Bennett Trim tab chord (legnth front to back)

[serpa4]

I almost have a C30 (2018 working on buying). I test drove it and it went well, but the bow rides a bit high. I'd like to add drop downs to it like airplane winglets, but pointing down.
I don't own the boat yet, so I cannot measure it.
What is the length of the trim tabs front to rear? 12"?
Thanks.

 

[serpa4]

I guess if you can, what is the width also?

 

[scross]

Bennett makes a drop fin set for their 12” cord trim tabs. They are special order through Bennett’s dealers. I bought my set from Defender for about $45. Took 3 weeks to deliver. Just installed them 2 weeks ago.
Four predrilled holes in each drop fin that you use to drill holes in the trim tab to attach.
Very important to align the drop fin parallel to the keel of the boat, not necessarily the edge of the trim tab! My trim tabs were 7 degrees off from being parallel to the keel!
Good luck!

 

[serpa4]

Bennett makes a drop fin set for their 12” cord trim tabs. They are special order through Bennett’s dealers. I bought my set from Defender for about $45. Took 3 weeks to deliver. Just installed them 2 weeks ago.
Four predrilled holes in each drop fin that you use to drill holes in the trim tab to attach.
Very important to align the drop fin parallel to the keel of the boat, not necessarily the edge of the trim tab! My trim tabs were 7 degrees off from being parallel to the keel!
Good luck!

Thanks, those are the ones I'm looking at. Price has gone down a little, $32 now at defender.
Where did you read about the angle to keel vs aligned with the tab edges?
Sound sort of logical....but not crossed my mind.
Any difference on your boat? What was your boat?

 

[scross]

Regarding making sure the drop fins are parallel to the keel - I spoke directly to the staff at Bennett Marine about the installation. They were quite adamant about that! Not having the fins aligned with the direction of travel (ie parallel to the keel) will cause excessive drag and could over stress the trim tabs resulting in failure of the tabs.
The price you mentioned was before shipping. The price I mentioned was delivered.
Haven’t tried them out yet, just installed them. Will have to wait until spring to see how effective they are in lowering the bow.
The second thing I’m installing are spacers to lower the trailing edge of the trim tab so that at full up the tabs are parallel to the hull. Right now my trailing edge is reflexed up almost a full inch. This means I have to drop the trim tabs 25-35% of their travel just to get them to start working. The spacers should get me close to having the trailing edge of the trim tab parallel to the hull.
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You can special order the spacers at Fisheries Supply. There is a several month wait to get them. I’m expecting delivery in January. Talk to Christine Chumbley at Fisheries, she’s familiar with the BEN A1124 spacers.

 

[serpa4]

Confused....
I cannot picture it.
If you are on plane, doesn't the water exit out the back of the boat at an angle? Like the shape
of the boat wake propagates out in a v shape. I'd think that the fins would be canted inward to match water flow. If you match the keel, then they would be canted outward like toe out in a car alignment.
Am I picturing this wrong? Thanks for you time helping me understand this.

 

[serpa4]

Ok, think I got it. If you drop the fins 90 degres dead down, the fins would be pointed inwards due to the v shape of the transom. So they should be canted outward to compensate.
How did you deter9the right angles? Did you somehow make a rig or measure?

 

[scross]

You should contact Bennett Marine and have them explain it to you.

Contact info:

M.J. Thomas
Client Services
Bennett Marine
A Division of Yamaha Marine Systems, Inc
550 Jim Moran Blvd
Deerfield Beach, FL
tel: (954) 427-1400 x319
fax: (954) 480-2897
MJ_Thomas@Yamaha-Motor.com
BennettTrimTabs.com

 

[BB marine]

I spoke directly to the staff at Bennett Marine about the installation. They were quite adamant about that! Not having the fins aligned with the direction of travel (ie parallel to the keel) will cause excessive drag and could over stress the trim tabs resulting in failure of the tabs.

This is not completely correct. I was one of the first to introduce the drop fins to the Cutwater and Ranger Tug (TugNuts) I did extensive research before installing them. The main reason for the install was the inability for the bow to come down. The bow road high and the trim range was not efficient. The main reason that the tabs were inefficient was the installation of them from the factory was incorrect. The leading edge gap bottom of hull to plane was installed at 5/8" above the bottom. The Bennett specification is 1/4 " above the bottom. This changes the trailing edge dimension reducing the trim by 30 percent. I have many pictures and descriptions of the install that I made based on information given to me from Bennett. I had the opportunity to work with a long time Bennett employee Oliver who no longer is working for Bennett. I purchased the drop.

