The International Canoe

75 litres of foam is not really enough to float a flooded IC anyway if it weighs 80+ kg plus sails and crew. Has anyone actually sunk a boat? So maybe Colin's interpretaion is a better idea, 70kg plus whatever is built into the hull skin would probably be enough to save the boat.

75 litres might be enough for a DC at 50kg but still would provide little support for the crew, and would be very difficult to tow.

I built in maybe double the required volume of foam and divided the hull space into four separate compartments. I like to be able to sail home if holed in a collision.

Other classes require separate compartments so that if one is flooded, the second saves the boat.

Curiously, the IC rules do not allow hull subdivision to count as in built bouyancy. Consequently, most hulls I have seen have no bulkheads at all (presumedly to save weight). Personally I think that hull subdivision is something that should be encouraged rather than discouraged. A block of foam contains a large number of very small subdivisions. A boat filled with plastic waterbottles contains a smaller number of larger subdivisions. Where is the cutoff point?

Mal.

Can someone clear up the concept of the rule for me:

'Reliable buoyancy to give at least 75kgs wt of positive buoyancy with hull flooded shall be provided'

Do we need 75kg + whatever is required to float the boat, or just 75kg as an absolute value?

The question is do we just want to prevent the boat from sinking, or actually want it to float enough to sit on it and get home. Most canoes will probably never sink even without foam. You won't loose the boat, but it won't take you home either.

The short answer is that you are all correct ! I believe the history has been that wood / csm canoes leaked, so to prevent sinking additional buoyancy in the form of bags were added. Later foam which did not soak up water was used. Then along came thin core foam sandwich, say 6mm thick hulls with wooden decks, foam still was added. In the recent past we have all thin foam canoes still with added buoyance foam. Now builders are using foam to support the structure in vast quantities and up to 50mm thick. This is a recent development and logic says that all this foam could be included in the 75 kgs that required. As a measurer , not the rule writer I will refer the matter to the BCU / ICF for clarification. Please also note the builder certifies that he has 75kgs of buoyance if it cannot be inspected. Its your responsibility

The IC / DC / AC appears to be one of the few boats that don't count sectioned hulls/tanks to be accepted as buoyancy.
The optimist is the other that comes to mind - tanks must have holes in them ( and then must have bags for the buoyancy ).

Most other development classes require 2 or 3 tanks / sections of hull that are airtight, so that a crash might hole the hull, but if only 1 tank is holed, the hull can float on the other 2.
The canoes generally have one big space which therefore can lead to problems if the hull gets holed. Even 75kg bouyancy is not much when there's a hole that gets water to all the hull.

I think the A cats have a similar to current IC rule, but the foam in the hull IS counted for bouyancy.

I would prefer a rule that requires 3 independent airtight tanks ( built into the hull ) - then there is the hull foam bouyancy, and probably at least 100 litres in each tank of additional bouyancy.

My boat has 3 independant tanks to satisfy my safety requirements, and extra bouyancy bottles to satisfy the rules.

I have to agree Andy this idea of one large tank is kinda worrying, any failure or hole could be a real pain. My intention is to keep the main bulkhead full height & likewise a second just aft of the daggerboard. We both know to our own costs whats happens to man & machine when Gurnard Ledge hits you at 8-10knots (6-8 in my case!) I personally dont like the idea of those loose bottles to satisfy the rules but the use of styrofoam 'fixed' into the hull seems infinatly more preferable.
ps work continues on 'itzakinda(more)magic' the carbon's not far off!
pps what time ferry have you booked for Oxford? Barry[/i]

My latest design has just about exactly 8 m^2 of surface area.
At 6.5mm thick this accounts for 52,000 cubic centimeters of volume.
The internal foam cored structures ( bulkheads trunks etc) add another 7,000 cubic centimeters of volume
Thus I have 59,000 cubic centimeters of volume or 59 kg of buoyancy.
The painted hull weighs just about 20 kg, so there is 39 kg of "positive buoyancy) in the hull structure. As I have move buoyancy than weight, the canoe will not disappear beneath the waves if it is completely flooded.
It won't float very high and I won't be able to stand on top of it and wave my arms for help.
The rule calls for 75 kg of Positive buoyancy, so this means I have to add something like 40,000 cubic centimeters of foam to the structure, or I have to add an air bag or two.
As luck would have it, an Optimist air bag is a 45 kg unit. I have some left over from when Dave and Willy were sailing square boats. So one if those gets added.
But I'm not worried about the boat sinking out from underneath me even if I didn't add the air bag.
SHC

Intent of the rule as I recall is that you should be able to flood the hull, all of it, put 75 kg on the hull and it would float. The old wooden hulls had structure but no bulkheads.

If we want to make a change we have to have some rule language on which people can vote. If you were working with compartments you should be able to float on one compartment of three compartments I would think.

Floatation does count when you weigh the boat.

Ben,
I don't see the intent the same way you do.
It has always been my understanding that the 75kg of flotation was to assure that the canoe would not sink if holed. In other words that it had enough flotation to support itself. I have never built a boat that would float 75 kg of ballast as well. Having done just about everything bad to an IC that it is possible to do, including blowing out the side of a centerboard trunk, lifting the deck off at the chainplates, and driving a mast through the bottom of the boat, they have all made it home to be repaired. So I think the 75 kg surplus is unnecessary.
SHC

Well, I seem to have a bit of a debate with what I thought was an innocent enquiry! 75kg of displaced water and 83kg all up weight in a holed boat doesn't sound like a winning combination to me, although I assume the seat is usually buoyant as well and it would be a bit of a game to manage to hole a boat such that there weren't any air pockets.

I shall put my boat back together with two tanks and a generous amount of foam and endeavour to keep my mouth shut (difficult task you'll all realise) next time I can't do my sums.

Maybe the powers that be could get together after the worlds and issue a clarification (not before, that's a can of worms only a supplier of table tennis balls in industrial quantities would like to open)... I think it would be nice if the rule worked out so that a typical mass helm could sail a holed boat back with the decks awash.

Was there ever a definitive answer on this one ? Apologies if it was mentioned in another thread.