[PUP] PPM

[John Marshall]

The Dashews differ with your perspective on stabilization, based on  
their experience with their FPB. In his latest articles, based on  
about 35,000 miles on that boat now, Steve talks a lot about the  
stabilization system, which he overbuilt in size compared to most  
boats, and considers it an essential.

And he keeps his boat heavy. As he burns fuel, he replaces the weight  
with water, and is even able to move that water to higher and lower  
tanks (even has a tank up in roof area of Great Room that he can pump  
to) to control roll rate. I don't think anyone else does this, but he  
still considers his stabilizers are crucial to their comfort.

Just because working fish trawlers don't always use them (and many do  
put down paravanes), doesn't mean they aren't needed on a cruising boat.

Any unstabilized boat will roll its guts out when the period of the  
waves approaches the intrinsic roll rate of the boat and the angle is  
right.

I will agree with comments that stabilizers have nothing to do with  
ultimate safety, only with crew comfort and reduced fatigue, which the  
Dashews put as the number two item on their design list, right after  
#1 -- ultimate safety through design.

John
On Nov 9, 2008, at 5:10 AM, hannu venermo wrote:

> Not at all, Georg.
>> The other thing that Hannu Venermo got wrong was that Idlewild was  
>> comfortable.
>>
>>
> Boats, and most complex systems, are a combination of factors.
> The comfortable hulls are *heavy*, ie fairly deep draft, as well as  
> slim
> and long, as I said in my post.
> Please do not mis-quote ....
> Idlewild, being lightly built in aluminium and made light for other
> reasons, valid for the intended purpose (portaging), is what made it
> roll easily.
> (I did misremember it being built in steel and not alu - I do  
> apologise
> for the un-intended error that however does not seem to me to be  
> material).
>
> Hull comfort is mostly a function of relative draught, only very far
> less a function of form, ie hull shape.
> The most comfortable hull in the world is a submarine.
> The next most comfortable one is a vlcc crude oil carrier when full -
> 90% of the hull is underwater.
>
> The unsailboat is according to the designers, the Dashews,
> internationally acknowledged as master designers and builders with 40
> years experience, and backed up by objective gravitometric sensor  
> data,
> far more comfortable than the best sailboats they built.
>
> A long slim hull, deep draft, ie. a very good passagemaker, is the  
> most
> comfortable hull form.
> A light hull, that sits mostly out of the water, is very "frisky" and
> rolls far, far more easily.
>
> Expending energy can somewhat mitigate rolling, be they
> flopper-stoppers, stabilisers, paravanes, gyroscopes or whatever.
> Their need is mostly a function of the relative displacement of the
> hull, ie how deep it sits in the water, and of course the weather
> conditions.
> Deep draft hulls do not, in general, necessarily need stabilisers.
>
> I am not saying someone should not fit them - if you have the money,
> stabilisers are certainly nice to have.
> However, a good passagemaker hull has little real need for them, and
> they are an additional comfort item. Their need should be based on
> personal preference.
>
> The real trawlers that do go out to sea all the time (re: see the  
> series
> "Most dangerous catch") do not have or use stabilisers or paravanes.
> They are also somewhat comfortable when empty and  very comfortable  
> when
> full (very heavy) - they are too full in the body, and inefficient, to
> be really good as the perfect passagemakers, as their main function is
> to carry large amounts of cargo ie load, and motor fuel vs hull
> efficiency has little effect on their operating costs. Of a 300k$ load
> of fish for a single trip, 20k$ might be spent on fuel, 5k$ on food !,
> and 10k$ on general repair & maintenance. Reducing the fuel by 50%, an
> impossible amount, would not affect appreciably their profits but  
> would
> very much affect their speed.
>
> The commercial trawlers need to catch large amounts of catch, move  
> very
> heavy loads, and sail in very heavy seas - all of these factors mean
> that their engines are 4-6 times larger than they would need to be  
> in an
> efficient passagemaker.
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