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

I just touched up my mast chafe area with some West g-flex epoxy, and I think a good bit of the chafe comes from the yard block rubbing the mast. Switching to no block for the yard, like Woodeneye has done, eliminates that problem!

Once we have worked out if the bleeter and vanghaul work well enough to be standard, I will update the rigging page to reflect these community created refinements.

Thank you everyone!

MIK

Okay, I'm lagging behind in the pursuit of the perfect bleater/vang/downhaul/outhaul rigging combination... and I don't see that changing too much in the near future.

But I have a question re the yard and since the yard is a spar and the boom is a spar - and we've got questions and answers scattered all around - I figured I'd ask my question here...

My yard measures 142 inches (yeah, I know - imperial system!) which is (roughly 3,606mm). The padeye/hard-attachment for the throat of the sail is 6 inches (152mm) from the foreward end of the yard. What does that foreward end of the yard do? Asked another way, what dire consequences result from shortening the yard to 136 inches (3,454mm)? (Yes the halyard attachment point may change as a percentage of the overall length, but really, what happens with a shorter yard?)

I've got some timbers to build a new yard and I now have access to a router table. I've drawn up a spar design/building method I think may result in a stiffer and yet lighter yard. If the building method works, I'll use a concept (adjusted for size) for a new boom.

Originally Posted by BobWes

Okay, I'm lagging behind in the pursuit of the perfect bleater/vang/downhaul/outhaul rigging combination... and I don't see that changing too much in the near future.

But I have a question re the yard and since the yard is a spar and the boom is a spar - and we've got questions and answers scattered all around - I figured I'd ask my question here...

My yard measures 142 inches (yeah, I know - imperial system!) which is (roughly 3,606mm). The padeye/hard-attachment for the throat of the sail is 6 inches (152mm) from the foreward end of the yard. What does that foreward end of the yard do? Asked another way, what dire consequences result from shortening the yard to 136 inches (3,454mm)? (Yes the halyard attachment point may change as a percentage of the overall length, but really, what happens with a shorter yard?)


I've got some timbers to build a new yard and I now have access to a router table. I've drawn up a spar design/building method I think may result in a stiffer and yet lighter yard. If the building method works, I'll use a concept (adjusted for size) for a new boom.

Go for it Bob. There's only about 3 months left anyway

Howdy ... a serious racing type would certainly trim the yard and boom of the Goat a little shorter. So go for it BobWes!

But advantage of the long ones is that we haven't had a single problem of a sail not fitting.

MIK

Ah, good point Mik, But I know the dimensions of my sail... I'll get the router table set up and work on the yard a bit this weekend.

Bruce - Three more months of what?

Hi Guys,

Been out a number of times this year in the Goat, and it's been a blast. She's a real pleasure, and now that I have some big lakes to navigate and not much in the way of commercial traffic to dodge, it's more fun than ever. I'm still very much a novice sailor, and am slowly learning the ins and outs of rigging, sail setting, and trim, but slowly I am beginning to think that my homemade rig may not be ideal. That, and I have a sneaking suspicion that my spars are too bendy. Dimension wise they are made to spec in the plans, but the spruce they are made of is not as tight grained as it should be so they are VERY flexible. I have not stripped the sail and measured deflection, but I will try to do this soon and submit the data to the wiki. I'm seriously considering ordering a professional sail, possibly from the outfit that made Simon's over the winter and building a new yard and box boom out of doug-fir. I like idea of the box boom insofar as being a bit bigger, though still pretty light and stiff, it has a little more room for a simple outhaul setup with a deadeye and a clamcleat on the clew end, and the same thing in reverse on the tack end for reefing. Is there a consensus on sizing and taper a hollow box boom yet? I'd be up to happy to make one up and test it out and post the data.

Also, and this is probably a sort of silly idea, but I figure I'd throw it out there. Has anyone considered a storm type sail lashed to smaller spars for heavier weather days? I've noticed when i have the boat reefed down past the first set of reefs, she barely wants to point into the wind at all. I suspect this is because of my own lack of knowlege of how to optimize the rig for said conditions combined with a not ideally cut sail, but i figured i'd ask anyway. There are many days when the wind is really blowing, and it's hard for me to go out flying a lot of cloth, but if i reef down too much I lose most of my windward ability. I'd be excited to play around with some tests in polytarp and see what happens....

Thanks all,

Just a suggestion here. Wood is approximately twice as strong in tension as in compression. For a beam which is loaded in one direction (which is basically what yards and booms are) having it made out of the same timber top and bottom, with the same thickness top and bottom, results in more bend and less strength.

A good example is racing oars, back when they used to be wood. To get the most strength and stiffness for a given weight, the compression face of the shaft was much wider than the tension face, and the compression face often had a denser layer of wood laminated to it as well.

If using a circular or square section for a yard it would make more sense to use a dense hardwood on the compression face, since compression strength is roughly proportional to density for a lot of timbers.

Originally Posted by Sumbloak

Just a suggestion here. Wood is approximately twice as strong in tension as in compression. For a beam which is loaded in one direction (which is basically what yards and booms are) having it made out of the same timber top and bottom, with the same thickness top and bottom, results in more bend and less strength.

A good example is racing oars, back when they used to be wood. To get the most strength and stiffness for a given weight, the compression face of the shaft was much wider than the tension face, and the compression face often had a denser layer of wood laminated to it as well.

If using a circular or square section for a yard it would make more sense to use a dense hardwood on the compression face, since compression strength is roughly proportional to density for a lot of timbers.

.

