Installing Bennett droptabs

[captstu]

I was fortunate to “win” a set of droptabs to bolt onto Shearwater’s trim tabs at the SW Florida Rendezvous raffle last week.

The boat is in the water with no trailer.

Is it possible to easily remove the trim tab in the water so I can drill it on the bench and reinstall the assembly in the water?

 

[stwendl]

Having installed drop fins myself recently, I appreciated for the rig to be on the trailer.

While the piston can be easily unscrewed from the tab, the hinge cannot without water entering the screw holes and possibly the inside (if the screws are that long). I did not remove the tab at all for the install. It may be possible to bend out the retainers on the hinge to slide the tab out. However I would not feel comfortable to do this under water.

Haul out is best, perhaps another owner with a trailer around?

When installing the drops it is important to align the angle with the chimes under the boat and not with the edge of the trim tab. For that alone, they need to be installed. Eying the alignment under water or if removed is not that easy.

If you align with the edge of trim tab the drop fins will be at a significant angle away from the water flow due to the fact that the stern is not perpendicular to the flow of the water.

There was another owner on the site who did this install and made same comment.

 

[captstu]

Swendl,

Thanks for the tip about alignment. The "instructions" show the droptabs aligned with the edge of the trim tab - but, clearly you are correct, aligning the droptabs with the water flow is a better plan.

I will look for a larger trailer in my are and pull the boat.

The only other Ranger nearby is Snug Tug, also in the water. /Stu

 

[BB marine]

If you align with the edge of trim tab the drop fins will be at a significant angle away from the water flow due to the fact that the stern is not perpendicular to the flow of the water.

You should have the boat on a trailer. Removal of the tabs in the water may be difficult and possible water intrusion in the transom. As far as the alignment of the drop fins with the center line of the boat. That is difficult to do with the standard drop fin. I'm not sure of the angle of the transom on the Tug but on the 26 and 28 Cutwater it is quite a bit. Last year when I first installed the Drop Fins I noticed the angle and talked to Oliver at Bennett. He said the straighter the fins are to the centerline the better. He also said because the boats speed is under 30mph it will not make that much difference in steerage or performance. The benefit of the drop fin will out way the slight misalignment and for me it was a significant benefit. The only issue that I noticed was some disturbance in the wake. This possibly did reduce performance slightly but the performance was as good as before installation and better trim attitude. This winter I removed the original Drop fins and made a set of my own design. I was able to use the original mounting holes in the tabs and install the drop fins to be true to the center line. My trim tabs now flow straight with the keel and added 2" of width to the tab. This should clean the wake up and possibly add a slight increase in performance. Here are a few pics of my modifications. You can also view my my installation in my photos ( Trim Tab modifications )


First installation running square with the trim tabs.


New fabricated drop fins. I have a larger mounting surface so I can have the drop fin running parallel with the keel.







Because of the swim platform supports, stern thruster, and prop tunnel the area for larger trim tabs is limited.The semi displacement hull is not really designed to plane so trim tabs are needed to bring the bow down. The drop fins work well in this application. The ironic part of the Drop fins is Bennett designed them for some of Dave Livingston's Bayliner's because they needed help getting stern lift. Captstu I know you have done a lot to get the bow down on your Tug. The Drop fins will be the icing on the cake!!!

 

[captstu]

Brian, Thanks - again - for the photos. I'll look for a trailer and follow your guidance. Stu

 

[Connerkip]

For those of you who added the drop fins, how did you put the bolt holes in? Drill, drill press, punch, or? And what was the degree of difficulty?

 

[quinsky]

Brian,
Could you please provide the dimensions of the drop fins you made? What size bolts did you use? I'm interested in have some made for my C28.
Thanks

 

[stwendl]

I drilled while on the boat supporting with my knee while sitting behind the boat. Make sure you have a sharp or new bit which makes it easier. Ss can dull bits quickly

 

[BB marine]

For those of you who added the drop fins, how did you put the bolt holes in? Drill, drill press, punch, or? And what was the degree of difficulty?

I removed the tabs and used a drill press. But it can be done without removing tabs. I used super titanium drill bits sized for 10-24 machine screws. I removed the tabs because I machined spacers to extend the travel range of actuators.

