Wide Beam vs Narrow Beam

[jenny2]

Originally Posted by hummingway

I don't think they make a number big enough to express the number of times a sunfish dumped me in the drink when I was a teenager

the fun days

[wolfenzee]

My boat is an old heay narrow, design it is fast in light air and comfortable in nasty seas. I am rebuilding the interior for two (there is actually room to add a small unobtrusive aft cabin if I wanted)...think cozy. The width of the cabin top on a Catalina 30 is about the same as my beam. Boats are about compromises I choose grace over space.

[wolfenzee]

Originally Posted by capn_billl

One item I noticed from above is "narrower boats often have more ballast". If thats true it would seem better to have more ballast for stability.

more ballast or displacement...the narrower/older design boats are usually wood giving more over all displacement compared to newer design wider lighter boats made of fiberglass. which actually often have MORE ballast to make up for the differance


example based on 30' LOA 25' LWL (my boat compared to a Catalina 30)

Atkin Captain Cicero / Catalina 30

LOA 30' / 30
LWL 25' / 25'
Beam 8'9"/ 10'10"
Displacement 14,000 / 10,200
Ballast 3,200 / 4250
Draft 5' / 5'3"
Mast height 45'/ 45'

here are some other examples, list of specs http://pages.sssnet.com/go2erie/wind02.htm

[CarlF]

I think it's very hard to generalize about beam and seaworthiness. Too many variables. And beamy bluff bow boats of the past are not anything like the beamy triangular boats of modern design.

I remember reading that Dixon's very beamy Moody 45 DS has a stability curve that never went negative. The triangular hull would "corkscrew" when knocked down because the fine bow would sink and the wide stern rise causing it to always right.

Of course, that assumes all that pilothouse glass stays in place while "corkscrewing"

Carl

[Adelie]

Originally Posted by Srah 1953

Old style boats have a proportionally narrow beam to length with a high ballast ratio; whereas nearly all modern mass-production boats have a relatively wide beam and low ballast ratio and depend upon form stability (ie width) to support their sail area. Unless one is proposing to sail in the South Atlantic or similar, does it really matter?

It's all about the odds, your seamanship and your stamina.

The odds of encountering a wave that could roll you over are pretty low over the course of years.

Slocum's boat 'Spray' had an Angle of Vanishing Stability of around 95 degrees I have heard. He mananged to go around the world alone. That would be an instance of superbe seamanship perhaps making up for the boat's defieciencies. Or he was a bit lucky or both, hard to say.

Exhuastion would be the inability to do what needs to be done. For a boat that requires active measures in a storm this becomes an issue.

Beam, draft, displacement, ballast and and ballast ratio all affect capsize resistance. A boat designed for better capsize resistance can make up at least some for bad luck, mediocre seamanship and or exhaustion.

[sneuman]

Originally Posted by Adelie

It's all about the odds, your seamanship and your stamina.

The odds of encountering a wave that could roll you over are pretty low over the course of years.

Slocum's boat 'Spray' had an Angle of Vanishing Stability of around 95 degrees I have heard. He mananged to go around the world alone. That would be an instance of superbe seamanship perhaps making up for the boat's defieciencies. Or he was a bit lucky or both, hard to say.

Exhuastion would be the inability to do what needs to be done. For a boat that requires active measures in a storm this becomes an issue.

Beam, draft, displacement, ballast and and ballast ratio all affect capsize resistance. A boat designed for better capsize resistance can make up at least some for bad luck, mediocre seamanship and or exhaustion.

Then again, he did disappear at sea in Spray some years later and no one knows quite what happened. So, go figure.

[u4ea32]

Hard to come up with a modern example, as everything is so similar today: boats are designed to fully fill out a standard slip.

So, rolling back the calendar to a day when there were two closely matched boats, one wide, one narrow: Windward Passage (wide) and Blackfin (narrow). Displacements were very similar (90K lbs for Passage, 110K lbs for Blackfin). Sail area very similar, both ketches, same waterline, same rating (maximum).

Upwind in smooth water and moderate to heavy air, Passage was faster. I think this was due to 'Passage having more stability, but it could have been also due to Blackfin's poorly designed keel foil section (sharp leading edge to the keel, and flat plate centerboard). In all other conditions, Blackfin seemed to be the faster boat.

Upwind in heavy seas, the wide hull handled very oddly: as the boat went over big (10 to 20 foot) seas, 'Passsage would have a very balanced helm when going up the face of the wave, and then tremendous weather helm going across the crest and back down into the trough. I had to turn the wheel about 180 degrees with every wave.

