Comparing Hulls

#76

Kevin I am Seated and ready to learn.

#77

X2 ProfessorK. Covering my keypad and taking notes.

#78

Land vehicles are pretty specialized and not very often used too far outside their area of specialization. A dragster (fuelie, rail frame, slicks and scooter tires up front) is hardly useful to drive to the beer store in the afternoon. While a small sedan may be a better choice for the beer run, a Peterbilt line tractor could do the job, but it wouldn't be needed unless you're hauling some fairly significant volumes of brew.

I'm just pointing out the level of specialization of most land vehicles. But the reason to point to these features in some different uses are the land or roadway these vehicles travel. We all accept that a 4x4 of some type and size is more useful offroading than the family sedan. It's obvious that the flatter and smoother the roadway (interstate) the less rough the ride and those conditions don't change unless you drive off the pavement, get in between the corn fields or onto the back roads- even onto a dirt track in the woods.

But that is not the same for boats. We can leave the harbor or the beach on an "interstate sea" as flat as a pool table for as far as the eye can see, but during the day that surface can change from the "interstate sea" pool table top into a tough, nearly vertical stretch of the Rockies with blowing rain, mud slides and falling rocks.

So, when we discuss boat performance we should look at the hull a bit in terms of where on the same hull do different boats deal with different seastates. In other words if our marine vehicle has to drive on all 'road surfaces' as the seastate changes; what areas on the hull do we deal with these various states?

I'll make three divisions for this observation. First when its flat calm up to a very short wave or even small chop, the boat's bottom between the chines and aft the forefoot is where the hull 'runs'. This is done at the highest speeds, just like traveling on the interstate in Nevada or Wyoming where is flat, empty and fast.

Next the waves get a bit taller, and the bow area of the forefoot and maybe just above the chines will be involved but usually only in a transition. There are places to run between crests, or just pitch the bow down and 'run into them' on some hulls. This is a second range of speeds usually a bit lower than the first 'all ahead full' state above.

Last is the sea state where we're in the rollers, or high enough waves that the slowest speed ranges are used. This range may have the wave coming all the way up the bow, or it may be over the bow depending on the boat, sea, wind, heading speed and on and on.... all those factors need to be defined in this last state to understand what part of the hull is involved.

But the main idea here is that a planing boat is designed to deal with all three ranges.

For the sake of our discussion, I'm going to label these three states as planing, semi-planing, and displacement hull movement modes.

All powered boats can move at displacement speeds; the slowest powered range on the water. In this state of movement the hull is held up by the force of buoyancy not by the lift of planing ("high speed, water molecule chain breaking" in my earlier terms above).

Next in increasing speed is the semi-planing range, and last the highest speed when the hull is on top of the water or planing.

We've already seen that the harder we push something onto on through water the more water 'pushes back', or the 'harder' water is but really we all understand this is called lift. Once the boat is lifted/resisted upwards/forced out of the water enough we can probably all agree it planing?

So I'll give some speed ranges for these 3 states, all of which you can find from the many authors before me who have addressed this.

Cheers,
Kevin Morin

#79

Just a note to reaffirm that I'm simplifying physics in these images, they're for the sole purpose of giving a mental picture, which is often said to help retain information.

I got a sort of disturbing email asking about details of one image posted above, the question implied that the image was the TRUTH, but they are, I've tried to explain, just a way to help imagine or visualize the ideas we're calling 'basics' before we apply these forces to hulls.

So this post is just a reminder that this entire thread is a: MOS- which I'd hoped express above as- a Massively Over Simplification (MOS)....

There are no logging chains in water, it just acts like there are- "sort of". Water tends to stay together if it's impacted at high speed but the force 'holding' it together, (chains in our images) get weaker the slower we push on or through water.

Cheers,
Kevin Morin

#80

We need to get into the terms used for the three speed ranges, a bit more exact than slow, faster and fastest.

Speed is affected by the shape of the boat, and OVERALL (not exactly) we'll say the speed of each range will be most influenced by the length of the boat. Remember we're only considering boats from about 20 to 36' LOA. The waterline is where the boat 'hits' the surface of water and where the resistance is going to happen, so... we'll add a 'length' for a 20' boat of a 18' waterline.

These ratios are Speed/Length ratios where we take the Square Root of the waterline length and multiply by a factor.
In our case the factors are
#1 0 to 1.4;
#2 1.4 to 2.5 (slowest planing state)
#3 2.5 to 3.0 (faster hulls' planing state)

We're going to listen to Dave Gerr, and use these ranges: displacement speed= up to S/L of 1.4 then semi-displacement speeds =S/L 1.4 to 2.5 and finally above 2.5 to 3.0 ratios all boats are planing.

