Making a "Park Avenue" Boom

[Meanz Beanz]

I want to make a "Park Avenue" boom, sort of like this one...

http://www.offshorespars.com/Products/product_images/parkavenueboom_swan62.jpg

Its about 3.8m long, to suit a Seawind 24. If you are not familiar with the idea basically its just a wide boom that is used with Lazy Jacks to provide a platform to catch the mainsail. A cover is attached to each side and zips up the centre. Its a quick easy way to store the main.

I need advice on construction, thinking along the lines of forming it in foam/cedar and glass/carbon with epoxy. Maybe be setting up to vacuum bag it. I am not sure which combination of materials will suit the best. I don't think that weight is the overriding concern, not to heavy but strong is good. Is cedar/carbon/epoxy a bit mad? I'm thinking that foam will be a problem if fittings need to move, be added etc.

Any thoughts?

MBz

[Meanz Beanz]

http://www.aes.net.nz/images/boomfrnt.jpg

[alan white]

I would think weight is the major concern. In a beam swell in light air, wouldn't a weighty boom tend to knock the shape out of the sail?
Another question, wouldn't it be difficult at times to see the sail shape from below?
A freind made a simpler boom----- light but wide, for a big tri. Instead of a big structure, he molded a few pairs of struts to each side of the boom and terminated the lazy jacks on the struts. Plenty of room to flake the sail, did everything a wider boom would do, made a good tent support, but very light and simple.
The struts were glass over foam, I think, screwed on to an aluminum extrusion boom. Oval-section pylons, maybe 12" base to tip, so his sail-catching area was about 30" wide.
If end plate effect is the desired result, struts as described could be fitted with fabric panels or flexible window material (to see through).
Gybing a big boom like the one pictured, maybe half the sail on it when reefed adding to the weight, no thanks.
That one Meanbeanz shows... looks like it would make a screamer of a dinghy all by itself!
Construction--- surfboard style--- sculpted from foam with bulkheads buried in the foam ahead of time, acetone poured in to cavities to melt foam out, kevlar and/or carbon, ply patches at key attachment points, all fasteners machine screws into threaded aluminum-reinforced epoxy putty, would be light and strong.
Alan

[frosh]

Got to agree with Alan on many of his points. Weight will be a big not a small issue, especially when that monster is moving rapidly in a gybe. Can anyone let me know where I can get one. Looks like it would go like stink with a modern high aspect sail and big outriggers to hike off.

[catsketcher]

Hello Meanz

It looks like the Seawind is getting a total makeover. I think the weight of the park avenue boom may be much higher than the alloy one. I went on board the new Sobedo yesterday and they had stuts as stated by Frosh et al.

A mate of mine has made a park avenue attachment that goes on top of his normal boom. It is made from 10mm Nomex which is kerfed to get a curve into it. It is light and strong. You could do the same thing with Duflex. This would be easier to do than a whole boom.

cheers

Phil Thompson

[Meanz Beanz]

I would think weight is the major concern. In a beam swell in light air, wouldn't a weighty boom tend to knock the shape out of the sail?

When I said weight was not the primary concern I was still thinking light. Im' not sure that cedar would end up that heavy that it is an issue, but maybe. The mainsail is quite heavily battened so holds shape v well.

Another question, wouldn't it be difficult at times to see the sail shape from below?

If you can see the sail shape from bellow on a SW24 you have probably been knocked out and are just comming to! LOL This one is not a concern, the front end of the boom is about 300mm of the deck.

A freind made a simpler boom----- light but wide, for a big tri. Instead of a big structure, he molded a few pairs of struts to each side of the boom and terminated the lazy jacks on the struts. Plenty of room to flake the sail, did everything a wider boom would do, made a good tent support, but very light and simple.

The current extrusion is about 76mm / 3" in diameter, that is a good idea but I'd have to think about how it would work with what I have.

The pics are of Carbon Foam pro jobs, they are a little on the bulky side for what I want but they are the best I could find to illustrate the idea.

Thanks for the input Alan.

Cheers
MBz

[Meanz Beanz]

Got to agree with Alan on many of his points. Weight will be a big not a small issue, especially when that monster is moving rapidly in a gybe. Can anyone let me know where I can get one. Looks like it would go like stink with a modern high aspect sail and big outriggers to hike off.

I'm placing weight as second to strength because I cruise not race. I do want it as light as possible yet functional but I won't double the cost to save grams. Maybe that is a better way of putting it.

Cheers
MBz

[Meanz Beanz]

Hello Meanz

It looks like the Seawind is getting a total makeover. I think the weight of the park avenue boom may be much higher than the alloy one. I went on board the new Sobedo yesterday and they had stuts as stated by Frosh et al.

A mate of mine has made a park avenue attachment that goes on top of his normal boom. It is made from 10mm Nomex which is kerfed to get a curve into it. It is light and strong. You could do the same thing with Duflex. This would be easier to do than a whole boom.

cheers

Phil Thompson

Hey Phil,

Yeah, I have to work out what it would weight, maybe the attachment idea is a good one. Not thinking as bulky as the pics, just enough to contain the main easily & make pack-up quick. I have a tendency to sail for longer than I should, always rushing back LOL

Cheers
MBz

[alan white]

I think the effective solution would be fabric stretched from wide points. Structure isn't necessary----end plate effect is just a surface or barrier. Regarding flaking and gathering the sail, likewise, fabric is ideal.
I picture maybe four light conical struts with bases that are molded to match the boom. They are screwed into the boom and a length of light (3 oz) dacron is stretched tight to form a very shallow V. Not five pounds would be added to the boom's weight if the struts were carbon over foam.
another solution would be to use two aluminum tubes sprung out to each side, an elongated "eye" shape from above, with a pair of struts to stiffen along the length, then cover with fabric. Maybe safer in case bonked.
Cheap, light, does the job, looks okay. Can also have a zip-up cover rolled and tucked on each side.

