Auto trim


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Well-Known Member
Supporting Member
Jan 20, 2019
I was at a friend of mines shop today talking boats and I happen to notice a couple old boats he had laying around. I saw a brand new Prather 21 outboard and some old Dumas monos and stuff. He showed me a brand new still in the box K&B 21 ( he bought for the Prather hull ) but then he showed me something that I had never seen before.

He had a K&B 21 OB that for lack of a better word had a thing that looked like a tiller arm. This connected to the engine block and would turn side to side with the motor. The tip of this tiller went inside of a piece of aluminum that had a brass piece of metal with an upside down (V) cut out of it. Basically it would hold the engine trimmed up to fly the hull in the straight away, then as you turned the motor it would apply negative and tilt the motor downward. The more the motor turned the more negative was applied.

I understand the thought process here but was intrigued by it because I have never seen it before. I’m not a huge OB guy but have owned a few and have raced them over the years but just curious if this was ever a thing or just a fad or what. I’m guessing you would end up with a boat that wanted to spin out on you all the time when you gave it any right or left but was just curious if anyone had actually seen this run on a boat and what was the outcome.

This is purely out of curiosity and nothing more but I did think it was cool. I wish that I would have taken some pics.
It was actually designed to tilt the engine back lifting the nose when turned. Way back when, I fitted one to a boat. Made an evil boat worse. We also ran turn fins back then on most tunnels.
Yea, I explained it backwards. Now that I’m thinking about it you’re correct about lifting the nose in the turns.
The ends of the brass ramps are slotted so you can add as much up trim as you want in the turns. All K&B 3.5 outboards were raced with this system in them when I started.

One of my boats in 1974 this all wood modified Dumas Hot Stuff had the system installed.

I myself was introduced to model boating back in 78 and we have never really had a very strong OB presence in our part of the world. The few I did see racing around here as a kid never had anything like this. Because I have never seen this set up before, I found it interesting to look at. I have seen a bunch of different stuff that guys have tried through out the years so it usually takes something crazy like this to get me excited. I like to see stuff, when guys are thinking outside the box like this, it keeps me interested!!
I saw several people over the years experiment with OB trim devices. The funniest one I ever saw, a guy had a 7.5 OB on a Torch tunnel (which was a 3.5 hull!) He bolted a door hinge to the transom and the engine was bolted to the other side of the hinge with the hinge pin at the top. There was a servo in the boat that operated a push rod through the transom to push the hinge and thus trim the engine 'up'. I was shocked when he launched this boat and it started turning surprisingly fast laps and he knew exactly how to trim it in and out of the turns. Sometimes redneck engineering works great!