strength of bennett trim tabs?????

[bob johnson]

I have an application for the use of some hydraulic actuated trim tabs for my big MOD V boat. i have large 24 x 24 x 8" flotation pods welded to the back of the transom to add bouyancy to the stern. This is great for shallow water motoring and for offsetting big heavy outboards. But there is a catch 22 with them welded on....they drag badly when at speed. Most guys know the best speed is acheived with some bow lift while on plane...to get as much of the hull out of water as possible....but that hll angle makes the pods drag and act like a serious brake and forces the bow back down at speed.


the other side of the coin is if I alter the flotation pods to clear the water while at speed they dont offer much static bouynace at rest or while going slow.....which is their main purpose.

soooo
I have this idea to mount the bennett trim tab pistons to the top of some flotation pods that are only attached to the bottom of the transom with a hinge...and that the side close to the transom is angled for enough clearance to allow me to lift the pods when i want to go fast, out of the way.

i wonder if the pistons would b strong enough to allow a full grown man to stand on the flotation pods?

i use my pods to climb in and out of the boat often...so i would want to destroy the pistons if I put my weight on the top opf the pod after I have the trim tab pistons mounted


so ill ask here for all those who know about trim tabs

thanks

bob

 

[QC]

Re: strength of bennett trim tabs?????

So this is really not a trim tab question but a hydraulic ram question. You should PM TabMan and I bet he can give you the application info for their ram, but I would suggest that there may be something available that is more suited. Of course their rams are good in marine applications so maybe you're on the right track here.

 

[smokeonthewater]

Re: strength of bennett trim tabs?????

no, that won't work.... the cylinders are powered down and lifted by springs.... I (240 lbs)sometimes step on my tabs to climb onto the swim platform when the boat is on the trailer. I have to step right next to the transom AND support a quite a bit of my weight with my arms or the tab moves down.... if you step even a couple inches from the front your pod will drop. Further back and you'd very likely over extend and break the ram. Not to mention busting your backside from poor footing.

consider modifying the pod bottom to angle it up by just a by just a few degrees.... it may not need to completely clear the water but just ease up enough to not force the bow down

You could also hinge the bottom and use turn buckles with lock nuts to fine tune them.

 

[bob johnson]

Re: strength of bennett trim tabs?????

thats why i asked here... so the actuators are one way?

I really want the adjustable pods!! that way i can drive them down BELOW the hull even to lift the stern in real shallow water....it would add versatility.

along with my hydraulic jack plate the adjustable pods would give me all kinds of variables to motor or float out of shallow flats on tidal waters...


at slow speed the pod below the hul would no negative effect....then when i was in a little deeper water and wanted to pick up speed, i could just dial them up with a switch.

I figure i could rig up something with some spare TNT units...but the tabs, especially useds one looked cheaper.

bob

 

[smokeonthewater]

Re: strength of bennett trim tabs?????

yep, one way.
You COULD possibly use some I/O trim rams... like some from an alpha and two alpha trim pumps or some solenoid valves and one pump... I think you should build step platforms above your tanks and take the step feature out of the equation.... would be safer that way.

 

[oops!]

Re: strength of bennett trim tabs?????

I really want the adjustable pods!! that way i can drive them down BELOW the hull even to lift the stern in real shallow water....it would add versatility.

not really sure what you want here bob....

but you would need a huge pod to drive the stern up. one at least that will displace the weight of the boat.

so i really dont think the idea is doable.

for shallow water running....a jet boat or air boat is required

 

[smokeonthewater]

Re: strength of bennett trim tabs?????

oops, I was thinking the same thing at first but I THINK he meant adding stern lift while moving forward just as a trim tab would

 

[oops!]

Re: strength of bennett trim tabs?????

i agree smoke.

but for any serious lift, if you dont have forward momentum, you need displacement.

the kind of displacement he is talking about. would be over 3 feet in length and the full width of the boat. all of that behind the drive.

 

[Tabman]

Re: strength of bennett trim tabs?????

Bob,

The other posters are pretty much on target, standard Bennett Trim Tab actuators (rams) are single acting. They deploy down with a force of about 700 Lbs. They are returned upwards by a large internal spring with about 80 Lbs of force.

We do make some dual acting systems for larger yachts, commercial and military applications that power both up and down. However these systems would likely be much more than you would be willing to spend on this idea.

Since the actuators return at 80 Lbs or perhaps 160 Lbs if you were to use two per pod, using them as a boarding platform would not work.

Tom McGow
Bennett Marine

 

[Tabman]

Re: strength of bennett trim tabs?????

As a side note, you might be surprised how little you would need to angle the pods up (particularly the after portion of them) to get some additional bow rise at speed. If they can be modified to have a tapered section they might able to clear the water flow on plane and quickly add buoyancy as they are immersed with weight on them.

Tom
Bennett Marine

 

[kemo111]

Re: strength of bennett trim tabs?????

If you only climb on them on land I am sure you could build a lock bar that you could put on to hold them up. a d ring on the boat and a hole in the general area where the piston attaches to the flotation pod and a length of 1/4 ss steel rod with a small hook on each end. Or ss steel cable with a clevis on each end. It sounds like Bennett Trim Tab actuators would be strong enough to push them.

 

[bob johnson]

Re: strength of bennett trim tabs?????

well the pods add lift to the boat ...they are currently welded onto the transom . if the pods are underwater, the rear of the boat raises.... i never said i expected a foot of lift.... the pods probably only give me 1.5-2" of lift at the stern..mainly because they are not fully underwater...because the boat already floats so shallow..its a wide, long footprint( 2070 mod V)...but If i could drive the pod down to completly submerge the pods..i could expect another inch of lift maybe.....when running shallows for hundreds of yards or more....being able to motor with out the prop banging bottom is the goal... I like the benefit of the pods already...for the little lift i get and for a step into the boat. from the water and from a trailered boat. but i am trying to look for away around the negative effect of the pods dragging like a brake , when i want to lift the bow for speed!!
I can pretty much lift the bow with mega trim at slow speed to fight rough water.. I am trying to get back to being able to lift the whole front of the boats hull out of the water while on plane by trimming for max speed....right now the pods dragging totally kills that..... on plane i have more than 3/4 of the hull in the water!!!

bob