T&T: Old and new ideas to assist hull efficiency

[Arild Jensen]

Rich Gano wrote:
> A number of years ago, a shipyard owner acquaintance here in Panama City
> took me for a ride in a heavy metal displacement mullet net boat he had
> converted.  It was diesel-powered and maybe 30 feet or so in length.  He had
> added a hollow fixed ring (looks like a kort nozzle) around the single
> propeller.  Holes were drilled into the propeller side of this thing, and an
> air passage allowed for free communication to a stand pip running vertically
> from the keel to several feet above the deck.  He said the critical
> measurement was where the vertical plane of the holes in the ring was in
> relation to the propeller blade tips.  He had done something similar with an
> outboard motor.
>   
REPLY
The Canadian Navy had a similar situation like that at the Halifax 
base.  Called the BrasD'or   It was a hydrofoil. Worked too!  
But  due to  politics and  a shortage of funding. ( translated - cheap 
to build a prototype) the project was shelved.  When I was  sent to 
Halifax  it was already up on the synchro-lift drydock and I don't 
believe it ever left until the day it was scrapped.
Sadly it was an idea before its time. A decade later the USN  conducted 
experiments as well.  Had good results from what I recall.
Meantime  wave piercing power cats emerged on the scene and it now looks 
like this is likely going to be the preferred new development.
The Greeks and Romans had battering rams on their  rowed triremes and 
galleys.  Little did they realize  the ram was actually a very good 
concept  even nwhen not used for ramming.   Today we call that a bulbous 
bow.  And it does work.
The naval architect with whom I worked has a son who fabricated 
propeller nozzles.  Very successful  business and he can't keep up with 
orders. 
Unfortunately  prop rings or Kort nozzles  are most effective  in a 
narrow speed range.  This works quite well for tugs  and commercial 
boats running at almost the same speed  most of their working life.  It 
is questionable if it would be cost effective to apply to recreational 
trawler.  It would  be good on a commercial trawler which works more 
like a tug  dragging a trawl.

During the  early part of the last century  speed on the water saw some 
real innovation. like stepped hulls  and these ideas were successfully 
embodied in the "express commuter"  boats  built pre-WW2   Did anyone 
read the series on  search for speed by Donald Blount  published in 
Professional Boat Builder magazine?
The trouble is ;  until someone  spends the money and takes the risk, 
all of these innovations sounded like hare brained schemes.  They all 
defied  the conventional logic.
So how do you figure out which ideas are good and which ones are snake oil?
  Now that  Bill Gates is retired,  maybe  he might get interested  so 
he and his fellow Microsoft billionaire Paul Allen can go play boating   
with some new concepts.  Judging by Paul Allen's  yacht  I would think a 
prototype  experimental boat  wouldn't  put a dent in his annual boat 
budget. 
When his yacht was docked in Vancouver I saw the crew unload  the 
tender.  It was  what we mere mortals would call a 34 foot  luxury  
boat  in its own right. And that was only one of them.   Oh well!

The search for efficiency on the water continues.

Cheers
Arild