Canting keel forces

[Lima November]

Since the shock load is predominant, consider using an accumulator. Here is a page with a drop down menu giving many options. http://www.parker.com/Products/EPD/EPDResu...+5%3A24%3A14+AM
Essentially, it works like the shock absorber on your car. You know what a bendy rig is. This would give you a "bendy keel".

If you use an accumulator (which acts as a spring, I assume), you'd better have a fucking good damper in your hydraulic system. Otherwise - one more vibrating element, possible flutter, all sorts of trouble. Perhaps that's the reason why they don't do this?

 

[vibroman]

Since the shock load is predominant, consider using an accumulator. Here is a page with a drop down menu giving many options. http://www.parker.com/Products/EPD/EPDResu...+5%3A24%3A14+AM

Essentially, it works like the shock absorber on your car. You know what a bendy rig is. This would give you a "bendy keel".

If you use an accumulator (which acts as a spring, I assume), you'd better have a fucking good damper in your hydraulic system. Otherwise - one more vibrating element, possible flutter, all sorts of trouble. Perhaps that's the reason why they don't do this?

The accumulator itself usually consists of a nitrogen filled bladder inside a pressure chamber. This actually introduces a significant damping component to the system instead of stiffness (and therefore less response to external excitation). Accumulators also provide reserve pressure inthe event of a pump failure. Problem is ....big and heavy again. so probably not used.

 

[Codger]

Since the shock load is predominant, consider using an accumulator. Here is a page with a drop down menu giving many options. http://www.parker.com/Products/EPD/EPDResu...+5%3A24%3A14+AM

Essentially, it works like the shock absorber on your car. You know what a bendy rig is. This would give you a "bendy keel".

If you use an accumulator (which acts as a spring, I assume), you'd better have a fucking good damper in your hydraulic system. Otherwise - one more vibrating element, possible flutter, all sorts of trouble. Perhaps that's the reason why they don't do this?

The accumulator itself usually consists of a nitrogen filled bladder inside a pressure chamber. This actually introduces a significant damping component to the system instead of stiffness (and therefore less response to external excitation). Accumulators also provide reserve pressure inthe event of a pump failure. Problem is ....big and heavy again. so probably not used.

The trade off is weight in the rams versus weight in the accumulator. I'm not expert enough to do the design, but I think it's worth looking at. If you control the shock by damping it and spreading it over a longer time frame, you lower the peak value felt by the rams and might be able to downsize them while retaining enough overall shock resistance. Additionally, you use the protective rupture disc on the accumulator as your weakest link. If you overload the system, you screw out the old one and screw in a new one, less than 1 lb. in spare parts!!! No lost fluid either.

 

[dtoc]

No shock absorbation in system (not sure current systems are taking full advantage of this)

Maybe not full advantage, but they use it. They have some valve in the hydraulics that opens when the pressure in the cylinder gets too high, so that the keel drops a little on heavy impacts (I remember Bouwe Bekking mentions it somewhere). That limits the peak loads on the rams, by the way (for those of you who are computing those loads).

A pressure relief valve will not always work as desired / in the manner described, which is way these systems are failing even though they all have prv's.

A prv is a spring backed valve that as the pressure rises, the force opens the valve against the spring and any back pressure. (there are variations on the design, but this is the basic concept) Based on this it has a characteristic opening time.

It would most likely be installed in the control block, which is where all the valves to control the flow to the cylinders are.

For a prv to protect the ram it must be able to release fluid from the system as fast as the ram displaces it. Therefore the characteristic opening time must be less than the time it takes the pressure to build (the time it takes to stop the keel when the boat lands), it must be large enough to flow enough fluid from the system to drop the pressure and it must see the same pressure rise at the same time as the ram.

With these issues it would be almost impossible to design a prv into the system that would be effective at protecting the cylinder from over pressure when landing off of a wave. You also lose all of the energy from the system and have to pump the keel back up.

dtoc

 

[dtoc]

Since the shock load is predominant, consider using an accumulator. Here is a page with a drop down menu giving many options. http://www.parker.com/Products/EPD/EPDResu...+5%3A24%3A14+AM

Essentially, it works like the shock absorber on your car. You know what a bendy rig is. This would give you a "bendy keel".

If you use an accumulator (which acts as a spring, I assume), you'd better have a fucking good damper in your hydraulic system. Otherwise - one more vibrating element, possible flutter, all sorts of trouble. Perhaps that's the reason why they don't do this?

