So will the real “deadrise” please stand up? [any angle will do]

[Trevlyns]

I thought I knew what deadrise was but on reading these definitions, I’m now a little confused - and it don’t take much to confuse me!

What are these dominant terms “bottom of the boat” and “Widest beam” supposed to mean? – Reckoned to what – and in what direction?

"A 0 degree deadrise boat has a flat bottom". Is that (as illustrated) a flat bottom with straight-up sides (90 degrees when I was last in school) – then does the dashed illustration therefore not have a flat bottom? Where is deadrise measured in this example – angle A or B – or have I misinterpreted it completely in my attempts to gain just one more posting!

Can we solve world hunger?

Does her bum really look big in this?

Has Elvis really left the building?

So many questions – so little time!

[charmc]

Trev,

You've uncovered a nice mess of correct, incorrect, and irrelevant definitions of deadrise. That rat's nest is almost guaranteed to confuse any reader.

My understanding (which carries absolutely no guarantee of being correct) is that deadrise is the angle between the horizontal plane and the bottom of the hull, measured along a line extending from the centerline of the bottom to the chine. Relocate your angle B measurement to inside the chine and you've got it. In your illustration, of course, that would be an angle of 0 degrees. No particular reason the angle could not be measured as originating from a vertical plane along the centerline, but it just isn't, as far as I know.

Sorry, no time to answer the others, except for, "Honey, your bottom always looks great."

[Trevlyns]

Fanx Charlie - give me a few months to fathom that one out, mate!

[tom28571]

As Charmc said, the first thing to do is throw out all the material in your post. The angle of the sides, known as flair, has nothing to do with deadrise. The bottom of a boat is, in general terms, that part that is underwater. That can vary a little bit depending on the shape of the boat. On a flat bottom boat, the bottom would be all the underside between the chines that is flat, although some of this is usually out of the water.

Deadrise is the angle above horizontal of the bottom from the centerline (keel) to the chine.



There has to be a little confusion.

[rwatson]

And just to make an even bigger mess,
“Midship Deadrise Angle” is the angle, taken at midship, at which the hull slopes up from horizontal.
The deadrise can vary dramatically along the hull, very acute at the bow, to very small angles at the stern.
So the Charmc question of what is true deadrise depends on what hull station you are talking about in many situations.

[Landlubber]

Deadrise is when you have to get up early in the morning to attend the grandchild mate, congrats too.

Looking at the transom , for instance, it is vee shaped. The angle between the horizontal and the hull bottom on one side is the deadrise, measured in degrees. Yes a flat bottomed boat would have zero deadrise. A nice planing hull, suited for choppy conditions, would have about 17 degrees deadrise, like a berty 25, or as the originator of this type of boat Ray Hunt, (I believe) would put it.

[Frosty]

Do you mean deadrise is from front to back or just the side to side transom bit angles?

In other words a deep V is describing deadrise? Or is it the angle at witch the keel meets the bow stem.

Stupid word for it anyway,

Im as confused as a babies bottom in a ,--Hmmmm

[PAR]

Deadrise, as a number of other issues in boat design often do, require an element of compromise and understanding.

Simply put, deadrise is the angle you'd read off an angle gauge, if you placed it against the keel (or to one side of the centerline) flat against the bottom (athwartship). Deadrise is typically measured at the transom, midship and a slight distance aft of the bow, usually the first station line. A popular design of mine carries 45 degrees of deadrise at the bow (station 1), 15 at midship (station 5) and 6 degrees at the transom. This would be typical of a moderate warped V hull intended for protected and semi protected waters.

On a round bilge hull form, things have to be more compromising. An average angle is estimated based on sectional shape, as the bottom may have considerable curve, which prevents an accurate reading from a gauge.

Another similar difficulty is measuring entry angles (actually half angle). The curves prevent an accurate reading, but an approximation can be reasoned with a little bit of faith and a set of lines. Again, in plan view, the angle is averaged from the stem to the first station line.

Above the chine, on a single chine hull, such as the one drawn by Trevlyns, the planking is considered topside, not bottom, even though a portion of it may be immersed.

Widest beam, usually termed max. beam, is as the name suggests and the widest part of the boat. On some craft with considerable tumblehome amidship, the hull will be the widest, though most are from rail to rail at the sheer.

Widest beam is a consideration for trailering, berthing, storage, interior accommodations and hull volume. The location of widest beam is usually more important then the physical dimension. The dimension of the beam does have a relationship with the boat's length, but in this regard only for comparative reasons to a casual observer. Max. waterline beam is more important to one interested in understanding relationships and design elements, then max. beam.

[tspeer]

Originally Posted by Trevlyns

...
"A 0 degree deadrise boat has a flat bottom". Is that (as illustrated) a flat bottom with straight-up sides (90 degrees when I was last in school) – then does the dashed illustration therefore not have a flat bottom? Where is deadrise measured in this example – angle A or B – or have I misinterpreted it completely in my attempts to gain just one more posting!...

Deadrise is measured at the center plane. The flat bottom section you've sketched has zero deadrise.

The angle you've indicated is actually the flare of hull and topsides. Zero flare would make the topsides vertical. Positive flare makes the hull wider at the gunwale than at the waterline. If the hull curves back inward, making the gunwale narrower than the widest point of the section, that is tumblehome.

In the top row of the figure below, all three hulls have the same deadrise and different flare. In the bottom row, the first hull has low deadrise, the second hull a large deadrise angle, and the third hull is in between in terms of its deadrise.

[Trevlyns]

Always appreciated your input Tom. Many thanks!

[Frosty]

If I learn this much every day,--that'lle do for me.

[Trevlyns]

Touche