Bigger Tab without moving the actuator on a 2000 270 DA?

Loneranger

Loneranger

Well-Known Member
May 2, 2008
1,068
Knoxville TN
Boat Info
2000 SeaRay Sundancer 270
Engines
7.4l Mercruiser w/ Bravo III
I realize my tabs are undersized both from empirical use and other's posts in the forums. My current tabs are 11 1/4 inches chord x 12 5/8 inches span with 1 inch upturned wings on both sides. I have trouble getting on plane (although it has improved with a lower pitch prop). I also have trouble remaining on plane at slower speeds.

I know a 24 x 12 tab replacement (bigger span) may be ideal and the room exists; however, in the pictures below you can see how Sea Ray formed a specific location for the actuator into the fiberglass. I suppose I could move it over but what options do I have and leave the actuators in the current location? I have seen tabs with a longer chord (I know they are not as good as going with a larger span) and I have seen downward facing "wings" added.

How close to the side of the boat can I go? I have 5 1/4 inches between the outside edge of the current tab and where the hull starts to curve (picture 3). The radius of the curve is about 3 inches, so there is about 8 inches total between the edge of tab and the starboard side. If I could use 3 inches of that I could go to an 18 inches span and still have the actuator in the middle.

The last picture shows the formed actuator pocket well.

What do you think? Thanks.

John


trimtab001.jpg


trimtab002.jpg

trimtab003.jpg

trimtab004.jpg
 
Last edited:
BTW I know the boat needs a bath so no comments on that part. LOL.
 
John,

Installing 24" x 12" Trim Tabs will make a big difference and is what I would recommend. You are correct about the longer chord (fore to aft measurement) not being as efficient. Also longer chord Trim Tabs put more strain on the actuators and usually require two actuators one each one to cope with the increased loads.

I would not suggest mounting the replacement Trim Tabs further outboard. The part of the Trim Tab that will sit above the chine flat will be operating in the shadow of the hull and will not have good waterflow over its surface.

trimtab002.jpg


Also that configuration will tend to pull air in, creating spray and disturbing the waterflow under more of the Trim Tab further reducing its lift.

If you have 8" from the centerline of the outdrive and can fit the 24" x 12" Trim Tabs between that and the chine flat, then I would recommend that is where to mount them.

trimtab003.jpg


I would strongly suggest that the actuator be moved to the center of the 24" Trim tab and be mounted on the flat part of the transom. I know it's more work, but it is the best way to do it.

Tom McGow
Bennett Marine
 
Last edited:
I was afraid you would say that. No easy fix. When moving the actuator, do I need to keep the top of it above the waterline?

This is at the bottom of my project list so when I get around to it I may ask more questions.

thanks,
John
 
John,

There is no reason to keep the top of the actuator above the waterline. On most larger vessels the actuators are usually many feet underwater.

I'll be happy to answer any questions you may have in the future.

Tom
Bennett Marine
 
edited,
I just noticed, what forum this was in.
take it away Tabman


I think theres alot more to the problem if your having trouble planing out with a 7.4 bravo III setup.?

the size of your tabs would be the last item I would be concerned about.
what kind of load are you carrying in the boat? is it running the correct rpm?
and at what speed are you trying to stay on plane?
 
Last edited:
I'll defer to tabman's expertise regarding any advice he provides. I'm sure his background is math/engineering and Bennett is loaded with a bunch of those folks. My background is not close to that complex.

I could not widen the tabs on Saint Max. My 22*9's are now 22*18's with tremendous results.

Is it additional strain on the system? Hard to say. As stated. I'm not a math wonk. Actually, I used barnyard math to figure out the total area of the tabs without regard to the L*W part of the equation.

I used to have to run full tab at 3800 RPM to keep the nose over. Now I run MAYBE 1/4 tab at 3400 to achieve the same speed and a more level ride.

My 2 Centavos.
 
Hharris said:
I think theres alot more to the problem if your having trouble planing out with a 7.4 bravo III setup.?

the size of your tabs would be the last item I would be concerned about.
what kind of load are you carrying in the boat? is it running the correct rpm?
and at what speed are you trying to stay on plane?
Click to expand...

