Velvet transmission

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Dido

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Oct 25, 2023
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Dear all, my sailboat is equipped with a Ford Lehman 4D254 and a Velvet transmission 10-13-000-003, 2:1 ratio, 1.5 shaft diameter and 19x13 LH 3 blade propeller. When I turn off the engine and start sailing the shaft keep rotating regardless of the position of shifter, forward, reverse or neutral. Is this a sign of defective transmission, if not then are there a device I could install to immobilize the shaft during sailing.

Many thanks for your input.
 
Not a problem at typical sailboat speeds. Running on one engine at 10 knots for long periods could result in overheating. The oil pump is not pumping while free wheeling. If engine is not running a PSS seal ay high speeds might need an alterative source of water.
 
The Velvet Drive is a hydraulic trans, so once the engine stops turning and the pump on the trans input shaft stops, there's no more hydraulic pressure to engage the clutch packs and the trans ends up in neutral regardless of shifter position.

As long as it's not getting overly warm it's safe to let a Velvet Drive freewheel at typical sailing speeds. And assuming you have a fixed blade prop, it's almost always less drag to let the shaft spin than to lock it in place anyway.
 
Those Velvet Drive transmissions are specd in the manual to be ok to freewheel at sailboat speeds. And yes, it’s completely normal that they do that when the engine is off.

Ken
 
I have velvet drives as well. My question is at what speed would you not feel comfortable letting it free wheel? Sailboat boat of 6 kts is fine, what about 8 kts? I know I'm asking about the grey area here but wanted feedback.
 
We had a velvet drive on our sailboat. The freewheeling noise was loud. I first went with a shaft-lok then to a Max-Prop, a feathering prop. Expensive but worked very well. It also had equal thrust in forward and/or reverse.
 
Last edited:
I think 8 knots would be fine. The manual says this:

“Under sail with the propeller turning or at trolling speeds with one of two engines shut down, the design of the Velvet Drive gear maintains adequate cooling and lubrication.”

Ken
 
Thank you Ken for the information. Very Helpful!
 
Do you have self feathering/folding prop? If you do, it might be time haul the boat to verify it is feathering/folding. I could back down on my folding prop
 
The issue of drag produced by a non-powered spinning propeller versus one locked has been addressed here before, and I thought the engineering consensus was that a locked propeller produced less drag.
 
They do rotate, there was a charter ferry started by towing it in neutral and into gear at suitable speed.
 
rgano said:
The issue of drag produced by a non-powered spinning propeller versus one locked has been addressed here before, and I thought the engineering consensus was that a locked propeller produced less drag.
Click to expand...
Other way around. Assuming no excessive drag in the shaft rotating then in most cases a freewheeling prop is less drag. It's not the case for every prop design and running gear layout though, only most. A 2 or 4 blade behind a keel will sometimes produce less drag when locked if you can align the blades favorably behind the keel.
 
Beg to respectfully differ. A locked prop (usually) produces less drag, and indeed a locked shaft produces less drag than a rotating one. Hopefully someone has the research handy to quote.
 
Several years ago when the subject was being discussed again RickB (I think) posted a link to a water tank study regarding the drag of turning versus locked props. It’s in the archives somewhere, good luck.
 
Nautica said:
Beg to respectfully differ. A locked prop (usually) produces less drag, and indeed a locked shaft produces less drag than a rotating one. Hopefully someone has the research handy to quote.
Click to expand...
I've only personally tested it on one boat (sailboat with a fixed 2 blade prop, but not right behind the keel). On that boat, locking the prop created a noticeable increase in turbulence behind the boat (and correspondingly reduced rudder effectiveness) but also produced a slight decrease in speed. Letting it spin made more noise, but was otherwise the better option (and was the recommended method from the engine/transmission manufacturer).
 
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