Rick Willoughby | 4 Aug 00:24

Efficiency & Marketability

Larry
<
I don't imagine myself, with this ramble, to be telling most members
of this group anything they don't know, ...only to be speaking out
for more consistent balance in appraisal,... for recognition and
keeping-in-mind of the fact that efficiency, as measured by
speed-for-effort, is simply one-of, not THE consideration when
judging a proposed design, ...unless the activity-scope is narrowed
to racing.
 >

I do not disagree with what you have to say.  I have both cat and  
mono.  Horses for courses.

Not sure if you read Pete's web site.  It is directed at efficiency  
in the narrower sense of speed for power.

The comment on the Rocat is based on posts from Christopher Laughton  
some time ago.  I believe it is not widely known that catamarans  
suffer a 40% power disadvantage. I also have read a race report from  
a Rocat owner that indicated he was not initially aware he would be  
giving away so much to a monohull.  His expectations were not met.

All Hobie do is prove they have high bollard pull and they have used  
this as a real selling point.  Most owners are recreational users  
just out for time on the water.  On the other hand I have seen Hobie  
owners bitterly disappointed when they have been racing against  
conventional paddled canoes.

My wife just loved Mike Lampi's Nauticraft.  She has never tried one  
(Continue reading)

Larry Smith | 4 Aug 04:54
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Re: Efficiency & Marketability

>Larry
>
>[[Not sure if you read Pete's web site.  It is directed at 
>efficiency in the narrower sense of speed for power.]]

No, didn't visit the site. Was aware, though, as I noted, that speed 
did seem to be emphasized in the brief posted description of his 
proposal. If the cat's stability is not a high-priority item in his 
concept, then perhaps he should go with a mono,...but that wheel, and 
most of the stabilizing options, has been invented many times. Maybe 
more time spent in study would be beneficial before stepping out on 
such a well-worn path.

Re. progress still-to-be-made, IMO, your own experiments represent 
some of the most innovative and informative recent efforts.

>[[The comment on the Rocat is based on posts from Christopher 
>Laughton some time ago.  I believe it is not widely known that 
>catamarans suffer a 40% power disadvantage.]]

This surprises me, if by widely known, we mean to serious 
designer/builders.I would expect such people would have a grasp of 
the basic geometric differences in surface area, the wave-making 
issues with regard to hull length/beam, and that they most probably, 
in the research I imagine them to have done, would have tapped into 
the multihull work of people like Leo Lasauskas, re. hull 
interference, etc.

I quite possibly am making the common mistake of expecting others to 
use the approach I would take, and forgetting that cats are skinned 
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hpv | 4 Aug 16:47

RE: Efficiency & Marketability

> >   [[ On the other hand I was not interested in trying the 
> Nauticraft 
> >as I had the use of the Cadence.  I will put up with the twitchiness 
> >for the ability to hit 10+mph.]]
> 
> An illustration of the difference in where we draw our lines. I have 
> tried the  Cadence and think it is an exceptionally nice performance 
> boat, but prefer something more stable for my own more-relaxed water 
> pursuits.

You should try a Cadence with outriggers, Larry.

The amount of flotation is adequate to let people stand in the cockpit
and access the hatches without worry, too.

The outriggers can be positioned so they are both several inches above
the water, allowing you that much tilt (at the end of 3 foot akas) for
leaning turns, allowing small waves to pass without impeding the boat,
etc.

It is possible to unlock the akas while under way so that if you want
to have them in the down position, where they brush the surface. In
this mode there is no twitchiness regardless of how little sense of
balance you might have.

When I'm going to be alone out on the Sound for several hours and
there is a chance the conditions will change for the worse I typically
have them deployed in the raised "high speed/training wheel" mode.

When I'm doing demos for newbies I have them in the "low/more stable"
(Continue reading)

Larry Smith | 4 Aug 18:11
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RE: Efficiency & Marketability

Sounds very good Michael!!