Many of us struggle keeping on plane at low speed in rough seas. My 270 has a generator, extended swim platform, Magma grill, and cooler all at the stern. This makes a stern heavy boat take longer to get on plane. If I was on small lakes all the time I wouldn't make a change, but in the heavy seas of the Great Lakes it would be nice to have tabs that held plane at lower speeds. I usually come off plane at around 2700- 3000 depending on conditions. As Boykster indicates in this thread the replacement of undersized tabs made a significant improvement. MM

http://clubsearay.com/showthread.php/46138-Upsizing-trim-tabs-advice?
 
Hharris,

No worries about your post.

I answer questions here and at many other internet forums and I think about half of them are about fitting bigger Trim Tabs than what came on the boat from the factory. Yes there are indeed other factors to consider such as if the props are correct for the boat / engine combination. I defer to others with much better knowledge of that subject.

Many boats come from the boat builder with what we consider undersized Trim Tabs. If you look at our sizing guidelines for a 27 foot boat you will see that the smallest we would recommend is a 24" x 9" or an 18" x 12" but a 30" x 9" or a 24" x 12" is closer to the middle of our recommendations. Even with a correctly propped boat, properly sized Trim Tabs will allow you to stay on plane at lower throttle settings. As some of the others point out this is a great way to run more comfortably in a head sea. Being able to keep the bow down and sharp forward sections of the hull cleaving the oncoming chop makes a huge difference in the ride.

Using Trim Tabs to control the boat's attitude is far more efficient than using the outdrive's power trim. The Trim Tabs can be used to hold the boat on plane while the power trim can be used to keep the propeller parallel to the water flow. This results in the thrust being directed straight aft instead of downward and since the propeller is "screwing" straight into the water flow there is less slippage.

Larger Trim Tabs will also allow the boat to come on to plane much quicker with less bow rise. So you can see where you are going and there is far less laboring and strain on the drive train.

It is important to note that larger Trim Tabs create less drag than undersized ones. This is because they will generate the same, or more lift when deflected to a shallow angle, giving them a much better lift to drag ratio. This is what David is experiencing with the larger Trim Tabs on his 330.

Since properly installed Trim Tabs angle up slightly from the bottom of the hull when fully retracted they can be raised above the water flow. This effectively stops any lift from being generated and the boat can be run in a bow up attitude such as in a following sea.

MonacoMike is on target when he mentioned the generator, extended swim platform, cooler etc.. I think many boat builders don't take this into consideration when sizing Trim Tabs. Like people boats get heavier (and like people it's usually in the rear end) as they get older. They get fitted with options such as Mike said, and may even have a dinghy on the platform and they may not have had the larger engine option installed. I don't think many builders test new boats using the smaller engine option with a dingy on the platform, a full cooler in the back of the cockpit and a bunch of people on board. This is where having the proper sized Trim tabs installed really makes a difference in how the boat preforms.

I have been with Bennett for quite a few years and help people fit larger Trim Tabs almost every day and the results are always good. I have never in all those years had someone tell me they thought their Trim Tabs were too big. :)

Tom McGow
Bennett Marine
 
Last edited:
great info!

especially that "larger Trim Tabs create less drag than undersized ones"
I have owned mostly performance boats, and with the larger/longer K style tabs they really feel more efficient because I would get more response with just a little tab,
to get that same response with the smaller tabs they were burried most of the time. - makes alot of sense now!
 
I can get by with the tabs I have now but it is not really responsive. On inland waters I do not deal with following seas much. My biggest concern is time to plane and remaining on plane at a lower RPM. In response to a previous post, I have had different prop trials and had the engine looked at first (been there and done that). A prop change did result in improvement but I think with my stern heavy boat the tabs will make a lot of improvement. In the past if I have had full fuel, water, and 8 adults I have had to send some people to the front of the boat to get on plane. Like Monaco Mike said my boat is short and squat with a heavy butt.

