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Old 29-08-2016, 14:17   #1
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Mooring depth and waves

I am looking at having a mooring set off the coast. I have had a spot surveyed and checked out. The mooring ball will be set with a system that should be able to handle 2x the mass of my vessel.

The spot has 32-ft depth and is 650 ft from the shoreline.

If a major storm or swell came from the SW the boat would bear the full brunt of whatever was coming.

Being relatively close to the shore, I am wondering what wave height is going to become an issue, i.e. if the waves get so large they start to break. Or is that evening possible at that depth?

Basically, I'm not sure if anyone can answer this, but I'm trying to get an idea of how safe the boat will be on the mooring during a storm?
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Old 29-08-2016, 14:26   #2
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Re: Mooring depth and waves

Quote:
Originally Posted by PhaseSpace View Post
I am looking at having a mooring set off the coast. I have had a spot surveyed and checked out. The mooring ball will be set with a system that should be able to handle 2x the mass of my vessel.

The spot has 32-ft depth and is 650 ft from the shoreline.

If a major storm or swell came from the SW the boat would bear the full brunt of whatever was coming.

Being relatively close to the shore, I am wondering what wave height is going to become an issue, i.e. if the waves get so large they start to break. Or is that evening possible at that depth?

Basically, I'm not sure if anyone can answer this, but I'm trying to get an idea of how safe the boat will be on the mooring during a storm?
I've been to Hawaii enough to know you need to ask locals, not so much sailors. Totally location specific.
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Old 29-08-2016, 14:26   #3
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Re: Mooring depth and waves

Depth 1.3 times wave height. About a 25 ft wave in your case.
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Old 29-08-2016, 14:54   #4
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Re: Mooring depth and waves

Quote:
I've been to Hawaii enough to know you need to ask locals, not so much sailors. Totally location specific.
True!

Quote:
Depth 1.3 times wave height. About a 25 ft wave in your case.
Got it, I think you mean:

wave-height = depth * 1.3 (Correct?)

So basically waves larger that 70% of the depth are potential trouble....I will have to look at the local wave data (if there is any) to see how safe I am.
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Old 30-08-2016, 04:26   #5
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Re: Mooring depth and waves

No, depth = 1.3* wave height, so depth/1.3 =wave height when it begins breaking. Note the wave height is less than the depth of water. That's in a very clean (engineer's wave tank) circumstance. Intersecting wave fronts bouncing off shores could give you rouges, for example.
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Old 30-08-2016, 08:21   #6
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Re: Mooring depth and waves

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Depth 1.3 times wave height. About a 25 ft wave in your case.
The trades can really build up waves to 18 -28 feet quickly offshore. Storm surges can add another 10 feet or more. Really depends on where in the islands and if behind a reef or not. Problem with Hawaii is no really firm holding grounds given the crumbly nature of volcanic lava and coral reefs. Think his boat is doomed.
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Old 30-08-2016, 09:01   #7
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Re: Mooring depth and waves

how will your mooring anchor be secured to the bottom ? Large weighed blocks, or anchors driven into rocks.

How will you be securing the mooring line from the mooring ball to your vessel ? How strong is your mooring line from the bottom to the ball.

For normal mooring conditions in the south pacific and Caribbean, We use double bridles, and chafing gear and secure the bridles with proper cleat hitches to the individual bridles to port and starboard bow cleats.

If in an open roadstead, that is usually protected from the prevailing winds and seas, we have recommended to get the boat out of that usually safe mooring area should a low pressure storm, or santa ana winds, strong NE causing very high seas in association with those winds or storm systems.

Moorings can drag, lines part, deck cleats ripped out, or other vessels if moored or anchored can break free, or moorings can drag another vessel into yours.

Laying out additional anchors would be an emergency suggestion but if another boat drags into yours, and you are not on board to drop off and escape, well, lots of damage or worse.


Agree with talking with the locals. That means everyone including other boat owners. And the harbies or coasties if there are any in your area.


On Kauai Island, vessels that are moored or are in harbors, when storm warnings are posted, they get out and get to a more protected area.

On the north shore in Hanalei Bay, all boats are moved out of the mooring /anchorage area from November until about may. Due to the huge seas that come rolling in during those months from the super strong
storms up in the northern latitudes.


Were it our vessel, we would do a whole lot of research before putting in a mooring in an open roadstead, or along a coast line. Mother Ocean is one
tuff critter, and when joining forces with wind, weather, storms and powerful seas, not sure how much the weather gods pay attention to calculations.


when we owned our own vessels, Crealock 37, and Ericson Olsen 34, we paid the freight for well protected docks deep inside of harbors. That might not be possible in your situation.

Just FYI from our experience, and having to get out of harbors or bays when strong wind and high seas warnings were issued. Also, when sailing internationally, Australia, south pacific, Caribbean or coastal sailing, we do our best to find a protected anchorage or mooring area.

And, if moorings are available, we will pay the mooring fee for what ever time that we are staying. Hate standing anchor watches, and possibly having to play bumper boats at 2:00 am.
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Old 30-08-2016, 09:15   #8
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Re: Mooring depth and waves

Mooring Basics - How to Install a Permanent Mooring

Hope this helps. Also,check methods used in Maine-they leave boats on moorings year round in some pretty rough exposed areas.

