lifting keel mechanisms- hydraulics?

Anyone out there have experience with lifting keel mechanisms, either pulley or hydraulic systems?
I'm designing a 34' sloop with a 3000lb swing keel and am to the nitty gritty of specs for the lifting system. I think I've settled on using hydraulics, but haven't ruled out block and tackle yet.
Any tidbits of info out there regarding available lifting systems? hydraulics companies other than navtec? Much appreciate any leads from anyone with experience in this area.

 

swing keel?

In the 70's and 80's(at least) swing keels were keels that pivoted like a centerboard so that the lifting line or mechanism wasn't necessarily moving all the weight of the keel.
More recently some writers have referred to canting keels as "swing keels". If you lift(retract) a canting keel you lift all the weight. Seems to me that European/ UK mags like Seahorse have been leaders in this re -definition so you might want to be more specific....

 

Sorry,
Swing keel I'm referring to is swing fore/aft like a centerboard, pivot on an athwartship pin to raise the keel for reduced draft, not the CBTF type.

 

Navtec is well known for sailing yacht hydraulics but there are others, it is a while since I worked in the yacht building industry so I cannot recall the names but Seaway Powell Ltd is one small company that springs to mind. Alternatively and probably much cheaper, for a simple pump and cylinder arrangement installed within the relatively dry interior of the yacht you could use industrial components such as supplied by Enerpac and other companies. Enerpac for example supply a range of hand operated hydraulic pumps which could be fairly simply connected to either a cylinder from the Enerpac range or to any one of numerous commercially available hydraulic cylinders.

John

 

water addict,

I have been working on a "Pipe Dream" boat for a year now, I have come up with a configuration using standard off the shelf parts.
Parker 3L Series, Medium Duty Hydraulic Cylinder
Working Pressure 1000 (lbs/in2)

The swing keel is 595lbs, working pressure of the cylinder is around 250psi. The entire assembly is cast iron, with stainless pins. Let me know if this is any help.

Also Hunter has a swing keel on their 21-6 design.

If you would like to know more, let me know... rjmcgaughey@intergate.com

 

Thanks rjmac,
I looked at your drawing-pretty neat. Have you looked at grounding? Does the hydraulic setup handle that (some sort of relief built in)? Buckling at piston from grounding? I've been doing the calcs trying to decide on the hydraulic lift being on the tension or compression side to take into account grounding as well as dynamic loads, in case this thing gets out in a seaway and starts pounding. Have you any experience with that sort of stuff? I'd be curious to see how you computed those, if you did.
Thanks.

 

Yes that was an issue which is solved with a relief valve. Hydraulic Systems have an inherent forgiveness (the fluid is not totally incompressible). Yes I do have some spreadsheet calcs, will send them in the morning. As far as the cyclinder being in tension or compression, I do not believe it makes a big difference. I have no experience with seaway pounding, but hydraulic systems a very forgiving, if properly designed.

 

water addict,


The attached excel details the calculations for determining the moment arms, cg, and etc. There is a bit of a cost for this information though... Let me know if I have made any mistakes......

This is pretty basic stuff; the overall system is arranged with a single hydraulic line in mind, single action cylinder. When the keel is in the up position the maximum pressure required, 350psi. The reservoir tank is located near the hand pump for raising and lowering the keel, 1inch bore with 4inch stroke. The exit port for the relief valve feeds into a separate reservoir.

The cap on the front of the keel box is located above the LWL, if any water gets inside the boat the bilge pump should be able to handle it, minimal leakage. No matter how hard you try water always seems to find a way into the bilge….

Final note, this system is designed with the boat being on the trailer most of the time so the cylinder will be in the up position most of the time, this is just to keep the cylinder rod and seals in good shape, pressurized prior to launch.

Bob

 

Hi there, I don't know if anyone looks at "posts" from old topics , as I'm new to this forum.
For what it's worth, I'm building a large centre board yacht and intend to use the hydrulic - [ sh** I wish these things had spell check for ********* like me !!] pump assembly from a truck .
That is, on the larger trucks, they have a hyd-- pump, with built in tank & manual back up pump [ by hand - like a jack ] and it's all about 150 X 300 X 200mm .
Very compact, cheap - 2nd hand [ wreckers yard ] with ram to suit .
Don't write off this cheap but strong little unit, they are good for tonage, and as all systems should have on board , a reliable backup.
If one were to rig the ram to pull a cable to raise & or lower, worst case [ both 12 /24v & manual hyd- fail ] one could use a winch to pull the cable and with a cable, should it ground, the keel would just push up.
Yes / no !?.
Globaldude.

 

The self contained setup sounds good.....cheap is not always bad, just rebuild all the seals, etc. On all good designed hydraulic systems there is always a relief valve, this would take the mechanical shock. This would be the only modification, that could be changed to handle groundings. For the most part hybraulic cyclinders work most reliably when hard mount pivot points are used. A cable assembly is feasible, but there could be side forces that could cause problems with cylinder, this is only a thought.... The bottom line is what you feel safe with. Cables have a tendency to fry and break over time. I have read a couple sale adds about boats that have had the cables break and then the boat ends up permanently in that state, with the keel down.

 

IF a cable breaks it is undersized or of poor quality. NO system should not be able to lift a simple hinged vertical load.

 

Thanks all for comments and suggestions.

 

Either way, 1/2 dozen the other, a cable is a very common way to left the board. Like anything, if not maintained, it will fail.

As will the hybraulic system fail if not maintained. Concerning vertcal loads, it is done everywhere, all over the place, just look a steam shovel, or a backhoe.

 

I will hazard a guess on a system. Hydraulic pump, resevoir, filter, relief valve, etc. Cable and a pulley to convert the cylinder stroke, to only a straight horizontal one. The hydraulic cylinder should have a " cushion valve in the end that is used for down. It eliminates the hard stop at the end of the stroke for down. There are 1 way speed control valves that can be installed in a cylinder to slow down the rapid decent of the keel IF a hose breaks. Geometry of keel cable run is up to you depending where in the keel the cable dead end is placed.

 

I just bought a Stellar 30, designer Jim Kyle, built in Rockland, with a 2000 lb lifting keel which uses a Superwinch and 5/32 ss cable, kinda nobrainer. Just replaced the cable, probably first time since built in 1986. Old cable OK. Superwinch X3 has two part pulley arrangement, lifts 1000 lb. Seems like a good system and is compact accessible with no special tools.