Motion Control

[sailorboy1]

As a followup to the "speed vs comfort"; since we all know we should sail on lots of boats before buying ours, but of course we don't what to wait:

What is everyones option of their boats motion as to it's comfort and sailing ability in light to heavy winds?

If you feel the motion is low (comfortable) do you find yourself stalled out a lot in light winds wishing you weren't?

If motion is high (faster in light wind) do find yourself geting worn down from the motion if anything more that light winds?

If possible with answer provide boat, DLR, MCR (I'm not putting in the formulas as if someone knows/cares they will know how to do it).

[Tempest245]

see my reponse in " speed vs comfort" :-)

[bob perry]

I'll go ahead and poke the dog with a stick on this one.

If we limit ourselves to boats that are "normal" say with D/L's between 150 and 350 and eliminate the extremes of shape I don't think there is to much motion difference. Both boats will be uncomfortable in a seaway. The less initial stability you have the slower your motion but, generally speaking the slower the boat, generally speaking. We all seem to like stiff boats. The way I see it is rolling around slowly for 12 hours more comfortable than rolling around quickly for 8 hours? Sitting at the bar with a cold beer is comfortable. Also consider that for some rolling slowly thru a big arc is les comfortable than rolling more quickly thru a smaller arc. That said, most stomach's prefer the slower motion but I'm not even sure about that. I know the cat's that take people from Seattle to Victoria are notorious for makiing people throw up.

[DeepFrz]

Quoted by Bob Perry.
I know the cat's that take people from Seattle to Victoria are notorious for makiing people throw up.

Hi Bob,
Have no experience with cats so I may be way off here but I have heard that cats are very stiff. Could that be why the people are getting seasick? I have only been seasick once, on a fairly flat bottom boat, but it was after working on a clogged diesel fuel line. So it was probably the diesel smell combined with the motion that set me off.

[bob perry]

Deep:
You got it. Cats are initially very stiff. It is the excessive initial stability of the cat or any beamy, flat bottomed boat that gives it a quick motion. Sometimes in an anchorage, especially one that has some exposure to waves it's interesting to watch how the different moored boats react to the waves.

[maxingout]

I liked the predictable slow motion of my monohull, but at the end of the day, I didn't like all of the bruises on my legs and hips from getting knocked sideways and bumping into interior furniture.

I dislike the snappy quick motion on my catamaran when I go forward to work on the foredeck. It isn't as predictable as on my monohulls, and because of the quick motion, I feel slightly insecure on my footing as I go forward. Our catamaran's motion pivots around a center that is quite far aft, making a smooth ride aft that is quite comfortable. At the end of the day, I don't have bruises on my legs and hips like I did when sailing on my monohull. It is no bruising cruising on the catamaran. After twelve hours of sailing, I am not half as tired on my catamaran as I was on my monohull. It takes a lot of energy to hold on all the time.

I sailed 90% of the time in the tradewinds around the world, and running before the wind in our cat was easy and comfortable. Sailing in the higher latitudes (going to New Zealand x 2) gave a less comfortable motion than downwind sailing in the trades.

For me, it comes down to where you sail and how you sail. Both monohulls and multihulls can be quite comfortable, and both are compromises. For a downwind sail around the world, I prefer a catamaran. And then of course there's the admiral. She said that she would sail around the world with me as long as it was in a catamaran. We've been around once already in a catamaran, and she's ready to go again as long as it's on a cat.

[Hiracer]

Originally Posted by bob perry

I'll go ahead and poke the dog with a stick on this one.

If we limit ourselves to boats that are "normal" say with D/L's between 150 and 350 and eliminate the extremes of shape I don't think there is to much motion difference.

OK, I'll poke Bob with a stick and say between two boats within his 'normal' parameters (D/Ls of 240 and 295, or so) I felt a huge difference in motion comfort. Enough than I'm obnoxious and evangelical about it.

Hint, I think B/D, beam, and draft play a large roll in all this, not just D/L. (Pun intended.)

. . .

