Wake Height While On Plane, Accelerating and Decelerating

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Author Topic:   Wake Height While On Plane, Accelerating and Decelerating

moabelite posted 12-02-2014 08:17 AM ET (US)
I’m wondering whether any of you have previously encountered information or a study detailing the relative height of wake created when a vessel is accelerating, on plane and decelerating.
Clearly the mass of the vessel, beam, length and speed on plane would be among the variables of importance to the exact measurements. Practically speaking, there is plenty of observational evidence for the fact that the wake is larger when accelerating and decelerating than when traveling at speed on plane. I’m wondering if there has been a scientific examination and report of the same.

Jefecinco posted 12-02-2014 09:18 AM ET (US)
I'm sure the subject has been studied. For my purposes I simply attempt to avoid plowing. I know that the energy required to form a larger than necessary wake is wasted energy unless it's done for a purpose such as for "wake boarding".
jimh posted 12-02-2014 09:49 AM ET (US)
As Jefecinco suggested, a smaller wake is indicative of better efficiency. In propeller testing, I try to observe the wake and the height of the wake created by the boat with each propeller, which gives me a sense of efficiency of the hull and propeller combination.
I am sure there are scholarly studies of wave making of ship hulls, as a great deal of effort has gone into reducing the wave making of a ship hull. But, since large ships do not get onto hydroplane, I don't think the behavior of the wake at planing speeds or during the transition on-plane or off-plane has been the focus of much inquiry.
ASIDE: I read recently of a modification made to a ship's bulbous bow section. The bulbous bow is typically designed into the ship hull to reduce the bow wave. The article I read explained that a particular ship had been fitted with some new engine or other modification so that its cruising speed would be changed to new speed, probably a slower speed that the initial design. The shape and design of the bulbous bow was then changed in order to permit the wave making from the bulbous bow to be optimized at the new cruising speed. I thought this was quite interesting. It suggests that the improvement in hull efficiency by altering the bulbous bow shape to better suit the new cruising speed was going to be so great that the savings it produced would by much greater than the cost of the modification to the hull.
I don't think the wave making of recreational boat hulls, particularly moderate-speed planing-hull boats designed in the 1980 or earlier--which characterizes most of the Boston Whaler boats of the classic era--was ever studied particularly carefully or scientifically.
jimh posted 12-02-2014 01:22 PM ET (US)
MOAB postulates:

quote:
Clearly the mass of the vessel, beam, length and speed on plane would be among the variables of importance to the exact measurements [of wake height].
You did not mention draft. In terms of wave making for a planing hull, I think a good first approximation of wake height will be strongly correlated to the draft of the hull. When a hull is on plane there are lifting forces which reduce the amount of the hull that remains in the water. The less hull in the water, the less wake. At some point a planing hull could be lifted so high that only a very small portion--a planing pad--remains in the water, and most of the wake is generated by the gear case of the outboard engine or other propulsion apparatus immersed in the water.
This simple model also explains why the wake height is much higher when accelerating to on-plane: the bow often rises and results in an increase in draft at the stern. More draft makes more wake.
moabelite posted 12-04-2014 08:24 AM ET (US)
The scenario I am looking at is as follows:
A no wake zone on an inland lake “funnels” boats on plane into one corner of the lake. It does so by providing one area which gets boaters closest to the channel they are using to exit the lake (crossing the no wake line at other locations means a longer trip through the channel). My assertion is that, because the boaters are accelerating and decelerating in this one small area, the damage to nearby boats in slips is actually worse than it would be if boats were simply allowed to remain on plane or were required to move off plane evenly across the lake.
Hoping there is some empirical evidence of the same.
Jefecinco posted 12-04-2014 08:38 AM ET (US)
If you are attempting to effect a rules change a video taken over several hours on a busy day may be a more effective tool than a study.
My practice is to come to idle speed when approaching a "no wake" zone and to accelerate only after exiting the zone. This avoids creating excessive wake anywhere inside the zone. I believe this effectively lives up to obedience to the spirit of the requirement.
What I find annoying are those boaters who slow for a no wake zone only enough to sink the transom so deeply that they create a far taller wake than if they remained completely on plane.
Butch
jimh posted 12-04-2014 10:36 AM ET (US)
When a planing hull boat comes off plane, in order to disperse the wake it had while on plane the boat must slow down all the way--practically come to a stop--to break the wave train of the wake. If a planing boat does not do this, it will drag the old wake along with it and will keep those waves going. To transition to NO-WAKE from plane, the boat must really slow very dramatically. This will break off the old waves of the wake and stop putting energy into those wave trains. You have to let your old wake roll past the boat, then begin a new, much smaller wake, at slow speed.
If this is not done, now you have the worst case: a boat going slowly and spending more time in transit through the no-wake zone, but still making a wake, and perhaps a larger wake than it would have if on-plane.
The remedy to your problem of boaters creating large wakes in NO-WAKES zones is probably to be found in better enforcement. Having an on-water enforcement of no-wake and handing out some violations will probably be the best method to educate boaters about the harm caused by their wakes. A few days of that sort of enforcement should spread word.
Jerry Townsend posted 12-04-2014 11:03 PM ET (US)
moabelite -- In direct answer to your question, I am not aware of an analyses and documentation addressing the detailing the relative height of wake created when vessel is accelerating, on plane or decelerating.
But, in general, the wave is caused by the boat design and performance and a bit of fluid dynamics.
However, the U.S. Navy may have such information, but it may not be public information - and may not be applicable.
In addition, the shipping industry and others are using the bulbous bows - and may have had related studies conducted - but that may be induced by the energy consumed in generating that bow wake. But such information is not strictly related to our Whalers.
In fact, such an analyses could be a good masters study in fluid dynamics. But, the generation of the wave is caused by the boat - and everything after that is pure fluid dynamics. --- Jerry/Idaho
moabelite posted 12-06-2014 01:50 PM ET (US)
Thanks Jerry,
Yes, I think I am in a "doughnut hole" of sorts. The relevant information would relate only to vessels that are big enough (no canoes) and small enough to travel at speed on plane. That segment of the broader category is likely also the segment which has not been studied in depth (the Navy and shipping companies being much more concerned with a scale that eclipses recreational rigs and which does not operate on plane).
The good news, it seems, is that the general idea seems to be widely accepted on an intuitive level and that might just be enough to swing the relevant regulating bodies around.
Always appreciate the depth of knowledge I find here - would welcome any further thoughts and documentation!