I asked Oliver will the trim plane angles ( planes not running true to the boats center line) with drop fins disrupt performance. His answer was it is best to have them run with the center line. Installed on a boat that runs under 30 mph the performance will not be noticed and the handling will not be noticed. The will be disturbance noticed in the wake but the benefits of the drop fins will out way the disturbance.


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I ran my boat with drop fins not running true to the center line (keel) for a year. I noticed better performance and the bow road lower when at higher rpm's.
I also had spacer blocks installed which added more trim angle. ( these were the suggestion of Oliver to help regain some trim range because of the installation of the factory install of the trim tab plane.



The following year I made a custom set of drop fins that I installed and ran the boat for a year. The trim tab plane area was larger and the drop fins ran straight in the water. I did notice a cleaner wake and increased trim angle. I actually had more trim than was needed unless I had 4 adults in the cockpit. I had to use all travel. I also had spacer blocks installed which added more trim angle. ( these were the suggestion of Oliver to help regain some trim range because of the installation of the factory install of the trim tab plane.
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I highly recommend the use of drop fins. Is it better to have them run with the center line (keel) yes. Will they work if not running with the center line. yes
I am stating this because I have run sea trials and used them in both ways. The benefits out weighed the disturbances.

I am now running with larger trim planes. I plan on having the boat lifted with forks while in Florida. The drop fins may get damaged if the operator is not careful. I decided to install 18 X 12 planes. Replacing the 12X12 planes. I have ran operated the boat with the 18X12 and find they give slightly less than the custom drop fins that I made but are equal to the original drop fins. Based on the information I received from Oliver which was spot on the drop fins will equal the effects of the next size up planes. Basically the drop fins act as if you have 6" wider planes when installed.

The answer to the original post is 12". The defender price was 32.00

If you have questions about the install or drop fins I would be glad to explain further. I have installed or advised on the installation of these on several Tugs and Cuts. Email or PM
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[scross]

On my hull, which is probably different than your hull, the outboard section of the transom is raked slightly forward. The transom is thus a concave “circle” rather than a straight line.
I double checked my measurements using two different methods to determine how much the trim tab outside edges were different than being parallel. The easiest and most accurate method is very simple. Get a digital compass (like the one on a cell phone app) and, holding it level, measure the direction of the transom at the center. Then measure the direction of the transom directly above where the trim tabs are mounted with the compass level. Having the compass level for both readings is VERY important. In my case this showed a 7 degree forward sweep of the outboard transom compared to the center.
So, my drop fin set it mounted with the trailing edge of the drop fin 7 degrees towards the center of the boat as compared to the angle of the trim tab edge. At the forward edge of the outboard drop fin it is on the edge of the trim tab itself. The two drop fins on each side of the trim tab are parallel to one another. Hope that’s clear.
The second method involved using two long sections of square steel tubing (and was quite difficult). several plumb bobs, a large protractor and a steel yardstick but yielded the exact same result.

 

[scross]

BB Marine said, “ I asked Oliver will the trim plane angles ( planes not running true to the boats center line) with drop fins disrupt performance. His answer was it is best to have them run with the center line. Installed on a boat that runs under 30 mph the performance will not be noticed and the handling will not be noticed.”
I think we are saying the same thing that it is best “to have them run with the center line”. I spoke to M.J. Thomas who felt this was quite important.
And I agree that lowering the trim tabs trailing edge to be even with the hull is also very important. BB Marine fabricated spacers that attached between the lower actuator mounting bracket and the trim tabs vertical flange to accomplish this. M.J. Thomas thought there spacers, which mount to the top of the actuator mount was a better solution. The spacers are not very expensive and are easy to install so that’s the way I went.

Here’s the email I received on 11/6/20 from M.J.Thomas:
“ You can SPECIAL ORDER (read as NON-STOCK item, MANUFACTURED WHEN ORDERED ONLY) them from any of your local marine dealers, catalog &/or Internet retailers – area marine distributor. Please use our “WHERE TO BUY” webpage (https://bennetttrimtabs.com/find-a-dealer/) to locate someone in your area that will be able to help you with your Special Order (we are NOT setup for direct sales of our products).

