posted 09-12-2006 09:24 PM ET (US)        

This weekend we did a sea trial with two similar 13' Sports both with 3 cyl, 40 HP Mercs, mine the aforementioned 4 stroke and the other a 2 stroke.

Unquestionably the 2 stroke was a bit better on both acceleration to plane, acceleration to a faster speed and top end speed, but not nearly as quiet nor as fuel efficient.

The additional weight of the 4 stroke over my old motor (35 HP 2 cycle Force) puts the stern a bit deeper into the water than before but the other benefits far outweigh any negatives. The 4 stroke EFI starts every time (except that time I forgot the red cord). Tilt/Trim is extra nice too. I still need to measure my top speed.

Regardless, I would summarize it as fast enough, reliable, fuel efficient and QUIET.

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On a parallel note, while testing the two Sports we skillfully flipped the 2 stroke. We were on flat water with minimal current and no wind. When WOT, the 2 stroke boat would start to list to starboard in a manner best described as severe, that would inevitably end in a flip if not throttled back. Very weird.

Similarly to last year, when on a plane the wake would splash back onto the transom indicating poor planning performance. Since it was missing the steering anode tab thingy (a technical term) and the screen filter that is under it, we added the tab and adjusted it to almost center hoping it would improve. This is when the list to starboard started. After adjusting the tail of the tab to the starboard, the list was notably lessened. In talking to the Merc dealer, he said that the tab was only for steering adjustment and he had never heard of it causing a list or a flip. Regardless, let’s not forget that the tab adjustment definitely reduced the list.

BUT things got more interesting when we went back to playing with our Whalers (OK, no crude remarks here:).

My Brother in Law in the 2 stroke decided to jump my wake. He was fine going to my port but when he went over my wake to my starboard (which would have a tendency to lean his boat to starboard as he comes over my wake), the list kicked in and over the boat went. Complete turtle - What a rush.

After collecting all that floated, we beached, flipped, bailed and towed it back to the dock. After spraying it off and purging water from the cylinders, he got it running again. Kudos to Mercs.

Then off we went to the Merc dealer again to ask questions. Again nobody had heard of the steering tab causing a boat to flip, but they advised that the sloppy wake with water splashing back on the transom was unquestionably a result of the motor being too low.
Back at the rivah, we lifted the motor by about an inch and went back to the water trial again. Now the wake was clean and the list gone.

My theory - because 1) the tab is curved in an airfoil type design, and 2) the motor was too low, I theorize that the steering tab was deeper in the water than designed resulting in a force that was pushing the motor clockwise (with respect to looking at the transom from behind), which in turn cause the boat to list to starboard, and ultimately flip.

Any thoughts?

posted 09-12-2006 09:49 PM ET (US)            

1) motor when I run solo is adjusted bottom hole - if not I get porpoising
2) trim tab is set dead center - so when I let go of the wheel I get a yaw to starboard - more of an issue at high speed = I cannot let the wheel go or it will go right, right now. Plan has been to adjust tab trailing edge to starboard
3) thinking about your theory if tab has airfoil shape (hyrofoil) and low position w/ tilt forward, perhaps the tab generates enough lift to rotate the boat around centerline axis.
4) In my case it is difficult to recreate.

Now let's see if our engineer and tech geeks pick up on this thread and do some calculations.

Since my motor is Yam my bet is trim tab design is similar to Merc. The interesting question if once adjusted what happens to the phantom lift that might be generated?