BEAM how wide and YYYY

[Tank]

OK Y do I want one over the other? 8, 8.6, 9.6 and so on.
Is wider slower? Is wide more stable?
Thanks

[gcarter]

A boat planes on the leading edge of the hull bottom and the juncture of the water.
To an extent, the wider the beam, the more efficient the hull is.
The boat also planes on the widest leading edge. This is why when towing an inflatable dinghy, they will frequently yaw as the widest leading edge is the side of the dinghy hull.
In the days of wooden runabouts, often the upper end of the performance envelope was limited by the boat becoming uncontrollable since the hulls of the era were so narrow.
In a modern performance deep vee hull the rules are a little different as the vee gives a lot more stability and also forms a longer leading edge.
Typically the beam length ratio is about 3.5:1.

[gcarter]

There have been a few examples of poor design of Vee hulls in the past.....
Sonny Levi built a 28 footer (I think) in the late '60's w/a fairly narrow hull combined w/a deadrise of 30* !!!!!!!
The boat was almost uncontrollable.
There was also something about a very narrow Aronow owned race boat in the 60's. It rode on the chines a lot, I've heard.

[MOP]

George years back I read an article written by Bruce Roberts about the design and its limitations, my memory is not the greatest but I think he stated that at 28 degrees and after a certain speed when the hull rose high enough the boat laid over on it side. I like deep V's but I am a firm believer in modified V's for moderate speed due to them being far easier to power leading to better efficiency.

[gcarter]

You're right Phil.
The only advantage to a deep vee is it's able to absorb a lot of power w/o doing wierd things.

[Tank]

HI and thanks for the info!
I am looking at boats for a friend and he is looking at a 25.5 with 8ft beam
and a 26 with a 9.6 beam and we are trying to figure how much the big beam is worth in the water, towing not so good but we can.
SO both boats have 260 merc and alfas the 26 is 1000 pound more.
Do you think the speed will be close we thinking 50 to 60 mph?

[Ghost]

HI and thanks for the info!
I am looking at boats for a friend and he is looking at a 25.5 with 8ft beam
and a 26 with a 9.6 beam and we are trying to figure how much the big beam is worth in the water, towing not so good but we can.
SO both boats have 260 merc and alfas the 26 is 1000 pound more.
Do you think the speed will be close we thinking 50 to 60 mph?

I could not tell if you meant each boat had a single 260 with an alpha, or twins with alphas.

[Tank]

Sorry for that Ghost they both have twin 260 mercs.
I know prop pitch and all that need to be addressed but in general we think they will be close to 50 to 60 mph.
whats your fell on this?

[Ghost]

Lots of people here will know better than I, but your ballpark seems about right to me. What are the hulls specifically, if I may ask.

For instance, I have a Nova Marine 24 which is actually 24 ft 10 in, and 8 ft 3 beam I think. (I have not measured, just quoting specs.) Mine has v-drives and inboards so it is not a good comparison. But the hull sounds quite similar to the smaller of the two you are considering.

But the Donzi 7 meter is a slightly shorter version of this same hull. The numbers I have heard for it, with a pair of small blocks and outdrives, range from about 55-62 mph. I would expect your 50-60 range is about right for the smaller boat, the wider one, dunno, maybe as low as high 40s, but just a SWAG.

Other folks here have a LOT more experience than I. If they know exactly what hull make/model, I bet some can narrow your speed estimate to less than a 5 mph range.

Regards,

Mike

[Craig S]

Isn't wider more stable at low speeds? Wider is much more volume (ie a much bigger deck space). Wider takes more power. Thats why some people step their hulls down to a narrower beam at the boot stripe (I'm thinking of sport fish boats here).

oh, and wider beam should also plane a bigger load weight (and be much less sensitive to weight loading than a narrower beam.

imho

[Tank]

Thanks all
the one is a 1979 formula 255 liberator and the other is a formula 26 sc
Both look nice in the photos we have to drive out and go look at them!


Please wait
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[joseph m. hahnl]

trailering is definitely an issue, as over 8 feet may require a wide load permit.

Also when the beam is changed something else will change . It is simple trigonometry. wider beam same angle = deeper keel. Same keel depth with wider beam = different angle. so you see it is not necessarily the wider beam that would make it more stable, it can be the angle. Less angle much more stable. more angle better in the ruff stuff. Same angle one will ride higher in the water.

[Ghost]

trailering is definitely an issue, as over 8 feet may require a wide load permit.

Also when the beam is changed something else will change . It is simple trigonometry. wider beam same angle = deeper keel. Same keel depth with wider beam = different angle. so you see it is not necessarily the wider beam that would make it more stable, it can be the angle. Less angle much more stable. more angle better in the ruff stuff. Same angle one will ride higher in the water.

I thought 8 ft 6 inches was the magic beam limit before wide loads, no?

[joseph m. hahnl]

:kingme:
I thought 8 ft 6 inches was the magic beam limit before wide loads, no?
From what I see , it's a state issued permit. It is governed by each state as well as each city. different rules may apply for each state

New Jersey legal limits


LEGAL LIMITS DESIGNATED--- HIGHWAY--- ALL OTHER ROADS

Weight: Single -----------22,400 ------22,400
Tandem -----------------34,000 ------34,000
Tridum-------------------56,400------ 56,400
Gross Weight-------------80,000------ 80,000
Federal Bridge Formula Applies (http://ops.fhwa.dot.gov/freight/sw/brdgcalc/calc_page.htm)
Width--------------------8'6" --------8'
Height-------------------13'6"------- 13'6"
Length:Semi-trailers -----53'--------- 48'

[Tank]

Thanks to all for your help!
Lots to consider!
the trailer is more of a pane then anything, I don,t see that law enforced on privet stuff, but the tole both dos get small at 10ft.:shocking:
Thanks Tank