Here is a speculator for the forum
If the boat has a loose footed main does this make it more prone to bending the boom in a accidental gybe
Regards Don
In theory the loose footed main set up on the boom will be a bit more prone to plastic bending compression buckling deformation - that is permanent compressive buckling deformations are caused by the bending of the boom in the accidental gybe - the bending of the boom caused by means of the very high localised bending moment at the blocks and the compressive stresses on the leeward side of the boom as we saw here - which caused compression induced wall buckling on the leeward side of the boom. This is how alum cans buckle on the compressive side of them as you stamp on them.
An Aust Americas Cup yacht in the 90s sank due to compressive buckling of the deck due to encountering large seas in a race at the top end of the wind scale for them - around 25kts - and having not enough compressive buckling margin due to too many deck cut outs for crew pits etc..
For a mainsail with a foot bolt rope along the boom some of the clew end of boom total load perpendicular to the boom should be taken by the sail and foot bolt rope sort of uniformly distributed along the boom but the difference won't be much. As per prior input the boom should be designed to withstand an impact load of this type - ok 36knots virtually instantly will give a large force - would expect the design load case should be around twice this as per prior suggestions? The inertia load as mentioned before would be a very small fraction of the 36kt impact load case.
Hi r13
Thanks for your explanation
The way I was looking at it was with the loose footed main the wind force when the gybe occurs is concentrated at both ends of the boom and if the main sheet position is in the middle of the boom this might encourage the boom to bend at the block location as shown in stockies photo when the main sheet becomes taut after the boom has come across
Whereas with the bolt roped or slugged sail to the boom the force of the wind on the sail is spread along the foot of the sail when the gybe occurs and not just the ends
Regards Don
Select to expand quoteDonk107 said..
Hi r13
Thanks for your explanation
The way I was looking at it was with the loose footed main the wind force when the gybe occurs is concentrated at both ends of the boom and if the main sheet position is in the middle of the boom this might encourage the boom to bend at the block location as shown in stockies photo when the main sheet becomes taut after the boom has come across
Whereas with the bolt roped or slugged sail to the boom the force of the wind on the sail is spread along the foot of the sail when the gybe occurs and not just the ends
Regards Don
Hi Donk,
For a mainsheet attachment point in the centre of the boom...
Yes. A bolt rope setup would lessen the concentration of force being applied at the clew end of the boom.
This would shorten the lever arm pushing the end of the boom , lowering the amount of force being applied at the mainsheet attachment point. Agree with r13, I don't think it would be a huge difference.
If you move the mainsheet attachment point to the end of the boom, then the answer would become No.
But this creates other issues...
Hi Shaggy,
End boom sheeting, other issues. That's me. Anything I should be aware of?
Cheers
HI Sail,
Hail fellow end boom sheeter..er! Nothing you probably haven't already witnessed yourself... but for the discussion and in no order of priority:
- the span of the boom is unsupported, This means more susceptibility to bending the boom due to the resistance to compression forces acting on the end of the boom rather than a mid span attachment, so the boom section needs to be more resistant to longitudinal forces.
- much more mainsheet length. With the extra length, you need more winch revolutions to achieve the same boom position, so you have less load but spend more time at the winch. Add to that a 3:1 or suchlike and you have a lot more sheet to move to depower and recover quickly, so we tend to have someone on the mainsheet at all times in heavy airs.
- another thing trying to kill you. Like witnessed with the tragic loss of John Fischer in the Volvo, a loaded mainsheet sweeping across the cockpit has enough force to not just toss you out of the boat but really cause serious damage. I dont know what would be worse, getting pinned or thrown overboard.
- access in the advent of a failure. When ours failed we were running deep downwind in 30-35 knots. The damage meant the mainsheet, outhaul and reefs were all unusable. I'm looking at the mainsheet attachment point on the end of the boom hanging 5 feet above me and 15 feet out from the side of the boat thinking how the hell do I get out there????
Cheers,
SB
Select to expand quoteDonk107 said..
