Best Material for Trampoline Support

Doing it like the above will be a permanent affix, once it's under tension I can't imagine ever getting the rods out to take the tramp off, getting them back in would even be harder. So if the intersections need to be stitched, you'll have to do that in place by hand. If the intersections are stitched, if this tramp goes saggy, there will be no way to re-tension it. If the intersections are not stitched, one break and

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In this one, looking at the shadow, you can see the rods are in the same position as yours, but the lace line is what attaches it to the boat. That let's you easily remove the tramps, to keep out of the sun or repair or stitch, etc.

 

Yeah. Dang it. And I was feeling like some kind of genius

Lacing the thing up will be no walk in the park either. Last few nights I have been at the drawing board looking for a workable pattern. It makes my brain hurt. I might have to forget about the diagonal pattern and do "checkerboard" instead.

So, it looks like the options are
a. move forward as planned
b. use two rods, one inside the pvc and one attached to it outside to wrap the web around, and stitch up the intersections.

My thinking has been that even with a sudden failure the whole thing wouldn't come "unrove" quick enough to suddenly dump someone into the drink. I guess it depends on how "slick" the webstraps are and how much friction there would be in the turns. Maybe a system of rubber "stops" or something fixed temporary to the web straps would bind up in there if you had such a catastrophe. Or maybe using a larger dia rod ie 1/2 inch would help. Or maybe just some kind of safety line woven in the tramp temporarily would be the ticket.

Cargo Control sells sleeves of the same material as the webbing. I bought a sample and thought of using that at the turns as a chafe guard. Lot of work though.

 

Charly, the net i made for my Mac 36 was if i remember correctly was about 9' fore and aft and about 10' + wide, the fwd and aft sides were straight and parallel but of course the sides were curved like yours. I took measurements of the with every foot and lofted it out on a wood floor. I then subtracted about 4" all around and screwed down 1" pvc electrical conduit spaced up off the floor with 3/4" blocks to give space under for weaving the webbing. I connected the corners of the conduit with the nice gentle curved 90 degree bends that they sell to make up a continuous perimeter. I then weaved the 2" webbing on the diagonal and then as mentioned before, glued the junctions and had them sewn. The Mac had 1/4" ss hex bolts with a spacer and a fender washer under the head which you would lace the net to using Dacron line which allowed for tightening the net as it stretched over time. I never got to install the net as the boat burned up in a warehouse fire before i got the chance. I still have the net actually. I like the way you are attaching the nets to the hulls but i would lace it rather than weave it in situ as it will stretch and i don't think you will be able to tighten it with the ratchet straps, there will be hundreds of feet in a net. I could be wrong though. It would be a nice clean installation if you can pull it off.

Steve.

 

Thanks for posting that Steve. it sounds Like a good system. What kind of webbing material did you use? Polyester or nylon? Sorry to hear about the fire. I hope you get to use that. Net someday.

I have been thinking now about the possibility of letting the PVC tube and rod insert that will go next to the compression tube float... I could still attach it to the aluminum comp tubes with a variation of what I am calling the "dog collars", but rig it upso that I could adjust the tension there, either with a ratchet or just simple lashings. Then if I have to, I can also use a floating rod on the bow tube, that would be attached to the PVC/rod insert that would be glassed onto the aft face of the bow beam( my bow beam is plywood) this way I could tension the thing in both directions, but still have that clean transition at the hull/tramp interface and at the main beam. this is where the most traffic will be anyway.

The big unknown for me at this point is how much will this seatbelt stuff stretch?

 

I used 2" black polypropylene webbing, i think that nylon would have too much stretch and the samples i had received from Sunrise the polyester was too heavy and would get even heavier as it holds water. My main tramp between the mast beam and aft beam was polypropylene shade cloth and the original forward nets were poly fishing net.

Steve.

 

Hi Charley,
I should have said something the other day, it might have saved you some lost sleep, but...
I LIKE both Kurt & his designs. Given my druthers, & the nod from my wallet, I'd happily build one of his boats for myself (SOON!). The catch is, the same kind of drive behind his thinking which lets him design such light weight, quality boats, also leads him to go a bit wild when it comes to details. And in some of his past writings about nets on his boats, & how to attach them, he himself has said as much.

As to your boat, you may be trying to reinvent the wheel, re; your nets/tramps. If you want to go pro, get some spectra netting. Lash it in place, with or without rods, & call it good.
The stuff's not cheap, but then again, spectra's almost immune to sunlight. And for less coin, you can go with heavy fishing net. Just replace it every couple of years.

