Winches

Build Your Own Anchor Winch

Step #1 Get an Example

A ratchet pawl on the far side
prevents backwards travel.

Brent Swain has a design for a simple anchor winch in his book, and it's a perfectly good design for the most cursing boats but as RV Seeker is more work boat than cruising sailboat, I want a winch that has a few more capabilities, but I still don't want one of the fully electric or hydraulic commercial units you see on trawlers. Besides, we can't afford one of those anyway.

Out in my front yard was an example of a two speed manual trailer winch that will serve as a model for our anchor winch. The handles shaft can slide sideways when the latch on the left side is up. The small gear on the handle's shaft is either neutral, high speed or low speed. Spool gear: 42 teeth, Jack shaft gear; sm: 14, lg: 26. Crank: 9

The crank handle shaft can slid sideways when to lever on the opposite side is lifted.	The handle shaft is slid to the center position so the gear on the handle shaft is not engaged. This is the neutral position.
With the handle shaft pushed all the way in, the gear on the handle shaft is engaged in the high speed position.	Moved all the way to the right, the gear engages with a jack shaft with the low speed gears.

So the plan is to draw a plan based on the two speed manual winch that is on lots of boat trailers, and building something similar but much bigger with the addition of a crude brake and the possibility of powering it with an gear reduction or hydraulic motor. We'll have two of these units on the bow. The second will have smaller cable.

The boat winch reduction gear reduction calculates as follows: Spool gear: 42 teeth, jack shaft gear; small: 14, large: 26, and the crank has 9 teeth. So high speed is; 42/9 = 4.66 to 1. And low speed is 42/14 * 26/9 = 8.66 to 1.

3/4 " Cable Capacity
	Feet	Feet	Feet
	on	in	off
Layer	winch	layer	winch
16	621	56	0
15	565	55	56
14	510	51	111
13	459	50	162
12	409	47	212
11	362	45	259
10	317	42	304
9	275	40	346
8	235	38	386
7	197	35	424
6	162	33	459
5	129	31	492
4	98	28	523
3	70	26	551
2	44	23	577
1	21	21	600

Example of a narrow spool that
allows the cable to neatly layer
on without assistance.

Step #2 Drum Design

A really helpful tool is the Drum Capacity Estimator at: www.ingersollrandproducts.com/lifting/winches/drum.htm We want to be able to carry 500 feet of 3/4" steel cable on the anchor winch that will give us over 25 tons of working load. Our drum turns out to be tall and thin, mainly due to the distance between the bow and the drum which is about 8 feet. The drum will be: (A) 12 x (B) 36 x (C) 5.5 inches and carry a working load of 500+ feet of 3/4" cable. The details for the spool's capacity are listed in the chart, '3/4 " Cable Capacity '.

Step #3 Spur Gear Design

Forest Moon offers a free program for generating DFX files for specified Spur gears: www.forestmoon.com/Software/GearDXF Or you can use http://woodgears.ca/gear_cutting/template.html online application if you can convert from HPGL. If you'll need ring, rack or pin gears then for $26 you can get the full downloadable version of the Gear Template Generator program from http://woodgears.ca the outputs to DFX. I got the Gear Generator program from http://woodgears.ca because it will do inner ring grears, but the current version (2.05) calculates diametric pitch (DP) incorrectly, so if you need to covert DP to Pitch Diameter (PD) which is simply PD = Number of Teeth / DP. It also generates teeth with no Dedendum. So the best course of action is to generate all of your gears with the same program to help insure they work nicely together.

Need a quick lesson on gear ratios? See: http://www.teamdavinci.com/understanding_gear_reduction.htm
Gear Formulas: www.engineersedge.com/gear_formula.htm
PD = Number of Teeth / DP
DP = Number of Teeth / PD

Version #1	Version #2
40 ton holding, 7 ton pulling 18.57:1 ratio Nabrico winch. 12.75" D x 11.25" W drum holds 176 ft of 3/4" cable.

