I'm in the process of ordering new sails and want to fix the problem of a low boom in the process. Currently the boom hits me in the side of the head if I am standing in the cockpit.

When I measured the existing mainsail I realised that the angle of the luff and the foot was greater than 90 degrees. i.e.

Luff 12metres; Foot 3.7meters; leech12.71. My high school maths tells me that if the angle was 90 degrees the leech would only be 12.557 meters.

So I have a couple of options to get an extra 300mm of clearance in the cockpit:
1. cut the new main with a shorter leach to raise the end of the boom about 400mm;
2. raise the gooseneck and shorten the luff while maintaing a 90 degree angle at the luff and foot; or
3. a combination of 1 and 2

Also I am planning to keep the plastic slider mainsail cars that fit inside the mast extrusion, only because they seem to have worked well for the last 30 years. (in the photo below).

Any input from the brains trust would be gratefully accepted.

Morning Bird I would really appreciate knowing the measurements of your main and any advice you can give including the height of your gooseneck off the cabin top. ( I didn't think to measure mine yesterday, will update that tonight).

I think they call the extra length of the leech, the roach. This is the outward curve. That could account for the difference from your calculation.

www.ss34.org/index.php/the-ss34/specifications/
If of any help above Has all the mainsail measurements for old/new,short/tall rigs.

Not sure,but when the sail is full and has some twist in the leach then the angle will be closer to or less than 90 degrees. Maybe

Thanks Yarra but I measured a straight line from the head to the clew

Bananabender there's good info on there but my rig seems to have different dimensions

Riffraff I didn't think of that but it makes sense but still doesn't help because I would prefer to be certain I won't ever be knocked out by my boom

A flattening reef may be what you want. Raises the boom just a tad.

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cisco said..

A flattening reef may be what you want. Raises the boom just a tad.

I would be more inclined to stick with the original plan and learn to duck. My boom will hit my head too but eventually you get the message.

I know this may be obvious but as you are ordering a new main tell them the problem and they will cut to suit. Could it be existing main has stretched!

Andy,
hoist a couple of string lines up the mast to replicate the luff and leech. Mark your existing sail measurements on them first and also your calculated leech length. Finish the bottom of the triangle with the boom or another string from the tack with the foot measurement marked. Bring the marks together. You will be able to get a good picture of how much your calculated leech length raises the sagging boom. Remember to add in the boom dimension if using only string on the foot. You could even try the S&S sail dimension.

I should have mentioned you will need to tie the strings to a sail slug or something similar to hold them in the mast track at the top.

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Jolene said..
I should have mentioned you will need to tie the strings to a sail slug or something similar to hold them in the mast track at the top.

Would it be worthwhile checking the boom and mast with spirit level to confirm 90 degrees with sail up and at what angle to the mast the boom needs to be to give the extra height.

What's the boat?

Sail design has changed a lot over time and the dreaded drooping boom is evidence of that. Newer designs don't have that problem. We have a Seaway 25 which was designed during the JOG era and the idea was to maximise the sail area, so the boom hangs really low. Many Seaway owners have had the bottom of the main trimmed off. I did ours 2 years ago and it was one of the biggest improvements we've made to the boat. It has had zero effect on performance.

Thanks for that advice joelene I did that I found out my mast is a metre longer than the standard single spreader rig for an S and S 34 and the gooseneck is only 630mm above the deck so Im thinking I will raise the gooseneck to 900mm and have the new main made with a shorter luff

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slammin said...
What's the boat?

Sail design has changed a lot over time and the dreaded drooping boom is evidence of that. Newer designs don't have that problem. We have a Seaway 25 which was designed during the JOG era and the idea was to maximise the sail area, so the boom hangs really low. Many Seaway owners have had the bottom of the main trimmed off. I did ours 2 years ago and it was one of the biggest improvements we've made to the boat. It has had zero effect on performance.

Yep slammin I think that's what the original owner was thinking

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Ramona said...

cisco said..

A flattening reef may be what you want. Raises the boom just a tad.

I would be more inclined to stick with the original plan and learn to duck. My boom will hit my head too but eventually you get the message.

Knowing my luck it would knock me out of the cockpit and I'd be treading water watching my boat sail away

I was looking tonight at new yachts on the the net and to me they all seem to have there booms really high above the cabin top . It didn't look right to me

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HG02 said...
I was looking tonight at new yachts on the the net and to me they all seem to have there booms really high above the cabin top . It didn't look right to me

Yeah too high can look ungainly Hg. I think anything less than 1 metre should look alright