I do want to make this change. I was just hoping I could "get away" with changing the trim plate and not having to move the actuator (especially since it has such a nice little molded home for it already - LOL) . My boat is stored in a lift without a trailer and it is logistically more challenging to do work to the bottom of the boat.

John
 
Matt, PM sent.

For anyone else interested, I use East Tennessee Prop off Cherry street. They do not have an amazing website but by using them direct you save the marina middle man charge. I know Choto marina uses them and my mechanic uses them.

http://etnpropeller.com/

John
 
Loneranger said:
I can get by with the tabs I have now but it is not really responsive. On inland waters I do not deal with following seas much. My biggest concern is time to plane and remaining on plane at a lower RPM. In response to a previous post, I have had different prop trials and had the engine looked at first (been there and done that). A prop change did result in improvement but I think with my stern heavy boat the tabs will make a lot of improvement. In the past if I have had full fuel, water, and 8 adults I have had to send some people to the front of the boat to get on plane. Like Monaco Mike said my boat is short and squat with a heavy butt.

I do want to make this change. I was just hoping I could "get away" with changing the trim plate and not having to move the actuator (especially since it has such a nice little molded home for it already - LOL) . My boat is stored in a lift without a trailer and it is logistically more challenging to do work to the bottom of the boat.

John
Click to expand...

Tabman:

Jump in here if this is out of line or dangerous. I don't care if I eff up my boat. I would feel bad if my suggestions caused someone elses boat to get torqued.

====================

The reccommendation Bennett used to provide was 1 inch of span for every foot of boat. I never could find out if that one inch of span was for a 9 inch chord or a 12 inch chord. More on that in a minute. For a 330 dancer, I needed a 33" span tab. I had 22's.

As I stated earlier. I could not increase the span on Saint Max because of the prop pockets. Adding a second set of tabs inboard of the pockets was suggested, but dismissd because of the price.

So let's do some math.

Bennett recommended 33*9 = 297 sq in; or 33 * 12 = 396 sq in.

My barnyard math told me I needed to build a tab roughly 346 sq in (1/2 the area between 297 and 396 sq in) or bigger while maintaining the current 22" span.

I had 22 * 9 = 198 sq in. WAY short of even the minimum.


I removed both tabs ONLY from the boat by turning up the retaining "flanges" and sliding the tab off the transom assembly. This negates removing anything from the boat itself.

I brought the tabs to a local welding shop with my rough sketch of what I wanted. The welder did a final sketch and proceeded to go to town.

He took a piece of 3/8 stainless 28" * 21" and welded the existing tab to the TOP of what was to become the new tab. I want to say the extension is about a 1/2 inch aft of the hinge to allow for remount. He made the appropriate cuts in the tab to make the bends he designed. He bent ~3" of each side down leaving the 22" span with a 3" "skeg" on the left and right of each tab. The "skegs" provide aid in tracking (an unintended benefit) and provide stiffness to the chord. He bent the last 3 inches up to provide stiffness to the tab's span.

I remounted the original tab hinge with the new extension to the original transom assembly and mounted the actuator to the original mounts. Using the original mount was important from a simplicity and economic standpoint and why I insisted the extension be welded beneath the original.

The following is not my rebuild. As a matter of fact I just found it for the first time while looking for mine. For the sake of argument, it is the exact same concept. The difference is my stainless is thicker.

http://searay340restoration.blogspot.com/2011/05/trim-tabs.html



Again. Tabman, please chime in with comments.

HTH
 
David,

One quick question, am I correct that the Trim Tabs now have about an 18" chord?

If this is the case I would be a bit concerned about the additional leverage of the additional 6" of chord will place on a single actuator. On most Trim Tabs with more than 12" of chord we install two actuators on each one. The actuators are really quite strong and in likely will not be an issue. Bit there can be a problem if you back down hard. Water will "pile" up on the Trim Tabs and will exert a lot of pressure on the top of the Trim Tabs. This will force them down putting quite a lot of strain on the actuators and it could make the lower hinge fail, resulting in the loss of the Trim Tab.

As a precaution make sure your trim tabs are in the full up position when you might be backing down hard, i.e. docking.

