Effect of Deadrise Angle on Hull Performance

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Author Topic:   Effect of Deadrise Angle on Hull Performance

Sheila posted 06-05-2005 03:20 PM ET (US)
I understand how deadrise is measured. I'd like to understand its significance for the boat's handling. Thanks.
kingfish posted 06-05-2005 04:28 PM ET (US)
Sheila-
Simplistically, the [greater] the deadrise (to some point at which the hull would leave the realm of planing and enter the realm of displacement), the better the hull will take rougher water, by cutting the waves. Conversely, the [greater] the deadrise, the less stable the boat is at rest; it will rock and roll more in waves and when weight is shifted from one side to the other.
John
WHALER27CC posted 06-05-2005 04:45 PM ET (US)
It should also be noted that [the angle of deadrise on the hull that most people make referene to] is [the angle at] the stern of the boat to about the [midships] of the hull. [The deadrise of the hull at] entry is from the bow back to the [amidships]. Deep-V will have a higher degree deadrise, say 24-degrees, and generally run smoother in rough water. As that deadrise lowers to say 18-degree, the ride tends to be rougher but much more stable at rest. There are pros and cons to each depending on whether you are running in seas at a faster speed and need performance, or whether you are running at much lower speeds or anchoring and want less rocking. Lower deadrise boats tend to be wetter in seas. Whalers , classics that is have a lower deadrise, but that is where sponsons, or Smirk comes in to knock away the spray, quite effectively.
[Discussion of deadrise angle], Sheila, can turn into a Ford-Chevy debate. I am sure there will be a lot of opinions. Peter
Binkie posted 06-05-2005 05:03 PM ET (US)
Ray Hunt is the inventor of the constant-deadrise deep-V hull and also the co-inventer of the Boston Whaler. The first [hulls with constant deadrise] didn`t work because the hull just sucked down in the water, so he built strakes along the length of the bottom to create lift, and a new generation of boats were born. The negatives [of a constant deadrise hull] are they draw more water, take more power, and if it is rough they are uncomfortable to fish, unless you enjoy fishing and holding on at the same time. If you are prone to tossing your cookies like I am, very uncomfortable.
frostbite posted 06-05-2005 07:38 PM ET (US)
Besides the constant deadrise hull, there is also the [variable deadrise hull] shape: sharp entry forward for a smooth ride becoming progressively flatter aft, creating an efficient running surface that has stability at rest.
Sheila posted 06-05-2005 08:40 PM ET (US)
Thanks, guys!
jimh posted 06-05-2005 10:32 PM ET (US)
To have a planing hull you need some flat surface, particularly aft. The traditional shape for high-speed boats was to have a sharp entry which then tapered to a flatter surface aft. This gave good ability to cut through waves, yet allowed the hull to have plenty of lift and get on plane easily.
The Boston Whaler classic hull follows a different approach: it has a constant deadrise hull. This design was pioneered by Ray Hunt in a boat called MOPPIE. The boat was a break-through and inspired the entire BERTRAM line of hulls.
All boat designs are trade-offs of one dimension versus another. The deadrise angles at various stations along the hull are just one measurement. If one hull measures 18-degrees at the transom (a typical figure for a Boston Whaler Outrage series hull) and another measures 20-degrees, there is not anything hard and fast you can say about them. There are general tendencies.
jimh posted 06-05-2005 10:37 PM ET (US)
See this link for more information on MOPPIE and Ray Hunt:
http://www.oya.com/library/hunt.html
Sheila posted 06-05-2005 11:59 PM ET (US)
Thank you, Jim, for that interesting read.
Yesterday, when we had Winkie out in service to the outriggers, one of our passengers commented on what a stable, and nimble, craft she was. Coming from someone who races outriggers, and spends nearly every weekend riding along on safety boats that have beeen marshalled for the particular weekend's race, it meant something.
frostbite posted 06-06-2005 08:32 AM ET (US)
Jimh,
You dislike the term "warped hull"?
kingfish posted 06-06-2005 08:39 AM ET (US)
Jim-
Thanks for the clarifying edits in my post - I knew what I wanted to say, but as it sometimes happens, something got lost in the translation...
John

