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Board » General Discussion » Boat planning.

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Posted by
JB


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2013-03-07 08:54:34
2014-04-03 18:08:54 - Boat planning.
From Wiki:

“When it is at rest, a vessel's weight is borne entirely by the buoyant force. At low speeds every hull acts as a displacement hull, meaning that the buoyant force is mainly responsible for supporting the craft. As speed increases, hydrodynamic lift increases as well. In contrast, the buoyant force decreases as the hull lifts out of the water, decreasing the displaced volume. At some speed, lift becomes the predominant upward force on the hull and the vessel is planning.“.

So, is it possible to put some SOL boats planning? (I was not thinking on the 100 ft barge…).

Yes, it’s possible with just a simple adjustment on same parts of the boat Polar - have a look on the example for the VOR70 in the PDF attachment.

To keep the things interesting, the exact spot of the rising BS can be kept secret and up to everyone discover doing some extra time on helm.
Sail Fair.
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Posted by
bonknhoot


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2013-08-06 21:35:15
2014-04-03 19:39:05 - Re: Boat planing.
Hi Joao

Quickly from Wikipedia
V hull = 1.34 x sqrt{L}

where:
L is the length of the waterline in feet, and
V hull is the so-called hull speed of the vessel in knots

For a 70ft yacht, V hull is thus 8.37kn.

Hull speed is the speed at which the vessel pushing through the water creates two non-interfering waves, one at the bow and one at the stern, and without a good whack of extra power the vessel can't ride out over the top of the bow wave in particular, and leave it behind as it were. However, once it does it is effectively planing. So... lang verhaal kort, the VO70 already planes like an F16!
Clipping along
Posted by
sol


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2008-08-14 11:08:14
2014-04-03 19:58:55 - Re: Boat planning.
The various characteristics of a boat's performance are already incorporated into the composite polar diagram that enables 100% actualization unless changing course.

Posted by
kroppyer


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2014-04-03 20:01:14 - Re: Boat planning.
Boats like the VO70 will plane, they are designed to do so. For boats that don't plane, there is a sort of maximum speed, hull speed. For the VO70 that would be about 12kts (or a little more). So whenever a VO70 sails faster than 12kts it's probably planing. A VO70 probably starts planing before it reaches its boatspeed.

But what that means, is that the polar, as is, already includes speeds at which the VO70 is planing. Attached is an image of the VO70_v4 polar with a line at boatspeed=12kts

I reality there is a range in boatspeeds (also depends on wind/heeling angle) where the boat sometime planes, and sometimes doesn't. Usually you are surfing down a with a wave until you overtake it (or it overtakes you, when you're in a slower boat). So at some twa/tws the boatspeed is far from constant. The polar contains averaged speeds.

A way to simulate planing would be by simulating surfing off waves. Giving a 10% bonus for 1 or 2 jumps, and then a 10% penalty after for some jumps after that. Or something like that.

___
EDIT: I see I was a little late, it's (almost) all already explained.

--- Last Edited by kroppyer at 2014-04-04 08:27:59 ---
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Posted by
Rod


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2010-06-24 22:30:48
2014-04-03 20:13:43 - Re: Boat planning.
Surely the lines shown in the polar diagram already show the boat speed, wind speed and wind angle at which the hull is planing.
(Not to be too critical, it is "PLANING" without the double-"n", after the verb "to plane")
Planing is shown by a small bulge in the polar lines at certain wind angles and speeds.
Nothing further needs to be done!
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
bonknhoot


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2014-04-04 08:24:07 - Re: Boat planning.
A VO70 planing. As you can see, the bow wave has moved aft.
Clipping along
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Posted by
JB


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2014-04-04 10:21:06 - Re: Boat planning.
Thank you Jan, Kroppyer, Sol and Rod.

The first and my friend, for bringing some hydrodynamics to the subject.
The second for is enlighten on boat Polars (and, by the way, also for his superb tool “SPINNACER”).
Finally Rod, for bringing the “planing” in the right plane.

