Dead Rise...How important is that # ?

[Bridog]

O.K, I have seen this number listed in just about every major boat manufacturer web site. They list this number in the important spec's right along with length, width and weight so I know it must be pretty important. My question..... how important is this number in relation to a comfortable ride ?? Is a 21 degree deadrise(seems to be the SR average in this size cruiser) better than a 17-19 degree deadrise in a 30 foot cruiser?

 

[Dave S]

From what (little) I know Brian, the problem with just looking at the dead rise number (which is measured at the stern) is it tells you nothing about the rest of the hull. Just because you have 21 degrees at the transom, you may have a much shallower angle at the bow and it may just increase as it tapers towards the stern.

But some of the more seasoned veterans can probably give you some first hand knowledge on how hulls with different dead rise numbers might react while underway. I believe the trade offs are that the steeper dead rise hulls give you a smoother ride underway but conversely those same boats "rock" a lot more at rest than those with a shallower dead rise.

 

[jrirvine1]

Knowing the deadrise angle is necessary information for us layman to understand the very basics of the hull design. Of course a marine architect would throw about another half dozen terms at you to describe the hull, but for us this is not really in the need to know category.

For boating in the Chesapeake Bay, where there is always a chop due to the relatively shallow depth and large fetch, several captains have told me the best design is a deep “V†with not less than a 19 degree deadrise. This gives you a smooth ride but does burn more fuel.

Conversely, if you are a professional water skier, on small lakes with smooth water, then you want a boat with very little deadrise for rocket fast hole shots and the best overall speed and maneuverability.

 

[Four Suns]

The deadrise number alone means ka ka. Especially with a hull design that has large propeller pockets as the whole geometry is all messed up anyway. Deadrise is important... yes... but the geometry of the bow and the entry characteristics (compare a Sea Ray nose to a Bertram nose), balance of the wieght in the hull and CG (mid-engine straight shaft vs. rear engine v-drive), moment of intertia of the boat, etc. all play very important to how something rides on the water and what it was designed for... there is no "one best" hull design for all water and everything is a tradeoff. I fish offshore in my boat in the winter and cruise on it (and fish) in the summer. The 480 DB's nose loves to go underwater on occassion because it doesn't have that "carolina flair" on the front. But it does have a nice forward stateroom and private head. Darn wife... she always wins...

One answer... "Sea Trial in the type of water you want to boat in before you buy"

 

[goblue]

Sharp entry and deep V's make for good blue water seakeeping. Add a bit of keel and a bow flair and you generally get a good rough water boat. 21 degrees of deadrise generally gives you good following and quartering sea handling if you have big props that are widely spaced. As was pointed out, expansive cabins made from spoon bill entry designs detract from handling. The older Bertrams have rather small master staterooms but are great sea boats.

 

[Four Suns]

On the bigger boats, I just wish Sea Ray would sharpen the bow entry a little and raise up the nose a little as well... maybe one of those bulb-ous things underwater on the nose like the big tankers have. :grin: My 2 cents.

 

[Sea Ray 300]

The following is from
http://www.huntdesigns.com/corp_about_deepv_development.htm

It's a very interesing site. The company was formed by C. Raymond Hunt, the world renown designer of yachts and smaller hulls.

Is there one optimum angle of deadrise?

Yes and no. Ray Hunt’s original 24-degree angle has been proven in raceboats to provide the best performance in ocean racing. For boats whose speeds will be more moderate, particularly in the 20-35 knot range that is sensible for fast cruising and touring, we have had success with lower angles. Many of the yachts we design today have 22-degree deadrise.

A shallower angle would be more prone to pounding at extremely high speeds but is more efficient and more friendly (less draft) as speeds are reduced. The deadrise angle, within this narrow range, is determined by the intended purpose of the boat and the many aspects attached to its size, weight, power, etc.

 

[b_arrington]

The deadrise number by itseld only tell you a specific spot on the hull. I think many Sea Rays have a constant deadrise, but many types of boats have a variable deadrise, where the shape of the is different is various spots in an attempt to get the best of different hull designs.

For example, the sharp entry point is good for a smooth ride that cuts through chop. A flatter keel is better for planing and more efficient. So some boats have boat: a sharp entry that constantly changes as it flattens out toward the stern.

 

[Bridog]

Thank you all for your responses. :thumbsup: