# Slipway Winch

Discussion in 'Boat Design' started by abohamza, Jul 30, 2011.

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### abohamzaJunior Member

What is the minimum winch power required to pull a fishing boat 350 ton dead weight docked on marine railway?

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### judgegageJunior Member

This is from a website about vehicle recovery, it's very in depth and applies to winching and hoisting. Very good info. http://www.pirate4x4.com/tech/billavista/Recovery/

Surface resistance
A pull of 1/10 LW (Loaded Weight=Total Weight) will cause a free wheeling truck to move on a hard, level surface.

A pull of 1/3 LW will cause a free wheeling truck to move on a softer surface, such as grass or gravel.

15 degrees - add 25% of LW

30 degrees - add 50% of LW

45 degrees - add 75% of LW

Vehicle recovery on level ground - no correction

15 degrees - subtract 25% of LW

30 degrees - subtract 50% of LW

45 degrees - subtract 75% of LW

Hope this helps.

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Quick googling brought out this formula, which should apply if there is no friction (there always is, but on a railroad track type surface it is negligible).

M*G*sin(angle)

in which:
M = mass in kilograms
G = Earth gravity (9,8N)
sin(angle) = sin times the angle of the ramp

Double the result to be safe.

Lurvio

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### abohamzaJunior Member

Marine slipway winch

Thanks for reply ,I need to find the optimum winch power for the attached slipway;as an example.

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5. ### FrostyPrevious Member

Its the gear ratio that does it.

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Method.

Dear,

You need to exceed a pull speed of 3-3.5 cm/sec. (0,03 m/sec to 0,035 m/sec)
That means 1,8m/min to 2.1m/min or better 108m/hour to 126m/hour.

You need to install four (4) Wire Ropes - two (2) at Fore and two (2) at rear of the launching cradle PORT and STBD.
The wire ropes should be 40mm dia. And the two (2) winch drums for this rope should have a diameter not less than 0.75 m and not more than 1m Core Cylinder.

The applied Total Force to the launching cradle should not be less than 95 tons. (about 931.000 N).

The minimum Power should be 931.000 N x 0.035 m/sec = 32.5 kW x Safety Factor = 32.5 x 1.75 = 57 kW or 77.5 Hp (metric).

I suggest to install a eight(8) pole motor at 750 rpm / 50 Hz.
And the Reduction gearbox should have four stages and a total reduction ratio at 640:1.

You have also to install a Friction Disks Type Coupling between the Electric Motor's Output Shaft and the Input Primary Shaft of the Reduction Gear to success a gradual engagement of the Motor's Torque.

I hope that helps you to understand the size and the corners of what you were asking ....

If you need more informations you must give your winch data to have an estimation regarding the specific case and specially the inclination value of your rails and the dimensioning plan of your launching cradle as well.

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### abohamzaJunior Member

Dear,

Thanks, I would like to know how can I estimate that "The applied Total Force to the launching cradle should not be less than 95 tons".let me say that the railway slope is 4.5 degree ;is it affecting the estimation?

Abohamza

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### BATAANSenior Member

I used to work on a railway that hauled 400 ton vessels and we used a Ford V-8 engine hooked to the ancient winch. Remember, railways used to be powered by a big block and tackle (a couple of 4 sheave blocks) led to a capstan which had a long lever and a horse walking in circles.
A 1 hp railway will work if the gradient is low and mechanical advantage high.

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General

Dear,

On a rail level at 4.5° and a Ship weight of 350t we find two components forces.
1. Parallel to the rail level Fr= Weight x sin 4.5° = 27.46t directed to the sea side.
2. Vertical to the rail level Fv= Weight x cos 4.5° = 348.92t
The Vertical Component Force Fv is involved to Friction Resistance.
The Friction coefficient of Wet Wood without grease (worst case) is 0.2
The Resistance Force due to friction effect is F friction = Fv x 0.2 = 348.92t x 0.2 = 69.78t.
The Applied Force on the launching cradle that should be exerted from the Winch will be equal at least to Fwinch = F friction + Fr = 69.78t + 27.46t = 97.24 t.

Of course the launching cradle is greased that decreased the friction coefficient to 0.1-0.12
and at the selected Power of the Electric Motor we calculated with a Safety factor at 1.75

I hope all of that are useful for your case.

Please also see the attached file to have a graphic view for the case.

#### Attached Files:

• ###### Shipyard Abohamza.pdf
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10. Joined: Jul 2009
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To me it looks like there is a huge amount of rollers under the cradle. So the friction part is way smaller.

L

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### abohamzaJunior Member

Dear,
Please find the attached calculator for the results.

abohamza

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12. ### FrostyPrevious Member

By the time you've worked it all out and chewed the end of your pencil off I could have had it built.

Go look at the guys next door, is a fail proof method, bit of industrial espionage is Ok.

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### BATAANSenior Member

Not rocket science. A couple of large steel 3 sheave blocks, a lot of 1 1/4" wire rope, led to a ship's old deck winch with a car engine attached, at least 100 hp. Hauled vessel to 400 tons on this rig at a 1:12 slope. Don't forget the single sheave downhaul block in the mud below low tide. The car doesn't always go down as easily as you would expect.

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### abohamzaJunior Member

Dear Sir,

abohamza

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### abohamzaJunior Member

Dear BATAAN,

thanks,"Don't forget the single sheave downhaul block in the mud below low tide" is an important point to consider because the project will be in a country of considerable tide.

regards,

Abohamza

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