Freewheeling -- Damaging . . . or no big deal?

[Stephen]

I read recently that one should leave the diesel transmission in reverse when sailing, because if the transmission is left in neutral the spinning prop could overheat the transmission and damage it.

Is this feasible?

Likely?

How do the benefits of (presumably) slightly faster sailing weigh against the risks of damage to a transmission?

Stephen
"ELIZABETH"
CD 22D



sailing@star.net

[Joe]

I read recently that one should leave the diesel transmission in reverse when sailing, because if the transmission is left in neutral the spinning prop could overheat the transmission and damage it.

Is this feasible?

Likely?

How do the benefits of (presumably) slightly faster sailing weigh against the risks of damage to a transmission?

Stephen
"ELIZABETH"
CD 22D

Yes, freewheeling can result in damage to more than just the transmission.

Although you wouldn't think so, tank tests consistently show that a hull with a non-turning prop makes better speed than one that is freewheeling.

Joe



tgjournal@gestalt.org

[Matt Cawthorne]

Stephen,
Freewheeling does not hurt all transmissions. If you want to find out about your transmission call the manufacturer. For instance, the Hurth transmission installed in my CD-36 (it may not be original) is rated for freewheeling. The manufacturer said that the transmission is damaged if left in forward while sailing.
Matt

I read recently that one should leave the diesel transmission in reverse when sailing, because if the transmission is left in neutral the spinning prop could overheat the transmission and damage it.

Is this feasible?

Likely?

How do the benefits of (presumably) slightly faster sailing weigh against the risks of damage to a transmission?

Stephen
"ELIZABETH"
CD 22D

mcawthor@bellatlantic.net

[Lee H. Hodsdon]

Stephen,

I guess my response is 180 degrees from that of Joe, but here goes. My CD25D has a Westerbeke 10-2 (10 hp, twin cylinder)diesel. The owners manual specifically states the transmission should be kept in neutral when sailing. I have noted the following diferences between in and out of gear:

1. When out of gear there is less weather helm and better speed. I'd think if the non rotating prop increased speed, there wouldn't be much of a market for folding, or feathering propellors. No offense intended to Joe.

2. When I did leave the unit in gear while sailing, the transmission would appear to "unwind" when I started to motor, as though there had been a binding caused by the in gear sailing.

I guess you should check with the manufacturer of the transmission for the correct advice.

Sincerely,

Lee

I read recently that one should leave the diesel transmission in reverse when sailing, because if the transmission is left in neutral the spinning prop could overheat the transmission and damage it.

Is this feasible?

Likely?

How do the benefits of (presumably) slightly faster sailing weigh against the risks of damage to a transmission?

Stephen
"ELIZABETH"
CD 22D

lhodsdon@nh.ultranet.com

[Bill]

The owners manual on my 25D states to engage the transmission in reverse while under sail. (Yanmar 1gm Not sure of transmission type)

Bill
S/V Rhapsody



willie@clnk.com

[Joe]

I read recently that one should leave the diesel transmission in reverse when sailing, because if the transmission is left in neutral the spinning prop could overheat the transmission and damage it.

Is this feasible?

Likely?

How do the benefits of (presumably) slightly faster sailing weigh against the risks of damage to a transmission?

Stephen
"ELIZABETH"
CD 22D

This discussion has, in my opinion, gotten off the track.

First, transmission damage is only one part of the potential problems that can result from leaving a prop in freewheeling. Another one, which can be almost as expensive, is wear to the cutlass bearing. On a larger boat, the replacement cost can be very high. A turning shaft is always wearing the cutlass bearing no matter what kind of transmission you have.

Common sense would have you believe that a spinning prop creates less drag than a stationary one. Common sense would also have you believe that a stationary two blade prop would create less drag than a stationary three blade one. In both cases, common sense (no matter what personal experience might trick you into believing) is wrong. Other than a feathering prop (which has nothing to do with a stationary or spinning prop of any type), the least drag is created
by a stationary three blade prop. Tank tests of all conditions have shown over and over again that the energy needed to spin a fixed blade prop slows forward boat motion more than the drag created by the same prop in a fixed position. With a locked fixed blade prop, the same type of "vacuum thrust" that keeps an airplane aloft is created resulting in some forward thrust. A spinning prop only creates drag.

You can, of course, reduce drag by using a two blade prop, marking the shaft so that you can tell when the blades are parallel to the hull, and always moving the shaft into the marked position when sailing, which creates almost no drag. This is, however, a major pain in the butt.

Personally, I would rather be sailing and arrive ten minutes after the boat with the two bladed prop in the proper position (assuming it didn't take them ten minutes to get the prop in position) or the boat with the $2500 feathering prop.

Joe



tgjournal@gestalt.rog

[Walt Bilofsky]

Personally, I would rather be sailing and arrive ten minutes after the boat with the two bladed prop in the proper position (assuming it didn't take them ten minutes to get the prop in position) or the boat with the $2500 feathering prop.

Unless you're racing, of course - and Cape Dorys only race in 30 knots or more, so the prop effect would be negligible.



bilofsky@toolworks.com