This is not the last word in all cases, but for our discussion I think this will limit our potential for confusion and keep us on the 'straight and narrow course'.

Speed on the water is sometimes expressed in knots or one nautical mile per hour, versus expressed in land miles per hour. A knot is about 1.15 times as long/fast as a mile per hour because the nautical mile is longer by about 15% so one of these charts is in knots the other in land miles per hour.

The slowest speed range is from "dock lines on" (zero headway) to the first column value and I've labeled this 'displacement speed' sometimes this is called 'hull speed'. This is the speed a boat can travel IN the water, where all that holds the hull up; is buoyancy.

The next range is (NOT SHOWN) semi-displacement speed which is beyond hull speed, but not "up on top of the water" in a planing mode of hull balance. This is the speed in between the first speed column and the next where the water is not 'hard enough' to lift the boat onto plane.

Last I show two speeds where a hull is planing, one 2.5 S/L column, is for slower top speed flatter bottoms with little or no V. The S/L ratio column 3.0 is a good speed to assume all boats in our category of exploration are planing.

Speed Chart in Knots

Speed Chart in MPH

So let's read these once to make sure this all makes sense in a 'rules of thumb' type of statement. In the 3rd line on each chart in the left most column is the number 22' so this is the length of a boat's waterline. The boat will have a little overhang at the bow, as the stem is raked, so this entry (row/line/record) is for a 24 to 25' foot boat LOA.

Next the 1.4 column show a figure of 6.6 knts/7.6 mph as the top end of a the hull speed or displacement speed of this boat. Now this is approximate but a good rule of thumb, if this hull is traveling slower than this, its only lift is buoyancy.

To the right are two more columns, first the slowest speed this boat is planing, next the upper end of beginning to plane. That means if the hull has a 8deg deadrise at the transom, or is a 'jon boat', it may begin to plan at 11.7 knots/13.5 mph.
However if its not planing at the lower speed of 12knt/13mph then is surely is planing when it reaches 14.1 knts or 16.2 mph.

Above these speeds the 22' waterline length hull is going to be considered planing. So, we could say the water is hard enough to lift the hull up, when the hull hits the water at speeds at or above those shown in the charts?

This is a MOS because we are focussing on V bottom, planing hulls, with enough horsepower to push through the slower to speed ranges for any boat in our consideration and therefore reach the state we call planing.

cheers,
Kevin Morin

#81

I know this is a little late but I like the Visualization and explanations.

http://www.marinepolicy.net/cparsons/Oc ... 0Water.pdf

For me it helps me visualize the hydrogen bonds that make water. The bonds are a invisible force. The bonds are the invisible chains. Unlike a solid, the bonds/chains of water molecules can be separated easier.

Surface tension- The tension of the surface film of a liquid caused by the attraction of particles in the surface layer by the bulk of the liquid below?

My question is..... The physics that make a hull plane? Surface tension??? Water pressure created by hull movement over water???? Or the amount of water molecules that come in contact with the hull in a given time (increased density)??? Water Compression????

Thank you Kevin you explanations are effective for me

Sorry if that does not fall into MOS or KISS doctrin

#82

To me, I know my previous post may seem silly to others. I understand the principles of lift. As a kid I would get in trouble hanging my hand out the window holding it out flat at varying angles. Played and swam in rivers.... Holding my hand in the current at varying angles too. Later understanding how air plane's fly. Pressure differential from the lower half of the wing and upper wing. The curvature of the wing and airflow traveling faster over one half the wing.

This netherland between water and air. Yes I have skipped stones and found that magic angle and the best flat rocks. Imparted the spin with the flick of the index finger and wrist. That area of impact????? Water does not compress very easily. I could never dive well and belly flops stung. So is it speed over surface tension that causes the skip??? Pressure differential between air and water???? A bit of both and other factors..... Which force is the most influential? Just trying to help my TWISTED visualization process.

I know trying to keep MOS and just accept a mostly shallow v at a certain length and angle at waterline plus speed will plane. Less waterline less frictional drag.

#83

Mark, its not an instantly obvious idea, so spending time getting this concept is normal, I'm not sure I've got a handle on it!

The main event is how hard water is? So the force (adhesion) holding the 'chains'/molecules/droplets together is what gives the primary resistance to 'parting' or separating. That turns out to be called 'lift' even if there is NO actual force UP- (I mean boats don't jump out of the water!) UNLESS YOU'RE TRYING TO PART THE WATER BY MOVING THROUGH IT. But what's critically important it to see water's changing 'adhesion' to itself.

