kayakman7 wrote:
A sinking ama is potentially a much larger problem to deal with, especially if it wasn't noticed til the boat capsized...
Hmmm ... I wonder if the Foam-in-a-Can insulation squirted into the Ama drain hole would be a good idea
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| Flotation bags http://www.hobie.com/forums/viewtopic.php?f=71&t=43983 |
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| Author: | washedup [ Thu Jul 19, 2012 12:08 am ] |
| Post subject: | Flotation bags |
Hi I'm new to the forum and new to the Hobie AI, but mine has arrived this week and as you can imagine there is a lot to think about when getting it rigged out. In my other kayaks I have always added flotation bags to give extra security in case something happens and the kayak ends up getting swamped. I have added a 20L bag in the bow but am just a bit concerned about adding other flotation bags where they might get caught up with the rudder lines. Has anyone else added flotation bags and is there anything to look out for? Many thanks. |
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| Author: | kayakman7 [ Thu Jul 19, 2012 6:23 pm ] |
| Post subject: | Re: Flotation bags |
washedup wrote: Hi I'm new to the forum and new to the Hobie AI, but mine has arrived this week and as you can imagine there is a lot to think about when getting it rigged out. In my other kayaks I have always added flotation bags to give extra security in case something happens and the kayak ends up getting swamped. I have added a 20L bag in the bow but am just a bit concerned about adding other flotation bags where they might get caught up with the rudder lines. Has anyone else added flotation bags and is there anything to look out for? Many thanks. Hello, Floatation bags are unnecessary, there is enough foam in the hull to create positive floatation in the event of a flooded fully hull. If it makes you feel better to use them, there is nothing to interfere with in the forward hold. j |
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| Author: | washedup [ Thu Jul 19, 2012 10:37 pm ] |
| Post subject: | Re: Flotation bags |
Oh, thanks for that. I didn't realise the foam that was in there was enough to keep it afloat. |
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| Author: | Drewyaker [ Fri Jul 20, 2012 5:22 am ] |
| Post subject: | Re: Flotation bags |
Pool noodles. |
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| Author: | Tom Kirkman [ Fri Jul 20, 2012 6:16 am ] |
| Post subject: | Re: Flotation bags |
Same here - pool noodles. These boats only have enough positive floatation to float them while empty. If you put much if any gear inside, you may overcome what floatation currently exists. You can cut pool noodles in shorter sections and GOOP them in the bow or stern, so that they do not rub or interfere with the steering lines. |
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| Author: | kayakman7 [ Fri Jul 20, 2012 6:32 am ] |
| Post subject: | Re: Flotation bags |
Actually, there has been at least one AI that had a full camping load and filled with water. The user in question said he didn't even notice till he opened the hatch, it just sat a little lower in the water and sailed a little slower. |
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| Author: | kayakman7 [ Fri Jul 20, 2012 6:35 am ] |
| Post subject: | Re: Flotation bags |
A sinking ama is potentially a much larger problem to deal with, especially if it wasn't noticed til the boat capsized... |
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| Author: | PassWind [ Fri Jul 20, 2012 8:06 am ] |
| Post subject: | Re: Flotation bags |
kayakman7 wrote: A sinking ama is potentially a much larger problem to deal with, especially if it wasn't noticed til the boat capsized... Hmmm ... I wonder if the Foam-in-a-Can insulation squirted into the Ama drain hole would be a good idea
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| Author: | Tom Kirkman [ Fri Jul 20, 2012 8:14 am ] |
| Post subject: | Re: Flotation bags |
A lot of the possible flotation, or lack of it, depends on what you have inside the kayak. Different types of gear may or may not float. A tool kit will be more detrimental than a soft sided, foam insulated cooler. Unless you're carrying identical gear to the man who said he didn't even notice his AI had filled with water, I wouldn't bet on my floating in the same situation. |
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| Author: | KayakingBob [ Fri Jul 20, 2012 9:25 am ] |
| Post subject: | Re: Flotation bags |
One of my AI's took on water while we were sailing them. 85% full at takeout and we didn't notice much difference in performance, but we were in some good wind and waves. I think what helps is the two ama. If a ama fills with water, stopping for a couple of minutes to drain it would be doable, unlike when a hull fills. |
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| Author: | Tom Kirkman [ Fri Jul 20, 2012 9:36 am ] |
| Post subject: | Re: Flotation bags |
Good point. No doubt the Amas add considerable flotation to the package. |
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| Author: | tonystott [ Fri Jul 20, 2012 10:16 am ] |
