Dellenbaugh angle

[willfox]

Is it that gives the amount the vessel will heel at 1pound per square foot of pressure?

[TeddyDiver]

Like http://www.kastenmarine.com/sail_area_ratios.pdf

[Paul Kotzebue]

Dellenbaugh angle is useful for comparing the sail carrying ability of similar boats. It has too many assumptions to accurately predict heel angle or to compare different types of boats. Comparing Dellenbaugh angles of a heavy displacement cruising boat and a light displacement racing boat would not be meaningful.

[willfox]

Thanks for that Paul.....so is there any better ways to accuratly predict the heel angle of a boat? If i kept the dell angle constant only varying the wind pressure, sail area and heeling arm. Would this be acurate in saying that the heel angle is constant?

[TeddyDiver]

Originally Posted by willfox

so is there any better ways to accuratly predict the heel angle of a boat?

Yes, and Dellenbaugh angle isn't for that purpose at all.. It predicts somewhat tendernes/stiffness in small angles of heel not the actual heel..

[Çemberci]

A small excel program for dellenbaugh angle

Oktay Çemberci

[Paul Kotzebue]

Predicting the actual heel angle is difficult. When the heeling moment produced by the sails is equal to the righting moment at a given heel angle, the vessel is in equilibrium. The righting moment at various heel angles is not difficult to calculate, but the heeling moment is.

Most stability criteria involving wind heel assume the windage is projected to a flat plane at the centerline of the vessel. Sometimes a cosine squared function is used to account for the reduction of heeling arm and projected area as the boat heels. This gives an approximation of the heeling moment, but it is not accurate enough to predict the heel angle in real world conditions.

A designer has to rely on experience and careful comparison of stability data for known boats to reasonably predict the heel angle of a new design.

[dskira]

Paul, pretty cool

[Paul Kotzebue]

Thanks Daniel.

I think boats should be cool ... like this one of yours:

http://www.boatdesign.net/gallery/sh...hp?photo=15259

[dskira]

Originally Posted by Paul Kotzebue

I think boats should be cool

I agree hundred per cent. Thanks
Daniel

[gonzo]

The problem with many of those formulas is that they use formulas for static conditions. At different speeds the wave form changes. When the trough of the wave is in the middle of the hull (around hull speed) it decreases the floatation of that area. It means that the hull stability decreases. Tank testing and experience on a hull type usually prevent boats that become too tender at speed.

[dskira]

Originally Posted by gonzo

The problem with many of those formulas is that they use formulas for static conditions. At different speeds the wave form changes. When the trough of the wave is in the middle of the hull (around hull speed) it decreases the floatation of that area. It means that the hull stability decreases. Tank testing and experience on a hull type usually prevent boats that become too tender at speed.

I agree Gonzo, but we have to start somewhere. The formulas are not the answer, but are a guide. We can't start by sailing, then designing, we have to start with the design.
I agree that experience by sailing on other hull is necessary, if you don't be to comfortable with your experience and just repeat the hull over and over, as do to many designer. The fear of mistake, well documented.
A "formula" by experience is as detrimental.
Cheers
Daniel

[gonzo]

I agree. But there are few really radical designs that work well

[dskira]

Originally Posted by gonzo

I agree. But there are few really radical designs that work well

I know what you mean Gonzo, and yes radical design are not always succesful.
I was mostly talking designing boat out of the production line type, plain vanilla, boring with the same two triangular sail, no sheer, nothing to stop the eyes. Just corporate stuff, where nobody wrong, nobody right, nobody to take responsability.
A sea of white crap with blue biminis, this is the sight of marinas today. No difference, no feeling, just the bad smell of bad barbecues the Sunday.
That what I meant by lack of diversity, challenge and creation. Not automaticaly radical design, but different.
Cheers
Daniel

[gonzo]

You can thank CAD for a lot of the crappy looking designs.It made the job of designing look-alike boats too easy. When you use a pencil and splines, being creative is part of the job.