Interesting Technical Question

**Lakesailor** · 27-09-05, 20:17

Perhaps the initial question is wrong. Maybe it's not that interesting.

**Joe_Cole** · 27-09-05, 20:47

Naughty! You'll be told off. [img]/forums/images/graemlins/blush.gif[/img] [img]/forums/images/graemlins/blush.gif[/img] [img]/forums/images/graemlins/blush.gif[/img] [img]/forums/images/graemlins/wink.gif[/img]

**mikef** · 27-09-05, 21:08

You're welcome to the thread, gludy. Keep it, it's yours

**hlb** · 27-09-05, 21:18

Course he could always stick a set of mole grips on the shaft and let us all know what the result was, it's fairly simple to stop a shaft going round. For most!!

**Gludy** · 27-09-05, 21:19

I really do not understand why it upsets you so much when someone actually tries to get somwhere with a subject. Your personal attack in this case was without any foundation whatsoever ...... no sense of actually reading what has been written and then withdrawing your personal comments ...no, you simply take your ball away.

**Gludy** · 27-09-05, 21:20

yes- trouble with that is that you need fairly big mole grips and the means to measure fuel consumption ... a rare combination :-)

**Major Catastrophe** · 27-09-05, 21:28

[ QUOTE ]
My boat is GB42 Classic woody, with twin Lehman 120, approx. 5200 hours. My test ride has been carried out in very unstable wind & sea conditions, so that result may be accordingly inaccurate. I can provide complete table if someone interested, but real reason for this post is folowing simple experiment:
I choose speed 7 KN, and adjusted 1) only port engine, stbd freewheeling, 2) only starboard engine, port freewheeling, 3) both engines, to reach this same speed.

[/ QUOTE ]

To complete the experiment he should redone it with the second engine just in gear at idle speed. That gets over the drag/gearbox damage question.

**hlb** · 27-09-05, 21:33

It dont take the brain of britain to stop a shaft, a few lumps of wood would do, or an old vice, stiltsons???

It's quite easy to test. Go out on one engine till fuel runs out. Release prop and come back on other engine. you either make it or you dont!! [img]/forums/images/graemlins/laugh.gif[/img]

**Gludy** · 27-09-05, 21:35

Yes- obvious but I did not think of that - that is an easy experiment to do as well.

In fact I would think that has to be the best of all solutions (for the record, I do not know) because the prop is at least being turned in the right direction - no gearbox resistance and there must be less resistance than even a locked prop - set aginst that is the tickover consumption of one engine.

You have introduced an intersting third way here ... thanks.

This would make an inteesting set of tests for a mag to do.

**jfm** · 27-09-05, 21:36

Gludy we need to be careful, and be clear about parameters. If the constant against which you are measuring is a fixed 7 knots in a TSDY then 2 running engines might be better than one engine plus a load of drag from an undriven prop. In my case I was just referring to absolute highest mpg, regardless of speed, and that is achieved on our boat with one engine running at idle, 3.5knots,, and the other stopped.

I see you say it is accepted wisdom that a locked up undriven prop is less drag than one allowed to spin freely. I will happily be proven wrong but I gotta say i just dont get that. It seems intuitively correct to me that there must be less drag if the prop is allowed to spin. ??