Exhibit one: One ugly arse HF rear extender
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Exhibit two: Some sort of roller mounted on top of extender (not necessarily this one but you get the idea. I'm sure there are some boat specific foam padded ones to mount on a dock or something somewhere):
https://www.ultimationinc.com/replacement-parts/buy-rollers/heavy-duty-roller-with-bracket/?utm_source=adwords&device=c&kw=&matchtype=&placement=&location=9008342&network=g&devicemodel=&gclid=EAIaIQobChMIhJ-cupWy6gIVB5yzCh1ptwtxEAQYAyABEgI3W_D_BwE
Just do that for $80 bucks and be done with it.
I get what you are saying about having both options integrated into a THULE or YAKIMA. BUT.... They would charge an arm and a leg for it AND even if they did make it, it's not like you could use both simultaneously to take your boat/bike on a trip.
Sometimes the cheaper bike racks work better- less proprietary shaped stuff. here's mine (modified to fold up)- but even so, you can't use the bike rack/ boat carrier at the same time. You could certainly find a cheap one like mine on CL and mount it to the HF extender.
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