Version #3

Version #1

The first step is to simply scale up the boat winch design so that it fits on the the 36 inch tall drum for the cable. We also adjusted the reduction ratio to favor more power. Normally only 200 feet of cable will be used which is only the first 4 layers of cable on the spool, with about 50 feet and 7 (5.5/.75) wraps per layer. With a 5 to 1 drive with the high speed gears it will take about 7 wraps x 5 times gear reduction x 4 layers = 140 turns of the crank to real in 200 ft of anchor rode.

The maximum load on the boat winch is about 2000 pounds. The working load for 3/4" steel cable is about 12,000 pounds (Source). The boat winch handle is 7 inches long, 2000/7/12 = 23.8 foot pounds. With a 19" handle on the upscale winch it would be about: 12,000/19/12 = 52.6 foot pounds; doable but not easy. 35 pounds is considered the maximum recommended force to move a helm.

Version #2

Close to the same reduction ratios can be achieved with proportionally smaller gears which save weight, steel, and room. And another gear can be added that will allow a motor to dive the winch as well as the hand crank.

Another Example

I found a rebuilt Nabrico 40 ton winch for $2,800. These are mainly used a towing winches that raft together barges. It has a 7 ton pulling capacity with the 18.57:1 reduction.

Version #3

A hand wheel was added and the gear ratios changed to provide more power. The hand wheel is also an internal ring gear that can be optionally powered by a hydraulic motor. Turning by hand the high speed is 6:1 and the low speed is 36:1. So it will take 42 turns ( 6 x 7 warps) to pull in about 50 feet. In low speed, it will be able to pull with more that 7 tons for force.

Calculating a Bearing

Bearing performance is measured in pressure and velocity or "PV".
Solving for a working load of 10 tons on a 3" shaft with a 6" bearing (3" on each side) turning at 60 rpm:

V in feet per minute = 0.262” x RPM x diameter
                               = 0.262” x   60 (rpm)   x     3" (shaft)
                               = 47.16 fpm
P = total load / ( shaft diameter x bearing length )
   = 20,000 lbls / ( 3” [shaft] x 6” [bearing length] )
   = 20,000 lbs. / 18 sq in
   = 1,111 psi
PV = pressure x velocity
      = 1,111 psi x 47.16 fpm
      = 52,394

You can also use Oilite's bearing calculator: http://www.oilite.com/bearingCalc.asp You can increase the area to reduce the PV if needed, but anything under 75,000 will not be hard to find if the P is under 4000 and V is under 500. See: www.buntingbearings.com/data.html for some ideas.

Add a Motor?

The path of that 19" handle makes a circle with a circumference of about 119 inches ( C=dPi, 19 x 2 x 3.14). If we added a great that size it would have 108 teeth on it and it could be driven by a 16 tooth gear. A 2 hp DC motor from a treadmill is going to spin at about 4500 rpm. The large crank gear will then move at 666 rpm ( 4500 * 16 / 108 ). That's about 10 turns per second! Way too fast. So we need more gears and the best answer is likely a planetary gear set like is found on off road automotive winches. Harbor Freight has a 5000 pound winch with a 294 to 1 planetary gear set and a 3.4 HP, 12 volt motor. With a line speed of 5.3 ft. per minute off a drum that is about 6 inches in diameter the RPM is about 33 ( 5.3 * 12 / 6 * 3.15 ). If we added an 8.5 inch diameter, 24 tooth spur gear to the drum and mesh that with the 80 tooth gear on the anchor winch drum, then the anchor winch drum would spin at under 10 rpm ( 33 * 24 / 80 ). Pulling in about 200 feet of rode in 3 minutes. ( 7 wraps * 4 layers / 10 rpm)

Resources

Drum Capacity Estimator: www.airwinch.com/tools/drum.htm
Example: http://motivationdocksupply.com/winches/hand-winches.php
Brands: Beebe, Tulsa, Braden, Garwood, Hyster, Thern, Nabrico