Drive spinning

[FranklinGray]

Our new to us boat prop shaft spins and sounds like a high speed turbine while sailing no matter what I do with the gear shifter. It is a Velvet drive transmission bolted to a Yanmar 127 HP.

Are these transmissions supposed to spin freely in neutral or lock in place in reverse? I know something is wrong because no way is it supposed to sound like it did. Anybody can shed some light on what the problem is?

[meridian28]

You can lock the shaft to stop it. Use a vice grip or something similar. The velvet drive does not lock.

[FranklinGray]

Bummer it doesn't lock on it's own. The shaft is about 2" and the prop is a pretty big 3 blade compared to the prop I had on my 40 HP yanmar powered old boat; I'll need some really big vice grips to hold that while going 8-9 knots.

[zeehag]

mine did that until i changed my tranny fluid.
seems burned transmission fluid doesnot lube well.

[meridian28]

Try this
http://shaftlok.com/

[DougR]

Borg Warner "velvet drive" transmissions are hydraulically actuated. That is, there is a hydraulic pump on the input side ( engine side ) of the transmission, and when the engine is running this pump creates hydraulic pressure. The pressure is directed by a valve controlled by the shift cable to either the " ahead" or the "reverse" clutch pack, causing the prop to spin one direction or the other.

Unfortunately when you shut off the engine and go sailing, there is no longer any power driving the hydraulic pump and so there is no way to lock up the clutch packs, so the water created torque on the propeller just causes it to spin.

Normally in this sort of situation it's necessary to fit a shaft brake if you don't want the prop to spin. There are several types of brakes available in the market, and perhaps with some Google time you can find something which will fit your vessel.

Another option is a folding or feathering prop which usually can be made to not rotate without installing a shaft brake.

DougR

[Bill O]

I'd second changing out the fixed prop for a folding or feathering prop. A bit of an upfront expense, but IMO well worth it to reduce noise and drag. Also may help the boat reduce prop walk in reverse.
Personally we don't like to hear the whirring and we do like to go faster under sail, so for us it was an easy decision to switch.

The biggest challenge will be to decide which one.


Bill O

[Hasbeen]

I had a folding prop of about 16", with a centrifugal clutch on Alyth when I bought her. No reverse at all.


I installed a small Petter diesel, with a forward & reverse gearbox, but stayed with the folding prop system. It didn't matter if I put the thing into forward or astern gear, the prop would turn the little diesel, until I brought the boat speed down to under 5 knots.


Once down to that the prop would fold, & stay folded until driven again. It still was pretty useless in astern, or in slowing the boat. If I were doing it again I would fit a 3 blade feathering variable pitch prop, & hang the cost.


Later on tourist boats I had a relief skipper knock a blade completely off one 5Ft 6 inch prop on a twin screw 70 foot passenger launch. Nothing would stop that prop turning once the boat reached 3 knots. I could have clutch started the 150 BHP Volvo Diesel with just the 2 blades on that prop.


We had to put the thing along side a jetty arm at low tide, where we could work on it standing on the bottom, & remove the prop under water, before we could steam the 100 miles to the nearest slip capable of taking her.