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Old 02-12-2012, 12:35 PM   #1
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Increasing Boom Swing for Dinghy

I have a wooden mast and boom on my trawler. I use it to move the dingy on and off the deck. My problem is that I dont have enough boom swing for the dingy to clear the rail. I have to put the dingy on its side to lower it to the water. Due to this issue I cant have the motor on when lifting and lowering.

My plan is to splice 24" onto the end of the boom using the same techniques that they use when building mast made of multiple pieces of lumber, random splice and epoxy.*The second part of the project is to move the mast stays forward about two feet. This will improve the swing so the boom extends over the rail. I have looked a GB 42 aft mast stays and they are almost vertical with the mast. I dont think the aft stays have much load and believe it will be ok to move mine forward. The last item will be to install a small sailboat wench to the mast to manage the lines.

I would appreciate any ideas, insights, experience or are you nuts" input I can get.
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Old 02-12-2012, 12:59 PM   #2
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RE: Increasing boom swing for dingy

You could always replace your existing boom with an aluminum one piece section or 2 piece-sleeved*so*you get the 2 feet you need (6 feet sleeve should get you the 2 foot extension).* When you aren't hoisting the dinghy you could slide it back to it's original length.* Panted white, I'm not sure you would know it's not wood once your off the boat.
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Old 02-12-2012, 01:11 PM   #3
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RE: Increasing boom swing for dingy

Dave:

Now is the time for you to ditch that anachronistic wooden mast and get yourself into the 20th century. Your boat is far too new to use old technology for lifting your dinghy. You also should look at relocating your mast to the lower deck, with an attachment to the flybridge floor for bracing. Then you could remove all of the stays, as the mast would stand up on its own. For lifting a heavy load, like a dinghy with outboard, the stays can be attached during the lift. You should design the boom to reach 6" past the centerline of the dinghy when sitting in the water at the side of your boat. then you can lift it strait up, with the boom flat and at right angles to the boat. the mast head should be tall enough so your lifting lines form at least a 45 deg angle from the tip of the boom to the attachment on the mast. Your existing geometry won't allow that if all you do is extend the boom.
I changed my mast from a purely decorative one when I started bringing a Laser along. 150 lb, for which I don't need stays on the mast. Any heavier I would rig temporary stays. I had the whole thing fabricated for about a boat unit, about 15 yrs ago. I no longer bring the Laser along, and now the mast also carries the Radar.
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Old 02-12-2012, 01:29 PM   #4
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RE: Increasing boom swing for dingy

Larry,I considered shifting to an aluminium boom and believe I can pick up a broken sail boat mast that would do the job. I am still considering it.

Dave

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Old 02-12-2012, 02:52 PM   #5
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RE: Increasing boom swing for dingy

I agree with Larry regarding the aluminium. Check this link:https://www.onlinemetals.com/merchan...=74&top_cat=60

You can get a new boom for less than $80. A bit of paint and a few holes and voila.

As for the stays, all the load will be put on the forward ones so I don't think moving the aft ones forward will cause any problem. They are there mostly to keep the mast centered in your case.
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Old 02-12-2012, 02:57 PM   #6
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RE: Increasing boom swing for dingy

If you elect to stay with wood, I wonder if simply fabricating a new boom from a new full-length spar of the proper wood would be a better and easier option in the end than doing some sort of splice. Our boat has its original wood mast and boom and we see no reason to change it. Aluminum has its advantages but it has some disadvantages, too. Were we starting from scratch with no mast and boom at all we would probably elect to go with an aluminum rig, but if a wood mast and boom are in good condition, as ours are, I see no value in replacing it for the sake of replacing it.
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Old 02-13-2012, 03:19 AM   #7
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RE: Increasing boom swing for dingy

Aluminum has its advantages but it has some disadvantages,

Any lines that are attached may be vibrating in a breeze , and the tube will ring like a bell.

IF there are no internal lines , a spray can of cheap home foam will cure the problem.
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Old 02-13-2012, 08:13 AM   #8
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RE: Increasing boom swing for dingy

Keith, what is the basis for the "6 feet past the cenetrline on the dingy"? My current boom is 107" and only reaches the edge of the handrail with the current stay configuration. I am proposing a 131" boom that will get me a few inches of*clearance when I lower the dingy over the side. Your 6 foot suggestion would put my boom length at 159". A boom that long would stretch 2 feet has the transom. My boat has a 14' 6" beam.

Dave
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Old 02-13-2012, 10:43 AM   #9
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Increasing boom swing for dingy

Dont make it more complicated than what it is by changing the position of the stays. If you change the position of the stays you may have to change/strengthen the backing plates/roof.* That could become expensive and complex.* The best is to increase the boom by either a new boom or increasing the length of the boom.* The boom could be extended by a sleeve.** However the sleeve has to cover/slide over old boom about equal amount of the extension, so to lengthen 2 ft then a 6 ft would be needed.*
*
Also keep in mind the further out the boom, the bigger the angle the larger the force.* It takes less force to lift straight up and down then to lift the weight further out.* So dont lengthen the boom to much as it changes the forces. ***Also*Tube is*make in thin and thick wall tubing as aluminum does bend quite a bit so you might want to go with thick wall.* I replaced our old wood mast with 4 thick wall round tubing.* Round is stronger than square.**I did increase the size of the backing plates*as they where marginal.*****
*
So dont start changing to many things as its more complex than it seems.*


-- Edited by Phil Fill on Monday 13th of February 2012 01:13:08 PM
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Old 02-13-2012, 10:56 AM   #10
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Increasing boom swing for dingy

Quote:
fryedaze wrote:
My current boom is 107" and only reaches the edge of the handrail with the current stay configuration. I am proposing a 131" boom that will get me a few inches of*clearance when I lower the dingy over the side.
*The boom on our boat does as* you describe above--- in its horizontal position and 90-degrees out to the side it puts the inboard gunwale of the sailing dinghy we carry on the aft cabin top a couple of feet away from the hull of the boat.

One thing to keep in mind is the weight of the dinghy you will be lowering.* The mast and stays have a rated load strengh.* The load on the mast and stays will be the greatest with the boom straight out from the mast at 90 degrees.* In the case of our boat with its wood mast and boom and only two stays, the boat's original owner's manual calls out a maximum load of 200 pounds.* Anything more than that and the integrity of the mast and stay hardware is at risk.

Our little Montgomery 7-11 sailing dinghy weighs less than 200 pounds but not much less. So we're probably very close to the stated safe maximum load for our mast and boom rig when we launch it.

Extending your boom will also increase the leverage and thus the pressure a load on the end of boom puts on your mast and stays.* So you want to make sure that whatever you do,* the weight of the dinghy you are launching does not exceed the safe maximum load your mast, stays, and stay attachement hardware can accomodate.

I suspect there are some pretty basic forumulas that can be used to determine that with x-weight suspended from a boom of y-length that is attached to a mast z-high, the load on the mast and stays will be whatever.* But they are not formulas I ever learned, or else I didn't pay attention that day in physics class.* But if might behoove you to find out what they are so that you can calculate if your idea will safely work with your dinghy before you start cutting things.





-- Edited by Marin on Monday 13th of February 2012 01:00:17 PM
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Old 02-13-2012, 12:22 PM   #11
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Increasing boom swing for dingy

You could replace the aft stay attachment setup with pelican hooks (or something else workable) rated for the safe working load. This would allow you to quickly "loosen" the stay to the side you are working from (it's not being used anyway). That may allow the boom to swing far enough for you to raise/lower the dingy )I have to tip mine a bit too...but not so much to sink it putting it in.


-- Edited by psneeld on Monday 13th of February 2012 02:23:18 PM
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Old 02-13-2012, 02:53 PM   #12
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RE: Increasing boom swing for dingy

Quote:
fryedaze wrote:
Keith, what is the basis for the "6 feet past the cenetrline on the dingy"? My current boom is 107" and only reaches the edge of the handrail with the current stay configuration. I am proposing a 131" boom that will get me a few inches of*clearance when I lower the dingy over the side. Your 6 foot suggestion would put my boom length at 159". A boom that long would stretch 2 feet has the transom. My boat has a 14' 6" beam.

Dave
*Dave, I think Keith said 6 INCHES (") to give you 1/2 ft rail clearance when lifting up the side of the boat.
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Old 02-13-2012, 03:26 PM   #13
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RE: Increasing boom swing for dingy

Thanks Scott, thats an excellent solution. The starboard aft stay isn't loaded when I use the boom and mast as a lifting rig. You probably saved me some time and $$$$ on this.
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Old 02-13-2012, 03:52 PM   #14
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RE: Increasing boom swing for dingy

Dave:

I said ", not '.

Ideally, you would have an engineer give you the safe working load for your design. The first step, short of that, would be to wander the marina looking at what works for others. The most important thing for you is to increase your lifting capacity at a reach that will allow you to lift your present dinghy. You will need to know its weight, with all of the junk that might be left in it. To get that capacity, ideally you will raise the fastening point on the mast by more than the extra reach of the boom. So your proposed 24" boom extension will require a mast at least 24" taller. Otherwise you decrease the angle of lift and increase the force exerted on the upper part of your mast, and on your stays. If you really want to go for it, I would recommend increasing your mast height by at least 4 feet, thus decreasing the forces on the upper part of the mast and decreasing your dependence on stays. When I redid mine, the mast height went up 4' and down 2.5', as I moved the base to the lower deck, so I got an aluminum pile that was 6.5' longer than the old, useless one. I extended the boom so that instead of being unable to lift a Sabot out of the water without scraping it up the side of the boat, I could lift a Laser without touching, even with people running around, rocking the boat. Mine is also without stays, which in the original, crossed the ladder to the flybridge just at neck height, a major irritant.
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Old 02-13-2012, 04:18 PM   #15
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RE: Increasing boom swing for dingy

Quote:
koliver wrote:
Dave:

I said ", not '.

Ideally, you would have an engineer give you the safe working load for your design. The first step, short of that, would be to wander the marina looking at what works for others. The most important thing for you is to increase your lifting capacity at a reach that will allow you to lift your present dinghy. You will need to know its weight, with all of the junk that might be left in it. To get that capacity, ideally you will raise the fastening point on the mast by more than the extra reach of the boom. So your proposed 24" boom extension will require a mast at least 24" taller. Otherwise you decrease the angle of lift and increase the force exerted on the upper part of your mast, and on your stays. If you really want to go for it, I would recommend increasing your mast height by at least 4 feet, thus decreasing the forces on the upper part of the mast and decreasing your dependence on stays. When I redid mine, the mast height went up 4' and down 2.5', as I moved the base to the lower deck, so I got an aluminum pile that was 6.5' longer than the old, useless one. I extended the boom so that instead of being unable to lift a Sabot out of the water without scraping it up the side of the boat, I could lift a Laser without touching, even with people running around, rocking the boat. Mine is also without stays, which in the original, crossed the ladder to the flybridge just at neck height, a major irritant.
*I think he already has his solution...but I'm pretty sure that as long as the stays are connected near the top of the mast and so is the block to the boom...just about all the added pull due to the longer lever arm would just put the mast in more compression...so making it longer wouldn't really be necessary.* The stays would have more strain...but the mast should just be in compression.
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Old 02-14-2012, 07:38 AM   #16
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RE: Increasing boom swing for dingy

Everyone, thanks for all the great input. The reason this prject started was my beagle-blue tick daily doggy duty is a pain with the current system and I cant get the boy to pee in the scuppers(even after I showed him how). I cant keep the motor on the dingy and put it over the side with the current set up. The zodiac is a 275R at 9 feet and 99 lbs. I currently have a 3.3 HP merc at 32 lbs. I am buying a 5 or 6 hp four stroke this spring. The total weight of the rig will be 160 lbs. Thanks again all.
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Old 04-01-2012, 09:05 AM   #17
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Project complete

We have finished the extension and boom upgrades. I thought some folks may be interested in the details. This link has some pictures of the progression. I hope she holds up!
Fryedaze - Fryedaze Boom extension
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Old 04-01-2012, 09:09 AM   #18
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Very nice job.
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Old 04-01-2012, 10:33 AM   #19
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Looks great!
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Old 04-03-2012, 01:45 PM   #20
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Not really on point concerning your original question but having dealt with the at least a couple of dog to shore trips every day for years I'd really suggest the best answer: a good set of stern dinghy davits. There's a good chance that you'll consider it the best improvement you've made to the boat.
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