Standing rigging strength needs?

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Highlander
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Re: Standing rigging strength needs?

Post by Highlander » Tue Jun 09, 2015 9:58 pm

BOAT wrote:This is a pretty old post but since catigale has resurrected it I think I would like to add a point that was not brought up, upgrading the MAC rigging causes other trouble that can be dangerous.

It's not a good idea to upgrade the cleats on the deck of your boat so that the deck fails before the cleat does. Better to let the cleat rip off in a storm than a chunk of the deck. Same goes for other parts of the hardware: a stay should fail before a chain-plate, a goose-neck should fail before a mast, and so forth. Rigging needs to be sized to allow for the proper order of failure.

This was all taken into account when Roger built the boats. The factory rigging is just fine, these are very VERY light boats, not heavy ballasted keel boats.
Actually deck cleats can be up-graded if u r willing to do the proper re-enforcement , like bridging the deck & hull together with a bridge backing plate system , like I done when I built my 4ft double anchor roller bowsprit
The Bow bridge
http://i235.photobucket.com/albums/ee20 ... 010029.jpg

http://i235.photobucket.com/albums/ee20 ... 0012-1.jpg

http://i235.photobucket.com/albums/ee20 ... 010033.jpg

Hull Inside bridge section S/B & port sides
http://i235.photobucket.com/albums/ee20 ... 010012.jpg

http://i235.photobucket.com/albums/ee20 ... 010011.jpg

Deck bridge
http://i844.photobucket.com/albums/ab1/ ... 063342.jpg

All these 3 bridges combined together make my double anchor roller mounted rock solid

done the same with my anchor winch
this is the multi section bridge I made witch bridges the deck , anchor locker & hull all into one
http://i844.photobucket.com/albums/ab1/ ... 9a88cc.jpg

http://i844.photobucket.com/albums/ab1/ ... b5d86d.jpg

http://i844.photobucket.com/albums/ab1/ ... 1bd265.jpg

http://i844.photobucket.com/albums/ab1/ ... 3d6477.jpg

As long as it is done right & the load is spread out over a larger area :arrow: :idea: is a lot of hard work tho :)

J 8)
PS Though u,ll notice I have not up-grade the bow cleats as of yet :P

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mastreb
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Re: Standing rigging strength needs?

Post by mastreb » Tue Jun 09, 2015 11:18 pm

At the risk of inflaming the Internet, from an engineering standpoint large flat washers of the same thickness as a backing-plate are structurally equivalent to said backing plate, and much cheaper and easier to install. This is because the stress incumbent upon the backing plate fall off logarithmically from the distance from the bolt, to the point that the areas of the plate between the bolts do nothing useful.

That's why you see washers on all the new manufactured boats rather than custom drilled plates. Oh yeah, and they're cheaper.

Use washers of the largest practical diameter and thickness with the correct center diameter for your bolt, drill the hole to match the bolt diameter + 1/16", use the same sized washer on both sides of the RFP if possible (or be sure that both sides have equal clamping area), and you'll be fine. Of course prefer 316 stainless for bolts and washers, and prefer nylocks. Be certain you torque the bolts correctly for the material you're clamping, which for FRG is large, from 15 lbs. for a 1/2" diameter bolt to 110 lbs. for a 1" bolt. Smaller bolts are generally best at finger-tight plus one turn. Check the torque after the first loaded usage and re-torque to compensate for any compression of the FRP under the clamping pressure. Apply a small dab of paint to an easily visible side of the bolt to show any future motion--Loctite works well for that. Re-check bolt torques on anything under critical load pressure annually.

Matt

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Highlander
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Re: Standing rigging strength needs?

Post by Highlander » Wed Jun 10, 2015 12:27 am

I begg to differ I seen many a body washer on a stress related area cause serious stress cracks & loss of strength frp leaving said area as soft as rubber mat , the bigger foot print of a larger backing plate will prevent this , I have also seen body washers been pulled through an area of high stress from shock loading & the mac hull & deck r not a given thickness all the way along ur working area so u may have to add rubber matting to compensate for that or rubber tape

If u r gonna go to the trouble of doing something difficult do it right do it once ! Just Saying that,s all :wink:

J 8)

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Re: Standing rigging strength needs?

Post by Catigale » Wed Jun 10, 2015 5:26 am

I think the summary of this goes as follows.

A lot of folks read about forestay failures and then go to the "if 1/8 is good, then 5/32 is better" mantra.

If you group forestay failures into categories you find, in pseudo-random order

1 hitting mast on tree

2 failure under sail

3 failure on mooring/dock

Focussing on 2 and 3, the vast majority of these are fatigue failures to the best of my recollection here. I suspect most of these are caused by loose rigging.

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Re: Standing rigging strength needs?

Post by walt » Wed Jun 10, 2015 8:51 am

My 5/32 forestay is all made up and going on the boat next week.. but I completely agree with what is being said here that 1/8 is a better choice. One other thing to add about the 1/8 is that the wire looks like a spring over some small deflection and the smaller 1/8 will be a more flexible spring absorbing shock better (hooks law says it is linear i.e., delta deflection/delta force is the same from zero force until the wire starts deforming). The 1/8 wire is a more appropriate shock absorbing spring for our boats compared to the 5/32.

Also to add.. what I have seen is that forestays fail from the wire breaking at the top where the flexible wire interfaces with something rigid - and there wasn’t proper toggling (which almost happened to me on my first sailboat). Interesting that recently also a member here had one fail for the turnbuckle inside the drum winding loose and then of course there are cases where the pin came out because the ring failed or maybe just got overlooked when the mast was set up.

