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Old 07 July 2008, 18:21   #31
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Originally Posted by nikster View Post
chaps,

people need to understand that these boats moulds are not new - the technology for making ribs is increasing by the day as is the powerplants that we hang on the back.

I doubt very much that northcraft moulds are CAD designed, nor have they been in test tanks to prove capability, mosty of the RIB moulds we have today are moulds from 10/15 years that have been passed down the line.

I can tell you from experience that a proper brand new mould from scratch costs in excess of 40k...... the point i am making is that not many people stress test or fatigue test moulds/ powerplants as the industry does not have that type of investment available ......they.... calculate EU requirements versus empty weight versus transom thickness = power rating x kw

No audit procedure, no batch numbers of kit used, no stress testing, nothing - just whack it in the mould, lay it up, when its cured, bung the tubes on, hang the donk on the back, fit it out with whatever we have and try and marry it up with what the client wants - tea break - ready for friday just in-time for the weekend.......!!! maybe i have just been in this game toooo long.... more creme de month - i say!!!!!! hooorarrrr



Nikster ..I'm not new to RIBs.. so.. I think I know a bit out the gear .. but if the manufacturers plate says 300 ..sooo 275 should'nt be a problem. I made a point earlier in this thread about the way people 'code' their boats and I've learned from that.

The point I made was ..duh .. dont code your boat for 300 when you'd be lucky if it takes 200 .. and how do you rate the transom in the first place .. perhaps you could enlighten us on that because its kind of .. erm important?
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Old 07 July 2008, 18:26   #32
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Originally Posted by alystra View Post
Ah! Yes. But if they want to stay in business after this thread, they'll get some thicker plywood for the transom and knees, add a couple more layers of fibreglass and then have a beer, knowing they responded promptly to customer's needs and then advertise the virtues of their R & D department.
I doubt it..... after they way I was treated .. you would laugh at the repair job they did on my transom...... I'm saving this gem
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Old 08 July 2008, 08:51   #33
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Originally Posted by nikster View Post
chaps,

people need to understand that these boats moulds are not new - the technology for making ribs is increasing by the day as is the powerplants that we hang on the back.

I doubt very much that northcraft moulds are CAD designed, nor have they been in test tanks to prove capability, mosty of the RIB moulds we have today are moulds from 10/15 years that have been passed down the line.

I can tell you from experience that a proper brand new mould from scratch costs in excess of 40k...... the point i am making is that not many people stress test or fatigue test moulds/ powerplants as the industry does not have that type of investment available ......they.... calculate EU requirements versus empty weight versus transom thickness = power rating x kw

No audit procedure, no batch numbers of kit used, no stress testing, nothing - just whack it in the mould, lay it up, when its cured, bung the tubes on, hang the donk on the back, fit it out with whatever we have and try and marry it up with what the client wants - tea break - ready for friday just in-time for the weekend.......!!! maybe i have just been in this game toooo long.... more creme de month - i say!!!!!! hooorarrrr
As a manufacturer myself you're going to have to explain how a CAD designed mould would have any bearing on the strength of a transom?

In my opinion the strength of any boat lies in careful consideration of the stresses involved and making something "up to the job" and nothing more than that - of course how you get to that decision is the tricky bit. I am sure our surveyor makes all sorts of calculations as to the strength of everything when it comes to doing the CE stuff, but at the end of the day if we over stress everything and it all stays in the same place as it came out of the mould then it works for me - see photo!

The problem is that some manufacturing methods of attaching knees to transoms and the transoms themselves have not changed since the days that 100hp 2 stroke would be considered a lot, and the same construction would suffer with a 300 Verado on the back.

The only answer is to look at second hand well used examples of boats that have at least the same amount of HP you're thinking of putting on a new boat and hope that it isn't a Friday boat!
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When a boat looks that good who needs tubes!!!
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Old 08 July 2008, 11:43   #34
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I had a 7.4 Northcraft the transom was really thick had a 225 opti on it, boat was coded so lots of weight and upto 10 divers. Can't remember the thickness of transom but the donkey motor bracket would fit as it was to thick.
Have they reduced the thickness?? shame I thought the boat was great and most seem to be used for commercial purposes.
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Old 08 July 2008, 12:51   #35
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cookee...... im not sure i know of any Rib mfr's who have a Hydronamics expert on their books with the Savitsky spreadsheeds for working out all loads and stresses... when you have this data and model then put in your gucci design in to the cad machine, it works it all out to ensure nothing breaks and gives you the smoothest / optimum ride.

Thats why Halmatic cant make ribs for 30k!!!! the MOD takes no chances and Avon, Halmatic etc have departments that do nothing else other than model new boats and designs and work out the stresses, flexing momentum, maximum KW rating and rig the boats to a HUMS system to datalink the stresses through its operating environment and better understand computational fluid dymnamics and hydronamics.

Making fast ribs is fun, but making them properly that last for tens of years and remain structually sound for their life is something that the Rib industy is not renowned for.....!

I've only been messing about in them for 30 years, but as the saying goes - you get what you pay for, some rib mfr's are great, others are ok, and some we laugh at - but each to their own...
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Old 08 July 2008, 13:25   #36
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As a manufacturer myself you're going to have to explain how a CAD designed mould would have any bearing on the strength of a transom?
I don't know what the original poster had in mind, but I personally would assume (yeah I know what they say about that, LoL!) that if the mold was designed in CAD, the RIB itself would be as well. If so, a structural analysis can be performed and weak points identified and redesigned.

Regards,

Chuck
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Old 08 July 2008, 17:44   #37
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I seem to remember the Millenium Bridge and our local harbour defences were both designed by experts using CAD - I don't think Brunel had access to computers and yet I would far rather trust his engineering............
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Old 08 July 2008, 17:49   #38
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in the south atlantic i much preferred Halmatics...... and my one definately was a CAD design...
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Old 08 July 2008, 18:04   #39
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I seem to remember the Millenium Bridge and our local harbour defences were both designed by experts using CAD - I don't think Brunel had access to computers and yet I would far rather trust his engineering............
Shrug... There's an old saying when it comes to computers. "Garbage in, garbage out"

It's just a tool, but one still has to know how to use it.
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Old 08 July 2008, 18:09   #40
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Shrug... There's an old saying when it comes to computers. "Garbage in, garbage out"

It's just a tool, but one still has to know how to use it.
Very true - unfortunately the engineers they tend to employ today are taken on for their management skills rather than their engineering skills!!!
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