Trim Tabs for Dual Outboard Setup?

Hi all:


We are presently near Knoxville, Tennessee, on our boat. We will be heading downriver in about 3 weeks. Does anyone know of any knowledgeable marine shops that can evaluate possible trim tab installation, between here and Apalachicola?


I'd really like to find one up here in Knoxville before we leave, but so far my efforts to find a place have been in vain.


I know the vast majority here on TF have inboard vessels, but I'm sure that many of you have experience with trim tabs and with outboards, too.


We want to put trim tabs on our boat in order to get the boat up on plane. The boat planed before it was rigged with all the interior goods and cabinetry, but will not plane now. It will almost plane. It wants to plane.


I talked to a fellow at Bennett Trim Tabs and sent an email with photos and description two weeks ago. He promised to respond to my email and never did.


What we need is someone who can tell us if it is possible to locate trim tabs somewhere on the stern so that the tabs' action will not impede the water flow over the props. And if the installation of tabs will help the boat get up on plane.


We don't want to pull the boat and have tabs installed only to discover that they will not accomplish our goal.


Our boat is equipped with two 60 hp Suzuki outboards, LOA 43 ft, beam 10'9". Weight around 13,000 lbs loaded with fuel, water, provisions, and two dogs and two people. Top speed is 16-17 mph.


The stern of this boat is kinda unique, with two fiberglass outboard brackets 5' 4" inches apart from inside to inside, and then on the outside, 8" from the outer sides of the brackets to the outer sides of the boat.


Here are some photos of the stern:








The fore-and-aft attitude of the boat is that it is slightly stern heavy, more so when the gas tanks are full. Deadrise is 7°.


Our first concern is finding space on the stern for tabs; our second concern is that 120 hp may simply not be enough, i.e. the boat is underpowered.


I've even wondered if cavitation plates mounted to the motors might help get us on plane, because at full throttle we are so close to planing. But I don't know enough about the subject to even make an educated guess.


Please, no suggestions to contact the original builder. That won't happen.


Cheers,
Mrs. Trombley

I suspect you are underpowered. If you want to try putting a plate on the outboard without drilling holes in case it does not help, there is a company that makes plates that don’t require drilling holes. I had one on a previous boat but unfortunately I can’t remember the name. Maybe googling will find it. I am not an expert on trim tabs but I suspect they may not help with only 120 hp trying to plane 13k pounds. Good luck. Hope you figure it out.

You could mount 2 tabs -
1 one either side of the port & stbd. drain plugs going as far as
possible without touching the metal swim platform support.

That being said you are under powered if you truly want
to plane with the weight your boat now weighs.

Are you getting full RPM from your motors?

If not raising them up a hole and/or a lower pitch prop
might help but 13K pounds is a lot of weight for a pair of 60's.

When Trim Tabs are fully retracted they will not effect the vessel attitude or interfere with the propellers. Trim Tabs are installed on plenty of boats with brackets with no adverse effects. The basic installation instructions call for tabs to be installed outboard no closer than 3" from the chine and no less than 8" from the centerline of a drive leg. The reason for the outboard position is to provide leverage to make changes or corrections for port/starboard listing.

Not going to happen on your boat, but from the photo's it looks like your available mounting space is from the keel to within 8" or more of the centerline of the drives. 12" chord tabs with drop fins will provide the maximum available lift while the drop fins reduce any chance of prop interference. It looks like you may have at least 2ft on each side of the keel for tabs which will provide significant lift. You will lose the leverage for port/starboard trim, but you will get lift.

On my own 34ft Mainship I have a single 200HP inboard on a 14.000lb + boat, not planing without tabs. With tabs she will wallow up and stay on plane.

Your boat certainly sounds like she's underpowered, but to answer your question, I believe there is a good chance that tabs would allow you to get her up on plane, although you may need to keep her at WOT to stay on plane.

I doubt you will find anyone that will guarantee anything, but I have sold hundreds of trim tab sets and installed a few including on my own boat, so that's my $0.02

http://bennetttrimtabs.com/wp-content/uploads/2015/02/trimtab_es2000_installation.pdf

IMO you may get up on plane with the tabs at the optimum angle when the boat is at the optimum angle for planing and the OB tilt is set a bit in the “up” position to get the props in a state where they are at right angles to the flow of water. People usually tilt the engines down and the result is that the water flow through the props is at an angle. This usually just indicates a CG too far aft.

But for all these things to line up optimized is unlikely.
May get lucky though.
Getting the CG optimized re angle of attack and the outboards optimized re AOA and prop at the “hump” speed may get her up on plane where you can optimize cruise and hoping that there is enough power.

I agree that you might get it on plane with tabs and maybe removing some of the weight but you will probably be at or very near wide open throttle which means short lived outboards. We cruise at 10 mph and love it, maybe learn to love a slower cruise?

Try Erwin in Chattanooga. They own Chickamauga Marina plus have a downtown operation.

I think you’re doing pretty good with only 120 hp!

When you’re running wide open, does it feel like the bow is pointed too high and the stern is squatting? If the boat doesn’t feel like the bow is pointing at the sky, tabs won’t help.

You may want to talk to Lenco about it. I sold both Lenco and Bennett. Lenco was more
responsive to questions.

If you want to go faster, I think you’ll need more horses to be happy.

