Floating Pump Platform Design

I have a question that no one in my field (Pump Engineering) seems to be able to answer so I thought I'd ask you folks to take a look at it.

As an pump applications engineer, I often specify vertical turbine pumps for quarry/mine dewatering service or for pumping out settling ponds. These pumps are usually quite large (up to 25,000 lbs with motor) and flows up to 70,000 gallons per minute. That's the easy part.

Because of their location, I am also asked to design some sort of floating platform or barge for these pumps. I have seen these in operation before but never in a satisfactory manner. They either list or ride too low in the water or are too unstable to allow workers on the platform to maintain the pumps. I have contacted several fabrication shops in our area who are willing to try building one but I am convinced that they know even less than I do about this subject. The result is that the plant maintenance guys build it using pure guess work and I have to explain that my pumps are not designed to operate at a 25 degree angle or submerged or with their intakes stuck in the mud.

I want to design a platform to hold 2 vertical turbine pumps at 10,000 lbs each with motors. The pumps will have approximately 60% of their weight above the platform and will extend 8 ft. below it. I want to have 1-1.5 ft. of freeboard (is that the right term?) from the mounting surface to the water. It needs to be stable enough for 2 men with tools to comfortably service the pumps. Lastly, the platform needs to be able to remain fairly close to level when one of the pumps is removed for overhaul.

I understand a little about bouyancy and Archimedes Principle from college and I believe I can get the pumps to float. However, that is where my confidence ends. What further design criteria must I need to consider to ensure sufficient stability for this platform?

I realize this is not a "boat" question but I value your input. Thank you in advance.

 

Maybe the barges that list are relatively narrow monohulls. The way to keep the platform level is to make it wide, and get the flotation out to the edges away from the center.

If it has to move, that means a catamaran geometry, one pontoon on each side, width roughly half the length. If not, you get better bidirectional stability with four pontoons, all the way around in a square. But if the platform is anchored and there could be water flow past it in any direction, then you need more tank-shaped floats, one on each corner, so the water flows through the middle. If the pumps are very heavy, then the floats might have to be wider and the gap in the middle smaller, to reduce the stress on the deck.

But ultimately, the problem is mostly a matter of getting the flotation out far enough away from the center, in a way that's consistent with structural demands, motion of the platform and/or water past each other, and application-specific issues, for instance you preferably want pump intakes and exhausts to either pass directly through the deck into the water, or be balanced on each side.

 

Skippy,

Thanks for the information. Most of the platforms I have been asked about have been for quarry applications (no current). I like the idea of the square platform for bidirectional stability. It will probably have to be rectangular to the fact that the plan(top) view of the pumps are square and 2 of them by definition will form a rectangle. This may be advantageous when it comes to one of the pumps being removed for overhaul.

I have a couple of other questions. The first is how to handle the discharge lines. They will be 14" in diameter and will discharge horizontally about 1.5-2 ft. above the deck. Will it be a problem to have them both discharge on the same side of the platform. It seems as if the turning moments could be calculated but how do you offset this? Would it be better to use weight on the opposite of the barge or increase bouyancy on the discharge side?

The question is regarding the flotation devices. Is it better to have fabricated tanks or is there solid foam flotation capable of supporting this weight? I have seen the foam flotation on floating docks but that service is fairly tame and the loads are light compared to this. If there are such foam devices and they are durable, this would seem a superior method because there would be no corrosion and they would not spring holes and sink.

Any thoughts on these questions are very much appreciated. Thank you for your help!

SWomack

 

SW, am I right that you're drawing water straight up from below the surface and dumping it horizontally into a trough? What direction is the intake coming from? What's the flow rate per pump? How much does each pump weigh? How much would you expect the barge to weigh?

As near as I can figure, there's an initial downward tug on the pump when it's turned on, due to accelerating the water upward. Then once it's started, there's a smaller downforce from the weight of the water above the surface and the low pressure required to maintain the flow into the intake. Do I have that right?

The horizontal discharge will rock the platform away from the trough, but you should be able to counteract that by placing the pump a little closer to the discharge side and maybe widening the barge a little and/or adding flotation on the opposite side. Then all you're left with is tying the barge to the trough to deal with the horizontal force from the discharge.

I'm not sure about the foam, I would be interested in aluminum.

