Mooring Field Question

[Rick Starr]

What is a good rule of thumb for setting out a mooring field grid? I'm not looking for precision here, just a rough estimate for planning purposes.

Specifically I'm interested in distance of separation given the various factors of vessel length, water depth(mllw/stormhw etc.) and scope--typically 2.5-3x water depth, including, I suppose, pendant(pennant) length.

Anyone have any experience setting one up?

Thanks

[Hughman]

Think spokes. Draw a hub with radial lines and mark off intervals which form swing circles. The smaller boats are close in (which usually agrees with their shallow draft) where the lines are nearly adjacent; the lines and intervals get more separated as they move out.

Pennant length is roughly the same as boat length, the variable being the height of bow.

Mooring anchors can be the screw type, which don't move, but can be difficult to find if the gear is cut. GPS plotting and an underwater metal detector helps with this issue

http://www.premiumtechnical.com/marineapplications.php

(no affiliation with this co.)

[George Ray]

They have mooring fields everywhere and in the summer when the moorings are mostly occupied you can nearly walk from boat to boat (exaggerating). Some one from the neck of the woods could help or check out web sites and look for email addresses for CIty Island Yacht Club, Harlem Yacht Club.. etc (all on City Island NYC). In Manhassett, Oyster Bay, Rye etc etc etc etc etc you can find mooring fields so that would be a place to concentrate your search for expertise.

This link shows fields and numbers of boats which gives idea of boat density.
http://www.bristolri.us/documents/ha...ing%20field%22

Good info on moorings and mooring fields:
http://www.jubileeyc.net/moorings.htm

[rbgarr]

Where would you put in a mooring field at St. Croix?

[Ian McColgin]

The question is completely unanswerable as the huge variables include bottom type, extreme of operational weather and exposure.

Pennent length is unrelated to boat length but is related to bow height and shape as well as mooring ball (if any) attachment and design.

Some thoughts for:
Sand, grass and thick mud bottoms where mushrooms, blocks, helixes and such can be set;
Days and days of gale (Force 8, winds over 40kt) with short periods for storm (Force 11); and
No exposed fetch more than a couple of miles.

In otherwords, Nantucket Sound harbors.

The lowest density approach is individual moorings whether mushrooms, block or whatever excluding helix. The total scope planned for extreme high water and maybe a little surge will be about 4:1 with 1-1/2 depth in bottom chain, a like amount in the lighter top chain and about a depth in pendent.

These porportions will give about 38' swing at the bow at high water if his is 10', 77' at the bow if high is 20', but you really need to calculate the swing for low. If you had a 10' tide range in the latter example, the bow's swing would be 79'. To this you then add boat length and comfort factor.

We have a 3'-4' tide range so the bow swing in 20' max high becomes (figure 12' extreme lower low) still close enough to 79' bow swing. A lot of our mooring fields though are actually in only 12' normal high, figure calculate on 15'.

If the mooring field is designed with boats of a general type and does not have an extreme reversing current that could have some boats swinging to the current while others follow the wind, you can then put them much closer as they will all move more or less together.

I personally do not favor having them closer than ajacent moorings being under the perimeter of the bow swing. One reason for this is that the mooring will lie in the direction the boat was set when you left. So, as often happens in Lewis Bay where moorings are set this closely and sometimes tighter with helixes, you depart in a southwesterly and come home a day later with a northerly and find your ball and pick-up about under the neighbor's stern.

With the helix, the scope can get down to 2:1 counting pendent. The helix can take it and the chain can take it and modern kevlar pendents can take it but such a down angle in a h igh wind can actually damage the stem and mooring cleats.

A chain grid that's anchored in toto and has chain to ball connections at each grid intersection can have 1:1 on the chain to ball and pretty short pendents as the whole grid will rise and provide scope for all boats in high winds. In practice and counting pendents and allowing for low tide, boats end up 3-4 high water depths apart. This kind of grid is less and less favored for environmental reasons as it kills almost all bottom life. Also, it must be maintained and operated as a mooring field monopoly which means the operator and town must cope with a lot of Army Corps rigamahrole.

Pioneered in Manhassett, high density can be safely achieved with inter-lapping system where each mooring is actually 3 hooks at 120 degrees each on a radius about 4:1 depth connected to a chain to the ball that's more like 1:1 gives nearly as much density as the chain grid - boats are a bit over 4 depths apart - and is less damaging to the bottom. Heavy Bruce anchors really come into their own in this system.

Of high density methods, I like the three hook system best as you get the density of the helix but the gentleness of plenty of scope. However, it's much harder to lay out, especially if you have competative private mooring services doing the setting. The economics of density favor helixes except in hard rock bottoms.

[uncas]

I must admit, some of the mooring fields border on the crazy.
Went to Plymouth.. No anchorage and had to pick up a mooring. The first one pointed out to me was so close to another boat, I could have stepped aboard I was right up against the ball which, in turn, right up against another boat. Even the guy pointing out the mooring they had signed me up for thought the mooring ball was a bit too close.
The second mooring was a wee bit better. But my dink was still riding on the boat's bow behind me and the dink was tied in tight to the transom.

Sometimes, those who put these things out only think of the rental. No concept of what room is needed by any boat.
I mean, mooring balls on Nantucket were, with tax, 63.00/night

[Rick Starr]

Thank you for the wonderful and quite useful replies.

The national park is reviewing it's management plan and one of their mandates is that the existing recreational day-anchoring zone transition to a mooring system. They are trying to forsee visitation growth and design a mooring field which will accomodate that visitation as much as possible. The actual mooring field will be designed by COE or USCG or somebody, but for estimating purposes a rule-of-thumb guide is needed to balance the area available with the planned visitation usage.

Our tidal variation is about a foot and a half, the avg depth in the area in question is 10-12' and the bottom is some sand with hard pavement beneath. Permanent pins have been used sucessfully in the park in the past and are probably what will be used again, although that's just a guess on my part.

Over on our sister islands the mooring fields are so dense that one gets the impression each boat is swinging over the tackle of it's stern neighbor. As vessel size grows this becomes more and more of an issue.

[Tom Hunter]

Ian's post is great.

Here in Marblehead we have high density, in the main harbor there are thousands of boats packed into a space no larger than a sardine can. At least that is the way it seems.

One result of the high density is that the harbor master does have to seperate boats that become tangled together from time to time. It does not happen that often but it does happen.

[uncas]

What is too bad is that many of the old anchorages, spots you can actually drop a hook are disappearing and becoming mooring fields.
I understand but at the same time, there is a point where having visitors who want to anchor and not pay a mooring fee will go elsewhere. The town loses visitors, the shops lose customers. There may be an added gain in that a mooring price ranges from 25.00 in Annapolis to 63. in Nantucket. Compare that to the food, toys, memorobilia bought in the stores by people who prefer to anchor.
For some, who are expense conscious, if they are paying 63.00 for a mooring ball, they ain't gonna spend as much in town.

I'm gonna have to update my cruising guides...especially in reference to anchorages that no longer exist.

[rbgarr]

A friend told me that when he stopped at Edgartown on Martha's Vineyard this past July the available transient moorings were free.

[rbgarr]

Rick-

This mooring product 'might' avoid the problem of seabed scraping by chain moorings. Don't know how well it would work in such shallow waters though, especially if the spar buoy is 5' long.

http://www.hazelettmarine.com/