Tubes in the water under way. Drag or stability?

houser · 04 September 2006, 17:56

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.

Hightower · 04 September 2006, 18:37

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.

PeterR · 04 September 2006, 18:49

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.

pop · 04 September 2006, 18:57

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.

The Garfish · 04 September 2006, 18:59

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

houser · 04 September 2006, 20:16

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

Matt · 04 September 2006, 20:36

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.

Matt · 04 September 2006, 20:36

P.S. Cos of the way the tube will deform while underway in the water, it's gonna be really really inefficient.

codprawn · 04 September 2006, 20:48

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?

ribit · 04 September 2006, 21:15

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

Matt · 04 September 2006, 21:22

Suspect they're catching a bit of spray, rather than running in/through the water, whereas that redbay posted further up is running massively wet.

Alex Brown · 04 September 2006, 21:31

I am baffled as to why people need tubes, or what their purpose is if they don't touch the water at all (even at rest)

My tubes are well into the water when at rest which gives plenty of stability when it's nice and choppy. They do just touch the water at speed, but only right at the stern - as long as the tubes are pumped up to the required pressure, they're pretty solid, when slightly down, they make a slight drumming noise, and there is drag giving about 2knots reduction in speed.

For safety boat work, the little Avon 4m's with filling hull, and the baby Humbers at the yacht club are great - always resting solid in the water, which makes working with dinghies very easy without any rocking from side to side.

-Alex

Andy Gee · 05 September 2006, 08:42

Quote:

Originally Posted by houser

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

I would think that picture has been taken from the end of the pier as the boat is comming off the plane. My toobs are much the same as Codders

Andy

MarkWildey · 05 September 2006, 08:53

Quote:

Originally Posted by Alex Brown

I am baffled as to why people need tubes.

-Alex

Interesting comment for a RIB site.

I think its so we, well not me any more, can

1) Dress up in dry suits
2) Carry EPIRB's
3) Eat Kendal Mint cake
4) Wear helmets

Cheers

Mark

Lostboy · 05 September 2006, 09:01

My understanding (which is a. limited and b. mirrored by a few on here) is that tubes should provide stability at rest and little or no drag, meaning they run clear, at speed. Mine do that nicely!

Jono · 05 September 2006, 09:09

Quote:

Originally Posted by MarkWildey

Interesting comment for a RIB site.

I think its so we, well not me any more, can

1) Dress up in dry suits
2) Carry EPIRB's
3) Eat Kendal Mint cake
4) Wear helmets

Cheers

Mark

Now, now Mr Wildey. You know that being a recent convert to the "Jonny Fuller" school of hardboats, the Guru covers the topic much more thoroughly than your feeble attempt at "Mickey taking". Where are the references to a) Camo Paint b) Bowie Knives and c) Parking bumpers? I am going to have to have harsh words with the Master if his disciples are going to show such weak understanding of the value of a good dig at blow-up boating, given such a golden opportunity...

houser · 05 September 2006, 10:36

That is possible, but all the pictures on the Redbay site I see indicate at least
that the tubes are touching the water at the stern. But I guess they could be very close...
This one shows how deep in the tubes are at rest.
http://www.redbayboats.com/images/sf...0/DSCN5790.jpg
and this one:
http://www.redbayboats.com/images/sf...0/DSCN5803.jpg
that tye are at least close, and should at least touch the waves as they go thru.
In fact all th epictures here:
http://www.redbayboats.com/news/newbuilds/redbay10.htm
Indicate the same. (love that boat BTW)

I guess I wonder if the Redbay people are using the tubes to create a slightly more comfortable ride, by using the tubes and sacrificing some drag...and was hoping some Redbay owners here could comment?

TIA and regards
Janne A.

Quote:

Originally Posted by Andy Gee

I would think that picture has been taken from the end of the pier as the boat is comming off the plane. My toobs are much the same as Codders

Andy

Endeavour · 05 September 2006, 17:54

The RNLI's Atlantic 75's toobes seem to angle upward at the transom, to the stern.

DM · 05 September 2006, 18:45

Quote:

Originally Posted by Alex Brown

I am baffled as to why people need tubes, or what their purpose is if they don't touch the water at all

Err..... it's called buoyancy. Lots of it. Lots and lots of it. In fact, so much, that even if you fill your rib with water, it will still function adequately whereas the average hardboater will be behaving like a demented budgie making strange flapping motions with his arms.

I've been thinking about having a whip round for the recent forum hardboat converts. We need to buy them a mirror, a bell and a nice piece of cuttlebone.

DM

JIY · 05 September 2006, 18:49

My experience with the various RIB types I've driven regularly (6.8 Ribcraft, 7.5 Tornado, 8.5 Tornado, 10m Humber and 11m cabin Redbay) leads me to believe that having the tubes touching the water at rest is important, so that the boat remains stable at rest when people are embarking, disembarking and generally moving around the boat. On my 7.5 Tornado with outboard the tubes were clear of the water at rest, which was be a real pain when crewmembers moved around when coming alongside. At times the resultant list and steering effect made for a less than rewarding arrival!

At speed, the hull shape is certainly the important factor in achieving stability, but the tubes still provide dampening and roll limitation during rougher sea crossings, even if they are clear of the water. The drawback of tubes touching the water, other than drag, is that the flanges can take a bit of a beating, with possible long term wear damage.