I know exactly what he is talking about when discussing holding an exact speed that is on the brink of a plane. Plane out and the boat speeds up, don't plane out and the boat slows down. You could trim up, but won't it hurt your u-jont (I/O owners) if you drive trimmed up? I've seen people get lectured for flushing their engine with the outdrive tilted ever so slightly.
So, those of you that have pulled kids on a kneeboard or wakeboard know that you need a proper speed to or you are too fast or too slow.. and unfortunately, that speed can be right before you plane out. It sounds odd to say that.. but, it is what it is.. an odd speed for the boat where the boat wants to plane, but you can't let it because you are now going too fast. It is tricky! Kids are finicky!
I do have a question -- of the broken AV plates.. are they because the fin broke the plate or is it because the operator of the boat hit something with the fin and then the plate broke because the fin collided with an object?
Also, why is it dangerous to have one on an I/O? I'm just curious. I've driven boats with and without them and I can't really tell a difference besides planing at a slower speed.
as in my previous post trimming up will extend the non planing speed .... no it is not even slightly bad to run at max trim (not to be confused with tilt which is beyond trim range) which is controlled by the trim limit switch on the outdrive....... full trim any throttle position no issue EXCEPT you SHOULD keep an eye on the temp gauge (a lower pitch prop should prevent any potential overheating issue from towing and plowing)
I didn't SAY a fin was dangerous with an I/O... I said the two boats that were downright scary to operate with the fin were I/O's.... On the first it provided WAY too much stern lift when trimmed down and WAY too much bow lift when trimmed up causing porpoising with very little trim... there was no sweet spot and when trimmed to stop the porpoising the boat became unstable.... tight turns at speed the bow would dig and the stern would slide out possibly throwing passengers overboard and threatening to flip the boat...
On the second it did the same with different problems when at low to moderate speed the boat became VERY top heavy and would lean WAY too much in turns.... We joked that we could almost touch the water with our hands from the flying bridge... we couldn't of course but when making a fairly gentle turn at 15 mph the boat should NOT be leaning so far that people are reaching for hand holds and getting scared.... Removed the fin and the boat ran perfectly.
The first boat was a 20 open boat with a V-8 and alpha with a top speed of around 45 mph...
The second a Carver 2667 (26' flying bridge cruiser) with a 165 hp inline 6 and an alpha with a top speed IIRC of about 30
A third I have now remembered was an 18' aluminum bass boat with a 65 hp mercury outboard.... It behaved very similar to the first one with the engine mounted lower and while it got better with the engine mounted higher and the fin out of the water it started blowing out in turns unless trimmed way down which beside being very annoying would also put the fin back in the water and start the odd unpredictable handling.
The rest just ran better without the fin but weren't scary......... I don't claim that a fin can never improve how a boat runs but rather that USUALLY there is a better solution....
