I have a 32' motor sailor which is my office. It's in a slip at Pier 39 in San Francisco, which is great, but.....
Damn.
When the tide is coming in our out, it rocks like crazy, sometimes throwing itself forward so hard it has snapped 2 one-inch bow lines!
I've not got spring lines fore and aft, stern lines and bow lines. Many people here have tires chained to the dockcleats and then tie their lines to the tires, forming a shock absorber. Some use little commercial line-shock tools (that do almost nothing at this level of rock and roll), but there has to be something better.
I've looked at some sea-anchor type things, rocker stoppers, but they really need to hang off the side a foot or two. Since I'm in a slip, with very little room on each side, I can't do that.
I "think" the problem is that the slip is perpendicular to the flow of the bay, so my full keel catches the tidal flow and flops around like crazy. Adding ferry traffic and the constant in and out of water taxies and tour boats, it makes for a rough workday.
From your description flop stop is not going to work because the problem water flow goes all the way down to the bottom of your keel; it's not a surface wave that you can get under, and you have not got much of an arm. Sounds horrible.
Also from your description the dock is not floating and stays very much in one place. Snapping 1" painters is not socially acceptable behavior.
So, the shock absorbing/stabilizing route seems more promising. Using an old tire, given steel beads, really gives you only the stretch of making the tire oblong, not actually stretched. You might get somewhere between too stiff with a tire and much too soft with glorified bungee cords by using motorcycle tires.
And, you've got a tide. That interferes with damping the vertical movement.
I can think of one possibility. We use a weight (concrete block) handing in the water and cabled to a midship cleat to keep our boat near the dock. One or even two on each side of your boat would add inertia against the boat rolling, while adjusting to the tide.
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Never let anything mechanical know that you are in a hurry.
Have you tried facing the boat the other way round.???
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"I Love You.. ". Murray Roman.
Yet the 'useful idiots' still dance to the beat of the drums.
From your description flop stop is not going to work because the problem water flow goes all the way down to the bottom of your keel; it's not a surface wave that you can get under, and you have not got much of an arm. Sounds horrible.
Also from your description the dock is not floating and stays very much in one place. Snapping 1" painters is not socially acceptable behavior.
So, the shock absorbing/stabilizing route seems more promising. Using an old tire, given steel beads, really gives you only the stretch of making the tire oblong, not actually stretched. You might get somewhere between too stiff with a tire and much too soft with glorified bungee cords by using motorcycle tires.
And, you've got a tide. That interferes with damping the vertical movement.
I can think of one possibility. We use a weight (concrete block) handing in the water and cabled to a midship cleat to keep our boat near the dock. One or even two on each side of your boat would add inertia against the boat rolling, while adjusting to the tide.
It is unclear in your posting as to the motion(s) that you are specifically having issue with.
You mention abrupt forward motion which motion when moored in a slip is controlled by use of lengthy spring lines so as to derive resistance over a period of time to convert the kinetic acceleration energy derived in fore and aft motion into heat energy. The use of shock absorbing schemes would be beneficial to such springiness of your spring lines and reducing the peak loading on the hard point attachments to your boat and to your dockage. Tires are sturdy, foregiving, cheap and effective aides to tie to. If you fill the inner cavity with expanding spray foam they will float nicely with the rise and fall of the tide helping keeping your lines properly distanced. Make your spring lines long, tying to bow and aft hardpoints, not just midship hardpoints and tying to hardpoints on the dock or pilings as far forward and aft as possible so as to provide for greater length of spring. And of course one can utilize the various spring mechanisms to aid the spring lines energy absorbing capacities.
You state the boat is "flopping" which often is a term used to describe a roll motion / athwartship rocking which roll can be controlled by having vertical resistance applied to each side of the vessel. i.e. flooper stoppers.
Of keen issue with narrow slips is that the sideways space for rigging such extended flooper stoppers is limited and there are often pilings and underwater hazards that interfere with the deployment of such upward motion water resistance devices. One could attempt using heavy weighted objects strung over the sides to slow the motion, especially with the weights being set on the ground of the marina such that when the boat rocks the side rising is required to lift the weight by tugging on a rode and the side that is lowering during the roll does not impart any effort because the rode just goes slack with the weighted object resting on the bottom of the bay.
Alternatively one could deploy one or more flooper stoppers positioned directly under your boats hull and tie rodes to the flooper stopper over both of the sides of your hull say from midship cleats such that the rode tied to the rising side of the hull during a roll motion pulls against the flooper stopper and resists upward rolling motion to that side. The downward rolling side of a vessel does not gain resistance from motion most flooper stopper devices. You will desire to utilize chafe protection for the rodes that will rub over the rail and the hull side if a flopper stopper is deployed under the hull instead of deployed extended away from the hull. Do note that the effectiveness of a flooper stopper will be diminished if it does not have the aid of leverage of a deployed boom extension from the centerline of your boat. The leverage will be limited to the width the line hangs from your boat's side in the narrowness of a slip. Simple physics constraint. When your lever arm is limited one likely will need a larger flooper stopper device or additional flooper stoppers to achieve comparable effect of the longer lever.
