Pulley workload help (kayak hoist)

[chrisjpainter]

Maths and physics were never my strong points and if this goes wrong, it could see the death of my much beloved fishing kayak! With this in mind, I need some help on a project:

Due to space issues, I want to hoist my kayak on its end on the side of the house. It will be resting on the floor, but will need a pulley system to hoist it up - nose down, rudder up. So, here's my thing. I have some high quality sailing pulleys - Harken 29mm Cheek blocks - knocking around. They're small (29mm) but they have a working max strength of 150kgs. The yak's probably about 30kg. Would the stresses of raising and lowering the yak (nose on floor at all times) be too much, or is this a simple, cost effective way of raising the stern up into the vertical position? I feel like the actual working load should be less than even the 30kg, given that some of the weight is supported on the ground at all times - especially in vertical - but I may have made a complete hash of it and don't want my botched physics to break my pride and joy. Hopefully the images give an idea of the pulley element to the solution I have in mind.

 

 

 

Edited April 19, 2020 by chrisjpainter

[WalkedUp]

Should be absolutely fine.
 

The mass of the kayak is well below its bearing capacity and due to the ground pivot is never fully transferred to the pulley.

The lifting point is further from the fulcrum than the centre of mass so there is no adverse leverage. 

However to impulses, bearing capacity (n, Newtons, force) is not always directly translatable to mass (kg). If the kayak was free falling from height then an element of kinetic energy would need to be resolved by not only the pulley but also the rope and  any fixings. In your model the ability to gain energy falling is moderated by your release of the rope when lowering. In reality this is unlikely to be an issue as the boat is so light. 

[strimmer_13]

Pin it to the wall hard when it's up, nothing worse than hearing hollow plastic banging about in the slightest wind, it's like water torture to me 😅

[WalkedUp]

Good point. If outdoors two S/S eye hooks in the wall and a well tensioned bungee cord across the cockpit scoop should sort any rattling. 

[Mice!]

I would get some plastic facure boards for behind it, you don't want to be scrapping the underside of it against the house every time you put it up, take it down. 

[chrisjpainter]

Pigeonwatch wins again; thanks chaps.

1 hour ago, Mice! said:

I would get some plastic facure boards for behind it, you don't want to be scrapping the underside of it against the house every time you put it up, take it down. 

The garden hose is about fifteen times the length it needs to be, so I'm thinking of cutting some strips off and putting them in place to save the scratches. Looks like a small and unobtrusive solution has been found. 

[Mice!]

Just fix it up there with some ratchet straps save it getting blown around and the jobs a good un, hopefully 

[Modafinale]

2 hours ago, WalkedUp said:

Good point. If outdoors two S/S eye hooks in the wall and a well tensioned bungee cord across the cockpit scoop should sort any rattling. 

Please be careful with kayaks and bungee cord, in a earlier life I was doing the exact process in a Derby swimming pool after canoe club.

i thought I had hooked the bungee in the wall hook, but had not ! The energy returned hitting me in the eye and nose.

i could not see out of my right eye for a week and the pupil is still larger than my left 20 years later, broke my nose and had a nice flap of skin removed of the bridge.

so please use a strap and lock system 

[WalkedUp]

Another good point, hope your eye is ok. 

[henry d]

I can't remember the actual figures from my line rescue course but the higher up the house you have the block the less strain you put on the block and line, it's to do with angles. I'm sure if you give it a Google there will be something to explain it.

Here it is vector forces, imagine the picture upside down for your situation

Edited April 20, 2020 by henry d
Found a link

[Shufti]

Kayaks and canoes can go misshaped by gravity and/or sun.

Just saying HTH

[chrisjpainter]

4 hours ago, Shufti said:

Kayaks and canoes can go misshaped by gravity and/or sun.

Just saying HTH

True, which is why this will be on the ground all the time and will have some of its weight supported by cross beams too. It's also going down a passageway that's sandwiched between two houses and never gets the sun. It's either in the shade from our house or the house next door, so it's a good place. It'll also get a plastic covering (when I get round to working out the size I need)

5 hours ago, henry d said:

I can't remember the actual figures from my line rescue course but the higher up the house you have the block the less strain you put on the block and line, it's to do with angles. I'm sure if you give it a Google there will be something to explain it.

Here it is vector forces, imagine the picture upside down for your situation

That's really helpful, thanks. I wish I'd fought more to put a climbing wall up the side of the house, like I wanted! I could have just climbed up, hung on a rope and put the fixings in. Now it's gonna have to be a ladder job.

[Shufti]

You've got it covered , good luck with your project👍

 

[chrisjpainter]

25 minutes ago, Shufti said:

You've got it covered , good luck with your project👍

 

If you hear on the national news of a bizarre accident in Dorchester involving a kayak, a pulley and someone accidentally getting pulleyed up 20ft into the air, you'll know that I didn't!

[strimmer_13]

9 minutes ago, chrisjpainter said:

If you hear on the national news of a bizarre accident in Dorchester involving a kayak, a pulley and someone accidentally getting pulleyed up 20ft into the air, you'll know that I didn't!

Ill keep an eye in the Blackmore vale for you 😂

[chrisjpainter]

On 20/04/2020 at 17:43, strimmer_13 said:

Ill keep an eye in the Blackmore vale for you 😂

Alas, my 15 mins of fame will have to wait. She's up! And not even a little bit of bleeding.

Just the ratchet straps to fit and we're all done. The Reload's a bit of a beggar for this, because the handles are not centred; they're closer to the stern than the bow, which is totally the wrong way round! never mind. almost finished. Just need to get some of those galvanised plate rings for the ratchet straps and we're there. The hole for the tackle pod's come in handy as it can sit on a heavy duty ladder brace too.

As has the seat cushion for the sit-in-shower chair thing the previous owners left in. I took it out just before lock down, so it never made it to the dump! I've been harvesting bits off it ever since.

 

 

Edited April 24, 2020 by chrisjpainter

[henry d]

Wow, that's a tight space, well done!

[Shufti]

Cant see all, but would it fit horizontally?

Thinking ease of access...wheelbarrows etc, just a thought.....rare! 

[chrisjpainter]

On 28/04/2020 at 09:35, Shufti said:

Cant see all, but would it fit horizontally?

Thinking ease of access...wheelbarrows etc, just a thought.....rare! 

it'd be great if it could fit horizontally, but unfortunately a number of things get in the way. It's too long to fit between the side door and the passage gate and there's a drainage pipe exit from the downstairs loo that means it can't sit flush against the wall and makes it block the passage even more. I would put it on a pulley horizontally, but there's a window just at the wrong height. underneath and it's still in the way, above it and the sill would get in the way of raising and lowering it. Where it is you can still get a wheel barrow through (just) and the bins as well. The downside to owning a 15ft battleship as a kayak: storing it is a pain in the neck!

I've also flipped it the other way up now, so it's a lot more stable. The rudder is now removable thanks to a D-ring, so that just rests on the ground next to it. Next thing to get is a weatherproof cover.

[Shufti]

Yup 

PIA!.....but worth it.