When you push the boat forward, faster and faster, the resistance to parting of the water increases so the water becomes more and more 'solid' as you go faster. In the charts above, we can say:

"above 12-14 knots water is "hard enough to part" that it will lift a hull."

LIFT is the point at which water will resist moving (aside or being parted) so much the attraction of the molecules is greater than the force pulling them apart. This attraction isn't constant, its more when the rate of impact is more. In fact, a bullet moving at supersonic speeds will act like it hit concrete when it hits water.

That is a big deal.

The kicker is.... this 'lift' changes in proportion to the rate the object is moving on/through the water. As you increase speed/velocity water 'gets harder' (to part) so it 'pushes up' by NOT PARTING. (This is referred to as the Reynold's Number of water.)

Planing a hull, like our hulls at AAB.com, is a balance of forces. First, is a rigid shape that is thrust at a high enough speed/velocity to reach water's state of resistance (to parting/moving aside) high enough to force the hull up and out of the water, and remain in a balance of thrust and 'lift' or resistance to parting. (not all forces mentioned here!)

Don't add the Drag concept to this idea- yet.

This is why I used the logging chain to show the water 'holding together' at high speeds and each slower speed/weaker skip of the stone showed smaller and smaller chains. As you slow down, water becomes easier to part..... soo...... the boat comes 'off plane' and settles into the water and runs at semi-planing, then slower at displacement speeds.

This resistance to moving aside or lift happens (mainly) at the leading edge of the RUNNING waterline. Lift is our DESCRIPTION of the EFFECT of the water trying to 'stay together', so the EFFECT of moving over water at 18 knots is that the water tends to stay together so well, that objects of a certain size are 'lifted' on top of the water.

If you slap water as hard as possible flat handed, your hand will stop at the surface. If you slowly slip the same exact hand into water in the same exact flat handed orientation to the water, there is little or no resistance to immersing your hand.

Fast travel = water "hard" it sticks together more like a solid. Slow movement= water not "hard' it hardly sticks together at all. "Hard" water is more like a solid, "not hard" water is less like a solid and more like a fluid/liquid.

Still more step-by-step coming.

wait till we start looking at lift strakes!!! or reverse chines!! this all gets a bit complicated.

Cheers,
Kevin Morin

#84

I'm not sure where this post went yesterday but I'll repost this and see how we do?

this introduces a series of images and ideas dealing with planing a very simply jon boat shape. My reasoning to begin with a jon boat is t keep the geometry as simple as possible before adding V, reverse chines, and 'lift strakes' to the consideration of how planing happens.

As mentioned before, most of what is being posted is a MOS and is primarily intended to help get a common ground for the ongoing discussion of hull performance comparison.

This is a pair of views of one jon boat, the boat to the right has a waterline INSIDE the boat to make the port side image of a 'hole in the water' more clear. We know the water that fills that port side hole weighs the same as the boat , motor cooler and all.

The cooler is located forward to balance the motor, so the CG is over the CB, but if the cooler is removed then the CG will shift aft and the boat will be down by the stern/up by the bow some amount.

testing , testing,
Kevin Morin

#85

Reading you loud and clear..........sitting on the edge of my seat.

#86

Mojo, work is taking more and more screen time, sorry to be so lax in updating this post. And I'm heading to the old country for a week or so for the Thanksgiving week- so there won't be access on the road and I'm not packing drawing software with me!

the CB and CG located one over the other because the boat is balanced

close up of the two labels and what I'm using to show the approx locations of the these two centers.

Pull the cooler's bow wt and the boat goes down by the stern, CG shifts aft toward the larger mass of the engine.

here's the modified 'hole in the water' of the displacement when the boat is not level and trimmed flat but has more wt aft and is therefore 'down by the stern'.

Next we'll need to push this jon boat a little bit.

Cheers,
Kevin Morin

#87

The flat bottom, simplest shape boat shown, balanced, at rest with no thrust to push this particular 'hole in the water' forward, to the left and to the right that same hull as the engine thrust is added to push forward.

Adding a little thrust from the outboard at speeds below the planning speed changes the forces on the hull. First the push forward begins to meet INCREASED resistance at the leading edge of the waterplane since that if the first place the hull is trying to 'break' the changes of the water. But, at low speeds you may recall, these 'chains' of adhesion are not strong. In fact we all know that the boat could be polled along with almost no resistance at all? That is; at very slow speeds the water would offer such low resistance that the bow would not pitch up, due to the resistance of water to being parted, at all.

As the boat's speed increases, the water resistance increases too- so the result is the front edge of the waterplane's entry has more and more force upward, at 90 degrees to the bottom's surface (not plumb and vertical). Here that force is shown by a blue arrow.

