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Old 18-01-2021, 14:11   #1
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Required Rudder Torque

Howdy, in the process of changing from mechanical steering to hydraulic helm pump and ram.
The company i am dealing with does not normally do Sailboats so they are reluctant to say exactly what I need for their equipment. They suggested I see if I can find out what torque requirement needed to give full rudder at an estimated top speed of 9 knots.
Anyone here have the expertise to throw out a number?
I have lots of weights and dimensions to accompany this question if there are any takers.
Thanks
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Old 18-01-2021, 14:39   #2
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Re: Required Rudder Torque

Can't be done without detailed knowledge of the specific boat and rudder design.

E.g., is the rudder balanced or partly balanced; weight of the boat, turning moment desired, lever arm associated with turning the rudder, etc., etc.
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Old 18-01-2021, 14:58   #3
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Re: Required Rudder Torque

One of the AP web sites has a formula. Saw it a couple of months ago and used it to SWAG my gear size.

Cant recall which one.

OK, found it first try.

https://www.ls-france.com/en/power-p...the-system-gr/

See if this helps.
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Old 18-01-2021, 15:46   #4
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Re: Required Rudder Torque




That is not a large rudder-looks normal size for a 40 ft commercial boat.
From my personal experience installing many pilots,I am quite sure a smaller hyd. pump/ram will do the job.
For reference,I am sure a Raymarine M81130 linear drive would be no problem.Rated at 650lbs push & using a 6" tiller arm.https://www.westmarine.com/buy/rayma...-drive--342774


The most common "fault" of manual hydraulic systems is getting the correct match of helm pump volumn for your chosen hyd. ram so that you have no more than 4-5wheel turns HO-HO without a lot of muscle power. Suggest you consider power assist hydraulic.


Nice boats!




/Cheers Len
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Old 18-01-2021, 19:08   #5
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Re: Required Rudder Torque

Hello, the rudder is 34H x 35L, approximately 1200 sq niches or 8.25 sq feet
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