Don, your question makes no sense to me whatsoever. Why would a boat more comfortable than another 'stall out' in light airs? I don't get the question. Within the universe of my admittedly limited experience (two boats, one of average comfort--just about like most other boats--and one of greatly enhanced comfort) their light air sailing is just about the same, except maybe I detect that my comfortable boat might actually sail slightly faster in light airs.

I can say this without equivocation: I sail my comfortable boat in light airs lots more than I did the other, but largely because of a change in venue and I don't have much choice unless I learn to enjoy motoring.

In heavy airs the comfortable boat sails way better, largely because it doesn't have that IOR pinched stern that the more 'normal' boat did (we're talking hobbyhorsing here), albeit I reef much sooner in the comfortable boat because the B/D is lower.

[MarkJ]

Ours is a fairly light boat 7 tonnes at 39 feet, a Beneteau.

It goes well in light airs. When many boats would be splattering about thrashing the sails we will be doing 1 or 2 knots in 3 or 4kts wind. However do remember that that isn't satisfactory to many and they will put their engines on.

As the wind goes above 15 true close hauled there is motion in the boat and the more over canvassed the boat is, as the wind goes above 20 kts, the motion is larger. The boat heals.
It does't worry me as I am used to it from racing, used to it cruising and like it (OK not for 3 weeks solid!)

We have the first reef tucked in early, about 18 kts app, certainly by a consistent 20. Then a roll in the genoa.

Many people sail with far too much sail up. Modern boats are not meant to be sailed on their ear. This stuff about 45 degree heal is silly - so is 30.

I get the feeling (and from my very limited time on hobie cats) that people oncats may make the same error having too much sail up. Maybe even more so as wit a mono you know when its healing, with a cat its harder to tell.

So in my mind:

• Get used to the heal and motion of a boat. Once you have you will love it
• Furl the bloody sails earlier! Reef before you think of reefing.
• Hull speed is a theoretical maximum used by racing boats. I slow our boat down as soon as we hit 8kts. I don't want to approach our hull speed of 8.5
• Enjoy te sailing and then it doesn't matter if the voyage take a little longer

[Tempest245]

The last two vessels I've owned, a 29.9 Bristol and my current Sabre 34 both take early reefs. I agree, with Mark, I often see some sailors trying to carry way too much sail..heeled too far over, rounding up and stalling in the gusts.

When I replaced my headsail 2 years ago, I replaced the 150 roller furling with a 135 without regrets. When I replaced the mainsail, I switched it to a loose foot, which I like much better in light air.

I was always taught that increasing the wetted surface with excessive heel, while exhilerating at times, reduces speed, and certainly comfort. I try to reef early and sail faster and straighter. In some ways I liked the Bristol more, the boat liked to lay over early, but then tracked very nicely barely noticing the puffs.

Anyway, I agree, carrying the right amount of sail for the boat design and the conditions goes a long way to aiding in comfort level.

[Robertcateran]

Originally Posted by maxingout

I liked the predictable slow motion of my monohull, but at the end of the day, I didn't like all of the bruises on my legs and hips from getting knocked sideways and bumping into interior furniture.

I dislike the snappy quick motion on my catamaran when I go forward to work on the foredeck. It isn't as predictable as on my monohulls, and because of the quick motion, I feel slightly insecure on my footing as I go forward. Our catamaran's motion pivots around a center that is quite far aft, making a smooth ride aft that is quite comfortable. At the end of the day, I don't have bruises on my legs and hips like I did when sailing on my monohull. It is no bruising cruising on the catamaran. After twelve hours of sailing, I am not half as tired on my catamaran as I was on my monohull. It takes a lot of energy to hold on all the time.

I sailed 90% of the time in the tradewinds around the world, and running before the wind in our cat was easy and comfortable. Sailing in the higher latitudes (going to New Zealand x 2) gave a less comfortable motion than downwind sailing in the trades.

For me, it comes down to where you sail and how you sail. Both monohulls and multihulls can be quite comfortable, and both are compromises. For a downwind sail around the world, I prefer a catamaran. And then of course there's the admiral. She said that she would sail around the world with me as long as it was in a catamaran. We've been around once already in a catamaran, and she's ready to go again as long as it's on a cat.

