DIY Trampoline - some questions

[Dave_S]

I have some pricing in on custom trampolines for my boat......... over $3,000, a bit of a surprise.

I'll have a go at making my own . I am going to convert the boat from captive rope on two sides with cord attachments bridging 100mm gap on the other two sides to, bridging gaps on all four sides.

I have bought this netting - black knotless polyester 22mm 200Ply / 3.5mm. I will weave a rod through the mesh for the edging and attach to a captive rod all around the opening.

Two questions.

1/. Should I use elastic or cord to attach the mesh, not much flex in the polyester but probably enough ? If elastic - which one ?... If cord which knot ?

2/. How wide should I make the gaps, currently they are 100mm, I'd like to reduce it to 50 for looks. It would still have a total of at least 100 but the lesser gap will increase loads on the attachment points if the weight is closer to the fixing point. I don't think this is a problem but most boats have the wider gap. Not sure why

Thoughts...

[Franziska]

Hi.

About 2 years ago I replaced the tramps on Lady Rover (www.ladyrover.com).

By my experience knot less netting is way better than mesh as it does not suffer as much on wave impact.

We have a black 6mm net with about 50mm holes.
6mm is thick, but I figured it will last longer in UV light & constant wear.
Fairly cheap as well.

If you choose close attachment points it spreads the load better. Less wear on the net and hul/ deck attachment points result.
There is less risk if stepping into a gap that way too.

You do not want anything elastic to attach.
The stronger you can pull the tramp the more comfortable it is to walk & work on.
I use spectra line to attach the net. Does not wear easily, is strong and UV resistant.

[Tusitala]

I'd have to agree, that's the way we do it also.

[mikereed100]

No need to use elastic. You will find that your polyester netting has quite a bit of spring in it. You may find that it has too much, actually. You might also consider using a polyester or Dyneema bolt rope instead of threading rod through it as the rod will cause the netting to bunch up at the edges. We have about a 30mm gap with attachments every 6" and that works fine. On our old, polyester net we used polyester line for the bolt rope and attachments with no failures. On our new, Dyneema net we used all Dyneema attachments.

Just a thought. For about 1/3 the quote that you got for commercial nets you could use Dyneema. The advantages are more strength, longer life, smaller mesh and less 'bounce'. We used polyester similar to what you have for 6 years in the tropics and it worked great, but the large mesh and springiness made it a bit difficult to work on. We replaced it with Dyneema a couple of years ago and the difference is significant. Much easier on the feet and, most importantly, a more stable platform to work on when underway.

[Dave_S]

Can you get the dyneema in black ?

I would rather the dyneema but the only black I could find had 40mm mesh.

Ideally I would like about 13mm (1/2") mesh.

[44'cruisingcat]

Don't use elastic. They're not really meant to be used as trampolines!

I'd suggest getting the gap between the boat and the net as small as you can. Reduces the risk of something going overboard through the gap.

I've used stainless steel tubing for the frames on tramps, with solid rod for the corners, inserted into the tube. This allows the frame to expand as you tighten the lacing.

You need to allow for a fair bit of stretch as you tighten up. Also there's a bit more stretch over time.

Like anything on a boat, it's a bigger, longer job than you expect. Tightening the lacing gets pretty hard on your hands.

[mikereed100]

Originally Posted by Dave_S

Can you get the dyneema in black ?

Not that I am aware of. I used this stuff:
Ultra CrossNET Systems
It is kind of a wierd, gold color. There may be other sources nowadays. Another advantage of Dyneema is that you only have to tension it a couple of times and you are done. Our polyester nets needed periodic tensioning and were never really tight. As 44c points out, this can be tedious and hard on the hands. I found that a line tensioning grip, such as those used by windsurfers to tighten their rigs, helps a lot.

[Bean Counter]

Originally Posted by mikereed100

Not that I am aware of. I used this stuff:
Ultra CrossNET Systems
It is kind of a wierd, gold color. There may be other sources nowadays. Another advantage of Dyneema is that you only have to tension it a couple of times and you are done. Our polyester nets needed periodic tensioning and were never really tight. As 44c points out, this can be tedious and hard on the hands. I found that a line tensioning grip, such as those used by windsurfers to tighten their rigs, helps a lot.

What is the line tensioning device you use?, can't seem to find it on the net

[Tusitala]

It's just a clamcleat, usually aluminum, typically with a short lanyard on it. sometimes they're attached to a short piece of wood or aluminum. any windsurfing shop or website should have them, look for downhauls

[44'cruisingcat]

A couple of years ago when I did mine, Haverfords did have knotless dyneema netting in black.

[Dave_S]

Haverford's only had the poly in black.

I have the netting now so I'll pull it really tight and see how it goes. It looks good and the 22mm openings look perfect, I think the smaller holes that I originally wanted would be to small. I should have good visibility through the net and it feels like it will be comfortable.

[44'cruisingcat]

Ours is the 22mm and it's fine. Our original nets had diamond shaped holes, this is square, and it's much easier to lace onto the frames.

[fxykty]

We bought the 22mm knotless polyester netting from Haverfords as well. I’m still tightening the second tramp, having prestretched the nets for a couple of weeks with a ton of tension before installing them. They seem to be setting up very tight. They are much more comfortable than the previous knotted diamond netting we had that I think was original to when the boat was new.

We considered Dyneema netting as well, but the cost was higher and there doesn’t seem to be any difference in strength after a few years in the sun compared to polyester, and the total life is shorter (according to the suppliers). And we couldn’t get it in raw netting form as we could with the polyester net from Haverfords, which saved us a lot of money at the cost of a bunch of labour.

BTW, the previous nets were white (well, grey) and roughly match the deck and hulls colour. The new nets are black and are invisible at night. Kind of freaky to step out there in the dark.

[mikereed100]

The one thing I miss about our old polyester nets is the black color. It made it a lot easier to see the chain through the tramp while pulling anchor in the dark. I wish there were some kind of black UV coating that would stick to Dyneema.

I don't think strength is really much of an issue when considering polyester vs Dyneema. They are both bombproof, Dyneema maybe standing up to a bigger bomb, but how much weight are your really going to put on your trampoline? We had 12 people on our 6 year old polyester nets with no loss of life.