I was just thinking about the shape of modern 12's, and the hulls seem to be more oriented towards heavy weather performance. why has nobody come up with a displacement 12 that would surely dominate in light winds?
I have come up with this model as a possible idea
could i driect you towards the class rules?
I believe it is within the class rule, what do you mean?
Can I suggest you read sections on hollows and on gunwhale overhangs.
Unless things have changed you are not allowed any hollows aft of mid-length and the gunwhale overhang outboard of the sheerline its limited to 50mm.
The flare on this hull must be either hull or gunwhale so it must contravene one of those.
N12s are quite good at getting minimum waterline beam on a 2m wide hull with no hollows. It is one of the main challenges of the design. Another constraint to look out for is the rise of floor which whilst intended initially to avoid boats becoming overly narrow on the waterline, now measures a point about 35mm above the design waterline. Most hulls are spot in the minimum rise of floor by design and some are bumped to meet it. Feeling Foolish is a notable exception.
The "no hollows" rule was (I think) introduced to prevent the need for expensive cold moulded boats and was prompted by the arrival of the 505 with its flared topsides. (Makes it a late '50s rule).
Since we no longer have anything in the rules about "catering for those of limited means" (which was in the first couple of lines of the rules initially) and since we can mould concave surfaces as easily as convex ones, perhaps we should think about deleting the hollows rule.
It would make for a more interesting looking boat - only time will tell if it is faster but it would be interesting to allow someone to try it!
sothe hull isn't allowed to be concaved?
thats about the long and short of it. No hollows.
could somebody please explain the gunwhale overhang rule ?
This is an interesting concept and one that I certainly had to get to grips with in producing my latest creation N3503. The boat has no decks in the conventional sense, the topside of the hull simply comes up and rolls over to form a lip that constitutes the deck. However, as Derek has pointed out the deck or gunwale is not allowed to extend more than 2'' outside the shearline athwartships. Thus in order to create a wider lip to give us something to sit on I'm planning to add a strip that stands proud of the hull surface and runs fore aft around the hull 75mm below the shear line. The strip is only 1/8'' thick so it doesn't contravene the "no hollows" rule. The consequence of adding the strip is that the shearline is pushed more than 1/2'' outside the projection of the hull topside and the lip can therefore be wider than 2'' and is thus made more comfortable to sit on. This, I think, is the limit of what you can do at the moment.
From a construction point of view the boat was easier to build because the need to deck it was negated. However, having sailed the boat already this season we have noticed that it's easier to fill it up with water when tacking if we're not careful.
If someone remindes me how to put a photo on the discussion group I'll try and put one of the boat on here.
In summary it would be interesting to see what sort of hull shape one could come up with if the hollows and decking rules were removed but the rise of floor rule retained. As Derek has noted it shouldn't make construction any more onerous in this day and age: perhaps some scope for development, it would be interesting hear other peoples' thoughts particularly those on the technical committee!
Marcus
it would be really interesting...it may lead to a boat almost like an international moth for two people?!
Marcus,
Any pics of your boat during / after build? A description can be hard to follow - annotating a pic to show what you mean would be cool 8)
The RS300 type shape could also be a possibility - not sure how close this is to the rules currently. I'm not sure many would take a risk and why the Class seems to have only a small number of designs sailed at the top, FF is dominating the new builds now.
THG
I'm not sure that you would want to end up with a moth like boat; as I've said I think it might be worth revisiting the hollows and decking rules to give the designer more freedom above the waterline but if you remove the rise of floor rule as well then there's nothing to stop the boat becoming very narrow underneath and the consequences of this are that the boat would soon become unmanagable!
The best arguments for relaxing the aforementioned rules will, I guess, be based upon possible simplification of construction, developing alternative buoyancy disposition and evolving performance.
Marcus
[quote by=Marcus (Guest) link=Blah.cgi?b=Cool1,m=1196853525,s=10 date=1196863750]if you remove the rise of floor rule as well then there's nothing to stop the boat becoming very narrow underneath and the consequences of this are that the boat would soon become unmanagable!
Marcus [/quote]
If that were the case then surely the designs would self-limit to those dimensions which are not unmanagable. The designers would be free to experiment in order to find these limits. Or am I talking garbage as usual? ;)
Jim.
Geoff Camm and myself drew up something very similar, which could have been legal a few years ago (circa 2004) The rules have been tightened up to stop something like this being built.
Mike..
Why.. what evil was prevented by the tightening up?
Roger
Weren't the rules changed to prevent a 'Vortex' style 12 with twin 'hulls'?? But Vortex is a real dog in light winds and tacking round.
The rule change to stop the Vortex style hulls also eliminated some other options...
Either way, Timmy is right! sail better!
...and you can add to the list of designs getting top 10 places -
...."Bouncer" or something that once looked like Bouncer.
Maybe 'Bouncier'?
Double bounce?
Rebound?
Ok, of course we won't get to a Twelve looking like the boat at the top in the foreseeable future, but what do people think it would be like to sail if it was ever built? As a two-handed Moth type hull, would it tack on the river? and how would it plane? And would it be very much more difficult to sail than a current 12? Mikey - you have the Moth experience ...
Mike D
N3496
Not a 12 but stick a snout on it and you've got a Cherub.
Lately though, the Cherubs have seem to have moved away from solid wings and gone to bars as they have less windage and waterage (........well if you can have windage, why not!?)
John Claridge mada a 2 man Moth called the Tiger Moth
http://uk.geocities.com/dinghydata/TigerMoth.htm
John (1662)
[quote by=Mike_Day link=Blah.cgi?b=Cool1,m=1196853525,s=20 date=1196969343]Ok, of course we won't get to a Twelve looking like the boat at the top in the foreseeable future, but what do people think it would be like to sail if it was ever built? As a two-handed Moth type hull, would it tack on the river? and how would it plane? And would it be very much more difficult to sail than a current 12? Mikey - you have the Moth experience ...
Mike D
N3496[/quote]
I've no idea really, teamwork would be key, it would no doubt be difficult, but as the waterline beam wouldn't be much narrower than normal I wouldn't say it would be outrageous - there would just be no safety margin when it heels as the buoyancy wouldn't ramp up.
What strikes me as strange in this debate is that the shape shown is intended to be a displacement hull, so intended for light weather or inland. The sections are almost parallel and look very skiff-like. This means lots of wetted area for the required displacement.
There is even less displacement when heeled than when upright so if you roll it to tack, it will stop because it will sink deeper into the water, the corner of the transom and probably the wing will dig in.
If you are seeking to make a displacement hull, more rocker and some move volume in the topsides around the crew c-of-g would help. This will lift the ends out when you tack, shortening the boat as it tacks and losing less speed as you drag the ends through the tack.
If you take the hull shape and work out where the design displacement puts the waterline with the sheerline on the water, it will show you how long the waterline is when you tack. Short is actually good for tacking!
Baggy has no displacement in the topsides and a very low sheer so hard to tack.
Modern boats have less rocker and so tend to be harder, or at least slower to tack.
A great favourite for inland sailing is Pipedream which has a fine U'd entry and a straight rocker forward but loads of bussle (rocker in the last ~3ft) and a fairly small transom together with good volume in the topsides around 8-9 ft from the bow.
If you can find one it would be worth a look.
Does anyone have a set of Pipedream lines?
I have a set of Pipedream 'plans'. They are just co-ordinates and detail sketches rather than lines but should be easy to convert. I'll try and think of a way to copy them if anyone is interested
I would be interested in pipe dream plans. You can get me on angus3 at tesco dot net