What do sponsons do?

[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

[Pete7]

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

[roycruse]

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.

[Poly]

my boat (http://www.rib.net/forum/showthread.php?t=11371) 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

[Jono]

JW uses 'em to keep all that free air in... just in case they start taxing it soon.....

[jwalker]

Yeh, that's why I pump 'em up hard.

[codprawn]

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.

[Matt]

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.

Originally Posted by codprawn

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

[codprawn]

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!!!

[Matt]

In that case, what's the point of having em. Might as well have a hard boat.

[codprawn]

Originally Posted by MadMat

In that case, what's the point of having em. Might as well have a hard boat.

Not at all - think about it - what would you rather hit if you fell off a building - a big squashy thing or a big hard thing.........

[Poly]

Originally Posted by codprawn

Also there is less bouyency with anything other than air.

I doubt that is a real concern. The benefit of permanent bouyancy probably outweighs the very slight increase in volume required to achive the same bouyancy (or the marginal loss in bouyancy from the same volume filled with foam instead of air).

But I think the disadvantage is that most foams - even closed cell foams - eventually start to soak up some water if there is any leak and drying it out is a nightmare.

Thanks,

Neil

[jwalker]

Originally Posted by Madmat

..... they're almost useless against, for example, a stuff - unless you're prepared to pump your tubes up over 70psi.

Depends on the boat and tube shape because you are ignoring the fact that the direction of the water flow is altered and the angle of attack of the tube is significant in preventing the bow going down in the first place. Also, in proper ribs, the shape of the hull will be designed with the tubes in mind and the two can work in harmony. This is in contrast to a hard boat hull with toobs stuck on.

The pics below may give you some indication of what I'm blethering about. You'd have a bit of a job getting that lot to submerge. I've never stuffed my bow but I have often had a big wall of water issuing outwards from a semi-submerged tube. The tubes flexed inward but they never were squeezed to collapse. That doesn't mean I believe the thing is unstuffable, of course.

[boatster_sr4]

stability at rest- Mines a Searider so even more so since it sinks in. I don't get sinusoidal rocking like a hardboat would.

keeping the boat level when traveling across the chop in the channel. The tubes really absorb alot of wave impact keeping the boat more level than an equivalent size hardboat.

buoyancey safety factor.

Simplicity of maintainance: tubes won't fill with water like foam. If its leaking you will know soon enough and fix it.

I also think the fact that it has tubes allows the hull to be a complete V throughout giving the specific characteristics of a rib at such a small size. The V hull for on the go, the tubes for keeping stable in chop and while at rest. The tubes complement the v hull and vice versa.

[Jimbob]

Ribs, will provide you with Stability and Buoyancy they also have good load bearing capacity. I think that’s why people are beginning to go for cabin ribs over hardboats, we intent to do so,,,if we can find the right one

[Pete7]

Toobs mean you don't have to polish all that fibre glass, so can go out and use it more often. Just look at all those speed boats sat in harbours never being used

Pete

[Matt]

Ah, but less polishing time merely means you have more ole drilling and console changing time.

[Pete7]

lol, 15 all

[Rogue Wave]

I'd like to take this opportunity to point out that we will be stocking a new and exiting range of Cleaning materials in our chandlery at Drivers Worf.

It's called 606 and it's twice as fkkn good as anything with a three in it


I have always though of toobs as outriders really and I think they are kinder to you when you hook than a hard boat, but they do reduce speed!

[Matt]

Scratcher, do you have a space heater in your shed?