Seaplane deadrise

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Georden

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Joined
Sep 17, 2006
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154
Location
Calgary, AB Canada
Google tells me standard deadrise is between 15 and 25 degrees. If operating from smooth water (1' waves max, 4-6" typical) can this be reduced to draw less water and get on step faster?
 

AirSharkII

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Jan 20, 2010
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57
Location
Chico, CA
The SeaRey has a deadrise of 12* and gets off in 14 seconds at 1430lbs with 100hp and can handle 12" chop with no problem.
 

Head in the clouds

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Joined
Mar 11, 2012
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1,983
Location
Gold Coast, East Coast of Australia
Google tells me standard deadrise is between 15 and 25 degrees. If operating from smooth water (1' waves max, 4-6" typical) can this be reduced to draw less water and get on step faster?
Early floatplanes and some ultralights which were only intended to operate off/on smooth water had completely flat-bottomed floats (with a step) and had the least possible draft and were quicker to plane than if they had had any deadrise.

That's all very well for floats because they can easily be exchanged according to changed requirements.

From a little experience of float/seaplanes and lots with powerboats I would be very careful about reducing the deadrise of a seaplane hull to less than 20 degrees if it was constant from nose to step. Many hulls have a higher deadrise angle at the bow and less at the transom/step to improve their handling in a bigger seaway.

As I see it the problem is that it's all very well planning to always operate from flattish water but there may be times when it doesn't work out that way - unless you always stay within glide of a flat waterway the conditions at your destination or an emergency landing may be a lot worse than expected and a flatter hull will be uncontrollable in a bigger chop/swell before a sharper one would.

Just 2c
 

Himat

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May 5, 2011
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2,868
Location
Norway
Google tells me standard deadrise is between 15 and 25 degrees. If operating from smooth water (1' waves max, 4-6" typical) can this be reduced to draw less water and get on step faster?
Depending on different other parameters. It’s not only the deadrise that affect what pounding load the hull gets. One other important parameter is the length/beam ratio. A boat designers thought’s can be found at: http://sassdesign.net/Efficient%20alternative%20to%20%20deep%20V-bottom.pdf

There have been several threads discussing seaplane hull’s included skis on this forum. The ski is one example where the deadrise can be shallow but the ride ok as the ski is narrow.
 

Rick McWilliams

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Joined
Feb 27, 2011
Messages
274
Location
Santa Paula CA
The mermaid amphibian has 15 degrees dead rise. It takes 5 seconds to get on the step, and 10 more to take off. I would consider 18 inch chop as the limiting sea state. 1430 lbs, 90 Hp rotax.

Lifting strikes, scallops, and spray rails are important for hydrodynamic lift. The water attitude is critical, there is a rapid drag rise above and below the optimum. Step height, and sternpost angle are involved with the planing transition.
 
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