boom as crane?

[FLHippy]

I've been a trailer sailor for a few years now and I've just bought a bigger boat which will be on a mooring (soon I hope).

I've got a 1970 Irwin 25. I assume the mast is original, it's 34.5 feet up there, deck stepped.

I don't plan on keeping my 7.5 4-stroke honda outboard on the boat while it's at the mooring. My plan is to use the boom to hoist the motor on/off the boat. I've got a 3/16" SS cable topping lift and a nice built in vang just under the topping lift hook which I can attach a block to get the motor on/off the boat with.

I assume the weight is focused on the topping lift cable and does not affect the gooseneck or sail track slide much so long as the weight is opposite the topping lift cable connection??

Should I be concerned about the weight of the motor on the boom when using it as a crane like this?

What is the maximum reasonable weight I can expect to lift when using my boom as a crane? Can I assume the boom will support the cable's rated weight limits without problems?

Thanks in advance.

 

[tommays]

Are you sure the toping lift is 3/16 wire as thats really BIG and rated at thousands of pounds ?

 

[druid]

I'd say No Problem. I used the boom to move rolls of roofing material from the cockpit to a dinghy - worked really well! You probably exert more force on the backstay when you snug down the mainsheet than a 7.5 outboard is gonna put on it.

If you're nervous about it: 1) try hanging from the end of the boom yourself. You probably weigh more than an outboard. and/or 2) hook the main halyard to the end of the boom as well - it will easily take a few hundred lb.

druid

 

[Ron20324]

I put a large boom bail on the end of my boom for just such a purpose as yours- a crane. Your system would/should be stout enough to lift MOBs out of the water.

 

[DougM]

I've used my boom to move the dinghy outboard from the rail mount to the seawall. It's an 8hp Yamaha 4 cycle that weighs about 80 lbs. No problem. The topping lift is strong enough. I can get additional lift by disconnecting the vang, and by running a halyard through a snatch block on the boom, I can further raise and lower a load.

I've seen my neighbor use his boom many times to hoist his inflatable out of the water, and also to move batteries from the seawall to the boat and vice versa.

 

[Scott]

Druid - Uh, I am really curious . "I used the boom to move rolls of roofing material from the cockpit to a dinghy - worked really well!"

 

[Ross]

I have a boom gallows and no topping lift but my main halyard serves perfectly. I have a friend that used his boom to hoist a Yanmar 10 hp engine into place from the ground. A come-a-long and a little ingenuity can go a long way.

 

[kloudie1]

some quick and dirty example numbers.. if the top of the mast is 34 feet from cabin top and the boom is 2 feet higher than the cabin top, assuming the boom is 8 feet long, the compression load through the boom and gooseneck is 61 pounds with a 250 pound guy hanging from the boom tip. Not a problem for a reasonable gooseneck.
Shorter distance from boom to top of mast is worse as is longer boom. At very high loads, you could ding the mast at the gooseneck attachment point..

 

[kloudie1]

Ohh I meant to add.. 3/16 stainless cable has a listed breaking strength of 3700# so for a safety factor of 4, max load should be limited to about 900# .. For practical purposes, I would limit the load to 250 max, or pretty close to that IF the connections are in good shape.. that is close to the load that ya get when you sheet in the traveller hard, beating up into a 20 kt breeze..

 

[Hermit Scott]

Druid - Uh, I am really curious . "I used the boom to move rolls of roofing material from the cockpit to a dinghy - worked really well!"

Druid was putting a new roof on the cabin. Duh!

I am thinking as long as your connection point for the force downward(motor) is directly below the topping lift than the force on the boom is only in compression toward the mast. And that component of the force is only a small percentage of the force of the motor. Jsut make sure all your connections are strong.

 

[Sumner]

I've made a hoist using the mast support for our trailer-able Mac to lift the main outboard on and off the transom and the dingy outboard (shown above) on and off its mount up on the pushpit.

The details are here.....

http://purplesagetradingpost.com/sumner/macgregor/outside-16.html

Let us know how what you have in mind works out,

Sum

Our Trips to Lake Powell, UT - Kootenay Lake, Canada - Priest Lake, ID

Our Mac Pages

Mac Links

 

[RichBone]

It seems to me that the boom would have to be long enough for the aft end to be over the outboard to be able to lift it. And you'll be doing this in a dinghy. 85# of awkward deadweight can get pretty hard to handle.
Why do you want to remove it?

Rich

 

[Maddog]

I do this all the time, no problems with a 75# OB. I rigged a block and tackle for hoisting. I hold the line, wife swings the boom, son guides the OB onto the digny. We do it all in about 5 mins.

 

[Nereussailor]

Druid - Uh, I am really curious . "I used the boom to move rolls of roofing material from the cockpit to a dinghy - worked really well!"

Yeah, Me Too. You building an outhouse on the boat?

Dave

 

[FLHippy]

Why do you want to remove it?

RBone, I want to remove it because people steal small outboards left on sailboats and also because it's what powers my tender to the mooring and back.

Thank you everyone for your replies. Thank you very much.

 

[Joe]

no problem...... cruisers do it all the time.... It's also a good way to get MOB back in the boat.

However, why don't you just get a length of chain and secure the motor to the boat and save the hassle. Mine is secured to the rudder post, you may have to use something else.

 

[zeehag]

i used my boom on my formosa to lift the old engine block out of the saloon.....should be able to lift what you want to lift----cannot weigh as much as the weight o0f the sails with a gooood gust in them......LOL