Trim Tab size Question

[RUSTYNTABATHA]

definately need tabs on my 20 and i only have the tower of power 115 on the back !!! I am looking at the bennett tabs and trying to decide on the m90 or m120... 20 ft is the breakover point on the tabs according to bennet and thinking more tab is better if the price is the same ?
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[parrott]

I have lenco 17" x 12" on my MA and would not go any smaller for my application. I had edge mount ones on it before but were just not enough tab to push the bow down like I wanted it to.

[ct9amr]

You could call bennet as they have very good customer service. I would go with the larger ones.

I have been very happy with the those tabs on all my boats.

[Blue_Heron]

Originally Posted by RUSTYNTABATHA

I am looking at the bennett tabs and trying to decide on the m90 or m120... 20 ft is the breakover point on the tabs according to bennet and thinking more tab is better if the price is the same ?
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I have Bennett 12x9s on my 20 SF and I like the way they perform. They are also a good fit for the outer step of the hull.



Dave

[CHANCE1234]

Perhaps we should try to figure out why you "definitely" need tabs with only a 115 on the back. I don't want to sound like a jerk, but I don't think you should NEED tabs on a 20 with a 115 for power. What is causing your boat to ride so arse heavy?

[Bushwacker]

Chance,

Anyone that says you don't need tabs on a 20 hasn't really spent much time on the boat or tried to run very far in a serious chop! The one exception might the I/O Seafari 20. I asked Carl Moesly about the CG difference between the I/O and OB models, and he confirmed that the CG is further forward on the I/O model, even with a lightweight 60's vintage 260-300 lb OB on the transom! A recent ride in an I/O Seafari w/o tabs revealed that it did indeed plane at about 12 mph, and rode very well in a short steep 2' chop.

On my first Bahamas trip in 1976, we made a 20 mile run from Green Turtle Cay to Man O'War Cay headed SE into a 20-25 kt SE trade wind breeze in Abaco Sound, which is only about 20' deep. That long fetch in shallow water produces "square" waves, 2' high and about 2' apart. I didn't have trim tabs then but I discovered that the boat actually rode better at 25 mph than it did at 20! The reason is that once you get on plane, the running angle continues to decrease up to about 25 mph; it's flat above that. (Check out the plot of running angle vs. MPH for the 20' Seafari in the Boating Magazine test in the Literature section.) At the time I was running a 300 lb 1975 115 Evinrude motor on a 20" transom. I concluded that what would really improve the ride was to have that flat running angle, but at a lower speed so I didn't hit the waves so hard! I installed 12x9 Bennett tabs for the trip the following year and what a difference . . . I swear the boat thought it was about 3' longer with the trim tabs! With the tabs, I could plane at about 10-12 mph and easily ride through 3' square waves, SITTING DOWN, at 14-15 mph! That was undoubtedly the best $300 (in 1976 size $!) that I ever spent.

Another benefit of the tabs is that in conditions where the waves are approaching at some angle off the bow instead of head on, you can use them to roll the boat AWAY from the waves, which essentially increases the hull deadrise relative to the waves. Just a few degrees of roll can soften the ride substantially. (Any deep V will tend to lean into the wind . . . I believe the reason is that the wind blows you off course, so when you crank the helm over to get back on course, the hull leans over, just like it does any time you make a turn.) Now that I'm running a 25" motor on a bracket, that different geometry seems to provide more leverage, such that engine trim has a much more powerful effect on running angle than it did with the previous configuration, so I use engine trim to control running angle, and use the tabs to set the optimum roll angle relative to the waves. You can accomplish the same thing by moving crew and/or ballast around, but it's a lot easier to just tap one of the tab switches a couple of times! Denny

[CHANCE1234]

Awesome reply Denny. I have not had hardly any time in a 20 but suspected with such a great hull that something was amiss if they needed tabs. ,clearly, not always the case. Great reply, it helped learn a little more about they effectiveness of tabs

[WillyC]

I have the M120's on my 20' SF. They work great. I need them with a 410 lbs. motor on the back. Will have to test the minimum planning speed this weekend but I suspect its about 18-20 mph.

[PigSticker]

My previous Seacraft was an 05 20 ft which i ordered new and without tabs and had a Yam hpdi on the back..cussed that boat up and down the first few times in a chop..put on Lenco 12x9 and the diff was night and day..like Bushwacker said i swore the boat grew 3ft..a bigger tab would prob be even better because you would have the response you need with much less tab being dropped into the water = better performance

[FishStretcher]

Well, I don't need tabs. But my CG is further forward on my 75 MA. The tank is under the console, and the batteries are there, also. Plus, I have a 4 blade stern lifter prop. Minimum planing speed is 13ish loaded with a 4 stroke and a 4 stroke kicker. So there are other ways around it for pitch control. But I don't have roll control that tabs would give me . On the other hand, with the static CG proper, the boat drains better and that aspect of pitch control can't fail, unlike a trim tab. Personally, I would start there.

I suppose with tabs I might get a 10 knot planing speed which would be nice, but with the mass forward it handles the mouth of the Merrimack and the Piscataqua really well until you get square 5 footers.