Drop Fins - Do They Work?

rpasquarello

Member
Dec 8, 2010
486
Long Island (Suffolk County)
Boat Info
2010 240DA,GPSMAP441,Camper Pkg,AC/Heat,Eclipse DSC GX1000S, Ext. Swim Platform, Neutra Salt System
Engines
MerCruiser 5.0L MPI ECT w/Bravo 1 sterndrive standard engine (260 hp - 194kW)
I am thinking of adding drop fins to my stock tabs as my boat stinks getting onto plane.

Do they really help?

Pros/cons?

Part number?

Cost?
 
I am thinking of adding drop fins to my stock tabs as my boat stinks getting onto plane.

Do they really help?

Pros/cons?

Part number?

Cost?

I enlarged and added drop fins to my tabs. What size are your current tabs? We can work from there.
 
David,

Not sure offhand. The boat is under shrink and is 45 minutes from my house on a rack 20' up......

I would need to reach out to SeaRay to ask, but they are the stock tabs.
 
OK, got it. Here is the recommendation i received from Bennett from many years ago. Using tabs that are nine inches in chord (distance from transom to trailing edge of the tab) the tabs should be one inch in span (width port to starboard) for each foot of boat.

Accordingly, your tabs should be 24 x 9. I guarantee you they are not. The original tabs on Saint Max were 22 x 9 on a 33 footer.

Applying some simple math that made all the difference in the world on my boat we can come up with the following:

24 x 9 = 216 square inches of required tab per side. Lets say for the sake of argument your tabs are 12 x 9. That's 108 square inches, leaving you 108 square inches short per side.

Making the tabs 12 x 18 would do the trick, however would probably place too much stress on the system. However if you went from 12 x 9 to say 15 x 14 you are close enough to 216 square inches to make a noticable difference in lift without placing undue stress on the system. You are neither doubling the length nor the width.

I had the extensions for my boat done at a welding shop. I designed them myself. I am not an engineer, but did sleep at a Holiday Inn Express the night before I came up with the plan. It has worked very well for me. Actually, it has worked too well. I could easily stuff the nose if I failed to remember the extra tab. I take her out once each spring in the middle of the week to practice docking and to renew how the boat feels. The extra tab is something I forget until the bow comes over REAL FAST!

Here is my initial sketch for Saint Max:

Sea Ray 330 Tab Modification 1.jpg

The blue corners get cut off.

Use stainless. I think mine is 3/8 or 1/4 inch. Going too thin will create more problems than it cures. I can tell you the damn thing is heavy, but it works.

Because of the additional area, I would recommend getting an automatic tab retractor. The device pulls your tabs all the way up every time you put the boat in reverse.

The drop fins do little for lift, however, she tracks a LOT truer than without.

HTH.

Good Luck!
 
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I will be watching your progress. My fathers '87 270DA has drop fins and they work well.

I looked into adding to or replacing my current tabless fins with tabbed fins, but did not get too far. One concern that my mechanic raised was being sure that if installed that they could raised to a position where they would not be in the way of lift bunks, forklift bunks, and/or trailer supports.
 
Jim,

I spoke to Bennett today. They said to order the DF12 drop fins which should fit onto my standard tabs. They have a MSRP around $30 (relatively inexpensive IMHO) and they said I should see a noticeable difference getting onto plane. I think I will try them in the Spring but order them now as a "stocking stuffer."

The forks and bunks are far enough in from what I've seen when the boat was hauled and stored. I don't trailer this boat, but they should be far enough back out of the way there as well. Nonetheless, the marina definitely needs a heads up about them being there.

David,

I'll keep the customization plans/instructions on hand as a plan "B" after I assess the above as yours offers the benefits of both upsizing the tabs and adding the drops.

I'm still curious to hear if anyone added them to their stock tabs and if they saw a difference after doing so.
 
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The larger the Trim Tabs the less "overall" impact adding drop fins will have. For example if the Trim Tabs are 36" x 12" adding drop fins will contribute less additional lift than adding them to 12" x 12" Trim Tabs.

If at all possible the best thing to do is enlarge the Trim Tab's span (side to side measurement) as this provides the most additional lift if there is room to do that.

Tom
Bennett Marine
 
The larger the Trim Tabs the less "overall" impact adding drop fins will have. For example if the Trim Tabs are 36" x 12" adding drop fins will contribute less additional lift than adding them to 12" x 12" Trim Tabs.

If at all possible the best thing to do is enlarge the Trim Tab's span (side to side measurement) as this provides the most additional lift if there is room to do that.

Tom
Bennett Marine

Tom,

I hear what you're saying about the better way to go and I likely have the room for slightly wider span (need to look in the spring to be sure).

I am leaning towards the drop fins for next season and then seeing if there is a noticeable difference first. It seems like a small investment to make with no appreciative negatives.

Am I correct in assuming that installing wider span tabs would potentially involve replacing/relocating all of my current setup (ie tabs, piston, pump, etc.) that are currently there?

-Rocco-
 
Rocco,

If there is room for larger span Trim Tabs all you will likely need to do is relocate the existing actuators (pistons) so that they are in the middle of the span. The current system could handle Trim Tabs up to 42" x 12" using a single actuator and pump as you now have. Larger than that we would simply use two actuators per Tab.

