"Pitching""or "Hobby-horsing"

[keithw]

Can I ask those with experience of double-ended vessels to advise or comment on which out of the huge number of such designs pitch more or less? How can a novice read a set of lines to guage how much a vessel might be prone to pitching? Are the later double-enders (eg, "Vixen"/ Paul E Johnston's designs) better than the originals in this regard? If so, how come the old guys didnt suss out how to reduce pitching - or are there trade offs in which a pitching-prone shape has offsetting advantages?

My own interest stems from wanting to sail back to New Zealand, westabout. Thats a lot of water with oftentimes too little wind. I need food and water and some fuel to keep me alive for a min of three months - poss on my own or with one or two crew if circumstances dictate: so 20,000 lbs displacement is a guide point. But if the boat pitches too much when loaded up like that, we won't get anywhere and I'll need another 1500lbs of provisions -then we'll go slower, so I'll need.....

[Ian McColgin]

Almost any boat will pitch if the sea's period matches her own oscillations in some way.

Firstly, let me dispell some bugaboos about double enders. I live on one of the finest, a Marco Polo by LFH and I've sailed many. They are not necessarily better than any other stern - no mysticism about parting the overtaking wave - nor are they more of a problem than any other stern with being pooped due to a lack of reserve bouyancy.

A good stern is a good stern is a good stern whether pointy or wineglass or barn door.

Part of predicting pitching looks at the boat's volume distribution. Disporportionate volume amidships joined with pinched ends, especially a pinched bow, below the water joined with lots of end volume above the water will make a boat bounce as it hits waves.

Especially if the weights are also ultra concentrated amidships.

On the other hand, a boat that is really narrow, like the english style "plank on edge" cutters of a century ago, will really power through - and I mean drenchingly through - waves.

A good boat is the sum of many many compromises. It needs to have enough volume in and be light enough in its ends to lift with a wave. But not so much that it squirts out of the wave crest and then must really smash the trough.

For displacement boats such as you'll be contemplating for this cruise, boats of moderate and harmonious looking form are most likely the ticket. Study LFH's "Sensible Cruising Designs" and Brewer's book on design and any collection of classic plans like Alden and Rhodes and Stevens and Atkins and Garden and Perry and Creelock.

G'luck

[Charles Burgess]

The traditional built pinky is double ended, and pitches less than many modern double-ended designs.

The older style was built more for stability than for raw speed. The difference is in the length-to-beam ratio.

A double-ended design with a narrow beam will pitch alot, but will sail faster; a traditional wide beam pinky that pitches less; but sails somewhat slower.

[RodB]

Read Atkin's remarks about "Vixen" in the post on this forum on double-enders...maybe it will help... I think his later designs were much improved over earlier ones...
Double-enders discussion...

Rb

[keithw]

Rod - thanks - BUT!! In that thread, I asked a similar question - if we look at the lines to see the "flatter buttocks" which we understand helps both speed and reduces pitching, where exactly do we need to look - and how can we pick up this feature when comparing lines of similar boats? My untutored eye can't pick this up from the lines given in that thread.

Isn't it easier to get flatter buttocks in a transom-sterned vessel?

If we accept that the prime functional requirement of Norwegian sailing lifeboats was to
sail to windward under storm conditions, and this led them to develop double-enders, how do we account for the very different shape of the British (and French pilot) cutters? Both coasts have prevailing westerlies and rocky coasts.
Can we hypothesise that in stormy western winds the pilot cutters didnt need to be so fast to windward as the vessels needing pilots were thundering east driven by that same wind? Seems a bit of a tenuous argument to me. Am I right that Scottish fishing vessels of the same period (lets say 1870 to 1940) were predominantly transom-sterned? So there must be a specific reason for the Archer style which doesnt apply to the British Isles, despite their proximity....

How about the argument that the Archers were designed to tow vessels to windward and the only job of a pilot cutter was to race to windward to get the pilot to the arriving vessel as fast as possible? Plus a pilot vessel needed to sail steadily downwind with maybe just a lad on board to get the boat back for the next trip..

Plus I would want a rescue vessel to handle really well when I was trying to stop alongside a person in the water, not to slip sideways. The Pardeys argue that their type of vessel NEEDS to slip sideways in storm conditions (to create the slick they say is necessary) - do double-enders perform the same way under such conditions? Or with more under-body and symmetry, maybe they hardly slip off at all?

As to weight distribution and pitching, theory is often quoted to support the notion that weight needs to be concentrated amidships to reduce pitching. I have experimented with crew members amidships and distributed fore and aft. I havent got any definitive conclusions yet except that maybe one thing works under some circumstances and in other others you need a different approach - not a very useful useful piece of knowledge! I have hauled an anchor a bit up the mast to reduce rolling with success, tho...

[RodB]

I would hope some of the more informed on this forum could compare the lines of "Eric" to "Vixen", plus interpret Atkin's remarks to hopefully offer a clearer explanation of what Atkin was saying...Also to elaborate more on comparing the different double-enders from different designers.

