drogue attachment strategy

[markxengineerin]

I am looking for the best way to attach a galerider drogue to the stern of the boat, using limited resources (what is on board). The best option for location seems to be the stern cleats, although the fairleads are angled properly for dock lines (going off to the left in photo), not trailing a drogue bridle (off to the right in photo). The edges are well-rounded already and have good backing plates.


If going with just the 5/8" 3 strand (9000 lb breaking strength I believe), would it be better to chafe guard, or not? I think I read somewhere that the chafe guard just causes the line to overheat on stretch/unstretch.


I also read that the fairleads should be fully enclosed, so thinking about adding a plate on top like this:

temporarily made from G10 bar stock, but eventually I'd replace with something bronze and smoothed out to look pretty. I can imagine the drogue accidentally getting above deck level and line popping out, so this seems like a smart move.

Possible idea to reduce chafe: I have enough 3/16" dyneema to do an endless loop or soft shackle around a thimble for the 3 strand. This way the dyneema would take the awkward corner/direction change. I think I would use 2 or 3 loops rather than the 6 shown, to be strong enough.


Comments/ideas welcome, thank you

[Benz]

The last idea, definitely. I make a selvagee like this whenever I want to reduce line sawing in the hawse.

[LakeSuperior]

You may want to install closed fairleads as it will be problematic to place them in the open fairleads when deploying and having them remain while running. Think of the pitching motion and dynamics of the boat in a storm situation.

[NSboatman]

What size/displacement boat and drogue are we talking about here?

Looks to me like those fairleads are simple screwed into the teak rail; which is NOT going to work. You can expect loads close to the full displacement of your vessel on a properly sized drogue in storm conditions (which is when you will use this). I don’t care what those screws are or how your rig it - those fairleads will be ripped right off in storm conditions. And probably the cleats too.

What you’ve shown (either approach) is fine for lighter gale conditions when you simply want to stop for a break. Maybe. But it’s marginal even then. And what happens if you deploy thinking it’s just a wee gale; and then conditions deteriorate? It will give up on you just when you need it most.

Series drogues are awesome- but useless if you don’t give them a strong enough point of attachment. Watch a few YouTube vids of them in action to get an idea of the sawing, yawing and loads involved. You can’t under-bake this one.

This is NOT an area to cheap out on. Either install massive external, thru-bolted chain plates projecting aft on either side of the stern; or heavy thru bolted d-rings on each corner of the transom itself; or some similar outboard, clean and clear running and chafe-free attachment point… or sell the series drogue and don’t head for that kind of weather.

A half-baked safety system is worse than none at all- it gives a false sense of security and leaves you in truly desperate situations when it fails.

Chain plates are not complicated. Just pieces of 316 stainless flat bar with holes drilled in them. Any fool can make them or get them made, and installation is basic. This a $200 solution- max.

[Pete7]

There is a comment in the JSD instructions that the maximum load can equal the weight of the boat. This may not apply to the Galerider, but does give an indication of the loads.

I have seen one of our sister yachts (with a flat transom) have two large stainless plates added just under the topsides to deck join, one on each quarter. they looked similar to chain plates and heavy bolts secured to similar glassed in plates on the inside. The hole in the end which stood proud of the transom had been fitted with a welded thimble to take two large D shackles.

We are never going to need a drogue, but if we did, I would copy something similar. Whilst our cleats do have backing plates etc, I am not sure I want to use them for this. the line out of the stern could easily touch the push pit too going down a wave.

Pete

[LakeSuperior]

Originally Posted by NSboatman

What size/displacement boat and drogue are we talking about here?

Looks to me like those fairleads are simple screwed into the teak rail; which is NOT going to work. You can expect loads close to the full displacement of your vessel on a properly sized drogue in storm conditions (which is when you will use this). I don’t care what those screws are or how your rig it - those fairleads will be ripped right off in storm conditions. And probably the cleats too.

What you’ve shown (either approach) is fine for lighter gale conditions when you simply want to stop for a break. Maybe. But it’s marginal even then. And what happens if you deploy thinking it’s just a wee gale; and then conditions deteriorate? It will give up on you just when you need it most.

Series drogues are awesome- but useless if you don’t give them a strong enough point of attachment. Watch a few YouTube vids of them in action to get an idea of the sawing, yawing and loads involved. You can’t under-bake this one.

This is NOT an area to cheap out on. Either install massive external, thru-bolted chain plates projecting aft on either side of the stern; or heavy thru bolted d-rings on each corner of the transom itself; or some similar outboard, clean and clear running and chafe-free attachment point… or sell the series drogue and don’t head for that kind of weather.

A half-baked safety system is worse than none at all- it gives a false sense of security and leaves you in truly desperate situations when it fails.

