Reply
 
Thread Tools Search this Thread
 
Old 20 October 2004, 14:43   #1
Member
 
Country: Norway
Town: Tofte
Make: Tornado 750
Length: 8m +
Engine: 250 Suzuki
Join Date: Sep 2004
Posts: 164
Aliminium vs steel in A-frame ?

Why is almost all european A-frames made of steel, and not aliminium ?
__________________

__________________
RibRoy is offline   Reply With Quote
Old 20 October 2004, 14:50   #2
Member
 
Country: Sweden
Town: Stockholm
Boat name: Osprey & Ring
Make: Osprey & Ring
Length: 9m +
Engine: Plenty
Join Date: Mar 2003
Posts: 860
Steel is hard, alu is softer.
Its pretty hard strain when you jumping in waves etc and to get alu as durable/lasting as SS it has to be very thick and then it will be more expensive than SS

Specially in the Sweden were SS has high quality and not that expensive for what you get.
__________________

__________________
www.grandrib.se
Petrov is offline   Reply With Quote
Old 20 October 2004, 14:53   #3
Member
 
Country: UK - Wales
Town: Southampton
Boat name: DynaMoHumm/ SRV/deja
Make: Avon8.4, 5.4 & 4.777
Length: 8m +
Engine: Cat3126 Yam 90 &70
MMSI: 42
Join Date: Dec 2003
Posts: 6,559
Funnily enough I think most ofd the Mil spec boats have Alu frames/ Avon seariders have an Ali option and I think pacific's are Alu
__________________
Here it comes again, I don't stand a chance
Soul possession, Got me in a trance
Pullin' me back to you - Deja Voodoo
Rogue Wave is offline   Reply With Quote
Old 20 October 2004, 14:58   #4
Member
 
Country: Norway
Town: Tofte
Make: Tornado 750
Length: 8m +
Engine: 250 Suzuki
Join Date: Sep 2004
Posts: 164
Quote:
Originally Posted by Petrov
Steel is hard, alu is softer.
Its pretty hard strain when you jumping in waves etc and to get alu as durable/lasting as SS it has to be very thick and then it will probably be more expensive than SS
I,have cracked my steel-frame several times, The local police Goldfish rib has a reinforced one off, several small cracks, another local charter rib has dismounted it because it has cracked several times.
Talked to a guy with a Hurricane with ali-frame, no cracks yet.

Want to build a one off for my eventually new boat, and i want it to last this time. Cost no big issue.
__________________
RibRoy is offline   Reply With Quote
Old 20 October 2004, 15:04   #5
Member
 
Country: Sweden
Town: Stockholm
Boat name: Osprey & Ring
Make: Osprey & Ring
Length: 9m +
Engine: Plenty
Join Date: Mar 2003
Posts: 860
Quote:
I,have cracked my steel-frame several times, The local police Goldfish rib has a reinforced one off, several small cracks, another local charter rib has dismounted it because it has cracked several times.
I only heard of one frame that got a small crack on the boats i have bought and it started on a spot were it was made a welding so it was more of a bad work than the material.

If you have a well known company that is really good in welding and SS i dont think you will have the problem.
Just make sure that you dont under dimension the frame (have seen that a lot of manufacturers can do that some times)
I have no experience of alu frames.
__________________
www.grandrib.se
Petrov is offline   Reply With Quote
Old 20 October 2004, 15:09   #6
Member
 
Country: UK - Wales
Town: Southampton
Boat name: DynaMoHumm/ SRV/deja
Make: Avon8.4, 5.4 & 4.777
Length: 8m +
Engine: Cat3126 Yam 90 &70
MMSI: 42
Join Date: Dec 2003
Posts: 6,559
Over the years Stainless becomes brittle.
__________________
Here it comes again, I don't stand a chance
Soul possession, Got me in a trance
Pullin' me back to you - Deja Voodoo
Rogue Wave is offline   Reply With Quote
Old 20 October 2004, 15:18   #7
Member
 
Country: Sweden
Town: Stockholm
Boat name: Osprey & Ring
Make: Osprey & Ring
Length: 9m +
Engine: Plenty
Join Date: Mar 2003
Posts: 860
Quote:
Over the years Stainless becomes brittle.
And Alu?
__________________
www.grandrib.se
Petrov is offline   Reply With Quote
Old 20 October 2004, 15:18   #8
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
Alloy is ideal BUT the tubes will need to be of greater diameter - also the strongest alloys aren't the most corrosion resistant hence the need for good coatings or anodising. Should the coating fail you will have probs.