Hi r13
Thanks for your explanation
The way I was looking at it was with the loose footed main the wind force when the gybe occurs is concentrated at both ends of the boom and if the main sheet position is in the middle of the boom this might encourage the boom to bend at the block location as shown in stockies photo when the main sheet becomes taut after the boom has come across
Whereas with the bolt roped or slugged sail to the boom the force of the wind on the sail is spread along the foot of the sail when the gybe occurs and not just the ends
Regards Don
Boom brake will take away the shock.
Select to expand quoteshaggybaxter said..
HI Sail,
Hail fellow end boom sheeter..er! Nothing you probably haven't already witnessed yourself... but for the discussion and in no order of priority:
- the span of the boom is unsupported, This means more susceptibility to bending the boom due to the resistance to compression forces acting on the end of the boom rather than a mid span attachment, so the boom section needs to be more resistant to longitudinal forces.
- much more mainsheet length. With the extra length, you need more winch revolutions to achieve the same boom position, so you have less load but spend more time at the winch. Add to that a 3:1 or suchlike and you have a lot more sheet to move to depower and recover quickly, so we tend to have someone on the mainsheet at all times in heavy airs.
- another thing trying to kill you. Like witnessed with the tragic loss of John Fischer in the Volvo, a loaded mainsheet sweeping across the cockpit has enough force to not just toss you out of the boat but really cause serious damage. I dont know what would be worse, getting pinned or thrown overboard.
- access in the advent of a failure. When ours failed we were running deep downwind in 30-35 knots. The damage meant the mainsheet, outhaul and reefs were all unusable. I'm looking at the mainsheet attachment point on the end of the boom hanging 5 feet above me and 15 feet out from the side of the boat thinking how the hell do I get out there????
Cheers,
SB
Hi Shaggy
Did you ever make any changes to stop the mainsheet catching on the wheels or are you just more careful now when gybing
Regards Don
Select to expand quoteDonk107 said..shaggybaxter said..
HI Sail,
Hail fellow end boom sheeter..er! Nothing you probably haven't already witnessed yourself... but for the discussion and in no order of priority:
- the span of the boom is unsupported, This means more susceptibility to bending the boom due to the resistance to compression forces acting on the end of the boom rather than a mid span attachment, so the boom section needs to be more resistant to longitudinal forces.
- much more mainsheet length. With the extra length, you need more winch revolutions to achieve the same boom position, so you have less load but spend more time at the winch. Add to that a 3:1 or suchlike and you have a lot more sheet to move to depower and recover quickly, so we tend to have someone on the mainsheet at all times in heavy airs.
- another thing trying to kill you. Like witnessed with the tragic loss of John Fischer in the Volvo, a loaded mainsheet sweeping across the cockpit has enough force to not just toss you out of the boat but really cause serious damage. I dont know what would be worse, getting pinned or thrown overboard.
- access in the advent of a failure. When ours failed we were running deep downwind in 30-35 knots. The damage meant the mainsheet, outhaul and reefs were all unusable. I'm looking at the mainsheet attachment point on the end of the boom hanging 5 feet above me and 15 feet out from the side of the boat thinking how the hell do I get out there????
Cheers,
SB
Hi Shaggy
Did you ever make any changes to stop the mainsheet catching on the wheels or are you just more careful now when gybing
Regards Don
G'day Don,
Yes, we ended up changing our processes. I couldn't bring myself to make more clutter in the boat. So, the process now is:
- run the boat as deep as you can.
- traveller up to centreline and locked.
- mainsheet on hard
- gybe.
- Ease. Really really quickly.
What I was doing wrong was not running deep enough prior to the gybe. As you bring the traveller up and sheet on, you're powering up of course and we'd simply overpower the boat, it would take off like a scalded cat and I'd have little or no steerage right when you're trying to gybe
. As a result, we were not sheeting on enough, which is kinda like putting a bandaid on the issue rather than correcting the root cause.
