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Go Back   SailNet Community > Boat Builders Row > Beneteau > Sailing ... transmission in reverse?
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Thread: Sailing ... transmission in reverse? Reply to Thread
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Topic Review (Newest First)
06-09-2014 03:30 PM
gamayun
Re: Sailing ... transmission in reverse?

I went out in my 2-blade fixed sailboat about a week ago to meet friends across the bay so no rush to get anywhere. I had consistent 15-knots on a port tack so I would head into the wind periodically, shift into reverse or neutral, and see what that did to my SOG when the sails powered back up. Did it a few times. It was pretty consistent with 7.3 to 7.4 knots on the fixed prop and 7.6 to 7.7 on the spinning prop.
06-09-2014 01:53 PM
Missingyou
Re: Sailing ... transmission in reverse?

I used to slip my boat into gear to stop the annoying whirring noise, but only for a few months of ownership, then I installed a Flexofold over the winter.

Many years ago I worked for a company that flew us daily to the job site in a twin engine Piper Navajo. That was until we blew the right engine, complete with a brief fire over Southern Ontario. What are the first things a pilot is taught to do? Feather the prop and cut the fuel. If the prop is not feathered there is sufficient drag to make the plane very difficult to fly. As it was I got a great view out of the side window of the runway from my left seat as the plane crabbed it's way down final on the power of the left engine only.

Just imagine taking an 18" fixed blade prop and trying to hold it down in a 5 or 6 knot current, first spinning, then locked. Maine Sails example of the engine on the tender is a great one! It would be easy for anyone to replicate, if you are willing to trust someone else at the helm while you are hanging out in the tender.
05-31-2014 07:20 AM
Maine Sail
Re: Sailing ... transmission in reverse?

Quote:
Originally Posted by gamayun View Post
This is what gets me about sailing. It is extremely difficult to sort out which variables apply to one thing and not another. Even though I posted that paper that said a spinning prop is faster on hull speed than a locked prop, I asked a couple of very experienced sailors, one of which is a pilot who said that if you need to glide to a landing without stalling your forward momentum, then you lock the prop and that keeps the plane from slowing down. He wondered if the paper was related to large vessels and not smaller sailing yachts. These two said they both lock their props; however, they also have folding ones....so maybe there's a difference with a 2-blade fixed prop? Feathering props?
We are NOT in planes or helicopters and not traveling at those speeds in that medium. The University of Strathclyde Ocean Engineering Department paper was specific to sailboat props as was the MIT Sailboat Prop study. MIT also found the SAME THING. I also tested this years back and still have the test jig for conducting the analysis. I put a video up on YouTube...

*Why will a folding prop remain open and spinning when under sail and the gear placed in neutral?

*why does the same prop slam shut the split second it is locked in reverse?

*why does my dingy motor leg stay down when being towed in neutral but the minute I lock it in reverse the prop lifts/tilts the motor...?


Beyond MIT & The University of Strathclyde Dave Gerr author of the Propeller Handbook says the same and the UK magazine Yachting Monthly also tested this specific to sailboat props... Lots of "experts" have been wrong on this for many years.
05-30-2014 11:38 PM
gamayun
Re: Sailing ... transmission in reverse?

Quote:
Originally Posted by Stumble View Post
As I said it depends on your transmission. But allowing the prop to spin, ie neutral without a shaft break, is slow.
Quote:
Originally Posted by fmueller View Post
This is incorrect. Their is no reason a spinning prop would create more drag than a fixed one (except folding props of course). The opposite is almost certainly true.
Quote:
Originally Posted by Maine Sail View Post
Sorry you have it backwards. A freewheeling sailboat prop has LESS DRAG not more..
This is what gets me about sailing. It is extremely difficult to sort out which variables apply to one thing and not another. Even though I posted that paper that said a spinning prop is faster on hull speed than a locked prop, I asked a couple of very experienced sailors, one of which is a pilot who said that if you need to glide to a landing without stalling your forward momentum, then you lock the prop and that keeps the plane from slowing down. He wondered if the paper was related to large vessels and not smaller sailing yachts. These two said they both lock their props; however, they also have folding ones....so maybe there's a difference with a 2-blade fixed prop? Feathering props?
05-27-2014 09:35 AM
Maine Sail
Re: Sailing ... transmission in reverse?

Quote:
Originally Posted by outbound View Post
So let me get this right. It's ok to either leave it in reverse or pop it into reverse briefly to get it to stop spinning given I have a max prop ?
I would pop it into reverse to get it to feather, then go back into neutral just in case some weeds force it to un-feather...
05-27-2014 08:51 AM
outbound
Re: Sailing ... transmission in reverse?

So let me get this right. It's ok to either leave it in reverse or pop it into reverse briefly to get it to stop spinning given I have a max prop ?
05-27-2014 01:57 AM
Stumble
Re: Sailing ... transmission in reverse?

I hate It when I'm wrong. Thanks for the correction.
05-27-2014 01:10 AM
Alex W
Re: Sailing ... transmission in reverse?

Note that Yanmar does allow you to shift into reverse while sailing if you have a folding or feathering prop. That's good since some props won't fold or feather without locking the shaft. Even so I usually put it into reverse for a few seconds, then back into neutral when the prop feathers.

When I had a non-feathering prop I did confirm on my own boat that freewheeling was faster than locking the prop shaft.

Putting on a feathering prop last winter was the best performance upgrade that I've made to the boat.
05-26-2014 09:55 PM
gamayun
Re: Sailing ... transmission in reverse?

See study results (link below) from 2008, which stated the following in its findings, though I still contend that a rotating propeller will Drive_You_Crazy: "The experimental results confirm that a locked propeller produces greater drag than does a freewheeling screw (up to 100% more drag was observed, this being at higher speeds). Furthermore, for the freewheeling case, the magnitude of the hydrodynamic resistance is significantly affected by the amount of frictional torque on the shaft, low torque being accompanied by low drag."

Sailboat propeller drag
05-26-2014 05:06 PM
Maine Sail
Re: Sailing ... transmission in reverse?

Quote:
Originally Posted by Stumble View Post
As I said it depends on your transmission. But allowing the prop to spin, ie neutral without a shaft break, is slow.
Sorry you have it backwards. A freewheeling sailboat prop has LESS DRAG not more..
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