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jimh posted 10-07-2009 09:45 PM ET (US)
This past weekend we spent several hours operating our Boston Whaler REVENGE 22 W-T WD at low speeds as we passed through long stretches of NO WAKE zones. I observed a curious phenomena.
During one stretch, ahead of me was a 1978 Boston Whaler OUTRAGE V-20. We were traveling at closely matched speeds. I observed the waves produced by my boat and compared it to the waves produced by the OUTRAGE V-20. The OUTRAGE V-20 was moving at the same speed, yet it was producing almost no waves. In contrast, my REVENGE 22 with Whaler Drive was producing noticeable waves, perhaps four to six inches in height.
At displacement speeds the wave making of a hull is generally inversely proportional to the hull length, and, on this basis, my longer boat should have been making less waves than the V-20.
What explains the very small waves produced by the V-20?
DeeVee posted 10-07-2009 09:58 PM ET (US)
Jim,
If I remember correctly, the V-20 has less dead-rise than the later Outrages. Hmmm, could that be the reason?
Just a thought,
Doug Vazquez
macfam posted 10-07-2009 11:08 PM ET (US)
Yup.
Jerry Townsend posted 10-08-2009 12:32 AM ET (US)
Jim - you are heading in pretty deep water with this question - that is, many years ago, a professor friend and myself would discuss such fluid related problems. It gets deep very quickly - and it will vary with the hull design, with the water (fresh 0r salt) - as the speed of sound is different in each medium and many, many other factors.
I have not heard of the inverse variation with length rule -but it makes sense - and certainly, the hull design and skin friction enter into the pictur. The same would hold for beam. ----- Jerry/Idaho
number9 posted 10-08-2009 03:52 AM ET (US)
REVENGE 22 W-T WD a thousand plus pounds heavier.
Your near level static trim angle produces a larger bow wave.
[Quoted without attribution a definition of the meaning of "no wake."]
jimh posted 10-08-2009 08:35 AM ET (US)
I am not interested in discussing the meaning of signs which designate areas as "NO WAKE." I am interested in comparing the wave making of different hulls of somewhat similar design.
Regarding the weight of the two boats in my comparison, I do not think they are drastically different. In any case, the weight can only affect wave making though an increase in draft. The specified draft of the two boats is
OUTRAGE V-20 = 11-inches
REVENGE 22 WD = 14-inches
deepwater posted 10-08-2009 09:35 AM ET (US)
3"of displacement is a lot,, Add forward motion and waters incompressibility and your boat might be a little bow heavy and you get larger waves
Jefecinco posted 10-08-2009 09:49 AM ET (US)
Jim,
Perhaps the trim, weight distribution, or load was significantly different between the two boats.
Due to the Whaler Drive adding some length to your hull and the more rearward bias of the engine's weight the aft trim of your boat at displacement speed may be much different. I assume the weight of your engine is also greater assuming your engine is of a greater horsepower than that of the 20.
Another possibility is the difference in the gear ratio and propeller of the two boats would result in an appreciable difference in propeller RPM at the same speed over the water.
Was the engine of the other boat fitted with a hydrofoil stabilizer? Could that be a factor?
Given the multitude of factors possibly affecting the wake produced by two boats of different sizes it seems quite difficult to determine the specific cause of the difference. Hopefully someone will have the answer.
Butch
Tom W Clark posted 10-08-2009 10:15 AM ET (US)
It's not the deadrise angle, it's not the Whaler Drive, It's the weight of the two boats.
Jim's boat weighs more than the Outrage V-20. It literally displaces a greater amount of water at displacements speeds.
Tom W Clark posted 10-08-2009 10:17 AM ET (US)

quote:
...weight can only affect wave making though an increase in draft
Jim -- Would you explain this strange statement?
Utik posted 10-08-2009 12:13 PM ET (US)
I suspect you are all wrong. My guess is the OUTRAGE V-20 was powered by a Mercury outboard motor vs Jim's Evinrude.
This would demonstrate another area where the Mercury products are superior to all their competitors. :-)
For the record, I am kidding. I have been the satisfied owner of both Mercury and Evinrude outboards and currently own an E-TEC. I just couldn't resist poking fun at some of the "my brand is better than your brand" discussions that occur here from time to time.
jimh posted 10-08-2009 12:42 PM ET (US)
Weight does not affect wave making directly, but can through draft changes. How weight affects draft is determined by the hull form.
As for the weight difference between the REVENGE 22 and the OUTRAGE V-20, it might not be as great as many think. The OUTRAGE V-20 carried a lot of gear on board which the REVENGE was not carrying.
If two hulls were very similar, and one was several feet longer, I would expect the longer hull to make less wake. I see 1,000-foot ore boats moving with almost no wake at speeds where my 22-foot hull creates a wake. Obviously, the 1,000-footer weighs more and has much deeper draft.
Tom W Clark posted 10-08-2009 12:52 PM ET (US)