The accumulator itself usually consists of a nitrogen filled bladder inside a pressure chamber. This actually introduces a significant damping component to the system instead of stiffness (and therefore less response to external excitation). Accumulators also provide reserve pressure inthe event of a pump failure. Problem is ....big and heavy again. so probably not used.

The trade off is weight in the rams versus weight in the accumulator. I'm not expert enough to do the design, but I think it's worth looking at. If you control the shock by damping it and spreading it over a longer time frame, you lower the peak value felt by the rams and might be able to downsize them while retaining enough overall shock resistance. Additionally, you use the protective rupture disc on the accumulator as your weakest link. If you overload the system, you screw out the old one and screw in a new one, less than 1 lb. in spare parts!!! No lost fluid either.

Accumulators are like a spring but have built in damping. The damping comes from having to flow the fluid through the connection to system which is a restriction. If the restriction is too great it won't control the peaks and if it is too small you can get oscillations. Considering how long it takes to move the keel, the restriction is probably not too small.

While they do incur a weight penalty, this would be more than made up for by reliability and performance.

A bursting disc could be a good addition. It would release the nitrogen/air charge, which would have to be pumped back up.

 

[star-sailor]

marian has the best (=high-res) photo of the keel-structure in his gallery. maybe you have not seen it yet:

http://www.bymnews.com/photos/albums/Gener...r-portimao4.jpg

 

[vibroman]

Do we know the failure mode of the hydraulic systems?

Are the cylinders bursting due to over pressure? Are the seals failing due to overpressure

or are the rams snapping?

Hard to see how a ram could fail due to pressure surges in the susyem as the load from the hyraulic pressure is all compressive.

 

[dtoc]

Do we know the failure mode of the hydraulic systems?
Are the cylinders bursting due to over pressure? Are the seals failing due to overpressure

or are the rams snapping?

Hard to see how a ram could fail due to pressure surges in the susyem as the load from the hyraulic pressure is all compressive.

The rams are double acting, so when one ram is pushig the other is pulling. The rod on the pulling ram is in tension and I believe this is the rod that has failed every time. Seals have also failed, or similar over pressure failures.

 

[vibroman]

Do we know the failure mode of the hydraulic systems?

Are the cylinders bursting due to over pressure? Are the seals failing due to overpressure

or are the rams snapping?

Hard to see how a ram could fail due to pressure surges in the susyem as the load from the hyraulic pressure is all compressive.

The rams are double acting, so when one ram is pushig the other is pulling. The rod on the pulling ram is in tension and I believe this is the rod that has failed every time. Seals have also failed, or similar over pressure failures.

I gotcha

Seems like a single acting ram system would be more robust (only working in compression). Also hard to design a support structure that is equally efficient in both compression and tension. Are all the systems double acting or are the ABN boats using a single acting system?

 

[couchsurfer]

No shock absorbation in system (not sure current systems are taking full advantage of this)

Maybe not full advantage, but they use it. They have some valve in the hydraulics that opens when the pressure in the cylinder gets too high, so that the keel drops a little on heavy impacts (I remember Bouwe Bekking mentions it somewhere). That limits the peak loads on the rams, by the way (for those of you who are computing those loads).

A pressure relief valve will not always work as desired / in the manner described, which is way these systems are failing even though they all have prv's.

A prv is a spring backed valve that as the pressure rises, the force opens the valve against the spring and any back pressure. (there are variations on the design, but this is the basic concept) Based on this it has a characteristic opening time.

It would most likely be installed in the control block, which is where all the valves to control the flow to the cylinders are.

For a prv to protect the ram it must be able to release fluid from the system as fast as the ram displaces it. Therefore the characteristic opening time must be less than the time it takes the pressure to build (the time it takes to stop the keel when the boat lands), it must be large enough to flow enough fluid from the system to drop the pressure and it must see the same pressure rise at the same time as the ram.

With these issues it would be almost impossible to design a prv into the system that would be effective at protecting the cylinder from over pressure when landing off of a wave. You also lose all of the energy from the system and have to pump the keel back up.dtoc

....here's a response Juank gave to a query I sent in late november ........I was asking if there's any form of 'accumulator' type of shock absorption......a fair bit of details to help SA's engineering department.....

