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Old 30-08-2017, 18:16   #1
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Trimaran nets/trampoline attachments

We are in the middle of a total refit and renovation of our 44ft trimaran.
We would like to get some better attachment om the trampolines.

We will have 6 trampolines (3 on each side). The middle section we are thinking about glassing in PVC tubes and have a thinner tube (fiberglass/metal or similar) inside. Bu cutting the outer pvc tube we attach the trampoline to the inserted pipe.

On the front trampoline (triangular ) there is a wire, but the question is if I can replace the wire with a beam from hull to aka. For example, can I make a fiberglass beam out off PVC pipe? Or laminate a wood beam? This is to get a tighter trampoline which is harder do achieve with wire.
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Old 30-08-2017, 18:52   #2
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Re: Trimaran nets/trampoline attachments

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Originally Posted by andreas.mehlin View Post
We are in the middle of a total refit and renovation of our 44ft trimaran.
We would like to get some better attachment om the trampolines.

We will have 6 trampolines (3 on each side). The middle section we are thinking about glassing in PVC tubes and have a thinner tube (fiberglass/metal or similar) inside. Bu cutting the outer pvc tube we attach the trampoline to the inserted pipe.
I think that this is pretty common, as is bolting on aluminum toerail track. The type with pre-machined holes in it. Though, obviously, ensure that such holes have eased/rounded edges.

On the front trampoline (triangular ) there is a wire, but the question is if I can replace the wire with a beam from hull to aka. For example, can I make a fiberglass beam out off PVC pipe? Or laminate a wood beam? This is to get a tighter trampoline which is harder do achieve with wire.
The beam would have to be quite strong (SIC) to resist the loads from tensioning the tramps alone. Not to mention those created by someone jumping or falling onto the nets. So given this, attaching such a strong, stiff member to both hulls in a way to allow the hulls to flex independently could prove a challenge. It's certainly doable, but would need to be thought through. That said, the beams which hold Wharrams together are flexibly mounted, ditto older outrigger canoe designs.

Also, I've been told that the below tool is handy when tensioning the lashings which hold the trampolines to their anchor points. As it lets you get a much better grip on the lashing lines, especially if they're something slippery like Spectra.
Power Grip - Single Hander | APS
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Old 30-08-2017, 18:53   #3
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Re: Trimaran nets/trampoline attachments

Yes, you can fiberglass in a PVC pipe sliced in half, lengthwise. Then string through some cable rigging, cut holes in PVC pipe at regular intervals and you have your attachment points.
I've read that this doesn't offer attachment points that are as strong, but it seems to work adequately.
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Old 30-08-2017, 20:44   #4
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Re: Trimaran nets/trampoline attachments

Quote:
Originally Posted by andreas.mehlin View Post
SNIP

On the front trampoline (triangular ) there is a wire, but the question is if I can replace the wire with a beam from hull to aka.

SNIP
Maybe the real question is do you need a NA to answer this question.

You mention using PVC you have cut in half and putting something inside. Without knowing if you would be using 1/2" PVC or 6" or something in between answering your question would only be speculation. As another poster mentioned there is also the issue of flexible or rigid beams. I am sure there are big differences in strength requirements for flexible as opposed to rigid beams.

You might want to provide more details about what tri you have and the size and attachment method of the beams. But even a NA would probably want to bail on the answer.
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Old 30-08-2017, 21:08   #5
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Re: Trimaran nets/trampoline attachments

You might replace the wire with some (polished) heavy wall stainless pipe, & lash it at the ends heavily to the padeyes for the current wire, using Spectra. You'd have to check the end lashings regularly of course, even more so than the tramp lashings.


What is it about the wire that you can't tension it well enough to keep taught trampolines? Pics would help of course. But still, unless the weight of a person in the forward tramps is pulling the bows closer together enough to loosen the tramps... then where's the issue. And do you/your crew routinely hang out on those tramps? Other than in port/on the hook I mean.
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Old 30-08-2017, 21:26   #6
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Re: Trimaran nets/trampoline attachments

Woah there

Be really careful about what you want to do - for two very important reason.

Tramps on tris should not run from the front of the main hull to the bow of the ama. This is bad practice. Unlike cats, tri amas often slice through wave tops and often get deeply immersed in large waves downwind. They should be as free of drag as possible to do this properly - no nets near the bows of the amas.

