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-   -   Redneck engineering / boat lifting suggestions needed (https://www.thehulltruth.com/dockside-chat/1102781-redneck-engineering-boat-lifting-suggestions-needed.html)

FinReaper069 07-24-2020 02:50 PM

Redneck engineering / boat lifting suggestions needed
 
Here is the situation, it is what it is and not what I would have done, I would have installed a boat lift, but it’s what I have to work with now. Have a house in the Keys that has 15,000 lb davits and a small aluminum cat I want to launch. The previous owner had a 28’ boat, so the davits are set up and spaced about 30’ apart. Since this is a vacation home that is used by myself for one weekend a month and two stays for one week each during the summer, I am trying to come up with the cheapest, easiest method.

I have an 18’ aluminum cat with a 70 hp on it, weighs less than 1,500 lbs total, so not a huge boat or amount of weight. The house is elevated and I can park the boat/trailer under the house while I’m not there. There is street to water access with plenty of room around the davits to maneuver a trailer. Currently, I have to pull the boat to the nearest ramp (about 10 minutes by road), launch the boat and drive it back to the house and have someone drive the truck/trailer back as it’s a community ramp and no room for parking. Have to repeat to put the boat away, do able, but realistically It takes about an hour to launch or retrieve and I can’t do it by myself.

I would like to be able to use the davits to launch/retrieve the boat from the house and cut out the ramp all together. I have a small Kubota tractor I was getting ready to sell, but it has a 3 point hitch on it and I could leave it down there to easily move the boat around.

Here are my redneck engineering thoughts that I need help with. First, I could pull the boat along side the davits and use them to lift it off the trailer and swing it out over the water, but the boat is only 18’ long and the davits are much further apart than that, so I’m afraid instead of the davits having a straight up and down pull (or close to it) the cables are going to be coming from an angle and possibly putting stresses on the boat it wasn’t designed to handle (pulling forward/backward and up), rather than pulling it more straight up and down.

My first thought was to make a cradle like they use in the dry stacks for cats, basically 25’ or so long aluminum I beams that are connected together that could be lowered into the water, the boat floated over and then the cradle with boat on it lifted up. If I went this route, I would just set the boat and cradle on the ground and that’s where it would stay rather than on the trailer under the house.

My second thought, since there is room to move the boat forward on the trailer so the transom is forward of the rear cross member of the trailer. Pull the trailer under the davits, hook the one davit with the spreader bar to the rear corners of the trailer and hook the other davit to tongue and drop the whole boat/trailer into the water and submerge the trailer deep enough to float the boat and reverse the process for retrieval. Plenty of clearance and depth to do that. Rinse the trailer off and park it back under the house when I leave.

Launching and retrieving from the davits can be done by myself, which should make it quicker and easier since I won’t have the ramp/truck logistics......although my wife is great, when I’m ready, it may be another 10-15 minutes or longer until she is ready or available, which eats up even more time and its not exactly what she wants to be doing.

Any thoughts, ideas or suggestions? Anyone want to volunteer to hold my beer the first time I try it?

dev 07-24-2020 03:00 PM

No good suggestions, but please let me know when you try whatever ideas you get, I want to watch that.

mikefloyd 07-24-2020 03:12 PM

I would do it right by installing a lift or use the ramp.

Kaper 07-24-2020 03:20 PM

Do you have enough clearance to use rigging beam?

FinReaper069 07-24-2020 03:29 PM

Not sure what a rigging beam is, but there is pretty much unlimited space around them.....sea wall and water on one side and nothing within 20í in any direction on land, clear sky above them.

mwgoldman 07-24-2020 03:31 PM

You could use a single davit instead of both of them. One strap to the front and 2 to the back or better yet get an I beam with one strap on one side and 2 on the back. Tie a line to the bow to control the swing. And youíre done. Plenty of single davit examples out there.

FinReaper069 07-24-2020 03:35 PM


Originally Posted by mikefloyd (Post 13887271)
I would do it right by installing a lift or use the ramp.

If it was going to be there more, a lift would be an option......but with the cost of the lift and the amount f times I would use it in the next 5 yrs, it would probably work out to well over $100 per use and thatís not happening. Ramp is used for now, but time consuming and a pain when your only there for 30-40 hours from time of arrival to departure.

Boats are lifted all the time by three points on a davits, why couldnít a trailer or cradle That is far below the davits lifting capacity be lifted that way? 15000lb davits and boat/cradle or boat/trailer combo would be probably less than 2000 lbs, 2500 Lbs at the most. Could also put a spreader bar on each davit so itís lifted by four corners and not three points.

Just throwing around ideas and what ifs.....

BLUESMAN 07-24-2020 03:41 PM

If davits are in good shape, Iíd set up a lifting beam and just use one davit. What is weight of 18í boat, 3000#?

FinReaper069 07-24-2020 03:41 PM


Originally Posted by mwgoldman (Post 13887336)
You could use a single davit instead of both of them. One strap to the front and 2 to the back or better yet get an I beam with one strap on one side and 2 on the back. Tie a line to the bow to control the swing. And youíre done. Plenty of single davit examples out there.

Never thought of that, just assumed Utilizing the two davits would be better than one.

Iím guessing if using one I beam lengthwise above the boat, the davit cable would have to be attached closer to the transom since itís heavier to keep the boat level....seems if it was placed in the middle, the transom would want to go down while the bow went up.

FinReaper069 07-24-2020 03:43 PM


Originally Posted by BLUESMAN (Post 13887361)
If davits are in good shape, Iíd set up a lifting beam and just use one davit. What is weight of 18í boat, 3000#?


