Genie - the rest of your post was great - but this part was a little off I think. People keep throwing this one around: that when chuting off the bow, the boat falls off the wave backwards with great force - slamming the rudder. Well if the chute is out there doing it's job you're only doing 1 knot leeward and waves are passing under you, just like with the JSD.
To be fair, if the above scenario were the case with a chute, then with the drogue in the same scenario the boat is going to fall forward off the wave and pitchpole.
So the rudder slamming argument doesn't hold up real well unless something has gone bad wrong. If the boat is being virtually held in place and the seas are passing under it as intended - one could make the argument that bow in is better for the rudder.
At the end of the day, if either of these devices is doing its job you're probably going to be in pretty good shape. Unless the monster falls on you. Then you're just screwed.
Not quite, Smack. The resistance in a chute situation comes from a single point - where the chute is. Normally you let out enough scope so that the boat and the chute are in synch, that is, when the boat is on the front of a wave the chute is also in the same relative position, though one or two waves behind. Should the wave period change or should a "freak wave" develop (not necessarily a huge wave, just one that is not in synch with the others) the rode will go slack, leaving you in a situation similar to suddenly losing the chute. Aside from the terrific shock load experienced under this scenario that would take place when the rode tightens again, there is the very real possibility of the boat sliding backwards while the rode is slack and either turning more broadside to the waves or putting tremendous strain on the rudder as it slides backward. Not necessarily doing a reverse pitchpole (with double gainer) but enough to damage the rudder. A chute needs to be monitored so that the boat and the chute are both on the front or back of a wave at the same time to avoid the problem of slack rode alternating with multiplied shock loading if the boat is on the front of a wave while the chute is on the back of another or vice versa.
With a JSD, the many cones - usually over 100 - assure that a large number of cones will always be in the water regardless of what the waves are doing, so the resistance is never slacked and therefore you 1. have less chance of being tossed beam on and 2. you avoid the shock of the sea anchor suddenly "biting" again. True, an elastic nylon rode mitigates this effect somewhat, but I have often enough felt the shock that comes when a boat "sails" at anchor and comes to the end of a swing. Multiply that by an order of magnitude when dealing with a big storm at sea.
Try a little experiment. Put the transmission in reverse and let the boat get some way on backwards with the rudder held firmly amidship. When moving briskly backwards turn the wheel one way or the other, making sure you have a good grip on the wheel (or tiller). Multiply the pressure you feel by the the kind of forces you would be experiencing in a storm condition and you'll have an idea of what I'm talking about. (disclaimer - not responsible for damage sustained by someone who tries this while going at or near hull speed)
Incidentally, another thing i like about the JSD is the bridle attachment. If the boat swings to one side the bridle set up means that one of the legs of the bridle will go slack - the one that is on the side toward which you have swung. All the pressure on the other leg will act to pull you back so that you are stern to the waves again.
Again, I cannot reiterate enough that each boat and each storm and each crew is different. Get into a nasty situation and all the theorizing goes out the window and you stick with what keeps you alive and afloat. I really think that both systems can, and do, work, depending on the boat and the situation. And either is better than being unprepared and unequipped. I lean more toward the JSD but I can see where other tactics/gear might, in some situation, work better.
__________________
genieskip
Northeast
J40
1991
Last edited by genieskip : 06-05-2009 at 02:32 PM.
Genie,
I've seen a big guy with a broken arm from doing something like that (tiller). So don't try this if you care about your vessel or bones
Quote:
Originally Posted by genieskip
Try a little experiment. Put the transmission in reverse and let the boat get some way on backwards with the rudder held firmly amidship. When moving briskly backwards turn the wheel one way or the other, making sure you have a good grip on the wheel (or tiller). Multiply the pressure you feel by the the kind of forces you would be experiencing in a storm condition and you'll have an idea of what I'm talking about. (disclaimer - not responsible for damage sustained by someone who tries this while going at or near hull speed)
That's exactly what we liked, it relieved us from the pressure of steering, and generally it FELT like everything calmed down.
