Deadrise ??
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Grady Wahoo
Member
- Joined
- Feb 25, 2005
- RO Number
- 16408
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- 438
This should get you started.....
"Planing hull— Achieving high speeds on the water requires a hull that easily transitions into the planing mode. Characteristics of a planing hull include flat bottom surfaces from amidships aft (from the middle to the back of the bottom) and flat transom (back of the hull). The transom must meet the bottom at a sharp angle. At certain speeds that vary with each bottom, the boat is supported by the same dynamic forces that keep a water skier on top of the water. Put simply, it planes.
The sharp angle (or "break") between the transom and the bottom is critical to a planing hull. It allows water flowing beneath the boat to come free of the hull without climbing up the transom and where it would create speed-robbing suction. The smooth, rounded shape of a displacement hull does not allow the water to break free in this manner.
Absolutely flat bottoms, a sub-species of planing hulls can be extremely fast, but are not easy to control and tend to bull their way through waves like a pile driver. Giving the bow a pointed shape allows a hull to slice through waves instead of slam into them. For a boat to operate above displacement speed, the V-shape of the bow must "warp" into flatter planing surfaces near the stern.
Stand at the back of a planing hull boat and you will notice that the bottom angles upward from the keel. This angle is known as the "deadrise." Prior to the 1950s, designs had little or no deadrise to the bottom at the transom in order to achieve acceptable performance with the smaller engines of the era. As more power became available, designers were able to increase the deadrise angle to give boats a softer ride and better control.
Here are a few more terms you're likely to encounter in bottom design:
Round bottom— These are used mostly on vessels intended for displacement speeds. Round hulls provide a gentle ride with little fuel expenditure, but tend to roll from side to side in certain sea conditions.
Low deadrise bottom— Sometimes called shallow-V bottoms, these running surfaces have a deadrise angle of 20 to 25 degrees amidships which reduces to 5 degrees or less at the transom. (Deadrise is the angle measure of the "V" in the bottom. It is generally greater at the bow, or "entry" of the boat, and shallower at the transom, or stern of the boat.) This provides a smoother ride, but it still retains the quick ability to plane of a flat-bottomed boat.
Deep-V bottom— This type of hull has a deadrise of 25 degrees amidships with reduces only slightly to 20 degrees at the transom. This shape allows high-speed operation in rough water.
With few exceptions, planing hulls have chines and strakes. Chines are the angles on the hull where the vertical topsides meet the bottom. Older designs often had rounded or "soft" chines. Today's hulls almost universally have a sharp corner or a "hard" chine. Round-chine boats tend to roll a bit more, so they're not favorites with anglers who prefer the stiffer characteristics of a hard-chine boat. (A boat that resists rolling is said to be "stiff.")
Strakes are those little "ridges" you see below the chines. Their primary job is to provide lift, which is important in the planing process and overall running efficiency.
Now and Then
Hull shapes evolved slowly during the era of wooden boats because wood only bends and twists so much without splintering. Designers became free to explore their imaginations when fiberglass became the dominant material for boats. Not all of their ideas were good. Many early attempts at cathedral hulls (more on those at the end of this story) resulted in hard-riding, sluggish hulls that required inordinate amounts of fuel. Other designs like the deep-V proved their worth and remain popular. A couple of hull forms are particularly popular today
Ski boats— Hulls of competition water-ski boats are designed to minimize wakes at certain speeds so that slalom skiers can slice through them more easily. Ski-boat builders spent years creating running surfaces that produce the flattest, softest wake. Funny twist? Those same designers have revisited those designs in their wakeboard boats, where the goal is to provide big wakes at certain speeds.
Stepped hulls— One of the earliest attempts to increase boat speed involved putting small "steps" in the hull. Steps are, essentially, elevation breaks that create multiple running surfaces. As the boat speed increases, it rides on these surfaces, with area of contact with the water moving progressively further aft. The results? Less hull in contact with the water, less friction and more speed with less power than a conventional deep-V hull. The knock, at least against some stepped-bottom boats? Less wetted surface in the water, less friction and reduced lateral stability and control.
Beam, or the width of the hull at its widest point, is important in determining the boat's fuel efficiency and ride through choppy waters. The trend in recent years has been toward wider boats because increased beam (width) allows more room for interior accommodations. Wider boats also feel more stable, which makes them popular for dockside entertaining. In addition, they are less likely to roll from side to side while underway.
These benefits come at a price. A wider a boat is more likely to pound (slam into waves) as it moves through choppy water. Plus, it can take more fuel to move a wide boat at a given speed than a narrow hull of similar length.
