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Post by RKC on Nov 14, 2008 12:57:18 GMT 12
From: russ39 (Original Message) Sent: 21/10/2008 8:42 p.m.
Hi guys,new to this site but not to dredging. Need a bit of info regarding motors please. Have a old 10hp Honda with 2 to 1 reduction box. Any ideas if this will run a 5 inch dredge or am I hoping for to much? Also have 8hp Briggs motor,will this do the job? Also thinking of running two 5.5 Honda's on a 5inch dredge so will these need to be run full throttle at about 2 metres or not?Any help appreciated as saves a bit of time in the field. Really want some answers before labor weekend if possible.
Thanks Russell
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Post by RKC on Nov 14, 2008 12:58:05 GMT 12
From: alluvial0 Sent: 21/10/2008 11:35 p.m. Hi Russ,
Welcome to the site. Check out the posts towards the end of "Building A Small Dredge" posts. Rob has some pics & info on a twin motor/pump powered 5" Dredge Alluvial
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Post by RKC on Nov 14, 2008 12:59:28 GMT 12
From: RKCNZ Sent: 22/10/2008 12:52 p.m.
G’day Russ ( russ39 ), I would like to add my welcome to the Gold Dredging Forum! I regard 10 hp as the minimum power requirement required for a 5-inch surface dredge … and to get a total of 10 hp you could obviously use a single motor of 10 hp, or alternatively two 5 hp motors. On a 5-inch dredge I used prior to using the 5-inch dredge pictured above in the Arrow, I used a single 10 hp Honda motor and I was more than happy with the suction. However, I found the one disadvantage of having a heavy motor was that it often made it difficult to move around and get into a river. I unfortunately lost that dredge when it was stolen from a house where I had it stored in Papua New Guinea. So, when I got back to Australia I had to make another 5-inch dredge, and I made the replacement dredge nearly the same except that I decided, for the sake of portability, to go with two 5 hp motors instead of the single 10 hp Honda motor. Going to two small motors has the one only advantage of, portability. There is extra cost in buying two motors rather than one and increased petrol costs involved as running costs … just depends on how important the issue of portability is to you. And there are a few other disadvantages such as the complicating factor of having two motors (an extra foot valve, time lost priming two pumps, etc). You already have a 10 hp motor so that’s probably the path of least resistance for you … you will have to remove the ‘reduction box” however, and you will need a pump that couples straight on to the type of shaft on your old Honda motor. You might get away with using your 8 hp Briggs ... but nothing will stuff a Briggs motor quicker than running it at maximum revs. I referred above to 10 hp being the “minimum” power required, but, issues with dredge design can mean more power is required. For example, if you are using a suction hose that’s heavily ribbed inside then this can significantly sap power, also if an over sized power jet is used then this will definitely require more power to be employed. I would not like to run any dredge motor/s at full throttle for any length of time. You should aim to run your motors a maximum of three quarter throttle. On my 5-inch dredge with two 5 hp motors I had to, if I remember correctly, run with more revs than I would be happy with these days. What probably saved the motors was that I exclusively used a fully synthetic oil from when the motors were run in to throughout their life. If I had used two 6 hp motors I would have then probably had sufficient suction and would have been able to run at reduced revs. If I was making a 5-inch dredge today I would probably go with two 6 hp motors (providing I could find suitable pumps to couple them to). If you would like to post some photos of your dredge here, I’d be most interested in seeing them. Good luck on getting it all organized before the Labor weekend. Its great to have the long weekend finally come around as its when we can at last put winter behind us and can be confident the season has finally commenced.
Regards, Rob (RKC)
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