I was wondering what other builders used for the boom. I can't find the 2 in. full round called for in the plans, which say to use a 2x3 as an alternate. Is that the route most builders took? i.e., use a 2x3 or 2x4 and shape it down to fit?
I used 3 pieces of African mahogany laminated together. Nice and heavy and the laminations tend to keep it from warping out of shape.
I cut all of my spars out of a douglas fir 2X10. You have to be really careful when buying douglas fir to get a suitable grade. I later bought some fir for some other spars and it was absolutely terrible compared to the 2X10 mentioned above. I have also had great luck with white pine 2X bought from Home Depot though it is more flexible than good fir.
Personally I'm planning on just cutting down a spruce 2X4. The challenge will be to find one without knots or a grain pattern that will weaken it.
Ahoy,
Someone help me here, but did I read somewhere that the boom needs to be heavy? By that I mean, no hollow spars, except for the mast. Is that right?
Heavy boom, light mast.
Like Steve, I would go for laminated stock. It's stronger and much less likely to twist or cup.
Steve,
A number of builders have used 2" round stair rail with the flat side on it to make up the booms, this will work just fine. Heavier stock will be better than light weight stock. Mahogany, Douglas Fir, Spruce, Hemlock, Southern Yellow Pine, White Oak, Ash. Just avoid a piece with knots or a lot of grain run out on the sides. You want as straight a grain as you can get.
You want more weight on the boom to help hold the foot of the main sail down. A 2X3 on edge will do the trick well. As with many other areas on a boat, the grain will make a difference. A straight grain, knot free, quartersawn piece of stock will be better for this use than a plain sawn piece of lumber. Doug Fir is good and it's weight will be a bonus when compared to say White Pine. Sitka Spruce would be a good choice for strength to weight ratio but any clear, straight grain Spruce would be fine.
Southern Yellow Pine will work too. Mahogany works well if clear of defects and not too much run out on the grain.
Fortunately twist or cupping isn't a huge factor on a boom as long as it remains reasonably straight. But then I've seen some really twisted up pieces of wood used as some of the booms in the Carribean. And some of those boats are fast with a lot of sail area.
Laminating one from 1X2 stock is a viable option as well and will be strong. Four layers of this laid with the flat sides joining and shorter lengths will work as long as the butt joints are staggered. Also ripping and joining from a larger board and reversing each course so that the grain is alternated will make up a good boom from material cut from 2X __ boards. Again they don't have to be full length as long as the joints are staggered. If you are using epoxy don't clamp it too tightly or you may have a weak joint in that area. This is one place that the Gorrilla glues and the Plastic Resin glues work very well. If you use biscuits to join the lengths together it will have incredible stability and strength. But you can use screws or nails to help hold the layers while they cure.
I cut mine from a recycled piece of 4 X 4 X 12' Douglas Fir post that I got the boom, bow sprit and a lot of other pieces for the boat from. It was ugly but cheap and turned out to be vertical grain as well once I got the sides cleaned up and a few nails pulled from it. Very tight, close grain wood that will serve me well. Paid just a little more for it than you might pay for a good clear 2X4 of that length at a box store.
The heavier the boom the less the twist to the sail and the bigger the bump on the head if you don't move it out of the way quick enough. Twist is when the gaff a the top of the sail is at a different angle then the boom. This means that only a part of your sail is actually trimmed correctly for the angle of wind. The less twist, the more of the sail that can be trimmed correctly and the more speed you will get.
Other ways to address twist include: 1) a boom vang that goes from the base of the mast up to the boom about 2-3' from the front. This vang pulls down on the boom eliminating twist. 2) some sort of horse or traveller for the mainsheet at the back of the boat. This only addresses twist when close hauled to the wind.
I don't know how much a difference the weight of the boom makes.
The heavier the boom the less it will tend to want to lift when in moderate to moderately heavy winds or stronger. As Scott is stating it helps to control the amount of twist as well as making it easier to flatten the sail when working up wind.
Think if it this way perhaps. If the wind were totally constant in its speed and even, with no variables in direction or puffs to change how it affected the sail, it would be easier to set the trim of the main and it would remain constant until you made a change in direction. But a puff or heavier burst of wind will want to bag the sail out, lifting the boom and changing the attitude and trim of the main. A heavier boom helps to keep the foot down and compensate to some extent for the changes that happen as you sail.
That makes it a lot easier to handle and control the main in heavier wind conditions
You shouldn't have to duck too much if everything is set up correctly. There should be enough head clearance to make it easy to control. :wink:
Traditional gaffers used solid booms to keep it from lifting when the wind was abeam or farther aft. The use of a vang can eliminate this need and a hollow boom could be used, which will save weight, which is always a good thing in small craft. A well thought out main sheet can also provide some downward pull to keep the boom from riding up. One of the simplest vang arrangements I've seen on a gaffer was a stick, that fit into a notch on the boom and a matching one on the mast. It was fitted above the boom and prevented it from rising, but permitted some flexibility at the sheet end. No moving parts, no block and tackle, no lines, cleats, just a hardwood stick. I prefer a tackle vang. On boats where attaching permanently to the mast and boom isn't easy, like Weekender 'cause the cabin is in the way, I usually have a tackle hanging from the boom around it's half way point, or a couple of tackles waiting on the side decks. During a jibe I just clip it to the new leeward side, if it's hanging from the boom, or clip the leeward side to the boom if it's deck mounted. You have a lot more control of sail shape with a vang then with a heavy boom, which is particularly handy when the winds freshen.
A laminated boom will be least likely to warp and economical use of materials can be used. A "T" shaped boom (just like the Americas Cup guys) will offer the most sail performance, acting as a "fence" to help prevent air spilling over the boom. A loose footed boom needs to be stronger then an attached foot boom.
I used two 1x3's laminated with opposing grain direction to prevent warping. Once the glue set, I used a round-over bit along the length of it, and left the end by the gooseneck squared off.
Looks sharp, appears to work well.