A third approach is a counterweighting that slides or rolls up a piling wherein a rode is tied to the cleat at midship up to a pulley on the piling that causes the pulling against a counterweight hung around the piling or simply hung from the dock when the side of the boat rolls downward with a passing swell or wake.
Finally, one could install a lift to raise your boat out of the water so as to eliminate the acceleration associated with water movement, or move to a more protected slip or marina.
It is unclear in your posting as to the motion(s) that you are specifically having issue with.
You mention abrupt forward motion which motion when moored in a slip is controlled by use of lengthy spring lines so as to derive resistance over a period of time to convert the kinetic acceleration energy derived in fore and aft motion into heat energy. The use of shock absorbing schemes would be beneficial to such springiness of your spring lines and reducing the peak loading on the hard point attachments to your boat and to your dockage. Tires are sturdy, foregiving, cheap and effective aides to tie to. If you fill the inner cavity with expanding spray foam they will float nicely with the rise and fall of the tide helping keeping your lines properly distanced. Make your spring lines long, tying to bow and aft hardpoints, not just midship hardpoints and tying to hardpoints on the dock or pilings as far forward and aft as possible so as to provide for greater length of spring. And of course one can utilize the various spring mechanisms to aid the spring lines energy absorbing capacities.
You state the boat is "flopping" which often is a term used to describe a roll motion / athwartship rocking which roll can be controlled by having vertical resistance applied to each side of the vessel. i.e. flooper stoppers.
Of keen issue with narrow slips is that the sideways space for rigging such extended flooper stoppers is limited and there are often pilings and underwater hazards that interfere with the deployment of such upward motion water resistance devices. One could attempt using heavy weighted objects strung over the sides to slow the motion, especially with the weights being set on the ground of the marina such that when the boat rocks the side rising is required to lift the weight by tugging on a rode and the side that is lowering during the roll does not impart any effort because the rode just goes slack with the weighted object resting on the bottom of the bay.
Alternatively one could deploy one or more flooper stoppers positioned directly under your boats hull and tie rodes to the flooper stopper over both of the sides of your hull say from midship cleats such that the rode tied to the rising side of the hull during a roll motion pulls against the flooper stopper and resists upward rolling motion to that side. The downward rolling side of a vessel does not gain resistance from motion most flooper stopper devices. You will desire to utilize chafe protection for the rodes that will rub over the rail and the hull side if a flopper stopper is deployed under the hull instead of deployed extended away from the hull. Do note that the effectiveness of a flooper stopper will be diminished if it does not have the aid of leverage of a deployed boom extension from the centerline of your boat. The leverage will be limited to the width the line hangs from your boat's side in the narrowness of a slip. Simple physics constraint. When your lever arm is limited one likely will need a larger flooper stopper device or additional flooper stoppers to achieve comparable effect of the longer lever.
A third approach is a counterweighting that slides or rolls up a piling wherein a rode is tied to the cleat at midship up to a pulley on the piling that causes the pulling against a counterweight hung around the piling or simply hung from the dock when the side of the boat rolls downward with a passing swell or wake.
Finally, one could install a lift to raise your boat out of the water so as to eliminate the acceleration associated with water movement, or move to a more protected slip or marina.
The motion is erratic. There's the standard "flopping", which doesn't really bother me at all and isn't too big a deal, but every once an a while, the boat will thrust forward or aft very hard, and at random angles. That jerk is what's most damaging. I think, if I put a concrete block hanging from a pulley on either side, and just tied off to the midship cleats, that would slow down the lurching behavior.
Honestly, there's so much motion, I feel like I should be able to hook it to a generator and charge my batteries with it!
That's been a problem ever since they built Pier 39. Decades ago. This is nothing new. Have you considered talking to your neighbors and finding out what they do? Have you considered asking them to change your slip, perhaps moving closer to the land side?
Good luck.
PS - I lived in SF from 78 to 16, I know the area and that marina.
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, SR/FK, M25, Rocna 10 (22#) (NZ model)
The motion is erratic. There's the standard "flopping", which doesn't really bother me at all and isn't too big a deal, but every once an a while, the boat will thrust forward or aft very hard, and at random angles. That jerk is what's most damaging. I think, if I put a concrete block hanging from a pulley on either side, and just tied off to the midship cleats, that would slow down the lurching behavior.
Honestly, there's so much motion, I feel like I should be able to hook it to a generator and charge my batteries with it!
By observing the live webcam, one can see the nature of motion at Pier 39, well at least the K dock side where the seals have taken ownership [erhhh, refuge]. Noisy neighborhood what with the seals and the tourists.
That's been a problem ever since they built Pier 39. Decades ago. This is nothing new. Have you considered talking to your neighbors and finding out what they do? Have you considered asking them to change your slip, perhaps moving closer to the land side?
Good luck.
PS - I lived in SF from 78 to 16, I know the area and that marina.
