The boating industry has long claimed that all marine drive manufacturers are united in their stand against propeller guards. Drive manufacturers say their united stand is an example of how unsafe propeller guards are, the problems they create, and of the impossibility of designing a safe, functional propeller guard. Some marine drive manufacturers have voided the warranty of drives due to propeller guards being mounted on them.
Yanmar may not have installed them, but they set their drives up to use them. Yanmar Service Manual. Diesel Outboard Motor. Models D27A & D36A. Manual # A0A5055-JC03. Model Year 2000. The cover page, and page 141 are reproduced here.
It is obvious from these images that Yanmar built drives with the full intent of them being used with propeller guards AND did so at the request of their customers.
Those objecting to propeller guards sometimes claim the holes drilled for mounting some guards could cause the drive to corrode. Yanmar solved that problem by pre-forming the holes.
Others have claimed that outboards and stern drives were not designed to support propeller guards or the loads they might generate in use. Still others have claimed the drilling of mounting holes could weaken drives and cause them to break.
Long ago, we suggested marine drive manufacturers beef up the drives most likely to have guards mounted to them if necessary, and supply “knock-outs” that could be easily punched out to create mounting holes for propeller guards.
Propeller Guard Paradox Defeated by Ant Farm
Propeller Guard Information Center
“Drive manufacturers could design their drives in advance to accept their own propeller guards by beefing areas needing reinforced and by incorporating any necessary mounting holes either as pre-formed holes or as “knock outs” that could be easily removed.”
Yanmar took that approach one step further (even before we suggested the idea). They went ahead and drilled or formed the holes in an optional lower leg.