Less, itís an aluminum boat...hull is 1,050 lbs and motor is 250íish. Iím guessing 1,500 lbs with batteries, portable gas tank, etc.....

evernic 07-24-2020 03:45 PM

How much for a third davit. One with weight capacity you need, mount it 18 feet from one of the others, right size for your boat
Iím a Virginia red neck 😊

autobaun70 07-24-2020 03:50 PM


Originally Posted by FinReaper069 (Post 13887351)
If it was going to be there more, a lift would be an option......but with the cost of the lift and the amount f times I would use it in the next 5 yrs, it would probably work out to well over $100 per use and thatís not happening. Ramp is used for now, but time consuming and a pain when your only there for 30-40 hours from time of arrival to departure.

Boats are lifted all the time by three points on a davits, why couldnít a trailer or cradle That is far below the davits lifting capacity be lifted that way? 15000lb davits and boat/cradle or boat/trailer combo would be probably less than 2000 lbs, 2500 Lbs at the most. Could also put a spreader bar on each davit so itís lifted by four corners and not three points.

Just throwing around ideas and what ifs.....

what you are suggesting is an overly complex way to save a few bucks, in relation to what you have invested overall.

Kaper 07-25-2020 07:55 AM


Originally Posted by FinReaper069 (Post 13887327)
Not sure what a rigging beam is, but there is pretty much unlimited space around them.....s


Originally Posted by BLUESMAN (Post 13887361)
If davits are in good shape, Iíd set up a lifting beam and just use one davit. What is weight of 18í boat, 3000#?


Originally Posted by FinReaper069 (Post 13887364)
Never thought of that, just assumed Utilizing the two davits would be better than one.

Iím guessing if using one I beam lengthwise above the boat, the davit cable would have to be attached closer to the transom since itís heavier to keep the boat level...

Rigging beam, lift beam etc, I think you got it now. I was asking for vertical clearance as lift beam will take up some of vertical raise.
Yep, use single davit and you would balance attachments on lift beam depending on the boat center of gravity.

kmagnuss 07-25-2020 08:27 AM

https://cimg3.ibsrv.net/gimg/www.the...35bf5d03e9.jpg

Originally Posted by mwgoldman (Post 13887336)
You could use a single davit instead of both of them. One strap to the front and 2 to the back or better yet get an I beam with one strap on one side and 2 on the back. Tie a line to the bow to control the swing. And you’re done. Plenty of single davit examples out there.

This....
You can figure out a way to get the load perfectly balanced by using a couple nuts on some threaded bar in the middle so you can adjust your lifting point. Look at engine lifts (cherry picker) for a reference.

tommyjones 07-25-2020 09:43 AM

This is how I set my davit up to lift my duck boat. It is coated 1/4 inch cable with appropriate fittings. I used thimbles and swagged connectors for the cable. I added a section of chain to the front cable to allow my to fine tune the balance. I also use it To accommodate the change in CG when my boat blind is on her.
the white cylinder is just a weight to keep tension on the cable when the boat is not being lifted.
https://cimg9.ibsrv.net/gimg/www.the...daf793a2f.jpeg

my davit rotates, so if I want to put the boat on the trailer I just back the trailer over, spin the davit and winch the boat to the front of the trailer as I lower it.

OldPete 07-25-2020 09:53 AM

Pay no mind to the tools on here with nothing to offer. That's just typical THTism.

Two different ways to do this.

A) Put a beam across to both lifts, then rig spacing on beam for two new lift points. This is the probably the "strongest" and "safest" way to do it - if done correctly.

B) Just use one lift and get the cable distances right so that things are balanced.

I'd do the beam method...

OldPete 07-25-2020 09:57 AM

https://cimg6.ibsrv.net/gimg/www.the...e75f62d8f.jpeg

MikeeBooshay 07-25-2020 10:06 AM

Here you go - showing how to lift a small boat with a lifting beam and single davit, in a storm nonetheless.


https://cimg3.ibsrv.net/gimg/www.the...4b8ae56d84.jpg
https://cimg5.ibsrv.net/gimg/www.the...a02b2ce7ed.jpg

Pretty sure that these skiffs weigh a lot more than your rig, took about 30 minutes to load six of them in the rain.

Problem using two davits, is coordinating the use of both of them together. I do a LOT of rigging on a pretty much career long basis, unless you have help ( and sounds like sometimes you don't ), running between two sets of controls, or keeping two sets coordinated, can be a hassle. A single 15,000# davit should pick your boat up full of water no problem. Then just build a simple cradle on land to leave the boat on, problem solved.

SeaCat22 07-25-2020 10:20 AM

A couple of things to consider when designing your rigging and davit use.
Cranes and lifting booms don't like to be side-loaded. Try and keep the load as directly under the boom tip as possible.
Consider the CoG and rotational forces when attaching rigging to the load. Low attachment points in relation to the CoG increase rotational forces.
The critical angle for bridles is 120deg. At this angle, your attachment points and rigging see 100% of the load. It increases a lot as the angle widens.
Use appropriate shackles, slings and rigging hardware.
If using wire rope and making your own terminal connections, never saddle a dead horse with the clamps.


SeaJay 07-25-2020 10:33 AM

Real rednecks (Bobby Joe, Skeeter, Bubba, etc.) Would get their buddies, pick a lil 1,500 pound boat up and place it in the water. Dropping it 6 or 8 feet into the water would be of no concern to those characters.


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