Trim Selection-Does size matter??

Thanks Tom,

The lip does not stick out too much but it will sightly limit the total downward deflection of the Trim Tabs. On thing we have done in these instances is to to make a small mounting block the same width of the shim on the bottom for the actuator (ram) to sit on the transom. This puts them in the same plane and restores the designed geometry and therefore total travel of the Trim Tab. I have used nylon material, like "Starboard" to fabricate these pads.

If she were my boat (and I wish she was!) I would fit 12" x 12" Trim Tabs that had 3" Dropfins on the sides. These larger Dropfins capture water pressure that normally escapes out the sides of the Trim Tabs and channels it aft to generated additional lift.

A 12" x 12" with these Dropfins would create the most lift possible in a 12" span.

Lenco does not offer (last time I checked) 3" Dropfins but we make some "add on ones" that you may be able to fit to a standard Lenco 12 x 12.

IMG_0365.jpg

IMG_0364.jpg

I hope this is of some help,

Tom
Bennett Marine
 
Tabman,

How much of a difference do the dropfins make? I've got Bennett tabs that were installed by the factory and sometimes I'd like to keep the bow down a bit more than my current setup allows. Also, will they cause a problem with a boat that is in dry storage since they will always stick down below the hull? Finally, a brief search of your website didn't turn up any info on drop fins...can you point me to the page with info on them?

Thanks!
 
20dauntless":2rfmjqdg said:
Tabman,

How much of a difference do the dropfins make? I've got Bennett tabs that were installed by the factory and sometimes I'd like to keep the bow down a bit more than my current setup allows. Also, will they cause a problem with a boat that is in dry storage since they will always stick down below the hull? Finally, a brief search of your website didn't turn up any info on drop fins...can you point me to the page with info on them?

Thanks!
Click to expand...

Dauntless,

3" Dropfins make a pretty big difference in the lift a Trim Tab will generate. We only make them in 12" chord (fore to aft measurement) Trim Tabs. The additional lift they make is more noticeable on shorter span (side to side measurement) Trim Tabs, such as a 12 or 18 inches. Roughly a 12" x 12" with Dropfins will equate to about an 18" x 12" flat Trim Tab.

You are on target with the possibility that they may be damaged by a forklift if the boat is kept in a dry rack. A knowledgeable forklift operator who knows that are there won't have a problem, but the day a rookie hauls the boat, well there may be a problem. . .

The M120 and M80 Sport Tabs have smaller Dropfins that are level or slightly above the hull bottom when retracted and therefore don't get in the way of a forklift, but they don't generate quite as much additional lift.

The Dropfin Trim Tabs aren't on our website (I am going to bring this to the attention of our webmaster). If you are interested in fitting them let me know the size of the Trim Tabs you have now and I will be delighted to help you with the part numbers.

Tom
Bennett Marine
 
Here is a picture of Bennett Trim Tabs on a 1984 C-Dory, so i guess they could be installed on my 1985 C-Dory as well. I see that the tabs are located towards the inboard side of the transom drain holes.I supect that they would work great for lowering the bow but not to well in lateral stability due to the fact that they are positioned quite a bit closer to the boats center-line than you would normally do. Tug

http://i1201.photobucket.com/albums/bb3 ... mTabs2.jpg
 
Tug":3cqje4t1 said:
Here is a picture of Bennett Trim Tabs on a 1984 C-Dory, so i guess they could be installed on my 1985 C-Dory as well. I see that the tabs are located towards the inboard side of the transom drain holes.I supect that they would work great for lowering the bow but not to well in lateral stability due to the fact that they are positioned quite a bit closer to the boats center-line than you would normally do. Tug

C-DoryTrimTabs2.jpg
Click to expand...

Tug,

While we would normally want to see the Trim Tabs about 3" or so from the chine, the ones in the picture are still outboard enough that they will likely give adequate side to side control. It's a lot better than not having them or moving the scupper. . .

Tom
Bennett Marine
 
Tom, I realy like the drop fin idea. a brat made his own pair a while back and I was thinking of doing the same but have no way to bend heavy stainless. I might just order a pair when the time comes.
 
Tom, thanks for the reply.I wonder if one could cut a hole in the Trim Tab mounting plate to match the transom drain hole, but doing that might weaken the whole thing. Tug
 
Tug":185f70ua said:
Tom, thanks for the reply.I wonder if one could cut a hole in the Trim Tab mounting plate to match the transom drain hole, but doing that might weaken the whole thing. Tug
Click to expand...

We actually make some hinge plates with a hole cut in them for a scupper, but the one in the photo looks too low. I think it would interfere with the "curl" of the hinge itself, so I can't recommend cutting it.

