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Old 24 August 2016, 17:42   #11
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Jeff the potential for this bulge effect has been in pretty well every air flor SIB I've owned. Its severity depends on speed, outboard power, load carried, floor length, wave conditions etc. It's worse the flatter the floor shape and with under inflation. In all cases where I've experienced it the floor pressure has been correct.

The amount it is commented on by any particular owner also depends on their preconceptions of how travelling in a SIB feels... some hate it and others barely notice.
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Old 25 August 2016, 03:06   #12
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thanks david i did have a small honwave for a while but only used at displacement speed but i was amazed on how solid the air floor was.

cheers
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Old 25 August 2016, 09:03   #13
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Unless I'm going for all-out speed I never really notice the bulge, but of course that's when it's most frustrating and as Fenlander says, so many things affect it including the difference between following waves and cutting through them... If I was simply running a 10HP I'd never notice, but I am at the limit of what the boat is rated to carry from an OBM perspective so perhaps little niggles are to be expected under certain conditions?

Undoubtedly the longer the hull the more scope for it to appear/be a problem but, aside from Aerotecs I think every inflatable floor's SIB has the potential to suffer this affliction... I dare say even a 4m Aerotec might be pushed into this with the right (wrong) combination of set-up/conditions.
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Old 27 August 2016, 12:46   #14
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Before I realised that plonking the boat in cold water knocked a little off the air pressure, my aerotec 420 suffered from this.

I now inflate the floor to 12psi so that the cold water effect knocks it down to the correct 11.2 pressure or thereabouts. No problems since.
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Old 27 August 2016, 12:49   #15
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To be honest I'm fairly confident that the airfloor and tubes can survive being a little overinflated so that's what I tend to do. 3.6 psi in the tubes, 12 in the floor.
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Old 27 August 2016, 13:01   #16
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I bet their tested twice the pressure before they burst carnt imagine the working pressure is too close to failure. Good question if anyone knows?
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Old 30 August 2016, 06:10   #17
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Originally Posted by Stigomery View Post
Unless I'm going for all-out speed I never really notice the bulge, but of course that's when it's most frustrating

Well, I've had the Honwave out the last 3 days and it was beautiful, however I suffered "the bulge" worse than ever before. It drove me to distraction. I'm not sure what it was, badly balanced boat, trim, conditions... but it was insufferable.

I also carved up a chunk of the sea bed with my prop, those Eastern sandbanks are a killer.

I tried to take a picture of the bulge but it's impossible to get the right perspective.

I've often wondered if it would be possible to put down a hinged wooden floor that wedges the V down but not yet experimented.

You can only just make out in this photo how the front, round the fuel tank, is being sucked down into the water and how the rear, by the engine, is being forced upwards...

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Old 30 August 2016, 06:56   #18
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Stig this is super techy but a research paper on the performance and design of inflatable boat hulls part funded by the RNLI.

http://eprints.soton.ac.uk/183099/2/...r_Halswell.pdf

In section 5 it explains exactly how this bulge develops and moves under the boat floor.

If you look at the area where the bulge appears on yours the V is so shallow it would be quite hard to make any sort of inner wooden floor that would help to any extent.

If you notice in the report it says rough water tends to largely prevent this effect and I've said before our most extreme experience has been on millpond flat lochs with a Zodiac air floor.

Trust me if you find the Honwave annoying you would tear your hair out with a conventional flat air floor and blow up keel. The only way to move away from this is a GRP hull or an Aerotec where this effect is unable to develop in the same way as... 1) the floor is as stiff as it could ever be with the near constant V right to the transom... 2) if a pressure bulge does try to form it "spills" up the V harmlessly away without getting trapped under the floor. Very very rarely this does happen and can be felt as a slight steering effect as the pressure spills to one side.
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Old 30 August 2016, 07:07   #19
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it seams that your all in the middle off the boat 4 people/fuel/kit box to some degree point loading problem?,at the top of the picture tube line to floor seems as if its pushing the floor down going towards the bow as if the bow is trying to fold backward and the tubes moving outwards exposing more of the floor which is hidden at the stern?
i suppose the big difference between the air floor is its got a lot of rigidity over its length were as the ali/wood floor has an hinging effect at the bow and each floor panel allowing it to snake along as it were.
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Old 30 August 2016, 08:05   #20
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it seams that your all in the middle off the boat 4 people/fuel/kit box to some degree point loading problem?.

In that photo not quite and we did play around with the loading quite a bit (see sketch for rough loading in that photo).

When I was on the Scottish SIB trip I hardly suffered the bulge, but the seas were far from glass like.

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