From JUAN K--''I think shock absortion is more that adequate,but it's a good point. For the

volvo boats we have a pressure release system that is adjusted to release

the oil on the canting cylinders [one each side of the keel] before the

fin itself can get to undesireble levels of stress. This setting is usually

between 200 and 250 Bar [depends on the cylinder diameter] but equates to

about 400Mpa flexural stress on the fin.''

''Simply there is a pressure valve that opens up at a set pressure and

therefore allows the oil in the cylinders to leave and go back into the

reservoir to be pumped up again a bit later. There is not such a thing as

dampening other than letting the oil out.''

''This system is adjustable to account for the friction on the keel axis bearings which increase after a

few days at sea and are replaced regularly.------ If the boats would not have this they will be in pieces by now''END QUOTE

 

[born2sail]

MEMO

To: SA Engineering Dept

From: SA Non-engineering Dept

Subject: Ram Differences & Similarities

Are the rams and canting systems on the AA boats somewhat similar or dramatically different that those employed by the other boats? And did everybody start out with Ti rams or were the AA boats SS to begin with?

Last dumb question...did all the boats with broken keel systems also experience structural damage and if so, did the structural damage occur before, during or after the keel system went kaput?

 

[dtoc]

....here's a response Juank gave to a query I sent in late november ........I was asking if there's any form of 'accumulator' type of shock absorption......a fair bit of details to help SA's engineering department.....
From JUAN K--''I think shock absortion is more that adequate,but it's a good point. For the

volvo boats we have a pressure release system that is adjusted to release

the oil on the canting cylinders [one each side of the keel] before the

fin itself can get to undesireble levels of stress. This setting is usually

between 200 and 250 Bar [depends on the cylinder diameter] but equates to

about 400Mpa flexural stress on the fin.''

''Simply there is a pressure valve that opens up at a set pressure and

therefore allows the oil in the cylinders to leave and go back into the

reservoir to be pumped up again a bit later. There is not such a thing as

dampening other than letting the oil out.''

''This system is adjustable to account for the friction on the keel axis bearings which increase after a

few days at sea and are replaced regularly.------ If the boats would not have this they will be in pieces by now''END QUOTE

Very Interesting!

They appear to have gotten the engineering of the PRV's right, as their boats have not broken. I still believe there is a lot of room for optimization that will add performance to these systems and adding an "accumulator" to the system should be part of this.

The other interesting point is the steady increase in friction in the keel axis bearings. Probably because they are in salt water all the time. This would definitely add siginificant damping to any keel oscillations.

 

[Codger]

....here's a response Juank gave to a query I sent in late november ........I was asking if there's any form of 'accumulator' type of shock absorption......a fair bit of details to help SA's engineering department.....

From JUAN K--''I think shock absortion is more that adequate,but it's a good point. For the

volvo boats we have a pressure release system that is adjusted to release

the oil on the canting cylinders [one each side of the keel] before the

fin itself can get to undesireble levels of stress. This setting is usually

between 200 and 250 Bar [depends on the cylinder diameter] but equates to

about 400Mpa flexural stress on the fin.''

''Simply there is a pressure valve that opens up at a set pressure and

therefore allows the oil in the cylinders to leave and go back into the

reservoir to be pumped up again a bit later. There is not such a thing as

dampening other than letting the oil out.''

''This system is adjustable to account for the friction on the keel axis bearings which increase after a

few days at sea and are replaced regularly.------ If the boats would not have this they will be in pieces by now''END QUOTE

Very Interesting!

They appear to have gotten the engineering of the PRV's right, as their boats have not broken. I still believe there is a lot of room for optimization that will add performance to these systems and adding an "accumulator" to the system should be part of this.

The other interesting point is the steady increase in friction in the keel axis bearings. Probably because they are in salt water all the time. This would definitely add siginificant damping to any keel oscillations.

Juan K also said the boats could be driven too hard. The drivers needed to learn to slow down when conditions warranted.

We could do a top down penalty system to reign in their over-enthusiasm. Sort of Formula One chicane (or NASCAR restrictor plate) for VOR 70s. Simply tee in a series of graduated air chambers (think of a pipe organ - the chambers themselves would be similar to what is on your domestic water system to prevent water hammer) with each isolated from the normal flow by a rupture disc. Set pipe 1 at a burst pressure equal to 2Gs, pipe 2 at 3Gs, pipe 3 at 4Gs. That way the driver who stays below the operating pressure rato of 70% (1.4Gs with a system design peak of 1.3Gs) has a durable system. Go too hard and he can break disc 1. Go a bit harder and break disc 2, go close to the edge and break disc 3.