Alan

[Meanz Beanz]

Now there's some food for thought!

Thanks Alan.

[Meanz Beanz]

I was thinking that for a crusing boat these things would make a great fresh water catcher... skin fitting on the mast end and a tube into the tank. No?

[alan white]

Good idea. If the mast rotates. If not still doable. What comes down the sail would be substantial. Hey....

[waikikin]

That boom looks groovy Meanz Beanz & if wide enough would make like a stretcher hammock & even better with some cushions, imagine kikin' back in that as you harness the powers of the elements, but you might find it "interacts" with the shrouds when sheeted out, butterfly frames of staino or alu tube with or without the fabric work nice & 2 or 4 "wings" leaving out the bit of boom in line with the shrouds may be the way to go esp' if you've got the original boom, although I do like the boom you've shown heaps. Regards from Jeff:cool:

[DanishBagger]

How about a boom shaped somewhat like a windsurfer-boom - you know, like a compressed oval. You could use cloth or string between the two poles - string would be enough to hold the sail, but the cloth would work as an "end-cap". Heck, if done properly, the sail-cover could double as the end-cap by simply having it on top of the strings.

This way you could propably make it just about the same wight as the boom you have now, and you wouldn't have struts sticking out, wating to hit you in the eye.

[alan white]

Yeah, struts would impale the unwary. The split boom, with a couple of cross-bars, is a good idea. Unzip, drop the sail, zip back up. Tramp webbing under.

[Meanz Beanz]

That boom looks groovy Meanz Beanz & if wide enough would make like a stretcher hammock & even better with some cushions, imagine kikin' back in that as you harness the powers of the elements, but you might find it "interacts" with the shrouds when sheeted out, butterfly frames of staino or alu tube with or without the fabric work nice & 2 or 4 "wings" leaving out the bit of boom in line with the shrouds may be the way to go esp' if you've got the original boom, although I do like the boom you've shown heaps. Regards from Jeff:cool:

LOL yeah if the boat was big enough that would be great!

Being a cat the boom rarely meets the shrouds, you tend to reach everywhere as its quicker! In fact I must admit I don't know if the mainsheet goes far enough!

Still puzzling over this one.

Cheers
MBz

[Meanz Beanz]

How about a boom shaped somewhat like a windsurfer-boom - you know, like a compressed oval. You could use cloth or string between the two poles - string would be enough to hold the sail, but the cloth would work as an "end-cap". Heck, if done properly, the sail-cover could double as the end-cap by simply having it on top of the strings.

This way you could propably make it just about the same wight as the boom you have now, and you wouldn't have struts sticking out, wating to hit you in the eye.

Now thats a thought!... I will have to get the sketch pad out and doodle!

Thanks

MBz

[Meanz Beanz]

Yeah, struts would impale the unwary. The split boom, with a couple of cross-bars, is a good idea. Unzip, drop the sail, zip back up. Tramp webbing under.

Sounds reasonable for my boat ! Misses out on the water catching idea but for a small cat it is light weight and practical.

Cheers
MBz

PS. Sorry about the tardy replies... emails not getting to me????

[eponodyne]

I kind of like Alan White's idea (great minds think alike, and hey, ours do too...); build it exactly like the wing tip of a tube-and-rag homebuilt airplane. You could even use Ceconite to cover!

[scupper]

I've been thinking of building one of these. Mainly I'm concerned with ease of building and I'd rather it never broke. So far the plan I've come up with is, for my 300 square foot main with a foot of just under 14' would be to find a nice piece of aluminium angle iron, like 8"x8" probably 3/16" or 1/4". Weld some flat bar or some plate across the hypotenuse of the triangle, along it every six inches or so. I figured this would be something I could have a shop weld up for me in a half hour or so if I just cut all the gussets out. For my reefing blocks I was thinking I could just run a bolt horizontally though the angled sides of the boom and just make some some beveled bits of plastic to tighten the nut against,you could put the sheave on the bolt and I guess you'd have to pop rivet some cheeks around each sheave. But this would get rid of the issue I've being having about whether I run my lines inside or outside of the boom. This would let me just run them along the inside of the boom which would be pretty much open except for the flat bar every six inches. My current boom is five inch sch. 40 pipe so an 8x8 would be much of a change.
If anyone's still following this thread I appreciate your thoughts.

[scupper]

Another thing that pointed me in the direction of a wide boom was I remember reading in some sail trim book that having a wider boom along the foot helps to seal in the surface pressure along the sail rather than just to let it spill out over the foot and so helps to keep in the lift. Much like wing tips on a plane of a keel for that matter.

[michael pierzga]

Didnt read all the replies but a simple " T " shaped boom is also elegant and simple to build. The structural part of the boom is a vertical box section , tapered in the ends. The "T" , horizontal section wings , are a secondary structure to hold the lazy jacks and give a platform for the flaked main to rest The T boom is simple because all the reef lines can be led on the outside of the main boom structure and the " wings can be a secondary bond because they carry little load..

Lazy jacks on " spreaders " growing out of the side of the boom to give a nice platform for the main to flake never work well. Spin sheets and lines catch the lazy jack spreaders , the flaked sail sags between jacks , reef line get tangled......