I'll chip in - I like a good auxilliary thread.
Does your Destroyer transom look like this. Screen-grab from a video on YouTube. (2020 boat)
Usual equation is 1hp per meter but you can increase that. It will push the RIB at displacement speed, if nothing else than to keep you out of danger while you radio for help or get the main engine going. Then consider whether 2-stroke or 4 stroke. 2 strokes will be lighter, usually shallower cowl width. Some including up to 5hp usually have fuel tank built in, but you can carry fuel and oil, or have separate feed tank. You might get away with a standard shaft - I opted for long-shaft.
If the main outboard is a 90hp 2-stoke, then that will help. It's all about having enough clearance for the main unit on hard-lock to hard lock without fouling the auxilliary engine.
The transom thickness may be an issue, measure it and see? Auxilliary outboards will be hand clamped, so that's something to consider.
I fitted a Mariner 4hp (long-shaft) on my Ribcraft 4.8 and it stays there all the time.
Ignore adjustable brackets if you end up going down that route. They rattle like a box of spanners. If you go for a fixed bracket - you may end up getting one fabricated. I was genuinely shocked at the cost of them.
Lastly - if you get the auxillary fitted, then consider putting a ratchet strap around the engine block and through the pull-starter aperture on the cowl and fix on the deck of your Humber with a stainless U bolt. That gives you peace of mind and security so it doesn't end up in the drink!
This is on YamPower's site - 6m Destroyer with auxilliary mounted next to main unit. I assume that's just for transit and it can be mounted directly on the transom in an emergency.
https://www.yampower.co.uk/product/h...rib/#iLightbox[product-gallery]/8
Sula
