| MudmotorTalk.com https://www.mudmotortalk.com/mmt_v2/ |
|
| Rotax long tail https://www.mudmotortalk.com/mmt_v2/viewtopic.php?f=6&t=23974 |
Page 1 of 1 |
| Author: | jrrdmercer [ Sun Nov 13, 2011 11:20 am ] |
| Post subject: | Rotax long tail |
Hi I am new to the mud motor world. I would like to build a long tail setup. I have a rebuilt rotax 503 rated at 50hp @ 6500rpm and 41ftlb torque @ 6000rpm. Using direct drive what prop would I need? It will be used on a 17' drift boat. Any sugestions or insight would be great. |
|
| Author: | scottfarm [ Sun Nov 13, 2011 5:02 pm ] |
| Post subject: | Re: Rotax long tail |
You are better off running a reduction gear. 4 cycle's work better in this application because of better torque at lower rpm. I had a 503 on a Kolb and it is a bad ass engine for that application. |
|
| Author: | Blacknasty [ Sun Nov 13, 2011 11:42 pm ] |
| Post subject: | Re: Rotax long tail |
I agree, if you can work a out a reduction of somewhere between 1.5:1 to 2:1 that would be best. The props at very high RPM tend to loose efficiency. If you aren't running a reduction and the prop is turning 6K I'd say a 9X6. With the reduction maybe a 9X10 or 9X11. Please understand these are just estimates based on boat size and the torque of you engine. I've never see a boat with a similar set or even a two stroke at that. If you decide to do this build please post pictures or videos. We would be curious to see how it comes out. Best of luck |
|
| Author: | Blacknasty [ Sun Nov 13, 2011 11:52 pm ] |
| Post subject: | Re: Rotax long tail |
If you have a target speed use the equation (pitch in inches)/12 X (estimated max loaded RPM)X60/5280 to get MPH. This would be a condition with no prop slip. Slip is normally around 20% so multiple that the MPH by .8 to get a closer approximation to top speed. Here is the example using a direct drive and a 9X6 prop for your rotax spinning 6000 rpm. 6/12 *6000RPM*60/5280=34.1 MPH then account for slip 34.1*.8=27.3mph After seeing these numbers and considering the torque and HP of your motor maybe you could go up on the pitch a little. However I will say with a mud motor its much better to have a slightly under pitched prop compared to a slightly over pitched prop. Best of luck |
|
| Page 1 of 1 | All times are UTC - 6 hours |
| Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group http://www.phpbb.com/ |
|