Tom
Bennett Marine
 
Tom, quick question, why have a 90 degree angle in the tab extension with screw heads sticking down into the water way? why not a flat piece of stainless and bolt it to he up right part of the tab? that way no added drag to the tab. Now I am backseat quarterbacking here but it look like it would be less drag, Not enough to make a difference but...
 
starcrafttom":3ltpupmh said:
Tom, quick question, why have a 90 degree angle in the tab extension with screw heads sticking down into the water way? why not a flat piece of stainless and bolt it to he up right part of the tab? that way no added drag to the tab. Now I am backseat quarterbacking here but it look like it would be less drag, Not enough to make a difference but...
Click to expand...

Tom,

Normally, if purchased from Bennett as Dropfin units the fins would be one piece with the Trim Tab, simply folded down in the same shape as the add ons you see in the picture. It's a nice clean design.

The add on units are designed to be installed on flat Trim Tabs, without the up fins you see in the picture (I'm at home and that was the only picture I had). So they sit on top of the flat surface and there is no vertical fin to bolt through as you suggest.

I worked with the owner of the boat in the photo and he was not getting enough lift with the existing Trim Tabs and adding the Dropfins was the easiest and least expensive route since he had no metal working ability and wanted it fixed ASAP. The screw heads undoubtedly added a bit of drag, but he was delighted with the results.

If the Trim Tabs you purchase have small upfins to stiffen them then I think adding the by bolting them through the upfins as you suggest would be a very good idea. Some Lenco Trim Tabs have the edges bent upward at a shallow angle;

l1212.jpg

I don't like this design since a 90 degree bend adds much more stiffness and the shallow angle actually encourages more pressure lose out the sides by creating low pressure in those areas. It would also make adding Dropfins a lot harder. So make sure that you see if you can get ones with the 90 degree up fins.

Tom
Bennett Marine
 
Can I point out here what a great company Bennett is?

WHen I moderated the Powerboat Forum for Sea Magazine Tom would stop by and answer trim tab questions, and even helped answer questions for posters with competing products.

Is Bennett the best tab out there? I don't know. But their customer service is superb, and the reason that I recomend their product.
 
Tabman, great to have you onboard. I'm going to start mooring our boat in a saltwater marina for the first time and just purchased trim tab zinc anodes. Where's the best place to mount them on our M-120's?

Peter
C-Dancer
 
Jazzmanic":2x31198g said:
Tabman, great to have you onboard. I'm going to start mooring our boat in a saltwater marina for the first time and just purchased trim tab zinc anodes. Where's the best place to mount them on our M-120's?

Peter
C-Dancer
Click to expand...

Peter,

Did you buy the disk type?

r-3.jpg

The best way to install these is to mount one half of them on the top of the Trim Tab (no need to put half on the bottom, and it will just cause drag).

Put it between where the actuator (ram) is attached to the Trim Tab and the hinge on the transom pretty much right in the middle. Remember not to paint or prime underneath the zinc so good electrical contact is maintained with the Trim Tab.

Tom
Bennett Marine
 
Hey Tom, I haven't yet but I will. I hadn't even thought about the zinc issue. M120s are in my West Marine "cart" waiting for a few more bits and pieces.

Thanks for all your help-it is much appreciated!!

Peter
Bermuda
 
Tabman,

Actually, I bought these ones. I guess they're made to screw onto the actuator screws. However, the M-120's have the actuator on the top middle of the tab.
bennett_trim_tab_zincs.thumb.jpg
bennett_diagram.thumb.jpg


Will these work?

Peter
 
Peter

The actuator on the M120 attaches to an angle in the middle of the Trim Tab.

M80sportab%202.jpg


You should be able to install it against the angle in the same way it's attached to the "lip" on the Trim Tab shown in your picture. If the ends of the zinc hit the part of the M120 that angles upwards you could cut them a little to fit.

I do prefer the round zincs mounted on top of the Trim Tab even though you have to drill a hole in the Trim Tab the first time you install them.

They have a large contact surface, can be purchased just about anywhere, are inexpensive. Also they do not use the actuator mounting screws to hold the zinc in place. Even though the one you show has stainless inserts to keep the mounting screws from becoming loose as the zinc dissolves there is still a chance that the actuator screws can become loose so keep an eye on them.

Tom
Bennett Marine
 
Size definitely matters. I would go with the Bennett's M120's if I were doing again......probably, but I chose the Lenco's primarily due to the simplicity of install with the electric and not having to deal with the hydraulic lines, etc. (fewer hole syndrome)

I like many others found the performance inadequate. Lenco didn't do themselves or users any favor by tapering the tabs, thereby cutting the surface area. I made a cardboard mockup of what I wanted to do and had the local sheet metal fabricators make some stainless steel wings for the tabs. I designed a turndown on the wings to channel the water a bit which clearly improves tight handling around the dock & slip area. This design changed the effective surface area of each tab from 108" factory to 144" which like a difference of night and day. They are extremely effective now and I am really happy with them. It was a pretty simple and economical solution. Biggest hassle I had was the slow going drilling stainless.

I just put some pics on "3rd Bytes" album (bottom of page 4) if anyone wants to check it out.

You all have a super day!
 
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