Gearbox ratio for w33 and Discus

[capetown]

Hi, Does anyone know the gearbox ratio of the Beta 35 used on the above?
Tia

 

[Tranona]

Depends on the propeller and which gearbox you have. There is no "standard" reduction ratio, but the most common would be 2:1 with a 16" 3 bladed prop. The TMC60 box has options of 4 different ratios and the PRM 125 mechanical 2, The PRM 150 hydraulic box is also available as an option again with a choice of 3 ratios. There should be a plate on the box showing model and reduction ratio.

 

[capetown]

Depends on the propeller and which gearbox you have. There is no "standard" reduction ratio, but the most common would be 2:1 with a 16" 3 bladed prop. The TMC60 box has options of 4 different ratios and the PRM 125 mechanical 2, The PRM 150 hydraulic box is also available as an option again with a choice of 3 ratios. There should be a plate on the box showing model and reduction ratio.

Thanks Tranona, I should have listed more info.
This will be my first brand new engine.
It’s replacing the Merc. So are you saying whatever ratio that is already fitted, I should choose?
I understand that the w33/Discus has limited space for a prop?
Going for a FeatherStream, so I’ll ask them what size to go for.

 

[Tranona]

Thanks Tranona, I should have listed more info.
This will be my first brand new engine.
It’s replacing the Merc. So are you saying whatever ratio that is already fitted, I should choose?
I understand that the w33/Discus has limited space for a prop?
Going for a FeatherStream, so I’ll ask them what size to go for.

OK. You will probably find a recommendation for a 17" but you will have to measure whether there is enough tip clearance. The larger the diameter the better. Check with Beta what the maximum rated revs for the 35 is. The brochure says 2800rpm, but I seem to remember it is actually closer to 3000rpm. The aim with the reduction ratio is to get the shaft speed in the 14-1500rpm range and a 2:1 will do this. That will allow a 16 or 17" diameter prop. I have just been through this exercise with a Beta 30 in a Golden Hind and the ideal prop diameter is 17". This engine revs to 3600rpm so I chose a PRM 2.5:1 which gives a shaft speed of 1440rpm. strongly recommend a PRM 125 rather than a TMC60

The other thing you have to consider is your shaft size which is probably 1 1/14" or maybe 30mm. With the Feathersteam you can get a 16 or 17" with the small hub, but this will only take a 25mm taper so you may have to get the shaft machined to 25mm just at the taper. This is what I did with my 30mm shaft. The advantage of using the small hub is that it is cheaper and gives a bit more blade area.

Suggest you talk to Chris at Darglow as he may well have done a similar setup. He will give you a template of the small hub with different blades so that you can draw it out and measure what clearance you have.

This is my 17" Feathersteam

Hope this helps

 

[capetown]

OK. You will probably find a recommendation for a 17" but you will have to measure whether there is enough tip clearance. The larger the diameter the better. Check with Beta what the maximum rated revs for the 35 is. The brochure says 2800rpm, but I seem to remember it is actually closer to 3000rpm. The aim with the reduction ratio is to get the shaft speed in the 14-1500rpm range and a 2:1 will do this. That will allow a 16 or 17" diameter prop. I have just been through this exercise with a Beta 30 in a Golden Hind and the ideal prop diameter is 17". This engine revs to 3600rpm so I chose a PRM 2.5:1 which gives a shaft speed of 1440rpm. strongly recommend a PRM 125 rather than a TMC60

The other thing you have to consider is your shaft size which is probably 1 1/14" or maybe 30mm. With the Feathersteam you can get a 16 or 17" with the small hub, but this will only take a 25mm taper so you may have to get the shaft machined to 25mm just at the taper. This is what I did with my 30mm shaft. The advantage of using the small hub is that it is cheaper and gives a bit more blade area.

Suggest you talk to Chris at Darglow as he may well have done a similar setup. He will give you a template of the small hub with different blades so that you can draw it out and measure what clearance you have.

This is my 17" Feathersteam

Hope this helps

Thanks, yes it does help. You’ve explained it in a way that I can take it on board. I’m at the boat today so wil measure gap for prop. Also ordered the PMC 2:1 box.
Thanks once again.