 

[BB marine]

Brian,
Could you please provide the dimensions of the drop fins you made? What size bolts did you use? I'm interested in have some made for my C28.
Thanks

The outside drop fins, port and starboard leading edge is 2 3/4" wide trailing edge is 1" wide. The inside drop fin, port and starboard leading edge 1" trailing edge 2 3/4". Four holes per side 8 holes per tab, screw size 10-24 stainless 1/2" long, washers, locknuts. 14ga 304 stainless steel material. I made mine out of a set of old Bayliner drop Fin trim tabs purchased on ebay for $50.00. I cut them to the dimensions given above with a Metabo cut off saw. The original bolt on drop fins I purchased from defender worked good. I'm hoping these work better running straight with the keel, lifting strakes and chine.

 

[Chop]

Did the drop fins help with the wake hitting the dinghy? I have a 2017 C28 with dinghy on davits similar to Brian’s set up, anything above 14 knots or so I have a lot of water hitting the dinghy. Thanks

 

[BB marine]

Did the drop fins help with the wake hitting the dinghy? I have a 2017 C28 with dinghy on davits similar to Brian’s set up, anything above 14 knots or so I have a lot of water hitting the dinghy. Thanks

Unfortunately it doesn't eliminate the wake hitting the RIB. I installed the drop fins and the weaver davits and Rib at the same time so I can't make a comparison. I don't get spray at 14 knots it starts at 16 kts. and anything above. I offset my installation of the RIB so the transom tubes (RIB) hang past the port side 2" and starboard hull side 7"(RIB) past hull. The 7" is the bow section of the RIB so it is much higher then transom tube. The spray is minimal in normal seas but in heavier seas it increases. I am currently making 3.5" stainless steel spacers to raise the 4" offset davits. I will be able to install the spacers for open water cruising and remove them and have the standard elevation for inland cruising and inter-coastal cruising. I will post pictures when I complete the spacers and confirm that they help.

The Drop fins definitely help with hull attitude , bringing the bow down. I can't imagine not having them with the RIB and outboard mounted on stern. I am anxious to see how the new drop fins that I made this winter work. The original installation was not running parallel to the center line. The new drops are running parallel and 2" wider.

 

[Red Raven]

Did the drop fins help with the wake hitting the dinghy? I have a 2017 C28 with dinghy on davits similar to Brian’s set up, anything above 14 knots or so I have a lot of water hitting the dinghy. Thanks

There are several threads on the dinghy spray subject.

Here is one that might help.

http://www.tugnuts.com/viewtopic.php?f=2&t=6518&hilit=+Dinghy+spray

 

[rocklobster]

What do drop tabs do? I’ve never heard of them.


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[BB marine]

What do drop tabs do? I’ve never heard of them.


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Drop Fins were intended for boats with limited room to mount large enough span Trim Tabs, such as those with propeller pockets or stepped hulls. Drop Fins are downward facing fins on the sides of Trim Tabs that capture water pressure that normally escapes and channels it aft to increase the lift. I needed more stern lift to get the bow down. When Cutwater installed the trim tabs on our C26 they mounted them to high. The leading edge of the tab was mounted 5/8" above the bottom of the boat and the trailing edge 7/8" above the bottom. Bennetts spec is leading edge even to 1/4" above bottom and trailing edge 5/8". I had to run full tabs all the time and needed more ,especially when I had extra weight of passengers aboard. I had the choice of moving the tabs down where they are supposed to be mounted and doing some glass work or trying the drop fins. I installed them and they worked. I did a few other modifications to the tabs and now I can get the bow to come down and still have trim range left. With the added weight of the RIB and motor the drop fins were a nice addition to the boat. I have a few pictures of the drop fins in this post and more in my album.

 

[rocklobster]

Thank you for the detailed explanation. I wonder if I will need them on my 2017 C28? I just got the boat A few days ago


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[BB marine]

Thank you for the detailed explanation. I wonder if I will need them on my 2017 C28? I just got the boat A few days ago


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That is a decision you would have to make. I would say most do not feel that drop fins are needed and are very comfortable with the way there Tugs and Cuts perform. There are some that have installed them like me that found a benefit from them. We used our boat for a season before I looked into making some revisions to the tabs. My results were positive and I would not want to operate the boat without them the way our boat is equipped.

