The International Canoe

OK guys, I'm having complete brain fade here... what surface area of 50mm thick 45kgm^3 density foam do I need to make the rule requirement for buoyancy? The number I'm getting doesn't seem to match with what I remember taking out of the boat in grotty old stuff... Maybe I shouldn't do te sums in the middle of the night!

I've got 1.6sq m twice on separate nights... sure feels more than what came out. I suppose it could have been wrong. Anyone feel like checking my sums?

Jim,

I get about 1.5 m^2 for 70kg bouyancy. Don't forget that the foam core in the layup counts, so there may not have been that much foam in there.

Mal.

Please remember the rule states ' positive ' buoyance , the foam in the hull / deck is not counted. Even with 70kgs of additional positive buoyance the IC floats very low. Ask our class chairman about his sinking experience at Lymington. Put the foam / bags in please.

Colin, I have never heard that you didn't count the structure of the hull and deck ( ie foam in the core) as part of the bouyancy.
That is the way we have been doing it here for a long long time.
Another case of two great nations devided by a common language?

I'm really confused now!

Having read the rule again it seems unclear... I suppose a rule ought to be consistent, so not counting the hull material would mean that the reserve buoyancy of a hull built of non buoyant material (eg monolithic glass) would be less than that of one built of buoyant materials.

How much foam is there in a hull anyway? I don't know that I could be bothered to calculate it. Working out the actual volume of the foam I use with it being irregular shapes is going to tax my poor ability at sums anyway... From the measurer's point of view excluding the hull shell is obviously easier to validate, except that how do you measure it with the deck on anyway?

And then I'm using high compressive strength styrofoam to help support the deck. Has that become part of the hull foam and thus according to the no hull foam interpretation not counting towards buoyancy?

yours confusedly, JimC

Both the existing IC rule and the proposed DC rule share the same wording. 'Reliable buoyancy to give at least 75kgs wt of positive buoyancy with hull flooded shall be provided'
In the UK we have always added additional foam / bags etc to comply with this rule. Both of our builders add foam. The builder certifies that this is present.
I will seek further clarification on this issue.
As an aside, I think that 6mm foam in hull, deck etc. would give about 60kgs of buoyancy.

I'm definitely on a dumb week this week...

Assuming the purpose of the rule is to give 75kg buoyancy to support the crew above what is needed to stop the boat actually sinking when the boat is holed then are these the correct sums? Its rather more foam than I thought I needed. Fortunately a single pack was much more than was needed too.

Foam boat
------------
Positive Bouyancy required: 75kg
Hull weight - 83kg
Shell buoyancy + 60kg
Extra foam (or bags/ bottles/whatever) required
+ 98kg.

Wood boat
------------
Positive Bouyancy required: 75kg
Hull weight - 83kg
Hull buoyancy + 20kg (guess!)
Extra foam (or bags/ bottles/whatever) required
+138kg.

Solid Glass boat
------------------
Positive Bouyancy required: 75kg
Hull weight - 83kg
Hull buoyancy 0kg
Extra foam (or bags/ bottles/whatever) required
+158kg.

So as I'm rebuilding 257 with foam shell and bulkheads and wood decks I probably need to run about 125 kg equivalent of foam, not 75, less however much (if any) I manage to get the boat down below 83kg by... Or am I completely on the wrong track here?

Jim,

I think you're forgetting to factor in the SG of the construction material, e.g. the bouyancy of an all glass boat is not zero. In fact it would not be much less than the weight of the boat. I would assume that Colin's estimate of 60kg for a foam core is over and above the weight of the boat. The only way to be sure is either to calculate for the volume and SG of each material in the boat, or flood the actual boat and see how much added weight it will float.

Mal.

Good point... I suspect the SG of a monolithic glass laminate is a lot more than 1, but it was wrong of me to assume the buoyancy was negligible.

According to my model the suface area of a Nethercott Hull is about 6.2m^2. Decks around, what, 3.5m^2. I've used about 3m^2 in internals, carriage etc. Lets say 6mm thick layup, that's 12.7 * .006 m = 0.0762m^3= 76kg buoyancy. So maybe not, but I've ignored the seat...

Its amazing how complicated the simplest rule can get if you put too much casual inaccurate thinking at it! At current (slow) progress I have about three weeks before final decision on what goes in mine, so lets have the definitive news by then please measurers!

I suppose an obvious clarification might be that boats constructed substantially of buoyant materials (wood, foam sandwich) shall carry 75kg of extra buoyancy, and that boats constructed of non buoyant materials shall have sufficent extra buoyancy to allow for that. But it does make things awkward if like me you are deliberately using buoyant materials as part of the engineering structure...

If that's not going to count towards my buoyancy then I'm going to have to considerably rework my build, which is a bit distressing having bought the materials, especially the expensive high strength styrofoam. I should have read and understood the rules more carefully I suppose.

cheers, Jim C

I have strongly advised that now and in the past, that if you are trying a development beyond the norm, take advice first! Remember, there is nothing new in canoe sailing, Uffa and a whole string of potential rule dodgers will have been there before you. The class has an outstanding history of development.

Fair comment.

But having observed photos of Canoes with standard grade styrofoam partially supporting the "dancing floor" it didn't occur to me that upgrading the styrofoam so I needed less reinforcement on the ply was going beyond the norm. I can just ditch the styrofoam, put a skin of carbon each side of my ply deck (or make a foam deck), and put in buoyancy bags or something but I was trying to avoid cloth on the plywood so I could have a varnish finish.

My sympathy is entirely with Jim.

I don't want to spend time going back and looking through the old Forum Postings, but I am quite sure that this was talked about many times in the past and it was always suggested that the buoyancy within the constructed parts of the canoe, including the hull counted towards the 75Kg of required buoyancy.

Of course this is an international Forum and I guess it is possible that those postings were from outside the UK, but still it is a pity that there is not an international agreement on this point.

Still, seems a bit daft to me.

Are we really saying that if the buoyancy is built into the structure of the boat it is no longer considered buoyancy?

In other words, if foam is used for some other dual-purpose other than explicitly as buoyancy, you can't count it???

If you have foam that is loose it counts - but if it supports the deck - then suddenly it is no longer considered buoyancy?

Seems very strange to me and rather counter-productive.

Like Jim, I really had no idea that using foam to build some buoyancy into the structure was really such a 'development beyond the norm'.

It just seemed obvious to me.

cheers

eib

Yes but the foam added is maybe only 30 litres, to make the total buoyancy of 60 + 30 = 80 kg which exceeds 75 kg., and not 80 litres of non structural foam or bags.

What does Rob say on this, and about all the boats he's built with some extra foam- that apparently now doesn't count as bouyancy?

As I read the rule it doesnt state the bouancy cannot be part of the structure or provide some sort of structral support to the hull or deck etc. Also I dont read where it says the bouyancy a foam core provides cannot be included in the sum to provide the 75kg of boyancy.

From photo's Ive seen of Rob's boats he has built the foam appears to support the ply dance floor.

H.