Then there is the structural issue. Cats again have a huge compression beam to deal with the tight net issue, tris don't. You will put huge forces on the ama pulling it inwards if you tighten the net with a wire. Unless youput a large beam on the front of the net it will just bend under load - and you can't use a beam because of the rule above.

So put the wire from the main hull bow (or about 1 metre back) to where the front crossbeam meets the ama (or close to) this is lower load. Tighten the nest between the crossbeams very tight but the bow nets should stay loose.

As to attachment - I glass over 20mm PVC tube with two layers of 400 gm double bias. Then cut slots in every 100mm or so. Then a piece of stainless or aluminium tube inside to attach the net onto. I would not use track and screws unless as a last resort as I have a wooden boat.

cheers

Phil
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Old 31-08-2017, 22:04   #7
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Re: Trimaran nets/trampoline attachments

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Woah there

Be really careful about what you want to do - for two very important reason.

Tramps on tris should not run from the front of the main hull to the bow of the ama. This is bad practice. Unlike cats, tri amas often slice through wave tops and often get deeply immersed in large waves downwind. They should be as free of drag as possible to do this properly - no nets near the bows of the amas.

Then there is the structural issue. Cats again have a huge compression beam to deal with the tight net issue, tris don't. You will put huge forces on the ama pulling it inwards if you tighten the net with a wire. Unless youput a large beam on the front of the net it will just bend under load - and you can't use a beam because of the rule above.

So put the wire from the main hull bow (or about 1 metre back) to where the front crossbeam meets the ama (or close to) this is lower load. Tighten the nest between the crossbeams very tight but the bow nets should stay loose.

As to attachment - I glass over 20mm PVC tube with two layers of 400 gm double bias. Then cut slots in every 100mm or so. Then a piece of stainless or aluminium tube inside to attach the net onto. I would not use track and screws unless as a last resort as I have a wooden boat.

cheers

Phil
Phil, I think you missunderstood. It's from main hull to aka, not ama.

Why I wanted this beam was more of a security thing. Feels more safe having a beam to be able, something more solid and stable.
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Old 31-08-2017, 22:51   #8
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Re: Trimaran nets/trampoline attachments

It looks as if you guys have the tri Hot Sauce, the Trevor Banks 44'. I was curious about her last winter, & if memory serves, her construction is fairly light. Including her topsides being made out of plywood. Which, if that's the case, then bonding tubes in place to attach the tramp's to may not be wise. As when you pull hard on glass that's bonded to plywood, especially point loads, sometimes some of the plywood's surface veneers will suffer a shear failure, & tear out with the layer of glass attached.

In my Searunner, which was glass over plywood, the nets were attached using a variation on the jib track method I mention above. The difference being that angle aluminum was used instead of jib track. And despite it's being unanodized or otherwise coated, it held up to the marine environment pretty well.
Plus it's cheap, & easy to source. Though of course if you wanted to, you could have angle aluminum anodized or flame sprayed, after all of the machining is done on it/the holes for tying the nets to are setup as you'd prefer them. And standard, non-exotic coatings work too.
Obviously you have to through bolt the stuff in place, but leaks shouldn't be an issue. They never were on my tri.

There are some multihull groups on facebook, which perhaps could be helpful. And one boat/crew that might be helpful is the trimaran Spirit. As they did a couple of huge refits, much of which is documented in pics on their website, as well as some on Facebook & Youtube. Here's one link trimaran spirit - Home
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Old 01-09-2017, 05:21   #9
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Re: Trimaran nets/trampoline attachments

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Originally Posted by UNCIVILIZED View Post
It looks as if you guys have the tri Hot Sauce, the Trevor Banks 44'. I was curious about her last winter, & if memory serves, her construction is fairly light. Including her topsides being made out of plywood. Which, if that's the case, then bonding tubes in place to attach the tramp's to may not be wise. As when you pull hard on glass that's bonded to plywood, especially point loads, sometimes some of the plywood's surface veneers will suffer a shear failure, & tear out with the layer of glass attached.

In my Searunner, which was glass over plywood, the nets were attached using a variation on the jib track method I mention above. The difference being that angle aluminum was used instead of jib track. And despite it's being unanodized or otherwise coated, it held up to the marine environment pretty well.
Plus it's cheap, & easy to source. Though of course if you wanted to, you could have angle aluminum anodized or flame sprayed, after all of the machining is done on it/the holes for tying the nets to are setup as you'd prefer them. And standard, non-exotic coatings work too.
Obviously you have to through bolt the stuff in place, but leaks shouldn't be an issue. They never were on my tri.