Chain plates are not complicated. Just pieces of 316 stainless flat bar with holes drilled in them. Any fool can make them or get them made, and installation is basic. This a $200 solution- max.

Said very well?

[NSboatman]

Originally Posted by NSboatman

What size/displacement boat and drogue are we talking about here?

Looks to me like those fairleads are simple screwed into the teak rail; which is NOT going to work. You can expect loads close to the full displacement of your vessel on a properly sized drogue in storm conditions (which is when you will use this). I don’t care what those screws are or how your rig it - those fairleads will be ripped right off in storm conditions. And probably the cleats too.

What you’ve shown (either approach) is fine for lighter gale conditions when you simply want to stop for a break. Maybe. But it’s marginal even then. And what happens if you deploy thinking it’s just a wee gale; and then conditions deteriorate? It will give up on you just when you need it most.

Series drogues are awesome- but useless if you don’t give them a strong enough point of attachment. Watch a few YouTube vids of them in action to get an idea of the sawing, yawing and loads involved. You can’t under-bake this one.

This is NOT an area to cheap out on. Either install massive external, thru-bolted chain plates projecting aft on either side of the stern; or heavy thru bolted d-rings on each corner of the transom itself; or some similar outboard, clean and clear running and chafe-free attachment point… or sell the series drogue and don’t head for that kind of weather.

A half-baked safety system is worse than none at all- it gives a false sense of security and leaves you in truly desperate situations when it fails.

Chain plates are not complicated. Just pieces of 316 stainless flat bar with holes drilled in them. Any fool can make them or get them made, and installation is basic. This a $200 solution- max.

Sorry- I missed that you said Galerider and not Jordan series drogue. My bad.

The thinking with the galeriders is that the static loads are not quite as high as series drogues for a given size comparison; but because they are a point drag device (as opposed to a series extended drag device); they can ‘pop out of a wave face’, or tumble and collapse in a breaking wave front. They seem to recover quickly- but the few seconds of zero drag can result in nasty accelerations of the boat, and of course that means large spikes in dynamic snap loads on the bridle and securing gear.

The logic remains the same for either drogue- There is no free lunch here. Build it strong enough to take your full displacement being decelerated from 5 knots in a second or so; and it should be fine.

Lesser attachments will let you down when you need them.

Or- just don’t sail in those conditions. Ever.

[markxengineerin]

Original idea

Modified idea

Blue is a thin piece of lexan screwed into the teak, to protect it. All edges fully rounded/deburred. Green is a new fairlead (through bolted, at the correct angle) made from stacked up G10 fiberglass bar stock I have on board.

The bronze fairleads are only screwed in, no backing plates, so I'm leaning towards the latter option. That said, if the fairleads were to rip out, it wouldn't immediately be the end of the world, but there'd be a loss of control and probably more chafe issues and collateral damage, not something I'd want to experience.

The cleats themselves have backing plates, but I have not investigated the core material (or how far out any reinforcement extends beyond the cleat), which I think matters a lot here.

Strengths:
5/8" 3 strand bridle leg: 9000ish pounds (per leg)
3/16" dyneema bridle to cleat "endless loop" 5000*4 strands active per leg = 20,000 lbs.(is this correct?)
Cleat mount screws: 1/4-20 bronze (~90ksi uts), quantity 4, will support 11,444 pounds in tension, 6869 pounds in shear, worst case scenario. Really, they won't see all the shear if they're torqued up, but I suspect they're the weakest link right now.

Deck: 1/2" thickness, unknown core, looks solid fiberglass or maybe plywood, hopefully not balsa
Backing plates: 5"x3" rectangle, unknown thickness (1/8"?), unknown material (stainless or aluminum probably)
16"length*0.5" thickness = 8in^2 of shear area for ripping backing plate through the core.
Some relevant testing I could find is here: https://www.practical-sailor.com/boa...ate-need-to-be
They also had 1/2" thick deck, 1/4" bolts, in their case, balsa core. Their conclusion sounds too extreme to me

Our testing found that a 1-inch washer is too small for a structural backing plate for a quarter-inch bolt in a cored deck. We suggest either a backing plate extending 1 inches beyond each fastener, or a minimum of 3 inches in diameter for high-load applications.

But I guess that shows the necessity of using something other than balsa core in high load locations. If the deck is balsa core, it needs something stronger for an area enclosed by a 37" outline, according to the above logic.

My core needs a shear strength of 1500 psi or higher (at existing backing plate size) to ensure the 3 strand is the weak link- this does not sound challenging for a plywood or solid glass core. Anyone have numbers for rip out force for marine plywood (glassed or not?).

Overall interpretation so far, I think these cleats will work even with my long term plan (not yet purchased Jordan series drogue kit) pending the core not being balsa, and having really good "plates" on top and bottom of deck. I will re-make these and they'll be very thick + tapered, and probably use higher strength bolts and/or add some if I can figure out a way.

