Stop my boat from flopping around in my slip

[Montanan]

Originally Posted by fish53

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.

A small stabilizing mooring / anchor sail is generally only beneficial when there is wind to derive tautness against the mooring lines so as to inhibit the range of travel against a line thereby mitigating the boat accelerating under wave forces arising from the range of motion on a slackened line. The wind in effect being a resisting force against motion precluding acceleration and inertial energy development. A canvass biasing force spring of sorts.

One can hoist small stabilizing sails while at dock but certainly not anything large. Also depends on the marina rules, some don't like shading adjacent boats, or have concerns about control during a blow. On occasion I sail into our marina under full or partial sail when the motor is not functioning, tests one's maneuvering and docking skills. That's when you hope the fairway remains clear of traffic.

[Montanan]

The images below are of rather properly configured mooring spring aided dock lines.

The use of safety chains provide protection if the mooring spring was to break. Such fail safe chainage should be sized in length allow for a fullest extension of the spring. Note the dock line has a metal thimble eyelet to avail chafe protection when connecting to a shackle attached to a safety chain / mooring spring and / or to the chainage tied to the dock hard point.

Springs can be connected in series to avail greater length of travel and thus enhanced dampening time and distance thereby diminishing peak loading / jarring.

Note the use of tubing / hose for chafe protection on your boat hardpoints and deck, simple and very effective at rub points.

Also note that chain can be used to connect to your dock hard points to mitigate against chafe at the fixed cleats, bull rail, ring, bollard or piling ring. I commonly use a loop of chain that has been passed through heavy duty clear tubing for attaching around a piling. A chain with tubing would work well for a tire that has been filled with foam to float on your pilings.

Or you could impose a No Wake zone for the entire S.F. Bay,

[Montanan]

Close up image of a proper mooring spring line configuration.

[JPA Cate]

I'd be tempted to try more lines, of lesser diameter, because you want the stretch to be easier. Maybe go down to 1/2" line, nylon 3 strand. Since the surge is a problem, besides tying up the four corners, consider an additional line from the aft cleat on the dock to the forward bow cleat, and from the forward cleat on the dock to the aft cleat on the boat. If you have a midship's cleat on the boat, you could run the springs to there, but you may be better off with the longer runs. With the long runs, you'll get easier stretch, and you may want to put fenders out so there is no chafe on the hull. People often can work out ways to add the midship cleats, and they are very useful. Sometimes marinas will allow you to place an additional dock cleat. If your present cleats are too small, consider using dyneema soft shackles and eye splices in the nylon, using thimbles.

I am not positive this will work for you--Pier 39 is notorious--but it should help a lot, and maybe it will be enough.

The principle is that the 7/16 or 1/2 inch 3 strand will stretch more readily than the 1 inch that you snapped. And doubling up with the springs will add the strength you need for your motorsailer.

[sail sfbay]

Originally Posted by coldfish

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.....it rocks like crazy, sometimes throwing itself forward so hard it has snapped 2 one-inch bow lines! ..................So, anyone have any ideas?

I docked my sailboat at Pier 39 last September for 2 nights and never again due the tidal swells and current cause severe rocking, which stresses the boat. I do not think there is any good solution to stop the severe rocking at Pier 39. My suggestion is to move to Emeryville, Alameda, Richmond or Sausalito where you can avoid this.

[boatman61]

Originally Posted by coldfish

Unfortunately, I can face it towards the bay or towards land, but the tide runs in and out.

But is it the same either way.. underwater form may affect you more one way than the other with the cut away at the bow..
I assume its a full keeler so presume going bow in is favourite being the easier option.

[DEAN2140]

Pier 39 is notorious for surge. If your neighbors haven't figured out how to deal with it, my only suggestion is to move to another marina.

[rmesfo]

Good Luck! Feel your pain as I docked there for 2 days last summer. After the first night, I was trying to find ANYWHERE close that had a slip. I was in the guest berths and it was uncomfortable due to the ferries being 50 ft away and the currents. I understand the private docks on the east side are better but not much. My neighbor came down from Canada and had been there for a week and already a broken cleat. Let us know what you find because if it works there it will work anywhere.

[SV__Grace]

As someone who lives full time and works remotely on our boat, often in very rolly anchorages, I sympathize. We've visited Pier 39 many times in our boat and it is by far the rolliest marina we've ever seen. I have no more wisdom to share than the others here and look forward to your post of your solution!

[HBrew]

I stayed in Puerto Lucia in Ecuador for a few months and the marina there has a well documented issue with surge, so I bought a couple of snubbers called Snubber One after reading this article https://www.pbo.co.uk/gear/pbo-teste...snubbers-45131

Well, they self destructed within 5 minutes, the first time the boat really surged forward.

I later tried the Unimer U-Cleat and they worked really well on long spring lines that smoothed the forward surge and saved my docking lines (which are 20mm lines, so pretty strong). They lasted weeks without any sign of damage so they might help you. Once I got the lines adjusted with the right tension the motion was smooth and all of the sudden jerks when docking lines were fully extended were eliminated.

Good luck, I feel your pain. It’s horrible to have your boat jerking around like that.

[Mike Banks]

You said it yourself--you do not use springers. You need to use LOOONG lines--and crossed springers, and you need fenders and fender-boards and perhaps runners..

If you are sufficiently desperate , you can hang weighted tallow greased hardwood or softwood square or natural round clean poles as runners from shore cleats and run your fender boards fastened to your vessel and over your fenders against those.

Nothing will stop your boat surging up and down the fender board poles--(most good moorings have them as part of the pile or mooring structure) but long springers will stop your vessel running forwards and astern between surges.

For what it might be worth, I often run a length of about ten feet of half-inch chain to the jetty or wharf cleats secured and padlocked. That weight sags and keeps some extra give in the lines--but more importantly--stops some envious rotten bastards from easily setting your vessel adrift. Believe me--it can happen.

[lo2jones]

Wow. Pier 39??? Good luck in getting the boat to sit still. Flopping around beats what I’ve seen other boats do there. The surge is strong and currents run right through the marina.

[dgmyles]

This may be a completely dumb idea but what about trying some 4 wheel drive style snatch straps.

You can get them rated to 10 or 12 ton and they are designed to stretch under load. If you were to replace 2 of your spring lines with these they may help absorb the schock and smooth the motion.