Should I put M-80s on my 18?

[follybob]

I picked up a set of Bennett M-80 trim tabs on a whim now I'm thinking maybe I don't need them on an 18. Who thinks I should install them and why? Who thinks I should leave them off and, why? Who's done this on a small Seacraft before? I'm familiar with tabs but I guess I'm thinking the benefits will not outweigh the time and effort to install on this boat.. I would love to hear all your thoughts!

[Bushwacker]

If you're running a relatively light (~300 lb) motor that the boat was designed for, you may feel that it's well balanced enough with a low enough min planing speed (~12 mph) that you don't need tabs. Tabs can do more than just help you stay on plane at low speed however.

A deep V tends to lean into the wind because the wind blows you off course and when you crank in some rudder to windward to compensate, the boat will bank into the turn. If you use differential tab settings to roll the boat AWAY from the wind/waves just a few degrees, you'll find that it makes a significant improvement in ride because it increases the deadrise relative to the waves!

Your decision may depend how often you run offshore in a chop, especially when waves/wind are at some angle off the bow. Although I made my first trip to the Bahamas with a 300 lb motor and no trim tabs, I installed them AFTER that first trip! Although the boat rode great in head seas on the trip over with all the gear I had up front in the cabin, it was a day trip I made with the family a couple days later with a much lighter load that convinced me of the value of trim tabs!

We made the 20 mile run from Green Turtle down to Man 'O War Cay in shallow Abaco Sound, straight into the 20 kt SE trade wind breeze with a fetch of about 30 miles. As with many places on the shallow Little Bahama Bank, this sets up a pattern of square waves, typically about 2' high and 2' apart! I discovered that the boat actually rode better at 25 mph than it did at 20, because the running angle is flatter at 25 than it is at 20! (Check out the running angle plot vs. speed/rpm in the Boating Magazine test of the Seafari 20 in the literature section under Classic SeaCraft Home.) Note that you're much more sensitive to ride quality in a Seafari than you are in a CC, because you ride SITTING DOWN about 10' fwd of transom instead of standing in the back where there is less motion and using your knees as a shock absorber! I concluded that if I could hold the boat flat but not hit the waves so hard, the ride would be even better! Trim tabs will do that. After installing the tabs, I discovered that even without a bunch of gear in the cabin, I could trim everything down and ride very comfortably SITTING DOWN in 3' square waves at about 14-15 mph! Adding tabs made the boat ride like it was about 3' longer and 1000 lbs heavier, and I subsequently made 5 more trips to the Abaco's, so the tab addition was the best money I ever spent on the boat!

Even when I'm not running in steep head seas where I need to hold the running angle flat, I'll use differential tab settings to roll the boat relative to the waves to make things a bit more comfortable!

[wattaway2]

A great response as usual -- just wondered what if any difference the addition of the o/b bracket made to the reaction of the trim tabs

[Bushwacker]

The trim tabs are still very effective on lateral trim (roll angle), although they are probably a bit less effective at controlling running angle since the boat is now significantly stern heavy with a 430 lb motor set back 30". However motor trim has MUCH more effect on running angle than it did before with a 20" motor hanging on the transom, so tab effect on running angle is somewhat irrelevant! I suspect that the 30" longer lever arm called the bracket is the prime cause, but the longer 25" shaft motor may also have something to do with it.

[Tabman]

Bushwacker nailed the reasons Trim Tabs will be beneficial. Here is a link to a SeaCraft 20 that installed them you may find interesting http://www.bennetttrimtabs.com/viewp...oat.php?vID=69

Tom
Bennett Marine

[FishStretcher]

Bushwacker - as usual, a very informative reply. I run a 20 without tabs and it is fine in a head sea, but experienced the issue you described in a sea 45 degrees off the port bow in a short close chop.