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Author	Topic: Wake Height While On Plane, Accelerating and Decelerating
moabelite	posted 12-02-2014 08:17 AM ET (US) I’m wondering whether any of you have previously encountered information or a study detailing the relative height of wake created when a vessel is accelerating, on plane and decelerating. Clearly the mass of the vessel, beam, length and speed on plane would be among the variables of importance to the exact measurements. Practically speaking, there is plenty of observational evidence for the fact that the wake is larger when accelerating and decelerating than when traveling at speed on plane. I’m wondering if there has been a scientific examination and report of the same.
Jefecinco	posted 12-02-2014 09:18 AM ET (US) I'm sure the subject has been studied. For my purposes I simply attempt to avoid plowing. I know that the energy required to form a larger than necessary wake is wasted energy unless it's done for a purpose such as for "wake boarding".
jimh	posted 12-02-2014 09:49 AM ET (US) As Jefecinco suggested, a smaller wake is indicative of better efficiency. In propeller testing, I try to observe the wake and the height of the wake created by the boat with each propeller, which gives me a sense of efficiency of the hull and propeller combination. I am sure there are scholarly studies of wave making of ship hulls, as a great deal of effort has gone into reducing the wave making of a ship hull. But, since large ships do not get onto hydroplane, I don't think the behavior of the wake at planing speeds or during the transition on-plane or off-plane has been the focus of much inquiry. ASIDE: I read recently of a modification made to a ship's bulbous bow section. The bulbous bow is typically designed into the ship hull to reduce the bow wave. The article I read explained that a particular ship had been fitted with some new engine or other modification so that its cruising speed would be changed to new speed, probably a slower speed that the initial design. The shape and design of the bulbous bow was then changed in order to permit the wave making from the bulbous bow to be optimized at the new cruising speed. I thought this was quite interesting. It suggests that the improvement in hull efficiency by altering the bulbous bow shape to better suit the new cruising speed was going to be so great that the savings it produced would by much greater than the cost of the modification to the hull. I don't think the wave making of recreational boat hulls, particularly moderate-speed planing-hull boats designed in the 1980 or earlier--which characterizes most of the Boston Whaler boats of the classic era--was ever studied particularly carefully or scientifically.
jimh	posted 12-02-2014 01:22 PM ET (US) MOAB postulates: quote: Clearly the mass of the vessel, beam, length and speed on plane would be among the variables of importance to the exact measurements [of wake height]. You did not mention draft. In terms of wave making for a planing hull, I think a good first approximation of wake height will be strongly correlated to the draft of the hull. When a hull is on plane there are lifting forces which reduce the amount of the hull that remains in the water. The less hull in the water, the less wake. At some point a planing hull could be lifted so high that only a very small portion--a planing pad--remains in the water, and most of the wake is generated by the gear case of the outboard engine or other propulsion apparatus immersed in the water. This simple model also explains why the wake height is much higher when accelerating to on-plane: the bow often rises and results in an increase in draft at the stern. More draft makes more wake.
moabelite	posted 12-04-2014 08:24 AM ET (US) The scenario I am looking at is as follows: A no wake zone on an inland lake “funnels” boats on plane into one corner of the lake. It does so by providing one area which gets boaters closest to the channel they are using to exit the lake (crossing the no wake line at other locations means a longer trip through the channel). My assertion is that, because the boaters are accelerating and decelerating in this one small area, the damage to nearby boats in slips is actually worse than it would be if boats were simply allowed to remain on plane or were required to move off plane evenly across the lake. Hoping there is some empirical evidence of the same.
Jefecinco	posted 12-04-2014 08:38 AM ET (US) If you are attempting to effect a rules change a video taken over several hours on a busy day may be a more effective tool than a study. My practice is to come to idle speed when approaching a "no wake" zone and to accelerate only after exiting the zone. This avoids creating excessive wake anywhere inside the zone. I believe this effectively lives up to obedience to the spirit of the requirement. What I find annoying are those boaters who slow for a no wake zone only enough to sink the transom so deeply that they create a far taller wake than if they remained completely on plane. Butch
jimh	posted 12-04-2014 10:36 AM ET (US) When a planing hull boat comes off plane, in order to disperse the wake it had while on plane the boat must slow down all the way--practically come to a stop--to break the wave train of the wake. If a planing boat does not do this, it will drag the old wake along with it and will keep those waves going. To transition to NO-WAKE from plane, the boat must really slow very dramatically. This will break off the old waves of the wake and stop putting energy into those wave trains. You have to let your old wake roll past the boat, then begin a new, much smaller wake, at slow speed. If this is not done, now you have the worst case: a boat going slowly and spending more time in transit through the no-wake zone, but still making a wake, and perhaps a larger wake than it would have if on-plane. The remedy to your problem of boaters creating large wakes in NO-WAKES zones is probably to be found in better enforcement. Having an on-water enforcement of no-wake and handing out some violations will probably be the best method to educate boaters about the harm caused by their wakes. A few days of that sort of enforcement should spread word.
Jerry Townsend	posted 12-04-2014 11:03 PM ET (US) moabelite -- In direct answer to your question, I am not aware of an analyses and documentation addressing the detailing the relative height of wake created when vessel is accelerating, on plane or decelerating. But, in general, the wave is caused by the boat design and performance and a bit of fluid dynamics. However, the U.S. Navy may have such information, but it may not be public information - and may not be applicable. In addition, the shipping industry and others are using the bulbous bows - and may have had related studies conducted - but that may be induced by the energy consumed in generating that bow wake. But such information is not strictly related to our Whalers. In fact, such an analyses could be a good masters study in fluid dynamics. But, the generation of the wave is caused by the boat - and everything after that is pure fluid dynamics. --- Jerry/Idaho
moabelite	posted 12-06-2014 01:50 PM ET (US) Thanks Jerry, Yes, I think I am in a "doughnut hole" of sorts. The relevant information would relate only to vessels that are big enough (no canoes) and small enough to travel at speed on plane. That segment of the broader category is likely also the segment which has not been studied in depth (the Navy and shipping companies being much more concerned with a scale that eclipses recreational rigs and which does not operate on plane). The good news, it seems, is that the general idea seems to be widely accepted on an intuitive level and that might just be enough to swing the relevant regulating bodies around. Always appreciate the depth of knowledge I find here - would welcome any further thoughts and documentation!