quote:
Weight does not affect wave making directly, but can through draft changes. How weight affects draft is determined by the hull form.
No, I am not buying that. If we take your reasoning at face value, draft is the only influence on wake, and we know that is not true. Sailboats do not throw large wakes.
What would you estimate the loaded weight of your boats was? What is your estimate of the Outrage V-20?
A 1990 Revenge Walk Through Whaler Drive weighs 60 percent more than a 1978 Outrage V-20. That is far from insignificant.
Tohsgib posted 10-08-2009 12:57 PM ET (US)
My 13' will make a huge wake if I am alone in the boat going say 1000rpm. If a person is sitting in the bow the wake is half. As a kid we used to run through the no wake zones in reverse as it did not make much if any wake at higher speeds. Honed your driving skills as well. My 19 Revenge being the bow heavy biotch she is makes a small wake compared to my 20' Hydra-Sports which had a 24 degree V compared to my 10?. My 24' Baja with also had a 24 and weighed almost double the Hydra-Sports, made a much smaller wake. So...I say weight transfer is the best factor..
Tom W Clark posted 10-08-2009 01:37 PM ET (US)
Nick may be on to something. Outboard powered boats tend to be much more efficient at slow speeds when they are bow heavy. I have always noticed this while rowing an outboard equipped skiff too.
The bow will tend to wander more but what happens is the V-shaped part of the hull is pushed down in the water more while the flatter, more squared off portion of the hull is lifted.
If you were underwater looking up at the hull you would see the silhouette of the hull at the waterline which will become more "canoe shaped" as the bow goes down and the stern comes up allowing water to flow around it more easily with less turbulence at the stern.
Buckda posted 10-08-2009 02:06 PM ET (US)
THat is my experience with a heavy-in-the-stern 18' Outrage. Bigger wake at slow speeds than with single 150 when compared (speed over ground/speed over ground). I have to go much slower in front of LEO's now.
Dave
Jerry Townsend posted 10-08-2009 04:32 PM ET (US)
Weight plays a significant part of the wave generation - as the wave is created via displacement - and weight plays a significant part in the displacement - along with length, beam, et al. ---- Jerry/Idaho
Jerry Townsend posted 10-08-2009 05:01 PM ET (US)
Another point - speed is, most obviously, also involved. The point here - the bigger, heavier boat will probably have to slow down to avoid creating a wake. --- Jerry/Idaho
Utik posted 10-08-2009 06:31 PM ET (US)
I suspect you are all wrong. My guess is the OUTRAGE V-20 was powered by a Mercury outboard motor vs Jim's Evinrude.
This would demonstrate another area where the Mercury products are superior to all their competitors. :-)
For the record, I am kidding. I have been the satisfied owner of both Mercury and Evinrude outboards and currently own an E-TEC. I just couldn't resist poking fun at some of the "my brand is better than your brand" discussions that occur here from time to time.
deepwater posted 10-08-2009 08:10 PM ET (US)
This is all stern wake ,,right?
contender posted 10-08-2009 08:59 PM ET (US)
How about its the amount of boat in the water, meaning at a low speed your boat is pushing more water, high speed your boat is on a plane riding on the surface, less surface area touching the water, less water being pushed out of the way....
contender posted 10-08-2009 09:00 PM ET (US)
Speed would be another factor as hull design...
jimh posted 10-08-2009 09:23 PM ET (US)
The boat speed was the same for both hulls, as I clearly mentioned in my initial article.
In my estimation, the amount of wave making is proportional to the amount of power needed to move the boat through the water. If this is true, the OUTRAGE V-20 requires less power than a REVENGE 22 WD. While my analysis is simple, it is based on a clearly understood principle. If the two boats move at the same speed, there must be extra power being used to move the water in the waves that are produced by the boats. If one boat produces larger waves, they represent more power having been used.
We know that the hull shapes of the two boats are very similar, with the principal difference being in the angle of the v-hull. The REVENGE 22 has a v-hull with about 18-degrees deadrise angle at the transom, and the OUTRAGE V-20 has a v-hull with about 10 to 11-degrees of deadrise angle. I suspect that the OUTRAGE V-20 hull is more easily moved through the water than the REVENGE 22 WD hull. This was already mentioned by Doug as a factor in the wave making, and I concur.
WT posted 10-08-2009 10:25 PM ET (US)
I'm guessing it's mostly due to weight too.
Imagine a ski boat with ballast tanks. The same boat throws a bigger wake at the same speed when weighted down with water in the ballast.
Warren
WT posted 10-08-2009 10:33 PM ET (US)
The same ski boat filled with water needs more power to go the same speed when ballast tanks are empty.
That extra power needed to move the heavier boat at the same speed also moves more water, thus a bigger wake.
Warren
number9 posted 10-08-2009 11:02 PM ET (US)
OK, I would like to say again without quoting the Michigan Boating Handbook.
1. According to the CW Reference, Dimension and Production History, the boat dry weight of the REVENGE 22 W-T WD is 1,100 lbs. heavier that the OUTRAGE V-20.
2. Observing photos posted on this site the REVENGE 22 W-T WD referenced to in this topic has a near level static trim angle. A typical OUTRAGE V-20 has more of a bow up static trim angle.
