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Old 24 March 2016, 07:25   #1
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Tube diameter

More modern inflatable boats appear to have larger tubes than the older boats, especially the small boats. Based on experience here, does it make much difference regarding a dry ride? Some of the boats I have looked at in the circa 3.4m to 4m range have had tube diameters ranging from 38cm to as much as 48cm. I do see the benefit of larger tubes but there must come a point where the internal space is reduced for these smaller boats.

Is there an optimum size for a 4m sib?
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Old 24 March 2016, 07:42   #2
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Quote:
Originally Posted by Arctic View Post
More modern inflatable boats appear to have larger tubes than the older boats, especially the small boats. Based on experience here, does it make much difference regarding a dry ride? Some of the boats I have looked at in the circa 3.4m to 4m range have had tube diameters ranging from 38cm to as much as 48cm. I do see the benefit of larger tubes but there must come a point where the internal space is reduced for these smaller boats.

Is there an optimum size for a 4m sib?
my mercury is 48 cm i wouldn't want anything less as i like to sit on the tubes with bent knees at the right height, plus more load carrying capacity with the bigger tube more free-board safer feeling there are some 50 cm too OMO

cheers
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Old 24 March 2016, 07:57   #3
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Cheers. My last boat had 45cm tubes and those seemed about right.

Do you happen to know the internal dimensions of your boat and, if so, how they are measured? The spec. sheet for my last boat stated an internal width of 84cm but I am not sure if they measure that at deck level or if it is the min. distance between the tubes.
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Old 24 March 2016, 08:18   #4
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here you go cheers
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File Type: pdf MERCURY HD 365.pdf (408.8 KB, 30 views)
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Old 24 March 2016, 08:18   #5
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The main reason for this was 4 stroke engines.
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Old 24 March 2016, 08:56   #6
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Excellent, thanks for that. Now I see the internal width specified is between the tubes as the tube diameters plus the width specified equals the total width. Seems that these type of boats have got wider to allow for the bigger tubes.

That makes sense, 4 strokes are quite heavy, although my latest Suzuki 20hp isn't as bad as they used to be.
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Old 24 March 2016, 09:00   #7
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>>>does it make much difference regarding a dry ride?

Yes and to the overall feeling of security out in iffy sea states.
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Old 24 March 2016, 09:11   #8
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All boats differ, eg the Aerotec has a very narrow beam whereas Suzumar boats are big open wide things.....but the bigger tubes are always a better idea in my book
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Old 24 March 2016, 09:32   #9
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Thanks. I will aim for a boat with reasonably sized tubes then. Never had a boat with less than 45cm diameter tubes and, as mentioned, they seemed fine and the ride was as dry as it can be for a SIB I suppose.
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Old 24 March 2016, 09:36   #10
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In My opinion bigger tubes is not allways better. If the boat is fitted with an oversize tubes I believe it will act like a reverse chine and will result in a harsher ride in adverse sea conditions. My Valiant dr 490 has a tube diameter of 0.48 M. I suspect that these are a bit big for the size of the hull but great to sit on.
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