I am sorry Skip but you did not mention nor emphasis one of the most important properties of a marine prop and that is where water cooling plays a role and that is "PITCH" and the" Amount of it in relation to the Diameter".
More pitch ,more turgue required,the drive works harder and generates more heat.
Large diameter moderate to high pitched props will use a lot of power compared to the same size diameter prop with a small amount of pitch.True or not true?
Put no pitch on the same prop and there is virtually no torque required except to turn the shaft and the prop is now a disk and no thrust is produced.
There are grafts and charts to demonstrate those facts by Marine Engineers and it is Directly related to our hobby weather we like it or not.
Many vessels have even variable pitch props so that the torque to motor and fuel cusumption and heat dissipation can be dealt with,kind of like having a second gear box or more gears like trucks have to get up hills with heavy loads,Tugs and Ocean going Tugs have this capability and some cargo ships and some military vessels.
I bet they all have water cooling,but that's just my observation of what Marine Engineers do.
"Not so! The larger the prop diameter is, the slower it will turn for a given amount of thrust. But few people realize that the relationship between power and prop speed is not linear. To double the speed of a prop requires something on the order of 4 or 5 times more power.End Quote.
Yes depending on the pitch.
No mention of pitch nor the amount of it.
I do my home work and NOT just in the realm of RC Subs but as the marine engineers have , gee discovered over a long time of mathematical and practice real word research,believe me if they could get away without the added expense ,complexity of adding water cooling to the vessel than they would,but not so.
Absolutely gear ,or belt ratios play a huge rule and is of a primary concern and I don't build subs with no gear reduction unless its going to be a torpedo or have Jet Drive,short fast run time ,and even the full sized torpedo has some form of water cooling.
Sorry for not having the full understanding of just what it takes.
More gear reduction the torque is multiplied from the motor and the motor works less ,we all agree on that.
However ,no matter how well your drive to prop to hull design is "heat build up is a fact of life" with any powered vessel except a sail boat .
Its not a symptom but a fact of physics,in subs one of the most "effective" cures is water cooling,air cooling would be nice if casings where open to the air.
If I had too much load on the motor than why does the ESC not even get warm after a long run? Its not water cooled and its ratted for 9.6 volts!
On many ESC's water cooling is available where a "Hotter" set up is required for high speed or just to keep another set up cooler.
Most RC subs have low to moderate pitched props as do the full scale subs.Now put a gas high speed boat prop on say a Robbe Sea Wolf ,geared 3.5 :1 water cool it and the running distance and time increases tremendously because the motor has to work much less to obtain more thrust,the main reason why "PITCH" of the prop and more distance is covered by each revolution of a small diamiter prop.And man what a power curve,one has to have a ESC with a low start rate but not high amp rate.
Its a very interesting combination of factors that make up a submarines RC drive or full size vessels and I am no expert at it but I know from experience from test tank and pond runs ,countless motor drive set ups which works best on a particular sub,and they all have water cooling wheather it was "absolutely necessary or not" that point is not at issue here but to get longer run times ,a cool motor cooler and a happy one plus increased reliability ,I concluded that hay if the full size ones do it WHY NOT I.
With the resent discovery of mine of being able to use perhaps the most important tool available to any Captain in this hobby till "now"since the Rc Radio was invented. Inexpensive Telemetry that ant one can use.We , or a Marine engineer can see in real time the difference between water cooling a sub and not ,it all comes out in black and well green for that matter,no "guessing" no matter how experienced that observation may be that this fellows set up is too hot or there is an overload condition,even the props speed is measured and displayed.
Helix flyers do it,Aircraft flyers,do it,ser face boats do it,why should we not?
I don't want to sound corny but YES WE CAN!
Believe me if I see that a set up is not doing well ,I take it right out and start over,been there done that it saves money to right,but R and R is costly.lul.
Now you can build in that extra amount of safety,reliability and piece of mind into your subs or not ,I am not here to preach you all from a thrown ,pulpit or what ever, its just a simple application to solve a fact that is with all subs.From one Captain to another,its done that way to in the real world
Skip I have always loved and admired your subs they run flawlessly and are gorgeous works of art. I'm sure low in maintenance as are mine that's why I love to build them so much and improve on older designs and if I don't get the expected results I start all over again till it does from components that are made well but don't cost a lot.
I believe your WWII subs could benefit in having telemetry for many reasons as mentioned.Just an opinion ok.
Also the reason your subs run well without water cooling is because you did match the prop size,pitch,diamiter and then the inherent pointed bow "all add up" to a very efecient desighne and you dont get over working motors ect.But they get warmer under water due to increased drag.But you could make them even happier.Its cheaper having to replace that good old Pitman motor.
I have as I statted before never had to replace a cheap can motor or costlier drill motor yet do to exsesive heat.I'm sure that is true in your WWII subs.
The added minor complexity is good as long as it has more benefits than negatives and not all subs can be able to use water cooling for instance due to size constraints.
But even the Japanese Aqua racers have water cooled drives ,just to show how small a space water cooling can fit into a design.
I prefffer aluminum cooling tubes because it's lighter ,easer to bend and much cheaper than copper and copper corrodes more ,stainless is good to but the cost is high.But that's my findings.
Sure one could find ways to improve my desighne,if needed but would it be cost effective?
The coolant flow is very good since there is about 3 feet of tubbing serface area in direct contact with water all the way around the tubes and the pump dose not run at full motor spped since full power is not necessary at normal cruise and is just about never used on my subs as the drive to pitch to hull desighn is good.just the lower end of the stick travel is used about half or less.
We can debate all the ramifications and micro analize till the cows come home ,but I like to keep it inexpensive and yes simple.
Any one can build it, it's not my magic only.
And more constructive input or critisim is more than welcome and encourraged thats the spirit of this and other Forums.
Dave Amur Sub Yard