Best / Len
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Old 30-08-2016, 10:07   #9
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Re: Mooring depth and waves

Quote:
Originally Posted by PhaseSpace View Post
The spot has 32-ft depth and is 650 ft from the shoreline.

If a major storm or swell came from the SW the boat would bear the full brunt of whatever was coming.

Basically, I'm not sure if anyone can answer this, but I'm trying to get an idea of how safe the boat will be on the mooring during a storm?
You can find some very good information on breaking waves in shallow water in the write-up of the Low Speed Chase incident on the US Sailing web site. We asked a variety of experts about the safe depth when there is a significant wave height of X feet.

http://www.ussailing.org/wp-content/...port-FINAL.pdf

You don't have to read the entire document, although I think you'll find it fascinating.

Cheers,

Chuck Hawley
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Old 30-08-2016, 10:16   #10
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Re: Mooring depth and waves

You do not want to be moored in breaking waves. Once the waves begin to break around the boat, you can pretty much kiss your boat goodbye. Here in Kona depths of 50' or greater seem to be as safe as a mooring can get which isn't all that safe. That seems to put the boats far enough offshore to be clear of the break in high wave conditions. We lose about a boat a year off the moorings in the Bay off Kailua town. The problem usually isn't the mooring, if it's been maintained, but the pendants chafing through.

Kona is in the lee of our rather substantial Island and Maui County upwind to moderate the severe wave conditions, 30' plus, that make most of the other shores of the Islands impossible to anchor long term off of in the winter. so relatively protected water for Hawaii. About the only other year around mooring area is the Ka'anapali coast, Lahaina, off Maui. They lose boats regularly there in the winter though. Spent a summer/early fall on a mooring off Kailua-Kona. Rollyest anchorage I've ever experienced in calm conditions. Had growth halfway up the topsides after 5 months. Luckily was able to get a mooring inside Kawaihae Harbor for the winter and even that wasn't pleasant. Not because of wave action but regular bouts of 30mph winds gusting to 50. When the winds were up, had to swim out to the boat daily to adjust the pendants to keep from chafing through.
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Old 30-08-2016, 10:16   #11
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Re: Mooring depth and waves

You and your boat are going to be incredibly uncomfortable on an unprotected mooring. Anchoring for just a few hours in such a place is awful.
You will save some money but wreck your boat and your boating
Sorry
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Old 30-08-2016, 10:53   #12
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Re: Mooring depth and waves

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Originally Posted by deblen View Post
Mooring Basics - How to Install a Permanent Mooring

Hope this helps. Also,check methods used in Maine-they leave boats on moorings year round in some pretty rough exposed areas.

Best / Len
Helped me. Thanks for sharing!
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Old 30-08-2016, 11:04   #13
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Re: Mooring depth and waves

Thanks everyone for your replies.

The mooring is going to be installed just north of Lahaina near the boat ramp. So there are lots of other moorings there.

I am having two manta-ray anchors installed which will connect via chain to a mooring ball. The manta-ray anchors are driven into the bottom and spread open, and the chain is held up by the buoy mid-depth to keep it from touching the bottom area. This is apparently the new system that will be used from now on. I needed two because I have an old heavy boat (26,000 lbs), and a single anchor would have a short safety margin.

I just wanted to get an idea of when I needed to move the boat out of there.

I spent a month moored off the Lahaina coast in August last year. Was a great time. When the waves did get a little rolly I uses a bucket tied to my spinnaker pole, and pointed out the side of the boat. Slowed the rolling a lot. (Home depot buckets are strong!)

Here is the mooring design I had drawn up:

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Old 30-08-2016, 11:15   #14
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Re: Mooring depth and waves

If you are planning on a permanent mooring in the Lahaina roadstead you will need state permission since its a marine protected area. In the winter, there are hurricane winds blowing through that roadstead when winds start to veer south and whip around Haleakala. Be aware, virtually all protected marinas are full, so trying to find a protected spot before a storm hits is mostly futile. The other issue is the reversing currents in the roadstead. Can get a good 3-5 knot current that shifts from south to north during the day. Finally, not a good idea to leave the boat for long periods of time. Vandalism does exist. Watch out that you are no where near areas already claimed by others(hotels, surfers, boaters, etc). Open water areas are very very territorial. Boats have been cast adrift that poach on someone else's area.

Also that area gets real rough so your deck fittings need to be strong. Personally would not have a mooring there. If you can not get into the harbor or nearby marina would suggest going up to Oahu. Molokai's harbor has barge traffic that can do real damage to unattended moored boats.

The only real bay that is safe to moor in is Kaneohe, and again you need state permission.
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Old 30-08-2016, 11:21   #15
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Re: Mooring depth and waves

Yes, I am going through the permit process. The mooring is near the Mala boat ramp, and is selected in an area near other sailboats, so I'm not expecting any major issues. I'm hoping to have it installed by the end of this year.

If I'm not there, I was thinking of having cameras on the ship should someone try to board when I'm not there. Overall, there is little you can do if someone decides to come on the ship. I have not heard of any issues in that area so hopefully it will be okay.
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