Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 8:18:48 GMT
As title! I wonder if either bodger or @magnetman can point me in the right direction of a suitable prop to use on the Elderly 28lb Shakespeare Sigma? The current prop is a 3 blade roughly 8" X 4" Left Hand, it has a 5/16" (8mm) bore and is held in place with a 1/8" split pin - no shear pin is provided for. I'm not even sure this is a suitable prop for the outboard? it looks original mind. I cant find an identical prop - all the later stuff is held in place with a nut and shear pin. Any ideas on a suitable replacement?     Thank you please  |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 8:26:59 GMT
Why do you need to replace it?
I'm not quite sure where you would get a prop but it looks reasonable. If it's off balance how about filing off exactly the same amount from each blade.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 8:28:36 GMT
Why do you need to replace it? I'm not quite sure where you would get a prop but it looks reasonable. If it's wobbly how about filing off exactly the same amount from each blade. It is pretty beat up TBH, shaky hand at medium - high speeds  |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 8:30:10 GMT
I'd be tempted to try to do some filing to balance it. It's a lovely old motor |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 8:47:39 GMT
Re:- prop suitability - not being able to measure WOT RPM has me all out at sea regarding prop size - I have been able to measure current draw while underway, a shade over 9A in low speed, around 11.5A at medium speed. Didn't run it flat out for long this time around 🤦♂️
I wonder if a different prop would give better results? no doubt trolling motor can be over propped just like an IC powered outboard.
|
|
|
|
Post by bodger on May 18, 2020 9:12:12 GMT
Re:- prop suitability - not being able to measure WOT RPM has me all out at sea regarding prop size - I have been able to measure current draw while underway, a shade over 9A in low speed, around 11.5A at medium speed. Didn't run it flat out for long this time around 🤦♂️ I wonder if a different prop would give better results? no doubt trolling motor can be over propped just like an IC powered outboard. that seems to be a very low current draw. my 32lb MK draws about 30A at full chat.
that 3 blade prop looks the part, much better than the 2 blade jobbies used by most e-motor manufacturers, but maybe there is a technical reason why 2 blades are preferred.
I agree with the suggestion that you should try to trim and balance the existing prop - you may never find an alternative prop that fits.
Can you provide a pic showing the dimensions of the shaft (length) and the position of the pin hole? It may match a standard MK or aftermarket prop.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 10:26:48 GMT
Re:- prop suitability - not being able to measure WOT RPM has me all out at sea regarding prop size - I have been able to measure current draw while underway, a shade over 9A in low speed, around 11.5A at medium speed. Didn't run it flat out for long this time around 🤦♂️ I wonder if a different prop would give better results? no doubt trolling motor can be over propped just like an IC powered outboard. that seems to be a very low current draw. my 32lb MK draws about 30A at full chat.
that 3 blade prop looks the part, much better than the 2 blade jobbies used by most e-motor manufacturers, but maybe there is a technical reason why 2 blades are preferred. I agree with the suggestion that you should try to trim and balance the existing prop - you may never find an alternative prop that fits. Can you provide a pic showing the dimensions of the shaft (length) and the position of the pin hole? It may match a standard MK or aftermarket prop.
Brief reply - just leaving the office! I'll have a measure up when I get in this afternoon. TTFN |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 12:49:57 GMT
Forgot to mention.
It's scrap. I could take it off your hands for a small consideration. Please?
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 12:54:45 GMT
Re:- prop suitability - not being able to measure WOT RPM has me all out at sea regarding prop size - I have been able to measure current draw while underway, a shade over 9A in low speed, around 11.5A at medium speed. Didn't run it flat out for long this time around 🤦♂️ I wonder if a different prop would give better results? no doubt trolling motor can be over propped just like an IC powered outboard. Depending on weed problems RC plane props work wonders on trolling motors. The floating electric beer drinking platform has a 28lb Minn Kota I put a Graupner composite 8x6 pusher prop on it. It means forward and reverse is other way around but I use a remote PWM controller anyway so no problems. As I have mounted it on a stainless steel hinge arrangement I can clear any light weed by giving it a blip of reverse which lifts the prop out of water and slings any weed off it. The RC props don't like weed but are very very efficient and effective for propulsion. Another prop which may be adaptable is the Minn Kota "vanishing prop". |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 17:35:11 GMT
That prop is toast. Any attempt to file it then balance the prop by filing the other blades will alter its profile so far it will lose a massive amount of efficiency. While fettling my ever-more shiny 102, I mused on your problem. Seagull props use a bush not a spline...I've just measured a propshaft (they are all the same size except the QB models) which shows as about 12.5mm (although the precise diameter will be in imperial of course). So if your propshaft is about 8mm that gives you a bit of wriggle-room to insert some sort of bush of your own device but the original bush can be removed with some heat and patience if you needed more. You would ideally need someone with a lathe and the skill to use it but I once managed a surprisingly good job of enlarging the i.d. of some stainless tube with a BF drill. Plenty of people sell tubing on ebay. The prop made for the Silver Century Plus is a 'hydrofan' design and those that claim to know say that was the most efficient one. However there was a later 'weedless' type for that model that looks a lot like your prop (except it had four blades). Silver Century Plus Hydrofan (approx 9") ![]()  Later 'weed-free' Silver Century Plus (model 80) prop approx 11" (I think, from memory)  Later 'weed free' Silver Century (model 75) prop approx 9"  They look like hell in a 'used' state but some effort can make them appear like new. The last pic is the most aesthetically pleasing but you cant see it when its under water... |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 18:36:33 GMT