Option C would be to have someone stitch up some custom, webbing or mesh tramps for you. Using UV resistant thread. And definitely, also, make sure that the thread's heat resistant too, as it can get REAL hot stitching things like tramps. Hot enough to destroy a good bit of the strength in some types of threads. Plus, things that are black can reach 200 degrees plus in 80 degree sunlight. And some of the synthetic cordage & webbing out there starts to loose it's strength at temps a good deal lower than that.

There's plenty of info on here about tramp's if you care to do some digging. The above's just my $ 0.02 worth. And, um, I hate to say it, but the easy way to attach them to the hulls & such, is to get some angle aluminum, or aluminum toe rail with the holes for blocks in it, & just bolt it in place. The former is what was on my Searunner, & it worked out fine... for some 20+ odd years.
When it was time to repaint the boat, I just did the aluminum right along with it. And during each once in a decade overhaul, it got re-bedded & bolted. Though had it really been done right, it would have been bolted & bedded in place using the WEST system method. Then it'd have been more or less, do it once, & forget about it.

Just as an FYI, the point loads on the nets can get pretty high too, in addition to them just supporting folks lounging on them. Like when a buddy & I (both of us slightly north of the #200 mark) carried my diesel back onto the boat, crossing the nets in the process. Or the times I needed to bail out of the cockpit, mucho rapido, & jumped down 4' (vertically) onto the netting, to run forward.
Also, a tighter weave does have it's virtues. Like making it a little tougher to accidentally "give" dropped tools or winch handles to Neptune. - If I run across some pics, I'll throw'em up so you can see what mine looked like.

Good luck,
Andy


PS: As to how much your proposed webbing will stretch, I can think of one possibility. Back when all of the low stretch cordages started making their debut, one of the big (live & online) rig shops created what they called "The Punisher". It was just a long stretch of steel I-beam, with attachment points for line at one end, & a hydraulic ram, along with a linear measurement scale at the other end. And they'd splice up line type X in size Y, & measure how much stretch & creep it had at various percentages of it's breaking strength. I think it was www.Layline.com who had one/did it. Though it could have been www.APSltd.com and odds are West Marine & a few others have one too.
You might try making a few calls, & then send them some webbing to test, if you're truly that curious about it's stretch characteristics. Although too, it's maker likely has numbers on such a thing also. So if you're up for spending 20min on the phone with them to find the guy who's worked there for a few decades, & knows the ins & outs of all of the materials which they use, such may yield up said numbers as well.

 

thanks guys for all the feedback. Another angle here that I had not much considered is the wind age and wave permeability of webbing vs everything else. Consensus among cruisers is that webbing doesn't shed water quick enough and makes the tramp more vulnerable to forces from wave slamming. This is not really an ocean cruiser I am building, but she will definitely see blue water and will be crossing the Gulf Stream. Enough said.

one guy over on another forum used spectra line, woven cris cross and attached o the hull in a similar manner to my setup. It wouldn't,t cost too much. anyone here have opinions on using spectr or Dacron or polyprope? I just want the dang thing to be strong and hold up to abuse. but not too heavy. Or expensive.

 

I'm not sure, but I think using the words Spectra & cheap together is an oxymoron.
Barring my poor attempt at humor, I hope you wont mind my thinking aloud a bit on this topic. Have you looked around online to see if there are any multihull builders forums? Sometimes a few guys will get together & do a group buy on common items, perhaps including netting. You might try anything resembling a Farrier forum, or asking your boat's designer for references/POC's to other builders. And it's a stretch, but down in Oz, they build a lot more cats than we do up here, so it might be worth asking some folks down there for ideas. Including designers there too.
That, & you can also ask the manufacturers of production & semi-custom multis. To include that even on the production boats, the nets don't last forever, so...

Also, you can do searches for netting used for other things which might work in your application. And ask some of the major rope manufacturers directly; Samson, Yale, New England... their commercial divisions, as well as recreational.

If you do find some good leads, I'm sure that there are those of us who'd appreciate it if you could post them on here. As have others in the past.

Good luck, & if I come up with anything, I'll drop you a line.
Andy

PS: Be cautious about things polypropleyne (sp?), as in the yellow rope that's at times used for waterski tow ropes. It gets eaten by UV FAST. Although there may now be proprietary coatings for it, or blends containing it, which mitigate this.
It's not quite as bad as PBO, but...

