Trim Tab Movement on 43DC

[Will]

My trim tabs were replaced at one time and I'm not sure they are installed properly. Hydraulic cylinder travel is normal but I'm not sure that they are mounted in the correct position with respect to the tabs. They are attached to the tabs at the outside edge which is probably correct. However when the tabs are full up, the outside edges of the tabs are noticeably above the bottom of the boat (maybe about 15 degrees or so). When fully down, they are only slightly lower than the bottom of the boat (maybe about 5 degrees or so). At 1800 RPM, the boat runs about 13kts with tabs up and 14 kts with tabs down.

Does this seem right to you folks?

Thanks - Will

 

[eze2bme]

The OEM Bennett trim tabs on my 1979 43DC have the tab mounts slightly aft of center on the tabs. When fully "UP" they are almost parallel to the bottom and when fully "DOWN" are probably near 30 degrees off parallel to the bottom.

 

[CaptnRick]

I will check on my tabs (1973 43 DC) this pm after work and get back to you.

 

[67hat34c]

what size are the tabs, i ask because over size tabs do not need much travel to do the job. for instance we have a 34c with the original 48" x 9" bennett tabs, they opperate with electromechanical actuators. the movemen is only a few degrees beyond 0

 

[CaptnRick]

My tabs line up just about the same as EZE2BME's tabs as shown below.
Not sure but I think mine may be original. I would have expected them to lower more than 30 degrees off parallel but not the case. They were smaller that what I was expecting for a 43 DC. Heck, I had bigger tabs on a 34 Carver I previously owned and the tabs lowered to at least 45 degrees at full extension.

EZE2BEME Comments:
The OEM Bennett trim tabs on my 1979 43DC have the tab mounts slightly aft of center on the tabs. When fully "UP" they are almost parallel to the bottom and when fully "DOWN" are probably near 30 degrees off parallel to the bottom.

 

[Will]

Thank you eze2beme and CaptnRick,

Well, I finally found a chance to measure my Bennett Trim Tabs. They are 36" x 8" with the outside edge about 12" inboard of the hull at the water line. How do these dimensions compare with yours? I am wondering if moving the cylinder attachment point further in toward the hull which would lower the tabs, might not create an overload either on the tabs or on the cylinders in the tab down position. Moving the cylinder inward would give the tabs more leverage on the cylinder and on the part of the tab outward of the cylinder, would it not? I have no idea of the amount force applied to trim tabs, but assume it to be considerable.

Also, At what speed on your 43' do they seem to take effect? What difference do yours make in speed when in the down position?

I both value and appreciate your input.
Thanks - Will

 

[CaptnRick]

Will,

Will get back to you on the exact measurements of the tabs. Meanwhile, the tabs on my 43 DC "turtle" have "moderate" response at 10 to 12 kts (e.g. not as dramatic as on a lighter and smaller Carver that I previously owned). I got an increase of only 1-2 kts at best. That being said, I have had the boat only in the lower Chesapeake Bay and the James River since I have owned it so there has been little opportunity to put it through its paces - yet.

 

[eze2bme]

Will ... I'll be away for the next two weeks but as I recall my OEM trim tabs are appx. 12" x 40". At 1800 rpm's I get between 1-2 knots extra with the tabs down ... just depends on wind/wave height, loads on the boat and water depth.

I am guessing but I'd say that they are about 20 degrees off of parallel with the bottom. Once I found the best setting I just leave it there since I don't do any hard backing like the SF guys might.

 

[Finalee]

Finalee's tabs have an effect from 8 knots up. There is a solid 3 knot gain at 2300 rpm. The boat needs the tabs down to plane at an angle I can see over the bow.

 

[Trojan]

If my tabs are not fully down. My 43 WILL NOT even get on plane. Mine is a 73DC. Planing starts at 13 MPH and will move up to 20 MPH at 2450 RPM on a good day in shallow water and 18 MPH in deep water. Just guessing my tabs are at 20 degrees and start at the chine with an approx 8 inch gap in the center.

BILL