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What about Beam?

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Old 08-13-2009, 01:46 PM
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Default What about Beam?

What's the effect of Beam on how a V behaves?

I'm looking at 27-30' stepped V's that have various Beams from 7'-8.5'.

Superboat y2k (7')
Kryptonite 29 (8.2')
Progression 27 (8')
Nordic 28 (8.5')
Pantera 28 (8')

What are the tradeoffs in terms of handling?

-Ross

Last edited by rbarna; 08-13-2009 at 02:23 PM.
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Old 08-13-2009, 03:55 PM
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the narrow beam boats handle ruff stuff better. The y2k and the 28 pantera will be the best runners of what you have listed. I believe the 28 pantera may be under 8 feet though, it is based on the 27 Magnum hull.
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Old 08-13-2009, 03:58 PM
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Be aware that BEAM is measureed at the widest part of the boat, not the edge of the hull that is in contact with the boat. To get a real compariosn, measure the "foot print" of the hull.
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Old 08-13-2009, 04:02 PM
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I'm interested in this topic, as my father and I often disagree about it. If a narrow beam boat is better in the rough, why are most boats 8' or 8' 6"? Weren't the original 36' Cigs with the 9' 6" beam supposed to be amazing in the rough? I thought they went to the narrower-beam Top Gun because it was faster with equivalent power?
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Old 08-13-2009, 06:05 PM
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Dont forget to look at Laveycraft's 2750 NuEra, 28' EVO, 29 NuEra, and 32 NuEra...
I believe the 2750 and 28 evo are just under 8' 6"
But the 29 and 32 are 8'6"
All of them are excelent rough water boats.
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Old 08-13-2009, 09:36 PM
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A narrow beam boat has better rough water handling.

A rough ride is when the boat experienced high rates of vertical acceleration. Coming into the water, its really deceleration (the boat is free falling downward until it hits the water, then is rapidly stops going downward -- you hope!). Getting bounced back into the air by the next wave the boat of course accelerated upward. But engineers and naval architects still always call this property "vertical acceleration" regardless of the direction up or down.

The vertical accelerations in a seaway are related to the cube of the beam: a very small reduction in beam results in a substantial reduction in the roughness of the ride.

Comparing a boat with 9 foot beam to an 8 foot beam:
vertical accelerations in the same sea state for the narrow boat will be 8^3/9^3 or 70% as much, or 30% less! There is a reason all offshore boats are narrow.

The superboat (7') compared to the Nordic (8.5') will be (7^3/8.5^) or 55% as much or 45% less!

Of course, as mentioned before, this assumes the CHINE BEAM is 7' and 8.5' and of course both boats have some flair to the hull.

Perhaps counter-intuitively, a flat will make the re-entry smoother, because on re-entry the hull looks to be just as wide as the flat for the first fraction of a second. With no flat, just a pure V, the boat gets to the full-beam deceleration much more suddenly, so the peak vertical acceleration is much higher -- a bigger jolt.

Strakes act similar to flats of course.

It may be surprising to realize that deadrise has a much smaller effect: its basically linear with deadrise angles you normally see. So the difference between, say, 22 and 25 degrees only about 10%.

The reason cats can be such good rough water machines is because each planing surface is so narrow that the deadrise can be dramatically reduced and you still get comparable vertical accelerations to deep V bottoms.

And since lower deadrise is also lower drag, and because cats get a lot of aerodynamic lift from the tunnel, cats are faster than deep V bottoms as we all know. (Yes, I own a Fountain, and I'm a fan of the Cat Killer, but I still know).
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Old 08-13-2009, 09:38 PM
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Oh:

I've owned a very narrow V bottom, and the one draw back is that they lean A LOT into curves, and are also more sensitive to cross winds.

Its easy to control with trim tabs, but you NEED to have trim tabs.
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Old 08-13-2009, 10:10 PM
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carcrash: That was an excellent explanation! I appreciate the references to naval and marine engineering-- I worked in the NAME department at the University of Michigan for a few years (but not as a Naval/Marine Engineer, as a programmer).

So if I want to compare the hulls I have to take into account the Max Beam, Chine Beam, deadrise and strake configurations? Yikes, I don't really have all that information on each boat. How would I get it?

Next question: How would steps effect the vertical acceleration of a hull? Would 1 step be different than multiple steps? Would the height of the step matter?
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Old 08-14-2009, 08:28 AM
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I think your better off figuring out how you want to use your boat and testing a couple, it's more than hydrodynamics (or whatever) take a ride on some of the boats and see what suits your style.

The other drawback to a narrow beam is space, I have an 8'6" beam and like the space it offers, most of my boating is simply hanging out and rafting up with friends so I wanted a comfortable boat.
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Old 08-14-2009, 08:53 AM
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...and don't forget about weight. A heavier boat of the same hull design will ride smoother (reduced vertical acceleration) due to this thing called 'inertia'. Although, you won't go as fast! The nice ride is one of the reasons I like my pig Formula...

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