Narrow deep-V hulls, on the other hand, tend to slice through waves, and because they have less wetted surface and less friction, they can be more fuel efficient than wide-body boats of the same length. On the downside, they tend to roll from side to side more while underway and offer less interior space.
Most boat builders are aware of the relationship of beam to length when it comes to performance. High-speed powerboats tend to have narrow hulls with relatively large deadrise angles that often approach a traditional deep-V design.
Cruising boats are much wider. Today it's not unusual to see the hulls of a cruiser with a beam approaching one-third of the boat's overall lengths. Modern, high-horsepower engines allow these wider boats to move at speeds faster than the so-called "speedboats" of a generation ago. The penalty, of course, is more fuel consumption.
Compromise a Constant
While this series isn't devoted to fishing boats, offshore anglers face a dilemma that illustrates why all boat purchases require accepting compromises between speed, comfort and function.
Offshore fishing often requires long runs through rough seas. For that job, a relatively narrow, high deadrise hull is best. But, once on at fishing grounds, a stable platform with a large cockpit for both anglers and their gear is a must. While drift fishing, a wide boat with hard chines and a relatively flat deadrise is desirable. Obviously, one hull can't meet both demands. Fishing skippers have to choose a mixture of deadrise, beam, length and hull shape that is best for their needs.
With cruising boats there are fewer conflicting demands on the hull. Maximum interior accommodation is the overriding consideration. Most of today's cabin boats have wide beams to allow for extensive galleys, large beds and comfortable saloons. A rougher ride is less of a consideration because family cruising is primarily done during fair weather and gentle sea conditions.
Until powerboats were mass-marketed, hull shapes reflected the types of conditions faced on waters surrounding individual boat builder's shops. Boats for shallow water areas where choppy conditions predominate tended to be narrow, with fine entries (narrow bows) and small planing surfaces aft. Contrast that with the wide-beamed, relatively flat-bottomed boats built in areas where crossing sandbars with following sea (running in the same directions as the prevailing swells) was the major problem."
As far as the 18 vs 20 degrees goes, The 20 will do better cutting through the waves heading offshore, but the 18 will do better once the boat slows down/stops as it will rock less trolling or at anchor. So, what type of boating do you plan to do?
"Planing hull— Achieving high speeds on the water requires a hull that easily transitions into the planing mode. Characteristics of a planing hull include flat bottom surfaces from amidships aft (from the middle to the back of the bottom) and flat transom (back of the hull). The transom must meet the bottom at a sharp angle. At certain speeds that vary with each bottom, the boat is supported by the same dynamic forces that keep a water skier on top of the water. Put simply, it planes.
The sharp angle (or "break") between the transom and the bottom is critical to a planing hull. It allows water flowing beneath the boat to come free of the hull without climbing up the transom and where it would create speed-robbing suction. The smooth, rounded shape of a displacement hull does not allow the water to break free in this manner.
Absolutely flat bottoms, a sub-species of planing hulls can be extremely fast, but are not easy to control and tend to bull their way through waves like a pile driver. Giving the bow a pointed shape allows a hull to slice through waves instead of slam into them. For a boat to operate above displacement speed, the V-shape of the bow must "warp" into flatter planing surfaces near the stern.
Stand at the back of a planing hull boat and you will notice that the bottom angles upward from the keel. This angle is known as the "deadrise." Prior to the 1950s, designs had little or no deadrise to the bottom at the transom in order to achieve acceptable performance with the smaller engines of the era. As more power became available, designers were able to increase the deadrise angle to give boats a softer ride and better control.
Here are a few more terms you're likely to encounter in bottom design:
Round bottom— These are used mostly on vessels intended for displacement speeds. Round hulls provide a gentle ride with little fuel expenditure, but tend to roll from side to side in certain sea conditions.
Low deadrise bottom— Sometimes called shallow-V bottoms, these running surfaces have a deadrise angle of 20 to 25 degrees amidships which reduces to 5 degrees or less at the transom. (Deadrise is the angle measure of the "V" in the bottom. It is generally greater at the bow, or "entry" of the boat, and shallower at the transom, or stern of the boat.) This provides a smoother ride, but it still retains the quick ability to plane of a flat-bottomed boat.
Deep-V bottom— This type of hull has a deadrise of 25 degrees amidships with reduces only slightly to 20 degrees at the transom. This shape allows high-speed operation in rough water.
With few exceptions, planing hulls have chines and strakes. Chines are the angles on the hull where the vertical topsides meet the bottom. Older designs often had rounded or "soft" chines. Today's hulls almost universally have a sharp corner or a "hard" chine. Round-chine boats tend to roll a bit more, so they're not favorites with anglers who prefer the stiffer characteristics of a hard-chine boat. (A boat that resists rolling is said to be "stiff.")
