Deadrise & “Deep V”

When comparing boats these days you get a lot of information about “deadrise” or “deep V” but no explanations. Some of the calls we get here at IBC regarding those topics warrant a look and explanation for our inflatable boat customers.

Deadrise is explained as such: the angle of the horizontal plane to the hulls surface. What this means is how much of a V shape there is at any given position from the centerline or keel on a horizontal line to the angle or line of the hulls surface which is expressed in degrees.

bombard-commando-deadrise-angle

Boats generally have a varying amount of deadrise fore to aft as a result of their design and intended purpose. Most deadrise is measured and expressed at the transom due to when the boat is on plane this angle or measurement determines how stable a boat will be. Boat manufacturer statements that use “deep v or deep vee” are usually talking about the forward section of the craft as this dictates how well a boat will perform in cutting thru blue water and chop. Don’t be confused this is still a function of deadrise, but marketing has put forward “deep v” as a selling point to the uninformed user.

When negotiating heavy seas the crafts deadrise forward or “V” will dictate how softly it comes down between the swells and chop (expressed as frequency) and generally a “deeper V” means it cuts thru and dissipates the forces by using a broader surface area and reflection of energy away from the boat which in part translates to the water breaking and turning into spray. Basically the energy is partially transferred into the destruction and deflection of the water it’s self, while a portion of that same energy is transferred into the shock we as passengers feel.

Most inflatable boats have an inflatable keel that is a bit more rounded at the centerline that pushes down against the fabric to form the “V”, in the case of the Bombard Commando series it’s a more pronounced sectional wooden keel that better reproduces the traditional fiberglass or metal boats keel/hull design. That is to say the Bombard Commandos are often preferred by more professional users due to it’s more traditional boat hull shape and design attributes.

Zodiac developed and patented the inflatable keel in 1960 as Pierre Debroutelle made improvements to simplicity of assembly and storage. The inflatable keel was largely developed due to the “Leisure Society” movement occurring at the time and the desire to cut down on parts and bags to put them in. Zodiac inflatable boats were largely commercial and military items until then but a growing number of ex-military and maritime professionals had come to adopt and use the technology in various disciplines such as racing and fun with the family.

All inflatable boats featuring a keel have varying degrees of deadrise and different performance levels for the areas of interest they were designed for. It’s worth mention that all of IBC’s boats feature a “V” in their hull with the exception of bucket boats and alongside tenders that aren’t designed with rowing or planning in mind for their day to day use.

I hope this has made the topic a bit clearer for those of you that were confused between the two terms of “deadrise ” and “deep V”. We’ve attached some more pics below of a Bombard Commando C5 to help you on your way. As always feel free to give us a call here at the IBC shop (503)235-2628 when shopping for your next or first inflatable boat and make sure you get the right boat for the job at the right price.