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Old 17 February 2008, 02:06   #1
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Another A Frame question

I was wondering how you all fit your A frames to the floor of your ribs. The one I bought has bolt holes in the bottom but to do this I will have to go through the floor and also the hull. Has anyone gone through and used stainless dome head bolts and rubber washers/ silicone to reduce drag. There appears to be only about 40mm from floor to the u/s ot the hull with a 10mm gap in the middle so just bolting to the floor is not an option. Does this make sense??
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Old 17 February 2008, 03:53   #2
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Ribtec do bolt through the hull on there 535s, but if you have a gap tightening up the bolt is gong to pull the hull and deck together when they shouldn't be. Willing to bet there will be a big crack in the hull if you over do it. If the frame has a feet how about using glass cloth and epoxy resin to glass it down, wouldn't cost much to have a pair of feet welded on btw.

Pete
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Old 17 February 2008, 04:09   #3
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A Frame Fixing

Not sure that it will help you, but here are some pics of how the 'A' frame was fixed in my old XS 550. This was a deliberately solid fixing, being designed for towing. the tube diameter is 2". It is bolted to the transom, and through the deck and hull. Have to say that I am in favour of transom fixings, as by its nature the transom is a solid point of the boat.
The first pic shows the fixing to the transom. Second is taken from inside the boat, and shows the fixing from above deck. Third is inverted, showing the view from the underside and the fixing plate on the outside of the hull for the through deck/hull fixing. You can just see this in context in picture 4.
The final picture shows the general arrangement.
Whilst this type of fixing may not suit you, it does show a through deck/hull type fixing that was done professionally. The bolt heads on the exterior of the hull did not appear to cause problems, as with this hull when on the plane the fixing points were usually clear of the water.
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Old 18 February 2008, 02:07   #4
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Thanks Pete and Ian. Thats exactly what I was looking for.
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Old 18 February 2008, 05:46   #5
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My Humber's A frame has two large flanges welded parallel (in line with? tangent to?) to the tube. Four large bolts, two each side, fasten it to the transom. The flanges present large bearing surfaces to the transom and so spread any load (i.e me leaning on it for a 'comfort break ). Eight years with no apparent problems. As the tube is clear of the deck, it's easy to feed in all the wiring too.

This is probably useless without pictures, but I've just looked and don't have one at the moment
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Old 18 February 2008, 08:51   #6
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Mine is thru' bolted at a point above where the under deck hollow stops, tween the toob and the hollow bit if that makes any sense. It's done with a U - bolt each side (and a matching set up forward) as the boat was originally an FRC (to use the modern terminology) and so was equipped for slinging in a previous life. I have about 3/4" of thread poking out the bottom of the boat in eight places! The transom attatchements are similarly done, but with the "U" of the U bolts on the outside to give anchor points for towing bridle / trailer tie- down. Scream if you want some pics.


I have a plan..... soon I will get it out on the water and get someone to point the camera at it while it's on the plane. I reckon the forward bolts will be well clear of the water, however I'm not so convinced about the rear ones. The idea is that if they are "in" then I'll replace the U- bolts with Pan head screws with the head on the outside as suggested above, but use eye nuts - not because I want to sling it, but becase they make remarkably good fuel tank tie -down points! As it was slung the backing plates are both enormous and thick (5mm) so they will be replaced with something a little more appropriate and streamlined (i.e thin!). Alternatively if I find they are clear of the water, then the whole lot will stay put! (tho' I might cut the threads down a little)

Alystra, does your frame look like it's been welded up from mini scaffold pole? It sounds like we may have similar attatchments. I also have a lump of copex stuffed up the bottom of the upright with the cabling in........
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Old 19 February 2008, 18:53   #7
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Quote:
Originally Posted by 9D280 View Post
.........
Alystra, does your frame look like it's been welded up from mini scaffold pole? It sounds like we may have similar attatchments. I also have a lump of copex stuffed up the bottom of the upright with the cabling in........
Here's some pics of it. I think it's 1.5 ins. dia - or maybe 2 ins. From Humber anyway. Two aluminium oars and a telescopic boat hook are lashed to it, which may help with the scale. If you look past the coffee and biccies you can just see the 'flange' and one of the securing bolts. There's a very large 'penny' washer on the outside of the transom to spread the load.

Copex??? I've just got wires up my tubes.
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Old 20 February 2008, 07:09   #8
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Here's some pics of it. I think it's 1.5 ins. dia - or maybe 2 ins. From Humber anyway. Two aluminium oars and a telescopic boat hook are lashed to it, which may help with the scale. If you look past the coffee and biccies you can just see the 'flange' and one of the securing bolts. There's a very large 'penny' washer on the outside of the transom to spread the load.

Copex??? I've just got wires up my tubes.
Ok, my frame is somewhat more agricultural than yours, but the mounting theory looks similar. I also have a brace that comes forward from about 6" above the top of the transom (in a not too dissimilar style to the old Avon SR transom braces) and thru bolts the floor.

Copex - Flexible conduit - primarily to protect the cabling as it wanders across the deck to the centre console, I have another run carrying the engine cables. My frame tube is 40mm OD, so the 30mm OD "conduit" stuffs nicely up inside for a few inches to create a "seamless join" and looks like it was designed to fit! I'll try to get some pics up later when I can persuade the camera to talk to the PC.......
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Old 20 February 2008, 16:30   #9
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Thanks for that Alystra and 9D great help as usual.
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