Receive a time penalty in hours equal to the number of Gs squared. 2Gs gets a 4 hour penalty. Add the 3G penalty of 9 hours and the total is 13 hours. Break Disc 3 at 4Gs and the total penalty goes up to 29 hours (4 + 9 + 16). Total weight would be under 10 pounds. And the air chambers would have at least a minor damping effect, the system would become a bit spongy, like the brake system of your car with air in the lines. The advange is that the discs break instantaneously and yet there would be zero leakage of fluid from the closed chambers. And yet Humpty Dumpty can't be put back together again. Slow learning drivers get to wear a DUNCE CAP!

 

[Lima November]

Juan K also said the boats could be driven too hard. The drivers needed to learn to slow down when conditions warranted.
We could do a top down penalty system to reign in their over-enthusiasm. Sort of Formula One chicane (or NASCAR restrictor plate) for VOR 70s. Simply tee in a series of graduated air chambers (think of a pipe organ - the chambers themselves would be similar to what is on your domestic water system to prevent water hammer) with each isolated from the normal flow by a rupture disc. Set pipe 1 at a burst pressure equal to 2Gs, pipe 2 at 3Gs, pipe 3 at 4Gs. That way the driver who stays below the operating pressure rato of 70% (1.4Gs with a system design peak of 1.3Gs) has a durable system. Go too hard and he can break disc 1. Go a bit harder and break disc 2, go close to the edge and break disc 3.

Receive a time penalty in hours equal to the number of Gs squared. 2Gs gets a 4 hour penalty. Add the 3G penalty of 9 hours and the total is 13 hours. Break Disc 3 at 4Gs and the total penalty goes up to 29 hours (4 + 9 + 16). Total weight would be under 10 pounds. And the air chambers would have at least a minor damping effect, the system would become a bit spongy, like the brake system of your car with air in the lines. The advange is that the discs break instantaneously and yet there would be zero leakage of fluid from the closed chambers. And yet Humpty Dumpty can't be put back together again. Slow learning drivers get to wear a DUNCE CAP!

Now that is bloody unfair... the peak loads come from freak waves, after all, which can't be predicted completely. So you happen to be in one bad spot for 30 seconds, BANG, you pull 4G and lose the race.

Besides, your idea is basically already in use, and it has generated a shitload of bad comments here. In the cuurent boats, the breaking discs are replaced by the keel, mast etc. Drive too hard: BANG, something breaks and you get a time penalty, because you go slower.

 

[snorky]

:lol:

Acid test. next leg.. hopefully will blow.. I reckon they have gone too hard without testing or not investing in analysis, or alternatives for supporting the keel business which seems to work.. the person who flogged them the titanium rams.. and the suckers fell for it... next volvo CEO?.. note not VOR..

Proof in the next two legs.. but methinks design wrong for hydro';s without taking into account the sailing dynamics, harmonics, rc circuits they are establishing, damping etc as per our analysis... now wonder they are getting massive failures.. very very poor if you think of the volvo car thing..

I reckon they are complely up the wrong path.. how about electrics motors and locks?..

B)

 

[woof]

:lol:
Acid test. next leg.. hopefully will blow.. I reckon they have gone too hard without testing or not investing in analysis, or alternatives for supporting the keel business which seems to work.. the person who flogged them the titanium rams.. and the suckers fell for it... next volvo CEO?.. note not VOR..

Proof in the next two legs.. but methinks design wrong for hydro';s without taking into account the sailing dynamics, harmonics, rc circuits they are establishing, damping etc as per our analysis... now wonder they are getting massive failures.. very very poor if you think of the volvo car thing..

I reckon they are complely up the wrong path.. how about electrics motors and locks?..

B)

a reasonable answer, but the problem is - as soon as you come to a 'lock' you have a heap of load on that point (you can dissipate it in various ways, but ultimately any system is only as strong as its weakest point). You may as well have hydraulics and a lock.

A system should be designed so that something relatively easily replaceable breaks first - think of a sheer pin that would cope with the loads that have been calculated. It's like a mechanical version of an electrical fuse.

