Heavy Monohulls vs Light Catamarans

[roam]

Originally Posted by Chotu

All the time I have chosen and been building my lightweight catamaran, I was after comfort. <snip>

What are you building ?

[Cheechako]

Multi hulls have a jerky motion... light or heavy...it's tiring at times.
Mono hulls have a rolley motion...light or heavy.. it's tiring at times.

For comfort alone, I lean a bit toward multi.
Pick your poison!

[tomfl]

Originally Posted by Dockhead

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.

What I do know is there is no such thing as a generic monohull or a generic multihull.

There are plenty of heavy monohulls that are very uncomfortable in lots of conditions; probably more than are comfortable in lots of conditions. Same can be said of light multihulls, some are good and some are bad.

Specificity is the key; without knowing just which designs are being compared it is silly to comment.

[nuvaslacker]

I think a case can be made for a motor-sailer catamaran with wider hulls not necessarily of semicircular underwater cross section. Most people daysailing will use their motors against the wind to get home, most on ocean voyages will use the old routing charts for favourable winds.

The 30ft Oceanic that rounded Cape Horn with a family of two adults and two toddlers found it important to keep the engines running when under bare poles in the forties so that way was kept in the troughs of the waves. The Swales found it a comfortable family voyaging vessel; they even flew a spinnaker on occasion. It was, of course, a heavy catamaran, even by the criteria of the time.

[slug]

If you enjoy sailing you choose a monohull

If you’re interested in a floating condo ,,,with maximum surface area for solar arrays, windmills, bbqs.... you choose a multihull

[Pauls]

I agree with Chotu. More weight = more inertia = a slower, steadier movement. Basic physics. I'd also add that there are other factors which also strongly influence this. "Form stability" is a common phrase, and it is appropriate as regards righting moment. But on an ocean with waves "form stability" translates to "surface following force". Which means, for sea kindliness, that form stability is a source of the motion we are trying to not have.

For sea kindliness low form stability combined with a high righting moment from ballast will create the highest sea kindliness, for a given size of boat.

Marchaj, in his excellent book "Seaworthiness, the forgotten factor" covers this in detail. Dave Gerr also recommends heavy boats for comfort.

[Slainte1]

If you can put up with heeling and rolling downwind the by all means go for a mono but I prefer a fast multi that is already home or anchored in a quiet anchorage. I will have a drink ready for you when you get in....if it's not too late

[Training Wheels]

Originally Posted by slug

If you enjoy sailing you choose a monohull



If you’re interested in a floating condo ,,,with maximum surface area for solar arrays, windmills, bbqs.... you choose a multihull

Umm.....no.









[ATTACH]218567

[Rapanui]

It is not true that heavy boats roll less than light boats, its all a matter of how tuned the roll period of the boat response is to the encounter period of the forcing due to encountering a series of waves. The closer the vessel roll period is coincident to the wave encounter period, the larger the amplitude of roll. The amplitude of roll is determined by the amount of roll damping present from sails, hull shape etc, the absence of which would mean the amplitude of the roll would increase infinitely at coincidence of the roll period and wave period. Round hull monos often associated with heavier displacement typically have less damping than wide beam modern designs because of the non-linear increase in roll stiffnes with increasing roll angle of the latter. Flopper stoppers work by increasing the dynamic roll stiffness, i.e. the faster the stopper moves through the water, the higher the resistance.

Most monos, unfortunately have a roll period which is right in the range of wave encounter periods you are likely to experience at sea and so the tendency to roll is excited.

Catamarans do roll but they possess 2 factors in their favour which means the roll amplitude is much less, the roll period is much shorter than the wave encounter period because of their beam and lower weight plus the roll stiffness is extremely high.

[waterman46]

Originally Posted by Muaddib1116

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

Aye, and probably has about the same performance and comfort as a big heavy mono, but at nearly twice the cost for almost everything.

If you want a cat, you really need to go light for all the benefits it will bring.

BTW the OP mentioned enclosed steering as if it is unique to cats. You can have enclosed steering just as easily on any center cockpit monohull, with a good cockpit enclosure.

[s/v michaela]

My ketch is 75' and weighs in at 100,000 lbs (50 tons) .. I had a nice light 45.2 jeanneau before this one. Night and day difference in an anchorage... Sailing the big boat is like driving a semi, the Jeanneau like a sports car. I don't feel the sea now like I did before,, but I can sleep in any anchorage without rolling out of my berth!

[thinwater]

Originally Posted by Palarran

I disagree.

I like that response. It's compact and leave the reader with plenty of room to infer.

[thinwater]

Originally Posted by slug

If you enjoy sailing you choose a monohull

If you’re interested in a floating condo ,,,with maximum surface area for solar arrays, windmills, bbqs.... you choose a multihull

As Training Wheels said, "Uh, no." Not even close.


Tris can go fast, point high, tack on a dime, and have all the helm feel you could ever want.


Down sides? Yup. But not boredom.

[Scaramanga F25]

When I was a small boat manufacturer in Florida in the late 70" I did design work wit a winning sailboat architect.
Chotu is just misinformed.
Instead of a lengthy lesson in sailboat architecture I would suggest you study what the Dashews have on You tube. Their extensive experience can be scalled down.
Also I have owned early on, a very heavy monohull, then an ultralight monohull and 4 others in between. This takes almost lifetime. I see so much rubbish here but I still try to steer sailors in the right direction.
Boats cost by the pound.

[Dockhead]

Originally Posted by tomfl

What I do know is there is no such thing as a generic monohull or a generic multihull.

There are plenty of heavy monohulls that are very uncomfortable in lots of conditions; probably more than are comfortable in lots of conditions. Same can be said of light multihulls, some are good and some are bad.

Specificity is the key; without knowing just which designs are being compared it is silly to comment.

It's certainly true that weight is not the only factor which influences motion comfort and speed, but as an extremely influential factor, it is not indeed "silly to comment". A boat with D/L of 400 is going to be slow, slow, slow -- it doesn't matter how much you tweak the hull form. And with extremely rare exceptions it's going to be quite comfortable compared to boats of the same length with half the D/L.



In this thread we've also gotten into form stability and beam and other factors which influence this. Not a silly discussion at all.