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Old 10-12-2014, 15:57   #61
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Re: Prop Rope Cutter

One method that can help is to run a piece of 2-300lb test line from 2 SS screws-one in the back of your keel,close to bottom & the other in the bottom of rudder skeg,or the pivot point of rudder,if no skeg.It helps to keep floating rope from rising to prop level as boat passes over. This line may be sacrificed @ next lift out,by aft strap,but it is cheaply replaced before re-launch.
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Old 10-12-2014, 17:21   #62
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Re: Prop Rope Cutter

Kort Nozzle, used on almost all the Diver Propulsion Vehicles, Believe it was actually designed with the use of a Cray supercomputer way back in the day, but maybe that's Urban legend.
Anyway look at prop guards used on life boats and some boats like at Wakulla springs for Manatee guards for ideas.
I think just have dive gear and deal with it when it happens.
I ran over many of them at night in the Florida bay, only way I knew I ran over them is when they popped up behind us and you could see them in the stern light.
IP has what they call a Lobster strap between the keel and the bottom of the rudder, seems to work.
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Old 10-12-2014, 17:50   #63
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Re: Prop Rope Cutter

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Originally Posted by a64pilot View Post
Kort Nozzle, used on almost all the Diver Propulsion Vehicles, Believe it was actually designed with the use of a Cray supercomputer way back in the day, but maybe that's Urban legend.
Anyway look at prop guards used on life boats and some boats like at Wakulla springs for Manatee guards for ideas.
I think just have dive gear and deal with it when it happens.
I ran over many of them at night in the Florida bay, only way I knew I ran over them is when they popped up behind us and you could see them in the stern light.
IP has what they call a Lobster strap between the keel and the bottom of the rudder, seems to work.
Hmmm…me thinks that "supercomputer" would be urban legend if one is speaking of the original designs and concept.

Somewhere I saw that the patent was in 1934. So, older than Cray technology, probably made using slide rules and human brain power, the original super computer.

Here is a clip from wikipedia:
"Luigi Stipa[1] and later Ludwig Kort (1934)[2] demonstrated that an increase in propulsive efficiency could be achieved by surrounding the propeller with a foil-shaped shroud in the case of heavily loaded propellers.

How it works: The Physics
In a Kort nozzle, the inflow velocity is increased, reducing pressure. This lowers thrust and torque of the propeller. At the same time, a circulation occurs, resulting in an inward aimed force, that has a forward component. The duct therefore has a positive thrust. This is normally larger than the thrust reduction of the propeller. The small clearance between the propeller and duct reduces tip vortex, increasing efficiency.

As drag increases with increasing speed, eventually this will become larger than the added thrust. Vessels that normally operate above this speed are therefore normally not fitted with ducts. When towing, tugboats sail with low speed and heavily loaded propellers, and are often fitted with ducts. Bollard pull can increase up to 30% with ducts."


What is COOL about those Kort's is that they can increase the pull (Bollard Pull) by up to 30% and that is worth some money, along with better fuel economy (making them smart investments on some boats)..
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Old 10-12-2014, 23:58   #64
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Re: Prop Rope Cutter

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Originally Posted by a64pilot View Post
IP has what they call a Lobster strap between the keel and the bottom of the rudder, seems to work.
Called a "weed shoe" in the rest of the world.
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Old 11-12-2014, 17:03   #65
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Re: Prop Rope Cutter

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We think alike!

I had thought of a prop cowl, shroud, duct, or nozzle for the same reasons.

But, after watching the way the net, lines, ropes, and wires were sucked into that prop (see the video I linked earlier in this discussion), I think the prop VORTEX is what pulls that line into the shaft and wraps it prior to entanglement of the blades. In other words, it appears to me that the shroud/duct/cowl/nozzle may NOT prevent the vortex from capturing the line and wrapping the line or material around the prop shaft as it turns. It may help, but I think a line cutter (like Spurs) installed would be more likely to prevent the snag and prop stoppage.

Also, the RICE tube or nozzle (like a Kort Tube) was tested to be the most efficient for reducing fuel consumed and for increasing the thrust. Pretty cool stuff. Rice is Nice.

Here is a Kort Tube (or Kort Nozzle) for those like me who like to see what we are discussing:
.

I doubt the various ducted props will avoid pullin lines in also. Here is a tutorial on the various types and their advantages. The shroud reduces the trailing vortex off the blade tips & so increases the efficiency at low speed where the duct itself adds little drag. Much like the winglets on aircraft and as a bow thruster does by default.

http://www.ccfi.ca/pdf/Vessel/presen...20shafting.pdf
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Old 11-12-2014, 17:44   #66
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Re: Prop Rope Cutter

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Originally Posted by Neeltje View Post
Who would have thought there were that many crabs to trap in the first place?
A dwindling supply of crabs and lobster = more traps to catch the dwindling supply of crabs and lobster.
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Old 27-12-2014, 00:57   #67
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Re: Prop Rope Cutter

I'm sorry guys , I simply can not believe what I'm reading here.
Many just think there is no need for a rope cutter on a sailing boat , oh boy , how wrong can you be.
However , there's some thruth in these statements , either you install a GOOD cutter or you don't install one at all !
Mine is a disaster-type and after experiencing the same ordeal last summer - this time with no devasting consequences - as 4 years ago , I will get my cutter off asap.
Read this story ( link down) and please try to neglect the grammatical errorts as english is not my home language , but I'm working on it though.
Anyway , when sailing the Med. , occasionally , no , usally close to the shore and often during the night , you/we run a great danger of entanglement .
Even at serious depths , + 100 meter = > >300 feet , you're sailing through a minefield.

Have fun.
P bracket repair

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