I think this is a safe alternative to "drogue plates" and better looking, what do you think?

[thinwater]

Put the Galerider on the winches using a bridle. This will allow you to adjust the rode length (to avoid pulling out or waves) and offset according to conditions.


A Galerider does NOT create high forces, like a JSD or parachute. Considerably less than jib sheeting loads. Yes, I've done the testing.


You will still need to address chafe. On my boat the spinnaker sheet turning blocks give a fair lead aft, so we used them. The turning angle is much less than when sheeting, so plenty strong.

[Lee Jerry]

Originally Posted by markxengineerin

Original idea

Modified idea

Blue is a thin piece of lexan screwed into the teak, to protect it. All edges fully rounded/deburred. Green is a new fairlead (through bolted, at the correct angle) made from stacked up G10 fiberglass bar stock I have on board.

The bronze fairleads are only screwed in, no backing plates, so I'm leaning towards the latter option. That said, if the fairleads were to rip out, it wouldn't immediately be the end of the world, but there'd be a loss of control and probably more chafe issues and collateral damage, not something I'd want to experience.

The cleats themselves have backing plates, but I have not investigated the core material (or how far out any reinforcement extends beyond the cleat), which I think matters a lot here.

Strengths:
5/8" 3 strand bridle leg: 9000ish pounds (per leg)
3/16" dyneema bridle to cleat "endless loop" 5000*4 strands active per leg = 20,000 lbs.(is this correct?)
Cleat mount screws: 1/4-20 bronze (~90ksi uts), quantity 4, will support 11,444 pounds in tension, 6869 pounds in shear, worst case scenario. Really, they won't see all the shear if they're torqued up, but I suspect they're the weakest link right now.

Deck: 1/2" thickness, unknown core, looks solid fiberglass or maybe plywood, hopefully not balsa
Backing plates: 5"x3" rectangle, unknown thickness (1/8"?), unknown material (stainless or aluminum probably)
16"length*0.5" thickness = 8in^2 of shear area for ripping backing plate through the core.
Some relevant testing I could find is here: https://www.practical-sailor.com/boa...ate-need-to-be
They also had 1/2" thick deck, 1/4" bolts, in their case, balsa core. Their conclusion sounds too extreme to me
But I guess that shows the necessity of using something other than balsa core in high load locations. If the deck is balsa core, it needs something stronger for an area enclosed by a 37" outline, according to the above logic.

My core needs a shear strength of 1500 psi or higher (at existing backing plate size) to ensure the 3 strand is the weak link- this does not sound challenging for a plywood or solid glass core. Anyone have numbers for rip out force for marine plywood (glassed or not?).

Overall interpretation so far, I think these cleats will work even with my long term plan (not yet purchased Jordan series drogue kit) pending the core not being balsa, and having really good "plates" on top and bottom of deck. I will re-make these and they'll be very thick + tapered, and probably use higher strength bolts and/or add some if I can figure out a way.

I think this is a safe alternative to "drogue plates" and better looking, what do you think?

I don't think your analysis is correct. The primary loading on the cleat will be shear. I don't understand the (second) highlighted statement at all. (And I think the first is a little higher in strength, but not enough to make a big difference.)

Since the loading is shear, the primary strength members of import are the shear area / strength of the boats and the compressive strength of the top skin of the deck - i.e. it's thickness. Everything else, including the backing plate and the core material, are of secondary or tertiary importance.

In summary, I don't think the cleats are strong enough for this application, based on the line you plan attach unless the actual load from the drogue will be less than that 9000 lb breaking strength, in which case I would go down in size (or at least add a fuse) to ensure the line breaks before the cleat pulls off the deck.

[markxengineerin]

Yes, I've done the testing.

Can you describe how that test was done? The galerider in question is the 36" size advertised for boats 10 to 30K in displacement. I'm maybe 17 or 18k lbs. Adjusting the bridle doesn't seem like a realistic way to change wave patterns when the bridle has only 25' long legs (my case, not sure what the recommendation is there?)

The primary loading on the cleat will be shear.

In theory, yes, but in a storm, other loads could happen. I'm thinking about the cleat being ripped directly out of the deck, and loaded in shear, to make sure it's safe for both cases or a combination of the two. The numbers I posted calculate the tensile stress in the bolts if there is an upward force on the cleat, and a shear stress in the bolts if the cleat is pulled horizontally (and rigid enough to load each bolt equally). If the bolts are tight and the joint is rigid in reality, the bolts will not see any shear at all, that's how bolted joints work. I don't know if that's the case here or not, but that's an easy one to figure out, does not worry me.