Strakes are those little "ridges" you see below the chines. Their primary job is to provide lift, which is important in the planing process and overall running efficiency.
Now and Then
Hull shapes evolved slowly during the era of wooden boats because wood only bends and twists so much without splintering. Designers became free to explore their imaginations when fiberglass became the dominant material for boats. Not all of their ideas were good. Many early attempts at cathedral hulls (more on those at the end of this story) resulted in hard-riding, sluggish hulls that required inordinate amounts of fuel. Other designs like the deep-V proved their worth and remain popular. A couple of hull forms are particularly popular today
Ski boats— Hulls of competition water-ski boats are designed to minimize wakes at certain speeds so that slalom skiers can slice through them more easily. Ski-boat builders spent years creating running surfaces that produce the flattest, softest wake. Funny twist? Those same designers have revisited those designs in their wakeboard boats, where the goal is to provide big wakes at certain speeds.
Stepped hulls— One of the earliest attempts to increase boat speed involved putting small "steps" in the hull. Steps are, essentially, elevation breaks that create multiple running surfaces. As the boat speed increases, it rides on these surfaces, with area of contact with the water moving progressively further aft. The results? Less hull in contact with the water, less friction and more speed with less power than a conventional deep-V hull. The knock, at least against some stepped-bottom boats? Less wetted surface in the water, less friction and reduced lateral stability and control.
Beam, or the width of the hull at its widest point, is important in determining the boat's fuel efficiency and ride through choppy waters. The trend in recent years has been toward wider boats because increased beam (width) allows more room for interior accommodations. Wider boats also feel more stable, which makes them popular for dockside entertaining. In addition, they are less likely to roll from side to side while underway.
These benefits come at a price. A wider a boat is more likely to pound (slam into waves) as it moves through choppy water. Plus, it can take more fuel to move a wide boat at a given speed than a narrow hull of similar length.
Narrow deep-V hulls, on the other hand, tend to slice through waves, and because they have less wetted surface and less friction, they can be more fuel efficient than wide-body boats of the same length. On the downside, they tend to roll from side to side more while underway and offer less interior space.
Most boat builders are aware of the relationship of beam to length when it comes to performance. High-speed powerboats tend to have narrow hulls with relatively large deadrise angles that often approach a traditional deep-V design.
Cruising boats are much wider. Today it's not unusual to see the hulls of a cruiser with a beam approaching one-third of the boat's overall lengths. Modern, high-horsepower engines allow these wider boats to move at speeds faster than the so-called "speedboats" of a generation ago. The penalty, of course, is more fuel consumption.
Compromise a Constant
While this series isn't devoted to fishing boats, offshore anglers face a dilemma that illustrates why all boat purchases require accepting compromises between speed, comfort and function.
Offshore fishing often requires long runs through rough seas. For that job, a relatively narrow, high deadrise hull is best. But, once on at fishing grounds, a stable platform with a large cockpit for both anglers and their gear is a must. While drift fishing, a wide boat with hard chines and a relatively flat deadrise is desirable. Obviously, one hull can't meet both demands. Fishing skippers have to choose a mixture of deadrise, beam, length and hull shape that is best for their needs.
With cruising boats there are fewer conflicting demands on the hull. Maximum interior accommodation is the overriding consideration. Most of today's cabin boats have wide beams to allow for extensive galleys, large beds and comfortable saloons. A rougher ride is less of a consideration because family cruising is primarily done during fair weather and gentle sea conditions.
Until powerboats were mass-marketed, hull shapes reflected the types of conditions faced on waters surrounding individual boat builder's shops. Boats for shallow water areas where choppy conditions predominate tended to be narrow, with fine entries (narrow bows) and small planing surfaces aft. Contrast that with the wide-beamed, relatively flat-bottomed boats built in areas where crossing sandbars with following sea (running in the same directions as the prevailing swells) was the major problem."
As far as the 18 vs 20 degrees goes, The 20 will do better cutting through the waves heading offshore, but the 18 will do better once the boat slows down/stops as it will rock less trolling or at anchor. So, what type of boating do you plan to do?
Grady,
Thanks much. I will read through it a few more times but on the first go around I am already better informed.
What type of boating ???? I am looking at 24' - 26' Walkarounds. So far I have narrowed it down to a Sea Pro 255 or something similar in the Pro Line. The issue of Deadrise came up in comparing the 2 with SP ** 18* and PL ** 20*
Why the walkaround? Well for my first real adventure in boating I want something where I can have the best of both worlds. For more than 25 years I have been an inland lake/river boater. Strictly day use and that is it. Now, I have a place in FL and I want to venture into exploring the ICW and the Gulf. I would like to do some fishing but also I would like to just get away and do some cruising. So, I think, this type of vessel should be a good start. I may be happy with it and stay with it or I may decide I prefer one or the other and then "upgade" to a crusier or a Sport.