Making a great boat even better.:-)

Best wishes,

Larry

>[[You should try a Cadence with outriggers, Larry.
>
>The amount of flotation is adequate to let people stand in the cockpit
>and access the hatches without worry, too.
>
>The outriggers can be positioned so they are both several inches above
>the water, allowing you that much tilt (at the end of 3 foot akas) for
>leaning turns, allowing small waves to pass without impeding the boat,
>etc.
>
>It is possible to unlock the akas while under way so that if you want
>to have them in the down position, where they brush the surface. In
>this mode there is no twitchiness regardless of how little sense of
>balance you might have.
>
>When I'm going to be alone out on the Sound for several hours and
>there is a chance the conditions will change for the worse I typically
>have them deployed in the raised "high speed/training wheel" mode.
>
>When I'm doing demos for newbies I have them in the "low/more stable"
>mode.
>
(Continue reading)

Rick Willoughby | 4 Aug 06:39

Re: Efficiency & Marketability

Larry
One of the current problems with this site is that we have lost  
history and are continuing to do so.  A few years ago I would spend  
hours perusing the archives to take in the well trodden ground.  We  
seem to have lost that ability.  That is partly why I have suggested  
the Boatdesign forum.  There are now a few participating on the pedal  
boat thread.

I have kept my own HPV posts and you would need to go back to  
November 2006 to see the exchange on cats I am referring to.  Sadly I  
do not know whether the archives have been lost.  It means people  
coming to this site fresh have no history to scan.

I believe you give more credit to boat designers than they deserve if  
you believe most understand the fundamental advantage of displacement  
monohull over displacement catamarans.  At the limit though a sailing  
catamaran is a skinny mono so it will perform exceptionally well at  
that point.  Certainly the average boat buyer would not be aware of it.

Rick Willoughby

Larry Smith | 4 Aug 09:51
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Re: Efficiency & Marketability

>[[I have kept my own HPV posts and you would need to go back to 
>November 2006 to see the exchange on cats I am referring to.]]

 From 11/13/06. 12:10 PM +1100:
[[So if you have a length constraint and want good stability then it is 
hard to go past a cat.   The 15% extra drag translates to about a 5% 
reduction in speed for the same power input.]]

I had only a poor recollection of this item from your older 
discussion, Rick, but it helped form  my foundational understanding 
that stability could be had, if desired, at a speed-cost that was 
sufficiently small not-to-bother someone whose interest was not 
racing. ( I'm sure I could have worded that more succinctly. ;-)

Thanks for the reminder of where-to-look, in my files.

Your 5% speed-reduction figure is a small price to pay, IMO for the 
peace of mind offered by the "good stability". Speed record seekers 
will of course feel differently, but for my own recreational uses, 
9.5mph with more stability beats 10mph with considerably less. In any 
case, at 68, achieving either "max" would be an extremely short-lived 
anaerobic exercise that no longer fits this senior's  definition of 
re-creating on the water.

I have not re-read all the pertinent exchanges, but a cursory look 
suggests that your comments about which designers know what are well 
founded.

It is a shame that all the old posts are not available, both to 
newcomers, and to forgetful old-timers.
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Larry Smith | 4 Aug 18:01
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Mono vs cat (both optimized)chart?

 From 11/13/06. 12:10 PM +1100:
[[Of course the whole situation changes once you consider hulls of 
different form.  For example if you apply the same length constraint 
to both the mono and the cat the penalty for the cat may not be as 
great.  I did an example for Cory based on a length limit of 4.3m 
optimised for 10kph and the power required for the cat was only 15% 
higher than a 4.3m long mono.

So if you have a length constraint and want good stability then it is 
hard to go past a cat.   The 15% extra drag translates to about a 5%
reduction in speed for the same power input.]]