The other change is the waterplane's leading edge moves back under the hull. This happens because not only is there a force upward (water's resistance to 'parting' or separating) at the lead edge of the hull's 'hole in the water' but there is some force all along the hull's bottom surface. Remember the entire hull is 'parting' the water; trying to 'break the chains of adhesion'.

The hull's bottom is lifted slightly at this lower speed but mostly the waterplane shortens because the boat is pitched up by the bow.

Just to add the boat in the foreground to confirm the other images. If you look at this boat as it begins to 'harden' the water in front of the hull, by moving faster through that water, the 'chains' are getting bigger and stronger because the boat is pushing harder and harder as we speed up. The harder the boat is pushed the stronger the chains will get.

The boat's travel speed is not as high as the skipping rock yet, so the bow-up pitch is due to the small change in resistance of the water at rest to the speeds where the hull will begin to plane. One other event not shown is the bow wave, which will also lift the boat's bow to some degree.

This boat is more like the rock slowing down! than the rock skipping at full (initial) speed. This jon boat is going to increase speed to the point where the forces parting the water are equal to the displacement of the hull. The primary lift of this boat is still buoyancy, with the bow up trim an 'unbalancing' force; not a large enough force, yet, to lift the entire boat, but enough to trim up by the bow and down by the stern.

cheers,
Kevin Morin

#88

No problems on posting up Kevin I appreciate the effort of teaching us amatuers.

Have a great and safe Thanksgiving Holiday.

#89

Found this online. I hope this adds to the discussion.......... http://www.orca3d.com/support/manual/in ... uction.htm

Fisherman · #90

Talking about forefoot earlier, here is a boat hull that is common in southern CA. It is not aluminum, but it is interesting to see the lack of forefoot. It is designed for heading back home in the afternoons with a stiff breeze and following seas at its stern. This is a 26' boat with a 17* deadrise at the transom, weights around 6,500 lbs dry if memory serves correctly.

: Radon Boat Hull; 26rv1lg.jpg (35.67 KiB) Viewed 13633 times

Sorry to digress from the latest topics discussed here, but just found it interesting and noteworthy.

#91

Hello Kmorin, I hope things are going well in your neck of the woods. I realize the time it takes to post detailed information on such a complex subject. Hull design and it's interaction with a marine environment is quite a task indeed.

Please if you have the time, I for one would like to continue reading the knowledge you graciously share.

#92

Mark, I took on a design project a few months ago, (Thanksgiving or so) and I've been covered getting it ready to go.
I'll be back in a month or two when I sell this project's output and resume our Shape vs Movement discussion.

In the meantime; my drawing time is all going for this industrial design project.

Cheers,
Kevin

#93

Mark, here is a 'draft level' image of four of sixteen different pump/pipe/flow runs similar to this set. There's lots to model, more to design and plenty to write spec.s for and to find suppliers, catalog numbers (most have 2 dozen figures in the #) and make sure the features of the controls, pumps, flows, valves, and electrical controls all work together.

I know lots of people find this work boring but it is something to do in the non-boating season here in the frozen Northern wastes- but it is taking up all day, every day, but I'm not bored and its fun to design systems once in while instead of boats. I have had a few new boat design ideas while doing this work- so I'm looking forward to getting done enough to draw some new boats.

All's well, just busy.

Cheers,
Kevin

tazmann · #94

dang Kevin
I thought some of the filter stations I plumb in got confusing but after looking at yours they are a walk in the park
Is that for gas/ oil ?

#95

Tom, how are things in the land of "oranges & almonds" ? I'd think you were looking to immigrate to some more work oriented piece of geography with all the crazy things in the news there?

The job is a new college simulation lab to train oil and gas operators and instrument technicians. An old friend, who is consulting engineer, got me the job designing this lab for a local contractor who's not instruments and controls oriented; but has the entire building contract so they had to come up with some lab equipment.

I'm just doing the lab process simulator; six pump trains, 20 some actuated control valves (Fisher EZ or Masonelian Camflex) six tanks and inter-ties to the entire set of tanks and pumps. The electrical EMT; about 1/8th the flow line tie-ins; the air supply tube and the rest of the control circuits are still 'happening'. The entire lab teaches pressure, level, temperature and flow and is PLC loop controlled with an HMI supervisory interface. A scaled down version of a gas or oil production facility as a 'trainer'.

Cheers,
Kevin

#96

Too cool professor K

Quite a few engineering disciplines to design that pipe job. My head was spinning from a sprinkler manifold

The more I read about your posts.......... You sir are a Renaissance Man with my deepest respect.

