RIB Seaworthiness

It's said that the increased seaworthiness of a RIB over a standard powerboat is due to the inflatable collar being able to deflect upon impact with waves. I've driven RIBs quite a bit and the collar never goes near the water, except when you punch into a sea and manufactures have started fitting hard noses to combat damage to the tubes.(I've seen the tubes ripped of the front of the boat). Take two RIBs one with the tubes at 3 psi and one with them at 100 psi (I know), is one more seaworthy.

 

Not sure what brand of RIB you run with only 3 psi tube pressure, but wouldn't doubt that the low pressure would give troubles. My experience is with the Zodiac Hurricane brand on the Canadian West Coast, and I cannot remember the tubes being ripped off by the Coast Guard or Navy. I do remember some transoms from other brands tearing off because they didn't have the aluminium reinforcing we used. Haven't seen the hard noses you speak of, but they seem to defeat some of the benefits of the RIB, similar to people thinking that hard (alloy or FRP) tubes improve the design of a RIB. The truth is that RIBS are expensive to build, specialized craft that give up a lot of interior space for stability, and heavy weather performance, at least in the larger sizes. I have talked to boaters that cannot believe the cost of a professional RIB, until they realize that the Coast Guard isn't going out to rescue them in the same type of boat that is in trouble. My two cents, for what it is worth.

RWL

 

For RIB with hard nose: see http://www.redbayboats.com/ribs/stormforce_91.htm

 

Looks like a nice vessel. The use of the hard nose (looks like the bow of a normal hull) makes sense for mooring etc. I notice they only think the bow tube could tear off running into a large following sea at speed, but don't say it has been a problem. I think the design shown probably solves the problems that the operator had, namely, mooring wear and tear. The compromise is that the RIB will not be much good at coming along side another vessel that is moving. The common technique used by the Coast Guard is to place the hull at a 30 to 45 degree angle to the moving vessel's hull and apply some throttle to keep it there, so that personnel can step over the port or starboard bow, whichever is effectively glued to the moving vessel's hull. I realize that isn't the technique used by everyone, but was found to be easiest and least damaging to both vessels by the "rubber ducky" fleet in Western Canada. Cheers

RWL

 

Zodiac recommends using quite high pressures for their tubes; different for each boat size but much higher than people would normally inflate them. The high pressure makes the tube fit tighter, reduces the risk of tube damage and detubing, and reduces chafe/wear.

RWL's absolutely right that big RIB designs are specialized, very expensive craft that sacrifice a lot of space for their performance. Zodiac Hurricanes are designed not to travel in calm water, but to be thrown from wavetop to wavetop at odd angles and high G-forces, all day, every day. The ability to safely nose-up and transfer people while underway is unique to inflatables; try this in a rigid (or hard-bow RIB) boat and you will do serious damage to one or both vessels. Likewise, only the RIB concept allows for both sufficient buoyancy and stability for rescue work, and enough agility and low enough freeboard to get in close and pull people aboard.

The increased seaworthiness is due more to the huge inherent buoyancy and the shock-abosrbing capability of the tube, rather than any flex on impact. Once that tube touches water it becomes extremely difficult to roll the boat any further; RIBs can stay more-or-less upright with large off-centre loads or very big waves.

 

Explains everything.

 

It acts as an "air spring", right?

Do you know if anyone makes a foam filled chamber RIB? What I'm thinking about is the same shape but instead of air, a spongy bouyant foam which is protected by the outer fabric.

This is what gave me the idea:

http://www.aks.r52.ru/eng/mars.phtml

The normally air-filled cushion is foam filled on this Russian hovercraft (lower skeg used to say foam somewhere - I think).

Edited for grammer and spelling - must of been in a hurry.

 

For foam collar see: http://www.wing.com/foam_collars.html

 

Thank you, this is similar to what I was thinking of.

Now I'm wondering is the air bladder can be made to be "self-sealing" like a fuel tank.

I've noticed on a few designs what might be called a double vertical tube bladder. That is to say tubes bonded together but acting differently or independantly one over the other. Think of it as the figure/number eight in section. I'm guessing they are celled seperately and are held at different air pressures. The top tube cell for along side boats acting as a bumper and adding back-up bouyancy. The bottom tube cells is in contact with the water and has a different function/characteristic - that comes along with water contact. You can kind of see this in that unusual Russian hovercraft link I gave as well.

I laughed when a friend though part of a Chuck Norris movie was real. It's probably his first "Braddick" movie, the one when he goes back to Vietnam to find M.I.A.'s. Anyway, Chuck's looking to buy a fast inflatable on the Black-Market and the seller say's it's industructible because it's made of Kevlar. Chuck Norris takes an machine gun (AK-47) and fires at the tube raft. The raft survives unscathed so he buys it for a many thousands dollars. I did not say my friend was very smart.