When you get a chance post a photo of the existing Tabs and their measurements and I will be delighted to help.

Tom
Bennett Marine
 
Rocco,

If there is room for larger span Trim Tabs all you will likely need to do is relocate the existing actuators (pistons) so that they are in the middle of the span. The current system could handle Trim Tabs up to 42" x 12" using a single actuator and pump as you now have. Larger than that we would simply use two actuators per Tab.

When you get a chance post a photo of the existing Tabs and their measurements and I will be delighted to help.

Tom
Bennett Marine

Will do, but that'll be in the Spring as the boat is tucked away and wrapped up in a rack until then..

:smt024
 
I really don't have anything to add to the drop tab issue but the 2010 240DA suffers from the same issues as my 2006 260DA does when it comes to getting on plane. Unless you have already moved the "celery stick" on your outdrive, I would recommend you try that first. The change this makes is amazing in terms of getting the boat on plane. In this picture of my outdrive I have circled the rear mount for the hydraulic rams.
DSC02908-1.jpg

The mounting hole in the outdrive is elongated. When you unbolt the rams you will see a nylon bushing that is shape like a piece of celery (hence the term celery stick). This bushing fills one end of the space in the elongated area and the ram bolt itself fills the other space. Sea Ray installs the celery stick in the rearward most position (closest to the props) which means the outdrive will not tuck under as far as it can when it is down all the way. By moving the celery stick to the forward most part of the elongated hole (closest to the transom), the drive will then tuck under further. Once you make this change the difference is absolutely night and day in terms of the boat popping up on plane. Any number of CSR owners who have our vintage of 240DAs and 260DAs have made this change and will attest to this.
 
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I really don't have anything to add to the drop tab issue but the 2010 240DA suffers from the same issues as my 2006 260DA does when it comes to getting on plane. Unless you have already moved the "celery stick" on your outdrive, I would recommend you try that first. The change this makes is amazing in terms of getting the boat on plane. In this picture of my outdrive I have circled the rear mount for the hydraulic rams.

The mounting hole in the outdrive is elongated. When you unbolt the rams you will see a nylon bushing that is shape like a piece of celery (hence the term celery stick). This bushing fills one end of the space in the elongated area and the ram bolt itself fills the other space. Sea Ray installs the celery stick in the rearward most position (closest to the props) which means the outdrive will not tuck under as far as it can when it is down all the way. By moving the celery stick to the forward most part of the elongated hole (closest to the transom), the drive will then tuck under further. Once you make this change the difference is absolutely night and day in terms of the boat popping up on plane. Any number of CSR owners who have our vintage of 240DAs and 260DAs have made this change and will attest to this.



Dave,

I found this manual online ' www......./merc/Install/gas/86017211.pdf . The disclaimer about changing the position is on page #4 and the diagram is on page #85. My boat has a Bravo 1 drive.

-Rocco-
 
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For some reason that website is banned on this site. The correct website is b-o-a-t-f-i-x.com without the dashes.
 
For some reason that website is banned on this site. The correct website is b-o-a-t-f-i-x.com without the dashes.

Is my last reply OK or should I delete the link? I don't want to do something improper on the CSR forum....

:huh:
 
Dave,

I found this manual online ' www......./merc/Install/gas/86017211.pdf . The disclaimer about changing the position is on page #4 and the diagram is on page #85. My boat has a Bravo 1 drive.

-Rocco-

I didn't notice you had a Bravo 1 and wasn't aware of the mounting difference, It looks like your celery stick may already be positioned in the way I mentioned in accordance with that pdf you referenced.

Still though it is worth taking a look because Sea Ray may have changed it when they installed the outdrive. You can tell where it is positioned without removing the Ram Bolt since the mounting boss for the ram is raised along the circumference of that elongated hole. If you see more of the raised boss towards the front of the ram (closest to transom) than you can see at the rear (closest to the prop) then it is in the correct position.

It is my understanding the adjustment slot is provided to take into account the both the angle of the transom on specific boat models as well as performance characteristics of certain boats. It is interesting that you have trouble getting on plane with the Bravo I when changing the celery stick seems to improve the Bravo 3 model of the 240DA and 260DA a lot.
 
OK, I realize the post is old, but I splashed this past weekend with the new drop fins in place. Unfortunately, I didn't time getting onto plane -- but it did seem to do so faster than last season.

I also left the celery stick as is (Factory setting) and only put the zincs on the tops of the tabs.

I'll repost at the end of this season with my experiences after different conditions and loads....
 
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I had the extensions for my boat done at a welding shop. I designed them myself. I am not an engineer, but did sleep at a Holiday Inn Express the night before I came up with the plan. It has worked very well for me. Actually, it has worked too well. I could easily stuff the nose if I failed to remember the extra tab. I take her out once each spring in the middle of the week to practice docking and to renew how the boat feels. The extra tab is something I forget until the bow comes over REAL FAST!
David, did you remove the original tabs, or attach the new ones to the existing tabs?
 
David, did you remove the original tabs, or attach the new ones to the existing tabs?

Yes to both. I removed the old tabs and brought them to a welding shop. The new tabs were welded to the underside of teh existing tabs. That allowed me to use all the existing hardware and mounts without any modifications.
 

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