Hard versus Soft Nose!? - Page 4

tsunami · 04 July 2003, 15:21

Mark,
before I fall into anybodies hads I actually make a living by designing and building mostly hard boats up to about 60 ft!
However there is certainly a point where a hard boat or rib will be much better in a certain application than the other!
If a boat is intended to run at a maximum of around 40ish knots and is anything up to about 12m and is intended to be used in widely varying sea conditions then I don't think you will find a better boat than a Rib to do that job.
Rib's obviously have the advantage of having the cushioning effect of the tubes to make their passage through a rough sea much more comfortable. This on most ribs is not aided in anyway by having a soft nose! It simply acts as a brake when you stuff the nose! This is where a hard nose is so useful. You still get the cushioning effect and the stability from the tubes up the side of the boat 100% of the time and then in the event of stuffing you have the hard nose to punch it's way through the wave in a much smoother motion.
Hard boats of this size and speed have other factors to deal with. When they are being thrown about by large seas they have a hard hull side taking all of the impact and sending a large force through the whole boat and it's fittings. As the top deck of the boat is mounted to the hull side by a solid joint, this takes a lot of punishment which a rib doesn't. On a hard boat you have screens and fittings mounted to the topsides and hull sides which obviously are going to experience these knocks and bangs also!

BUT, once you start going beyond these sizes, speeds and weights then I think you would have to seriously question whether a rib is the right choice. On much bigger heavier boats in heavy weather applications there is no way that the tubes would be able to handle the forces they would be presented with!
I don't know much about very fast racing boats, but obviously Jon does. But I would think that in boats that go very fast 60+knots that the important think in driving them fast is to run the boat as level as possible and let the hull do the work! And in this case i would think that it would also be of benefit to have hard sides as you would know what to expect at these speeds when the boat was to land off centre rather than onto a tube than can perform differently depending on how much pressure is in them at the time!

Jonny Fuller · 04 July 2003, 16:00

Well I'm not a rib designer, but I can tell you that even 40 Knts is going quick if you think there's a chance of your tube getting 'emersed'! For example, at 35 mph the stagnation pressure of water is 1.175 ton/Sq foot, or about 17.5 psi, there's only 2 or 3 psi in your tubes, so you don't need to be a rocket scientist to work out where your tube's gonna be, squashed flat against the front of ya oddly shaped hard boat, coz thats what it is once that tube is clinging to it.
at 60 Knts (70 ish mph) the SP is up to 4.7 tons/sq foot (70 psi) now there's definately no place for a tube that might find itself being stuffed!

as tsunami says if ya boat is getting a bit of quality time on it's side, at speed, this will introduce all kinds of drag and tube failures, even at the lower speeds (30+knts)

thewavehumper · 04 July 2003, 16:19

I agree with CH (that could be a first!), when I was looking at the pictures I was wondering if there was another bit that helped to secure the tubes.

JF I may be being obtuse ( thatwont be a first) but doesn't the fact that the Rib tube is

1: Shaped in a POINTYFASHION,
2: Made from a non rigid material
3: Pneumatically filled to dissapate the shock

have some bearing on your calculations

Jonny Fuller · 04 July 2003, 16:26

Wave, if you make a trifle in a pointy fassion, and throw it as hard as you can at a brick wall, you'll get the same thing coz thats the difference in hardness between a rubber bag with 2 psi in it, and the solent at 70 mph! (or 4.7 tons/SQft if that sounds harder to you)

P.S. this is not a rib knocking session, I'm just stating facts about hydrodynamics!..double the speed..square the SP.

Jonny Fuller · 04 July 2003, 16:37

Quote:

Originally posted by Dirk Diggler
Fabio Buzzi would seem to know the answer to this question

Haven't you learned anything from Manos? italians are all twats when it comes to boat design, especialy if it's rough!

Seriously though, you need a design that keeps your achilles heel out of the water! so to speak. and make it as 'slight' as poss fwd so as to minimise it's risk. Running at 107mph, that FB is well 'on top' of things, and it should be high and dry most of the time.

EDDO · 04 July 2003, 18:36

How about a nose designed in section like a wheel rim with an inner tube fitted? Dont know anything about rib design but this works on my bike. Hello all.

Aging Youth · 04 July 2003, 19:16

Gentlemen!

For what they are worth my thoughts on the subject, what about engergy dissapation on impact.

If you have a hard nose the shock of impact would surely be sent through the nose and into the Hull thereby affecting the integrity of the hull because it cannot absorb the impact energy. The boat depending of shape of nose would probably crush on impact.

