Tube height

Arctic RIB · 22 July 2005, 20:31

Doesn't it seem like the tubes are too high to really have any affect except on very sharp turns? Wouldn't that defeat the purpose of a r "I" b? Maybe it's just lightly loaded.

seawolfribs · 22 July 2005, 20:49

Quote:

Originally Posted by Arctic RIB

Doesn't it seem like the tubes are too high to really have any affect except on very sharp turns? Wouldn't that defeat the purpose of a r "I" b? Maybe it's just lightly loaded.

The RIB in the picture is loaded with 1.3 tons of fuel, and has been designed to carry a very heavy pay load, as they are workboats.

Arctic RIB · 22 July 2005, 21:49

Wow that's a lot of fuel, it is a very nice looking RIB, on other work RIB's it seems the tubes are closer to the water near the transom effectively increasing the beam giving different turning characteristics in shallow turns and also much less roll in rolling seas? I guess what I'm wondering is wouldn't it handle more like a conventional boat in force 4+ seas? I suppose you would save on fuel and have a higher top speed. I'm no expert boat builder just making observations. Maybe it's just because the RIB is travelling at a high rate of speed causing the hull to plane very high out of the water.

codprawn · 23 July 2005, 02:43

You do have a good point - many boats these days are just normal designs with tubes attached - not a true RIB as you say.

The 9m above is on the borderline I would say - with a good load and at lower speeds or in big waves the tubes are still doing something - unlike some designs where they are just there for fendering!!!

Hightower · 23 July 2005, 08:27

Welcome seawolfribs.

My tubes are in the water even when I'm on the plane, but when is a RIB not a RIB. I mean, there are designs out there where the tubes are miles out of the water and you could even execute a high speed turn without them getting wet, take em out into a F7 and they still aren't realy doing any work.

On my RIB the tubes are a part of it's design and without them wouldn't work. Is it that with outher designs they're just an added safety device and little else?

Andy

seawolfribs · 23 July 2005, 10:36

Quote:

Originally Posted by Arctic RIB

Wow that's a lot of fuel, it is a very nice looking RIB, on other work RIB's it seems the tubes are closer to the water near the transom effectively increasing the beam giving different turning characteristics in shallow turns and also much less roll in rolling seas? I guess what I'm wondering is wouldn't it handle more like a conventional boat in force 4+ seas? I suppose you would save on fuel and have a higher top speed. I'm no expert boat builder just making observations. Maybe it's just because the RIB is travelling at a high rate of speed causing the hull to plane very high out of the water.

The tubes are slightly higher to allow for a heavy pay load, she has been tested in heavy seas, force 8+ and is very stable, she has been tested by military forces both home and abroad.

Richard B · 23 July 2005, 10:44

This debate about tubes in or out of the water comes around from time to time, and there a few interesting points which have been made. One of the most interesting I think was Mark Wildeys account of the difference in handling he encountered when he once had a puncture in the rear section of the tube on one side. No difference at all.

codprawn · 23 July 2005, 13:03

Quote:

Originally Posted by Richard B

This debate about tubes in or out of the water comes around from time to time, and there a few interesting points which have been made. One of the most interesting I think was Mark Wildeys account of the difference in handling he encountered when he once had a puncture in the rear section of the tube on one side. No difference at all.

Well if that's the case we may as well all get rid of our RIBS and join boatmad instead!!!

Richard B · 23 July 2005, 14:04

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Originally Posted by codprawn

Well if that's the case we may as well all get rid of our RIBS...

You haven't got yours yet!

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and join boatmad instead!!!

You did! http://www.boatmadforum.co.uk/member...nfo&userid=457

Truth is that different designs of RIB use the tube in different ways, and you need to know why you want/need the tube. For high speed, keep the tube clear of the water when planing. For stability at rest (diving/fishing etc), you need at tube that's touching or in the water at rest. But if your RIB depends on the tube inflation to keep afloat, that's bad design. And if your tube is in the water at speed, you will have very poor high speed handling. I suspect that many RIB owners who think that their craft suffer from chine walking at speed actually suffer from tube-bounce. Good hull design will give you all the high speed and rough weather capabilities that either a RIB or non-tubed hard boat needs, but the tubes will give you one thing that it's difficult to get without, and that's buoyancy when swamped, making RIBs safe in conditions where this a possibility.

