New Posts New Posts RSS Feed: V Twin
  FAQ FAQ  Forum Search   Register Register  Login Login

V Twin
 Post Reply Post Reply Page  <1 9495969798 142>
Author
  Share Topic Share Topic  Topic Search Topic Search  Topic Options Topic Options
RS400atC View Drop Down
Really should get out more
Really should get out more


Joined: 04 Dec 08
Online Status: Offline
Posts: 3011 		Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Topic: V Twin
    Posted: 25 Apr 12 at 9:52am
Originally posted by ASok

Sealing a mast has to be the way forward. I don't care what the calculations say about weight of water in water etc. but when you try and right a boat that has a mast full of water its near on impossible to get from near 90degrees to upright.

Previous points are very valid regarding the need for this boat to invert if it goes over. The sheer size of the thing and its design as a light weight - its going to drift off down wind quicker than you'd every be able to swim.


A Dart of course has a very high volume mast. A modern carbon dinghy stick is quite different.
Most of the boats I sail have internal halyards, so sealing is not an option. The RS800 is the exception, I think that is supposed to be sealed but leaks a bit, but we don't often invert.
On the 400, righting is only a problem when the mast is in the mud. I keep meaning to drill some more drain holes in the foot so it empties as the boat comes up, to avoid that pendulum effect of a mast full of water, but TBH, we don't capsize enough to put this in the 'urgent' pile.
Back to Top
johnreekie1980 View Drop Down
Groupie
Groupie


Joined: 11 Jun 07
Online Status: Offline
Posts: 91 		Post Options Post Options   Quote johnreekie1980 Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 10:23am
If we assume the mast is a 50mm diameter round section for simplicity then it has a volume of around 1.9litres per metre length. This is probably an overestimate as it does not include for the tube thickness. Therefore a 7m sealed mast may have around 13 litres of bouyancy. This is probably quite close to the weight of the rig. Given how wide the boat is for its mast height then I would imagine that the boat would be a fair bit past 90 degrees when equilibrium kicks in.
 
I would not go with air in the wings as with the boat on its side the the centre of effort of the boat may well be on the wrong side of the lift from the air in the wings thus making it turtle even quicker. This will then have the side effect that when turtled the wing will be even harder to get the wing under water to get back to the 90 degree position.
 
As is seen in nearly all high performance boats the best way to right from a turtle is to get the windward side lifted out of the water and let the wind do the work. It I capsized a 49er or a Musto then the quickest way was often to go through turtled instead of righting the boat with the mast downwind.
 
GRF will find out to his dismay that this type of boat was never likley to be righted from turtle in any conditions with his 60kg even with a righting line and him standing on the wing bar edge. This is a simple moment calculation around the centre of effort of the boat at any given angle calculations. My 70kg could not right a 49er on my own so given the size of the twin he has no chance.
 
As with most things in life it is better to do the maths prior to the endeavour and not after.    
Back to Top
RS400atC View Drop Down
Really should get out more
Really should get out more


Joined: 04 Dec 08
Online Status: Offline
Posts: 3011 		Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 11:03am
Originally posted by johnreekie1980

.....
 
GRF will find out to his dismay that this type of boat was never likley to be righted from turtle in any conditions with his 60kg even with a righting line and him standing on the wing bar edge. This is a simple moment calculation around the centre of effort of the boat at any given angle calculations. My 70kg could not right a 49er on my own so given the size of the twin he has no chance.
 
As with most things in life it is better to do the maths prior to the endeavour and not after.    


I think there is mileage in thinking less about the weight of the rig, and more about moving the cenre of buoyancy towards the rig when the boat is on its side.
The leverage of your mast by your sums is 45.5kg.m The leverage of a GRF might be 60kgm if he can get 1m from the centre of buoyancy, but moving the centre of buyoancy a small distance makes a huge difference.
On another note, capsizing and deliberately inverting could be very expensive if the water is not as deep as you expect. As it's your deliberate action to invert, it might not be covered by insurance!
Back to Top
tickler View Drop Down
Really should get out more
Really should get out more


Joined: 03 Jun 07
Location: Tunstead Milton
Online Status: Offline
Posts: 895 		Post Options Post Options   Quote tickler Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 11:12am
I just thought. the boats that come up easily are the ones that flood. As I said earlier  the V twin on its side with its bulk sticking up in the air and its mast pointing down will never stay like that.....if it is on its way up or on its way down. How depressing if you get the mast up from inversion only for it to go back down again. How about the twin hulls being deck-less with mesh on top then the hull on the undeside would just sink laying the mast allong the water. With no transom (s) it would drain a treat. We had a Javelin which we frequenly capsized, usually kite up, and I remember swiming round getting it down with the boat floating on its side, no worry about inversion. It rolled up dead easy as well and we just swam back in.....took a bit to get the water out though. The V twin design would have a much smaller water capacity. I suppose this solution would mean starting again from scratch......"I'll get me coat"
Back to Top
RS400atC View Drop Down
Really should get out more
Really should get out more


Joined: 04 Dec 08
Online Status: Offline
Posts: 3011 		Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 11:20am
Originally posted by tickler

