T&T: Active stabilizers

[LRZeitlin@aol.com]

In a message dated 10/7/06 12:01:20 AM, Dave writes:


> I just worked on a project where the stabilizer salesman and the dealer 
> were
> recommending a set of stabilizers to fit the space available not the needs
> of the boat and conditions it will encounter. I suspect the "data base" that
> Milt refers to is still held at the manufacturer's level and the sales
> people ignore it. Moving up a level or two in size can have a significant
> impact on your wallet. Better to have the granite counter tops than a well
> stabilized boat in all conditions? I don't think so....ah boats always
> compromises ;-)
> 
At last year's Norwalk Boat Show I had a long and fruitful discussion with 
one of the chief engineers of Naiad. Their factory is in Connecticut and many of 
the staff were in attendance. The main topic of discussion was "What is the 
smallest (and slowest) boat on which active stabilizers are effective?" This 
was a hot topic on the Willard list at the time.

The general consensus, after a few beers, was that a 30 ft. displacement boat 
is just too small and slow for practical stabilizers to be effective. The 
stabilizing force increases with the square of the boat speed and either very 
large fins or speeds above 7 knots would be required. The mechanism for the large 
fins would take up too much space and cruising at 7 knots or above is 
uneconomical. I know some of you have crammed active systems into 30' boats. Don't 
flame me.

A 40 ft. boat is at the margin for active stabilizers, according to Naiad. 
They work, but large deflections are required for the size fins usually fitted. 
Of course they will be happy to sell active systems to anyone who has the 
bucks. I mentioned the several Nordhavn Transatlantic Rally failures and they 
suggested that continuous operation for long periods of time probably contributed 
to the troubles. Most recreational boat stabilizers operate for only a couple 
of hundred hours per season and rarely more than 24 hours at a time. 

If a 40 ft. boat has a roll period of 4 to 5 seconds, typical for boats of 
this size, then the stabilizers will operate nearly 20,000 cycles per 24 hour 
day. Multiply that by the number of days a transatlantic voyage takes and you 
have a pretty good idea while mechanical systems fail.

I'm all for active stabilization but the engineering limits of the system 
have to be taken into account. Heavier, larger, continuous duty components have 
to be specified for ocean crossing use. Most of us would balk at the cost, 
space, and power required.

Paravanes may be less elegant but might be better for long periods at sea. 

I favor steadying sails myself - but then I have a motorsailer.

Larry Z