barge to service moorings

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.

 

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.

 

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.

 

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.

 

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.

 

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

 

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.

 

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