High prismatic coefficient reduces much of the pitching moment. Down our way, (EDEN NSW) many of the commercial cats build long bow bulbs to damp the motion. If you notice the tendency of many of the modern cats to go to revere sheer to increase the time of impact of the waves and give a more gradual and earlier rise to the waves.

[bob perry]

Robert:
Could you please take the time to exlain that last part about the effects of reverse sheer. You have lost me there.

Hi:
You are making a mistake of thinking the seas act on a boat as functions of indiovidual components and ratios. It does NOT work that way. Rm alone takes ALL the things you mention into consideration.The sea see's the whole boat. Of course, every ratio plays a part in how a boat behaves. A boat is not a collection of individual ratios it is one thing.

[Bash]

... I agree with Bob's observation that there isn't too much difference in the motion of boats within the "normal" range. However, I would posit that the biggest factor in motion comfort is how closely the "normal" boat sits to its designed waterline. The real rollers among the cruising fleet seem to be the boats that are so overloaded--especially in the bow and stern--that the boats don't have a chance to behave in a seaway the way they were designed to behave.

An Overload 33 is never going to have the comfy motion of a Waterline 54 if it's being forced to carry the amount of stuff most of us want to carry on a cruise. By "stuff," I include such necessities as a spare rudder, and a dink with an outboard, and an eight-man liferaft, and a watermaker, and three hundred feet of chain, and solar panels, and...

[bob perry]

Bash:
I'm with you there. I think in the relm of normal boats when they are "overloaded" most of that overload goes above the DWL. Almost all normal ( and I use that term we have more or less identified it here) have a VCG around the DWL or slightly above, say 4 to 6" above the DWL. Given volume restrictions the "overload" almost always raises the VCG and once that boat starts to roll more than 5 degrees that change in VCG is going to have a major effect. Your point is well taken. The 37'er ready for a world cruise will probably have the same extra gear weight that a 48'er will have including the same amount of 3/8" chain etc.

[cal40john]

Originally Posted by Tempest245

The last two vessels I've owned, a 29.9 Bristol and my current Sabre 34 both take early reefs. I agree, with Mark, I often see some sailors trying to carry way too much sail..heeled too far over, rounding up and stalling in the gusts.

When I replaced my headsail 2 years ago, I replaced the 150 roller furling with a 135 without regrets. When I replaced the mainsail, I switched it to a loose foot, which I like much better in light air.

I was always taught that increasing the wetted surface with excessive heel, while exhilerating at times, reduces speed, and certainly comfort. I try to reef early and sail faster and straighter. In some ways I liked the Bristol more, the boat liked to lay over early, but then tracked very nicely barely noticing the puffs.

Anyway, I agree, carrying the right amount of sail for the boat design and the conditions goes a long way to aiding in comfort level.

I know that most boats are different so it's dangerous to generalize. My Cal 40 is well balanced up to about 20 degrees of heel. I have experimented and found that while close hauled, not exceeding the 20 degrees of heel, which also pretty closely correlates to keeping the weather helm to under 5 degrees, makes the boat sail faster. On the other hand, sailing on a jib reach, I have found that even with the boat heeled over so far that to maintain course I have the tiller in my lap the boat is faster with more sail/heel.

I have also done the jib reach test on a chartered Privilege 39, more sail resulted in higher speeds even though the helm was bad. How bad was it? It was so bad something was binding in the steering system. At first we thought we had it hard over to the lock, but as we got off of each wave and the load eased up, the rudder had more to go. We decided this was a bad idea and tucked the reef back in. This was our second charter in the Caribbean, and both boats (first was a Centurion 41) had so much mast rake that I had come up with a theory that charter companies deliberately did that to force you to depower. Follow up charters disproved the theory, at least in the general case.


And for those that gasp, "I would never!", yes I have two modes, (informal) racing and cruising. In cruising mode balanced helm and flatter boat is preferred.

John

[Tempest245]

Bob, Bash...Given that. On my centerboarder, would lowering the board ..some or all....on a broad reach..to a run...where I'm surfing with say 6 to 8 footers...aid the motion or hurt it? Or, have no effect at all?