Monohull or Multihull Sailboat?

[BigCat]

[quote=jackdale;157744]It is that short quick motion that I do not like. The weight of a monohull seems to temper any motion.

Hi, Jack - Ted Brewer designed a calculation for comparing the heave of monohulls (to each other,) to predict which would have the slowest and most comfortable motion.

"It is based on the fact that the faster the motion the more upsetting it is to the average person. Given a wave of X height, the speed of the upward motion depends on the displacement of the yacht and the amount of waterline area that is acted upon. Greater displacement, or lesser WL area, gives a slower motion and more comfort for any given sea state. Beam does enter into it as as wider beam increases stability, increases WL area, and generates a faster reaction. The formula takes into account the displacement, the WL area, and adds a beam factor."


more at the source at: Ted Brewer Yacht Design


Of course, the lack of heeling and deep rolling of a multihull is also a source of comfort. I remember the awful, corkscrewing motion of sailing in 40 knot with the wind on the quarter in 12 foot swells, for a week or so on my otherwise very comfortable monohull when sailing from LA to the Marquesas.

[schoonerdog]

I've been at anchor surrounded by monos which were pitching from side to side like metronomes while we stood completely still. I've actually had people abandon their monos and come stay with us in storms because the motion on theirs was so horrible even though our PDQ 36 was 7 ft shorter than their mono. Sooooo, the debate continues.

[BigCat]

I don't think it is really a debate, because the two different types excel in different conditions. In rolly anchorages, or any other condition where deep, rhythmic rolling is likely for a mono, cats are nicer. In other conditions, heavy monos are nicer, except perhaps when heeling a lot. Pretty much everything in yacht design is a compromise, where one choice shines in certain conditions, and another is not as good, but shines in other conditions by comparison. Partisans may try to make out that one choice is best in all conditions and for all purposes, but they are just showing their ignorance. ~De gustibus non est disputandum.~

[ssullivan]

Interesting, BigCat.

The very reason I didn't like my mono was the rolling at anchor (and since we live at anchor, it's a real issue). I can remember times when I was in the calmest water, in an anchorage protected from the sea in all but one direction... of course... ha ha


Of course that was the direction the swells would come into once in a while.

The "swells" were maybe 4-6" high and were *just* the right frequency to make us fly back and forth like a pendulum, even though they were tiny and it was completely calm.

This happened more times than I figured it would and drove me batty a few times.

I have still to sort out my aft-heavy problems on the current cat, so my bows love to leave the water and reach for the sky... but I have more weight coming on board and it's all going as far forward (and low) as i can get it. Hopefully, she will behave a little better then when confronted with seas to the bow.

[Tropic Cat]

Originally Posted by ssullivan

I have still to sort out my aft-heavy problems on the current cat, so my bows love to leave the water and reach for the sky... but I have more weight coming on board and it's all going as far forward (and low) as i can get it. Hopefully, she will behave a little better then when confronted with seas to the bow.

Sean, I just added about 5 pages of content to my website. Some are factory updates concerning maintenance issues, boat trim and sail trim. You'll find them on the Owners Page and they're worth glancing over.

[Therapy]

Originally Posted by rickm505

. You'll find them on the Owners Page

I don't see an "Owners Page".

[Tropic Cat]

really? Hmm.. It's called The Owner's Corner & Factory updates

There's a link to it on the first page of the site. In any event this link will take you there.

[44'cruisingcat]

Originally Posted by ssullivan

Interesting, BigCat.

The very reason I didn't like my mono was the rolling at anchor (and since we live at anchor, it's a real issue). I can remember times when I was in the calmest water, in an anchorage protected from the sea in all but one direction... of course... ha ha


Of course that was the direction the swells would come into once in a while.

The "swells" were maybe 4-6" high and were *just* the right frequency to make us fly back and forth like a pendulum, even though they were tiny and it was completely calm.

This happened more times than I figured it would and drove me batty a few times.

I have still to sort out my aft-heavy problems on the current cat, so my bows love to leave the water and reach for the sky... but I have more weight coming on board and it's all going as far forward (and low) as i can get it. Hopefully, she will behave a little better then when confronted with seas to the bow.

Exactly our experience with our mono, Sean. Sometimes (and it always seemed to happen at night) you couldn't even SEE any real waves, but the boat was rolling it's guts out.

I recently spent a night in a cat anchored at Middle Percy island, which is a beautiful spot, but a notoriously rolly anchorage. There were small swells bending round the island to enter the anchorage at 90'. It would have been hell in a monohull. Bad enough that no mono's even tried anchoring there that day, only cats. It was perfectly comfortable for us.

