question on I/O lower unit hydraulic rams

bob johnson

Rear Admiral
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Feb 25, 2009
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4,304
I am wondering how much force these units have in either direction. I want to "adapt" a set I have on a junk boat I acquired for parts. the boat appears to have a clean mercruiser gimbal set still installed with the twin hydraulic ramps for TNT action, with the pump. I am thinking of using these rams as a heavy duty form of TRIM TAB. Only the trim tabs are not just a sheet of SS... they are 24" long 18" wide flotation pods that are usually welded (sometimes bolted) the transoms of shallow water boats to help lift the stern. I had these pods welded onto my LOWE 2070 and I loved them, except they killed the top end because they were welded on flat and level with the bottom of the hull.... so when I was trying to get on plane....I actually did it in an instant, but they dragged and prevented clean top end speed.. the way they were attached gave me 100 % excellent use when not in motion or going very slow in shallow water.... the more of the pod I had under water, the more buoyancy they provided.....so my rig could actually motor in about 6" of water...because I had a jackplate . this is a 1200 lb 22.5 ft (with the pods) long boat!!! sporting a 325 lb outboard!.....so I love the pods for sitting still or going slow in the shallows, BUT I don't want them when I am on plane at speed....

so my idea is to have them on a heavy duty hinge on the bottom and attached to the hydraulic rams on top... and deploy them down when shallow of static, and pull them out of the way( maybe 10 degrees upward) when under half or more power!

so the question is....are these rams good for dual acting pressure?

I had thought about this last year using real trim tabs.... but the tabs only had power one way...downward.... since I climb into the boat often via the pods...they have to support 200-300 lbs when climbing in and out over the pod..... the trim tabs where just on a spring, and they would just stretch out if you forced them downward...


bob
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
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47,306
They are...... with a caviat.

the stock rams normally have prop thrust and gravity to help. hence the larger rod diameter, and small area on the rod side of the piston. you should calculate what you need for the force and work backwords to ensure you have the right cylinder for the job .there is a limit to the rod side gland seals as far as pressure.

I do know that the extend pressure is much higher than the retract pressure (I think extend is about 2400 psi, retract about 1100, however need to verify). you may need to adjust the retract pressure on the pump (have to pull the pump out of the reservoir). instructions for the adjustment can be found in the oildyne 108 manual (look on line). max pressure from the oildyne 108 pump is 3400 psi

bennett trim tabs operate at a much lower pressure (about 300 psi) they are hydraulic extend, spring return.

verify your geometry, the outdrive rams have a long stroke. your description of what you need sounds like a relatively short stroke with about a 2" bore. you may need to find a better cylinder that matches your needs
 

bob johnson

Rear Admiral
Joined
Feb 25, 2009
Messages
4,304
you are correct, I had thought the rod were way longer than I needed, but it is what I have for free now... I was figuring id have to come up with a way to just limit the throw somehow... the downward force I need is similar to a trim tab... it only need to overcome the force of the water....actually not even that , because the greatest force of water will be at speed, which is when id want them out of the way!.....I am thinking I need strength in preventing EXTENSION, so when I stood on the pod with the boat on the trailer....the ram doesn't pull out of the cylinder!!...or when I am in shallow water and I climb into the boat over top the pod.....which is one of the second best things about the pod!! that nice step to get in.

let me ask you this... if I come up with another cylinder, the PUMP is still good to use??

what if I mounted the pods in the up position with the cylinder 80% extended already... then the throw I needed to force the pod down, would be at the end of the cylinders stroke...thus stopping itself... and on retract the pod would contact the transom as a solid stop..... would I be trying to rip the rod end mount onto the top of the pod , off....with the retract?? the cylinder doesn't have that much power does it?


bob
 

bob johnson

Rear Admiral
Joined
Feb 25, 2009
Messages
4,304
I know the Bennet trim tab cylinders have a spring to retract the tabs... so they wouldn't work for my application. But a look at lenco actuators and they are a ball screw...so they have to be driven in BOTH directions..... I may try to find a used pair of those with the 2-1/4: stroke. Anyone know much about Lenco trim tab actuators?


bob
 
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