Having said that there are plenty of examples where alloy is used - mountain bike frames - tent poles - ice axe shafts - airframes etc etc.
__________________
codprawn is offline   Reply With Quote
Old 20 October 2004, 15:22   #9
Member
 
Country: UK - Wales
Town: Southampton
Boat name: DynaMoHumm/ SRV/deja
Make: Avon8.4, 5.4 & 4.777
Length: 8m +
Engine: Cat3126 Yam 90 &70
MMSI: 42
Join Date: Dec 2003
Posts: 6,559
Quote:
Originally Posted by Petrov
And Alu?
Not so quickly and it has a little more resilience. I believe that Alu tanks are standard for raceboats (as opposed to stainless steel) because they have less tendancy to crack
__________________
Here it comes again, I don't stand a chance
Soul possession, Got me in a trance
Pullin' me back to you - Deja Voodoo
Rogue Wave is offline   Reply With Quote
Old 20 October 2004, 15:53   #10
Member
 
Country: Norway
Town: Tofte
Make: Tornado 750
Length: 8m +
Engine: 250 Suzuki
Join Date: Sep 2004
Posts: 164
The original ss fueltank in my present rib cracked where the "chamber walls" ( Dont know the word for skvalpe-skott in english ) was welded. The tank was 6 years old. Got a new one from a local blacksmith in ss. told him to make it very sturdy, no expence spared. Took it for a test drive to Skagen. Discovered gas in the bottom of the boat before we got half the way. Same prob again. I now have a tank in 3 mm ali made by proffessionals, and no leaks yet. Goldfish, known to make very fast ribs use ali-tanks.

I,m quite shure ali is the best material, wether its for tanks or A-frames. Just cant figure out why so few manufactures are using it.
__________________
RibRoy is offline   Reply With Quote
Old 20 October 2004, 15:56   #11
Member
 
Country: UK - Wales
Town: Southampton
Boat name: DynaMoHumm/ SRV/deja
Make: Avon8.4, 5.4 & 4.777
Length: 8m +
Engine: Cat3126 Yam 90 &70
MMSI: 42
Join Date: Dec 2003
Posts: 6,559
I think the english word might be baffles, I'll ask my skipper hes a Norse.

i think the reason is that Alu is more difficult to weld and therefore more expensive. Also As Codprawn says it needs some coating also so this makes it dearer and for the average 6 metre rib bouncing round at 30 to 40 knots it's not so much of a problem
__________________
Here it comes again, I don't stand a chance
Soul possession, Got me in a trance
Pullin' me back to you - Deja Voodoo
Rogue Wave is offline   Reply With Quote
Old 20 October 2004, 16:14   #12
Member
 
Country: UK - England
Town: Southampton
Boat name: SMH Rib / War Shot
Make: Ribtec / Scorpion
Length: 4m +
Engine: 10hp Yam / 150hp opt
Join Date: Sep 2003
Posts: 1,945
RIBase
Quote:
Originally Posted by RibRoy
Why is almost all european A-frames made of steel, and not aliminium ?
Not as shiny?
__________________
Searider is offline   Reply With Quote
Old 20 October 2004, 17:17   #13
Member
 
Country: UK - Wales
Town: St Davids
Boat name: 6 vessels -various
Make: Quinquari/Humber
Length: 10m +
Engine: Twin ETEC200s
Join Date: Nov 2003
Posts: 130
frames

We use ali on all of our frames and it serves well. Codprawn is right in that the diameter has to be thicker (but not the wall thickness if designed right)which, in the case of 10m boats can look better but not so for smaller boats.

As a single frame a minimum of 50mm but we would rather 75mm. For a double frame which is our norm we use 50mm.

A lot of workshops dont like ali as it is defined as a difficult metal to weld and work. This is not the case, it is just buying the gear, getting used to it and in particular its ability to conduct heat and distort. Bending of ali pipes can be difficult depending on the grade. We use MIG welding for speed and TIG for finishing.

Corrosion is an issue as it oxidises but a frame should well do the life of the boat. The big issue comes in when you introduce s/steel fixings as this brings in electrolysis. On our consols this will cause paint blistering over a period.
Never never put ali and brass/copper together - the ali will corrode in weeks.

For tanks we consider ali to be a good value material and would price an ali tank much less that a s/s tank and it would suffer far less with hysteresis.

However correct bonding is essential to ensure that it is not the tank that is sacraficial and there is a risk area where the tank sits in the hull --- you have the grp (producing a slight alkali/some water then the ali and you will find pitting of the ali in this area at approx 50% greater rate than s/s.

You will also finf the problem with the tank that somewhere you will have another metal introduced eg. the fuel sender and this can make the ali sacraficial.

It is though a brilliant material for weight/strength and many superb boats such as SWs Ocean Dynamics will testify to that. If I remember Shaun did a good article in RIB INT last month discussing its properties.

And yes - it dont shine like s/steel !

Cheers

John
www.quinquari.co.uk
__________________
quinquarimarine is offline   Reply With Quote
Old 21 October 2004, 14:02   #14
Member
 
Country: Norway
Town: Tofte
Make: Tornado 750
Length: 8m +
Engine: 250 Suzuki
Join Date: Sep 2004
Posts: 164
Thanks Quinquarimarine. I'll go for the ali-frame. Just have to find a experienced workshop to make it. Ali on a boat cant be that bad, after all sailboats been using it i the rig for a long time.


Roy
__________________
RibRoy is offline   Reply With Quote
Old 24 October 2004, 14:02   #15
Member
 
Country: Norway
Town: Tofte
Make: Tornado 750
Length: 8m +
Engine: 250 Suzuki
Join Date: Sep 2004
Posts: 164
Found this picture of A-frame on rib in Bear Grylls' Trans Atlantic Arctic Expedition- Anybody got a better picture of this A-frame ?
Attached Thumbnails
Click image for larger version

Name:	settingsun.jpg
Views:	143
Size:	13.8 KB
ID:	8892  
__________________

__________________
RibRoy is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 02:00.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
×