Freewheeling Prop

[Charlie]

Recently Purchased my 1981 Hunter 37 Cutter and it has a 3 blade prop. When under sail above 4 knots I can hear the prop freewheeling. I've even tried putting the transmission in gear but I still hear it freewheeling. My question, is this doing any damage to my transmission and what can I do to fix the problem. Charlie S/V Destiny

 

[Ernie Rodriguez]

Depends on your transmission

What you should do when with the prop when sailing depends on your transmission and what it is designed for. In my case, the engine is a Yanmar with a KM3A transimission. It has a cone clutch and in order to lock the prop from free wheeling, it needs to be put in reverse. If it is put in forward, the cone clutch will slip and wear very quickly, in which case you will need to have the transmission overhauled...If you want to have the prop free wheel by leaving the transmission in nuetral, you need to make sure the transmission has sufficient lubrication in that mode.There is quite a bit of controversy as what to do. Some say that a free wheeling prop will present more drag than a locked prop, others say vice versa. My preference is to lock the prop.Good luck.Ernie

 

[Ed Schenck]

Ernie is right.

I always sail my H37C(1979) with the tranny in reverse. There was a thread when Torresen was here that discussed this in detail including which make of transmissions should be in reverse. To further put my mind at ease I installed a folding prop(see link).

 

[Kevin l. Woody]

To free or not to free

Dear Charlie, Thanks for your note. Ernie is correct, in some cases the act of freewheeling the propeller can and will cause undo wear and possible damage to a transmission. Most mechanical transmissions only lock up in reverse gear. Locking the transmission in reverse, depending on the speed and the load produced, could have a wearing affect to the locked trans. If the transmission is left to freewheel under sail, lubrication may not be taking place. Most transmissions are not oil bathed gears, but lubricated by a pump, which is activated when the engine is driving the transmission. You may find looking in your transmissions instruction booklet that if the transmission is freewheeled more then X hours the engine needs to be started and the transmission rotated for X hours in order to re-lubricate it. We at PYI believe that the “to freewheel or to freewheel” is driven by the vessels speed at that given time. We believe that the propeller should be freewheeled up until apx. 4 knots. Any speed after that, the shaft should possibly be locked down. As the vessel speed increases the shaft rotation will begin to slow in proportion, causing it to create greater drag. At some point in the boats speed the drag of the transmissions bearings, shaft bearings and water flow efficiency will slow the prop shaft down thus slowing the boat speed down.Hope this helps.Kevin.