Now we run deep and stay deep until the mainsheet is taken up fully. If we overpower just keep digging deeper, no more gybing where the mainsheet is loose at any point.
I purposefully steer a higher course now , I aim for a few boat lengths higher than the gybe point so when we run deep we're not screwing our track around the course. We spend more time in the actual gybe playing ddw but the boat speed is higher overall throughout the maneuver (smoother). And I don't destroy wheels!
Cheers,
SB
Select to expand quoteRamona said..
They all seem to need a $13 climbers figure 8 and a lump of old rope and rig up a boom brake.
So eloquently put and so true. 
Select to expand quoteUncleBob said..Ramona said..
They all seem to need a $13 climbers figure 8 and a lump of old rope and rig up a boom brake.
So eloquently put and so true.
Hi Uncle Bob,
I agree but it's still horses for courses, a boom brake is suited for cruising not racing, you can get into more trouble with a brake than without in race mode. Besides, I have to have a brake hanging off the sidedeck, no chance of fitting under the boom. Which if I'm honest is more a preventer than a brake in that position, just a weird anomaly in the boat design I guess.
Select to expand quoteshaggybaxter said..UncleBob said..Ramona said..
They all seem to need a $13 climbers figure 8 and a lump of old rope and rig up a boom brake.
So eloquently put and so true.
Hi Uncle Bob,
I agree but it's still horses for courses, a boom brake is suited for cruising not racing, you can get into more trouble with a brake than without in race mode. Besides, I have to have a brake hanging off the sidedeck, no chance of fitting under the boom. Which if I'm honest is more a preventer than a brake in that position, just a weird anomaly in the boat design I guess.
Maybe I should consider a boom brake, more $$$ but it might offer a potential saving. I'm not a big fan of running dead square, but occasionally that what your delt.
Regarding the different mainsheet attachment options, together with a loose footed main, I guess the aim is not to do uncontrolled gybes! The pluses for the sheet arrangement and the loose foot, I think in a cruising configuration, are worth having.
The fact that my new dyneema full covered 8mm halyard got the covered shredded as well, indicated to me there was a lot of force acting and something or perhaps multiple items had to yield to those forces.
Now if Selden were amendable to supplying the boom extrusion for customers to pop rivet and bolt their existing ends on, well that would make the whole affair reasonable.
From what can gather, the decision by them to only sell v
complete booms is recent, as I have seen on a you tube blog, some cruisers receiving a section in a remote island to fix theirs.
Richard
A few years ago I experienced a gybe at night somewhere north of Mooloolaba as the breeze shifted quickly from a NE to a land breeze. I had a preventer rigged which snapped but probably limited damage. I decided to get a boom brake. At the time Don McIntyre was selling the one I installed. He said he wouldn't go offshore without one. Just for the record, I had a rectangular section Selden boom
The vang on my Swanson has a snap shackle on the bottom which l can unclip and clip onto the toe rail when running square .Cheap and effective
Regards jb
Select to expand quoteStockie said..
Maybe I should consider a boom brake, more $$$ but it might offer a potential saving. I'm not a big fan of running dead square, but occasionally that what your delt.
Regarding the different mainsheet attachment options, together with a loose footed main, I guess the aim is not to do uncontrolled
Climbers descender is about $13. I have a flash one and I paid a bit more. The rope is an old headsail sheet, 14mm seems to offer the right amount of resistance when both sides are tensioned. Turning blocks on the toe rail abeam the descender and the rope goes to cleats either side of the cockpit. I only use it when I'm forced to gybe crossing the local bar in fresh conditions. Recently I had to gybe after I had crossed the bar in sloppy conditions and I had not tensioned the brake. Snapped my boom vang at the wire strop and broke the strut. If I was to sail dead downwind in fresh conditions I would definitely tension both sides.
www.ebay.com.au/itm/35KN-Figure-8-Descender-Belay-Device-Rock-Climbing-Caving-Rappelling-Rescue-Gear/264103856001?hash=item3d7dd10781:g:BHgAAOSwCx5bKHSj
Select to expand quoteRamona said..Stockie said..