I'm also not concerned about failing the deck in compression from tightening the bolts- the existing design already has tight bolts and it's not broken. But I can't say I agree with this: "Everything else, including the backing plate and the core material, are of secondary or tertiary importance"- The fiberglass is the unimportant thing- it's extremely strong in compression- the reason it could fail is if it goes into bending, not compression, if the core is weak. The core is the most important thing here.

My concerns are breaking the bolts (easy to analyze, done) or ripping the backing plate thru the deck (harder to analyze, working on it). Tension case is the easier one, which I described, it's a bit more complicated to think about how the deck would fail in shear loading. Shear on the cleat puts a moment on the deck. I believe that how that's reacted is again largely a result of the core material and the "plates" above and below.

[Lee Jerry]

Originally Posted by markxengineerin

Modified idea


Green is a new fairlead (through bolted, at the correct angle) made from stacked up G10 fiberglass bar stock I have on board.

Originally Posted by markxengineerin

In theory, yes, but in a storm, other loads could happen. I'm thinking about the cleat being ripped directly out of the deck, and loaded in shear, to make sure it's safe for both cases or a combination of the two. The numbers I posted calculate the tensile stress in the bolts if there is an upward force on the cleat, and a shear stress in the bolts if the cleat is pulled horizontally (and rigid enough to load each bolt equally). If the bolts are tight and the joint is rigid in reality, the bolts will not see any shear at all, that's how bolted joints work. I don't know if that's the case here or not, but that's an easy one to figure out, does not worry me.

I'm also not concerned about failing the deck in compression from tightening the bolts- the existing design already has tight bolts and it's not broken. But I can't say I agree with this: "Everything else, including the backing plate and the core material, are of secondary or tertiary importance"- The fiberglass is the unimportant thing- it's extremely strong in compression- the reason it could fail is if it goes into bending, not compression, if the core is weak. The core is the most important thing here.

My concerns are breaking the bolts (easy to analyze, done) or ripping the backing plate thru the deck (harder to analyze, working on it). Tension case is the easier one, which I described, it's a bit more complicated to think about how the deck would fail in shear loading. Shear on the cleat puts a moment on the deck. I believe that how that's reacted is again largely a result of the core material and the "plates" above and below.

If you are putting the new fairlead as shown in your picture or closing the existing one as you proposed, then the angle to the cleat is fixed. I don't know the exact heights, but that pull is essentially horizontal (relative to the deck), and that means the loading on the cleat is essentially shear. This is the normal intended condition, i.e. the primary loading. (Yes, there is a small overturning moment caused by the rope being slightly above the bolts.)

If the fairlead fails (or you don't install), then other loads can be introduced into the cleat. "Vertical" angles / loads can be applied (to either the fairlead or cleat) due to the pitch and roll of the boat. I think the pitch is fairly limited, roll can be much higher. However, the roll angle does not correlate 1:1 with the angle of the cleat load. So a 45deg roll does not put a 45deg vertical angle on the fitting. It is (or gets) complicated but give it some thought. However, assume the combined motions of the boat do give a 45deg lead into the fitting, that means the tension will then equal the shear (for the short duration of that event). So it would take a larger motion event to make the tension load higher than the shear. Thus, these vertical loads are secondary to the cleat (if the fairlead is installed, if not then some vertical load on the cleat should be considered primary as well). The importance of the backing plate will be "proportional" to how much vertical load is designed for. (If the loading were actually pure shear, like with rope at deck level, then no bolts or backing plate would be needed, it could be pinned to the deck.)

Whether the joint is a shear joint or a friction joint will depend on how the cleat is mounted. Note that the base of the cleat is rather small. If it is mounted just metal on fiberglass (which I hope it's not), then I think the friction coefficient, and thus force, would be pretty low. Even with some silicon or other sealant, I would think it is still pretty low. If an actual adhesive was used (like 3M 5200 or 4200), then it probably is or does have some friction joint properties. But again, due to the small base, I'm not sure how strong it would be. Plus, what's the shear strength of gelcoat?

Deck fittings, especially original ones like a mooring cleat, should be installed into solid FRP with no core. If mounted / retrofit onto a cored deck, then there are several options to deal with the core, such as the common over-drill and fill, and once this is done then core becomes essentially immaterial.

[thinwater]

I'm late to this thread, but having used a gale Rider ....


The best solution is to attach it to the sheet winches. The load will be far less than the windward genoa load (based on measurements) and this will allow you to adjust the drogue in and out and side to side, minimizing helm load and maximizing stability.


The ability to adjust the rode length cannot be overstated. In strong conditions it helps you keep it out of phase with the boat (the drogue must be on the back of a wave when you are being pushed). In lighter conditions it allows you to reduce the load by pulling it close. And it allows you to recover the drogue easily, making it more likely you will actually use it.


You will still need to address chafe, but this is easily done with webbing over the rode and moving it in and out periodically.