Another Trim Tab conversation

[todd brinkerhoff]

I know this topic has been exhaustively covered, but I just pulled my 10.8 Meter express for the winter and I had a chance to look the boat over, and found myself scratching my head. I probably have one of the most substantial boats in the yard, but I also have one of the smallest set of trim tabs, measuring 18X8.

Now I think to myself, Trojan must know what they were doing when they put such small tabs on these big boats. I mean the trim tab companies are just looking to make money when they say you should have one inch of span for every foot of boat, Right?? That would be a 36" to 40" tab.

So I think back to a story a buddy told me after he bought a used 24' Wellcraft open bow boat with a 454 ci (330 hp) Mercruiser motor. He had a mechanic go through the boat, but never did a sea trial before he bought the boat. The first time out, the boat maxed out at 25 mph. He was extremely disappointed and started asking the marine mechanics if this is accurate, and they tell him he needs to get a different prop. But one guy asks him about his trim tabs. My buddy says the boat did not come with tabs. So he decides to install a set of 24" tabs. The boat now does about 50 MPH. Holy crap...You mean Wellcraft put out a boat with an issue that could be solved with proper tabs...

My 10.8's performance is pretty consistent with the 10 Meter express numbers I've seen on the forum, and had about a 27 MPH top end with 22X22 three blade screws. But even going 26 or 27, with the current tabs all the way down, the back end is still buried and the water spray is toward the back of the boat.

What was Trojan thinking with the dinky tab? Could the performance be that far off with these tabs. I know there is a limit, but could big tabs make a different performing boat?

So I need to find someone who is willing to put 36" tabs on their 10/10.8 express boat before I go out and spend $1000.00 and put more holes in my hull.

[RWS]

not to worry, no more holes are needed.

I've cut and snipped an old post for you here.

There is a bolt in replacement available from Bennett. I met the Bennet rep at the Ft Lauderdale boat show in 2003, showed him my numbers and he suggested that we replace the factory 9x24 tabs with a bolt on 12x24 with DROP FINS. The drop fins come off the fore/aft sides of the tabs and trap water there, effectively nearly doubling th eeffectiveness of the tab.

First of all, from my own experience with the gas engines, if I had 8 or 9 people oin board, the livewell full and the extra on board freezer on deck as well, yes she would be ass heavy in the water and not ride well. My engines were a bit worn though, and she just didn't have enough stuff. This might be similar to your own experience.

The factory tabs are 9" front to back. I upgraded mine to Bennett 12" with a drop fin which was a direct factory replacement, didn't have to change the actuators or anything. The additional lift with these made a huge difference for the vessel especially when she was heavily loaded, and changed the running angle. With these changes and also opening up the exhaust deflectors, increasing the size of the engine breathers and lubricating the spark advance mechanisms I was able to find a sweet spot economical cruise speed @ 17.3 mph with a flowscan reading for both engines of .93 statute mpg !

My gas engines were a bit tired so my data will be different than for fresh 454's and I babied them, rarely running her above 3000 RPM. Also if yours is has different transmissions, props & shaft angles, comparisions will be different as well.

The diesels changed everything. Now the boat runs like it should, the props provide enough lift that I never have to touch the tabs. She remains at plane at 12 statute mph (no tabs), has a top speed of 32 mph and I can cruise all day at 25 mph and go twice as far on a gallon or tank of fuel which costs about .50 cents less per gallon on the water.

You can get an inexpensive bubble type incline level device West Marine/Boat US and attach it to a side window while at rest in the water with full water & fuel tanks. Then take the boat out and check your running angle. With the gas engines I ran 4.5 degrees @ 2700 RPM and 5.5 degrees @ 3200.

RWS

[prowlersfish]

Believe it or not the larger the tab the less drag too . reason being the larger the tab the less angle needed for a given amount of lift.

[Tabman]

Todd,

Larger Trim Tabs will indeed make a huge difference in how your 10.8 runs, and it doesn't have to cost $1000.00!

In just about all cases you can install larger Trim Planes and reuse the rest of the system. The only new holes will be where you reposition the actuator (ram) so that it is in the middle of the new Trim Planes. It is not too hard of a job for most boat owners.

Do you know if they are Bennett Trim Tabs? I would be delighted to help you if you decide to install the larger Trim Planes.

Tom McGow
Bennett Marine

[todd brinkerhoff]

Unfortunately no. They are boat leveler tabs. Is there an adapter? I was also thinking if going to the local metal and welding shop could help out. Any suggestions would be great.

[k9th]

Todd,

Larger Trim Tabs will indeed make a huge difference in how your 10.8 runs, and it doesn't have to cost $1000.00!

In just about all cases you can install larger Trim Planes and reuse the rest of the system. The only new holes will be where you reposition the actuator (ram) so that it is in the middle of the new Trim Planes. It is not too hard of a job for most boat owners.

