barge to service moorings

[Chuck Losness]

There is only one guy left who services moorings in Morro Bay. He is looking to retire. His barge is old and he is having to make constant repairs to his equipment. We are considering having our own barge to service the club moorings.

We have 25 moorings. The biggest blocks weigh 5000 lbs and are made of concrete. Lots of lakes in the area so aluminum pontoon boats are plentiful at reasonable prices. How big of a pontoon boat would we need to safely pick up a 5000 lb mooring block. I know that we would need an aframe crane and other equipment to pick up the blocks. But a stable barge is the first issue. If that is doable then we can get into the other stuff.

Looking for suggestions.

 

[gonzo]

A pair of 24 inch diameter by 24 feet long pontoon will displace approximately 4,700 lbs at half submersion. You would need double that to account for the weight of the barge, crane, crew and miscellaneous stuff. Small mooring barges usually have the crane mounted at the center. For convenience you can build the barge with a U shape deck. There should be a removable beam at the bows to stiffen the structure.

 

[BlueBell]

What design was the previous guy using?
Do you have pictures?

Your 5000 pound concrete blocks will only weigh ~3000 pounds submerged due to buoyancy.
However, they will be full weight once clear of the water and on deck.

How deep are they?

 

[kapnD]

What design was the previous guy using?
Do you have pictures?

Your 5000 pound concrete blocks will only weigh ~3000 pounds submerged due to buoyancy.
However, they will be full weight once clear of the water and on deck.
How deep are they?

I’ve moved some comparable weight anchors by submerging them then tow to location.
Get the boat right over the weight, and sling it below midship for safety.
Go slow and don’t neglect to carefully crunch the numbers before you attempt it.

 

[Chuck Losness]

The current guy uses a barge that he made. It looks to be steel and around 40' to 45' long by around 15' wide. I believe it is two hulls about 4' wide but could be wrong on that. The middle of each end is open for about 10'. The water depth varies from 10' to 30' in our mooring field.

Ideally we would like it to be trailerable so it doesn't have to be stored on one of our moorings. We only have 25 moorings and 6 of those have to be reserved for transient boats per our lease with the city. The more I think about it I don't think that even a big pontoon boat would work. Not enough displacement to handle the weight of the blocks as Gonzo pointed out.

 

[TANSL]

You should not use circular pontoons because, with a draft greater than their radius, they lose stability and the centimetres per tonne of immersion are greatly reduced.
With parallelepiped pontoons you will not have this problem and, in addition, you can give them the vertical dimension you need, regardless of the length or width of the pontoon.
It would be advisable to place the hole for anchoring the blocks in the centre of the deck.

 

[rangebowdrie]

Once again William Atkin comes to the rescue.
Atkin & Co. - Giant (mysticseaport.org)

 

[BlueBell]

This is a challenging design given the SOR so far.
You may want to look beyond a forum.
Trailerable will be an issue for such high payloads.

 

[Chuck Losness]

The Club has given up on having their own barge for servicing moorings. Not enough moorings to justify the cost.

Thanks for everyone's suggestions

 

[Chuck Losness]

The club is again exploring servicing our moorings. The guy who has serviced the moorings in the past has more than doubled the cost. Close to $2000 per mooring plus parts. One of our newer club members spent 18 years servicing the moorings in Jamestown before retiring several years ago. He is sharing his knowledge. There is a storage yard not far from the lunch ramp in Morro Bay. The barge can be wider that 8'. I am thinking about using two pontoon hulls on each side and maybe a hull halfway down the center or a floatation block. That should provide sufficient buoyancy to pick up a 5k concrete block and all of the equipment needed to service a mooring.

This barge will never travel far and speed is not important. Less than a mile from the launch ramp to our mooring field. No waves or swell to contend with.

Before I got to the trouble of calculating displacement and weights, do you guys think that this might work?

 

[TANSL]

The more asymmetrical your hull is, the more stability problems can arise. What about a totally prismatic hull with a large square hole in the center?

 

[Chuck Losness]

A large hole in the center won't work. Has to be open on one end to be able to access the mooring ball. The moorings have a concrete block resting on bottom, then 1" bottom chain followed by 3/4" chain up to the mooring ball. The boat attaches to the mooring ball with a 3/4" 3 strand pendant 5' to 10' long.

To service a mooring the barge anchors up current from the ball. Then moves so the ball is centered on the end of the barge. A chain hook is attached to the chain at the mooring ball. The boat on the mooring is then tied to the barge and the pendant is removed. The mooring ball is then pulled into the open area at the end of the barge. The ball and chain is lifted onto the barge and the block is brought to the surface but not placed on the barge. Every thing is checked and any excessively worn parts are replaced. The block is released and the chain and ball goes back into the water. Finally the boat is reattached to its pendant. The whole process takes on average 1 hour 15 minutes.

The barge currently being used is "H" shaped. 40' LOA by 20' beam. Each hull is 6' wide with 8' between the hulls. The openings on each end are 8' wide by 10' long. A skiff with an outboard is used to move the barge.