So, the VOR70 can plane upwind?
From the CSV file, at TWS = 12 kts and TWA = 51º, the corresponding BS = 12,154 kts (see also “SPINNACER” graphic in the attachment), which is above the hull speed calculated with empirical formula (note: dimensions are not coherent, speed units vs. length units),
V,hull = 1,34 x sqrt (L) = 1,34 x sqrt (70) = 11,211 Kts.

Or is it just possible for the VOR70 to be above his hull speed but not yet in planning mode in those conditions?

Well I’ve never thought that the VOR 70 Polar already incorporated the planning effect, as it curves shapes doesn’t show it at all ( in a mathematic perspective: no “really” singular points in the curves).

My primary idea was to bring some further interest and action to the race. An extra BS coming from planing would be nice, especially if the Polar zone for that purpose had to be discovered by each one (hence the different shapes suggested for that particular zone).
In another perspective: a premium for being more time at the helm.
I think the “non-routers”, namely, would appreciate that.
Sail Fair.
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Posted by
A2


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2009-10-26 00:39:42
2014-04-04 16:06:49 - Re: Boat planning.
*(Posted earlier as sol)

Everyone is given equal marks for skillful sailing such that the competition is decided by the judgement of the afterguard regarding navigation with respect to the weather & optimum route to destination.

--- Last Edited by A2R at 2014-04-04 16:24:44 ---
None so blind
Posted by
Rod


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2014-04-06 18:05:18 - Re: Boat planning.
There is something of a difference in the planing of a motorized speedboat hull, compared with planing in a sailing yacht. The equations describing the speed above which planing can occur assume that a considerable increase in horsepower is available, and that the hull will then plane.
This is usually not the case in sailing boats, where sail pressure results in max hull speed. Any increase in speed beyond this point must come from a large increase in windspeed. This is unlikely to occur in sailing because it usually results in a 'knock-down'.
Instead, what we see happening is that hull speed gradually increases with increasing windspeed, and that natural result of this is that the hull gradually rises in the water, due to its shape. With reduced drag comes additional hullspeed, so that the hull is moving a small amount faster than it could if it still maintained the same immersed volume and surface area that it would have if measured while at rest. This explains why a polar diagram can indicate a higher hullspeed than the simple equation should allow.
The net effect of all this is that a displacement sailboat approaches planing speeds gradually.
This phenomenon interests me because I have been sailing and designing small radio-control sailboats in the Footy Class, and they exhibit a phenomenon called "nose-dancing", where the pressure of the wind on the sails causes the bow to submerge. Unlike larger boat classes, this is an almost stable condition that may continue for several seconds, until a broach occurs.
The object of my current interests in Footy design involve trying to prevent "nose-dancing".
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
JB


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2014-04-07 11:12:34 - Re: Boat planning.
Dear Rod, I’m no specialist on boat design. Anyhow, this is what I think.

The Footy has a short hull - see pictures and plans in the attachment (data from http://www.scalesailing.com ).
Without any disregard for the Footy, she has a shape like a “cube”: short length, high freeboard.
The mast position is pushed to the bow and the bottom of the hull is banana shaped and very light, so, the extremities lack material/buoyancy, principally the bow.
Dynamically speaking, the result has to be a boat with a high frequency longitudinal motion in both planes (short pendulum like):
1 - In the vertical plane (passing the boat’s “CG”) - causing the so called “nose diving”, with this motion helped by the curved hull shape;
2 - In the horizontal plane - causing the “nose dancing”.

She doesn’t have enough length to cushion in due time the instability created by the above mentioned motions, so , Rod , she must be very hard to control, even in light wind conditions (immediately transferring the boat’s reaction to the bow when the wind enters and promoting the “nose diving”), and, I just imagine her sailing in little choppy waters…

If the class rules permit, try to bring aft the mast’s application point and some weight.
Maybe she will:

3 - Lose some upwind ability;
4 - Gain stability, and,
5 - a little downwind speed.
Sail Fair.
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