Regarding what Boat said, Sumner and I have the same boat (26S) and he recently had his rudder chock fail. I think this is one of two weak spots on the 26S (the other is that you can flood the boat if you heavily load the rear and leave the ballast inspection hole open and the bottom valve open). He put a lot of solar panel area in the back of the boat and some of it fairly high up. No problem in light wind but if you try and sail in heavier wind with this, as you heel the sail lift reduces. But.. as you heel, the solar panels will increase their "angle of attack" into the wind. This will increase both the lift and the drag of the panels (you don’t need a foil shape to get lift, hold a 2x4 out the window of a car - you can get lift out of it). Both of the L/D of the panels is at the rear of the boat and would tend to try and push out against the rudder - a force the boat was not designed for. In one of his blogs he said the boat had a tendency to round up and I think that was likely due to all that solar panel area force causing the rudder to stall (I just have a 10 watt panel on my 26S and it doesn’t do this). Maybe that rudder chock would have failed anyway.. but I cant help think that sailing with all that solar panel area had a big influence on the rudder failure.. Im sure what he comes up with for the fix wont ever fail again..

Yep.. changing the original design can have some unintended consequences..

Ill keep an eye on the 5/32 forestay... I don’t think I will live long enough to ever see any issue from it.. but like I said before, if I was going to do it over, I would stick with the 1/8.

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Re: Standing rigging strength needs?

Post by walt » Wed Jun 10, 2015 9:38 am

I suspect most of these are caused by loose rigging.
This one I really dont know since its very rare to know what tension was on a rig that failed.. but when I almost had my forestay failure (furler, 1/8 wire on a 16 foot boat), it had a very tight forestay but no toggle. Also see this link about a forestay failure and the rig was also tight..

http://www.macgregorsailors.com/forum/v ... =8&t=18807
I do rig with correct tensioning, and have done so since day one.
No mast pumping, shock loading, loose shrouds, etc.
Ever.
Tight and well tuned, so I really can't imagine going down that road, IMHO.
Its more the poor toggeling that I see the correlation with but certainly if you have a very loose rig you are probably asking for trouble.

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Re: Standing rigging strength needs?

Post by BOAT » Wed Jun 10, 2015 9:50 am

First off, all bets are off if you are going to include the Highlander boat in regards to upgrading.

The highlander boat does not just have larger forestays, it has MULTIPLE HEADSTAYS.

It’s a completely different animal. It's a cutter with extra spreaders and a backstay and multiple headsails and really has no relation to the original factory rig at all. The Highlander is a custom sailboat with an extra 1000 lbs. of weight - it's not the same as our boats. The Highlander boat also carries a compliment of sails that put forces on the rigging that none of us would ever encounter and also that boat has the extra weight to handle it. If you could put that much force into the sails of my boat without knocking it over it may pull the boat right out of the water. If any of you doubt the structural integrity of the "thin" hull of the MAC M some complain about just watch at the Highlander boat in rough Canadian seas.

The MAC was not well designed because Roger is some sort of genius boat builder. On the contrary, Roger Macgregor had no traditional boat building foundations at all! I was raised in the old traditional sailing methods and had left sailing altogether for many years because I was fed up with the toil and work of heavy boats – Roger was aware of our complaints and instead of immersing himself in traditional design like Peter Barrett and Stan Miller and other of his contemporaries, (competitors), he started with a fresh empty box. That’s exactly what was needed to get away from the traditional heavy designs and create something new. The MAC has EVOLVED by thousands of people calling the factory over many decades reporting what fails, what works, and what needs changing. If something is gonna break it would have 5 years ago to a hundred other people already. THAT is the ‘genius’ of the MAC, it was designed by TESTING, trial, and error. After all these years there was just nothing left for the factory to do. Seemed like a good time to pack up and quit to me, too.

In regards to hull structure: some ignorant think 'thicker' is 'stronger' but that's not true. People who build ski boats have known this for 20 years. Most of the 'thicker' in other sailboats is from excess resin, not more layers of glass. The truer statement is 'thicker' is 'HEAVIER’. Squeezing out every last drop of excess resin in the MAC hull before curing makes the hull lighter.

We all bought into the MAC ideology because we understood the engineering behind it. Let’s not go backwards in our thinking and return to that same crowd that is still stuck in the 1800’s medieval dark ages of boat architecture. There are a lot of other websites for that kind of info.

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Re: Standing rigging strength needs?

Post by Catigale » Wed Jun 10, 2015 11:41 am

mastreb wrote:At the risk of inflaming the Internet, from an engineering standpoint large flat washers of the same thickness as a backing-plate are structurally equivalent to said backing plate, and much cheaper and easier to install. This is because the stress incumbent upon the backing plate fall off logarithmically from the distance from the bolt, to the point that the areas of the plate between the bolts do nothing useful.

That's why you see washers on all the new manufactured boats rather than custom drilled plates. Oh yeah, and they're cheaper.

Use washers of the largest practical diameter and thickness with the correct center diameter for your bolt, drill the hole to match the bolt diameter + 1/16", use the same sized washer on both sides of the RFP if possible (or be sure that both sides have equal clamping area), and you'll be fine. Of course prefer 316 stainless for bolts and washers, and prefer nylocks. Be certain you torque the bolts correctly for the material you're clamping, which for FRG is large, from 15 lbs. for a 1/2" diameter bolt to 110 lbs. for a 1" bolt. Smaller bolts are generally best at finger-tight plus one turn. Check the torque after the first loaded usage and re-torque to compensate for any compression of the FRP under the clamping pressure. Apply a small dab of paint to an easily visible side of the bolt to show any future motion--Loctite works well for that. Re-check bolt torques on anything under critical load pressure annually.

Matt
But all that engineering jargon aside, a backing plate looks stronger, so it must be stronger. Washers are just bad juju.

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