So where I work we score from 1 to 5 (non marine industry). 1 "will probably never happen but might" to 5 "will almost certainly happen". Consequence 1 "no harm, minimal harm" through to 5 "catastrophic" (catastrophic is what we call death but it sounds nicer!). So to put consequence into RIB / watersports terms:
1. Near Miss, Minor damage not affecting the passage. Very minor injuries (bruises, grazes etc).
2. Passage cut short, no outside assistance required. Possibly cut short more as a precaution. Minor injuries not requiring emergency service assistance.
3. Outside assistance needed but no lives in danger. Tow home? Possibly a Pan Pan. Injuries not life threatening but requiring hospital care (probably not admitted to hospital > 24hrs)
4. Outside assistance needed. Mayday justified. Injuries which could be life threatening. (May include injuries that have a protracted hospital stay)
5. Loss of boat or crew, or life changing injuries.
1. Improbable - not very likely to happen but can't be 100% excluded. e.g. May require 2 things with low failure rates to fail at the same time.
2. Remote - there have been a small number of cases but they are relatively rare compared to the number of times it "could" happen.
3. Occassional - it does happen - but its not something that happens a lot.
4. Probable - there are past examples of it happening and you would expect recurrence.
5. Certain. There are numerous past examples of it happening.
We multiply the two numbers together so you get score from 1 to 25.
Determining what the risk is is often the tricky part... Not the score - the underlying risk event. So if the risk was described as "Tube failure" you would score it as Possible or Likely - something like 3 on the score for a 40 year old boat.
The consequence of tube failure (with NO CONTROL MEASURES [no life jackets etc]) would be a 5. So overall score is 15. You already have life jackets etc so you would probably argue the consequence is a 4 rather than 5. So you have mitigated the risk already to 12.
The point that most people are trying to make is that if you go for a 3 chamber boat (no further modifications) and 1 chamber fails you will reduce the likelihood score because its newer material (lets say to 2). But because you have 3 chambers not 2 the consequence before even wearing a lifejacket becomes probably 2 (end your trip out but limp home) or at worst a 3 (pan pan). So your baseline score before mitigation is probably 6. Wearing a lifejacket probably doesn't mitigate this risk at all. I know its theoretically possible for 2 tubes to fail but that has to be a likelihood of 1, consequence 5 - mitigate to 4 with lifejacket. Overall risk score lower than 1 tube failing.
Now... lets assume you foam fill the tube on your existing boat. You can possibly reduce the likelihood of failure. BUT will you reduce it to any less than a 2? The foam is still held in place by 40 year old fabric and 40 year old glue. 1 mile out you notice the fabric is loose and you can see foam. How sure are you the fabric doesn't come off completely and while you may have a lump of foam to hang onto the consequence has got to be a MayDay which I'd suggest is a 4. Overall Score 8. Now 8 out of 25 is not appalling. So you need to decide do you want 6/25 or 8/25 or 12/25. Is the extra investment required to get to 6 justifiable. Not sure how much foam would cost.
Are you sure it reduces the risk of failure? I'm not. There are a whole matrix of variables here: if probability remains a 3 then I'd be making a Pan Pan for fear that it would worsen. So thats a 9 overall? If probability actually increased (see below) it scores as 4 x 3 = 12.
Lets score your balls... ;-)
Does it reduce the likelihood of the tube seem failing no. So score remains 3*. Does it reduce the consequence? Only if the failure is < 20mm diameter. If its bigger than that - common with seam failures - you'll know you have a failure as a nice stream of balls shoots out the tube!! But they will have no impact on your consequence score. For a failure < 20mm diameter they would impact your consequence score. - You aren't in the water. But for fear of enlarging the hole and loosing the balls I'd be making a PanPan which i think is score 3 for consequence. Effectively you split a 12 score for Tube failure into two scores. Tube failure hole > 20mm and Tube failure hole < 20mm. If you had modern fabric and glue I'd say hole > 20mm would be 1 or 2 likelihood and <20mm would be 2 or 3 (with no mitigation like avoiding sharps). You have old fabric and we think the seams are your biggest risk which I think means >20mm is likelihood 3 and <20mm is a 2 or 3. You mitigate your <20mm by banning knives and being sensible where you take the boat to say a 2. You add the balls and you reduce the <20mm score to 2x3 = 6. But you continue to have a 3x4 risk from the > 20mm issue.
Does adding balls or foam add any other risks / problems?
1. Extra weight - increases load on the seems. So you may actually increase the likelihood. Rescore all likelihoods 1 score higher and see what happens! Foam becomes 4 x 4 (if the foam parts company) : 16! Higher risk. Balls, hole > 20mm 4 x 4: 16! Balls, Hole < 20mm (e.g. small seem leak) 3 x 3 = 9!