If both vessels were equipped with identical weight of persons, motor and gear the REVENGE 22 W-T WD would displace approximately 1/3 more water.
At low displacement speeds a boat operates with the bow down in the water and the wake in primarily generated by the bow wave. At the same speed the REVENGE 22 W-T WD has more bow down in the water.
The most simple explanation:
"A boat displaces its own weight in water. When the boat is moving, it must push that much water out of the way as it goes forward. Since a heavy boat has to push more water out of the way, it makes bigger waves."
jimh posted 10-09-2009 05:56 AM ET (US)
Wave making is more complex than being simply related to weight. It is understood that wave making is related to speed and length. Generally if two vessels go the same speed, the longer vessel will make smaller waves. What makes my observation interesting is its contradiction of this general rule.
The notion that wave making is related to weight is easily dismissed by observation of a large ship. A large ship might have a displacement of 50,000-tons, or about 100,000,000-lbs. Such a ship would weigh 50,000-times more than a Boston Whaler. If wave making were proportional to weight, we would expect that such a ship would generate waves 50,000-times larger. As I mentioned, the waves produced by movement at low speeds were on the order of four inches high. Thus a large ship would have to make waves 50,000-times larger, or about 16,666-feet tall. Clearly that does not occur. Even more interesting, it is entirely possible that the waves produced by such a large ship moving at the same speed as my Boston Whaler would be smaller, at least at the low speeds mentioned here.
I would characterize the waves being generated as coming from the stern of the boats, not from the bow.
The notion that the trim affects the wave making is reasonable, but it has been applied in complete contradiction. If a REVENGE 22 sits on a level trim, this implies its draft is probably less than an OUTRAGE V-20 sitting with a trim low in the stern.
The notion that wave making is related to the volume of water pushed out of the way is also wrong. See my comments about large ships, above.
macfam posted 10-09-2009 08:40 AM ET (US)
Wake generation has several factors:
Hull design efficiency, weight distribution, speed, and that particular boat's "hull speed"(found by multiplying the sqare root of the boat's water line x 1.32)
As a planing boat exceeds its hull speed, it also starts to squat lower in the water. But planing hulls have either a "deep V" or a "V bottom" forward and a relatively flat section aft, which allow it to climb out of the hole and attain much higher speeds. Depending on the boat's size, the size of its props, and the efficiency of its design, a planing hull may create a fairly large wake, but not as large as the wake it creates as it struggles along at lower speeds—somewhere between hull speed and efficient planing speeds.
Is the Whalerdrive appendange considered part of the waterline?
If the wake is larger on the 22 Whaler, than the 20 Whaler, obviously, the "hull speed" of a 22 Revenge with Whalerdrive is quite low. The weight of the 225 hp outboard is "extended" aft due to the Whalerdrive appendage. This MAY have an affect on shifting weight distribuion aft. Shifting weight aft is known to increase wake size.
An interesting experiment is to have exact 22 Revenge models with similar 225 hp outboards.
One with, one without Whalerdrive.
IF the Whalerdrive appendage is NOT part of the waterline, then the "hull speeds" should be identical. the only difference would be the weight distribuion aft, caused by the 225 outboard being approx 2 ft further back from the "actual" transom, and the weight of the appendage itself.
Because the "hull speeds" are the same, but the weight distibuion is dissimilar, the Revenge with Whalerdrive will leave a larger wake until planing speed.
Jefecinco posted 10-09-2009 09:31 AM ET (US)
Another consideration is engine trim.
When running on plane our engines are usually trimmed out as far as possible to obtain best on-plane performance and efficiency. Upon approaching a "no wake" zone we throttle back to around idle speed in order to minimize wake.
Some of us probably do not adjust engine trim for slow speed operation because it is unnecessary unless maneuvering around tight spaces or onto the trailer. If the engine is trimmed out for optimum on-plane performance while at idle the propeller will tend to pull the stern downward. If the trim is adjusted for slow speed the downward thrust is not present.
In my case optimum slow speed trim is seldom used except when approaching the ramp to retrieve the boat. Instead, I adjust trim in only to prepare for on-plane operation.
Butch
boatdryver posted 10-09-2009 10:09 AM ET (US)
I also think "stern squat" is the main factor in wake making at low speeds. Unless the boat is moving at idle rpm it is not at static trim.
In my hobby of photographing sailboat races (19-22 ft dinghy sailors) in flat water) I'm constantly fighting to keep my wake to a minimum as I carefully maneuver at 1000-1500 rpm among the racers.
I find that a small change in rpm which increases boat speed only half a knot will greatly increase the wake. At the same time the increase in "stern squat" is easy to notice. I have a 200 Dauntless (about 18 degree deadrise at the transom) with 450 lbs of fuel in the stern tank.
JimL
Utik posted 10-09-2009 10:28 AM ET (US)
First, I apologize for the double post of my stupid joke. I am not quite sure how I did that.

