Dave Culp and Water Ballast in Multihulls by Joseph Oster

Strings

Water ballast is never optimal in multihull design.

As I recall, that discussion concluded that; when beam is constrained,
water ballast *can* be an advantage. 90' beam on a 90' LOA boat sounds
pretty "unlimited," but it is in fact constrained.

Water ballast isn't needed until there's enough heeling moment that the lee hull or foil is supporting the whole craft.
After that point, one can use down-force on the windward hydrofoil or an equivalent amount of water ballast in the
windward hull. If you elect to use water ballast, the lift on the lee hydrofoil has to increase by an equal amount,
which will incur a drag penalty. If you elect to use hydrodynamic down-force, the lee hydrofoil still has to oppose
the down-force and incur the same drag penalty. But in addition, the windward hydrofoil has its own drag penalty.

-------- Original Message --------
Subject: Water Ballast
Date: Mon, 18 Mar 1996 12:48:44 +0200
From: johns@bilpin.co.uk (John Shuttleworth)
Reply-To: johns@bilpin.co.uk (John Shuttleworth)
To: multihulls@ronin.com

> Clearly monohulls have used the concept of ballast with great
> effectiveness, yet every expert concludes that a multihull is
> always better without ballast...  There is a mystery here for
> me.  Is ballast only effective (as in monohulls) when it is more
> than 40% of total displacement?  What about that area where the
> ballast is only 10..20% of total weight and on a long multihull
> lever arm?  Especially on the Pacific proa where such a shift
> brings righting moment to that of a heavier catamaran?

> Thanks in advance, Joseph Oster

I haven't actually done the calculations for a Mono, but logic tells me
that it power could be increased if the rig of a Mono was more upright.
Adding ballast - crew (as in the  NZ America's cup attempt in '88) or water
clearly works. In a Multi particularly a wide one with large volume
ourtiggers, the improvement in L/D by changing the heel angle from say 10
degrees to 5 degrees by adding weight, does not pay off. In a Cat the heel
angles are less, and the beam is less so water balast is even less
worthwhile here. The pacific proa is a different case. Water ballsat would
definitely reduce speed unless the limit of stability had been reached.
Water would only add to the displacement and hold the windward hull down
into the water - increassing wetted surface area. Once the windward hull is
flying, then water ballast would improve speed as the wind increased -
provided it did not put the hull back into the water.

Of course all this discussion is about pure speed and has nothing to do
with how well you can sleep on a cruising boat at night!!!
If I want to sleep well I choose wide beam and nice big outriggers (150% of
total Displacement minimum), and no water ballast, and put in a reef before
retiring. I have done it - in fact I once reduced to storm jib and two
reefs just to get a sound nights sleep after bashing to windward for a
week.

John Shuttleworth

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Fact #2: I'm not at all sure that functional water ballast exists aboard any
multihull *not* designed and built by Russ Brown. Try this: Google "water
ballast multihull."

Next step is to add water ballast to stern, so as to keep main hull stern down when required,
and a stern ballast tank is standard on the F-85SR and F-32SR, with float sterns tanks optional.
This weight again can be got rid of for the 90% of the time when it is not required.

Both carbon-fiber giants feature engines to run hydraulic
systems that trim their sails and move water ballast from one
hull to another, a first in America’s Cup history.

Firstly, Alinghi carries water ballast to provide original righting moment as required.

Competitors will be able to use water ballast in the coming 33rd America’s Cup commencing in
Valencia on Monday, provided that the amount used to benefit performance is also in position
when the boat is measured. 

This verdict of the International Jury was made tonight following a hearing in Valencia.
'It puts the onus on the measurer to guarantee that the amount and location of ballast
aboard for measurement is solely to enhance performance, not circumvent the waterline
requirements of the Deed of Gift,' said GGYC spokesman Tom Ehman.

The phrase "speaks with a forked tongue" means to deliberately say one thing and mean another
or, to be hypocritical, or act in a duplicitous manner.  In the longstanding tradition of many
Native American tribes, "speaking with a forked tongue" has meant lying, and a person was no
longer considered worthy of trust, once he had been shown to "speak with a forked tongue".

Harry is a particularly extreme and un-seamanlike Pac proa, IMO, but he's a Pac proa, nevertheless
(OK, that should guarantee a slag from *both* Joe and from Rob. My work is done... 

I'll argue long and hard that a "traditional modern" Pac proa (Oster) optimizes the construction,
sailing and seakeeping qualities a cruising or long-distance racer wants in a boat, at lowest
reasonable cost and highest reasonable performance level, but Rob will disagree, and his points
are as valid as mine or Joe's.

Dave Culp and Water Ballast in Multihulls by Joseph Oster

Eat crow Dave

Conclusion

Addendum