Chunky.

hmmmm

back to the kennel kalculator

ww

 

[snorky]

As you said mmmmm..

Time for inspiration.. perhaps a beer in the local by the sea, river etc.. to ponder...must b a better way.. :blink:

 

[couchsurfer]

Juan K also said the boats could be driven too hard. The drivers needed to learn to slow down when conditions warranted.
We could do a top down penalty system to reign in their over-enthusiasm. Sort of Formula One chicane (or NASCAR restrictor plate) for VOR 70s. Simply tee in a series of graduated air chambers (think of a pipe organ - the chambers themselves would be similar to what is on your domestic water system to prevent water hammer) with each isolated from the normal flow by a rupture disc. Set pipe 1 at a burst pressure equal to 2Gs, pipe 2 at 3Gs, pipe 3 at 4Gs. That way the driver who stays below the operating pressure rato of 70% (1.4Gs with a system design peak of 1.3Gs) has a durable system. Go too hard and he can break disc 1. Go a bit harder and break disc 2, go close to the edge and break disc 3.

Receive a time penalty in hours equal to the number of Gs squared. 2Gs gets a 4 hour penalty. Add the 3G penalty of 9 hours and the total is 13 hours. Break Disc 3 at 4Gs and the total penalty goes up to 29 hours (4 + 9 + 16). Total weight would be under 10 pounds. And the air chambers would have at least a minor damping effect, the system would become a bit spongy, like the brake system of your car with air in the lines. The advange is that the discs break instantaneously and yet there would be zero leakage of fluid from the closed chambers. And yet Humpty Dumpty can't be put back together again. Slow learning drivers get to wear a DUNCE CAP!

...not necessary--the boats give their own consequences!! :blink:

 

[couchsurfer]

:lol:

Acid test. next leg.. hopefully will blow.. I reckon they have gone too hard without testing or not investing in analysis, or alternatives for supporting the keel business which seems to work.. the person who flogged them the titanium rams.. and the suckers fell for it... next volvo CEO?.. note not VOR..

Proof in the next two legs.. but methinks design wrong for hydro';s without taking into account the sailing dynamics, harmonics, rc circuits they are establishing, damping etc as per our analysis... now wonder they are getting massive failures.. very very poor if you think of the volvo car thing..

I reckon they are complely up the wrong path.. how about electrics motors and locks?.. B)

a reasonable answer, but the problem is - as soon as you come to a 'lock' you have a heap of load on that point (you can dissipate it in various ways, but ultimately any system is only as strong as its weakest point). You may as well have hydraulics and a lock.

A system should be designed so that something relatively easily replaceable breaks first - think of a sheer pin that would cope with the loads that have been calculated. It's like a mechanical version of an electrical fuse.Chunky.hmmmmback to the kennel kalculatorww

.....I'm interested to hear if ANY canters have experimented with the accumulator type absorption.Sailing is definitely ALL about fluid dynamics,so it seems nutters to try have a solid system to suspend 6TONS of lead on an angled fulcrum as you drop it from -X- meters.

.....Accumulator absorption allows farmers to drive their very large combine tractors ~3x the speed through bumpy terrain-- this technology exists for a reason--SHOCK ABSORPTION

 

[dtoc]

It is very interesting what the different teams have shared about their keel systems.

Movistar has definitely been the most open, with the Greg Waters piece on The Daily Sail, Bouwe on SA and the pictures that are out there. POC has been the most secretive, there still seems to be a little confusion over whether they will have SS or Ti rams for the next leg. Ericsson has given some info and a few pics in a new article in TDS, but nothing showing how the system is actually setup. The Cariboni trio hasn’t had problems but details on the system are still available from Cariboni and the correspondence between Michael and Juan K. Brunel??? Maybe it’ll be relevant with the reconfigured boat when it arrives in Annapolis.

I continue to support Movistar and hope that the increased strength of the rams gets them through the next leg at full power. From the pics it’s clear that there will be some uneven loading between the 2 rams.

Will Ericsson’s “custom” Ti rams solve the problems that have plagued them? High risk considering that symptoms and haven’t found the root cause or significantly increased the strength of the parts.

POC, well they’re in ghost ship mode. We know they’re out there and are always dangerous, but until they come out of the fog, who knows.

Who know's, maybe they'll request some input from the SA engineering dept. No, it'll never happen, we don't charge enough.