Winch Power Ratios

[Gixer]

I'm looking at replacing some old Lewmar 7 winches with self tailing.

I've been doing some research and come to the conclusion that the 7's are so small that even the smallest and cheapest self tailing winches will be a vast improvement.

Part No.	Model Finish	Gear Ratio	Power Ratio	Weight	D Drum Dia	B Base Dia	H Height	L Line Entry	Line Size
L49014000	14ST	1st	1st	2.3kg	65.7mm	121mm	121mm	58mm	6-10mm
OCEAN	Grey	(2:1)	(15.8:1)
	Alloy
L49016000	16ST	1st	1st	2.9kg	65.7mm	121mm	145.5mm	58mm	8-12mm
OCEAN	Grey	(2:1)	(15.8:1)
	Alloy
L49515057	15ST	1st	1st	2.6kg	66.8mm	121mm	119mm	58mm	6-10mm
EVO	Grey	(2:1)	(15.8:1)
	Alloy
L49007030	7	1st	1st	0.8kg	65mm	108mm	102mm	40mm
7	Alloy	(1:1)	(7.9:1)

The only difference I can see between the three ST winches above is the rope size that they take, and possibly a slightly lower build quality of the EVO.

My question is, does the gear ratio gives you the power ratio or is there more to it? all the ST's seem to have double the power of the 7 if I understand it correctly.
Also am I missing a specification which will sway my choice? All the PCD's are different to my 7's, grrrr.

Thanks

 

[Concerto]

A quick Google gives this result.

A sailing winch's power ratio indicates how much force is multiplied when pulling a rope. For example, a winch with a 40:1 power ratio means that a 1 kg force on the handle will result in a 40 kg pull on the rope. This ratio is determined by the winch's gear ratio and the relative sizes of the winch handle and drum.
Winches use gears to multiply the input force. A 2-speed winch has different gear ratios for different tasks. A higher gear ratio (e.g., 4:1, 6:1) means more pulling power but slower line speed. A lower gear ratio (e.g., 2:1) means faster line speed but less pulling power.
The power ratio is typically calculated as: (handle length / drum radius) * gear ratio. For example, a winch with a 10:1 gear ratio, 10" handle, and 2.5" drum radius has a power ratio of (10/2.5) * 10 = 40:1.

When I changed the halyard winches on my boat from Lewmar 16 to Antal 40ST, the difference the extra power made was amazing. The genoa winches have been upgraded from Lewmar 25 to Lewmar 43ST. This is on my 32ft Westerly Fulmar. Most of the time I can use just one hand for most tasks, but in strong wind conditions I still find using both hands on the handle is still very hard work. Always fit oversized winches if you can mount them and can afford to buy them.

 

[Gixer]

Thanks Concerto,
I did do a search, but still couldn't work out why Lewmar quoted both the gear ratio and the power ratio. They looked to be the same thing to me. Now reading again, I can see that the numbers would be different if it was a two speed winch. Makes sense, thanks.

 

[Bodach na mara]

Oh dear, a lot of confusion here which is not helped by Google getting the explanation half right but the other half completely wrong! Firstly let's dump the word "power" as it is not appropriate to either section of the discussion. There's no such thing as a "power ratio" in the basic engineering or physics discussion of machines. That comes later.

First, the tables supplied are most useful but they are confusing in that all the winches appear to have two 1st gears. The model number of each winch appears to correspond approximately to a parameter of the machine (when operated in the higher gear) which engineers and physics teachers refer to as the Velocity Ratio. This parameter can be calculated from the knowledge of the geometry and measurements of the system. This is the bit that Google got right. When teaching the subject, it is usual to consider at least 3 exemplar machines, starting with a simple lever, moving to a block and tackle system and then thinking about a gear box, winch or similar machine. The VR of a lever is simply the ratio of distances from the application points of load and effort to the fulcrum point. For a block and tackle system the VR is often the number of chords on the load block, but remarkably complex systems can be devised. For a gear box, counting the teeth on the meshing gears is required. The term VR is one that I have always hated as in reality, it not speeds that students have to think of but movements. Time, as implied by the word velocity, doesn't enter the analysis. Now the force ratio, called the Mechanical Advantage, is another kettle of fish. It is often close to the value of the VR but can only be determined by experimental measurement. In practical machines, the MA is always less than or equal to the VR. For a light lever on test the MA and VR are exactly or nearly equal but I used a demonstration 5:1 pulley system to show that, although when not moving the load was 5X the effort force, to actually move the load took a higher effort force.

Now to reintroduce power. The efficiency of the machine can be shown to be MA / VR and as MA is less than or equal to VR the efficiency is always less than 1 for any practical machine. That can be translated to say that the "Power Ratio" is always less than 1.

 

[Gixer]

Bodach na mara, thanks you so much for your detailed response.

I have to be honest and say I struggled to follow what you had written, but the block and tackle analogy really helped to make thing clearer.

Thanks again.