Edit: Does the discharge pipe hang out beyond the edge of the platform? If so, how much?

 

The float needs to be designed specifically for the pump or pump set. The barge needs to be wide, deliberately ballasted to be heavy and keep the pump very low slung (perhaps below waterline). The pump fuel tank will need to be precicely on the centre of buoyancy of the barge so that when the fuel supply drops, the barge still floats level, and the pump inlet manifold could also then be higher than the bottom of the barge (located in any or all of the sides as a manifold) so that if the water level drops to the point that the pump is sitting on the mud, the inlet will still be above the mud. If you're interested, I can design this for you. e-mail me.

 

removing pump for servicing

You may want to consider a water ballast system to keep the platform stable when removing a pump for servicing - after all, you already have the tanks and pumps.

Kevin Barry

 

Floating pump stations

Swomack....I am a civil engineer in Virginia and I recently completed a pair of floating pump stations in Chesapeake virginia. They were raw water for the drinking water plant and the flow was 15 million gallons per day. Normal operating pressure was 155 PSI and the barges are located out in the lakes. I used vertical turbine pumps and discharged thru rubber and ball joint ductile iron pipe. Please email me @ alan.edwards@hdrinc.com if you would like some more info and pictures on floating pump stations and any help with this project you have.

The boat design aspect of the project...as this is a boat design page...prefabricated galvanized deck structure over plastic encased foam floats...we used lite weigth waffled concrete for the actual decks.....40'x40' was the overall dims. we used a prefab building on top to enclose the equipment and we had a 3 ton bridge crane to load the pumps etc... on and off for maintenance.

 

Have you considered using large submersible pumps on the floating barge instead of vertical turbine pumps?

We are planning to use two VFD submersible pumps (620 HP and 90 HP)on a floating pump station that will be used to drain a large (3.8 billion gallon), deep (150 feet) groundwater recharge basin that covers an area of 135 acres. The larger pump will be able to pump 17,000 gpm @ 117' TDH with an efficiency of 86%. The pump station capacity will range from 9,900 gpm to 24,800 gpm.

We have never used a floating pump station before so I would appreciate any recommendations you may have from "lessons learned" form your experience. We want to be able to easily lift/raise up the pumps high enough out of the water on board the barge so our crews can perform routine maintenance such as changing the oil. we plan to use an onshore winch to pull the floating pump station close to the shoreline and use a crane to remove the pumps when major repairs are required.

please e-mail your recommendations and comments to me at bperalta@ocwd.com.

thank you.
Ben

 

I was involved in a project, some years back. By the inventor, it was named the "BulClaimer". Some of the main parts here were rather large sentrifugal pumps (Svedala slurry pump), in the area 1000 hp) and floats. The system were bought by SembCorp in Singapore. One float was sircular and in the middle, was this rather large pump, and a pretty, tiny Hagglund hydraulic motor. Worked fine. The other pump were fitted to a square shaped float, worked also. We had it designed so that the intake was well below the surface.

The idea was to use a bulc ship for transport of loose mass (sand), instead of expensive specialized ships, to fill the ship with sand/ water (slurry), let the pumps float around in the starage area running on idle speed, draining out the water, letting the slurry to settle. Emptying the ship it should be oposite; water cannons whirvelling up the sand/ water, rev up the pumps and empty the ship. The first tests as I recall gave an estimate of 8-10 hous to empty a 67 000 dwt boat.

Some tension to consider from the torque....
(Hey, it was a prototype.... we got that fixed....).

 

Floating Barges for up to 8ea. 900 HP Pumps

Marine Dynamics Corporation (www.marinedynamicscorp.com) is a manufacturer of large pump barges, as well as small ones and operates nationally. We have very large barges on the water in several states done for companies such as HDR Engineering and Jacobs Engineering.

We custom design each barge for each application although we use a proprietary modular system. As far as we know we are the only company to have successfully installed bridge cranes on these type structures including the ones mentioned above by the HDR Rep. Pictures of these barges are located on our website. Jonnie Enloe, Managing Dir., Marine Dynamics 903-235-5454

We have over 25 years experience in the floating structure business and can furnish a large list of references

 

this is exactly the sort of problem for my expandable tinker-toy concept.

this is exactly the sort of problem for my expandable tinker-toy concept.


Whatever the load and stability required, you just keep bolting on beams and hulls.