As I said previously, there will be conditions where your mono would have been more comfortable, particularly since it was 10 feet longer, but overall I think the cat will win out for comfort.

Re your boat's pitching - I think I would be trying to move the weight that is currently too far aft closer to the centre of the boat, (or better still, out of the boat altogether) rather than adding more weight further forward.

[ssullivan]

Rick: I just read through all that info on your site. GREAT STUFF! Much of it is exactly what I had experienced. One thing I had done wrong once and figured out for myself was that you can't tack our boats under main alone. You need the jib up as well. I stalled and flailed about, just like they said in the article. Everything they say in that section is right on the money.

44Cruising: Yes, exactly! The swells were so tiny, I could barely even see them. They were long frequency and very small in size. Some of the worse night's sleeping ever.

With the weight, I can't just pitch my engines, batteries, diesel and dinghy overboard, although I'd like to. I need to balance out the weight with some forward to get those bows down. They weigh nothing in comparison to the after part of the boat and pop up too quickly. Remember, the heavy dignhy and outboard as well as twin Yanmar 3YM30's were not stock equipment, nor was my arch, 600AH battery bank or solar and wind stuff... all back there where they weigh down the stern.

I have additional weight coming on because I have some more stuff for liveaboard times (rather than the delivery I'm on right now) and that stuff will head forward, to make up for the weight aft. I already have the amid-ships area loaded (water tanks are located there, tools, food, etc...)

Originally Posted by 44'cruisingcat

Exactly our experience with our mono, Sean. Sometimes (and it always seemed to happen at night) you couldn't even SEE any real waves, but the boat was rolling it's guts out.

I recently spent a night in a cat anchored at Middle Percy island, which is a beautiful spot, but a notoriously rolly anchorage. There were small swells bending round the island to enter the anchorage at 90'. It would have been hell in a monohull. Bad enough that no mono's even tried anchoring there that day, only cats. It was perfectly comfortable for us.

As I said previously, there will be conditions where your mono would have been more comfortable, particularly since it was 10 feet longer, but overall I think the cat will win out for comfort.

Re your boat's pitching - I think I would be trying to move the weight that is currently too far aft closer to the centre of the boat, (or better still, out of the boat altogether) rather than adding more weight further forward.

[Therapy]

Originally Posted by rickm505

really? Hmm.. It's called The Owner's Corner & Factory updates

There's a link to it on the first page of the site. In any event this link will take you there.

Sorry, did not compute "page" for "corner".

[Tropic Cat]

Originally Posted by ssullivan

Rick: I just read through all that info on your site. GREAT STUFF! Much of it is exactly what I had experienced. One thing I had done wrong once and figured out for myself was that you can't tack our boats under main alone. You need the jib up as well. I stalled and flailed about, just like they said in the article. Everything they say in that section is right on the money.

I've had those updates for longer than I care to mention, and just realized that some of them were on old thermal fax paper and the text was slowly disappearing. This was the motivation to get them posted.

I'm glad they're helpful

[rexposeidon]

I like rolling at anchor it reminds me of being a small child, my mother rocking me to sleep in the rocking chair; which is why I always choose the top rack in my Uncle Sam's boats too.

[44'cruisingcat]

I'd suggest you've never experience REAL rolling at anchor. When stuff gets thrown all over the boat, when the dishes and pots are rattling and clanking in the cupboards, when the boat is creaking and groaning like crazy, when you are nearly being thrown out of bed.....

Not like mothers arms at all.

[GMac]

Originally Posted by 44'cruisingcat

I'd suggest you've never experience REAL rolling at anchor. When stuff gets thrown all over the boat, when the dishes and pots are rattling and clanking in the cupboards, when the boat is creaking and groaning like crazy, when you are nearly being thrown out of bed.....

And why would one be anchored in a spot that bad?
That's a user issue not a boat design/type issue.

[rexposeidon]

Originally Posted by 44'cruisingcat

I'd suggest you've never experience REAL rolling at anchor. When stuff gets thrown all over the boat, when the dishes and pots are rattling and clanking in the cupboards, when the boat is creaking and groaning like crazy, when you are nearly being thrown out of bed.....

Not like mothers arms at all.

First I have to agree with GMac. Second, you should have rigged your boat for heavy seas, nothing rattles when properly rigged. Third, I'd suggest you've never sortied a ship into a hurricane either. Since I have, ... I need to say nothing more to you.