Quote:
Originally Posted by genieskip
Incidentally, another thing i like about the JSD is the bridle attachment. If the boat swings to one side the bridle set up means that one of the legs of the bridle will go slack - the one that is on the side toward which you have swung. All the pressure on the other leg will act to pull you back so that you are stern to the waves again. .
I've tried to rig a sea-anchor in calmer conditions, but never really felt that it could be trusted, and I've not been able to rig the "Pardey bridle" thing, and don't believe it works for most vessels (it obvously does for Lin and Larry).
If anyone knows the trick on how to do that, I'd really like to know how?
/Joms
__________________
I had the ambition to not only go farther than man had gone before, but to go as far as it was possible to go.
-Captain Cook, on his voyage to the Pacific in Endeavor
Genie,
I've seen a big guy with a broken arm from doing something like that (tiller). So don't try this if you care about your vessel or bones
Quote: Originally Posted by genieskip
Try a little experiment. Put the transmission in reverse and let the boat get some way on backwards with the rudder held firmly amidship. When moving briskly backwards turn the wheel one way or the other, making sure you have a good grip on the wheel (or tiller). Multiply the pressure you feel by the the kind of forces you would be experiencing in a storm condition and you'll have an idea of what I'm talking about. (disclaimer - not responsible for damage sustained by someone who tries this while going at or near hull speed)
Joms
You are absolutely right. Let me delete the word briskly above and replace it with the word SLOWLY. You'll get the idea of the forces involved on the rudder when going backward. Then visualize doing it fast and hard.
It was just to reinforce what you said, I don't have a problem with your wording - I mean if people cannot understand that it would be potentially dangerous from your original wording, Darwin will be there to help us (at times).
And thanks for your insight on this topic.
__________________
I had the ambition to not only go farther than man had gone before, but to go as far as it was possible to go.
-Captain Cook, on his voyage to the Pacific in Endeavor
Of course, some of the rudder problem is determined by the rudder design. It will be far worse on unbalanced rudder designs, with pintle/gudgeon hung designs that are mounted on the leading edge of the rudder being the worst and almost balanced spade designs have the least issue...
__________________
Sailingdog Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
If you're new to the Sailnet Forums... please read this POST.
Genie - I see your point. And I honestly appreciate your walking me (and others) through this. I'm definitely just approaching this whole thing from a theoretical standpoint based on reading...and, of course, advanced degrees in mathematics, physics, and hydrodynamics (the last part is complete BS). The only thing I've deployed thus far while sailing is an anchor and my 8-year-old kid.
Anyway, I wholeheartedly agree with your assertions about the forces and redundancies of the JSD as compared to the chute. There is obviously more opportunity for failure in a single-point system like the chute. No doubt. And I see your point about the rode slack issue of a single chute compared to the progressive loading of the the JSD. Great points.
BUT let's go back a few steps. No one's yet addressed the fundamental issue; that is - which end of the boat is better suited structurally to dealing with the stresses of oncoming waves? This really is a pretty important starting point. And this was the part of Dog's comments that didn't make much sense to me (e.g. - that the boat would suffer more serious damage if it were bow-to-waves).
Let's pin our theoretical boat down at 1 knot of leeward drift - completely disregarding the means of anchoring at this point and the issues of cleat strength, etc. That stuff will come later. Now, we know that waves can travel stupid fast and vary in "speed" (celerity) due to wave type, depth, etc. But, for kicks, let's just say our waves are traveling at 20 knots and have breaking crests that are nasty, but not deadly.
Again, completely disregarding the device that's holding the boat in place, when that breaking water hits us at 19 apparent knots, which end of the boat is more structurally suited to safely bear the brunt? The bow or the stern?
Take it another step. Keeping with your rudder experiment above, is the rudder more likely to suffer the damage you describe if it is "facing into" this breaking water (bow to waves) or "facing away" from it (stern to waves)? Wouldn't the latter be what you described above?
To be clear - I don't know what the true answers are here. This is why I'm asking - and this is why Dog's comments about more serious damage happening to a bow-on boat didn't make sense.
Last edited by smackdaddy : 06-09-2009 at 02:01 AM.
And this was the part of Dog's comments that didn't make much sense to me (e.g. - that the boat would suffer more serious damage if it were bow-to-waves).