There are some multihull groups on facebook, which perhaps could be helpful. And one boat/crew that might be helpful is the trimaran Spirit. As they did a couple of huge refits, much of which is documented in pics on their website, as well as some on Facebook & Youtube. Here's one link trimaran spirit - Home
Thanks
Yes, I see your point with the weakness of glass it into plywood. I will look into it more. We are trying to reduce number of holes.

Yes it's HotSauce. Plywood in deck and super vertical sides of super structure. Hull, amas and underside of aka is foam

Yes,we have been in contact with Spirit (last was actually yesterday). They did a really nice job with their tri.
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Old 01-09-2017, 08:28   #10
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Re: Trimaran nets/trampoline attachments

I have had good luck with regard to glassing in PVC pipe with glass rods inside. In the picture below, you are seeing 1/2" sched 40 PVC, roughed up slightly with 60 grit bonded to my engine pod with 4 to 6 layers of 6 ounce eglass and epoxy. Probably overkill, but it has not budged.





The grommet lacing did not work out. After one season, I converted to a glass rod in the edge of the tramp to better distribute the loads.

This is working out great! The rod distributes the load along many lacing points. The lacing is 3mm dyneema and shockcord.

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Old 01-09-2017, 13:18   #11
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Re: Trimaran nets/trampoline attachments

We also have pvc pipe glassed into the hull and decks with a fiberglass rod running down the center. Works well and gives a clean look but we have to watch for chafe where the lines hit the edge of the cutout. Maybe more care with the placement of the grommets would have helped.Click image for larger version

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Old 03-09-2017, 04:28   #12
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Re: Trimaran nets/trampoline attachments

If you are worried about ripping the PVC track off the ply veneer then stitch it on.

I love stitching objects on with uni strands - my jib tracks are actually PVC pipe with glass over. I don't like bolt holes.

I have seen the glassed PVC tramp attachments ripped off. To stop this drill two larger holes over the top of the glassed PVC. Then tie the PVC on with chopper gun uni strands. Use a plastic needle from a sewing shop to do this. About 4 turns of doubled over uni strands into the inside, around a backing pad, and back out will make it bulletproof. Fill up any voids and paint. I love doing this - my jib tracks get a heap of load and don't move. To move the car (which never happens) I tack, pull out the stainless rod, move the block into the next slot and put the rod back in. Cheap, light and best of all not rot and no leaks ever.

cheers

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Old 03-09-2017, 10:47   #13
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Re: Trimaran nets/trampoline attachments

We are having a heatwave in Southern California, and elsewhere, so last night I slept on my bow net, the first time since installing the new ones. Wow, super comfortable. Two inch mesh web, supported on three sides with Spectra lacing to epoxy/linear polyurethane wooden strip supports, the forward edge is a 1/4" stainless cable secured through the main hull and inboard side of the float deck, tensioned with a turnbuckle. VERY STIFF and flat, it was quite comfortable to lay on, but for overnight I laid one side of a light polyester blanket over it as minimal cushion. No issues whatsoever after several years of installation, walking on, carrying various loads.
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Old 05-09-2017, 05:37   #14
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Re: Trimaran nets/trampoline attachments

Roy, I'd imagine that one nice thing about living in San Diego, is that your wet items have a chance to dry out a bit.

Those wooden cleats epoxied down with LPU covering would not hold up here in the mid-Atlantic with the humidity. The lacing will abrade through the paint with use, introducing water, which won't dry out well. Rot follows. I know this from experience! Using cedar versus other woods would help in this regard.

I learned out here to let nothing abrade over a wood core, even if glassed.. and my original tramp fastenings taught me the lesson!

I do have some wood-core batten glassed into the side of my hull for some tramp connections, but the connection is through bolted and sealed, so no lacing abrasion occurs as you walk around.....
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Old 05-09-2017, 10:54   #15
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Re: Trimaran nets/trampoline attachments

My boat has a similar system to Roy's that it was built with almost 50 years ago and it is still working in the soggy PNW. The trick is apparently to use wood that doesn't need to be painted or glassed such as teak or? It is on my list of things to redo but doesn't rate a priority yet even though it breaks Catsketcher's rule about going out to the ama bows. While I intend to make the new system run diagonally to the beam instead it hasn't caused problems because The Nicol wing deck goes far forward with a gentle curve on the underside for a scow bow lift that keeps the ama bows from diving deep.
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