I hear you on the trade off of 20* vs 18* but is there that significant of a difference at 2*. Will the 20* really rock much more than the 18* at slower or no speeds
Thanks again for the info
PAT
Thanks much. I will read through it a few more times but on the first go around I am already better informed.
What type of boating ???? I am looking at 24' - 26' Walkarounds. So far I have narrowed it down to a Sea Pro 255 or something similar in the Pro Line. The issue of Deadrise came up in comparing the 2 with SP ** 18* and PL ** 20*
Why the walkaround? Well for my first real adventure in boating I want something where I can have the best of both worlds. For more than 25 years I have been an inland lake/river boater. Strictly day use and that is it. Now, I have a place in FL and I want to venture into exploring the ICW and the Gulf. I would like to do some fishing but also I would like to just get away and do some cruising. So, I think, this type of vessel should be a good start. I may be happy with it and stay with it or I may decide I prefer one or the other and then "upgade" to a crusier or a Sport.
I hear you on the trade off of 20* vs 18* but is there that significant of a difference at 2*. Will the 20* really rock much more than the 18* at slower or no speeds
Thanks again for the info
PAT
Grady Wahoo
Member
- Joined
- Feb 25, 2005
- RO Number
- 16408
- Messages
- 438
Pat, I have a 25' walkaround, so I hear what you're looking for! It's nice having 360 degrees of freedom around the boats perimeter and to have a shelter. Great for fishing, and rarely does that boat whose anchor has slipped have a collision course for my stern, I like being able to grab a boat hook and and quickly get forward or to either side to firmly plant my feet to fend off a possible impact. Happens at least once a weekend at the beach I frequent (tidal current factor high). I don't think 2 degrees of deadrise is "much" of a factor, there are so many others. Beam, weight, vertical center of gravity, quality of build are just a few. Test ride a few to get a feel. My Grady is 22 degrees where I installed my transducer, I'm sure the angle increases forward to 25 or so. I will tell you it rocks like heck on the hook and at one cove where I overnight it's almost unbearable. Course again length, beam and weight factor in here too. Cuts through anything though! 
Apparently there are some 12, 14 and 16 degree deadrise boats out there as well.
There's a nasty, yet humorous "for sale" thread going on elsewhere that has turned quite hostile, and since it's over a deadrise issue, (Reply to ad: "How does this boat take on a chop with that 12 deg deadrise?") I'm adding some comments to this discussion:
"quote"Chop.....a rediculas question really. Because my chop isn't the same as your "chop"."end quote"
"quote"What an a$$hole.
Let me tell you a bit about selling:
If you answer a question from a prospective buyer, you should not say it is “ridiculas”. If you do, then you would have sent him looking somewhere else. A 12 degree deadrise is shallow for an offshore boat and the question stands. If you need a lot of bow-down trim to make the ride bearable on a “chop”, then it is not what I´m looking for.
The tone of your answer only makes me think that your boat has a very lousy ride. Thanks for your answer."end quote"
"quote"but in a following resoponse he indicates that this will be last post on this topic as if he were just tire kicking and really not interested in buying the boat. And for some one with so much boating knowledge it looks like they would know what a 12 degree dead rise hull handles like."end quote"
After reading all this I'd possibly vote for the 20 Pat.
Apparently there are some 12, 14 and 16 degree deadrise boats out there as well.
There's a nasty, yet humorous "for sale" thread going on elsewhere that has turned quite hostile, and since it's over a deadrise issue, (Reply to ad: "How does this boat take on a chop with that 12 deg deadrise?") I'm adding some comments to this discussion:
"quote"Chop.....a rediculas question really. Because my chop isn't the same as your "chop"."end quote"
"quote"What an a$$hole.
Let me tell you a bit about selling:
If you answer a question from a prospective buyer, you should not say it is “ridiculas”. If you do, then you would have sent him looking somewhere else. A 12 degree deadrise is shallow for an offshore boat and the question stands. If you need a lot of bow-down trim to make the ride bearable on a “chop”, then it is not what I´m looking for.
The tone of your answer only makes me think that your boat has a very lousy ride. Thanks for your answer."end quote"
"quote"but in a following resoponse he indicates that this will be last post on this topic as if he were just tire kicking and really not interested in buying the boat. And for some one with so much boating knowledge it looks like they would know what a 12 degree dead rise hull handles like."end quote"
After reading all this I'd possibly vote for the 20 Pat.