 

[trailertrawlerkismet]

Is it safe to assume the drop tabs are most beneficial for those that cruise at a higher speed? Meaning that at trawler speeds there may not be a need?

Jim

 

[BB marine]

Is it safe to assume the drop tabs are most beneficial for those that cruise at a higher speed? Meaning that at trawler speeds there may not be a need?

Jim

Jim I believe you are correct. If what you mean by trawler speed is hull speed there is no need for trim tabs use or drop fins to be added. I'm not sure of the size trim tabs the 29 has or the hull attitude of the 29 while cruising. There is a good chance the drop fins may not be needed at all regardless of speed on 29. The C26 has a hull speed of 5 KTS, I consider trawler speed 7KTS to 8KTS. The C26 runs 7.5 KTS at 2250rpm and is starting to dig at the stern. Adjusting the trim tabs from neutral position is necessary to lift the stern to help the platform from dragging in the water and keep the boat running level.The added drop Fins on our C26 has helped at this speed. Before drop fins were added I would use all trim travel to get a reaction. Now I use less travel to get a reaction. The biggest advantage like you said is cruising at higher speed. Before drop fin I never had enough trim travel. We ran full tabs from 2250 to WOT and only used the tabs for port or starboard listing. Many times when guest were aboard the option to run at a fast cruise was not possible because the bow ran so high. We really like running at 7.5 KTS and cruise at that speed more often when the water is calm, or if we are cruising in inland waters. When we are in open waters and the water is kicked up I find that our C26 handles better at 14KTS this is where the drop fins really help I can adjust the port - starboard attitude and also find a good trim angle for the forward / aft attitude and have trim travel left. I'm sure every model and size Tug and Cut handles differently and for many it is not an issue at all.

 

[BB marine]

I have had several emails and private messages about the dimensions of the fabricated drop fins that I made and installed last winter. The new design worked flawlessly and improved running attitude and loaded performance of the boat at speeds above 2250 rpm. The most noticeable is 3200 to 3400 rpm, the added trim range helps lift the stern when additional weight is located in the aft storage areas, cockpit and platform, passengers, dingy, dingy motor, cooler, waste tank and my added auxiliary fuel tank. I can lift the stern and flatten the wake. The fabricated design allows the drop fins to run parallel to the center line (keel). I have removed the assemblies from the transom to make more modifications to trim tabs for next season. So I can now show the modification of a couple of old Bayliner drop fin trim tabs made into Cutwater add on drop fins.


This is a photo of the original Bayliner drop fin tab purchased on e bay $50 ea. Next step was to strip paint and clean up, then remove center support and cut in half.


After cutting in half the drop fins were c-clamped to trim tabs on the boat and the fins were aligned to run to the center line of the boat. Measurements were taken to make final cuts and hole locations for mounting screws.



This is the dimension of the drop fin. If you are making a set this will save you a couple of steps. The dimensions allow for the drop fins to be installed the same as the factory made Bennett drop fins that can be purchased from Defender. The difference is the fins run straight with center line.



Photo taken of drop fins installed to tabs. You do not have to remove the tabs from the transom to install the drop fins. I removed them so I could use my drill press to drill the holes. If you are not removing the tabs. Purchase a couple of good cobalt or titanium coated drill bits to cut holes. I used 7/32 drill bit for 10-24 SS screws.


Installed on the boat.


I found the benefits to be well worth all the efforts. I no longer have to shift all weight forward or ask passengers to come inside so the bow will come down. I can comfortably cruise with the RIB and motor on stern 4 passengers sitting in the cockpit, without moving all my gear forward so I can see out of the windshield. With pro's there are cons. The one down fall is rack storing the boat. The drop fins can get damaged by an incompetent fort truck driver. I plan on rack storing in Florida next fall and winter. I am looking into installing larger 18x12 tabs. According to Oliver at Bennett the drop fins I have would be equivalent to 18x12. The 18x12 are very tight because of the angled transom and the thruster location. If I wasn't going to rack store I would much rather keep my drop fins. They have proven to me to be beneficial. I hope this information answered some questions that Tug and Cuts had about the modified drop fins