We make a Retention Device for sportfishing boats, commercial and military vessels that back down hard and it might be worth considering if you experience any problems.

rd1.jpg


It is designed to take the load off the actuator if the Trim Tab is forced down hard.

A few other notes:

I like the 3" drop fins, we use those quite a bit and they work well.

I was going to say that you did not need 3" turned up on the trailing edge, 1 or 1-1/2" would be sufficient to stiffen the Trim Tab. But I got to thinking that the 3" up fin on the trailing edge may act as a dam when the boat is backing down, interrupting the water flowing on top and creating turbulence that will lessen the downward force applied to the Trim Tabs. So I would leave them there.

We are not fans of welding stainless steel that will be underwater. Welding alters the properties of the stainless and can promote corrosion, this is why there are no welds on our stock Trim Tabs. When we do weld a Trim Tab (some boat builders design Trim Tabs that are welded) we re-passivate the stainless in an acid bath to reduce the possibility of corrosion at the welds. So make sure the trim tabs are well zinced if you are in salt water and inspect them often and replace the zincs when needed.

OK, I know that's a lot, but I work for Bennett and have to point out what we have learned over the years. The real proof if it is a good design is if it works well and holds up on your boat.

Tom
Bennett Marine
 
Last edited:
I like that retention device a LOT. I try to remember to retract the tabs every time I go into reverse but do forget at times.

I know you have a retraction device that activates when the ignition is cut. If there is no way to adapt that to retract the tabs when I shift to neutral then I shall have to look into the retention device.

I am in brackish water and do keep a sharp eye on the zincs. The water this past summer was more saline than usual due to a lack of rain in the past couple of years. Don't ask me, one of my dock mates is a scientist. I quit trying to understand!!!

So far the system has been bullet proof shy one problem. I take the boat out one day during the week before the season gets underway to get the feeling of her again. The tabs as big as they are make it easy to over compensate for any given situation. For example; remember I said I had to run full tabs at 3800 to keep the nose over? With full tab from a dead stop, I'm on plane in 5-6 seconds with virtually no bow rise. If I don't start retracting the tabs as the bow comes over, I could see me stuffing the bow.

I will tell you this. Passenger motion around the boat unless it is a bunch of folks settling in one place from another has no effect on the boats attitude. One person moving around? Don't even notice it. I'm thinking the only thing that could perfect it is the auto trim device you sell.

In that I am not the only person who has done this modification, I wish Bennett could convince Sea Ray to go with the proper size tabs to begin with. The boat I bought and the boat I drive is not the same boat since the mod.
 
dpmulvey said:
In that I am not the only person who has done this modification, I wish Bennett could convince Sea Ray to go with the proper size tabs to begin with. The boat I bought and the boat I drive is not the same boat since the mod.
Click to expand...

I did enlarged my trim tabs in Feb 2010 with the great help of David. Had stock 35cm x 35xm and did 40cm x 49cm=15,74"span x19,29"chord.

Once again great thanks to him for got back my boat's real performance again.

I did both stifennings for downward at chord, upward at trailing edge and 3 rectangular from the vertical where piston is attached trough trailing edge. Also did the negative angle and no matter what my running trim angle is tabs are not touching to water even at the trailing edge point.

I had and have the single actuator and once on plane I fully retract them and don't have to deploy them to keep the boat on plane. Also have autopilot and it corrects the listing due to wind/passenger instead of deploying some tabs.

Here are pics of my new tabs. I didn't weld stock ones to new and did totaly new. After 20 months of having them have no issues of bending the tabs, damage to pistons and to the transom.

http://i998.photobucket.com/albums/af108/melida315/trim tabs/11052010765.jpg

http://i998.photobucket.com/albums/af108/melida315/trim tabs/11052010764.jpg

http://i998.photobucket.com/albums/af108/melida315/trim tabs/11052010763.jpg
 
You must log in or register to reply here.

Forum statistics

Threads
113,118
Messages
1,426,560
Members
61,035
Latest member
Lukerney
Back
Top