Reply
 
Thread Tools Search this Thread
 
Old 04 September 2006, 11:56   #1
Member
 
Country: Sweden
Town: Stockholm
Boat name: Sea Dachshound
Make: ..shopping for a RIB
Length: 5m +
Engine: Merc 90 4-stroke
MMSI: 265585460
Join Date: Jul 2003
Posts: 88
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.
__________________

__________________
houser is offline   Reply With Quote
Old 04 September 2006, 12:37   #2
Member
 
Hightower's Avatar
 
Country: UK - England
Town: Fareham
Length: 6m +
Join Date: Sep 2003
Posts: 7,855
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.
__________________

__________________
Andy

Looks Slow but is Fast
Member of the ebay Blue RIB cover club.
Hightower is offline   Reply With Quote
Old 04 September 2006, 12:49   #3
Member
 
Country: UK - England
Town: Essex/Vendee
Boat name: shockwave,Voluntry 2
Make: Pac 22/ searider5.4
Length: 6m +
Engine: 180hp turbo,yam 90
Join Date: Nov 2004
Posts: 1,015
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.
__________________
PeterR is offline   Reply With Quote
Old 04 September 2006, 12:57   #4
pop
Member
 
Country: New Zealand
Town: Paihia
Make: Scorpion
Length: 8m +
Engine: indoard yam 420 sti
Join Date: Feb 2006
Posts: 383
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.
__________________
pop is offline   Reply With Quote
Old 04 September 2006, 12:59   #5
exspyrd trayd membir
 
The Garfish's Avatar
 
Country: Ireland
Town: inn wiliks hed
Make: Redbay 6.5
Length: 6m +
Engine: Twin Etec 90hp
Join Date: Aug 2003
Posts: 962
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
__________________
luk arfter numbir wan, downt stepp inn numbir too
The Garfish is offline   Reply With Quote
Old 04 September 2006, 14:16   #6
Member
 
Country: Sweden
Town: Stockholm
Boat name: Sea Dachshound
Make: ..shopping for a RIB
Length: 5m +
Engine: Merc 90 4-stroke
MMSI: 265585460
Join Date: Jul 2003
Posts: 88
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
__________________
houser is offline   Reply With Quote
Old 04 September 2006, 14:36   #7
Member
 
Country: UK - England
Town: Farnborough
Boat name: Eleven
Make: Arrow
Length: 8m +
Engine: 557cu, 700hp
Join Date: Jul 2003
Posts: 1,255
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 is offline   Reply With Quote
Old 04 September 2006, 14:36   #8
Member
 
Country: UK - England
Town: Farnborough
Boat name: Eleven
Make: Arrow
Length: 8m +
Engine: 557cu, 700hp
Join Date: Jul 2003
Posts: 1,255
P.S. Cos of the way the tube will deform while underway in the water, it's gonna be really really inefficient.
__________________
Matt is offline   Reply With Quote
Old 04 September 2006, 14:48   #9
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
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?
__________________
codprawn is offline   Reply With Quote
Old 04 September 2006, 15:15   #10
Member
 
Country: UK - England
Town: poole
Make: ring
Length: 5m +
Engine: 150xr2
Join Date: Mar 2006
Posts: 180
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
__________________
ribit is offline   Reply With Quote
Old 04 September 2006, 15:22   #11
Member
 
Country: UK - England
Town: Farnborough
Boat name: Eleven
Make: Arrow
Length: 8m +
Engine: 557cu, 700hp
Join Date: Jul 2003
Posts: 1,255
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.
__________________
Matt is offline   Reply With Quote
Old 04 September 2006, 15:31   #12
Member
 
Country: UK - Wales
Town: Milford Haven
Boat name: Various
Make: Commercial
Length: 10m +
Engine: Screw / Voith / Jets
Join Date: Sep 2002
Posts: 792
Send a message via MSN to 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 (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
__________________
Flickr Photos
Youtube Videos
Alex Brown is offline   Reply With Quote
Old 05 September 2006, 02:42   #13
Member
 
Country: UK - Scotland
Town: Inverkip
Make: Redbay 11m Cabin
Length: 10m +
Engine: 2 x Yamaha422Sti 275
Join Date: Feb 2003
Posts: 567
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
__________________
Hard or Soft it's never BIG enough
Andy Gee is offline   Reply With Quote
Old 05 September 2006, 02:53   #14
Member
 
Country: UK - England
Town: Poole
Length: no boat
Join Date: Jul 2001
Posts: 673
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
__________________
MarkWildey is offline   Reply With Quote
Old 05 September 2006, 03:01   #15
Member
 
Country: UK - England
Town: Lee on the Solent
Boat name: Saintlee
Make: Leeway
Length: 6m +
Engine: Evinrude DI 115
Join Date: Jul 2006
Posts: 325
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!
__________________
Lostboy is offline   Reply With Quote
Old 05 September 2006, 03:09   #16
Member
 
Jono's Avatar
 
Country: UK - England
Town: Over here
Boat name: S.S. Nobstick
Make: Three Wise Monkeys
Length: 3m +
Engine: 44lbs of thrust....
Join Date: Nov 2003
Posts: 2,127
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...
__________________
Jono is offline   Reply With Quote
Old 05 September 2006, 04:36   #17
Member
 
Country: Sweden
Town: Stockholm
Boat name: Sea Dachshound
Make: ..shopping for a RIB
Length: 5m +
Engine: Merc 90 4-stroke
MMSI: 265585460
Join Date: Jul 2003
Posts: 88
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
__________________
houser is offline   Reply With Quote
Old 05 September 2006, 11:54   #18
Member
 
Country: UK - England
Town: Liverpool
Length: 10m +
Join Date: Feb 2006
Posts: 238
The RNLI's Atlantic 75's toobes seem to angle upward at the transom, to the stern.
Attached Thumbnails
Click image for larger version

Name:	atlantic 75.jpg
Views:	180
Size:	74.4 KB
ID:	21974  
__________________
Endeavour is offline   Reply With Quote
Old 05 September 2006, 12:45   #19
DM
RIBnet supporter
 
Country: UK - England
Boat name: Little Wing
Make: Searider 5.4
Length: 5m +
Engine: Tohatsu 90
Join Date: Aug 2002
Posts: 1,067
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
DM is offline   Reply With Quote
Old 05 September 2006, 12:49   #20
JIY
Member
 
Country: UK - Scotland
Town: Largs
Boat name: Spitfire
Make: XS850
Length: 8m +
Engine: 2 x 200 Verado
MMSI: 235905304
Join Date: May 2004
Posts: 174
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.
__________________

__________________
JIY is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 04:38.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
×