That prop is toast. Any attempt to file it then balance the prop by filing the other blades will alter its profile so far it will lose a massive amount of efficiency. While fettling my ever-more shiny 102, I mused on your problem. Seagull props use a bush not a spline...I've just measured a propshaft (they are all the same size except the QB models) which shows as about 12.5mm (although the precise diameter will be in imperial of course). So if your propshaft is about 8mm that gives you a bit of wriggle-room to insert some sort of bush of your own device but the original bush can be removed with some heat and patience if you needed more. You would ideally need someone with a lathe and the skill to use it but I once managed a surprisingly good job of enlarging the i.d. of some stainless tube with a BF drill. Plenty of people sell tubing on ebay. The prop made for the Silver Century Plus is a 'hydrofan' design and those that claim to know say that was the most efficient one. However there was a later 'weedless' type for that model that looks a lot like your prop (except it had four blades). Silver Century Plus Hydrofan (approx 9") ![]() Later 'weed-free' Silver Century Plus (model 80) prop approx 11" (I think, from memory) Later 'weed free' Silver Century (model 75) prop approx 9" They look like hell in a 'used' state but some effort can make them appear like new. The last pic is the most aesthetically pleasing but you cant see it when its under water... That's an interesting idea - the lathe and someone to drive it is not an issue 😉👍🍻 I can get hold of seagull prop to weigh up my options, the pedalo I'm working on uses one like your first image. One drawback is the weight penalty, I wonder if it would be a benefit once spinning (flywheel effect) or an impediment to allowing it to spin (overcoming inertia with a puny little electric motor?) |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 18:45:27 GMT
Weed is the biggest discussion area with electric outboards.
If there is no significant weed then an RC plane prop is the way to go. Suitably modified to allow the side entry grub screw.
If weed is a problem then you need a normal trolling motor prop.
Electric does not have the excess power associated with ice engines.
Having said that I have seen some discussion about using a seagull hydrofan prop on an electric outboard so it could work to be fair.
I still think knocking down the overall diameter of the prop by filing it down is an option. The damage seems to be mainly on the blade tips.
This is for child use so outright performance is not a huge issue.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 18:50:53 GMT
As it happens I just received a critical part in the post today to complete a brushless conversion of a Minn Kota trolling motor. It's going to be turning this 12.5x6 APC plane prop. I've got a few other sizes they are only a few quid each so will experiment. It may not look like much but these props soak up a huge amount of power in water and are incredibly efficient with hardly any slip. Amazing things. It's revolutionary when you are used to normal props. unless weed is a big problem I would definitely have a play with them. Only thing is you need to know the design amps for the motor so you don't melt the brush holders... APC 12.5x6. beast of a prop.  The reason I settled on a Graupner for the floating electric beer drinking platform is they do props with some GRP in which makes them a bit more durable than the APC props. And slightly more rigid. Under load the APC type will bend a bit and shed efficiency. Ideally you want props designed for IC engine planes which means high thrust and heavier construction. |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 18:50:58 GMT
Weed is the biggest discussion area with electric outboards. If there is no significant weed then an RC plane prop is the way to go. Suitably modified to allow the side entry grub screw. If weed is a problem then you need a normal trolling motor prop. Electric does not have the excess power associated with ice engines. Having said that I have seen some discussion about using a seagull hydrofan prop on an electric outboard so it could work to be fair. I still think knocking down the overall diameter of the prop by filing it down is an option. The damage seems to be mainly on the blade tips. This is for child use so outright performance is not a huge issue. It's not so much performance as smoothing it out - having seen bodger reply it would appear current setup isn't too demanding from a current point of view 🙈 Don't forget - I'm running out of jobs so I need something to keep the PMT at bay (Pre Mechanical Tension as a good friend of mine coined it 👍) often it's an excersise in because you can 🍻 |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 18, 2020 18:52:45 GMT
As it happens I just received a critical part in the post today to complete a brushless conversion of a Minn Kota trolling motor. It's going to be turning this 12.5x6 APC plane prop. I've got a few other sizes they are only a few quid each so will experiment. It may not look like much but these props soak up a huge amount of power in water and are incredibly efficient with hardly any slip. Amazing things. It's revolutionary when you are used to normal props. I less weed is a big problem I would definitely have a play with them. Only thing is you need to know the design amps for the motor so you don't melt the brush holders... APC 12.5x6. beast of a prop. The reason I settled on a Graupner for the floating electric beer drinking platform is they do props with some GRP in which makes them a bit more durable than the APC props. And slightly more rigid. Under load the APC type will bend a bit and shed efficiency. Ideally you want props designed for IC engine planes which means high thrust and heavier construction. That has crossed my mind (they are unbelievable cheap compared to marine stuff) I may well go for an RC one just to have a play. Weed usually isn't too much of an issue where it will get most of its use. |
|
