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Old 02-07-2020, 02:09   #1
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Heavy Monohulls vs Light Catamarans

All the time I have chosen and been building my lightweight catamaran, I was after comfort. Comfort at anchor from chop and rolling, comfort of an enclosed helm, comfort of not having to worry about everything going flying when a 70ft sport fisher goes by, comfort underway in any weather, staying upright while sailing, comfort of space inside and plenty of light, comfort of feeling like you’re in a nice home while at sea.

I have noticed something.

A heavy monohull can get you nearly all the same comforts a lightweight performance cat can.

It’s amazing. Monos should be heavy. Very heavy. And you should just accept that they are not speed demons, but will get you there safely and comfortably in a steady and smooth way.

Lighter monos and average displacement monos are all I owned before. I think a lot of us come to the multi/mono debates from a perspective of not having cruised in a heavy monohull. They are 90% as comfortable as a catamaran, just slower. But it’s not all bad if you relax and don’t worry about getting to your destination so quickly.

The startling conclusion I’ve come to is this:

The very best catamarans are ultra light weight.

The very best monohulls are ultra heavy.

It’s the in between stuff that stinks.
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Old 02-07-2020, 04:59   #2
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Re: Heavy Monohulls vs Light Catamarans

I disagree.
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Old 02-07-2020, 05:14   #3
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Re: Heavy Monohulls vs Light Catamarans

Why should monos, or anything be heavy? Heavy is just slow. You can find plenty of comfort in a lighter mono. If you want MORE comfort, just make it bigger, not heavier.
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Old 02-07-2020, 05:22   #4
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Re: Heavy Monohulls vs Light Catamarans

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Why should monos, or anything be heavy? Heavy is just slow. You can find plenty of comfort in a lighter mono. If you want MORE comfort, just make it bigger, not heavier.
The reasoning of my observation is:

Heavy means inertia. Inertia means less movement for a given input (like large chop). This makes for a more comfortable boat. Until you try to do the same on a catamaran, then heavy is just awful.

But yes, 100% in agreement. More waterline is always better. I’m assuming waterline is a constant.

These morning musings come from direct personal experience with owning all sorts of boats on all sorts of ends of the spectrum and in the middle. The ones in the middle were less comfortable typically. The cats on the light side and the monos on the heavier side tended to feel more comfortable for full time living and traveling.
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Old 02-07-2020, 05:27   #5
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Re: Heavy Monohulls vs Light Catamarans

With a mono, hull shape and such factor into comfort, not only weight. Some hulls just sit more comfortably in the water than others even if they're the same weight.
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Old 02-07-2020, 05:33   #6
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Re: Heavy Monohulls vs Light Catamarans

Can't speak about multis, but will agree you do want some weight in a mono hull to make it comfortable in a sea state. I'm certain very heavy is better for comfort ratio, but we are ok w/our boat length displacement ratio of ~265 (dry wt) and > 300 (3/4 load). We still get good boat speed in lighter air where a very heavy displacement (>400) boat, may not move as well.

The days are gone for us in a racing mono displacement as I feel the motion below is a bit much in an active sea state. While fast, I like arriving not feeling like I've been in a wash machine for a few days.

Now if someone would give me this boat I would totally suck it up and go for the fast boat again.

I'm certain others will feel differently based on their experiences and multis are a different critter all together
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Old 02-07-2020, 05:37   #7
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Re: Heavy Monohulls vs Light Catamarans

I bet a big heavy cat is pretty comfy and slow too.
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Old 02-07-2020, 05:42   #8
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Re: Heavy Monohulls vs Light Catamarans

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Originally Posted by Chotu View Post
The reasoning of my observation is:

Heavy means inertia. Inertia means less movement for a given input (like large chop). This makes for a more comfortable boat. Until you try to do the same on a catamaran, then heavy is just awful.

But yes, 100% in agreement. More waterline is always better. Iím assuming waterline is a constant.

These morning musings come from direct personal experience with owning all sorts of boats on all sorts of ends of the spectrum and in the middle. The ones in the middle were less comfortable typically. The cats on the light side and the monos on the heavier side tended to feel more comfortable for full time living and traveling.

Fair enough, but why in the world would you assume that weight is variable, but waterline is a constant? A given amount of weight is always more comfortable spread out over a longer waterline, and you get a huge boost in speed at the same time (compounded effect of increasing waterline length AND reducing D/L ratio).



I would say your less comfortable monos were just too small to be comfortable, not that they were too light. Making them heavier within the same waterline is the least effective way to improve anything. Note well also that COST is generally a function of weight, for a given level of quality and equipment. So a bigger boat will not even be more expensive, or not much more expensive, than a smaller boat of the same weight.



