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Old 20 December 2005, 07:51   #1
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What do sponsons do?

Sorry if this sounds a daft question, but as an engineer i like to question things from first principles in an attempt to improve.

Sponsons tend to be the Achilles heal as they can tear or puncture. Why then make them of an elastomer?

I suspect their primary purpose is to provide large volumes of sealed boyancy so why not make them from (for example) polypropylene. They would be tougher and retain their shape and bouyancy in the event of minor damage.

Taking this argument further, why not fill them with foam?

Really value any input

Regards
Cameron
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Old 20 December 2005, 08:30   #2
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In the early days divers saw the advantages of a rib over an inflatable and that sitting on the tubes was comfortable at dive boat speeds or whilst actually diving.

Foam and solid tubes seem to be favoured in the commerical world, pleasure boats tend to be looked after better especially as some top of the range models cost as much as a house.

Pete
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Old 20 December 2005, 09:43   #3
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Positives.

1. They act as a huge great fender all around your boat making a RIB ideal as a rescue or safety craft where coming alongside other vessels is common.

2. They add vast amounts of buoyancy to your boat for for very little weight. Thus giving you an unsinkable boat (unless you puncture all the compartments)

3. They act as shock absorbers for your ass when you sit on them.

4. When the boat is at rest they add a massive amount of stability.

5. A RIB is usually a lot lighter than the equivalent sized non RIB boat.



Negatives.

1. They can be punctured.

2. They take up a lot of room.



That's all I can think of for now - I'm sure others will have stuff to add.
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Old 20 December 2005, 10:14   #4
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solid sponsons

my boat (my new RB - Sparfel) which is styled to look like a RIB has moulded polyethylene sponsons. They are slightly more susceptible to damage from hitting solid objects (piers etc) - but if you want to see how tough they are ask MacBoats in Dundee (or NewZealand) to send you there demo DVD. The drop one 30ft onto a solid concrete car park and it bounces - the only damage is to one of the cheap plastic cleats!

Mine is a wee 3.9m boat, but there is a 5.4m RIB sytled version available from the same manufacturer and I think MacBoats do an even bigger one.

In reality - close up they don't look quite as "COOL" as a real rib, but I think they are a good compromise. The also offer more seating and storage space internally.

HTH

NEIL
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Old 20 December 2005, 12:18   #5
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JW uses 'em to keep all that free air in... just in case they start taxing it soon.....
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Old 20 December 2005, 12:24   #6
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Yeh, that's why I pump 'em up hard.
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Old 20 December 2005, 13:48   #7
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Quote:
Originally Posted by cameronke
Sorry if this sounds a daft question, but as an engineer i like to question things from first principles in an attempt to improve.

Sponsons tend to be the Achilles heal as they can tear or puncture. Why then make them of an elastomer?

I suspect their primary purpose is to provide large volumes of sealed boyancy so why not make them from (for example) polypropylene. They would be tougher and retain their shape and bouyancy in the event of minor damage.

Taking this argument further, why not fill them with foam?

Really value any input

Regards
Cameron

Quite a few boats have foam filled tubes - or even moulded plastic ones - some even have steel or ally tubes.

Obviously they will be far tougher BUT they will not absorb impact as well or shock from the waves.

Think of a car tyre - filling it with foam makes punctures less likely but the ride will suffer.

Also there is less bouyency with anything other than air.
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Old 20 December 2005, 13:54   #8
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You need to provide context for that statement. If you want to go properly fast, they're almost useless against, for example, a stuff - unless you're prepared to pump your tubes up over 70psi.

Quote:
Originally Posted by codprawn
Obviously they will be far tougher BUT they will not absorb impact as well or shock from the waves.
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Old 20 December 2005, 13:56   #9
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Quote:
Originally Posted by MadMat
You need to provide context for that statement. If you want to go properly fast, they're almost useless against, for example, a stuff - unless you're prepared to pump your tubes up over 70psi.
I would have thought LESS pressure would be needed to stop them bursting??? Like a football or a balloon - or an offroad tyre that you air down!!!
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Old 20 December 2005, 14:02   #10
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In that case, what's the point of having em. Might as well have a hard boat.
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