2. Resale value - pretty much NIL. So a boat you might be able to sell for £60 (??) now but costs you £40 to fill with balls or foam has a value of nil. So £100 becomes nothing overnight. Would it have been better to sell it for £60, add the £40 to it and buy something with the £100. Seago 260 260s inflatable SIB Boat tender dinghy | eBay
(I have no idea what your boat is worth)
3. Tube firmness: pretty much essential for performance and to reduce wear on the tubes. So with balls their are probably filled to be at atmospheric pressure or just above. You then put the air around them to a lot more than that and the balls will shrink. But it will take time to equilibrate all that which will make filling the tubes and getting pressures right difficult. Saggy tubes will increase strain on seams and I refer you back to point 1 above.
With foam you may have the same issue - foam selection is key! If its soft foam the foam will squash down and have same issues as balls. If its a rigid foam there may be too little flex. Its not something you can trial and error with once its in its in! While its obvious that SIB manufacturer doesn't use foam because it stops the boat being 'pack awayable' why are the only RIB manufacturers using foam the guys where the collar is intended as a big fender rather than for stability?
Don't know how much you've had to do with this stuff but its evil. It sticks like sh*t to everything, Put too much in your tube it'll be very dense. Put too little in how do you fill the extra space with air as I bet it will seal your valve off! Very rapid cure times on the stuff I've used. Not sure I could pour enough to fill a tube before it cured.
4. Heavier overall weight. Hard to imagine but you have 3.8m of boat there with a tube diameter of 10-12inches. by my crude calculations that is PI x ( 15 x15 ) x 380 x 2 of tube volume. Thats about 540litres of tube volume. Google tells me the weight of foam varies from 2Lb to 16Lb per cubic foot. Assuming you have 4lb per cubic foot, thats 4lb per 27l, - so 80lb extra weight. Thats probably more than your engine weighs,,, that will slow your boat down as well as increasing load on the toobs. A quick google for a 20mm ball gave me a weight of 1.3g per ball. My calculus isn't good enough to work out what the number of balls filling 540litres would actually be so I'm going to assume they are 20mm cubes (8ml volume) - so 6750 balls. So 9 kg of extra weight...? (20lb)
My conclusion is you can't reduce your likelihood of a seem failing on this boat only increase it.
You may be able to reduce the consequence. But not by much because you are already at 4 and I doubt you'd do anything less than a Pan Pan if a tube fails even with foam... The only risk you seem to be able to reduce might be the small holes and I think you'd be better preventing that happening than dealing with it when it does...
So to move onto your buoyancy aid vs lifejacket dilema...
You are mentally doing a risk assessment to determine:
- the likelihood you'll enter the water
- the consequence of doing so
If you are a dinghy racer you wouldn't wear a LJ because the high probability of being in the water means you'll end up terminating your sail... If you are cross channel sailing you'd probably not be swimming after the boat anyway so ease of swimming is negated by being held face up.
Your concern is that the life jacket is air filled...
So the risks would be:
Auto doesn't auto inflate (Likelihood - 2 to 3)
Manual mode doesn't inflate coz cylinder fails (Likelihood - 2)
Manual (breath) doesn't work coz lifejacket leaks (Likelihood - 1)
For each the consequence reverts to the item below it so the only risk is the lifejacket leaks air faster than you can top it up. The consequence is a 5. But the overall score is a 5 because the Likelihood is so rare (provided you mitigate the risk through jacket servicing/care etc).
Your bouyancy aid however will not turn an unconscious wearer over. So the risk is the likelihood of being unconscious before rescued... Influenced by sea temperature, location of rescue, activity (sailors like to bang heads). If you are in the sea without assistance nearby you stand a high risk of hypothermia causing unconsciousness ranging somewhere from 3 to 5, with a consequence of 5. 15 - 25 overall score. So the risk (15) is far greater than the likelihood of the lifejacket not working(5). You'd need to reduce the risk of unconsciousness to almost impossible levels...
The reason buoyancy aids have a role is if you look at the risk for say a laser dinghy sailor of capsizing its almost certain! It would score 5. So they need the consequence to be a 1 - carry on sailing. Put an auto lifejacket on and once its popped they are going home for the day - score 2, overall score 10. Compared to a risk of being unconscious, face down in the water for more than 3 minutes before a rescue boat arrives (Likelihood 1, Consequence 5); or wear a 50+N lifejacket that can inflate to 150N. Likelihood of a different risk - getting caught in rigging - goes from 2 to 4 (they are all bulky), consequence of getting caught in rigging remains a 5.. Score moves from 10 to 20 overall...
Put me in a sailing dinghy away from immediate hope of rescue - I want to keep my risk at 5 so I need the likelihood to reduce (sail in better conditions, put a reef in, sail with experienced crew, change my hull design for stability) because the consequence may well increase... Wayfarer Day Sailors would say they reduce their likelihood to 2, and Drascombe sailors to 1. The consequence is probably a 2 or 3 for both... but there was a Drascombe skipper who died at the weekend...
Thats all a rather long winded way of saying - nothing you do to a 40 year old boat will make it safer than a modern one.