...Over my head.

RB

[ 03-10-2005, 02:00 AM: Message edited by: RodB ]

[Jeremy Burnett]

Is not pitching primarily a function of sailing to windward into the sea? I would have thought for the voyage you have in mind there are other priorities.As you say the boat needs to be burdensome enough to carry the crew and stores,it should be fast enough to make passages in a reasonable time.In downwind sailing it is more comfortable if the boat does not roll excessively which can be very tiring,this maybe implies a certain beamyness.So one can visualise a craft of general moderation and comfort,nothing extreme, with plenty of stowage space and water capacity, and a seagoing bunk for each crew member.

[sawcutmill]

http://www.imagestation.com/album/pictures.html?id=2131148897&idx=5[/IMG]
Certain conditions will accentuate pitching/hobby-horsing, usually not enough wind and the right sea state will also add to this phenomenon.I find that it usually occurs with a winds under 20 kts, and seas of 3 -10 ft, wave peroid is critical, the closer together,near land, where tide and back wash are encountered, the effect is pronounced. The weight distrubution is critical too! But when where an why i have no easy answers.
Where I have encountered this the most is off of New England w/in a couple of miles from shore. It is a very complicated subject due to the many variables each vessel has in its inherent design flaws.Wave period design influence, weight distribution, fore n aft or centered each have their effect.I have no easy answers, but do know , that once Pitching starts it is very frustrating and uncomfortable.
Nevertheless, every boat(w / a few exceptions) will demonstrate bad habits, but and this is a big BUT, this is sailing and one must take the good with the bad. I sailed "Pelagic" across the Atlantic, 4300 miles and enocountered this phenomenon around Spain while attempting to leave Vigo. Sea state was horrendous, confused and on the nose. C'Est la Vie!

[Ian McColgin]

The reason I recommended some of the good general design primers and some design catalogues is that there are many many factors, compromises and interactions. For every rule there's an exception, usually caused by an unconsidered factor.

Take a light sloop. Going to weather this boat will not really power through a wave well and needs to go over. Getting the weight well concentrated amidships will help let the bow lift on the face of the wave and land less heavily in the trough - in otherwords hobbyhorse in a happy way. Off the wind you'll spread the crew out to dampen the motion and keep her surging with the following sea.

Loaded for cruising, you should stow denser stuff as much amidships as possible but you'll still have a fairly long fore and aft moment of inertia. This is good as it slows the pitching down.

That's just weight. The lines are a whole 'nuther set of illusions.

[sawcutmill]

Here is the photo i tried to post previous. "Pelagic" sailing into Dutch Harbor , Jamestown, RI , last summer. stephen

[Charles Burgess]

Originally posted by keithw:
Can I ask those with experience of double-ended vessels to advise or comment on which out of the huge number of such designs pitch more or less? How can a novice read a set of lines to guage how much a vessel might be prone to pitching? Are the later double-enders (eg, "Vixen"/ Paul E Johnston's designs) better than the originals in this regard? If so, how come the old guys didnt suss out how to reduce pitching - or are there trade offs in which a pitching-prone shape has offsetting advantages?

My own interest stems from wanting to sail back to New Zealand, westabout. Thats a lot of water with oftentimes too little wind. I need food and water and some fuel to keep me alive for a min of three months - poss on my own or with one or two crew if circumstances dictate: so 20,000 lbs displacement is a guide point. But if the boat pitches too much when loaded up like that, we won't get anywhere and I'll need another 1500lbs of provisions -then we'll go slower, so I'll need.....

No one can, by simply looking at the hull lines, determine whether the boat will pitch a lot. There are more factors involved than simply the hull lines.

Weight distribution is a major factor. Keel/rudder form and rigging balance are other major players too. Put is all together and you have to consider the loaded hull's natural frequency in relation to the expected wave frequency of the seaway where you wish to sail in.

Short (light) boats in shallow water where the frequencies of both can harmonize is the usual preface for severe pitching and heading into disaster.

As the traditional wisdom proves, all small craft are designed for the local waters, inshore and offshore. A design that performs well in New England (US) waters won't necessarily perform well in West Coast (US) waters. It is only larger vessels that can sail just about anywhere with reasonably equal performance.

Make sure that the engine is located in a neutral position in regards to the boats six degrees of freedom. Some designs I have seen seemed to ignore this and put the engine in some out of the way location of convenience. If the boat is to have an engine, then the interior layout should give priority to the engine's optimal placement in regard to dynamic stability of the vessel.

[ahp]

In Marchaj's book, "Sailing Theory and Practice" he states that based on tests at the University of South Hampton, hulls that had the same deadrise foreward as aft were likely to hobby horse, and British designers favored designs like this. Why? It is was refered to as symmetrical design. I owned one. It pitched.

Germaine or not, I recall seeing a series of closely spaced photos of the US defender passing the British challenger "Septer" in the first post WW II Americas Cup challenge. First Septer was pitched up, then down, while the US defender was doing very little pitching and passing Septer by.