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V Twin |
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G.R.F. 
Really should get out more 
Joined: 10 Aug 08 Location: United Kingdom Online Status: Offline Posts: 4028 |
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 Topic: V TwinPosted: 21 Jan 11 at 11:40am |
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Yes I've seen that before when I was trying to calculate a 'rough guide' to planing surface v sailor weight on windsurf boards, we ended up with board width = 10% of sail size and board volume in litres = approx sailor weight in kilos.. Which was when boards started being marketed by volume rather than length. Then width came in and screwed the equation. There is nothing absolute, it's like flight, the more you look into it, the more 'theoretical' equations appear and the more you realise no-one knows, well, not absolutely. Take all the calculations then take them to the Red Sea and Compare the result with what happens on Q.M. reservoir. Same with wind and sails, test a sail here in the cold damp atlantic breeze, then try and get it to perform the same in the faster less dense saharan spin off. At the end of the day, the only answer ever is 'suck it and see' and even then it wont taste the same to someone else.
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Posted: 21 Jan 11 at 10:56am |
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Dan Holman will be well familiar with Savitsky's work on planing hulls, but just for you grumph... http://www.boatdesign.net/forums/attachments/boat-design/12703d1177638152-savitskys-papers-savitsky_brown_76.pdf |
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G.R.F.
Really should get out more
Joined: 10 Aug 08 Location: United Kingdom Online Status: Offline Posts: 4028 |
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Posted: 21 Jan 11 at 9:59am |
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I'm not sure if I mentioned, this is a second attempt, the first failed badly by being a tad too small and not that well built (I used wood), I'll try and find a picture of the now infamous 'Water Pusher' as my nephew christened it at Weymouth speed week.
  It failed because the nose didn't contain enough volume to spring the device onto the plane in order to engage the twin surfaces. It was overwhelmed by mast foot pressure, something I've come to realise is even greater on a dingy than it is on a board where it is at least dynamic. The down force on the nose of even that RS100 is immense even in relatively light wind, I noticed it once whilst trying to trail it rigged down the beach in an offshore wind, virtually impossible to lift the tailor in the puffs, which is why the nose of the V Twin has so much volume, which, once on the plane should come clear. Obviously it will bounce down in waves, but again hopefully with so much comparitive volume it should quickly bounce back up again with out going down the mine. Anyway that's my thinking and how I've come to all this. |
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Posted: 21 Jan 11 at 9:50am |
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He He.
Actually he does comment on the boards and how good they are at making hulls.
He designed the Tasar ( you don't need too much training for that ) and it was his comments about hull "fine entry" and drag that lead to the Tasar hull design that lead me to believe that you might have trouble when it gets wavey with your current diagram design.
And given your design brief I thought you might be interested.
It's your requirements for "all round" conditions performance I think you may have trouble.
Interesting though.
Good Luck.....(kicking my backside that is)
 Timg
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winging it
Really should get out more
Joined: 22 Mar 07 Online Status: Offline Posts: 3958 |
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Posted: 21 Jan 11 at 9:45am |
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The only plate I care about is the titanium one going in the back of my hand any time soon.....good excuse to get out of the ironing for another year though. Early moth info, inc tunnel hulls. |
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the same, but different...
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G.R.F.
Really should get out more
Joined: 10 Aug 08 Location: United Kingdom Online Status: Offline Posts: 4028 |
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Posted: 21 Jan 11 at 9:31am |
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Not a big fan of anyone called "Bethwaite". Believe it or not, I do know a bit about 'drag' on "Hulls" have been wrestling with it on and off for close on forty years, both engine and sail powered, as an amateur and in a professional capacity, so in my total arrogance, I'm minded there's not much I'd learn from some Convict who designed a boat that clearly doesn't work unless you have the rest of your life to spend practising and only then if the sea doesn't move around too much. I'd trust our boys over Bethwaite any day of the week
Whereas I don't know if two split planing surfaces give better support than the sum of their surface thereby permitting reduced contact over a wider area.
This will either prove or disprove that theory as well as giving me something fast and easy to play with. One thing I am reasonably confident in achieving.. and that is kicking D1 backside all over the Ocean.  Edit: Doesn't look like many other folk like Bethwaite either judging by his facebook page Edited by G.R.F. - 21 Jan 11 at 9:39am |
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Posted: 21 Jan 11 at 9:01am |
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Graham,
I can't for the life of me remember if you dislike the "High Performance Sailing" book by Frank Bethwaite or not.
However, I dug it out last night and read the chapter on "HULLS" with your project in mind and there was a lot of stuff in there about waves and the drag of a hull etc.
I really think it would be worth a read.
Cheers
Timg
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G.R.F.
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Joined: 10 Aug 08 Location: United Kingdom Online Status: Offline Posts: 4028 |
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Posted: 21 Jan 11 at 8:34am |
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It's just you, is that a plate I can see in the sink that needs washing?
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G.R.F.
Really should get out more
Joined: 10 Aug 08 Location: United Kingdom Online Status: Offline Posts: 4028 |
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Posted: 21 Jan 11 at 8:32am |
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It's worked out about 2m wide, the split in .67 mtr bits, the hulls at the rear are .67 so is the gap in the middle so by the time it's splayed a bit it was 2.01 then with the racks either side it should be about 2.60.
I think Dan's narrowing it down a bit to reduce the wetted surface. Yes , I guess there will be enough room for two but that's not the intention, the extra width is to make up for light folk not having the leverage and to ensure it stays upright with a large amount of canvas. I suppose it could be made modular to suit one or two, now there's a thought, one concept you just decide what you want it to be. Single handed hiker, Trapeze, or Twin. It's conceivable I guess. If the darn thing works of course.
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timeintheboat
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Joined: 01 Feb 07 Location: United Kingdom Online Status: Offline Posts: 615 |
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Posted: 21 Jan 11 at 8:23am |
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Is it going to be wider than a wide dinghy like a Merlin or N12, does that mean two berths not one?
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Like some other things - sailing is more enjoyable when you do it with someone else
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