Cards on the table -- I am not a fan of small, heavy, slow monohulls. But of course -- to each his own
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Old 02-07-2020, 05:48   #9
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Re: Heavy Monohulls vs Light Catamarans

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I bet a big heavy cat is pretty comfy and slow too.

You would win that bet.


Cats are just like monos in that regard. For a cat to be really fast AND be pretty comfortable, it needs to be light and pretty big. I like the Atlantic 57's myself; that must be an absolute blast to sail.
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Old 02-07-2020, 06:20   #10
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Re: Heavy Monohulls vs Light Catamarans

We have a very heavy mono. I know that others in monos are much more bothered by a rolly anchorage than we are. The flipper stoppers come out, or they move, or put out second anchors. We also roll but clearly not as much.

44’ LOD, 37’ LWL, 40,000lb.

We are not fast, but we get there. And 90% of our time is spent in anchor, liveaboard. So if you look at it that way, weight helps 90% of the time and hurts 10% it’s a different argument. Now if you are a weekend or vacation sailor so that whenever you are on the boat you spend a lot of time sailing, say 50/50, well then the equation changes dramatically favoring lighter, faster boats.

The only constant is there no “perfect” boat.
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Old 02-07-2020, 06:30   #11
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Re: Heavy Monohulls vs Light Catamarans

Roll in anchorages is a combination of hull shape, beam, and weight distribution in the boat more than total weight, I think. Not a sailboat, by my own boat is very rolly at anchor or the dock compared to many other planing hulls of the same size, even ones a few thousand pounds lighter.

Looking around my marina the other day with just a little bit of gentle swell coming through, most of the powerboats I could see (mostly express cruisers from 30 - 45 feet and a 40 foot Mainship) were just pitching slightly and bobbing up and down a little with just a tiny hint of roll visible. The sailboats were gently rolling back and forth a couple of degrees, hard to notice unless you looked at the masts. The narrower sailboats (Pacific Seacraft 34, Southern Cross 35) seemed to be rolling a bit less than most, but not a dramatic difference. My own boat was rolling as much as the sailboats, but with a somewhat faster, sharper motion. Compared to other powerboats of almost identical length and beam, but slightly different hull design, the motion was significantly different.
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Old 02-07-2020, 06:34   #12
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Re: Heavy Monohulls vs Light Catamarans

Yes, the roll factor is a complicated one. Sometimes it just comes down to a bad resonant frequency making one boat easily oscillated back and forth while another damps the motion.

Monohulls only of course.

The resonant frequency of rolling on a catamaran is so short that there aren’t any waves that arrive in that frequency range.




Quote:
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Roll in anchorages is a combination of hull shape, beam, and weight distribution in the boat more than total weight, I think. Not a sailboat, by my own boat is very rolly at anchor or the dock compared to many other planing hulls of the same size, even ones a few thousand pounds lighter.

Looking around my marina the other day with just a little bit of gentle swell coming through, most of the powerboats I could see (mostly express cruisers from 30 - 45 feet and a 40 foot Mainship) were just pitching slightly and bobbing up and down a little with just a tiny hint of roll visible. The sailboats were gently rolling back and forth a couple of degrees, hard to notice unless you looked at the masts. The narrower sailboats (Pacific Seacraft 34, Southern Cross 35) seemed to be rolling a bit less than most, but not a dramatic difference. My own boat was rolling as much as the sailboats, but with a somewhat faster, sharper motion. Compared to other powerboats of almost identical length and beam, but slightly different hull design, the motion was significantly different.
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Old 02-07-2020, 08:23   #13
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Re: Heavy Monohulls vs Light Catamarans

Any of the previous poster have any experience as a naval architect?
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Old 02-07-2020, 08:29   #14
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Re: Heavy Monohulls vs Light Catamarans

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Any of the previous poster have any experience as a naval architect?
None here, other than a bit of empirical evidence from boats I’ve lived on and it not being at all hard to understand the concept of fundamental frequency as it pertains to roll motion of any object in the water with waves acting upon it.

And lots of amateur hour NA work done on my catamaran.
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Old 02-07-2020, 08:44   #15
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Re: Heavy Monohulls vs Light Catamarans

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Any of the previous poster have any experience as a naval architect?
Implying that no one posting in this thread is entitled to a view on heavy vs light displacement boats, and the other very basic boat design questions being discussed?

A lot of people on CF not only have lifetimes of experience on different boats with different characteristics, but also are quite knowledgeable about at least the main principles of boat design.

I haven't noticed any ignorant comments in this thread. If you have some greater knowledge, then, by all means, enlighten us.
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