Hey Grady, you and I are going to get along pretty well after all- I thought I was the king of long winded explanations !!!
Good job explaining the finer points of deadrise and hull bottoms. It really is a fascinating science...
When a customer comes to me at a boat show and asks that question, I usually say "all boats are pointy at the bow. Go to the stern and take a look. The pointier the bottom at the stern, the greater the deadrise angle..."
Of course that opens the door to the question, "which is better?" at which time I'd better print off a copy of Grady's explanation to hand out
...
!!!Good job explaining the finer points of deadrise and hull bottoms. It really is a fascinating science...
When a customer comes to me at a boat show and asks that question, I usually say "all boats are pointy at the bow. Go to the stern and take a look. The pointier the bottom at the stern, the greater the deadrise angle..."
Of course that opens the door to the question, "which is better?" at which time I'd better print off a copy of Grady's explanation to hand out
...Grady Wahoo
Member
- Joined
- Feb 25, 2005
- RO Number
- 16408
- Messages
- 438
Pete, I read this little book the other night titled "How to Win Friends and Influence People". It really is a fascinating science....
I too enjoyed reading all of that. I have a 1980 Searay 26 Weekender. Back then they made the boat with 23deg of deadrise, some nice strakes, a sharp entry and narrow flat spots along the chine. Terrific ride, but yeah, a little rough on the ole anchor.
Just a couple more thoughts. The deeper V is usually associated with greater power requirements, more fuel and slower speed. I'm not sure that came through as bluntly. Although it may cut through the rough water, the popularity of current flatter bottoms is to achieve more speed and less of everything else. Newer Searays of the same size get more speed with less power. (They work really well on a real nice day.)
Hull designs also include more flat space, especially just below the chine to help plane, but more importantly to suppress rolling at anchor or very slow speed.
I am suspecious of deadrise numbers since hulls are no longer a perfect triangle. Geometry was always easiest with the equilateral triangle. Once you get a V bottom with horizontal sections at the chine the measurement is less obvious. So the 2deg may be less than the margin of error.
Just a couple more thoughts. The deeper V is usually associated with greater power requirements, more fuel and slower speed. I'm not sure that came through as bluntly. Although it may cut through the rough water, the popularity of current flatter bottoms is to achieve more speed and less of everything else. Newer Searays of the same size get more speed with less power. (They work really well on a real nice day.)
Hull designs also include more flat space, especially just below the chine to help plane, but more importantly to suppress rolling at anchor or very slow speed.
I am suspecious of deadrise numbers since hulls are no longer a perfect triangle. Geometry was always easiest with the equilateral triangle. Once you get a V bottom with horizontal sections at the chine the measurement is less obvious. So the 2deg may be less than the margin of error.
"Plus, I am a little excited, in a boating sorta way, that you and the PBard are seeing eye-to-eye!"
Ahh, we're just a couple of big teddy bears. Well I used to be a teddy bear before the coronary and subsequent 30 pound weight loss. But I'm still a "wuss" at heart...
"How to Win Friends..." huh??? I was thinking more of "War and Peace" ...
Ahh, we're just a couple of big teddy bears. Well I used to be a teddy bear before the coronary and subsequent 30 pound weight loss. But I'm still a "wuss" at heart...
"How to Win Friends..." huh??? I was thinking more of "War and Peace"
...So Grady.
Dearise is not where it ends. Good, I now know to look at more and other details. This is just great news for someone like me who can get hung up in a big case of analysis paralysis.
So once again I must remember that everything is full of tradeoffs or that for every action there is an equal & opposite reaction. The good news is that there are only so many boats out there and one of them will fit.
Thanks to you and the others at least I know what to expect from what I am buying. I will take a beter look at the Pro-Line which is the 20* beside, at this point, there just are not that many Sea-Pro 255 on the market. There was a mistake on there part. Dropping the 255 in '05 and replacing it with the 238. Same plan just scaled back to be a bit to small.
later
PAT
Dearise is not where it ends. Good, I now know to look at more and other details. This is just great news for someone like me who can get hung up in a big case of analysis paralysis.
So once again I must remember that everything is full of tradeoffs or that for every action there is an equal & opposite reaction. The good news is that there are only so many boats out there and one of them will fit.
Thanks to you and the others at least I know what to expect from what I am buying. I will take a beter look at the Pro-Line which is the 20* beside, at this point, there just are not that many Sea-Pro 255 on the market. There was a mistake on there part. Dropping the 255 in '05 and replacing it with the 238. Same plan just scaled back to be a bit to small.
later
PAT