When you’re running wide open, does it feel like the bow is pointed too high and the stern is squatting?

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Hi Parks: Yes, exactly that.

I did have the boat up on plane once on Tampa Bay, but that was with near-empty gas tanks and before we were living aboard with all of our "stuff," and a strong wind astern. One to two-foot waves, short duration, and she cut right through the waves and remained on plane for ten minutes of full throttle. Another time I tried full throttle into the wind and she would not plane. So we are right on the edge of planing.



Thank you for the suggestion; I will be contacting Lenco today!


This is my first boat with dual outboards, and my first boat with outboard brackets. All of my other outboard boats were single engine mounted to the transom, so trim tabs were simple to install.


My concern with this boat is that the outboard brackets and the swim platform support stanchions are in the way of a potential tabs installation.


The graphic posted by KeysD shows that the tabs need to be only 8" from the lower unit. That surprised me a bit, but now I think this may be doable, depending upon the surface area of the tabs we will need for a boat this size and weight.


We are generally slow boaters, but occasionally it's nice to have some speed.


I will also call Erwin in Chattanooga about pulling the boat to have the tabs installed, if Lenco has trim tabs that will work for us. Thank you very much for that reference, BandB.


Will let you all know if we can get the Lenco tabs installed. Thanks again for the advice and information.


Cheers,
Mrs. Trombley
on the Tennessee River
with hubby Dan and boat pups Lucy & Birdie

Bennett hydraulic tabs would be my choice for a vessel that stays in the water. If any component of a Bennett System is going to fail there is a high probability it will be a component inside the vessel.
If a Lenco actuator fails, the vessel will need to be hauled to replace.

There are thousands of Bennett systems 10+ years old that have never needed servicing, I doubt Lenco can make the same claim.

I also suggested the "drop fins," which because of your limited space will increase the efficiency of your tabs while reducing the chance of prop interference.

Also with either brand, you can cut the hinge plate away for a platfrom brace with out any issues if it minimal and not near an end of a tab, OR, shorten the brace so it lands on the transom above the hinge plate of the tabs.

I am not without brand bias, full disclosure

Keysdisease said:

Bennett hydraulic tabs would be my choice for a vessel that stays in the water. If any component of a Bennett System is going to fail there is a high probability it will be a component inside the vessel.
If a Lenco actuator fails, the vessel will need to be hauled to replace.

There are thousands of Bennett systems 10+ years old that have never needed servicing, I doubt Lenco can make the same claim.

I also suggested the "drop fins," which because of your limited space will increase the efficiency of your tabs while reducing the chance of prop interference.

Also with either brand, you can cut the hinge plate away for a platfrom brace with out any issues if it minimal and not near an end of a tab, OR, shorten the brace so it lands on the transom above the hinge plate of the tabs.

I am not without brand bias, full disclosure

Click to expand...

I've only used Bennett as well. I'd wait until reaching the yard/marina and talk to them about their recommendations. They may look at the boat and have a reason to recommend a specific tab. I have no reason to favor one brand or the other as I've heard good about Lenco.

It may still be that the attachments to the outboards can accomplish what is needed. Don't overlook that option.

As others have said, you really don't have anyplace to put trim tabs that won't interfere with the water flow to your props.

Also outboards act as their own trim tabs. By tilting the motors down you are in effect adding trim- the cavitation plate and pushing the bow down which it seems is what you need. If that isn't enough to get you on plane then a tab that mounts to the cavitation plate of your outboard, like the Permatrim will add more force at the stern.

The C Dory crowd swears by Permatrim tabs. But these do require drilling holes in the cavitation plate to mount them. West Marine sells an SE Sport 300 outboard tab that uses their Sport Clip which doesn't require drilling. And they are about $70 each, much, much cheaper than adding Bennett tabs. See https://www.westmarine.com/buy/spor...rine-hydrofoils--P006_180_009_517?recordNum=3

You can also try flatter pitched props. These will let the outboard speed up as it is trying to get on plane and will add more thrust. The downside is that your top speed will be less.

Perhaps this isn't entirely relevant but I had a 9' dinghy with a 9.9 hp Tohatsu. It would barely plane with two people aboard. I added a Doel Fin (a small version of the tab above) and it would easily plane with two plus our 40# dog and groceries. I then changed to a lower pitched prop and it would plane with three people and the dog on board.

Basically your power is marginal, but flatter pitched props and/or cavitation plate mounted fins can surmount that to some degree. I would start with the fins. They should be easy to mount while the boat is in the water with the motors tilted up.

David

djmarchand said:

The C Dory crowd swears by Permatrim tabs. But these do require drilling holes in the cavitation plate to mount them. West Marine sells an SE Sport 300 outboard tab that uses their Sport Clip which doesn't require drilling. And they are about $70 each, much, much cheaper than adding Bennett tabs. See https://www.westmarine.com/buy/spor...rine-hydrofoils--P006_180_009_517?recordNum=3

Click to expand...

I'm thinking those may do the job too and hoping the yard has experience with them.

Another system to consider is the Volvo Penta Intercepter Trim System. I don’t have any direct experience with it but have heard good things. Might solve your space problem.
https://www.volvopenta.com/marinele...sterndrive-diesel-mb-ml/boat-trim-system.html