There should NOT be any type of downsides for this installation, since your trim tabs are mounted a bit too high from the start.

You can NOT use a SPACER BELOW THE LOWER HINGE of the actuator, since this will lift the LEVERAGE CONTACT POINT higher on the RIVETED/RIGHT ANGLE on the trim tab. This position will damage the RIVETED/RIGHT ANGLE & ACTUATOR over time with the chance of TRIM TAB LOSS in the future.

YES, the DROP FINS MUST BE IN LINE WITH THE WATER FLOW to work as designed. If not, they will act like “rudders” and cause undue STRESS/DRAG on the trim tabs & vessel to the point of TRIM TAB LOSS & ACTUATOR DAMAGE.”

 

[BB marine]

You can NOT use a SPACER BELOW THE LOWER HINGE of the actuator, since this will lift the LEVERAGE CONTACT POINT higher on the RIVETED/RIGHT ANGLE on the trim tab. This position will damage the RIVETED/RIGHT ANGLE & ACTUATOR over t

The spacer goes behind the lower hinge not under it. This spacer behind the hinge actually lengthens the ram by 3/8" and lowers the plane as if you extended the ram out 3/8". The placement of this 3/8 spacer actually strengthens the the right angled riveted anchoring support. This is a design that Bennett has used for years for adding stationary trim ram travel. The dimensions of the plate and install was given to me by Oliver ( worked for them 30+ years ). The advantage of this install is you can adjust the thickness according to what is needed. It is not permanent. It is a 5 minute adjustment. The spacers that mount between the hull and cylinder are doing the same thing (extending the length of the cylinder. The difference is the removal of the cylinder is required and adjustments are time consuming. I ended up using a 3/8" SS plate gallery2.php?g2_itemId=48580

The right way is to have them run with the center line fully agree. There are many Tug and Cuts that have drop fins running off set of the center line and still achieved benefits. At my top speed of 21mph with the tabs running off set of the center line I experienced no control issues. I did not experience any different handling other than the bow was riding lower.

I have operated my boat without drop fins 12 X 12 (bow high), with offset drop fins and 3/8 spacer behind hinge ( bow lowered) ,custom drop fins which increased the plane surface area fins parallel to keel 3/8 spacer( increased trim angle bow down). installed 18 X 12 planes no drop fins with 3/8 spacer (equals the 12 X 12 planes with offset drop fins) Now I am operating the boat with 18X12 planes without the spacer because the spacer keeps the trailing edge even with the bottom of the boat and when lifting with a fork truck the trailing edge of the plane gets pressure applied to it from the forks. The removal of the spacer was quick and easy and I can reinstall it any time.

Al, I'm not saying that your installation is wrong. You covered all your bases. I did the same thing installed the drop fins parallel to the keel to clean up the wake. For the boater trying to achieve a quick easy solution to a stern heavy boat that really never planes. Honestly none of the inboard Fluid motion products with semi displacement hulls plane. Having the drop fins 10 degrees or less offset is real not going to effect handling. I experienced both because I installed it both ways. I had to make custom drop fins. Oliver stated I would loose some of the gains if I offset the drop fins with in the surface area of the 12X12 planes. I did my offset outside of the 12 X12 surface area in order to accomplish this and never noticed any differences in handling.

Best is drops running parallel to keel
Better. is drop fins installed
OK no drop fins factory design

 

[scross]

Hi Brian,
Yes, I do understand that your spacer solution was quite different than the one M.J. Thomas was recommending not to use. If I had access to fabrication tools I probably would have made one like you built. I don’t have to worry about fork lift clearances and the trim tabs stick well out beyond my trailer’s bunks so that isn’t an issue for me.
I still can’t believe your C26 came with 12” wide trim labs while my older R-25 Classic came with the 18” wide trim tabs. Not sure what FM was thinking! And FM mounting the trim tabs to high on the transom is another issue.
I’m looking forward to testing out the effects of the drop fins and spacer in the spring.

PS to the OP: You may will need to reposition your trim tab sacrificial anode to clear the flanges on the drop fins. It’s easy to do - just one more hole to drill in each of the trim tabs. Use a cobalt drill bit at low speeds on the stainless for best results. And be sure to leave at least 3/4” clearance between the front of the drop fins and the trim tab hinge so when the drop fins rotate down they don’t ever make contact with the hull!