Ex Machina
Super Anarchist
And some parallels there with nose jobs and cheek bone definition etc
New Carkeek 45 splashed
- Thread starter Matagi
- Start date
Jambalaya
Super Anarchist
I spoke with one of the regular crew today and they are happy with the test sails to date
As for the design it is aimed squarely at the various 600 mile races and in particular the Fastnet
As for the design it is aimed squarely at the various 600 mile races and in particular the Fastnet
carcrash
Super Anarchist
For certain, I spend money on beauty. My time off work is essentially focused on chasing beauty. And I think we can all agree that beauty is in the eye of the beholder. I am all for people buying boats that are beautiful for them!
And lots of aspects of beautiful boats are echos of distortions caused by rating rules, such as long ends, fractional rigs, narrow beam, reverse transoms, and so on.
So if somebody thinks reverse bows are beautiful, more power to them.
But from a functional point of view, GIVEN VERY LIGHT DISPLACEMENT RATIO, those vertical or even reverse sloped bows with a knuckle at the waterline and very close to zero rocker forward are in fact a slow way to go, for all of these reasons:
1) Long waterline is ONLY an advantage with heavy displacement, where wave drag is a significant portion of total resistance. Many cruiser racers and race boats fitting into racing rules that seek to promote cruiser racers may well have sufficient displacement such that long waterline is fundamental to performance, and in those cases plumb bows make a lot of sense. But this specific boat under discussion is a very light displacement boat, where a substantial aspect of its performance is directly due to its light displacement and its ability to easily and greatly exceed hull (wave) speed.
2) Planing boats want a short waterline. The faster a boat planes, the shorter its waterline. As a boat planes, a RATIONAL designer, not a fashion designer, will want the point of maximum pressure (lift) to get as close to the center of gravity as quickly as possible so the boat makes best use of planing, of reducing its wave drag by getting out of the archimedes phase and into the lift phase. Lift REQUIRES an angle of attack. This is why all surfboards have rocker forward. No rating rule involved, just actual experience in what works for planing is involved.
3) In very light air, a RATIONAL designer, not a fashion designer, will seek minimizing wetted surface. The less like a hemisphere an underwater shape, the more wetted surface for a given displacement. So a shorter waterline with more rocker is desired. Since one still wants a flat run aft for high speed, this means a RATIONAL designer puts the rocker forward, hence does NOT utilize a knuckle at the forward end of the waterline.
Hence, while I do like the beauty of the Carkeek 45, it is a fashion statement, and slower that it would be otherwise.
And lots of aspects of beautiful boats are echos of distortions caused by rating rules, such as long ends, fractional rigs, narrow beam, reverse transoms, and so on.
So if somebody thinks reverse bows are beautiful, more power to them.
But from a functional point of view, GIVEN VERY LIGHT DISPLACEMENT RATIO, those vertical or even reverse sloped bows with a knuckle at the waterline and very close to zero rocker forward are in fact a slow way to go, for all of these reasons:
1) Long waterline is ONLY an advantage with heavy displacement, where wave drag is a significant portion of total resistance. Many cruiser racers and race boats fitting into racing rules that seek to promote cruiser racers may well have sufficient displacement such that long waterline is fundamental to performance, and in those cases plumb bows make a lot of sense. But this specific boat under discussion is a very light displacement boat, where a substantial aspect of its performance is directly due to its light displacement and its ability to easily and greatly exceed hull (wave) speed.
2) Planing boats want a short waterline. The faster a boat planes, the shorter its waterline. As a boat planes, a RATIONAL designer, not a fashion designer, will want the point of maximum pressure (lift) to get as close to the center of gravity as quickly as possible so the boat makes best use of planing, of reducing its wave drag by getting out of the archimedes phase and into the lift phase. Lift REQUIRES an angle of attack. This is why all surfboards have rocker forward. No rating rule involved, just actual experience in what works for planing is involved.
3) In very light air, a RATIONAL designer, not a fashion designer, will seek minimizing wetted surface. The less like a hemisphere an underwater shape, the more wetted surface for a given displacement. So a shorter waterline with more rocker is desired. Since one still wants a flat run aft for high speed, this means a RATIONAL designer puts the rocker forward, hence does NOT utilize a knuckle at the forward end of the waterline.
Hence, while I do like the beauty of the Carkeek 45, it is a fashion statement, and slower that it would be otherwise.
r.finn
Super Anarchist
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Please tell me they run those aero models with a rail full people hiked out.
I agree that in light air the wetted surface area of long waterlines are a disadvantage, but I would have thought that in mid ranges that's exactly where a long waterline would have the most effect. In the set of conditions between SA/WSA dominated to planing, the LWL is the dominant factor, especially at the faster end of that range. Once planing it's all about WSA again. How many boats plane upwind?
lostmydetailsagain
Member
- 412
- 59
If light displacement sail boats were actually capable of actual planing, correct highlight.