Hey Smack
I think you misunderstood the Dog - I don't think he said the boat would suffer more damage. This is what I think he said:
Also, most modern boats have far more buoyancy in the stern than they do forward, since the bows are normally fairly fine entry and on modern designs the beam is usually led pretty far aft. The stern will have a greater tendency to rise with the wave due to the greater buoyancy.
Unless there was an earlier post in which case I apologise for my oversight.
__________________ "I think it would be a good idea"
Response from Mahatma Ghandi when asked what he thought of Western Civilisation.
BTW, I probably did say that a boat being held bow to waves via a parachute sea anchor was far more likely to be damaged than one being held stern to seas via a JSD... this is not because of it being held bow to seas per se, but because a parachute sea anchor doesn't yield at all and increases the effective force the sea can hammer the boat with. That doesn't even include the damage to the steering gear that can occur to a boat that is bow to seas.
__________________
Sailingdog Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
If you're new to the Sailnet Forums... please read this POST.
BTW, I probably did say that a boat being held bow to waves via a parachute sea anchor was far more likely to be damaged than one being held stern to seas via a JSD... this is not because of it being held bow to seas per se, but because a parachute sea anchor doesn't yield at all and increases the effective force the sea can hammer the boat with. That doesn't even include the damage to the steering gear that can occur to a boat that is bow to seas.
Yeah Dog - that was your statement and I now understand the clarification above. BUT - you're still making some "definitive" statements that, all things equal, don't quite make sense. For example:
1. Your bolded statement that a chute anchor "doesn't yield at all" doesn't make sense. The HWS books I've read say that you do get 1-2 knots of leeward motion with a chute. Didn't you say that the JSD gives you essentially the same relative leeward speed (1-2 knots) - thereby "negating the need for steering and allowing the crew to drink heavily down below" (paraphrasing here) - again, like the chute? I do understand your point about the advantage of progressive loading of the JSD - and that makes a lot of sense. But not this other stuff.
2. Next, your statement "That doesn't even include the damage to the steering gear that can occur to a boat that is bow to seas." doesn't quite hold up either. First, this is only true IF the chute rode gets enough slack (as Genie mentioned) for the boat to "fall" back off a wave with enough force to damage the rudder. Though this assumption is certainly theoretically valid - I've not seen or read a lot of evidence that it's a widespread problem if the deployment is done correctly (which is another issue). Again, the chute technique IS in all of the HWS books I've read. And a lot of people seem to swear by it.
Now that brings us to the original question above - which is still open - and which comes into play with your statement about the "serious damage" incurred if a boat is bow-on...
3. If the boat does NOT fall off the wave - and is effectively held in place with 1-2 knots of leeward motion - and is hit with a 20 knot breaking wave, which end of the boat takes that breaking wave with less serious damage?
Last edited by smackdaddy : 06-09-2009 at 11:55 AM.
When hit by a breaking wave in really nasty conditions, it will NOT be confined to the aft or the bow of the boat. It will probably also be a freak that comes from an unexpected direction, thus you might take it in the cockpit when using a chute (or viceversa). The weakest point on many yachts are the cabin, and a breaking wave that smashes the cabin top is going to ruin your day
Talking about strenght, the bow and deck structure in the fore-triangle will probably be a little stronger than the cockpit, and the cockpit will contain a lot of water, but if you have a moderate size cockpit with a bridgedeck the difference should be negligible?
You MUST avoid breaking waves, and the JSD is probably the best device, yet, to ensure that. In non-breaking conditions a chute might be great, especially if you want to avoid a lee shore.
If you read Adlard Coles (my copy is rather old) there's evidence of streaming warps and using chutes, with no clear conclusion on what works. IIRC his conclusion were that "it depends" however many of the chutes broke their attachment points and lines. This is another thing that I do not like about chutes, the MASSIVE forces that they apply to the vessel, which the JSD or toher warps do not do to the same extent.
__________________
I had the ambition to not only go farther than man had gone before, but to go as far as it was possible to go.
-Captain Cook, on his voyage to the Pacific in Endeavor
"I think it would be a good idea"
