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I/O Conversions engineering?

Old 01-13-2022, 08:31 AM
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Default I/O Conversions engineering?

OK I see a lot of people doing this who is doing the engineering on mounting that bracket and hanging all that weight on the transom? It cant be just fill the I/O hole and bolt on, do you tie in the stringers or add angel or knee supports? What about the corners were the side and bottom meet the transom?

Also when you go to get insurance what do you say, do they just accept the fact that ok now its outboards?

I like the possibility, but I cant believe its just bolt and go.
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Old 01-13-2022, 08:46 AM
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Real outboard boats have knees tied into the stringers. IO conversion if done properly should get the same treatment. There are many, many things to consider though. Fuel tank placement, is the hull notched, cg, etc.
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Old 01-13-2022, 08:54 AM
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Saris is correct but a lot are just bolting on. Some fill, some put knees, I have seen one use aluminum plates bolted to the bracket then through bolted to the stringers as knees. I still think on a lot of these the CG has to be different than originally designed, particularly a couple stag I/O's I have seen converted, but I may be wrong since the weight is so much different. At the very least you would think fore aft may be right but would be higher then a I/O.
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Old 01-13-2022, 09:15 AM
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It all depends on the boat. Skater converted my 30 from Sterlings/Arnesons to 400Rs and didn't make any changes with the stringers/knees at the transom, but the boat was originally built with knees at the transom - like all inboard and outboard Skaters. We also didn't change the full bottom to a notched transom like so many outboard boats run, and it was one of the best running 30' Skater outboard ever (127mph w/ 400Rs and ran flat at speed, this claim verified by Bobby VanDine at Skater who also drove it). The CG didn't actually change (as verified on my hydrohoist lift, I didn't move the boat forward or aft and the lift still floated level after the conversion) because even though the weight was much further back with the outboards, there was a lot less of it. Though the CG didn't change, it doesn't mean the boat didn't run differently, it still was much flightier after the conversion, as the total dry weight went from 7,000#s as an I/O to 5,400#s as an OB - with the weight of the motors hanging off the back of the transom instead of being forward in the boat. We did put a lot of thought and effort into the conversion, so I'm not saying every boat is a simple job to make run correctly after going from I/O to OB, but it can definitely be done successfully. I'd recommend consulting with the manufacturer of the hull you're considering converting before spending any money towards the goal to make sure your I/O boat will work well with the conversion.
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Old 01-15-2022, 07:04 PM
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Originally Posted by Skater30 View Post
It all depends on the boat. Skater converted my 30 from Sterlings/Arnesons to 400Rs and didn't make any changes with the stringers/knees at the transom, but the boat was originally built with knees at the transom - like all inboard and outboard Skaters. We also didn't change the full bottom to a notched transom like so many outboard boats run, and it was one of the best running 30' Skater outboard ever (127mph w/ 400Rs and ran flat at speed, this claim verified by Bobby VanDine at Skater who also drove it). The CG didn't actually change (as verified on my hydrohoist lift, I didn't move the boat forward or aft and the lift still floated level after the conversion) because even though the weight was much further back with the outboards, there was a lot less of it. Though the CG didn't change, it doesn't mean the boat didn't run differently, it still was much flightier after the conversion, as the total dry weight went from 7,000#s as an I/O to 5,400#s as an OB - with the weight of the motors hanging off the back of the transom instead of being forward in the boat. We did put a lot of thought and effort into the conversion, so I'm not saying every boat is a simple job to make run correctly after going from I/O to OB, but it can definitely be done successfully. I'd recommend consulting with the manufacturer of the hull you're considering converting before spending any money towards the goal to make sure your I/O boat will work well with the conversion.
Same for me on my 32B. Boat runs flawlessly with 400Rs. Converted from inboard.
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Old 01-16-2022, 12:41 PM
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It depends a lot, on the hull.

A lot of them are designed to be either OB or IO w/minimal changes.

When we lived in Fla, I saw a lot of hack jobs, mostly fish boats or cheap pleasure boats.

Some just bolted the OB bracket over the IO hole!

Im just finishing a 25’ Checkmate single big block IO to twin OBs.

I test floated it as soon as was capable to ck float line and it was much closer than I thought.

According to my calculations, I’ve added approx 200lbs of weight.
But, moved that weight 5’ aft.

That resulted in the keel at the bow, to float about 4” higher than existing stain line.

The bigger change is in C of G which I am currently working on.
I built a galley for the cuddy and added a sink that I feed w/a 15 gl water tank I installed in the anchor locker.

And I added knees between transom/stringers and support across top of transom.

If you’re lucky enough to start w/a hull designed for either power packages, it wouldn’t be bad.

If you start w/a true IO boat as I did, it’s a HUGE project!

Last edited by Twin O/B Sonic; 01-16-2022 at 07:39 PM.
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Old 01-18-2022, 08:39 AM
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Yeah I just read this post,

https://www.tradeonlytoday.com/post-...eat-challenges
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