In an effort to make a more serious contribution, I think this might have something to do with drag coefficient.

Automobile tests frequently speak about the aerodynamic drag coefficient. I may be wrong, but I do not believe that this is directly related to the overall size or even frontal area of the vehicle. The amount of disturbance that a given automobile makes in the air is clearly not related to the weight of the automobile in any way. This is different in boats as the weight changes the amount of water that the boat displaces.

My thinking is that it is not how much fluid that the object displaces but rather the way it displaces the fluid. I think this is consistant with the observations that stern heavy boats make more wake. If you view a cross section of the frontal area this presents to the fluid it is probably much more blunt. It may be the tapered tail that sailboats and large ships present that is the key.

Consider two different objects. One is a very large and heavy tube shaped object with pointed ends front and back. The other is a flat board. Let’s say these two objects have the same surface area when viewed from the front. I suspect that these two objects moving through a fluid at the same speed will create dramatically different disturbances in the fluid.
I am certainly not a physicist or engineer. This is just conjecture, but it makes sense to me.
Now exactly what is different about the way these two boats present themselves to the water? My guess is that is an extremely complex topic.
Tohsgib posted 10-09-2009 03:52 PM ET (US)
If you want to wake to dissipate so it does not rock the boats around you...zigzag. My canal is long and straight. When i would come in and pull off plane the wake would kinda follow me and continue all the down the canal and rock the boats. If I come in and then turn an almost 90 degree angle the wave goes out in front and just dissipates in a couple yards like a ripple.
contender posted 10-09-2009 04:20 PM ET (US)
I just back in...
Stevebaz posted 10-14-2009 01:12 PM ET (US)
It may be due to your modern engine being mounted much higher than the old engine in the other boat.
Jerry Townsend posted 10-14-2009 05:47 PM ET (US)
Jim - I have been away for a week or so and have not read everything thranspired since - but, as I was suggesting - speed is important - but the speed that a given boat creates a wake - which is dependent on the beam, length and draft - which induced weight into the equation. The same "reverse" performance results too - weight is important - which will vary at different speeds. In other words, weight, speed, beam, length - and probably many other things - all have some interrelated affect on the wake. ---------- Jerry/Idaho
Utik posted 10-15-2009 09:03 AM ET (US)
I don't think weight is directly related.
Condsider the example I gave earlier. Think about a cigar shaped object with both ends pointed. Let's say it is 30 feet long and weighs 3 tons. Then think of a piece of plywood that weighs 2 lbs.
Both of these objects have a frontal area of 4 sq ft. Both are moved through a fluid at the same speed.
I would bet that the 2 lb board will disturb the fluid dramatially more than the cylinder shaped object.

