A Frames

brucehawsker · 29 April 2006, 17:33

Why are they double? If you are doing waterskiing, persumably everyone uses D bolts in the transom for the yoke. No one is going to put weight on the A Frame.

So why have such a hunk of metal. Why not a single arch?

Why not three pillars - one for each light and the ones on the side with cleats, and the one in the middle with a platform for radio aerial and gps aerial?

Alice · 29 April 2006, 18:05

Yep, we use the A Frame for wakeboarding. Wakeboarding requires the tow line to be higher than skiing. It makes jumping etc easier as the line is not pulling down. Mines a double tube well solid affair.

Millermob · 29 April 2006, 18:05

our avon has got a towing point at the top of the A-frame and i'm sure roycruses ribcraft has got one as well, it keeps the rope away from the prop.

BogMonster · 29 April 2006, 18:09

Mine has a single A frame, a very uninspiring black bit of pipe which is overdue for a coat of paint. Not sure if it came with the boat or was made by a previous owner, I suspect the latter.

A lot of it is probably people wanting a big bling shiny thing on the back of their boat

Coat on and heading for the door!!!

Alice · 29 April 2006, 18:26

Quote:

Originally Posted by Millermob

our avon has got a towing point at the top of the A-frame and i'm sure roycruses ribcraft has got one as well, it keeps the rope away from the prop.

Yep, Roy tows from his A Frame and he ain't no lightweight back there!!

Shaggy · 30 April 2006, 18:22

I use my double A frame for wakeboarding too, it does a proper job..

Shaggy

Rogue Wave · 30 April 2006, 19:17

How are your A frames fixed under the deck?

To answer your questions about single poles Bruce the Tohatsu's (extremely similar design to your boat) had a nav light pole with a pad for antenna at the top. Which I thought was a cracking idea, unfortunately they vibrate a lot because there is no bracing and this shakes things loose.

Same thing with single A frames so that's a good reason for a double A frame. Apart from that they do look kinda Snazzy.

Tim M · 30 April 2006, 20:47

I have double A frames on two of my RIBs. Would not hessitate about towing off either of them. In answer to your question they are bolted through the transom, and through the deck.

Downhilldai · 30 April 2006, 21:11

I fitted a single pole to mine for mounting the nav light and VHF antenna (like the Tohatsu, I suppose - never seen one). I went for this, as it leaves room for the auxiliary outboard on the opposite (port) side of the transom.
It's practical, but admittedly, doesn't look as good as an A frame. I'd also have to knock-up some more bracketry, if I wanted to fit a GPS antenna, radar reflector, etc.

roycruse · 30 April 2006, 21:17

I certainly do tow from mine - its designed for it though and has a rope attachment post at the top - I'm over 20st and no problems so far.

Cookee · 01 May 2006, 10:42

Our A frame is designed for wakeboarding, we were pulling up 2 monoskiers last summer without any problem - I'll give you a tow at Ribex if you like Roy!

Scrumdown · 01 May 2006, 16:37

I am looking to keep my new rib in my double garage but I am limited by height

So I'll either need an A frame that is low, removable (easily) or a folding pole that I can fold down for storage. Any ideas? Also if you know the height of the top of your A frame when the RIB is on the trailer that could help in my plans. Cheers

GED · 01 May 2006, 19:02

Not all A frames are the same

Under the Thumb · 01 May 2006, 19:58

If you use a high rope position to wakeboard or monoski , do you need to put extra weight in the bow to keep the nose down?

roycruse · 01 May 2006, 20:08

I dont seem to need any

Alice · 01 May 2006, 20:13

Quote:

Originally Posted by Under the Thumb

If you use a high rope position to wakeboard or monoski , do you need to put extra weight in the bow to keep the nose down?

Eh?!

Not heard of that one before. If the bow did rise surely a dab of the trim switch would cure it?

Rogue Wave · 02 May 2006, 01:06

Quote:

Originally Posted by Tim M

I have double A frames on two of my RIBs. Would not hessitate about towing off either of them. In answer to your question they are bolted through the transom, and through the deck.

I should hope the a frame is bolted through the transom and the deck, however what are they bolted to under the deck, a threaded insert or an under deck plate?

havener · 04 May 2006, 09:39

This could be controversial....

NEVER EVER tow from an A frame unless you have the manufacturer's certification to do that - and I mean from the hull manufacturer as well as as the frame builder.

By all means run a rope over or through the frame for towing, preferably using a bar to keep the rope out of the prop's way.

The end of the tow line, however, should be attached to a purpose built towing cleat on the deck, or even better tow via a bridle. This provides a number of advantages, and is good practice even if your frame is rated for towing -

1. By passing the rope over the frame, it puts the frame in compression rather than the tow line acting against the frame's joints and strength.

2. If you need to jetison the tow rapidly in an emergency, the helmsman or crew can cut the rope by the cleat (ensuring no-one is in it's recoil line) a lot quicker than you could if you had to climb onto the frame first.

Simon

DGR · 04 May 2006, 13:30

A couple of summers ago we were in Cyprus, and they were towing 6/8 man bananas from the A-Frame of a 6.5m RIB (Humber?). They had mounted it at the top of the A-Frame to make sure that the tow line stayed clear of the prop, but they had then run additional lines from the top of the A-Frame to the cleat at the bow of the RIB to support the A-Frame (the only people on the RIB were the crew - no passengers usually).

When stationary the lines weren't hanging loose, but were 'tight' like a guy rope of a tent (i.e. you could move them up and down a bit). Once under way and towing, the lines were rigid - and I was uncomfortable sitting anywhere near them!!

ANYWAY - my point - the forces applied to the top of the A-Frame are very big - hence the movement in the A-Frame and tightening of the ropes that were supporting it. I'd rather use the towing eyes than just tie to my A-Frame - unless the A-Frame is designed for it.

My towing bridle is just a piece of 3-strand nylon line spliced onto carabiners - but I've put some bungee cord through the 3-strand and clip that onto the A-Frame - when not under load the bungee pulls the rope up and away from the leg - and when under load, the bungee is stretchy enough that it lets all the load go to the towing eyes and not up to the A-Frame. I've not used it that much, but when I do, I haven't managed to foul my prop (yet

).

D...

BogMonster · 04 May 2006, 17:03

It's a simple matter of geometry - if you are towing off the top of the A frame the twisting force on the transom will be huge compared to if you are towing off the A frame just above the transom, for example.

I wouldn't even think of it on mine, it would break off immediately, but then mine isn't designed to stand up to that, it is a DIY job, built for a set of nav lights not a lardy person with their butt wedged into a tractor inner tube