Changing weight in keel

[BubbleheadMd]

Paul,

The boat is a Lapworth 24. I believe it's actually a Gladiator or Spartan. Here's some info: Lapworth 24's

[maru657]

I'm looking for lead ballast in the San Diego area.

[Jeff_H]

Originally Posted by svHyLyte

Unless you have a very light yacht indeed, the addition of a few hundred pounds to your keel isn't going to have much influence on your waterline. It will however, make the yacht "stiffer" but will also make her motion in a seaway much faster--and in some cases uncomfortably so.

FWIW...

At the risk of high-jacking this thread, and not wanting to nit-pick an otherwise useful post, I just wanted to comment on one aspect of this quote for a moment.

Assuming that the ballast is added low enough to do some good, it would add to the stability of the boat over all. It would not make the boat stiffer. 'Stiffer' as it is used in yacht design refers to initial stability (i.e. form stability). Adding additional ballast will generally increase the inertia of the boat and as such will actually slow the motion of the boat in a seaway, in other words, within reasonable limits make the boat's motion more comfortable.

Respectfully,
Jeff

[Gary M]

To explain a little further and build on what Jeff said, the boat that I extended the keel on was a 4000# 26 footer. It had 1700 pounds of lead fin keel and 4.0 feet of draft. We added 200 pounds of lead which was a 5.5 inch extension.

The weight added was not significant but the improvement to initial stability was quite noticeable. When we first stepped on the boat amidships, right after launching, we noticed it did not heel nearly as much. This improved initial stability meant that when sailing upwind a puff would tend to heel the boat less and drive forward more.

When we did get heeled the additional 200 pounds down quite low helped us maintain a reasonable degree of heel and was noticeably faster.

It was very much worth the effort.

[svHyLyte]

Originally Posted by Jeff_H

At the risk of high-jacking this thread, and not wanting to nit-pick an otherwise useful post, I just wanted to comment on one aspect of this quote for a moment.

Assuming that the ballast is added low enough to do some good, it would add to the stability of the boat over all. It would not make the boat stiffer. 'Stiffer' as it is used in yacht design refers to initial stability (i.e. form stability). Adding additional ballast will generally increase the inertia of the boat and as such will actually slow the motion of the boat in a seaway, in other words, within reasonable limits make the boat's motion more comfortable.

Respectfully,
Jeff

While Jeff is correct that increasing moment of inertia will certainly result in a decrease in angular velocity for a periodic rotation--just as a spinning skater extending his/her arms will slow the rate of his/her spin so that his/her angular momentum remains constant, our own experience with adding 500# of lead shoe to the keel of a 26' Thunderbird had the effect of making her motion rolling down wind under spinnaker feel "jerkier" in the sense that with a fairly constant wave period, more heavily ballasted she would build up a roll and then seem to "snap" back more so than she did before we added the extra ballast. Beforehand, she would lay down to leeward and oscillate over a more narrow range than afterward, rarely returning to vertical. This phenomena has been observed in other fairly narrow beam, heavily ballasted yachts in comparison with their lesser ballasted sister ships. For example, it was a particular complaint of Eric Hiscock of Wanderer III--a 30' yacht with a nearly 9 ton displacement on a 26.5' LWL x 8.5' Beam--during his trans-Atlantic and trans-Pacific passages with his wife. (Asked what improvement he would make to his yacht if any after the trip he responded "Greater Beam and a Sawn Off Counter"). (I suspect the foregoing arises due to the fact that it is the beam of the yacht that adds the "damping" to an otherwise undamped pendulum.)

On the other hand in the (better) daze of sail, San Francisco Timber Schooners were known to hoist bags of coal to their mastheads (thereby increasing their transverse moments of inertia) to slow their "snappy" roll in beam seas once their cargo's (and their cargos' addition to the ships' moments of inertia) had been discharged, making "deadhead" return voyages to "the City" (and, in fact, Mill Valley) more endurable for the crew.

As for the term "stiff", in the general "lay" vernacular, the term is used to describe a yacht's ability to stand up to her canvas but, just in case anyone misunderstood my meaning, that was the intention. A discourse in the technical vernacular might be more "accurate" but less well understood, no?

And here Homer Nods...