Looking forward to when you are able to continue the discussion.

tazmann · #97

kmorin wrote:Tom, how are things in the land of "oranges & almonds" ? I'd think you were looking to immigrate to some more work oriented piece of geography with all the crazy things in the news there?
Cheers,
Kevin

Hello Kevin
surviving , I still have a few good customers that keep me going so it makes it hard to pack up and leave
beside that not sure where to go anyway ?

Fisherman · #98

Kevin, any updates?

#99

It's been a while since we visited this subject and I've had some time to think of how to move ahead, and what to post in way of a review. We'll kick it back off with some generalizations and see if we can get back into the topic?

[For anyone just coming into this discussion, let's be sure you realize we're dealing is a subject so broad that I've taken the stance that we'd confine ourselves to 18-35' planing boats, and that we're using the agreed method of MOS (Massive Over-Simplification) to avoid having to take into account the limitless variations on our theme.]

#1. Hulls are supported on water by two different forces or a combination of two different forces; one is buoyancy which is the force lifting a hull- equal to the weight of the water moved aside by the hull. The buoyancy equals the actual weight of the entire hull and that is why the weight of a boat is called its 'displacement'.

#2. Water gets 'harder' or has more resistance which results in more LIFT ; the faster it's forced to move aside by a boats' passing. We used larger and large link size chains to show that the faster the boats impact water the more resistance water molecules have to moving aside and 'letting the boat through'.

#3. The other force is a lift force that results from water resisting moving apart and only begins to act as the hull is moving on or through water; the faster the boat moves the more lifting force there is acting on the boat's hull in contact with the water.

#4. A skipping stone shows that the lift force can be so powerful that a rock, which has too little buoyancy to float, will 'plane' or skip over the surface of water if it's traveling fast enough. But.. if that same rock slows down; the lift force holding the water together becomes less and less and a skipped rock sinks after losing energy of forward motion.

#5. Planing is the state of balanced motion of a boat where the forward thrust is high enough to create a rate of travel sufficient that water reacts with adhesion forces great enough to 'lift' that hull onto the surface of the water.

#5A. We could also say that planing is operating a boat where most of the weight is supported by 'lift' instead of by buoyancy.

#6. Hulls may be said to have three ranges of speed operation,
1 Displacement speeds where the main force supporting the hull is the buoyancy of the hull;
2 Semi-displacement speeds where the lift from forward velocity begins to add to the forces supporting
the hull, and;
3. Planing speeds where the primary force of support is the reaction of the water to the velocity
of the hull's contact/impact; resulting in 'lift'.

#7. Hull bottoms usually have three ranges of deadrise angles. The deadrise angle is formed by the bottom of a V shaped hull between the horizontal (waterplane) and either half of the V, measured at the keel.
1 Flat or nearly Flat deadrise 0 to 5 (maybe 7?) degrees
2 Medium V; deadrise of 5 (maybe 7?) to15 degrees
3 Deep V; deadrise greater than 15 degrees

#8. The combinations of the three shapes, in each speed range, in various sea states would give different paths of movement.

#9. The term Rate is used to describe a comparison or ratio of two values that are of different units or measure. For instance, the rate of travel, or velocity, is ratio of the distance crossed in a unit of time. Boats are said to travel five or ten miles per hour. Also the "rate of immersion" (sinking or sinkage) is the change in waterline of a hull in a given unit of time so a boat may be immersed 1" per minute or 1" per second if it were travel faster in waves.

#9. The rate of change of forces acting on a boat gives a 'feeling' called ride. A smooth ride is the result of the rates of motion of the boat combined with a given sea state acting on that shape of hull. A hard ride is the result of (very) short time changes in the rate of motion of a boat's hull.

#10. If a boat's hull and speed combine to change the rate of immersion in a very short time, different shapes of hulls will move in different paths; viewed from the outboard sides. From this path we can examine the 'ride' or feel of that boat's motion in those conditions.

#11. If the path of a boat is not smooth when viewed in slow motion from the Profile View, the ride is "rough". Generally, this hull is considered to have poor "ride" as irregular paths are most often result in a condition called slamming, where there is a angle point or 'knuckle' in the path of movement of that hull in those conditions.

#12. All hulls' paths will become hard or angular at high enough velocity combined with a high enough sea state.

I guess the next thing to do is to make a few images to help make these statements into more visible information and to make a table of the shapes at different speeds versus the sea states.

Cheers,
Kevin Morin

Fisherman · #100

Thanks for revisiting this discussion, Kevin. Just yesterday I referred back to this thread to look up some information in it. Looking forward to more.

AluminumAlloyBoats.com

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