Maybe I should consider a boom brake, more $$$ but it might offer a potential saving. I'm not a big fan of running dead square, but occasionally that what your delt.
Regarding the different mainsheet attachment options, together with a loose footed main, I guess the aim is not to do uncontrolled
Climbers descender is about $13. I have a flash one and I paid a bit more. The rope is an old headsail sheet, 14mm seems to offer the right amount of resistance when both sides are tensioned. Turning blocks on the toe rail abeam the descender and the rope goes to cleats either side of the cockpit. I only use it when I'm forced to gybe crossing the local bar in fresh conditions. Recently I had to gybe after I had crossed the bar in sloppy conditions and I had not tensioned the brake. Snapped my boom vang at the wire strop and broke the strut. If I was to sail dead downwind in fresh conditions I would definitely tension both sides.
www.ebay.com.au/itm/35KN-Figure-8-Descender-Belay-Device-Rock-Climbing-Caving-Rappelling-Rescue-Gear/264103856001?hash=item3d7dd10781:g:BHgAAOSwCx5bKHSj
Good idea and a good looking set up there Ramona. I like that it sits there with both port and starboard ropes ready to bring into action. I've got a figure 8 somewhere, I'll dig it out and give this a go. Far more elegant than my usual setup for running dead downwind!
Select to expand quoteshaggybaxter said..Donk107 said..
Hi r13
Thanks for your explanation
The way I was looking at it was with the loose footed main the wind force when the gybe occurs is concentrated at both ends of the boom and if the main sheet position is in the middle of the boom this might encourage the boom to bend at the block location as shown in stockies photo when the main sheet becomes taut after the boom has come across
Whereas with the bolt roped or slugged sail to the boom the force of the wind on the sail is spread along the foot of the sail when the gybe occurs and not just the ends
Regards Don
Hi Donk,
For a mainsheet attachment point in the centre of the boom...
Yes. A bolt rope setup would lessen the concentration of force being applied at the clew end of the boom.
This would shorten the lever arm pushing the end of the boom , lowering the amount of force being applied at the mainsheet attachment point. Agree with r13, I don't think it would be a huge difference.
If you move the mainsheet attachment point to the end of the boom, then the answer would become No.
But this creates other issues...
I think the loose foot design makes a big difference. Not only is the bending moment greater for a mid sheeted boom, but also there is an added compression load, with the clew taking most of the side load through a relatively shallow angle, resulting in a substantial clew attachment force multiplier.
Ok good point but my comments were based on the normal loose foot clew arrangement which has the loads perpendicular to the boom reacted by a very solid velcro strapping or spectra around the boom and through the clew ring of the sail, or a very solid metal slug in the boom bolt rope track if it had one, or a shackle onto a very strong slide and track secured to the end of the boom. The normal reefing system has such tracks secured to the side of the boom with pulleys able to suitably located so as to achieve the reef as well as the clew direction load needed to ensure the reefed sail does not bag. Like you seem to be, I prefer bolt rope mainsail foots to keep the foot captive and avoid wind flow leakage down between the sail foot and boom.
See some effusive links here.........
www.fxsails.com/article_loosefoot.php
www.cruisersforum.com/forums/f116/loose-footed-main-sails-274.html
Select to expand quoteshaggybaxter said..Donk107 said..shaggybaxter said..
HI Sail,
Hail fellow end boom sheeter..er! Nothing you probably haven't already witnessed yourself... but for the discussion and in no order of priority:
- the span of the boom is unsupported, This means more susceptibility to bending the boom due to the resistance to compression forces acting on the end of the boom rather than a mid span attachment, so the boom section needs to be more resistant to longitudinal forces.
- much more mainsheet length. With the extra length, you need more winch revolutions to achieve the same boom position, so you have less load but spend more time at the winch. Add to that a 3:1 or suchlike and you have a lot more sheet to move to depower and recover quickly, so we tend to have someone on the mainsheet at all times in heavy airs.
