I am trying to decide on props for my new HMS Beyham (Queen Elizabeth) class. I will be going with 1.75” props. I have used swampworks/strike props in the past and have been happy with them, other than the tendency to throw a blade . I have been reading the trend toward the PropShop Korst props. I was hoping that some of you who use them could elaborate on the advantages the Korst props give. Thanks Keith
Kort props are approximately constant pitch, the old style flat blade strikemodel / battlersconnection props increase in pitch from the inner part of the blade to the outside of the blade due to the flat blade geometry. This means kort props effectively use more of each blade to generate thrust, and the thrust is more evenly distributed across the projected area of the prop. This helps with turning because the velocity of the propwash is more evenly distributed with a kort prop. A flat blade prop moves the water closer to the periphery of the prop faster, meaning a lot of the high velocity propwash (and turning power) misses the rudder at moderate rudder deflections. Net result is ships with Kort props tend to complete a turn faster without losing as much speed, which gives Kort prop equipped ships a tactical advantage over ships with the easier to manufacture and cheaper flat blade props. It also seems to help acceleration from a standstill but I haven't figured out the mechanism for that, which likely has something to do with slippage. On Kort props the blades are also thicker and the whole thing is cast as one piece, giving them a significant durability advantage. Ron Hunt
Kort props also have airfoiled (waterfoiled?) blades that build more lift (thrust) in one direction. While in forward the acceleration and thrust can be amazing, the thrust when reversed can be pretty dismal 40 - 50% less. MWCI's rules effectively limit reverse rpm to the same rpm needed to make speed. This means the reverse on a ship can be pretty bad when using Korts mounted properly. A work around some people have done is to mount the korts on backwards to spin up the rpm to make speed, which gives a strong reverse acceleration at the same rpm. Korts come in metric sizes. I recommend the 1.7" for the QE. That prop size is bored and threaded for 4mm threads which can easily be cut into a 1.8" rod if used for a prop shaft.
When I choose them for my Bismarck it was because they are the LEAST directional of the cast props that PropShop makes and I wanted similar fwd/rev performance in a cast prop. (I actually emailed PropShop, explained the application to them and asked for a recommendation, they were the ones to suggest the Korts. And they are significantly less directional than the other PropShop props I have.) What Mike said is still true they are still fairly directional but not nearly as much as a lot of other cast props. Cast props are worth the hassle just since you dont have to replace them all the time. (Plus you can set them up for such sillyness as "super reverse" since when they (mwci) tried to fix the rules they left a giant loophole) Also prop shop will bore/thread the props however you want if you ask them too(free of charge), I get mine bored to either 1/8" or 5/32" and then braze the prop to the shaft.
:blink: If I were a conspiracy theorist......... Website temporarily unavailable, we will be back soon! Prop Shop Swan Precision Castings and Engineering Ltd Swan Close Road Banbury, Oxon OX16 5AL
I understand the concept of SUPER reverse, but have not seen it on a ship yet. I will talk to the members of our club about this at our next battle 9/21. I would prefer not to see this in our local boats as it run in the face of KISS. I will wait to see where the club stands on this before I make a decision here. Keith
Can anyone tell me what I should be asking for in the way of a hub. I am accustomed to a 1/8” shaft with a set screw. Do I need to also order a threaded shaft to use these cast propellers? Keith
When the order is made, you can request the company to bore the hub and/or thread it in a specific size. If keeping with the 1/8" shafts, ask for the props to be bored at 1/8" with no threads.
I prefer 5mm myself because it matches the readily available gears, but 5mm shafting is difficult to find. Ron Hunt
On my Vanguard, I think I used 5mm threaded bores on 3/16" shafts that were cut with 5mm threads. Slightly sloppy fit but worked. On the Barham, used 4mm threaded bores on 3/16" shafts cut with 4mm threads. Worked out very well though the ends of the 3/16" rod had to be turned down a little to cut the threads.
My new Kort Props next to a set of the Strike props. I have always use Swampworks props in the past. They work good, but tend to throw blades. I have been told that Stephen does a better job soldering/braising. I wanted to try some cast props for the Barham. I have a new set of Strike props for the Washington for comparison. I will need to cut the ends of the hubs off both sets.
Put the Korts on backwards. Have and ESC and be prepared to reduce the endpoint in reverse. 1.7" are too big for a QE despite what some say. for max turning you want 1.5", but you would need to remount your drive shafts to be correct. Have gear drive with a ~13k rpm motor. Also despite what some would say the kort props are very directional.
The Korts are very directional. In my estimate, as much as 50% less thrust in one direction. If putting them on backwards, be ready to spin them up rpm wise.
After building the rudders I can see where 1.5 might be better. You are a couple of months late in the advise .
