How to choose a windsurfing boom
First, it's important to be realistic about your ability and the type of sailing you do. In your dreams you may be riding radical waves, but if you’re really just improving and your actual goals are having fun blasting, jumping and mastering gybes, let that be at the forefront of your decision making.
Secondly - re-think your budget. Don’t focus on the cheapest, focus on lifespan. Often paying more now will cost you less later. If you’re on a tight budget now, the cheapest may still cost you in the short-to-medium term, so focus on value for money.
Thirdly. There are 'different horses for different courses'. With higher quality manufacturing techniques, adjustment ranges are reliable and wide these days. But will one boom do it all? Depending on preferences, larger sails/cammed sails can work better with different boom outlines. Be honest about if you will need more than one boom and if that means re-allocating your budget into more than one boom.
In either aluminium or carbon always look for ‘monocoque’ construction, which means they are all made in one shell, with a continuos tube from side-to-side, rather than separate arms on each side fixed into the head.
Do you want a direct feedback - or some element of absorbent, energy-saving feel?
Carbon delivers rigidity, weight reduction and can protect sail shape on cambered sails, especially in larger sizes at the higher end of the extension range. Aluminium can be more forgiving and disperse shock/load than more brittle, older carbon or non-pre-preg carbon booms.
Regular ‘R-Shape’ booms fit traditional cambered sail profiles/curves.
‘C-Shape’ booms are efficient and reduce stress on the wrist/forearms, promote good stance for more active, dynamic sailing (waves/freestyle), plus the more parallel tubes per additional strength. Modern C-shape booms with wide tails can be the best of both worlds in terms of stance/comfort and accommodating the deeper-bodied sails.
Tube thickness and profile
Boom diameter plays a big part in comfort. Those with smaller hands or in colder water can often prefer Reduced Diameter Grips (RDGs). RDGs or SLIM tubes are widely thought to offer a more ‘direct’ handling sensation for those that like to have a lot of feedback from their rig. Larger hands and/or racers often prefer Standard Diameter grips (SDG). In either case, a tapered tube arm often delivers both extra strength and the comfort you prefer (see below).
Much like masts, internal wall thickness will play a major part of strength of either variety. Some booms are Heavy Duty (HD) which means the tube walls are thicker.
Tube thickness can vary from section to section. Some booms offer a tapered profile with the grip area having a thinner tube than the tail for example. That means the tail end can still be durable . Others are consistent throughout the length of the arms.
Lastly, ‘V-Grip’ booms offer a different sensation and added rigidity. Some windsurfers prefer the ergonomic ‘wedge’ profile and claim it delivers a more energy efficient grip, while others find that movement up and down the boom on V-Grips causes added blisters. There are also OVAL grips that offer similar advantages but with a smoother ergonomics.
Tail Width and Shape
Large sails - again, in deeper bodied race sails for example — can benefit from wider tail shapes to prevent distortion of the lower leech.
Some modern wave sails also favour wider tails as more powerful, fuller shapes of sail, (usually to tighten up bottom turns when wave riding in onshore conditions), have the centre of effort further back and so added room at the rear end is preferable.
If you’re choosing one boom to cover a range of use consider the back end’s pulley system and whether it will accommodate an adjustable outhaul if you require it.
A lot of modern booms will offer both RDM and SDM mast compatibility, but check first before buying on what adapters may be required or if your favourite so far only accommodates RDM masts for example. (All Unfiber booms come with adapters and will fit either type of mast.)
Also check how much of the front end will have contact with the mast as those with a narrow contact area will point load the mast more. A longer head section delivers a nicer, more connected feedback sensation.
Another point to check off is whether the front is fixed or has an Axial head. An axial head means the boom can move up or down for varying clew heights without stressing the mast.