 

Hi Charly,
Boats I used to do a bit of work on & owned one had woven rope tramps. Spacing was about 50mm or a bit more. The fore & aft ropes were run first & didn't need to be incredible tight, then the athwart/across ones next, under the catwalk the cross ones just had bowlines tied in them & the tramp would be tensioned with simple 3-4mm venetian blind cord reeved to form a purchace between the bowlines & a few extra falls & then hitched maybe six times, the thickness of the rope forms a deflection in the weave & everything stays put, they were quite firm to walk on but did deflect a bit which helps spread load over more ropes.
The line I used was 8mm which I bought as "mini anchor spools" of 50meters back then(20 years) they were about $9.99, the boat was 7 years old when I sold it & I recon that the line had a couple of years left in it. The weave up took a couple of days & was raining.... bit tough on the hands.
Lately I've been running some netting over ship guard rails & get the net & foot rope from the local fish markets, the foot rope I'm using is 10mm black polyprop & uv stable & also has been "softened", that's what I'd use now & would probably do more splicing such as under the catwalk + elsewhere to neaten the job. You'd prolly do it for a couple of hundred plus your time now.

Jeff.

 

Thanks Jeff. I am going to explore that avenue a bit further. I think I have have seen a photo somewhere of one of Kurt's boats rigged like that .I can't find it now (blue q ?)

Anyone have any negative sea experiences with woven web tramps? As in wave slamming etc?

 

I was onboard a homebuilt F31 tri a few years ago that the builder had used a fairly heavyweight fishing net made of dynema i believe. He said he had bought it as offcuts for quite reasonable $$ but i have never been able to find a scource so if you find it please share. While i think the webbing would not be as good on a true offshore cat it is much much more comfortable to be on compared to nets of any kind which for a charter cat is a consideration.

Steve.

 

Here in this area there are a lot of shrimp trawlers. I have been too busy lately but I plan to check in with a few sources and see what might be available in that department. I will let everybody know what I find out.

The comfort factor in webbing is a plus, but someone also mentioned the heat. I imagine on a day like today it would leave some tasty looking sear marks on a big white butt like mine.

The website at cargo control, where I bought the webbing, markets this seatbelt stuff as a lighter weight alternative to their other polyester webbing. they say it (the other stuff) is UV resistant. I still wonder how long this seatbelt version will last unprotected. If I do use the seatbelt I had planned to have a cover of some kind for when it is not in use. I would hope that I could get a few years out of it like that anyway. If so it would be well worth the price.

 

I agree about using some kind of cover to protect the net. On the comfort subject, the Mac 36 has 2 nets ahead of the mast. The originals were woven out of about 3/8" black polypropylene rope and I cannot express strongly enough how uncomfortable they were to be on, not for bare feet imho. I would check the seat belt webbing, if its nylon i would think it may be too much stretch, good for anchor rodes, not so much for catamaran nets. I personally think for anything short of a true ocean going cat webbing makes more sense for the comfort factor.

Steve.

 

I should pass along this link that yo barnacle posted on my build thread. I don"t want this kind of material for a tramp, but the stuff is really pretty cool. It might be a cheap alternate way to rig an awning instead of sunbrella. great prices.

https://billboardtarps.myshopify.com/pages/faq

 

My friend Herbie, who I told you about in the other thread, had nets of some sort on his second boat, a trimaran he built. I don't remember what they were exactly, but they were comfortable to walk on and lay on. I seem to remember them as rope type stuff, not straps. Like shrimp boat netting.

When he built his third boat, a catamaran, the yellow 35' "JoDo BeEr", (which was sold here and might still be somewhere in this area,) instead of a net or web for the trampoline area, he just used cedar wood, pretty much like a house deck. It ran fore and aft, was about 6" wide with 1" or so spacing and I'm thinking it was about 1" thick, maybe thicker.

You can see on his obituary http://www.legacy.com/obituaries/sctimes/obituary.aspx?pid=159886970 that he was pretty experienced when he built the boat and decided to make the tramp that way ( I think it went all the way across, taking the place of that center section shown in post 17) and where he took the boat with no problems of 'windage'. I know he was pleased with the results.

I don't recall any flimsiness of individual boards when you walked on it so I'm thinking there were possibly a few 'strongbacks' on the bottom side, something like beveled 1x3's running side to side, that would transfer weight to adjoining planks.