Fiberglass reinforcements to restore an odd engine bed structure

[cadmus]

Over a year ago I started this thread:https://www.cruisersforum.com/forums...ts-238168.html



The title is not appropriate for the following question proposed here, but the photos and some suggestions are applicable. Having only worked on old boats with lagbolts screwed into wet soggy glassed in lumber I found this fiberglass engine bed to be quite an improvement on my new project boat. But, it had to be cut out to remove the fuel tank.


This is the engine bed before it was cut apart to remove the fuel tank.







Here we see tank removed and the engine bed bridge structure cut apart:




but imagine 8 or 10 on each side.

On one photo I drew buttress like supports (green).
Buttress might not be the term. It surely is not a flying buttress. I dislike the term “sinking buttress”. Web? Fillet? Open to suggestions.

Maybe just 3 on each side, as shown. Maybe 8 or 10.
I can not say i like the idea but Occam would agree it is the simplest and most recommended by salty and the non-salty handymen not stuck in a paradigm. It still allows through bolted bolts, not lag bolts. It preserves a position/location exactly where the old one was. Surely faster than some alternative ideas i had. But maybe not ideal and maybe not as good as some rattling in "your" brain. I am open to alternatives.
Please pitch ideas.




Most engine companies advise one bolts angle aluminum to the medial side of each stringer. Then bolt engine mounts to the angle aluminum or angle iron(stainless). All through-bolted… no lag screws.





I cannot do this angle aluminum approach as the engine and stern tube are deep in the hull. To widen the stringers any more would leave the stringers only 1/4" above the hull, way too short to bolt. To raise them up and move them out would raise the engine and that is not an option without altering the stern tube (no way). I can not rebuild the bridge like engine bed structure to the level it was. Nor can I widen the stringers.The traditional method is to encapsulate hunks of endangered species lumber in glass and lag screw engine mounts into them. It seems the tide has changed on this soggy lumber lag-screw method in the literature (for good reason).



Is this buttress path sound?
How does one calculate number of buttresses and layup schedule.
Is there a better term than buttress?
Do you have a better idea?

all ears.

[cadmus]

I am considering using COOSA board and making those green shapes.
https://coosacomposites.com/wp-conte.../Test-Data.pdf
https://coosacomposites.com/
The cost shockingly huge, but I like working with Coosa. This is a keeper boat not a fixnflip. Coosa is likely way longer lived than marine ply or foam. Correct me if you disagree.

I will prep with sandpaper and styrene, lay vinyl ester resin (the hull is vinylester), lay a bed of heavy wovenroven glass to hull and underside of bed stringers, place the buttresses under the existing remains of the hollow engine bed stringers, then glass them into place with an undecided(?) schedule of glass and vinyl-ester resin.


I should add that the remaining stringer like structure is really solid thick fiberglass as is. I can do pushups on them or sit on them with no flex. Some flex if i really wack it with a rubber mallet or kick it. I surely could not build something as perfectly aligned to the stern tube. Bedded to the hull way up past the cabinetry. The buttresses could be placed to allow the bolt spacing of a Yanmar (as shown), Beta. (Maybe Westie, Bukh. not sure yet) The bolts (some removed in the photo) would still be through-bolted, not lag bolts. Maybe not the desired angle iron/aluminum styles suggested by Vigor and Gerr and the engine manufacturers... but it is better than glassed soggy lumber lag bolts.

[Searles]

Don’t worry about the ends grind clean the inside of the beds and vertically down inside the hull below the engine beds ,fit two pieces of glass coated 3/4 marine ply ,glue and coach bolt the ply to inside the current beds plus heavily glass ply to hull at the bottom ,simple and secure.⛵️⚓️