- another thing trying to kill you. Like witnessed with the tragic loss of John Fischer in the Volvo, a loaded mainsheet sweeping across the cockpit has enough force to not just toss you out of the boat but really cause serious damage. I dont know what would be worse, getting pinned or thrown overboard.
- access in the advent of a failure. When ours failed we were running deep downwind in 30-35 knots. The damage meant the mainsheet, outhaul and reefs were all unusable. I'm looking at the mainsheet attachment point on the end of the boom hanging 5 feet above me and 15 feet out from the side of the boat thinking how the hell do I get out there????
Cheers,
SB
Hi Shaggy
Did you ever make any changes to stop the mainsheet catching on the wheels or are you just more careful now when gybing
Regards Don
G'day Don,
Yes, we ended up changing our processes. I couldn't bring myself to make more clutter in the boat. So, the process now is:
- run the boat as deep as you can.
- traveller up to centreline and locked.
- mainsheet on hard
- gybe.
- Ease. Really really quickly.
What I was doing wrong was not running deep enough prior to the gybe. As you bring the traveller up and sheet on, you're powering up of course and we'd simply overpower the boat, it would take off like a scalded cat and I'd have little or no steerage right when you're trying to gybe. As a result, we were not sheeting on enough, which is kinda like putting a bandaid on the issue rather than correcting the root cause.
Now we run deep and stay deep until the mainsheet is taken up fully. If we overpower just keep digging deeper, no more gybing where the mainsheet is loose at any point.
I purposefully steer a higher course now , I aim for a few boat lengths higher than the gybe point so when we run deep we're not screwing our track around the course. We spend more time in the actual gybe playing ddw but the boat speed is higher overall throughout the maneuver (smoother). And I don't destroy wheels!
Cheers,
SB
- run the boat as deep as you can.
- traveller up to centreline and locked.
- mainsheet on hard
- gybe.
- Ease. Really really quickly
Yep this is exactly what I do too and as long as I'm on the ball with the quick ease, it works well.
Select to expand quoteSunsetSailer said..
A few years ago I experienced a gybe at night somewhere north of Mooloolaba as the breeze shifted quickly from a NE to a land breeze. I had a preventer rigged which snapped but probably limited damage. I decided to get a boom brake. At the time Don McIntyre was selling the one I installed. He said he wouldn't go offshore without one. Just for the record, I had a rectangular section Selden boom
Hi Sunset, what diameter and type of rope was it that snapped out of interest? Reading through this thread and considering the loads and events like your experience, I'm thinking of using a length of old dynamic climbing rope to give the preventer system a bit more shock absorbtion.
Select to expand quote2bish said..SunsetSailer said..
A few years ago I experienced a gybe at night somewhere north of Mooloolaba as the breeze shifted quickly from a NE to a land breeze. I had a preventer rigged which snapped but probably limited damage. I decided to get a boom brake. At the time Don McIntyre was selling the one I installed. He said he wouldn't go offshore without one. Just for the record, I had a rectangular section Selden boom
Hi Sunset, what diameter and type of rope was it that snapped out of interest? Reading through this thread and considering the loads and events like your experience, I'm thinking of using a length of old dynamic climbing rope to give the preventer system a bit more shock absorbtion.
Long time ago but probably 10 or 12 mm double braid. While this would be low stretch, I don't think more shock absorption would have helped as the break resulted from high static pressure not due to a dynamic swing arrested.
Taking up some of the other points here, the sail was loose footed and end boom sheeting.
Comments re sheeting in before the gybe are fine for an intentional, planned gybe but don't happen in an accidental gybe.
On sheeting in, being able to do it quickly is important. Pic of the two speed, 4:1 and 8:1 set up not needing any winching. Plenty of purchase on the traveller too.
I have no knowledge of a climbers figure 8 but another pic of the brake I fitted under load tells its own story.