VEry nice point Sumebloak!

That method is often used for aircraft wings where there is a relatively large space for the structural components ... relative to boat spars anyhow.

The problem is that the stiffness component is much harder to achieve than the strength component. If something is stiff enough ... it is likely to be strong enough.

For a mast - most efficient masts are hollow and it would be possible to reduce the wall thickness using a hardwood to get either a minor reduction in wall thickness or the overall weight. But it is only a small efficiency because the cross section is so dominant in giving the required stiffness. A small change in diameter makes much more difference than changing species. Also with spars the wall should be 15 to 20% of the cross section. Though I have been known to fudge that a bit lighter with masts we have data on - like the Goat Island Skiff.

As similar argument can be made for a box boom.

With the yard there is a mix of a structural requirement for stiffness which tends to set the diameter - and at that diameter there are few failures of the spars to indicate that more tensile or compression strength is needed. Also the spars are relatively small diameter in this size of boat making a hollow spar of heavier species (to match the weight and diameter) too complicated to build.

Another factor is that I did some fiddling with analyses of this type and within small spaces it doesn't really pay off. The reason is that the neutral axis moves towards the stiffer and stronger timber - meaning that more load is put on the heavier timber compared to the light one. This has a bigger effect when the flanges are relatively thick relative to beam thickness.

But for bigger boats - your analysis is right and it can be a worthwhile consideration as loads can be much closer to critical ones where the structure can fail if something is a bit misaligned or set up wrongly.

Best wishes
MIK

Originally Posted by alzuger

Hi Guys,

Been out a number of times this year in the Goat, and it's been a blast. She's a real pleasure, and now that I have some big lakes to navigate and not much in the way of commercial traffic to dodge, it's more fun than ever. I'm still very much a novice sailor, and am slowly learning the ins and outs of rigging, sail setting, and trim, but slowly I am beginning to think that my homemade rig may not be ideal.

SNIP

Thanks all,

Howdy Al,

Remember that we are talking about only a few percentage points here. In a way it is more a point of pride than it is something of real importance. I'll never stop people from trying to improve their boat ... but just remember how nicely she is sailing already. You can start changing things over the medium term too as all the bits you are thinking about are 1 to 1 replacements. Take one off and put one on.

I would consider that we have quite good info about the yard now. The boom is still in flux.

Also remember that a properly trimmed homemade sail is WAAAAY more effective than a super nice racing sail which nobody has trimmed for the last 5 minutes!

MIK

Originally Posted by Boatmik

I'll never stop people from trying to improve their boat ... but just remember how nicely she is sailing already.

+1 on this.

I've been at least as guilty as anyone else here of obsessing about ways to improve my rig and its performance. But the blunt truth is that I haven't had the time this year to put more than a very few of my ideas to the test. For the most part, my rig is absolute standard, right out of the plans. And I have the oldest version of the Duckworks sail, modified only to fix some things that were really seriously broken, with foot lashed to a bendy boom.

Moreover, I am NOT a highly skilled sailor. True, I grew up sailing. Almost every summer day, in fact, on a wide range of boat types and sizes, until I was old enough to get a job. But I rarely raced and I was always soundly thrashed when I did. And then I took a couple of decades due off to lack of money and the presence of small offspring requiring my time and attention.

And yet, when I take my Goat out, I am NEVER embarrassed by our performance. It is fairly typical that we will do 5+ knots in a 7 - 8 knot breeze, the kind of performance I used to think was only possible with multi-hulls. I'm sure the boat could do even better with a more-skilled skipper.

Bottom line: all this performance stuff is fun to talk about and great for bragging rights. But it is NOT necessary.

Ok Ok,

You guys win the day this time, but come January, when the ice and snow has piled up i might just cut up some 2x12s and see what happens..

Having dropped out of engineering school - before I flunked out - I need someone to explain Sumbloak's comments re compression and tension: In a square/rectangle hollow spar, which faces are in tension and which are in compression?

My 40mm x 40mm square hollow yard is not tapered at all and has worked well for me. It is among the lightest and stiffest of the yards listed on the wiki document. I used inexpensive big-box store pine (eastern pine as near as I can tell) for all four sides. I'm experimenting some with a new design - aiming for the same cross-section - and hopeful for a lighter and stiffer yard.

The two hollow box booms I've built are relatively light and relatively stiff. The first boom (6mm ply sides and 12mm cedar top/bottom) is sort of tapered. The second one (58mm x 43mm, 11mm sides of white cedar) is not tapered at all. I am hopeful that the construction method I'm experimenting with (on the new yard) will produce a lighter and stiffer boom as well.

Tapering these square/rectangle spars takes more effort than it is worth to me. (Remember, I struggled assembling the tapered hollow box mast.)

Originally Posted by BobWes

Having dropped out of engineering school - before I flunked out -

Been there...

I need someone to explain Sumbloak's comments re compression and tension: In a square/rectangle hollow spar, which faces are in tension and which are in compression?

The faces nearest the sail are in compression; their opposites are in tension. Consider the bendiest boom that ends up banana shaped. The bottom face has become much longer than the top; it is stretched by comparison. Likewise, the inner curve is shorter as it's being compressed. So Sumbloak is suggesting that a denser wood on that face will do better to counter those forces. (Clearly I'm over-simplifying--and I might be technically innaccurate--but I think you get the picture).

He could also have suggested that instead of using wooden face in tension, we use instead a high strength wire. Simon could have jumped in with his carbon-tow technique for that face only. And MIK could then remind us all that the plans produce a pretty good boat as is.