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Author	Topic: Effect of Deadrise Angle on Hull Performance
Sheila	posted 06-05-2005 03:20 PM ET (US) I understand how deadrise is measured. I'd like to understand its significance for the boat's handling. Thanks.
kingfish	posted 06-05-2005 04:28 PM ET (US) Sheila- Simplistically, the [greater] the deadrise (to some point at which the hull would leave the realm of planing and enter the realm of displacement), the better the hull will take rougher water, by cutting the waves. Conversely, the [greater] the deadrise, the less stable the boat is at rest; it will rock and roll more in waves and when weight is shifted from one side to the other. John
WHALER27CC	posted 06-05-2005 04:45 PM ET (US) It should also be noted that [the angle of deadrise on the hull that most people make referene to] is [the angle at] the stern of the boat to about the [midships] of the hull. [The deadrise of the hull at] entry is from the bow back to the [amidships]. Deep-V will have a higher degree deadrise, say 24-degrees, and generally run smoother in rough water. As that deadrise lowers to say 18-degree, the ride tends to be rougher but much more stable at rest. There are pros and cons to each depending on whether you are running in seas at a faster speed and need performance, or whether you are running at much lower speeds or anchoring and want less rocking. Lower deadrise boats tend to be wetter in seas. Whalers , classics that is have a lower deadrise, but that is where sponsons, or Smirk comes in to knock away the spray, quite effectively. [Discussion of deadrise angle], Sheila, can turn into a Ford-Chevy debate. I am sure there will be a lot of opinions. Peter
Binkie	posted 06-05-2005 05:03 PM ET (US) Ray Hunt is the inventor of the constant-deadrise deep-V hull and also the co-inventer of the Boston Whaler. The first [hulls with constant deadrise] didn`t work because the hull just sucked down in the water, so he built strakes along the length of the bottom to create lift, and a new generation of boats were born. The negatives [of a constant deadrise hull] are they draw more water, take more power, and if it is rough they are uncomfortable to fish, unless you enjoy fishing and holding on at the same time. If you are prone to tossing your cookies like I am, very uncomfortable.
frostbite	posted 06-05-2005 07:38 PM ET (US) Besides the constant deadrise hull, there is also the [variable deadrise hull] shape: sharp entry forward for a smooth ride becoming progressively flatter aft, creating an efficient running surface that has stability at rest.
Sheila	posted 06-05-2005 08:40 PM ET (US) Thanks, guys!
jimh	posted 06-05-2005 10:32 PM ET (US) To have a planing hull you need some flat surface, particularly aft. The traditional shape for high-speed boats was to have a sharp entry which then tapered to a flatter surface aft. This gave good ability to cut through waves, yet allowed the hull to have plenty of lift and get on plane easily. The Boston Whaler classic hull follows a different approach: it has a constant deadrise hull. This design was pioneered by Ray Hunt in a boat called MOPPIE. The boat was a break-through and inspired the entire BERTRAM line of hulls. All boat designs are trade-offs of one dimension versus another. The deadrise angles at various stations along the hull are just one measurement. If one hull measures 18-degrees at the transom (a typical figure for a Boston Whaler Outrage series hull) and another measures 20-degrees, there is not anything hard and fast you can say about them. There are general tendencies.
jimh	posted 06-05-2005 10:37 PM ET (US) See this link for more information on MOPPIE and Ray Hunt: http://www.oya.com/library/hunt.html
Sheila	posted 06-05-2005 11:59 PM ET (US) Thank you, Jim, for that interesting read. Yesterday, when we had Winkie out in service to the outriggers, one of our passengers commented on what a stable, and nimble, craft she was. Coming from someone who races outriggers, and spends nearly every weekend riding along on safety boats that have beeen marshalled for the particular weekend's race, it meant something.
frostbite	posted 06-06-2005 08:32 AM ET (US) Jimh, You dislike the term "warped hull"?
kingfish	posted 06-06-2005 08:39 AM ET (US) Jim- Thanks for the clarifying edits in my post - I knew what I wanted to say, but as it sometimes happens, something got lost in the translation... John