Boom to mast angle

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JimC

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My boom sweeps the cockpit at the level of my temples. I'd prefer it to clear my head. I'll soon be in the market for a new mainsail and was thinking of specifying an angle at the clew of less than 90 degrees to lift the boom above the horizontal, the reefs would obviously be at the same angle. Any problems foreseen with this?
 
maybe this is the latest fashion trend? Racing boats seem to be getting lower booms, the vendee globe boats booms are not far off the deck and the americas cup boats mainsail touches the deck and seals to it to stop wind getting underneath !
 
I doubt you'll be lifting it high enough to matter, but I'd check that the ram's horns still work easily and that all the reef line/cunningham/flattener and outhauls all still have fair leads as they depart the gooseneck.
 
JimC said:
My boom sweeps the cockpit at the level of my temples. I'd prefer it to clear my head. I'll soon be in the market for a new mainsail and was thinking of specifying an angle at the clew of less than 90 degrees to lift the boom above the horizontal, the reefs would obviously be at the same angle. Any problems foreseen with this?
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loss of sail area
 
STOL71 said:
Why don’t you raise the boom at the mast and keep it at the same angle when you are ordering a new main?
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Good point. Mine is one of the early Hunter Channel 31s, later Hunters did move the gooseneck a bit further up the mast. I wouldn't want to do it as a retrofit though. It would also mean moving the reefing line fairleads and cutting out a new mast gate. Too much mast butchery and too many redundant holes remaining.
 
Some might think about the practicalities of being able to reach the boom to deal with reef lines etc?
There is also the point that as you lower the sail, unless you lift the boom on the topping lift first, it puts a lot of strain on the lower luff slides, asthe boom is no longer supported by the leach.
sheeting in hard also does different things to the sail if the outhaul is firm, pulling the boom down creates a lot of tension across the sail at 90deg to the mast, the sail needs to be cut with this in mind. Not usre how that would work with reefs where you'd expect to have the sail tight before sheeting in?
Have a look at a Musto Skiff, it's the only boat I've sailed with the boom angled up.
 
I think the drooping boom syndrome is more about more sail area that beats measurement rules. I can't imgine a boom being so low as to get an end effect from the deck/cockpit. So yes have the new main sail cut to lift the boom to at least 90 degrees to the mast or even higher if it will save your scone. ol'will
 
I can see no problem at all with this except minor loss of sail area.

I think the reason the IMOCAs have gooseneck down at the deck (and have done for ages) is to make better use of the strength provided by the deck. But that's just a guess. Certainly they manage reefing OK.
 
We needed to shorten our boom some years ago and our sailmaker suggested we set the boom is at an angle of about 70 degrees to the mast. This has worked really well; it gives plenty of headroom in the cockpit, the sail sets and reefs well, the boat is better balanced and it makes stowing the mainsail on the boom much easier as you are working at waist height rather than stretching up above your head.

Speak to your sailmaker.
 
LadyInBed said:
I think it's convention and is practical to have the boom parallel to the deck to maximize sail area.
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I'm going to be pedantic and point out that sail area is maximised (for a given luff and foot length) by having the boom perpendicular to the mast, not parallel to the deck.
 
TLouth7 said:
I'm going to be pedantic and point out that sail area is maximised (for a given luff and foot length) by having the boom perpendicular to the mast, not parallel to the deck.
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I'm going to be even more pedantic and say that you get extra sail area by having the boom below perpendicular to the mast.
 
RJJ said:
I'm going to be even more pedantic and say that you get extra sail area by having the boom below perpendicular to the mast.
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You'd think so, but it doesn't work out that way.

Remember that the area of a triangle is base x perpendicular height. If we take the luff as the base, then it is clear that as you drop the fixed length boom below 90 degrees the perpendicular length from luff to clew actually decreases, and so does the sail area.
 
TLouth7 said:
You'd think so, but it doesn't work out that way.

Remember that the area of a triangle is base x perpendicular height. If we take the luff as the base, then it is clear that as you drop the fixed length boom below 90 degrees the perpendicular length from luff to clew actually decreases, and so does the sail area.
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Its not about real sail area, its about measured sail area, two very different things. Droopy boom has a better true area vs measurements if done correctly.

Regarding the original post there is nothing wrong with raising the clew, all that needs to be ensured that it is not raised too far meaning the the distance between the clew and the bottom slide is shorter than the clew to the tack as this will load the slide rather than the tack.
 
JimC said:
My boom sweeps the cockpit at the level of my temples. I'd prefer it to clear my head. I'll soon be in the market for a new mainsail and was thinking of specifying an angle at the clew of less than 90 degrees to lift the boom above the horizontal, the reefs would obviously be at the same angle. Any problems foreseen with this?
Click to expand...

I wanted a bigger sprayhood, which meant the boom rubbed on the top of it. I also wanted a new mainsail, so i spoke to the sailmaker (the highly respected John Parker) and they made the sail to suit having the boom slightly raised, no problems. I don't think the angle of the boom looks at all out of place. The very end of the boom is raised by a small amount, so maybe i've lost a sliver of sail, i'm OK with that, i have a big enough sprayhood to provide some shelter in poor weather.
 
I had a wedge-shaped fillet taken out of a mainsail on a previous boat in order to fit a bimini, and relocated the reefing cringles. A fairly easy job for the sailmaker and made no discernible difference to sailing (boom raised by around 20cm on a 10m yacht)
 
It depends how your reefing is of course, but the first reef, of slab reefing normally lifts the boom. You could try it with a reef in, and see if it suits you.
 
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