| Post subject: | Re: Flotation bags |
I seem to recall reading that each TI ama provides 50kg of flotation |
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| Author: | kayakman7 [ Fri Jul 20, 2012 12:20 pm ] |
| Post subject: | Re: Flotation bags |
KayakingBob wrote: One of my AI's took on water while we were sailing them. 85% full at takeout and we didn't notice much difference in performance, but we were in some good wind and waves. I think what helps is the two ama. absolutely, the biggest problem with a waterlogged hull is not sinking, it's stability. a waterlogged hull will roll erratically, the water inside rushing from side to side and fore and aft unpredictably. the amas act as additional buoyancy cambers and increase the stability in all directions. as to adding floatation, I'm not saying it's a bad idea or that it will hurt anything, just that it is completely unnecessary. there is a tremendous amount of reserve floatation already. Floatation on a TI: 2 amas with 220 lbs of floatation each, enough foam in the boat to float its weight and then some, 10 to 20% of hull volume in which air is trapped, and any cargo stored in the hull displaces water and is generally lighter than water. as hull is flooded with water, it's weight does not increase. it's inertia and mass increase and floatation decreases. which isn't the same thing. for example, say the TI hull has 1440 lbs of floatation, 40 lbs of foam floatation, and 2 220 lb amas (these are theoretical to show my point but some might be close (18'*2.6'*.75'*.7= 24cu ft= 180gal*8lbs= ~1440 pounds of floatation in the hull where the .7 is a reducer for sections of the that were included in the measurement but not actually on the boat). that's 1880 lbs of buoyancy. the load: 200 lbs for the boat and 400 lbs for the crew. we have 1280 lbs of floatation. now we remove 90% or 1300lbs of the hull's floatation by adding water. it should sink at this point right? 1300 minus 1280 equals 20 negative pounds! nope! we still have the 40lbs of foam floatation plus as more of the boat sinks below the water the less it counts as negative weight. so, 80 lb boat 90% under water probably weighs only 30 pounds and much of our load is underwater now ie, you are sitting in a puddle which reduces your weight too. so 20% of the crew is underwater or 80 lbs. adding up the new figures: floatation: 440 amas +40 foam +140 hull =620 lbs floatation load: 120 rig +30 hull +320 crew= 470 lbs load 50 lbs positive floatation! if you are carrying cargo, say a camping load: every cubic foot equals 60 lbs of water displaced. not many things normally carried on a camping trip weight more than water does, so it's really hard to justify wasting valuable hull space with reserve floatation when that cargo is almost as effective as foam would be. every 15 liter drybag filled 2/3s full is 20 lbs of floatation. put a 5 lb stove in it and 2 tanks of propane (which is arguably the densest thing normally carried) and it will float or, at least, barely sink. carry a water bag on deck and it counts against you but carry it in a flooded hull and it has no weight and might even float slightly. deck cargo is the most dangerous thing we can carry because as we sink it will never add to the floatation and never reduces the load. in practice, the AI and TI can and will flood to the gunnels but both are virtually unsinkable, which provides you with time to self rescue or wait for help. so, given the choice between deck cargo, and extra floatation bags and foam noodles in the hull or everything packed into the main hull, i will always choose cargo in the hull. an interesting aside for the scuba divers here: 1 gallon of water is 8 lbs and 1 gallon of lead is 95 lbs. the tanks will float when empty, the gear is relatively light, but if you're sinking, ditch your weight belts! cheers! j |
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| Author: | washedup [ Sat Jul 21, 2012 12:02 am ] |
| Post subject: | Re: Flotation bags |
Thanks for all your input and help with this, there are some interesting points to consider. I think I will keep my 20 L bag in the front for now and see how I get on for storage space. |
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| Author: | georeubs [ Sun Jul 22, 2012 12:53 pm ] |
| Post subject: | Re: Flotation bags |
I have one of the early TI's that didn't include foam. One of the first things I did was to install NRS float bags inside the bow and stern. Both bags are clipped in so they're secure but easy to remove. I've never had a problem with interference of rudder lines, nor have I had any issues with storage at either end of the hull. I read all the posts above and was impressed with some of the math that others have done, and many suggestions are great ideas. Nonetheless, I simply feel more secure on the water with the purpose-built flotation bags. I was in a search and rescue helocopter squadron in the U.S. Navy, and one thing I learned is that water is absolutely unforgiving. As such, I'd never trust my life to simply cramming a pool noodle into the hull. You spent a LOT of money on the boat. A few more bucks for two flotation bags won't break the bank. |
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