I'm not familiar with bumper in this context.

港湾用防舷物 SANP series
https://www.nauticexpo.com/ja/prod/trelleborg-marine-and-infrastructure/product-22887-200590.html

(with picture of dock bumper)
https://www.kanae.co.jp/result/detail/?pdid=41
概要　防舷材は係船岸壁において、船舶と岸壁との間に使用するクッション材です。

https://www.discoverboating.com/resources/boat-fenders-and-bumpers
https://www.decks-docks.com/boat-dock-bumpers

https://www.sbt.co.jp/kaiyo/01kowan/11pa_olp
PA型防舷材は、空気の圧縮弾性を利用した型式ですので軽量で水に浮き、取扱いが簡単です。

https://www.discoverboating.com/resources/fenders-bumpers
Bumpers
Bumpers are also pads/cushions that prevent your boat from sustaining injury while it’s tied to the dock. What’s the difference between bumpers and fenders? Fenders are on the boat, while bumpers are on the dock. Same job, different approach.

nikk: (attached to boat or pier)
https://kotobank.jp/word/防舷材-381242
〘名〙 船が桟橋や岸壁・他船に横づけするとき船体を損傷しないように舷側や桟橋・岸壁につける保護材。〔ロンドン‐東京５万キロ（1962）〕

Quick image search shows that this applies whether hung from the boat, or hung from the dock.  Either way, it is boat-hull-protector.

In spite of the rigid separation suggested by my last reference, it appears that the terms:
boat bumper, boat fender, dock fender, dock bumper 
could all be used.

@@ -12,0 +13 @@
+<gloss>bumper (on a dock, pier, etc.)</gloss>

gg5, daijr