Soft tubes can absorb & disperse the engery through the tubes, by allowing for compression this can soften the blow on impact and in most cases reduce structural damage.

I am not a designer or builder, but I would imagine that in the same way the are crumple zones on car to absorb impact would this apply to any boat design Hard or Soft to prevent personall injury? Or is that not part of design/build process.

My view is that although the damage suffered by Magellan Alpha was unlucky at least the occupants came through it unharmed.

Could the same be said of a hard boat?

Pause for thought

Cookee · 04 July 2003, 19:29

As some of you may already know, I race a RIB at speeds of over 70 MPH. Mr Buzzis boat pictured actually had a large section (from the transom forwards) of the tubes removed during a world championships when it was driven by Charles Burnett the third, with Mark Pascoe as crew chief. The tubes were actually being ripped of the boat at the back by the water. Whether the diving had any bearing on this I do not know!

The boat was at Cowes last year being crewed by Mark Pascoe and I believe the tubes now stay on although I don't know what they changed if anything.

BTW just for the record, my boat has a hard nose and it was designed by Lorne Campbell that way!

We have been known to come done a little hard, and not always perfectly upright, and in those instances the tubes certainly cusion the landing nicely.

I am handing over the cash for the Poker run tomorrow, so unless some unforeseen disaster becomes me or the boat I would be happy to take anyone for a run in the BananaShark so that they can see what a 100% race RIB is like!

Dirk Diggler · 04 July 2003, 20:36

Quote:

Originally posted by Aging Youth

I am not a designer or builder, but I would imagine

We would never have guessed the first part, but the second part of your statement is obvious.

crazyhorse · 04 July 2003, 21:47

Cookee,there are a few of us with the ladys having a meal in downtown Southampton on the 18th are you up for joining us all.

The talk will be boats and ribs and its a chinese around 8pm,anybody else fancy a lighthearted meal then let us know as your all welcome,but we need book the tables. 10 so far inc wives ect.

thewavehumper · 04 July 2003, 22:37

I'd love a go in a fast rib Cookee if that offer is still on count me in.

Cookee · 05 July 2003, 07:43

Ok Crazyhorse - count me in for the chinky - probably for 2 but I'll let you know nearer the time if that's ok.

Wavehumper - You're on!

Charles · 05 July 2003, 07:49

Quote:

Originally posted by crazyhorse
anybody else fancy a lighthearted meal then let us know as your all welcome,

I'd love to come, only if I can sit next to Mr Fuller! Muahahaha.
Cookee, don't you need to come over here to check out a boat for the film shoot, that way I can get a ride in Bananashark, cheers

Cookee · 05 July 2003, 07:52

Charles - Not sure if that's still going ahead - Havn't got a trip planned to come over yet, but I'll let you know if we're coming over!

crazyhorse · 05 July 2003, 10:00

Im doing the seating Plan and if Mike and Di are comming then he is sitting next to Fuller ,as they got some making up to do.

Charles is that a yes your coming ?

Cookee you in for 2 ,and is kitten coming?

Charles · 05 July 2003, 12:38

Heh,heh....Jon C - I cannot make it - really, prefer a huge steak anyway

crazyhorse · 05 July 2003, 14:46

Na problem Charles it would of been nice to see ya all.

Next time I hope.

thewavehumper · 07 July 2003, 12:32

Count us in, what Chinky are you going to. There is a fantastic one in Swanwick and a good one near the Hamble.

We have some secure storage in the wharf next to Drivers so if any body needs to lock anything up they can use our container (the usual disclaimers apply) they are most welcome.

Cookee BRMMM BRMMMM what fuel do you run her on, unleaded Optimax or No2
Cheers
Stuart

Cookee · 07 July 2003, 17:29

Wavehumper - what the hell is No2? If it's the good stuff I'll take a 100 litres off you to try hahaha - trouble is we're only allowed to run unleaded for the racing

so if it's th really good stuff we can't use it!

Kitten isn't coming - he's got married man things to do - although if someone offered him a ride he might be persuaded - you never know!

Graham, my navigator might be coming as well s a young lady so I'm a bit short of seats already, so if anyone wants the services of a world class offshore navigator for some/all of the day let me know!

ps can I lock Graham up on Friday night cos he not quite as sharp with a hangover - especially after blue TVR's - I blaim Tony Hamilton for that one!

thewavehumper · 07 July 2003, 18:14

Cookee it's Nitrous Oxide looking forward to it already.

The Scorpion has got a couple of spare seats

cheers
Stuart