Jonny Fuller · 23 July 2005, 14:51

Now there's something you don't see very often!

A ribber wot finks..

good explanation Rickardo!

jwalker · 23 July 2005, 15:42

Quote:

Originally Posted by Richard B

...And if your tube is in the water at speed, you will have very poor high speed handling.

Yer reckon? I take it you've tested this? How about the extra buoyancy giving the boat substantial stability, especially in a beam sea, and allowing rapid progress when others will be rocking, rolling and falling off the crests. After all, a true rib is an upwards development of the inflatable boat.

Richard B · 23 July 2005, 19:36

Quote:

Originally Posted by jwalker

I take it you've tested this?

Yes.

I do take your point about beam seas, but I believe that's only going to be the case at low speeds where the hull has reached it's limit for the conditions. So for small craft, a lower tube will be useful. If the hull were still sitting out of the water, then its going to be using the hard running surfaces and not the soft tube. Hence the technique of "keeping on top" of nasty chop, ie incereasing speed when the conditions get uncomfortable.

Anyway, true RIB a development of the inflatable boat? They're mostly flat, fabric bottomed, whereas most RIBs bear a closer relationship to fast planing craft, speedboats if you like!

jwalker · 23 July 2005, 20:31

Quote:

Originally Posted by Richard B

..Hence the technique of "keeping on top" of nasty chop, ie incereasing speed when the conditions get uncomfortable.

I do that with my tubes in the water, it works fine. However, that technique is mostly only valid in a head sea. For the boats I've had experience of, the effect only really begins to happen at 30ish mph but it becomes reasonably effective at about 35mph+. Given that a reasonable sea is going to have waves advancing toward you at about 15-20mph then the combination of boat speed plus wave speed is in the region of 50+mph for the boat to start cresting the waves neatly. If you are in a following sea, then it would seam reasonable to assume that the boat speed is going to have to be in the region of 50+mph to achieve the same effect. However, because of the wave shape, it does tend to help by ramping the boat up the slope for the jump to the next wave so there is the benefit this gives. The upshot of all my blethers is, that you need a seriously fast boat to use that technique into anything but a head sea and even then the boat must be capable of a good turn of speed. And, if you don't have a very fast boat, in a following sea a comfortable speed to travel is just a couple of mph faster than the wave speed. This eliminates slamming and the boat doesn't attempt to dive into the face of the wave in front. Given that wave characteristics are essentially 'now you see them, now you don't', having the stability of the tubes in the wallowing sea if a definite plus. And, as I previously said, they're a plus in a beam sea too.

Tell me again why I don't want my rib tubes in the water...

Richard B · 23 July 2005, 20:41

I take it that you don't ever take any maths classes?

And you certainly don't want your tubes dragging in the sea in a following sea, I would want the least area presented aft - look at a "canoe-sterned" yacht.

jwalker · 23 July 2005, 21:14

Quote:

Originally Posted by Richard B

I take it that you don't ever take any maths classes?

Approximation for easy reckoning.

Quote:

And you certainly don't want your tubes dragging in the sea in a following sea,

Yes, I certainly do!

Quote:

I would want the least area presented aft - look at a "canoe-sterned" yacht.

That is to allow a following sea to pass by cos they travel slowly.

Richard B · 23 July 2005, 21:27

Quote:

Originally Posted by jwalker

Approximation for easy reckoning.

That's a new way of spelling wrong... I guess you don't take English classes either

So why, in a following sea, would you want to drag your tubes in the water?

And why would you want to exceed the wave speed by 45+mph in a following sea? Do you want to stuff it?

jwalker · 23 July 2005, 21:32

Richard, are you drunk?

Richard B · 23 July 2005, 21:33

No, but I think you are!

Louise · 23 July 2005, 21:33

I can assure you he isn't but you need to look at your figures again Jeff! (IMHO of course!) And please explain to me the advantage of having tubes in the water in a following sea?

(Cos I'm just a girlie!

)

jwalker · 23 July 2005, 21:43

Please, someone else, is what I've written unintelligible?