Downwind, both boats handled well and were very close to the same speed (Blackfin a little faster), but Blackfin handled a little better: Passage had to be steered (barely), while on Blackfin the contest was how many waves you could let the boat surf between touching the helm!

Also, the motion of the two boats was markedly different, with Passage pitching with much higher accelerations (more abrupt) than Blackfin.

The huge and convincing difference however was in the amount of work required to sail the two boats. The wide (therefore stiff and high wetted surface) 'Passage required a lot of sail under a lot of load. Blackfin could be sailed very fast with very small sails. In fact, the hardest lesson on Blackfin was just how quickly we needed to shorten sail to go fast: the required sail area was so little it was quite easy to sail Blackfin with as few as 4 people. I am quite sure 'Passage was never sailed with less than a dozen burley crew. This was in the times of no autopilot, no powered winches, and very heavy Dacron sails (modern sail cloth is MUCH lighter).

Based on these, admittedly dated, experiences, I feel that narrow is better in the following ways:

1) Better speed in nearly all conditions
2) Better handling, more fun to steer and sail
3) Better motion in seaway
4) Far less motive power required

But obviously, narrow is worse in the following ways:
1) More expensive dock fees for a given internal volume (fat fills the slip)
2) Less volume for a given length
3) More difficult interior arrangments

[David M]

Originally Posted by Srah 1953

Unless one is proposing to sail in the South Atlantic or similar, does it really matter?

It matters.

From my naval architecture and stability and trim class, doubling the beam cubes the stability (righting arm, (GZ)), at moderate angles of inclination.


Another factor is freeboard. Greater the freeboard the greater your angle of inclination before your metacentric height, GM, goes negative. More freeboard also gives you a larger dynamic stability curve...the area under angle of inclination vs GZ curve.

http://en.wikipedia.org/wiki/Metacentric_height

[hummingway]

Originally Posted by David M

It matters.

From my naval architecture and stability and trim class, doubling the beam cubes the stability (righting arm, (GZ)), at moderate angles of inclination.


Another factor is freeboard. Greater the freeboard the greater your angle of inclination before your metacentric height, GM, goes negative. More freeboard also gives you a larger dynamic stability curve...the area under angle of inclination vs GZ curve.

Metacentric height - Wikipedia, the free encyclopedia

Would it be correct to suggest that the at greater angles of inclination a narrower beam gives better righting with less ballast then a wider beam?

[phantomracer]

Doesn't matter. Older boat (classic designed) boats are prettier!

We like our moderate (10' 2") beam 1968 Ohlson 38. Everything is 'just right'

[barnakiel]

Originally Posted by goboatingnow

I have it and several others his conclusions are many ( also see beam and breaking waves ) he outlines the issues but doesn't necessarily conclude that one is better over the other.

Dave

That's interesting. In my copy he is very clear about it.

b.

[barnakiel]

Originally Posted by phantomracer

Doesn't matter. Older boat (classic designed) boats are prettier!

We like our moderate (10' 2") beam 1968 Ohlson 38. Everything is 'just right'

Not a pig either. Great boat.

b.

[Capt Phil]

Very interesting thread... not many contributions from folks who have made their living out there commercially. I don't recall, except in the rare instance, not leaving port because of weather. Not that we had a suicidal or macho streak, it is just that you weren't making any $ sitting in port. That held true commercial fishing, towing barges or delivering cargo as well as deliveries. I learned to always have a back up plan but rarely stood down due to weather. Over the years you develop a sixth sense about what a boat or crew can handle and experience was a great teacher. if you wait for perfect weather, you will never know what you or your boat can handle safely until you get out there in some messy weather. I would recommend starting slow but challenging yourself and learning from the experience. Pretty quick you'll find it exciting as hell but choose your crew, if any, carefully! Capt Phil

[Adelie]

Originally Posted by hummingway

Would it be correct to suggest that the at greater angles of inclination a narrower beam gives better righting with less ballast then a wider beam?

Almost certainly once you get past 90degrees, probably also anywhere past 45. I expect it depends on the boat. I don't know of any place to get a bunch of stability curves for free so I could do a comparison.

[Bash]

Originally Posted by u4ea32;

Based on these, admittedly dated, experiences, I feel that narrow is better in the following ways:

1) Better speed in nearly all conditions

This argument seems to ignore the latest developments in offshore racers. Farr 40s, for example have a beam in excess of 13'. Box rule boats such as the Transpac 52 are invariably built to the maximum beam allowed (which in the case of the TP 52 is just over 14' 6".)

Narrow isn't fast. It's just narrow.