John W posted 10-16-2009 06:45 PM ET (US)
In my experience deep vee boats always throw a bigger wake at anything but idle speed than similar, more flat bottommed boats. I believe hull shape probably has more to do with it than weight. Deep vee boats seem to "stern squat", as boatdryver said, more than flatter boats at displacement speeds, and they tend to climb a bigger hill when they are getting onto plane. They also throw a bigger wake on plane, for that matter.
Having said all that, I agree that weight distribution makes a difference. My 1971 Outrage throws up a bigger wake while getting onto plane since I repowered with a 150hp Suzuki 4 stroke than it did with the 2 stroke Johnson 150 it replaced. The weght difference is only about 100 lbs, but that weight hanging off the transom makes a significant difference in the wake at slower speeds.
sheikofthesea posted 10-17-2009 09:49 PM ET (US)
Unfortunately I can't follow the technicalities of this conversation but I fondly remember an interdisciplinary courses in Physics and Biology where we learned about the Bernoulli Principle, how different animal, plant and material solids interacted with water and air flow, and read a book called "Life in Moving Fluids." My 190 Montauk swerves at low speeds but does not create a wake.--Sheik
jimh posted 10-18-2009 09:32 AM ET (US)
My initial request for an explanation of the wave making properties of the two hulls and their differences may have been too overreaching. According to naval architect and author Harry Bedford, who was for a time head of the Department of Naval Architecture and Marine Engineering at the University of Michigan, and who has written an excellent book on the fundamental principals of naval architecture, predicting wave making is difficult. He writes:

quote:
"Naval architects simply do not understand in any quantitative way the physics of how a ship creates waves. Strictly mathematical approaches to analysis have been under study for several decades, but most design methods in use today still rely on empirical evidence from model basin work...or derive their conclusions from measured performances of existing similar ships."
Harry Bedford, Naval Architecture for Non-Naval Architects, (Jersey City, NJ: The Society of Naval Architects and Marine Engineers, 1991), p.92
Hoosier posted 10-19-2009 09:18 AM ET (US)
See
http://en.wikipedia.org/wiki/Wave_making_resistance
During the "test period" under discussion there were two Revenge 22s, one with Whaler Drive and one without, both had similar HP engines that were near the same weight. The one without Whaler Drive appeared to make significantly more wake. Interestingly, an Outrage 18 seemed to make a bigger wake than the Revenge with Whaler Drive.
jimh posted 10-19-2009 09:31 AM ET (US)
David--Thanks for the pointer to the article on wave making resistance. It provides a possible explanation for the performance of your Outrage V-20 hull at low speed and its small wave making. I refer to the comment,
"Another way [to reduce displacement] is to shape the hull so as to generate lift as it moves through the water."
The Outrage V-20 has a flatter bottom than the Revenge 22, and it probably generates more lift.
Hoosier posted 10-19-2009 09:45 AM ET (US)
Isn't google great? For you engineers in this "family", here's the source paper for the Wikipedia article.
http://legacy.sname.org/newsletter/Savitskyreport.pdf
It's a long one, I'm going to get another cup of coffee before I tackle the whole thing.
ConB posted 10-19-2009 07:52 PM ET (US)
Dave, I agree that the Outrage 18 wake seemed to be bigger than yours or Jim's. I could not keep up the pace and not make a small wake.
Con
roloaddict posted 10-19-2009 11:09 PM ET (US)
Perhaps the reason is a diffence in waterline length. One vessel with a certain length, at displacement speed, could produce a bow wave that is perfectly out of phase with the stern wave and thus cancels it. Where the second vessel with a different waterline length, at the very same speed, may produce a stern wave in phase with the bow an as such create a larger wave.
jimh posted 10-20-2009 01:37 AM ET (US)
David--I read the SNAME paper, but instead of coffee I got a glass of beer.
It was an interesting article, and it was filled with ideas. I saved a copy to my laptop. Curiously, I tried to access this article earlier, from a link in the Wikipedia article, and it was a dead link. I am glad you mentioned it, and gave a working link.
My favorite sentence (fragment):
"...high speed and high sea state usually have an adversarial relationship...."

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