Do you know if they are Bennett Trim Tabs? I would be delighted to help you if you decide to install the larger Trim Planes.

Tom McGow
Bennett Marine

Welcome to the forum Tabman.

I am not sure what tabs I have on my tri-cabin but it is being pulled for the winter today and I will be at the marina Saturday and can see what size they are. If I can change tabs and improve fuel burn and performance - sign me up. Can I PM you with the info to see what my options are?

[Tabman]

Tim,

Thank you for the welcome to the forum! I'm glad I found it!

Sure, PM me with what you find I will be delighted to help, or post it on the forum so other Trojan owners can see what is involved.

Tom McGow
Bennett Marine

[Stripermann2]

Tabman, welcome to the forum.

I remember a Tabman over on BE forums a few years back but have not seen him in quite some time...are you him?

[Tabman]

Unfortunately no. They are boat leveler tabs. Is there an adapter? I was also thinking if going to the local metal and welding shop could help out. Any suggestions would be great.

Todd,

Boat Leveler is a good company, I am sure once we figure out what size you can fit you can contact them regarding getting a set of larger Trim Tabs. The basic setup is the same as Bennett and I will be delighted to help with the project if you decide to go forward with it.

Tom McGow
Bennett Marine

[todd brinkerhoff]

Tom,

I just measured them. They are a 1991 Boat Leveler that measure 24X8. Are you suggesting a tab with a longer span, or a larger chord, say 12". I know RWS went with the Bennett with the 3" drop fin, and Boat Leveler does not have that option. Additionally, boat leveler tabs are much more expensive than Bennett, so I was trying to come up with the best option for the best price, if that is possible.

[RWS]

I thought the Bennett folks were(are) great to deal with.

Extremely knowledgable and helpful.

RWS

[Tabman]

Thanks RSW!

Todd,

You could install two new 14 x 11 Boat Leveler Trim Planes and see improvement. I don't really know how much they cost but it would be a relatively "painless" installation without having to re-drill any holes at all.

The best thing would be to increase both the Span and the chord if possible 30 x 12 or 36 x 12 if you can, and reposition the actuator to the middle. You could use Bennett Trim Plane Assemblies and drill new holes in them for the Boat Leveler actuator.

Or a slightly easier route would be to get a pair of Bennett 24 x 12DF (Drop Fin) Trim Tab Assemblies and position them where your existing Trim Tabs are now. You would not have to move the actuators, but will have to fill the old hinge mounting holes and drill new ones. As mentioned above you will have to drill new holes in the Trim Tabs for the Boat Leveler actuators. The 24 x 12 with the Drop Fins will give almost the same lift as the 30 x 12's without them.

I hope this helps. If you decide to go with Bennett Trim Planes let me know and I will check our scratch and scuff inventory to see if we have the size you need.

I hope this helps

Tom McGow
Bennett Marine

[captainmaniac]

I am a bit surprised at one of the things you said :

But even going 26 or 27, with the current tabs all the way down, the back end is still buried and the water spray is toward the back of the boat.

When you are running near WOT, generally, the tabs should not be all the way down... that position would normally only be used when you are trying to fight your way on plane. With my F32, my father's old 28 Sea Skiff, and my previous Liberator, as speed increased you generally wanted to give it less tab...

I would put the question to the other 10.8 owners - is there some element of your hull design that requires so much tab? If full tab is not normally required on this hull, I would wonder if you are over-tabbing, or are they simply not actuating properly (ie not really going down as far as they should), or if you really are squatting do you have a weight distribution issue or waterlogged hull?

[todd brinkerhoff]

No, the boat was wet tested and its very dry. I'm running a v-drive system, so the motors are set back in the boat. The water tank was about half full, but its in the middle of the boat. Fuel was about 1/2 tank. The boat gets to its max speed pretty well, and the speeds are pretty consistent with what I have seen on the forum for the mid cabins 10ms, but again, the motors are set back unlike the regular express and convertible boats.

Tabman,

What do you think of getting the Bennett 24X12 Trim board with drop fins and welding them to the existing Boat Leveler tabs. I would then redrill the holes for the actuators through both sheets. I'm trying to avoid drilling more holes in my boat and I have access to some very good welders.

[RWS]

the additional legnth of the 10.8 plus the different location of the engines with the V drives pushes much more weight aft of the center of the boat

Of the three versions

1) express (engines located under the helm

2) mid cabin (engines located under raised deck/rear cockpit sole)

3) 10.8 with v drives ((my assumption) engines farther aft from the forward waterline entry point than on any other 10 meter hull)

I think we could safely assume #3 has a significant load on the a$$ end as far as the % of weight distribution is concerned.

Kind of like when we set the portable freezer and all those big guys on the rear bench seat. Her running angle was just not right. I copuldn't measure it that day, but I could sure feel it.

I would love to see this 10.8 perform with the 315 hp turbocharged diesels. The additional lift from the bigger props and additional torque would make this a phenomenal overall vessel.

RWS