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blaze720 View Drop Down
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Posts: 1635 		Post Options Post Options   Quote blaze720 Quote  Post ReplyReply Direct Link To This Post Topic: V Twin
    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.
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RS400atC View Drop Down
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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!
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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"
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RS400atC View Drop Down
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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!
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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.    
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RS400atC View Drop Down
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Posts: 3011 		Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post 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.
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Iain C View Drop Down
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Posts: 1113 		Post Options Post Options   Quote Iain C Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 9:41am
Thinking laterally here...the easiest way to right a Contender is an Eskimo roll. Should you be trying to right it mast upwind, hopefully getting some wind under a rack and getting it flipped that way?  It's so bloody wide it would probably stop at the upright position and you would have your head in the air pocket between the hulls?
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tedm View Drop Down
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Posts: 174 		Post Options Post Options   Quote tedm Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 9:28am
Originally posted by bferry

How about using a wind surfing/kayak type lasoo tied to your foot or would this restrict moving about the boat/water?


Yikes..... sounds lethal.
It's a tricky situation, on it's side the boat is going to drift fast, but turtled it's difficult/impossible to right singlehanded.
Surely a lifting keel is the solution in this instance..... in fact you could make it canting, that would be cool :)
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rogue View Drop Down
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Posts: 978 		Post Options Post Options   Quote rogue Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 9:26am
I used to you a clip on my harness to hold my mainsheet when sailing my MPS... to be fair this was at a pond, so no real danger, I'm not so sure it would have been so wise had I done it on the sea.

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Posts: 1760 		Post Options Post Options   Quote maxibuddah Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 12 at 9:22am
the other problem with a mast with water in it, is not so much that it is difficult to get past level with the water but once it starts to come up it tends to keep going in a pendulum action capsizing the boat on top if you. I have seen this lots with phantoms.

I'm sure that a certain amount of water gets inside my sealed mast but it ain't much.

I can certainly see the benefits of getting a boat like the v twin to invert so it doesn't blow away, but lashing yourself to it might be almost as dangerous as not. if it takes off in a blow you would be dragged along with no way of getting free easily, and I don't think a knife would help as you are dragged through the water struggling to get a breath unless you are very calm. I would concentrate on trying to hold on to the mainsheet at the very least so you can pull yourself back to the boat.
Everything I say is my opinion, honest
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