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Old 22 November 2016, 12:16   #11
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Originally Posted by Pikey Dave View Post
Is it a single or double "A" frame? Either way 2mm will be plenty strong enough, the weak point will be the attachment point to the boat.
Pikey D is the total expert so listen to him. I'm surprised his mrs isn't made from marine grade stainless
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Old 22 November 2016, 12:17   #12
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Yer! Watch the video:

A Frame

I've never been convinced with the A frames that sweep out over the tubes, the footprint is too small for the mass & forces, all imho of course
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Old 22 November 2016, 13:12   #13
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Thanks for the replies.



The link below is what I'm wanting to have made.



New Aframe for my SR4



I'm guessing 2mm would be fine but just thought I'd double check first.

I used Nick's info for my SR4 A-Frame and went to Marine Fabrication to get it made, very pleased with the result, the frame is plenty strong enough for anything I'm ever likely to use it for and it looks great Click image for larger version

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Old 22 November 2016, 13:39   #14
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Old 22 November 2016, 13:43   #15
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Marine fabrications did a good job for me as well 3mm too 👍
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Old 22 November 2016, 17:15   #16
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Marine fabrications did a good job for me as well 3mm too 👍
Imogen looking good Kerny
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Old 22 November 2016, 17:25   #17
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Imogen looking good Kerny
Cheers Mr C......
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Old 22 November 2016, 17:52   #18
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If you are happy with larger sections, you could consider a change of material to aluminium.

A 65mm aluminium tube with a 5mm wall thickness has a 15% greater resistance to bending as a 50mm stainless tube with a 3mm wall thickness.

You could hang around 15% more weight off the aluminium tube before it started to fail.

The aluminium tube is 70% of the weight of the stainless tube.

I know you've had one made but it may be food for thought if someone else is thinking about it.
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Old 22 November 2016, 18:44   #19
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Thanks for all the replies guys.

I think I'm going to go with the 2mm tubing.

I can pick up 316 2"x2mm for £11.50 a meter which is much cheaper than I was expecting which is a pleasant surprise.

Judging from the comments and internet searching, the 2mm is plenty strong enough and as some have said, the welds or fittings to the boat would fail well before the tubing breaks/bends.

Had the boat been bigger I wouldn't of worried about the weight issue so much but I suppose with a small 4 meter rib, the weight is pretty sensitive and wouldn't want to jepodise the current performance of the boat as much as I could help it.
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Old 23 November 2016, 04:31   #20
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Quote:
Originally Posted by mwb.wright View Post
Thanks for all the replies guys.



I think I'm going to go with the 2mm tubing.



I can pick up 316 2"x2mm for £11.50 a meter which is much cheaper than I was expecting which is a pleasant surprise.



Judging from the comments and internet searching, the 2mm is plenty strong enough and as some have said, the welds or fittings to the boat would fail well before the tubing breaks/bends.



Had the boat been bigger I wouldn't of worried about the weight issue so much but I suppose with a small 4 meter rib, the weight is pretty sensitive and wouldn't want to jepodise the current performance of the boat as much as I could help it.

If it's not a personal question why are you going for 2"? If you are going for a double A frame 1.5 will be plenty & look more in proportion on a smaller boat. It will still be strong enough for anything you are likely to tow with that rig. You will pull the transom off before you snap a well made 1.5" double A frame.
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