 From 8/03/08. 10:53 AM -0700:
[[You may also be interested to know that a minimum drag catamaran 
requires 39% more power than a minimum drag monohull for the same 
displacement. ]]

Hi Rick,

If I had been more awake, I might have thought to ask this last night:

Looking at the two different % penalty for two equal hulls compared 
with one with the same total displacement, in the two posts quoted 
above, i.e. 15% vs 39/40%, am I correct in understanding that the 
difference is the result of the constrained vs. un-constrained length?

And given that practicality more often than not does induce a 
constraint, can you comment on a general rule-of-thumb as to the 
degree of change in the %penalty as the constraint lengthens?

(Continue reading)

Alex RIchards | 4 Aug 18:25
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Re: Mono vs cat (both optimized)chart?

Whilst on the whole Cat vs Mono debate, one thing springs to mind. Won't a
cat typically weigh more because of the spars, extra hull material etc? This
would surely mean a cat will have a higher displacement than a monohull, and
so we're back to ineffeciencies again.

Also, whilst a cat would at first appear to offer great stability compared
to a monohull, I'm not so sure how this translates in terms of feel. I've
had the pleasure of sitting on a becalmed Hobie Cat when hit by a wake and
it wasn't a hugely comforting experience. Ok the oscillating mast is
something we don't have on an HPB, but being further above the water than
when inside a monohull did leave me feeling a tad queesy.

So I'm wondering, from a pleasure/recreational boat whether a mono hull with
"training wheel" amas wouldn't actually have a better comfort/feel factor.

And that's before we move onto aerodynamics.

Larry Smith | 4 Aug 20:19
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Re: Mono vs cat (both optimized)chart?

>[[Whilst on the whole Cat vs Mono debate, one thing springs to mind. Won't a
>cat typically weigh more because of the spars, extra hull material etc? This
>would surely mean a cat will have a higher displacement than a monohull, and
>so we're back to ineffeciencies again.]]

Part of the acknowledged trade-off for stability.

>
>Also, whilst a cat would at first appear to offer great stability compared
>to a monohull, I'm not so sure how this translates in terms of feel. I've
>had the pleasure of sitting on a becalmed Hobie Cat when hit by a wake and
>it wasn't a hugely comforting experience. Ok the oscillating mast is
>something we don't have on an HPB, but being further above the water than
>when inside a monohull did leave me feeling a tad queesy.
>
>So I'm wondering, from a pleasure/recreational boat whether a mono hull with
>"training wheel" amas wouldn't actually have a better comfort/feel factor.

The greater stability of an outrigger or cat when compared to a 
mono-hull is certainly much more than an appearance. To translate in 
"terms of feel", try to sit on a 10 inch wide racing shell, and then 
on an equal displacement cat with, say, a 5 foot beam. At equal seat 
heights (which will need to be somewhat high in both, compared to a 
kayak) You will have just about time enough to register the "feel" of 
the rolling shell before you hit the water,...whereas on the cat, you 
can ponder the (nice dry) "feel" at leisure.

Re. wake scares: Any craft of wide-form based stability, with 
sufficient roll-countering force(buoyancy), will follow the surface 
of the water. If a large wave approaches from abeam, the boat will be 
(Continue reading)

hpv | 4 Aug 16:50

RE: Re: Efficiency & Marketability

> Larry
> One of the current problems with this site is that we have lost  
> history and are continuing to do so.  A few years ago I would spend  
> hours perusing the archives to take in the well trodden ground.  We  
> seem to have lost that ability.  That is partly why I have suggested  
> the Boatdesign forum.  There are now a few participating on the pedal  
> boat thread.
> 
> I have kept my own HPV posts and you would need to go back to  
> November 2006 to see the exchange on cats I am referring to.  Sadly I  
> do not know whether the archives have been lost.  It means people  
> coming to this site fresh have no history to scan.

I've retained what I thought were the most useful posts from the past
"n" years. If there is any way to post these in a searchable mode on
the web I'd be happy to do so.

Michael Lampi


Gmane