isn’t amazingly pretty to look at. lol

Interestingly, there are a few cats that appear to have a similar design concern to yours. The FP Lipari 41 being an example. Traveler is mounted to a hardtop like yours with just a few upright supports to transfer the loads down. What's not apparent to me is what they did to make the setup adequately strong. I don't see any more lateral support in their setup than what you already have.



I'm starting to think that provided your existing supports will handle enough upward force, a lot of the concern may be resolved by attaching that additional piece of square tube running across the hardtop. Tie it into both davit tubes as well as bolting it through the hardtop and you should be able to both stiffen the top significantly against flexing in multiple directions but also spread the mainsheet loads.

[Chotu]

Originally Posted by rslifkin

Interestingly, there are a few cats that appear to have a similar design concern to yours. The FP Lipari 41 being an example. Traveler is mounted to a hardtop like yours with just a few upright supports to transfer the loads down. What's not apparent to me is what they did to make the setup adequately strong. I don't see any more lateral support in their setup than what you already have.



I'm starting to think that provided your existing supports will handle enough upward force, a lot of the concern may be resolved by attaching that additional piece of square tube running across the hardtop. Tie it into both davit tubes as well as bolting it through the hardtop and you should be able to both stiffen the top significantly against flexing in multiple directions but also spread the mainsheet loads.

there are tons of them. That’s where I got the idea from.

in fact, more Catamaran have it on the roof than they do down to the beam. It’s the old fashion way going to the beam with it.

that’s why it’s kind of annoying. I am doing belts and suspenders with extra racking support when the average boat doesn’t do anything like that and I’m still getting people telling me I’m not doing a good enough job. frustrating.

fountaine pajot, leopards. all on the roof. same support columns

like I said before, the entire main sheet load went through some welded up aluminum arch that someone put on to hold solar panels on my last catamaran. And that didn’t fall apart either.

it also might have a little bit to do with technique. Or how people sail. Maybe some people have accidental gybes. I don’t know. I’ve never had one before. i’ve always been too nervous of them since back in the small boat days. So I don’t have accidental gybes. i don’t put boats into that danger zone. never used a preventer. I also don’t load the crap out of my sails and try to break things. i’m a cruiser

it’s just so annoying because more Catamarans have it where I am trying to put it than having it go to the beam.

So it’s frustrating

leopard 42 and 50:

[s/v Jedi]

Look at these…

[s/v Jedi]

Those Leopards have their boom where I have my lower spreaders…

[rslifkin]

Those pictures (and more that I found) all make me think that if you add support on the top to spread the load and stiffen everything (and tie into the davits so some of the load is spread forward into the roof as well), you'll be fine. Adding some triangulation to the existing supports outboard of them (1 additional leg per side) would add more safety margin. You could probably use dyneema or stainless cable for it, but if you could do it with tubing that would be best, as then it provides support in both directions. It doesn't need to be some massive, ugly brace though. personally I think your existing supports look pretty good, so adding another piece to triangulate them wouldn't look bad at all. They don't necessarily have to angle as far out as the drawing you did on page 5.

[Chotu]

bali, lagoon nautech

[Chotu]

Originally Posted by s/v Jedi

Look at these…

OK, the first one with the guy in the red jacket? That one scares me a little bit ha ha.

even the aluminum arch like I had similar to that on my last catamaran was much more robust. But look. That is also holding the main sheet load. I don’t know where we get these crazy fear factors from on this forum sometimes.

Like you can be doing something perfectly normal and somebody comes in and says you’re going to die. Lol

honestly those kind of responses are just useless.

This has been a very good thread until that post. That needless criticism and needless fear factor. kind of got everything off track. But hopefully things can go back to normal.

Especially now that we see everyone does what I’m doing.

[Chotu]

Originally Posted by s/v Jedi

Those Leopards have their boom where I have my lower spreaders…

ha ha ha ha. yes. Maybe not as high-performance.