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Old 04 September 2006, 12:56   #1
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Tubes in the water under way. Drag or stability?

Hello,

Something I have been talking to a number of people about.
"Should" the tubes be touching the water surface when your RIB is under way - or not?

Obviously different naval architecs do it differently and there are probably
pros and cons for each design.

Use the difference between a Redbay and a Parker or Boomeranger as an example.
The Redbays look like they touch the water at all times, or is very close
(never been in one so I could be wrong there).
Many other Ribs are well above the water surface when under way.
Some companies I have spoken to think creating drag by tubes touching the water is not only bad but dangerous.
The Redbays have such a great following on this site so it can't be that simple either I guess.

Ah well,
Your comments are appreciated.
TIA and regards
Janne A.
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Old 04 September 2006, 13:37   #2
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Well my thoughts on this are that if you have a RIB with tubes in water you will get more stability whilst underway but will compromise performance (drag).

Obviously with the tubes out the water then you'd get less stability whilst underway but more performance.

Now you get two choices of wheather you want a RIB with tubes in water at displacement speeds or not.

For us Solent RIBbers and anyone taking to the high Sea's I would guess that the Tubes in water whilst stationary and at displacment speeds and tubes out of water when planing would be the Ideal choice (cake and eat it).

Divers might have a different Idea on setup, but I wouldn't have a clue about that.
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Old 04 September 2006, 13:49   #3
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There are much more experienced ribbers than I but my experience with sports ribs having had 5 have had no adverse effects by haveing the sturn end of the tubes(sponsons)trailing in the water whilst under way..This however does not mean under certain circumstances would not be a problem comparded to one that does not.If that makes sense.For those dealers to say that and have some crederbility perhaps could explain in more detail.
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Old 04 September 2006, 13:57   #4
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the way i understand it is the sponson should just touch the water when at rest to optimize stability but when underway should be clear of the water so as not to make the tubes ware as they get dragged through the water at 45knots.
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Old 04 September 2006, 13:59   #5
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Quote:
Originally Posted by no fear
If that makes sense


i fynd dat ifn yew av wan toob stikkin owt morr thann de uvver yew cann gow rownd de iyal of wite wivowt oldin de stearin weel.

gArf
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Old 04 September 2006, 15:16   #6
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Redbay

This picture seems to show tubes more than touching under way...no?
http://www.redbayboats.com/images/sf...e/DSCN5936.jpg

Just curious.
My priority would be stability and safety under way in rough seas BTW.
Stability when at rest as for diving is no priority for me, albeit obviously
not a bad thing..

best
jtm
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Old 04 September 2006, 15:36   #7
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Just how much "stability" do you need? I reckon many inboard ribs would need to be approaching 90 degrees before they turned over. And one with toobs out of the water (ie, a higher gunwhale) would be the ones that can roll further before going over. Toobs too low mean that in a hook, or roll situation, the toob could dig in.

Stability of a planing vessel underway is from dynamic lift of the hull form, not displacement. Obviously there is a strong argument for diving boats to have toobs low to the water(while stationary), but beyond a specific task related need like that, it largely comes down to personal preference.
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Old 04 September 2006, 15:36   #8
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P.S. Cos of the way the tube will deform while underway in the water, it's gonna be really really inefficient.
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Old 04 September 2006, 15:48   #9
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My boats tubes just kiss the water at speed AND at rest - I would like more stern lift to lift them a bit further out - they must increase drag a bit so maybe a different prop or the trim tabs will help?
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Old 04 September 2006, 16:15   #10
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study the photo's of the fast one's, as regards tube position they must have the drag factor sorted out...ie scorpion race boat, revenger, ring, phantom, cookee's, adam's rib, ocke mannerfelt, and the master fabio buzzi, but then they are all fast hull's anyway and some stepped
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