Thread: The Search for the Perfect Lug Rig Boom for A goat Island Skiff

Good news...

I've reduced the cross-section of my boom from 45mm x 60mm to 43mm x 58 mm.

Bad news:

Didn't measure the flex/stiffness of the "new" boom (too HOT right now and too many other things to do).

I'll take it sailing in a week or so and report on its performance.

(guess I can always check the flex/stiffness later)

Every step is a step forward! Another option about to be tested.

I'll add it to the WIKI when we have the properties and user experience to report!

MIK

Mik,

Please correct me if I am wrong...

Checking the WIKI, I realize the data for my Mk II hollow box boom isn't listed.

From another post: After I rounded-over the edges, shaped the ends a bit, drilled a hole at each end and sanded a bit, the new box boom weighs 2.1kg (4.62lbs). Vertical plane deflection (with 12kg suspended at mid-point) is still 7mm and horizontal plane deflection is still 12mm. This boom measured 45 x 60mm with 10mm sides. This is the boom I used last month at the Small Craft Skills Academy.

In the interest of putting off other projects, I pared this boom down from 45x60mm to 43x58mm. The result of running the boom through the thickness planer is that the sides are now 9mm.

So, we have the data for the MK II and partial data for the MK II.2. I'll weigh the MK II.2 boom and measure the deflection this week before I take the boat north for some sailing.

Confused? Me, too.

I've added it to the WIKI page.

Thanks BobWes!

WIKI for setting up and tuning Lug and Sprit Rigs | Michael Storer Wooden Boat Plans

I've added it to the WIKI page.

Thanks BobWes!

WIKI for setting up and tuning Lug and Sprit Rigs | Michael Storer Wooden Boat Plans

Originally Posted by Boatmik

I've added it to the WIKI page.

Thanks BobWes!

WIKI for setting up and tuning Lug and Sprit Rigs | Michael Storer Wooden Boat Plans

MIK, that link takes me to a page that hasn't been updated since 2010. Stuffed if I can find the data anywhere. I also wanted to check if I'd added my own Mk 2 stiff boom data. Wasn't it on Google docs somewhere as well?

You will likely remember sailing Hakuna Matata with the new Meranti stiffer boom? It still does bend a little when higher loads are applied by the kicker, but if I only use downhaul in the normal position, it is stiff.

Edit:
PS. Found it. Forgot that I had to first log in through my own Google Docs account to see the data. I confirm that my Mk 2 data is there.

Hi Bruce,

Have a second look at the Boom section ... because it is a embedded document the page it is embedded in doesn't get changed when the google doc is edited.

If it is the current version of the googledoc you should see BobWes boom version 2 fully filled in and 2a waiting for deflection and weight info.

If you don't see this you need to tell me and I need to work out a way of dealing with it!



MIK

Originally Posted by Boatmik

Hi Bruce,

Have a second look at the Boom section ... because it is a embedded document the page it is embedded in doesn't get changed when the google doc is edited.

If it is the current version of the googledoc you should see BobWes boom version 2 fully filled in and 2a waiting for deflection and weight info.

If you don't see this you need to tell me and I need to work out a way of dealing with it!



MIK

Hi Mik

It's fine, just me at fault. I didn't notice the second slide bar on the page

How have you got the sail lashed to the yard at the throat?

Not sure whether a bendy boom attributes to this as a bendy boom will pull the sail down more over the lenght of the boom that a stiff one, thus removing creases rather than create them (in that area of the sail).

I don't get how a bendy boom will take the creases out. BLEAT's boom is bending vertically, not laterally, so that brings the two ends of the boom closer together in a fashion that points them to the sky-- I would also assume like Clint that that would contribute to that strange wrinkle that angles up from the clew along the battens.

Originally Posted by callsign222

I don't get how a bendy boom will take the creases out. BLEAT's boom is bending vertically, not laterally, so that brings the two ends of the boom closer together in a fashion that points them to the sky-- I would also assume like Clint that that would contribute to that strange wrinkle that angles up from the clew along the battens.

I don't think that the two ends of the boom are forced to point to the sky, I rather think that the middle of the bendy boom is forced to bend downwards more by applying downhaul tension (in other words, the ends may seem to point upwards, but the largest bend is in the middle of the boom). This bend than takes a lot, at least for my sail, draft out of the ail as the sail cloth is pulled downwards taking the sail cloth "down" with it.

I am not suggesting at all that there will be any lateral bending (there will not be much since the boom is supported by the mast and the sheet (attached to blocks on the aft end and the middle of the boom).

What I was trying to say is that the crease may (repeat: may, not automatically will) have been caused by the fact that the yard is not peaked up sufficiently (which may have in turn been caused by the way how the sail is lashed on to the yard at the throat: i.e. the downhaul force applied on the luff should continue to the head).

Just some ramblings tyring to feed a discussion on how to resolve this issue.

Joost

Joost, thanks

Indeed a definite issue is that I need to fix the throat of the sail at the yard so that the downhaul tension is restricted to the luff and does not pull through the head of the sail as well. Christophe, aka Callsign, showed this to me and it is quite evident that this needs fixing. I'd like to do it with the spectra I already have. I may glue a wood eye to the yard so the lashings are fixed.

I think you may be on to something, Joost. Maybe the middle does bend down vs the ends up. It is all relative. My sail is loose footed, so I do not have lashings along the foot of the sail.

In fact, I am most satisfied with my yard dimensions. I plan to take measurements of my yard and share them because, so far, they seem ideal. More experimentation will tell.

I sent a file to MIK with my thoughts on a boom and will get started on the new one asap as well as fixing the head of the sail to the yard. That is brilliant.

I think it would pull draft out of the sail is the sail was lashed to the boom, but Clint runs a loose-footed sail which I think is an important detail that wasn't mentioned before.

But great points Joost, I like that perspective.

Okay, we've been polluting Clint's thread with all this talk of box booms when it probably belongs here anyway. So I'm shifting over.

Here's an evil thought. Someone stop me before I do anything too egregiously stupid....

In the interim before I get a box boom built, what would be wrong with testing a "stayed" boom? I'm thinking of running a piece of Spectra down the length of the boom, pulled as tight as I can by hand. I hook the downhaul to that, rather than to the boom itself. Then I make a spreader out of something stiff and locate it right at the downhaul. The line distributes the downward pull to the ends of the boom, so the stress on the boom is mostly along its axis. The spreader prevents it from bowing.

The danger, of course, is that the line will snap under tension and take out my eye. But, assuming I have given informed consent and all that, is it a viable experiment?