Originally Posted by Projectile
The transom length on my boat was 18 inches and the shaft length on my outboard was 22 inches. Why couldn't they both just be 20 inches?
One should be able to get their boat to run well or at least reasonably well by just dropping an outboard on the transom and going.
Are you using a short or long shaft engine on a 18 inch transom ? If a short, its too short, probably water flow at fast speed/plane will pass skimming around AV plate, if so will have prop ventilation on choppy seas and at close turns.
As you have experienced, a boat/engine is not a car. It's not a matter of just droppimg engine on transom and voilá, in most cases will need to fine tune engine height for top performance. When sitting any engine need to have 3 important issues into : transom height, engine brand and very important tube's diameter.
That's why is irrelevant on sibs AV plate distance on a dry installation at home becuse you don't know how much or less sib will float once on water. As a enecdote, we installed 2 new 18 S Tohatsu on 2 diffrent lenght sibs. On the 380 experienced excesive water splash over transom, 420 worked perfect, why was that so ?
Very simple, 380 had 38 cm transom height and 45 diam tubes, 420 had 38.5 transom height and 50 diam tubes. The 420 floated much higher than the 380, had to raise 380 transom 2 cm to perfom exact same as the 420. The wider 420 diam tubes compensated having a shorter transom height compared to a higher one on the 380.