4- vs 5-bladed prop on Silver Century

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corich
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4- vs 5-bladed prop on Silver Century

Post by corich »

Hi, all. I recently picked up my first Seagull, a Silver Century Plus long shaft (WSPCL...) from 1977. It was sold to me with a 4-bladed prop that appears to be 9" diameter, which I think was original to a 40 Plus, but I understand the SCP motors came with the 5-blade, 11" prop. (Is this right?)

I've sourced a correct 5-blade prop on eBay, and will soon have a choice which prop to run. Aside from originality, what reasons might I have to choose one prop over another? Why would a previous owner have changed out the prop to the 4-bladed model? What are the different performance characteristics one would expect between the two propellers?
corich
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Location: Colorado, USA

Re: 4- vs 5-bladed prop on Silver Century

Post by corich »

(And to clarify, I understand that a larger prop should produce more thrust at a given RPM. I'm trying to figure out what the previous owner intended by making this modification, or whether the motor has simply been cobbled together with spares he had lying around.)
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John@sos
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Re: 4- vs 5-bladed prop on Silver Century

Post by John@sos »

Surprised it fitted, most hubs different depth! Grossly under size.

Seen a few with the 4 balde 11" hydrofans fitted to the Century Plus clutch drive, with Villiers carb.... and then swapped for the 5 blade so the motor could rev more......

Bit like the 'trolling prop' fitted to some forty Plus motors. It literally had half inch chopped off each blade! Got the jig to mark those props here, a real curio! The idea was you could run the Seagull harder to avoid oiled up plugs and go slower. Days of straight 30 grade oil in the mix!

Seagull only ever made one prop for each model, generally. On the Silver Century Plus clutch model and on the 2hp Featherweight, they did introduce the option of what they laughably called a 'semi weedless' prop. They were found not to procuce quite as much thrust as the original hydrofans and were more like weed magnets!

The Forty Plus clutch model I run on my tender came with one of these 'semiweedless' props, They all did, it was the only option. 100 yards on the local canal and you had to stop to remove weeds! Made progress from Heybridge basin to Tescos in Maldon a long putter!

john
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corich
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Location: Colorado, USA

Re: 4- vs 5-bladed prop on Silver Century

Post by corich »

Thanks, John. If I understand correctly, there's a chance this is the original "semi-weedless" option offered on the Silver Century Plus. But if that's not the case, then it's the incorrect prop for the motor - and even if it is "correct" it may not be desirable over the standard 5-bladed hydrofan.

I'll investigate further. If it turns out to be a later addition, I'll be interested to see whether the previous owner replaced the entire lower unit, including gearing, or if they've simply put the smaller prop on the existing lower. Stay tuned....
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John@sos
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Re: 4- vs 5-bladed prop on Silver Century

Post by John@sos »

Send me a few pictures via the website mail and I may be able to tell.

Regards,
John
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corich
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Re: 4- vs 5-bladed prop on Silver Century

Post by corich »

I believe the prop that came with the motor is indeed the "weedless" option, as it has the "CLW" casting mark in the spring notch. I received the (rather rough) eBay 5-bladed hydrofan prop yesterday, so I was able to perform a direct comparison. There's a photo of the casting mark, and another of the two props stacked atop one another, here:
https://imgur.com/gallery/VinzwG8
The hydrofan appears to be a little larger diameter than the weedless propeller, but I may have underestimated the size of the weedless prop in my initial post.

If I can find a suitable scale, I suppose I'm in a position now to do a little Science(tm) - measure the thrust of each prop and see how their performance compares. Unless that's already been done?
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John@sos
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Re: 4- vs 5-bladed prop on Silver Century

Post by John@sos »

Yes the CLW prop would be the semiweedless for the WSPC models...

They work but not quite as well as the 5 bade Hydrofan. Just look more modern!

Regards,
John
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