My neighbors use those tires. But, for the most part, very few people spend much time here. Since I'm using it as an office, I spend a lot more time here than others.
I do actually have a pretty busy slip. I'm way out on the end of C dock. It makes docking much easier, and my view is awesome at high tide, but the water is probably rougher than most slips.
I actually own the lease on the slip, which just leaves me with only a $368/month HOA (much cheaper than my previous office rent), but that also means I can't just swap out with someone else in the marina.
All in all, I think I'm just going to enjoy the bounce
The motion is erratic. There's the standard "flopping", which doesn't really bother me at all and isn't too big a deal, but every once an a while, the boat will thrust forward or aft very hard, and at random angles. That jerk is what's most damaging. I think, if I put a concrete block hanging from a pulley on either side, and just tied off to the midship cleats, that would slow down the lurching behavior.
Honestly, there's so much motion, I feel like I should be able to hook it to a generator and charge my batteries with it!
So the primary issue is the jarring fore / aft motion or angles thereto, not roll.
One can only hope to dampen such effects which are likely due to the passing of a significant wake wave through the marina.
I suggest long spring lines aided with mooring springs / snubbers.
Try to utilize the maximum safe amount of fore and aft motion that your slip and boat architecture allow for so as to utilize the fullest scope of length of damping travel to extend the energy absorbing capacity over time and distance.
Positioning multiple mooring springs and / or snubbers in series connection will aid in permitting longer length of scope of travel. Positioning mooring springs and / or snubbers in parallel configuration increases the total loading capacity but increases the peak loading and comparatively shorter length of travel and shorter time span of travel.
Examples of mooring springs pictured below. The second one pictured is massive having a capacity of 35,000 kg breaking capacity, far more than your spring line or the hard points that it would be attached to. Obviously size the spring or snubbers so as to be appropriate to your boat and dockage.
One could add kelts to the spring lines to provide a counterweight that will need to be lifted to tighten the line and which counterweights will draw the boat back towards a desired position in the slip. If your slip is tight then your range of safe motion is a major constraint. You may desire to move to a slip of longer length so as to avail greater safe fore and aft [and athwartship] motion so as to utilize longer dampening effect mechanics. If there is a tide or strong wind flowing through the marina then your boat will settle hard against the lines restricting such direction of travel and the boats response to a wake wave will be harsher then when the boat is not tied tight to a tidal or wind force.
You can't solve the problem by anything to do with your attachment to the dock or gizmos inserted in the lines. I had the same problem with a boat I kept in Woods Hole Mass. and the easy solution was a flat steadying sail. If you want to get technical you need to calculate your CG and CB as well as the submerged profile surface area. As I know no one wants to bother with that just size it by multiplying the draft times length and have a flat sail made that fits your mast and boom (you said motorsailer). Keep it very taut and it'll slow down to motion, you still need good chaffing gear as I doubt you actually broke one inch nylon without it chaffing some.
You can't solve the problem by anything to do with your attachment to the dock or gizmos inserted in the lines. I had the same problem with a boat I kept in Woods Hole Mass. and the easy solution was a flat steadying sail. If you want to get technical you need to calculate your CG and CB as well as the submerged profile surface area. As I know no one wants to bother with that just size it by multiplying the draft times length and have a flat sail made that fits your mast and boom (you said motorsailer). Keep it very taut and it'll slow down to motion, you still need good chaffing gear as I doubt you actually broke one inch nylon without it chaffing some.
You're right about the chaffing, I bought some canvas wraps that help.
I'm not sure what you mean about a steadying sail. I can't put up a sail while I'm in a slip.
My neighbors use those tires. But, for the most part, very few people spend much time here. Since I'm using it as an office, I spend a lot more time here than others.
I do actually have a pretty busy slip. I'm way out on the end of C dock. It makes docking much easier, and my view is awesome at high tide, but the water is probably rougher than most slips.
I actually own the lease on the slip, which just leaves me with only a $368/month HOA (much cheaper than my previous office rent), but that also means I can't just swap out with someone else in the marina.
All in all, I think I'm just going to enjoy the bounce
First world problems.
Indeed that is a rather exposed marina. The larger ferry boats and cargo ship wakes would seem to roll through if the breakwater does not go deep or to the bottom.
End of C dock means you are away from the seals and a least a long stones throw from the multitude of tourists.
Ha, will google earth you, be sure to wave. I'll look for your cup and shoes.
Was just visiting friends in S.F. a few days ago who live very near by Pier 39 on Lombard Street at Montgomery directly below Coit tower. Presently back in Montana [an 18 hour drive], just in time for experiencing our first real cold spell of the season, daytime highs to be in the minus single digits degrees of the fahrenheit scale, [around -20 C] Sunday through mid week. I was in shirt sleeves at 9:30 PM walking on Battery Street to the restaurant, the warmth of the Bay Area a great respite from winter.
Re: Stop my boat from flopping around in my slip
Noisy neighborhood what with the 
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