Re: Did I buy the wrong trailer
The main concern is going to be the height.
The majority of weight in an I/O boat is down low and towards the stern in most cases.
I'd start by moving the axles back at least another 30" or so.
Then get the center bunks set as low as they can be on that trailer. If side support is an issue add a set of side bunks or guide ons. Guide on bunks may be needed either way since you will no doubt have to be in pretty deep water to float that boat onto such a high trailer.
As far as the boat falling off on turns, its more likely that the whole trailer would upset rather than the boat just falling off the trailer. A little common sense when driving will prevent that.
I pulled a 24' Sea Ray cuddy cabin from Pittsburgh to NJ which was set atop a similar trailer. The boat was well balanced, but the thing sat on only two long 2x4 bunks and bunk brackets and the former owner had bolted those roller bunk strips on top of the wood. There was also a series of keel rollers down the middle. Most of the weight seemed to be on the rollers. The boat was about 2' too long for the trailer, and the trailer put the keel of the boat about 28" off the ground. The trailer had three 12" wheels, and one 15" wheel to make it even more interesting. Even so, the thing made it all the way home without incident. It actually towed pretty decent on the turnpike even though it certainly was far above and beyond what I felt comfortable towing with my Ford Ranger. The trailer had no brakes, never had them, and it had a GVW of 7700lbs on the frame sticker. The guy that gave it to me was in Ohio, he met me about half way, and towed the thing to Pittsburgh about 200 miles or so with a Jeep Cherokee. The guy had bolted trailer lights right to the hull, as was his license plate, which I left on to get it home. He had a combination of rope and several light ratchet ties holding the boat on. Plus some duct tape here and there to hold cabinets shut, protect straps, etc. When we switched it to my truck, he took his tie downs and I secured it to the trailer with four large 2" wide ratchet straps and two smaller ratchet straps holding the bow eye to the winch post. It had two nice transom tied downs on it which he left. My concern was it coming forward and hitting my truck, no falling off.
Believe me, I wouldn't have missed the boat if it fell off, it would have saved me getting rid of it. I only wanted the trailer for another boat I had. The trailer was originally built with 205/15 tires, not the miss matched set it had on it. When I got it back home, I realized that both equalizer bars were seized and it had 7 broken leaf spring leaves.
The wheel bearings were shot, well lubed but pitted badly, and the tilt mechanism was stuck open. The only thing holding the trailer down was the weight of the boat and the rope tying it down. I actually took a few back roads on the way home in hopes of maybe losing it but no such luck, the thing wouldn't budge off that trailer even once I untied it.
It wouldn't even roll or slide off the trailer at work, we had to use an excavator to pull it off the trailer and bust it up. There was no way it was just falling off. I'd venture to guess that it would have made the whole trip home even if it weren't tied down at all.
When I tried to dump the boat, I had backed up full speed and slammed on the brakes in the parking lot at work, all it did was lock up the trucks brakes and drag the truck backwards till it stopped. The boat never moved. In the end I got a free trailer that only cost me a tank of gas and a set of used wheels and tires when it was all done. I later converted it to a full roller trailer.