E27 + outboard install Qs

Installing a Nissan 9.8hp onto an E27 and have small questions:

- butyl tape or 4200 for the mount bolts?

Planning to use aluminum (3/16” most likely) for backing plate material:
- should one try to “prebend” the plate to fit the curvature of the transom or not worry about it. I plan to put plate on both inside and outside of the transom and don’t want to crack gel coat or create any “hot spots” of force along the perimeters of the plates

- worth laying any extra fiberglass mat on the inside of the transom for extra strength?

Am looking to optimize the speed of install but don’t plan to cut corners. Optimize for “do no harm” to the transom in case myself or future owner chooses to remove outboard at future date.

thanks for any input
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The transom may be cored with plywood in which case the bolt holes should be sealed with epoxy prior to installing the mount (some models have all fiberglass). I would use butyl tape. I would also be inclined to glass in a big piece of G10 as a backing plate on the inside to spread the loads. How will you control the motor? Remote throttle? Leave it fixed in place and just use tiller control or able to turn for close quarter maneuvering?

If I had to do this over I would have replaced the inboard engine.
Plan to bracket mount the outboard offset to starboard, the transom there is about 3/16”-1/4” frp. The G10 suggestion is good.
just going to use outboard tiller for throttle and we’ll see how much tiller rotation will be available for steering. I don’t need to reverse much in the marina and can often just use dock lines to guide when leaving the slip.

This is likely my “forever boat” and an inboard is not off the table for the future. It’s just too much of a time sink to consider for now. Have done quite a bit of work on the existing, original Volvo penta and it’s too time consuming/not sustainable to continue. For now an outboard is just the simplest thing that works.
Thank you for the reply @bigd14


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I seem to remember that the sides of the transom flexed a little so it might be good to add a layer or two of 1708 biaxial cloth before the backing plate to stiffen everything up a bit. The outboard and bracket will put a lot of stress on the area. Good luck with the project.