Reply
 
Thread Tools Search this Thread
 
Old 27 April 2010, 19:02   #1
Member
 
Country: UK - England
Town: gravesend
Boat name: curach/Earl
Make: seago/Lifeguard 4M
Length: under 3m
Engine: 3.3 marinar/10 hp
Join Date: Jul 2008
Posts: 802
Boyancy

Hi all this may be a silly question but when i go out on my small sib i feel relatively safe with the wooden deck if it filled up with water,but what would my 4m with a heavy 5 peice alloy floor do if flooded? would it float?
__________________
thornbackflound is offline   Reply With Quote
Old 27 April 2010, 19:04   #2
Member
 
Country: UK - England
Town: Dorset & Hants
Boat name: Streaker/Orange
Make: Avon/Ribcraft
Length: 4m +
Engine: 50Yam/25 Mariner
Join Date: Apr 2007
Posts: 5,551
Quote:
Originally Posted by thornbackflound View Post
Hi all this may be a silly question but when i go out on my small sib i feel relatively safe with the wooden deck if it filled up with water,but what would my 4m with a heavy 5 peice alloy floor do if flooded? would it float?
Yes it would - think of the force trying to hold a football under water in a swimming pool. I weigh 'several' stone and it keeps me up .Now think of how many footballs worth of air are in the tubes.............

If however you mean the floor - no
__________________
PeterM is offline   Reply With Quote
Old 27 April 2010, 20:41   #3
Member
 
Country: UK - England
Town: gravesend
Boat name: curach/Earl
Make: seago/Lifeguard 4M
Length: under 3m
Engine: 3.3 marinar/10 hp
Join Date: Jul 2008
Posts: 802
Quote:
Originally Posted by PeterM View Post
Yes it would - think of the force trying to hold a football under water in a swimming pool. I weigh 'several' stone and it keeps me up .Now think of how many footballs worth of air are in the tubes.............

If however you mean the floor - no
thats what i mean ,will the floor be so heavy with the weight of the water drag the sib down?
__________________
thornbackflound is offline   Reply With Quote
Old 27 April 2010, 20:52   #4
RIBnet admin team
 
Poly's Avatar
 
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: Tohatsu 30HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 11,627
Quote:
Originally Posted by thornbackflound View Post
thats what i mean ,will the floor be so heavy with the weight of the water drag the sib down?
No!

How much does the floor weigh? I'm guessing probably less than a person. So its just the same as throwing the floor overboard and having one more person on board.

When building a cardboard boat a few years ago we worked out that about 2 cubic feet of air will hold one adult completely out the water. So your tubes which are probably 20 cubic feet at least, will keep a lot afloat.
__________________
Poly is online now   Reply With Quote
Old 27 April 2010, 20:56   #5
Member
 
m chappelow's Avatar
 
Country: UK - England
Town: yorkshire
Boat name: little vicky
Make: avon ex RNLI
Length: 3m +
Engine: tohatsu
Join Date: Mar 2008
Posts: 2,310
most sibs/ ribs will stay afloat fully swamped and with the engine on and crew inside ,all you need to do is drop down the drain trunks and its inherant bouyancy should start to drain its self at least up to before it was swamped ,in theory though with waves filling the boat back up i doubt it in lumpy conditions ,even better though if the engines running and you can keep moving ,if you also have an inflatable keel that will give a fair amount of bouyancy and take a certain amount of volume space under the floor .just to give you some idea ,,rough guide is a 50 gallon oil drum when empty will support about a 1/4 ton ,,250 kgs so if you compare that with the tubes on you boat it will give you some idea just how much bouyancy there is in your boat , or think of even a 25 ltre drum and how much that takes to push under water ,,,
__________________
m chappelow is offline   Reply With Quote
Old 27 April 2010, 21:11   #6
Member
 
Country: UK - England
Town: gravesend
Boat name: curach/Earl
Make: seago/Lifeguard 4M
Length: under 3m
Engine: 3.3 marinar/10 hp
Join Date: Jul 2008
Posts: 802
Arh many thanks gents,yes i feel a lot safer now ,mind you my boat as you know is a lifegauard made boat,with inflatable keel,and crikey the tubes do take some air,she is nearly done so photos to follow real soon,trailer should be with me next wk and i have a 15hp marinar coming soon,,,,,,,,,,,,,,,, staying with original alloy flloor ,comes with it so is ment to be used sod making me own,lol whoopeeeeeeeeee ,deep joy
__________________
thornbackflound is offline   Reply With Quote
Old 27 April 2010, 22:38   #7
Member
 
m chappelow's Avatar
 
Country: UK - England
Town: yorkshire
Boat name: little vicky
Make: avon ex RNLI
Length: 3m +
Engine: tohatsu
Join Date: Mar 2008
Posts: 2,310
looking at some of the coding regs cat c and d your particular boat should ,, when fully swamped be capable of supporting its full outfit of equipment,the total number of persons it is allowed to carry and support enough mass to include the engine and a full fuel tank,
__________________
m chappelow is offline   Reply With Quote
Old 27 April 2010, 23:25   #8
Member
 
Country: Canada
Town: British Columbia
Make: Gemini
Length: 4m +
Engine: 40hp 2 str
Join Date: Oct 2003
Posts: 2,151
Quote:
Originally Posted by m chappelow View Post
looking at some of the coding regs cat c and d your particular boat should ,, when fully swamped be capable of supporting its full outfit of equipment,the total number of persons it is allowed to carry and support enough mass to include the engine and a full fuel tank,
...and still be quite stable! (unlike a hard boat)
__________________
prairie tuber is offline   Reply With Quote
Old 28 April 2010, 07:19   #9
Member
 
biffer's Avatar
 
Country: UK - England
Town: swanwick/hamble
Boat name: stormchaser
Make: custom rib
Length: 8m +
Engine: inboard/diesel
Join Date: Aug 2007
Posts: 3,848
from my diving days if i can remember, 1 litre of air equals 1 kilo of lift, it changes at depth but you're not going there, the big foot pumps we use are 10 litres, it don't take much working out you ain't going to sink
__________________
biffer is offline   Reply With Quote
Old 28 April 2010, 07:32   #10
Member
 
Country: UK - Wales
Town: Here
Boat name: doggypaddle
Make: Avon 5.4 Searider
Length: 5m +
Engine: yamaha 80
Join Date: Jul 2007
Posts: 1,107
Quote:
Originally Posted by biffer View Post
from my diving days if i can remember, 1 litre of air equals 1 kilo of lift, it changes at depth but you're not going there, the big foot pumps we use are 10 litres, it don't take much working out you ain't going to sink

Thats quite right Biff, but the relative density of seawater is greater than 1 so 1 litre of air will give you a kilo in fresh water, but is well over a kilo in seawater so even less likely to sink
__________________
I am usually not as green as i am cabbage looking.
doggypaddle is offline   Reply With Quote
Reply


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




All times are GMT. The time now is 11:06.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.