I just thought. the boats that come up easily are the ones that flood. As I said earlier  the V twin on its side with its bulk sticking up in the air and its mast pointing down will never stay like that.....if it is on its way up or on its way down. How depressing if you get the mast up from inversion only for it to go back down again. How about the twin hulls being deck-less with mesh on top then the hull on the undeside would just sink laying the mast allong the water. With no transom (s) it would drain a treat. We had a Javelin which we frequenly capsized, usually kite up, and I remember swiming round getting it down with the boat floating on its side, no worry about inversion. It rolled up dead easy as well and we just swam back in.....took a bit to get the water out though. The V twin design would have a much smaller water capacity. I suppose this solution would mean starting again from scratch......"I'll get me coat"

No need to start from scratch, just cut some holes in the deck and install a few bulkheads. If the sailing performance is what's wanted, the buoyancy can be sorted. A flooded compartment would drain through an Elvestrom bailer once moving. Perhaps a semi-self draining double bottom would work.
Don't let this issue distract from evaluating the hull shape!
Back to Top
blaze720 View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 28 Sep 05
Location: United Kingdom
Online Status: Offline
Posts: 1635 		Post Options Post Options   Quote blaze720 Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 11:34am
Greame

Maybe a trip to the local woods with a chainsaw might help .... we used to use the wooden stuff once upon a time and you would not have to play around with all those balls !  LOL

.. and if that does not appeal then use the chainsaw on the hull ....  er ... if only to reduce its buoyancy of course   Wink 

Mike L.
Back to Top
rogue View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 04 Dec 08
Location: United Kingdom
Online Status: Offline
Posts: 978 		Post Options Post Options   Quote rogue Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 11:37am
Graeme- I sent you a box of matches, the day has NOT come yet to use them.

Worse case scenario- you're restricted sailing when there's safety cover and in fairness you're unlikely to call upon that resource the more you sail it.  If you'd bought another skiff type boat, then the chances are you would have got more than your money's worth out of them, so don't worry about one crappy incident, chalk it up and get the boat back out there again... enough with the pigging around.

Back to Top
Guests View Drop Down
Guest Group
Guest Group
Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 11:45am
Quite. I think you just have to accept that a boat like that will be hard to right, but also (hopefully) hard to capsize. So just make sure there is safety cover around and concentrate on how it performs the right way up.

Letting the kicker off and uncleating the jib might help a bit.
Back to Top
G.R.F. View Drop Down
Really should get out more
Really should get out more


Joined: 10 Aug 08
Location: United Kingdom
Online Status: Offline
Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 12:21pm
A lot to sift through here, some good ideas and excellent hindsite, a skill I'm becoming increasingly expert at.

The boat has bulkheads, I guess it wouldn't be difficult to ensure the side tanks flooded, but then they would both have to flood, then er wouldn't that be called 'sinking?'.

The reason all this is taking the time it is, is because I wouldn't dream of taking it out without rescue cover and had already briefed the boys in the boat that it would likely be difficult to right and if I did go over, only sort me out after any or everyone else is sorted.

I'm not sure about the catching up with it, I've swum miles in my time chasing windsurf boards trapped in waves, and downed kites blowing out to sea, I can't believe a dinghy would elude me, but then my arrogance has punished me considerably already at my early assertion 'dinghy sailing how difficult can it be?'
 In fact I've lost boards only twice in my time, once like Hector in a dry suit (why I don't favor death bags) on Queen Mary when my rig separated from a displacement board (very round and sticky up) which sailed away merrily propelled by its centreboard and the other time in a force 10 squall at Hayling mid Grundig Marathon when the entire board and rig just blew up in the air and away, never saw it again, what you get sailing a board called a Superlight in a hurricane.
However On launching the twin on thursday into a big shore dump with a wind that had just swung dead offshore following a squall and had me temporarily washed off the back luckily only up to my waist so was able to jump forward and catch onto it, but remember wondering wether a surf leash might be an idea, because without an idiot like me on it, it wouldn't tip over, it would have been France next stop, so it is more problematic if ever we were to become separated, it would definitely carry on and probably faster and more efficiently without its crap helm slowing it down.

So some conclusions that I now draw from all this.

1) Dinghys are made to go over deliberately easily so they can be easily righted, I wish someone had told me that.
2) If they do go over it is better that they sink, at least partially, (now I understand the logic behind the Alto, not that it goes over often but if it does it comes up full of water which always irritated me in the past)
3)Windsurfing rigs that just fall over flat are so much better than these stupid things with wires holding them up, maybe I should just rethink how the mast is held up and fix it so it falls over rather than the whole thing going over, it would also solve the getting away from me problem if I did happen to fall in.


Edited by G.R.F. - 25 Apr 12 at 12:23pm
https://www.ease-distribution.com/
Back to Top
simonrh View Drop Down
Posting king
Posting king


Joined: 10 Jan 10
Location: United Kingdom
Online Status: Offline
Posts: 186 		Post Options Post Options   Quote simonrh Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 12:29pm
Didn't the catapult have shrouds that allowed you to leave the rig partially in the water when righting?
Vortex Asymmetric 1064
Dart 18 7118
Smartkat stunt sailor extraordinaire
Back to Top
 Post Reply Post Reply Page  <1 9495969798 142>

Forum Jump Forum Permissions View Drop Down

Bulletin Board Software by Web Wiz Forums® version 9.665y
Copyright ©2001-2010 Web Wiz
Change your personal settings, or read our privacy policy