Re: Is the Sting Ray XPII Hydrofoil better than Sting Ray XPI?
I never liked Hydrofoils for two reasons, one they put too much weight and stress on the drive and transom that normally wouldn't be there, and two they can create strange handling problems. I drove a buddies 16' speed boat which had one, both before and after, without the hydrofoil it would rail around sharp turns very predictably, with the Sting Ray mounted, it would both spray the occupants in the rear on turn and the boat would break loose and catch again on fast turns, the foil would 'dig' in on turns causing the boat to catch and stop abruptly, a very dangerous situation. Instead of predictably, drifting turns at higher speeds, the outer wing of the foil would catch the water causing the boat to lean away from the turn. All it took was to experience that effect once for me to dislike hydrofoils.
While this is an extreme case which can happen at higher speed maneuvers, the possibility is there for it to happen when least expected.
Many motor manufacturers also do not recommend their use either.
Here's a link to Mercury's site on this item:
http://www.mercurymarine.com/serviceandwarranty/outboardfaqs/index.php#3
What was actually happening on my buddies boat was that on a normal banking turn, the right fin of the hydrofoil would be out of the water, thus creating lift, this would in turn cause the rear of the boat and drive to ride upward and leave the water, when speed was lost, the result would be that same fin now pointing downward towards the water, digging in and nearly stopping the boat dead or at the very minimum causing a dangerous roll condition. This effect could be as little as an uncomfortable stop or as violent as hitting a wall depending on the speed. In effect what it was doing was causing the boat to come off plane suddenly while in a turn due to the prop being lifted from the water as the boat drifted into the turn, thus putting the boat into effect a slide for a moment until the fin of the hydrofoil again dug into the water causing the sudden 'roll' effect.
Smart tabs are the best option, if other items are in the way, then I'd have to consider moving them to a better location which will allow the use of tabs. There's no way I'd ever run a hydrofoil after seeing first hand their downside.
I've also seen anti-cavitation plated both cracked and completely broken off from the use of hydrofoils. I have several laying around the shop that still have parts of lower units still attached which had broken off. I removed one from a 1999 Mercury 115 the other day which had a cracked anti-cavitation plate and severe corrosion in the outline of the hydrofoil. It had held salt and harbored corrosion. It had all but fallen off from the bolts pulling through what was left of the motor's lower plate. The rest of the motor was still clean with no signs of pitting.
