Sunday, June 1, 2014

Re: [Electric Boats] Electric Goliath ASD Tug vs. Goliath Diesel Tug

 



Myles, I guess I have to say that I have lumped all the guards together.  There is specific criteria required to actually gain thrust by a nozzle-like structure.  Here are a couple of good links to explain what I dare not.
 
 
 
 
 
By the time you have read and digested the contents of these, you will see that the relief between the twin hoops on the prop guard are counter-productive.  There may be a miniscule increase in thrust, but not nearly as much as Kort or Rice have achieved with the 19a profile or the NACA 4415 profile and the like.  Years ago, I got a book of NACA cross section designs and started reading the results from the NASA and I think JPL testing... There are an infinite number of curved surface designs out there, but to break the line of the surface at mid-point, tends to give a major loss in the Bernoulli principle.  That being said, I also know there is ongoing research in the (forgot the name) stepped or notched wing designs.
 
Bottom line is the most important, .... If it works for you forget the "egg-head engineering", and go with what works in the "real world".  I worked my way up the ranks from illiterate to engineering tech.  Just because you have letters after your name does not make you smart or that your testing invalid.  I applaud the effort and experience.  Example: I was told many times by many "educated" people, "there is no harvestable wind resource in South Western Idaho."  I became the first private wind farmer in Idaho, and after 3 years of me proving what I knew, the big boys came in, and populated a plethora of hilltops, ridgelines, and air channels, with the 1MW turbines making a fortune daily.
 
FWIW,
Dan 
 
----- Original Message -----
Sent: Sunday, June 01, 2014 1:43 PM
Subject: RE: [Electric Boats] Electric Goliath ASD Tug vs. Goliath Diesel Tug

 

"Thank you for the suggestion Matwete,  However, I have found that prop guards specifically do nothing for the thrust.  With a Kort nozzle or a Rice Nozzle, the thrust and speed of the boat are drastically improved.  They report as much as 30% over an open prop in a Bullard pull, and 17% out in open water. increases in thrust, speed, maneuverability, etc."

AeroDan-

I'd  be curious to hear what your findings as regard Prop Guard ® thrust specifically were.  Or are you loosely lumping all "prop guards" from all vendors into this comment?  I was specifically referring to this manufacturer. www.propguard.net

Going to their website, their "Test Results" indicate significant gains in thrust (13-100%) and speed at RPM.

While that could be all sales pitch (doubtful), I personally have been very happy with my 9-10 years' use of the 14" PropGuard on my electric boat "The Reach Of Tide".  It was like night and day comparing the difference between my outboard without and with this installed.  I would rather invest money in a larger, shallower pitch prop at this point than keep the current prop and take a free Kort prop nozzle.  I just can't see the gains being much more than I've seen and it wouldn't look as good.

YMMV-

-Myles Twete, Portland, Or.

Moderator, ElectricBoats Forum

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Respectfully,
Dan Hennis
;-)>

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