Apart from the foiling boats (completely different story) just realise that a 45ft boat (say wetted length of around 12m/40ft) needs to be at or above 22knots of boat speed before it is planing. So why would you sacrifice wetted length (traditional hull speed calcs) for those few moments you are actually planing. In the range 13-22knots it is still semi-displacement stuff.
floater
Towards thee I roll..
can you explain this? (sorry, couldn't help myself)
carcrash
Super Anarchist
All wrong. Understandable, because just like the people who put those knuckles on the bows of planing boats, you are confused over the difference between resistance in non-planing speed regimes and planing speed regimes.
Like all things in engineering (applied physics), people use models (like the model that speed is related to length) so they don't need to deal with truth (quantum mechanics that nobody can effectively utilize for macro scale things). But models must only be applied to the extremely limited situations for which they were originally derived from observations. And always remember, the models only approximate the observations, and dramatically reduce the actual number of relevant factors so people can reason about cause and effect.
The two regimes (planing and non-planing) work completely differently, and the models (math expressions) used to reason about them are completely different. The semi-planing regime is essentially ignored because it's just too complicated, and predictions are just smoothed between the two models.
Remember that even CFD is a model, and is workable only because most of the factors that are still important, but less important, are ignored: Yes, a very limited set of information that does measurably effect fluid dynamics is actually used by CFD. This is why things still need to be tested and correlated. Navier-Stokes focuses on mass conservation, and not energy.
OK, here is Planing 101:
Planing is what happens when the angle of attack of the hull meeting the water is sufficient to cause an upward force greater than the Bernoulli effect that pulls hulls down (the depression in the water between bow and stern wake peaks), such that the displaced water become less than the weight of the boat.
If there is insufficient rocker forward, the hull remains glued to the surface, pulled down by the flow of water past the longitudinal convex curve of the hull, and the boat remains in the displacement regime regardless of length or velocity or displacement.
Since planing is about lift, and since lift/drag is directly related to aspect ratio, one wants the stagnation line to be as wide as possible versus the length of the hull. The stagnation line (the forward edge of the intersection between the hull and water) wants to be as close to athwartship as possible, which is why surfboards have flat bottoms, for the same reason sail planes do not have swept wings (swept wings are bad until transonic shockwave effects increase, and that never happens with boats). The width of that stagnation line versus the length of the immersed hull aft of that stagnation line provide the aspect ratio: the width/length, higher is better.
The faster you go on a surfboard, or windsurfer, or any planing hull, the less hull is in the water, the aspect ration and therefore lift to drag keeps getting better at the same (linear) rate that surface friction increases, while wave drag decreases at the same rate that aerodynamic drag increases. This is why planing powerboats get nearly identical miles-per-gallon at any planing speed.
The planning speed is related to the angle of attack at the stagnation point and the displacement. But since there are many effects, such as rocker or hook aft, sweep angle of the stagnation point (often measured indirectly by dead rise angle, beam, propulsion force vector, and so on, there is no simple number, but there are rules of thumb based on displacement length ratio, also called the displacement Froude number. Yes, same dude that recognized the dominant effect of length on speed for non-planing heavy displacement hulls, is also respected for the effect that displacement is fundamental to planing.
All agreed and common knowledge, though I might disagree about angle of attack. You still haven't addressed the part where no non-foiling boats are planing upwind, and how many 40 footers are planing in 10-12 knots TWS in any direction? It's possible that very few outluers may occasionally marginally plane on a beam reach in that windspeed but realistically?
dogwatch
Super Anarchist
I agree with your general argument on appropriate models but that is not a good example. Superconductivity is an example of a quantum phenomenon that manifests at macro scales. There are others.
floater
Towards thee I roll..
well. I heard they have a good sense of humor? (but I don't get the joke).
floater
Towards thee I roll..
this is decoherent.
shaggybaxter
Super Anarchist
My 40’ cruiser racer didn’t feel like it was in semi displacement mode at 13-22knots. Above 16 knots it felt exactly the same up to 22-23. The keel and rudder are doing all the work, the hull just snakes along for the ride.
At 10 knots is when the chatter off the transom morphs into a soft hiss and the wake flattens right out, so even at those speeds it feels more like planing than a semi displacement mode.
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Roleur
Super Anarchist
Seems to be as fast as Teasing Machine right out of the box and Teasing Machine (ie probably the best IRC boat in the world at the moment) owes them time. So?
If I were the owner I would be f*ing ecstatic.
If I were the owner I would be f*ing ecstatic.
Kenny Dumas
Non Binary About Anything
Go ugly early
3to1
Super Anarchist
maybe you need thicker glasses, 'cause there's no such thing as ugly fast boats, not in the real world.
Kenny Dumas
Non Binary About Anything
Especially all those type formed IOR boats? Speed is relative. Ugly is still ugly.
