What is "hobbyhorsing"?

[zAr]

I'm reading Chichester's account of his circumnavigation on board Gipsy Moth and shortly after he set out he discovered that the she hobby horsed. I've seen the word before but can't really find any adequate explanation of it as used to describe how a boat handles and why.

From Chichester's description it seems to be what happens when a boat dramatically loses speed as it climbs a wave, then approaches each successive wave with less and less speed. Almost is if the boat is stopped by the waves or loses impetus.

Is this a design flaw and can anyone explain what causes it?

[priscilla]

The bow lifts up, the stern drops down,...over and over and over again. You can't stand it for very long! The best solution is to drive off so you put the sea on either side of the bow. All boats have a tendency to hobby horse in choppy head sea but a poorly designed boat will hobby horse in even a slight sea.

[zAr]

Originally Posted by priscilla

The bow lifts up, the stern drops down,...over and over and over again. You can't stand it for very long! The best solution is to drive off so you put the sea on either side of the bow. All boats have a tendency to hobby horse in choppy head sea but a poorly designed boat will hobby horse in even a slight sea.

Do you know what it is about a boat design that will make it more or less likely to do this in a slight sea?

[Jeff_H]

The term refers to a boat which tends to pitch through large angles of rotation. (Pitch means rotational motion in a fore and aft direction, essentially like a seasaw motion). Boats with short waterline lengths relative to their leingth overall, heavy or tall rigs, and lots of weight in the ends (especially the bow) tend to be more prone to hobby-horsing than boats with plum stems, lighter rigs and boats with less weight in the ends.

The down side of hobby horsing is that the motion tends to disrupt the flow of air over the sails and water over the keel, slowing the boat, and increasing leeway. In extreme cases, the motion can be very uncomfortable and in really extreme cases, the force of impact of the bow on each rotation can just about stop the boat in its tracks.

CCA era boats (1950's and 1960's) with their long overhangs, relatively full bows, heavy hull weights, and heavy rigs were especially prone to hobby horsing, but many traditional designs were also guilty of this bad behavior.

Jeff

[JohnRPollard]

ZAr,

Hobbyhorsing is the tendency of a boat to pitch back and forth like a rocking or "hobby" horse. That is to say, to roll forward toward the bow along the longitudinal axis, then back toward the stern, repeating, with the horizontal axis as the pivot point. If "hobbyhorse" doesn't quite conjure the right image, think "seesaw".

The conditions that induce hobbyhorsing vary for different designs, but hobbyhorsing usually occurs in a certain amount of a seaway. Sometimes, it is not the seastate, but a motorboat wake that will induce hobbyhorsing.

To a certain extent, most boats will hobbyhorse somewhat in certain conditions. But some are more prone than others. Long overhangs at the bow and stern are one design feature that is often associated with excessive hobbyhorsing. Another is excessive weight concentration at the boat's extremities.

Hobbyhorsing can be a momentary condition, such as when a wake is encountered, or can be an ongoing issue in certain sea states during a passage. Abrupt hobbyhorsing can bring a boat to a stop -- such as when encountering a wake in light air.

But even moderate hobbyhorsing won't help boatspeed -- some energy that could be propelling the boat forward is instead partly expended in the pitching of the vessel or fighting it. In other words, the boat is rocking back and forth instead of simply moving forward, so some forward momentum is lost as the boat pitches back, on the return, toward the stern.

Not sure if this is making sense. Hopefully Jeff H will pop in and expand on this a bit more artfully. Edit: Oops, I see we cross posted. Too slow, I guess.

[FarCry]

In my world hobby horsing occurs when the wind speed drops below about 7kts and we are heading into seas in an area were the current and the wind are opposing eachother making for short steep waves. Ironically seconds after it begins I get the evil eye from the admiral which normally has me reaching for the ignition of the Yanmar!!!! With enough wind I can keep up enough boatspeed to go over or through the waves. As stated more eloquently above, once the motion begins, the sails loose most of their drive and forward motion decreases quickly magnifying the effect even more. Yes I sail on a fat short boat!!!!

[zAr]

Thanks everyone! That was very informative!

[bobmcgov]

Must be a CCA catamaran....

[sailingdog]

Of course, hobbyhorsing gets it name from the child's toy, the hobby horse.. which is basically a rocking horse that rocks forward and back... much the same as a boat that is hobbyhorsing.



Keeping weight out of the stern and bows will help a lot, as will having a boat with a relatively long waterline with short overhangs...

[CharlieCobra]

All designs hobby horse to an extent. It's a matter of wavelength and frequency as well as the speed of the boat. Even plumb bowed boats will do it in certain conditions. Getting the boat powered up or falling off to get out of that zone usually helps a lot. Some boats which are prone to it never can get out of that zone on a beat.