All parts are Container-able and tow-able with standard pickup truck.

If you needs expand or change it is simple to add any amount of additional barge.

Unlike most purpose built barges, the platform would be able to motor around quite nicely. Hopefully, this would mean less need to tricky operations in remote locations, and more fitting out at a base marina.

The beams could be anything: solid timber, boxed wood, fiberglass or any spec of alum or steel. With steel it would be simple to cut and weld a few jogs if you needed a platform closer to the water(or higher off the water).






this is the Modular concept.

Unlike a purpose built barge, after the project is completely the components would hopefully have considerable value and be easily sold, or returned to the leasing agency.

Generally, the idea is to have a known, pre-engineered system and simple proven methods of assembly.

With a tinkertoy deck it could be infinitely expanded in any direction or shape. Hulls could be adding pointing any direction for stability.

 

Have you considered vertical steel columns like oil rigs ?

They have the advantage of greater stability, and can be ballasted better than multihulls.

 

Floating Structures for Pump Stations

Pump Stations must be mobile, obviating the use of piling. In all cases, particularly on Corp. of Engineers controlled water, the method must be a proven method and the manufacturer must have had proven designs in the water for five previous. This goes back to the Marina Manufacturers Association whose members built the first of these. Most if not all of these projects require overhead cranes and large building structures which are exceptionally hard to stablize except on a unitary structure such as a space frame. When a FEA of the structure as a whole is done, structures of various and separate parts that are not hard bolted and ridgid fail miserably. We have built eleven of these project in the last 10 years and have tried everything from an engineering standpoint. Even to the point of throwing out everything and completely starting over and trying every concept under the sun. The continous wave action is simply too much for non-ridgid floating structures or floating structures ridgidly attached to the bottom. The last one we did had 4-ea. 900HP vertical pumps requiring an overhead crane at a 30 ft. eve height on the canopy. Owners simply will not take a chance on overturn problems or unproven methods and risk their populations water supply. Unless you have a tried and proven a particular design it is very unlikely that you can be successful first time out. You must find a small job with a willing engineer and get a prototype on the water before attacking larger jobs. I know this sounds like the old axiom, walk before you run, but nothing could be truer. We will share any info that we have with interested parties because we feel no threat in the market place. We know how hard it is to succeed with new designs.

The other major factors are wave studies, overturn studies and maintenance of the finished structure. Most such structures, require retightening of fasteners at least once a year. Until we redesigned, about 10 years ago we suffered this malady as well. However, since we redesigned to a totally modular concept which is harmonically sound from vibration standpoint, we have never had to retighten a single fastener on a single project in 10 years. Most buyers in the know that are knowledgeable of these factors will not allow anything less. However, like I say, we will share what we know so that no one should be at a disadvantage.

Jonnie Enloe
Managing Director
Marine Dynamics Corporation
enloe1@cablelynx.com
Longview, TX
www.marinedynamicscorp.com (under reconstruction)

 

Can you use spuds on the barges? A catamaran will give you more stability with the same floatation.

 

The loads are concentrated in the center of the barge normally. Then there is a trememdous surge downward as pumps are started loading the header and all discharges. During maintenance the cranes must extend beyond the end of the barge to load and unload tenders. Without full width floatation the loaded crane would pull it under if the load is concentrated say on two catamarans. The structural steel needed to span the cats would be about 50% more than required for full width space frame structure. Because of all of the circumstances encountered it is like trying to balance on a basketball in the water. The real killer are the engineers errors and omissions insurance; They want full historical records of types and calculations before putting their neck in the nose. An unknown design is almost impossible to get approved in advance which is required. We must calculate and guarantee viability before bidding process begins. Not a good time to take a chance regardless of viability. We want something we don't have to worry about. It was a huge step going to bridge cranes from monorails because of shifting loads all the way from end to end and side to side. I had to personally guarantee the viability on the first one, which was big gamble. That is where the rubber meets the road. When they want you to personally guarantee something that has never been done that might end up in 200 ft. of water and the city having to haul water to it's citizens. We kick new ideas around all of the time and that's great. But when it comes down to paying the fiddler after he calls the wrong tune and after the dance is over, that is an entirely different thing. I enjoy kicking things around though. Our current designs began 23 years ago when we were having problems at another manufacturer.